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1.  Bent waveguides for matter-waves: supersymmetric potentials and reflectionless geometries 
Scientific Reports  2014;4:5274.
Non-zero curvature in a waveguide leads to the appearance of an attractive quantum potential which crucially affects the dynamics in matter-wave circuits. Using methods of supersymmetric quantum mechanics, pairs of bent waveguides are found whose geometry-induced potentials share the same scattering properties. As a result, reflectionless waveguides, dual to the straight waveguide, are identified. Strictly isospectral waveguides are also found by modulating the depth of the trapping potential. Numerical simulations are used to demonstrate the efficiency of these approaches in tailoring and controlling curvature-induced quantum-mechanical effects.
PMCID: PMC4053736  PMID: 24919423
2.  Comparison of range-of-motion and variability in upper body movements between transradial prosthesis users and able-bodied controls when executing goal-oriented tasks 
Current upper limb prostheses do not replace the active degrees-of-freedom distal to the elbow inherent to intact physiology. Limited evidence suggests that transradial prosthesis users demonstrate shoulder and trunk movements to compensate for these missing volitional degrees-of-freedom. The purpose of this study was to enhance understanding of the effects of prosthesis use on motor performance by comparing the movement quality of upper body kinematics between transradial prosthesis users and able-bodied controls when executing goal-oriented tasks that reflect activities of daily living.
Upper body kinematics were collected on six able-bodied controls and seven myoelectric transradial prosthesis users during execution of goal-oriented tasks. Range-of-motion, absolute kinematic variability (standard deviation), and kinematic repeatability (adjusted coefficient-of-multiple-determination) were quantified for trunk motion in three planes, shoulder flexion/extension, shoulder ab/adduction, and elbow flexion/extension across five trials per task. Linear mixed models analysis assessed between-group differences and correlation analysis evaluated association between prosthesis experience and kinematic repeatability.
Across tasks, prosthesis users demonstrated increased trunk motion in all three planes and shoulder abduction compared to controls (p ≤ 0.004). Absolute kinematic variability was greater for prosthesis users for all degrees-of-freedom irrespective of task, but was significant only for degrees-of-freedom that demonstrated increased range-of-motion (p ≤ 0.003). For degrees-of-freedom that did not display increased absolute variability for prosthesis users, able-bodied kinematics were characterized by significantly greater repeatability (p ≤ 0.015). Prosthesis experience had a strong positive relationship with average kinematic repeatability (r = 0.790, p = 0.034).
The use of shoulder and trunk movements by prosthesis users as compensatory motions to execute goal-oriented tasks demonstrates the flexibility and adaptability of the motor system. Increased variability in movement suggests that prosthesis users do not converge on a defined motor strategy to the same degree as able-bodied individuals. Kinematic repeatability may increase with prosthesis experience, or encourage continued device use, and future work is warranted to explore these relationships. As compensatory dynamics may be necessary to improve functionality of transradial prostheses, users may benefit from dedicated training that encourages optimization of these dynamics to facilitate execution of daily living activity, and fosters adaptable but reliable motor strategies.
PMCID: PMC4164738  PMID: 25192744
Upper limb; Transradial amputation; Kinematics; Trunk; Prosthesis
3.  Visuomotor behaviours when using a myoelectric prosthesis 
A recent study showed that the gaze patterns of amputee users of myoelectric prostheses differ markedly from those seen in anatomically intact subjects. Gaze behaviour is a promising outcome measures for prosthesis designers, as it appears to reflect the strategies adopted by amputees to compensate for the absence of proprioceptive feedback and uncertainty/delays in the control system, factors believed to be central to the difficulty in using prostheses. The primary aim of our study was to characterise visuomotor behaviours over learning to use a trans-radial myoelectric prosthesis. Secondly, as there are logistical advantages to using anatomically intact subjects in prosthesis evaluation studies, we investigated similarities in visuomotor behaviours between anatomically intact users of a trans-radial prosthesis simulator and experienced trans-radial myoelectric prosthesis users.
In part 1 of the study, we investigated visuomotor behaviours during performance of a functional task (reaching, grasping and manipulating a carton) in a group of seven anatomically intact subjects over learning to use a trans-radial myoelectric prosthesis simulator (Dataset 1). Secondly, we compared their patterns of visuomotor behaviour with those of four experienced trans-radial myoelectric prosthesis users (Dataset 2). We recorded task movement time, performance on the SHAP test of hand function and gaze behaviour.
Dataset 1 showed that while reaching and grasping the object, anatomically intact subjects using the prosthesis simulator devoted around 90% of their visual attention to either the hand or the area of the object to be grasped. This pattern of behaviour did not change with training, and similar patterns were seen in Dataset 2. Anatomically intact subjects exhibited significant increases in task duration at their first attempts to use the prosthesis simulator. At the end of training, the values had decreased and were similar to those seen in Dataset 2.
The study provides the first functional description of the gaze behaviours seen during use of a myoelectric prosthesis. Gaze behaviours were found to be relatively insensitive to practice. In addition, encouraging similarities were seen between the amputee group and the prosthesis simulator group.
PMCID: PMC4022381  PMID: 24758375
Prosthesis; Myoelectric; Visuomotor behaviour; Design evaluation; Amputee; Upper limb
4.  Influence on fluid dynamics of coronary artery outlet angle variation in artificial aortic root prosthesis 
Because of higher life expectancy, the number of elderly patients today with degenerative aortic diseases is on the increase. Often artificial aortic roots are needed to replace the native tissue. This surgical procedure requires re-implantation of the previous separated coronary arteries into the wall of the prosthesis. Regardless of the prosthesis type, changes in the reinsertion technique, e.g., the variation of the outlet angle of the coronary arteries, could influence the coronary blood flow. Whether the prosthesis type or the outlet angle variation significantly improves the blood circulation and lowers the risk of coronary insufficiency is still an open question. The numerical calculations presented can help to clear up these disputable questions.
Two simplified base geometries are used for simulating the blood flow in order to determine velocity and pressure distributions. One model uses a straight cylindrical tube to approximate the aortic root geometry; the other uses a sinus design with pseudosinuses of Valsalva. The coronary outlet angle of the right coronary artery was discretely modified in both models in the range from 60° to 120°. The pressure and velocity distributions of both models are compared in the ascending aorta as well as in the right and the left coronary artery.
The potentially allowed and anatomic limited variation of the outlet angle influences the pressure only a little bit and shows a very slight relative maximum between 70° and 90°. The sinus design and variations of the outlet angle of the coronary arteries were able to minimally optimize the perfusion pressure and the velocities in the coronary circulation, although the degree of such changes is rather low and would probably not achieve any clinical influence.
Our results show that surgeons should feel relatively free to vary the outlet angle within the anatomic structural conditions when employing the technique of coronary reinsertion.
PMCID: PMC2275278  PMID: 18307786
5.  Simulation of epiretinal prostheses - Evaluation of geometrical factors affecting stimulation thresholds 
An accurate understanding of the electrical interaction between retinal prostheses and retinal tissue is important to design effective devices. Previous studies have used modelling approaches to simulate electric fields generated by epiretinal prostheses in saline and to simulate retinal ganglion cell (RGC) activation using passive or/and active biophysical models of the retina. These models have limited scope for studying an implanted human retinal prosthesis as they often do not account for real geometry and composition of the prosthesis-retina interface. This interface consists of real dimensions and location of stimulation and ground electrodes that are separated by the retinal tissue and surrounded by physiological fluids.
In this study, we combined the prosthesis-retina interface elements into a framework to evaluate the geometrical factors affecting stimulation thresholds for epiretinal prostheses used in clinical human trials, as described by Balthasar et al. in their Investigative Ophthalmology and Visual Science (IOVS) paper published in 2008 using the Argus I epiretinal implants. Finite element method (FEM) based computations were used to estimate threshold currents based on a threshold criterion employing a passive electric model of the retina.
Threshold currents and impedances were estimated for different electrode-retina distances. The profiles and the values for thresholds and impedances obtained from our simulation framework are within the range of measured values in the only elaborate published clinical trial until now using Argus I epiretinal implants. An estimation of resolution for the electrodes used in these trials was provided. Our results reiterate the importance of close proximity between electrodes and retina for safe and efficient retinal stimulation.
The validation of our simulation framework being relevant for epiretinal prosthesis research is derived from the good agreement of the computed trends and values of the current study with measurements demonstrated in existing clinical trials on humans (Argus I). The proposed simulation framework could be used to generate the relationship between threshold and impedance for any electrode geometry and consequently be an effective tool for design engineers, surgeons and electrophysiologists.
PMCID: PMC3177891  PMID: 21854602
6.  In Vivo Characterization of the Aortic Wall Stress-Strain Relationship 
Ultrasonics  2010;50(7):654-665.
Arterial stiffness has been shown to be a good indicator of the arterial wall diseases. However, a single parameter is insufficient to describe the complex stress-strain relationship of a multi-component, non-linear tissue such as the aorta. We therefore propose a new approach to measure the stress-strain relationship locally in vivo and present a noninvasively, clinically relevant parameter describing the mechanical interaction between aortic wall constituents. The slope change of the circumferential stress-strain curve was hypothesized as a contribution of elastin and collagen, which was noninvasively defined in the term of strain using only radial aortic wall acceleration, i.e., transition strain (εθT). Two-spring parallel was employed as the phenomenological model and three Young's moduli were accordingly evaluated, i.e., corresponding to the: elastic lamellae (E1), elastin-collagen fibers (E2) and collagen fibers (E3). Our study performed on normal and Angiotensin II (AngII)-treated mouse abdominal aortas using aortic pressure from catheterization and local aortic wall diameters from a cross-correlation technique on the radio frequency (RF) ultrasound signal at 30 MHz and frame rate of 8 kHz. Using our technique, transition strain and three Young’s moduli in both normal and pathological aortas were mapped in 2D. In the results, the slope change of the circumferential stress-strain curve was first observed in vivo under physiologic conditions. The transition strain was identified at the lower strain level in the AngII-treated case, i.e., 0.029±0.006 of normal and 0.012±0.004 of AngII-treated aortas. E1, E2 and E3 were 69.7±18.6, 214.5±65.8 and 144.8±55.2 kPa for normal aortas, respectively, and 222.1±114.8, 775.0±586.4 and 552.9±519.1 kPa for AngII-treated aortas, respectively. This is because of the alteration of structures and content of the wall constituents, the degradation of elastic lamella and collagen formation due to AngII treatment. While such values illustrate the alteration of structure and content of the wall constituents related to AngII treatment, limitations regarding physical assumptions (isotropic linear elastic) should be kept in mind. The transition strain, however, was shown to be an aortic pressure waveform independent parameter that can be clinically relevant and noninvasively measured using ultrasound-based motion estimation techniques. In conclusion, our novel methodology can assess the stress-strain relationship of the aortic wall locally in vivo and quantify informative parameters which are related to vascular disease.
PMCID: PMC4005899  PMID: 20138640
Aorta; Cardiovascular Disease; Collagen; Elastin; Transition Strain; Ultrasound
7.  Revision Rates after Primary Hip and Knee Replacement in England between 2003 and 2006 
PLoS Medicine  2008;5(9):e179.
Hip and knee replacement are some of the most frequently performed surgical procedures in the world. Resurfacing of the hip and unicondylar knee replacement are increasingly being used. There is relatively little evidence on their performance. To study performance of joint replacement in England, we investigated revision rates in the first 3 y after hip or knee replacement according to prosthesis type.
Methods and Findings
We linked records of the National Joint Registry for England and Wales and the Hospital Episode Statistics for patients with a primary hip or knee replacement in the National Health Service in England between April 2003 and September 2006. Hospital Episode Statistics records of succeeding admissions were used to identify revisions for any reason. 76,576 patients with a primary hip replacement and 80,697 with a primary knee replacement were included (51% of all primary hip and knee replacements done in the English National Health Service). In hip patients, 3-y revision rates were 0.9% (95% confidence interval [CI] 0.8%–1.1%) with cemented, 2.0% (1.7%–2.3%) with cementless, 1.5% (1.1%–2.0% CI) with “hybrid” prostheses, and 2.6% (2.1%–3.1%) with hip resurfacing (p < 0.0001). Revision rates after hip resurfacing were increased especially in women. In knee patients, 3-y revision rates were 1.4% (1.2%–1.5% CI) with cemented, 1.5% (1.1%–2.1% CI) with cementless, and 2.8% (1.8%–4.5% CI) with unicondylar prostheses (p < 0.0001). Revision rates after knee replacement strongly decreased with age.
Overall, about one in 75 patients needed a revision of their prosthesis within 3 y. On the basis of our data, consideration should be given to using hip resurfacing only in male patients and unicondylar knee replacement only in elderly patients.
Jan van der Meulen and colleagues show that about one in 75 patients with a primary hip or knee replacement needed a revision of their prosthesis within 3 years.
Editors' Summary
Though records show attempts to replace a hip date back to 1891, it was not till the 1960s before total hip replacements were successfully performed, and the 1970s before total knee replacements were carried out. These procedures are some of the most frequently performed surgical operations, with a total of 160,00 total hip and knee replacement procedures carried out in England and Wales and about half a million in the US in 2006. Hip and knee replacements are most commonly used as a treatment for severe arthritis once other approaches, such as pain relief medications, have failed. A total hip replacement involves replacing the head of the femur (the thigh bone) with an artificial component, typically metal; the socket into which the new femur head will insert is also replaced with artificial components. In an alternative procedure, resurfacing, rather than replacing the entire joint, the diseased surfaces are replaced with metal components. This procedure may be better suited to patients with less severe disease, and is also thought to result in quicker recovery. The techniques for hip and knee replacement can also be divided into those where a cement is used to position the metal implant into the bone (cemented) versus those where cement is not used (cementless).
Why Was This Study Done?
To date, little evidence has been available to compare patient outcomes following hip or knee replacement with the many different types of techniques and prostheses available. National registries have been established in a number of countries to try to collect data in order to build the evidence base for evaluating different types of prosthesis. Specifically, it is important to find out if there are any important differences in revision rates (how often the hip replacement has to be re-done) following surgery using the different techniques. In England and Wales, the National Joint Registry (NJR) has collected data on patient characteristics, types of prostheses implanted, and the type of surgical procedures used, since its initiation in April 2003.
What Did the Researchers Do and Find?
The researchers linked the records of the NJR and the Hospital Episode Statistics (HES) for patients treated by the NHS in England who had undergone a primary hip and knee replacement between April 2003 and September 2006. The HES database contains records of all admissions to NHS hospitals in England, and allowed the researchers to more accurately identify revisions of procedures that were done on patients in the NJR database.
They identified 327,557 primary hip or knee replacement procedures performed during that time period, but only 167,076 could be linked between the two databases.
76,576 patients in the linked database had undergone a primary hip replacement. The overall revision rate was 1.4% (95% confidence interval [CI] 1.2%–1.5%) at 3 years, with the lowest revision rates experienced by patients who had cemented prostheses. Women were found to have higher revision rates after hip resurfacing, and the revision rate was about twice as high in patients who had had a hip replacement for other indications than osteoarthritis. A patient's age did not appear to affect revision rates after hip surgery.
80,697 patients in the linked database had undergone a primary knee replacement. The overall revision rate was 1.4% (95% CI 1.3%–1.6%) at three years, again with the lowest rates of replacement experienced by patients who had cemented prostheses. Revision rates after knee replacement strongly decreased with age.
What Do These Findings Mean?
Overall, about one in 75 patients required a revision of their joint replacement, which is considered low, and cemented hip or knee prosthesis had the lowest revision rates. Post hip replacement, the highest revision rate was in patients who had undergone hip resurfacing, especially women. Following knee replacement, the highest revision rate was in patients who had undergone unicondylar prosthesis. However, in this study patients were only followed up for three years after the initial knee replacement, and it's possible that different patterns regarding the success of these differing techniques may emerge after longer follow-up. Importantly, this study was entirely observational, and data were collected from patients who had been managed according to routine clinical practice (rather than being randomly assigned to different procedures). Substantial differences in the age and clinical characteristics of patients receiving the different procedures were seen. As a result, it's not possible to directly draw conclusions on the relative benefits or harms of the different procedures, but this study provides important benchmark data with which to evaluate future performance of different procedures and types of implant.
Additional Information.
Please access these Web sites via the online version of this summary at
The website of the British Orthopaedic Association contains information for patients and surgeons
The website of the National Institute for Health and Clinical Excellence contains guidance on hip prostheses
Information is available from the US National Institutes of Health (Medline) on hip replacement, including interactive tutorials and information about rehabilitation and recovery
Medline also provides similar resources for knee replacement
The NHS provides information for patients on hip and knee replacement, including questions patients might ask, real stories, and useful links
The National Joint Registry provides general information about joint replacement, as well as allowing users to download statistics on the data it has collected on the numbers of procedures carried out in the UK
PMCID: PMC2528048  PMID: 18767900
8.  Total Aortic Arch Replacement: Superior Ventriculo-Arterial Coupling with Decellularized Allografts Compared with Conventional Prostheses 
PLoS ONE  2014;9(7):e103588.
To date, no experimental or clinical study provides detailed analysis of vascular impedance changes after total aortic arch replacement. This study investigated ventriculoarterial coupling and vascular impedance after replacement of the aortic arch with conventional prostheses vs. decellularized allografts.
After preparing decellularized aortic arch allografts, their mechanical, histological and biochemical properties were evaluated and compared to native aortic arches and conventional prostheses in vitro. In open-chest dogs, total aortic arch replacement was performed with conventional prostheses and compared to decellularized allografts (n = 5/group). Aortic flow and pressure were recorded continuously, left ventricular pressure-volume relations were measured by using a pressure-conductance catheter. From the hemodynamic variables end-systolic elastance (Ees), arterial elastance (Ea) and ventriculoarterial coupling were calculated. Characteristic impedance (Z) was assessed by Fourier analysis.
While Ees did not differ between the groups and over time (4.1±1.19 vs. 4.58±1.39 mmHg/mL and 3.21±0.97 vs. 3.96±1.16 mmHg/mL), Ea showed a higher increase in the prosthesis group (4.01±0.67 vs. 6.18±0.20 mmHg/mL, P<0.05) in comparison to decellularized allografts (5.03±0.35 vs. 5.99±1.09 mmHg/mL). This led to impaired ventriculoarterial coupling in the prosthesis group, while it remained unchanged in the allograft group (62.5±50.9 vs. 3.9±23.4%). Z showed a strong increasing tendency in the prosthesis group and it was markedly higher after replacement when compared to decellularized allografts (44.6±8.3dyn·sec·cm−5 vs. 32.4±2.0dyn·sec·cm−5, P<0.05).
Total aortic arch replacement leads to contractility-afterload mismatch by means of increased impedance and invert ventriculoarterial coupling ratio after implantation of conventional prostheses. Implantation of decellularized allografts preserves vascular impedance thereby improving ventriculoarterial mechanoenergetics after aortic arch replacement.
PMCID: PMC4117632  PMID: 25079587
9.  Effects of a powered ankle-foot prosthesis on kinetic loading of the unaffected leg during level-ground walking 
People with a lower-extremity amputation that use conventional passive-elastic ankle-foot prostheses encounter a series of stress-related challenges during walking such as greater forces on their unaffected leg, and may thus be predisposed to secondary musculoskeletal injuries such as chronic joint disorders. Specifically, people with a unilateral transtibial amputation have an increased susceptibility to knee osteoarthritis, especially in their unaffected leg. Previous studies have hypothesized that the development of this disorder is linked to the abnormally high peak knee external adduction moments encountered during walking. An ankle-foot prosthesis that supplies biomimetic power could potentially mitigate the forces and knee adduction moments applied to the unaffected leg of a person with a transtibial amputation, which could, in turn, reduce the risk of knee osteoarthritis. We hypothesized that compared to using a passive-elastic prosthesis, people with a transtibial amputation using a powered ankle-foot prosthesis would have lower peak resultant ground reaction forces, peak external knee adduction moments, and corresponding loading rates applied to their unaffected leg during walking over a wide range of speeds.
We analyzed ground reaction forces and knee joint kinetics of the unaffected leg of seven participants with a unilateral transtibial amputation and seven age-, height- and weight-matched non-amputees during level-ground walking at 0.75, 1.00, 1.25, 1.50, and 1.75 m/s. Subjects with an amputation walked while using their own passive-elastic prosthesis and a powered ankle-foot prosthesis capable of providing net positive mechanical work and powered ankle plantar flexion during late stance.
Use of the powered prosthesis significantly decreased unaffected leg peak resultant forces by 2-11% at 0.75-1.50 m/s, and first peak knee external adduction moments by 21 and 12% at 1.50 and 1.75 m/s, respectively. Loading rates were not significantly different between prosthetic feet.
Use of a biomimetic powered ankle-foot prosthesis decreased peak resultant force at slow and moderate speeds and knee external adduction moment at moderate and fast speeds on the unaffected leg of people with a transtibial amputation during level-ground walking. Thus, use of an ankle-foot prosthesis that provides net positive mechanical work could reduce the risk of comorbidities such as knee osteoarthritis.
PMCID: PMC3685554  PMID: 23758860
Amputee; Ankle; Biomechanics; Bionic; Gait; Loading rate; Prosthesis; Transtibial; Walking
10.  Design modifications of high-flexion TKA do not improve short term clinical and radiographic outcomes 
The prosthesis of contemporary total knee arthroplasty (TKA) has been modified to provide a more familiar environment for higher flexion angle of the replaced knee. The design modifications continue based on evidence reported in the literature. However, whether these modifications of the prosthesis design lead to improvements in clinical results needs further investigation. We determined whether the prosthesis modifications based on recent evidence improve clinical and radiographic results following high flexion TKA.
524 patients who underwent primary TKA using two different high flexion prostheses were divided to Group 1 (HF-1) using a high flexion prosthesis, group 2 (HF-2) using the more recently devised high flexion prosthesis, which claims to be adopted from evidence proposed in the literature. Clinical outcomes included ranges of motion (ROM), the Knee Society knee and function score (KSKS and KSFS), the Western Ontario and McMaster Universities Arthritis Index (WOMAC) score, radiologic evaluation, and complication related to surgery.
No differences in terms of clinical and radiographic results were observed between the groups at the 2 year follow-up. The mean ROM was 123°and 124° in the HF-1 and HF-2 groups, respectively. KSKS were 90 and 89.1, KSFS were 76.6 and 81.8, and total WOMAC scores were 23.1 and 24.9 in the HF-1 and HF- 2 groups. No differences of the incidences of radiolucency on radiographs (1.4% in HF-1, 2.1% in HF-2) and dislocation (1 case in HF-1 only) was observed.
Even if recent modifications in the design of high flexion TKA prosthesis were based on evidence in the literature, they did not provide meaningful improvements in short-term clinical and radiographic outcomes after TKA. Surgeons should consider our findings when choosing a prosthesis for their patients.
PMCID: PMC4301904  PMID: 25510950
Total knee arthroplasty; High-flexion knee; Outcome scores; Range of motion
11.  In-vivo assessment of the morphology and hemodynamic functions of the BioValsalva™ composite valve-conduit graft using cardiac magnetic resonance imaging and computational modelling technology 
The evaluation of any new cardiac valvular prosthesis should go beyond the classical morbidity and mortality rates and involve hemodynamic assessment. As a proof of concept, the objective of this study was to characterise for the first time the hemodynamics and the blood flow profiles at the aortic root in patients implanted with BioValsalva™ composite valve-conduit using comprehensive MRI and computer technologies.
Four male patients implanted with BioValsalva™ and 2 age-matched normal controls (NC) underwent cardiac magnetic resonance imaging (MRI). Phase-contrast imaging with velocity-mapping in 3 orthogonal directions was performed at the level of the aortic root and descending thoracic aorta. Computational fluid dynamic (CFD) simulations were performed for all the subjects with patient-specific flow information derived from phase-contrast MR data.
The maximum and mean flow rates throughout the cardiac cycle at the aortic root level were very comparable between NC and BioValsalva™ patients (541 ± 199 vs. 567 ± 75 ml/s) and (95 ± 46 vs. 96 ± 10 ml/s), respectively. The maximum velocity (cm/s) was higher in patients (314 ± 49 vs. 223 ± 20; P = 0.06) due to relatively smaller effective orifice area (EOA), 2.99 ± 0.47 vs. 4.40 ± 0.24 cm2 (P = 0.06), however, the BioValsalva™ EOA was comparable to other reported prosthesis. The cross-sectional area and maximum diameter at the root were comparable between the two groups. BioValsalva™ conduit was stiffer than the native aortic wall, compliance (mm2 • mmHg−1 • 10−3) values were (12.6 ± 4.2 vs 25.3 ± 0.4.; P = 0.06). The maximum time-averaged wall shear stress (Pa), at the ascending aorta was equivalent between the two groups, 17.17 ± 2.7 (NC) vs. 17.33 ± 4.7 (BioValsalva™ ). Flow streamlines at the root and ascending aorta were also similar between the two groups apart from a degree of helical flow that occurs at the outer curvature at the angle developed near the suture line.
BioValsalva™ composite valve-conduit prosthesis is potentially comparable to native aortic root in structural design and in many hemodynamic parameters, although it is stiffer. Surgeons should pay more attention to the surgical technique to maximise the reestablishment of normal smooth aortic curvature geometry to prevent unfavourable flow characteristics.
PMCID: PMC4263057  PMID: 25488105
Composite valve-conduit; Aortic valve; Aortic root; Aortic prosthesis; BioValsalva; Computational fluid dynamic
12.  Effects of lumbar artificial disc design on intervertebral mobility: in vivo comparison between mobile-core and fixed-core 
European Spine Journal  2010;21(Suppl 5):630-640.
Although in theory, the differences in design between fixed-core and mobile-core prostheses should influence motion restoration, in vivo kinematic differences linked with prosthesis design remained unclear. The aim of this study was to investigate the rationale that the mobile-core design seems more likely to restore physiological motion since the translation of the core could help to mimic the kinematic effects of the natural nucleus. In vivo intervertebral motion characteristics of levels implanted with the mobile-core prosthesis were compared with untreated levels of the same population, levels treated by a fixed-core prosthesis, and normal levels (data from literature). Patients had a single-level implantation at L4L5 or L5S1 including 72 levels with a mobile-core prosthesis and 33 levels with a fixed-core prosthesis. Intervertebral mobility characteristics included the range of motion (ROM), the motion distribution between flexion and extension, the prosthesis core translation (CT), and the intervertebral translation (VT). A method adapted to the implanted segments was developed to measure the VT: metal landmarks were used instead of the bony landmarks. The reliability assessment of the VT measurement method showed no difference between three observers (p < 0.001), a high level of agreement (ICC = 0.908) and an interobserver precision of 0.2 mm. Based on this accurate method, this in vivo study demonstrated that the mobile-core prosthesis replicated physiological VT at L4L5 levels but not at L5S1 levels, and that the fixed-core prosthesis did not replicate physiological VT at any level by increasing VT. As the VT decreased when the CT increased (p < 0.001) it was proven that the core mobility minimized the VT. Furthermore, some physiologic mechanical behaviors seemed to be maintained: the VT was higher at implanted the L4L5 level than at the implanted L5S1 level, and the CT appeared lower at the L4L5 level than at the L5S1 level. ROM and motion distribution were not different between the mobile-core prosthesis and the fixed-core prosthesis implanted levels. This study validated in vivo the concept that a mobile-core helps to restore some physiological mechanical characteristics of the VT at the implanted L4L5 level, but also showed that the minimizing effect of core mobility on the VT was not sufficient at the L5S1 level.
PMCID: PMC3377809  PMID: 21153595
Total disc replacement; Lumbar spine; Segmental motion; Intervertebral translation; Prosthesis design
13.  Surgical Technique: Unicondylar Osteoallograft Prosthesis Composite in Tumor Limb Salvage Surgery 
After resecting tumors confined to one femoral condyle, a unicondylar osteoarticular allograft can be used for reconstruction without sacrificing the uninvolved condyle. However, unicondylar osteoarticular allografts have been associated with a high rate of joint degeneration. We describe a unicondylar osteoallograft prosthesis composite reconstruction replacing only one side of the joint to reduce compartment degeneration and avoid contamination of the tibia, but the survival, function, and complications of a unicondylar osteoallograft prosthesis composite are unclear.
Description of Technique
We located a bone resection plane intraoperatively as planned before surgery using a computer-assisted navigation system. The tumor then was removed en bloc and the unicondylar defect filled with a size-matched allogeneic unicondyle. The allograft cartilage was removed. Thereafter, the condyle of the femoral component was resurfaced with a unicompartmental knee prosthesis to form a unicondylar osteoallograft prosthesis composite, however the tibia was left undisturbed. Navigation allowed precise apposition between the unicondylar osteoallograft prosthesis composite and host bone to ensure mechanical alignment and congruency of the joint surface before fixation with a plate.
We retrospectively reviewed 12 patients who underwent unicondylar osteoallograft prosthesis composite reconstructions after unicondylar resection for tumors. One patient died from tumor-related causes without unicondylar osteoallograft prosthesis composite failure after 18 months. We observed the survival rate of unicondylar osteoallograft prosthesis composite reconstruction and related complications. Function and radiographs also were documented according to the Musculoskeletal Tumor Society (MSTS) functional scoring system and the International Society of Limb Salvage radiographic scoring system. The minimum followup was 8 months (median, 37 months; range, 8–65 months).
At last followup, 10 of the 12 unicondylar osteoallograft prosthesis composite reconstructions were still in place. Three reconstructions failed owing to two local recurrences (both treated with amputation) and there was one infection (treated with revision and maintenance of the implant at last followup). The average MSTS functional score at last followup was 27 points and the radiographic score 91%.
Our observations suggest unicondylar osteoallograft prosthesis composite reconstruction might be a reliable technique with relatively few major complications and at least short-term maintenance of the tibial cartilage.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3492634  PMID: 22752800
14.  Improvements in survival of the uncemented Nottingham Total Shoulder prosthesis: a prospective comparative study 
The uncemented Nottingham Total Shoulder Replacement prosthesis system (Nottingham TSR) was developed from the previous BioModular® shoulder prosthesis taking into consideration the causes of the initial implant's failure.
We investigated the impact of changes in the design of Nottingham TSR prosthesis on its survivorship rate.
Survivorship analyses of three types of uncemented total shoulder arthroplasty prostheses (BioModular®, initial Nottingham TSR and current Nottingham TSR systems with 11, 8 and 4 year survivorship data respectively) were compared. All these prostheses were implanted for the treatment of disabling pain in the shoulder due to primary and secondary osteoarthritis or rheumatoid arthritis. Each type of the prosthesis studied was implanted in consecutive group of patients – 90 patients with BioModular® system, 103 with the initial Nottingham TSR and 34 patients with the current Nottingham TSR system.
The comparison of the annual cumulative survivorship values in the compatible time range between the three groups was done according to the paired t test.
The 8-year and 11-year survivorship rates for the initially used modified BioModular® uncemented prosthesis were relatively low (75.6% and 71.7% respectively) comparing to the reported survivorship of the conventional cemented implants. The 8-year survivorship for the uncemented Nottingham TSR prosthesis was significantly higher (81.8%), but still not in the desired range of above 90%, that is found in other cemented designs. Glenoid component loosening was the main factor of prosthesis failure in both prostheses and mainly occurred in the first 4 postoperative years. The 4-year survivorship of the currently re-designed Nottingham TSR prosthesis, with hydroxylapatite coating of the glenoid baseplate, was significantly higher, 93.1% as compared to 85.1% of the previous Nottingham TSR.
The initial Nottingham shoulder prosthesis showed significantly higher survivorship than the BioModular® uncemented prosthesis, but lower than expected. Subsequently re-designed Nottingham TSR system presented a high short term survivorship rate that encourages its ongoing use
PMCID: PMC1964758  PMID: 17683577
15.  Measurement of biaxial mechanical properties of soft tubes and arteries using piezoelectric elements and sonometry 
Physics in medicine and biology  2011;56(11):3371-3386.
Arterial elasticity has gained importance in the past decades because it has been shown to be an independent predictor of cardiovascular diseases. Several in vivo and ex vivo techniques have been developed to characterize the elastic properties of vessels. In vivo techniques tend to ignore the anisotropy of the mechanical properties in the vessel wall, and therefore, fail to characterize elasticity in different directions. Ex vivo techniques, have focused their efforts in studying the mechanical properties in different axes. In this paper, we present a technique that uses piezoelectric elements to measure the elasticity of soft tubes and excised arteries in two directions while maintaining the natural structure of these vessels. This technique uses sonometry data from piezoelectric elements to measure the strain in the longitudinal and circumferential directions while the tubes/arteries are being pressurized. We conducted experiments on urethane tubes to evaluate the technique and compared the experimental results with mechanical testing done on the materials used for making the tubes. We then performed sonometry experiments on excised pig carotid arteries assuming that they are transversely isotropic materials. To evaluate the sensitivity of this technique to changes in the material properties, we changed the temperature of the saline bath in which the arteries were immersed. The calculated Young’s modulus from sonometry experiments for the urethane tubes and the mechanical testing values showed good agreement, deviating no more than 13.1%. The elasticity values from the excised arteries and the behavior with the temperature changed agreed with previous work done in similar arteries. Therefore, we propose this technique for nondestructive testing of the biaxial properties of soft materials tubes and excised arteries in their natural physiological shape.
PMCID: PMC3129600  PMID: 21558593
Arterial elasticity; elastic moduli; piezoelectric elements; sonometry
16.  Endovascular Repair of Descending Thoracic Aortic Aneurysm 
Executive Summary
To conduct an assessment on endovascular repair of descending thoracic aortic aneurysm (TAA).
Clinical Need
Aneurysm is the most common condition of the thoracic aorta requiring surgery. Aortic aneurysm is defined as a localized dilatation of the aorta. Most aneurysms of the thoracic aorta are asymptomatic and incidentally discovered. However, TAA tends to enlarge progressively and compress surrounding structures causing symptoms such as chest or back pain, dysphagia (difficulty swallowing), dyspnea (shortness of breath), cough, stridor (a harsh, high-pitched breath sound), and hoarseness. Significant aortic regurgitation causes symptoms of congestive heart failure. Embolization of the thrombus to the distal arterial circulation may occur and cause related symptoms. The aneurysm may eventually rupture and create a life-threatening condition.
The overall incidence rate of TAA is about 10 per 100,000 person-years. The descending aorta is involved in about 30% to 40% of these cases.
The prognosis of large untreated TAAs is poor, with a 3-year survival rate as low as 25%. Intervention is strongly recommended for any symptomatic TAA or any TAA that exceeds twice the diameter of a normal aorta or is 6 cm or larger. Open surgical treatment of TAA involves left thoracotomy and aortic graft replacement. Surgical treatment has been found to improve survival when compared with medical therapy. However, despite dramatic advances in surgical techniques for performing such complex operations, operative mortality from centres of excellence are between 8% and 20% for elective cases, and up to 50% in patients requiring emergency operations. In addition, survivors of open surgical repair of TAAs may suffer from severe complications. Postoperative or postprocedural complications of descending TAA repair include paraplegia, myocardial infarction, stroke, respiratory failure, renal failure, and intestinal ischemia.
The Technology
Endovascular aortic aneurysm repair (EVAR) using a stent graft, a procedure called endovascular stent-graft (ESG) placement, is a new alternative to the traditional surgical approach. It is less invasive, and initial results from several studies suggest that it may reduce mortality and morbidity associated with the repair of descending TAAs.
The goal in endovascular repair is to exclude the aneurysm from the systemic circulation and prevent it from rupturing, which is life-threatening. The endovascular placement of a stent graft eliminates the systemic pressure acting on the weakened wall of the aneurysm that may lead to the rupture. However, ESG placement has some specific complications, including endovascular leak (endoleak), graft migration, stent fracture, and mechanical damage to the access artery and aortic wall.
The Talent stent graft (manufactured by Medtronic Inc., Minneapolis, MN) is licensed in Canada for the treatment of patients with TAA (Class 4; licence 36552). The design of this device has evolved since its clinical introduction. The current version has a more flexible delivery catheter than did the original system. The prosthesis is composed of nitinol stents between thin layers of polyester graft material. Each stent is secured with oversewn sutures to prevent migration.
Review Strategy
To compare the effectiveness and cost-effectiveness of ESG placement in the treatment of TAAs with a conventional surgical approach
To summarize the safety profile and effectiveness of ESG placement in the treatment of descending TAAs
Measures of Effectiveness
Primary Outcome
Mortality rates (30-day and longer term)
Secondary Outcomes
Technical success rate of introducing a stent graft and exclusion of the aneurysm sac from systemic circulation
Rate of reintervention (through surgical or endovascular approach)
Measures of Safety
Complications were categorized into 2 classes:
Those specific to the ESG procedure, including rates of aneurysm rupture, endoleak, graft migration, stent fracture, and kinking; and
Those due to the intervention, either surgical or endovascular. These include paraplegia, stroke, cardiovascular events, respiratory failure, real insufficiency, and intestinal ischemia.
Inclusion Criteria
Studies comparing the clinical outcomes of ESG treatment with surgical approaches
Studies reporting on the safety and effectiveness of the ESG procedure for the treatment of descending TAAs
Exclusion Criteria
Studies investigating the clinical effectiveness of ESG placement for other conditions such as aortic dissection, aortic ulcer, and traumatic injuries of the thoracic aorta
Studies investigating the aneurysms of the ascending and the arch of the aorta
Studies using custom-made grafts
Literature Search
The Medical Advisory Secretariat searched The International Network of Agencies for Health Technology Assessment and the Cochrane Database of Systematic Reviews for health technology assessments. It also searched MEDLINE, EMBASE, Medline In-Process & Other Non-Indexed Citations, and Cochrane CENTRAL from January 1, 2000 to July 11, 2005 for studies on ESG procedures. The search was limited to English-language articles and human studies.
One health technology assessment from the United Kingdom was identified. This systematic review included all pathologies of the thoracic aorta; therefore, it did not match the inclusion criteria. The search yielded 435 citations; of these, 9 studies met inclusion criteria.
Summary of Findings
The results of a comparative study found that in-hospital mortality was not significantly different between ESG placement and surgery patients (2 [4.8%] for ESG vs. 6 [11.3%] for surgery).
Pooled data from case series with a mean follow-up ranging from 12 to 38 months showed a 30-day mortality and late mortality rate of 3.9% and 5.5%, respectively. These rates are lower than are those reported in the literature for surgical repair of TAA.
Case series showed that the most common cause of early death in patients undergoing endovascular repair is aortic rupture, and the most common causes of late death are cardiac events and aortoesophageal or aortobronchial fistula.
Technical Success Rate
Technical success rates reported by case series are 55% to 100% (100% and 94.4% in 2 studies with all elective cases, 89% in a study with 5% emergent cases, and 55% in a study with 42% emergent cases).
Surgical Reintervention
In the comparative study, 3 (7.1%) patients in the ESG group and 14 (26.5%) patients in the surgery group required surgical reintervention. In the ESG group, the reasons for surgical intervention were postoperative bleeding at the access site, paraplegia, and type 1 endoleak. In the surgical group, the reasons for surgery were duodenal perforation, persistent thoracic duct leakage, false aneurysm, and 11 cases of postoperative bleeding.
Pooled data from case series show that 9 (2.6%) patients required surgical intervention. The reasons for surgical intervention were endoleak (3 cases), aneurysm enlargement and suspected infection (1 case), aortic dissection (1 case), pseudoaneurysm of common femoral artery (1 case), evacuation of hematoma (1 case), graft migration (1 case), and injury to the access site (1 case).
Endovascular Revision
In the comparative study, 3 (7.1%) patients required endovascular revision due to persistent endoleak.
Pooled data from case series show that 19 (5.3%) patients required endovascular revision due to persistent endoleak.
Graft Migration
Two case series reported graft migration. In one study, 3 proximal and 4 component migrations were noted at 2-year follow-up (total of 5%). Another study reported 1 (3.7%) case of graft migration. Overall, the incidence of graft migration was 2.6%.
Aortic Rupture
In the comparative study, aortic rupture due to bare stent occurred in 1 case (2%). The pooled incidence of aortic rupture or dissection reported by case series was 1.4%.
Postprocedural Complications
In the comparative study, there were no statistically significant differences between the ESG and surgery groups in postprocedural complications, except for pneumonia. The rate of pneumonia was 9% for those who received an ESG and 28% for those who had surgery (P = .02). There were no cases of paraplegia in either group. The rate of other complications for ESG and surgery including stroke, cardiac, respiratory, and intestinal ischemia were all 5.1% for ESG placement and 10% for surgery. The rate for mild renal failure was 16% in the ESG group and 30% in the surgery group. The rate for severe renal failure was 11% for ESG placement and 10% for surgery.
Pooled data from case series show the following postprocedural complication rates in the ESG placement group: paraplegia (2.2%), stroke (3.9%), cardiac (2.9%), respiratory (8.7%), renal failure (2.8%), and intestinal ischemia (1%).
Time-Related Outcomes
The results of the comparative study show statistically significant differences between the ESG and surgery group for mean operative time (ESG, 2.7 hours; surgery, 5 hours), mean duration of intensive care unit stay (ESG, 11 days; surgery, 14 days), and mean length of hospital stay (ESG, 10 days; surgery, 30 days).
The mean duration of intensive care unit stay and hospital stay derived from case series is 1.6 and 7.8 days, respectively.
Ontario-Based Economic Analysis
In Ontario, the annual treatment figures for fiscal year 2004 include 17 cases of descending TAA repair procedures (source: Provincial Health Planning Database). Fourteen of these have been identified as “not ruptured” with a mean hospital length of stay of 9.23 days, and 3 cases have been identified as “ruptured,” with a mean hospital length of stay of 28 days. However, because one Canadian Classification of Health Interventions code was used for both procedures, it is not possible to determine how many were repaired with an EVAR procedure or with an open surgical procedure.
Hospitalization Costs
The current fiscal year forecast of in-hospital direct treatment costs for all in-province procedures of repair of descending TAAs is about $560,000 (Cdn). The forecast in-hospital total cost per year for in-province procedures is about $720,000 (Cdn). These costs include the device cost when the procedure is EVAR (source: Ontario Case Costing Initiative).
Professional (Ontario Health Insurance Plan) Costs
Professional costs per treated patient were calculated and include 2 preoperative thoracic surgery or EVAR consultations.
The professional costs of an EVAR include the fees paid to the surgeons, anesthetist, and surgical assistant (source: fee service codes). The procedure was calculated to take about 150 minutes.
The professional costs of an open surgical repair include the fees of the surgeon, anesthetist, and surgical assistant. Open surgical repair was estimated to take about 300 minutes.
Services provided by professionals in intensive care units were also taken into consideration, as were the costs of 2 postoperative consultations that the patients receive on average once they are discharged from the hospital. Therefore, total Ontario Health Insurance Plan costs per treated patient treated with EVAR are on average $2,956 (ruptured or not ruptured), as opposed to $5,824 for open surgical repair and $6,157 for open surgical repair when the aneurysm is ruptured.
Endovascular stent graft placement is a less invasive procedure for repair of TAA than is open surgical repair.
There is no high-quality evidence with long-term follow-up data to support the use of EVAR as the first choice of treatment for patients with TAA that are suitable candidates for surgical intervention.
However, short- and medium-term outcomes of ESG placement reported by several studies are satisfactory and comparable to surgical intervention; therefore, for patients at high risk of surgery, it is a practical option to consider. Short- and medium-term results show that the benefit of ESG placement over the surgical approach is a lower 30-day mortality and paraplegia rate; and shorter operative time, ICU stay, and hospital stay.
PMCID: PMC3382300  PMID: 23074469
17.  Clinical and functional outcomes of the saddle prosthesis 
The implantation of a saddle prosthesis after resection of a pelvic tumor has been proposed as a simple method of reconstruction that provides good stability and reduces the surgical time, thus limits the onset of intraoperative complications. There are no studies in the literature of patients evaluated using gait analysis after being implanted with a saddle prosthesis. The present study is a retrospective case review aimed at illustrating long-term clinical and functional findings in tumor patients reconstructed with a saddle prosthesis.
Materials and Methods
A series of 15 patients who recieved pelvic reconstruction with a saddle prosthesis were retrospectively reviewed in terms of clinical, radiographic, and functional evaluations. Two patients were additionally assessed by gait analysis.
Long-term functional follow-up was achieved in only 6 patients, and ranged from 97 to 167 months. Function was found to be rather impaired, as a mean of only 57 % of normal activity was restored. Gait analysis demonstrated that the implant had poor biomechanics, as characterized by very limited hip motion.
Though the saddle prosthesis was proposed as advance in tumor-related pelvic surgery, the present study indicates that it yields unsatisfactory clinical and functional results due to both clinical complications and the poor biomechanics of the device. The use of a saddle prosthesis in tumor surgery did not provide satisfactory results in long-term follow-up. It is no longer implanted at our institute, and is currently considered a “salvage technique.”
Level of evidence
Level IV.
PMCID: PMC3349025  PMID: 22527147
Saddle prosthesis; Gait analysis; Tumor surgery; Bone tumors; Resection
18.  Resect or not to resect: the role of posterior longitudinal ligament in lumbar total disc replacement 
European Spine Journal  2009;21(Suppl 5):592-598.
With regard to the literature, several factors are considered to have an impact on postoperative mobility after lumbar total disc replacement (TDR). As TDR results in a distraction of the ligamentous structures, theoretically the postoperatively disc height and ligamentous integrity have also an influence on biomechanics of a treated segment. The purpose of the study was to evaluate the influence of posterior longitudinal ligament (PLL) resection and segmental distraction on range of motion (ROM). Six human, lumbar spines (L2–L3) were tested with pure moments of ±7.5 Nm in a spine loading apparatus. The ROM was determined in all three motion planes. Testing sequences included: (1) intact state, (2) 10 mm prosthesis (PLL intact), (3) 10 mm prosthesis (PLL resected), (4) 12 mm prosthesis (PLL resected). The prosthesis used was a prototype with a constrained design using the ball-and-socket principle. The implantation of the 10 mm prosthesis already increased the disc height significantly (intact: 9.9 mm; 10 mm prosthesis: 10.6 mm; 12 mm prosthesis: 12.7 mm). Compared to the intact status, the implantation of the 10 mm prosthesis resulted in an increase of ROM for flexion/extension (8.6° vs 10.8°; P = 0.245) and axial rotation (2.9° vs 4.5°; P = 0.028), whereas lateral bending decreased (9.0° vs 7.6°; P = 0.445). The resection of the PLL for the 10 mm prosthesis resulted in an increase of ROM in all motion planes compared to the 10 mm prosthesis with intact PLL (flexion/extension: 11.4°, P = 0.046; axial rotation: 5.1°, P = 0.046; lateral bending: 8.6°, P = 0.028). The subsequent implantation of a 12 mm prosthesis, with resected PLL, resulted in a significant decrease of ROM in all motion planes compared to the 10 mm prosthesis with intact PLL (flexion/extension: 8.4°, P = 0.028; axial rotation: 3.3°, P = 0.028; lateral bending: 5.1°, P = 0.028). Compared to the intact status, the 12 mm prosthesis with resected PLL only decreased lateral bending significantly while the 10 mm prosthesis with intact PLL increased axial rotation significantly. The resection of the PLL during TDR results in a significant increase of ROM in all three principle motion planes. But it still remains unclear if this increase which is in median not more than 1° may alter the clinical results. Moreover, the destabilizing effect of PLL resection can be reversed using a higher implant. The prosthesis height seems more crucial than PLL preservation to maintain the primary stability after TDR.
PMCID: PMC3377805  PMID: 19882178
Lumbar disc replacement; Range of motion; Posterior longitudinal ligament; Biomechanics
19.  The Surgeon’s Role in Relative Success of PCL-Retaining and PCL-Substituting Total Knee Arthroplasty 
HSS Journal  2014;10(2):107-115.
The orthopedic literature has not shown a universal and replicated difference, outside of flexion, in clinical results between posterior cruciate ligament retention and posterior cruciate ligament substitution in total knee arthroplasty.
This study was performed to compare the restoration of flexion and knee function in a large series of cruciate-retaining and cruciate-substituting total knee arthroplasties (TKRs). In addition, we aimed to study how other variables, such as those unique to each surgeon, may have affected the results.
Patients and Methods
The current study evaluated 8,607 total knee arthroplasties in 5,594 patients performed by six surgeons, each using one of four prosthesis designs (two posterior cruciate ligament retaining, two posterior cruciate ligament substituting). Knees were compared at the level of cruciate-retaining and cruciate-substituting knees, at the level of the four prostheses, and at the level of surgeon-implant combinations. Least squared means scores were obtained through multiple linear regression, analysis of variance, and the maximum likelihood method.
At the level of posterior cruciate ligament treatment, posterior cruciate ligament substitution as a whole showed 3.2° greater flexion than posterior cruciate ligament retention. At the prosthesis level, cruciate-substituting models provided greater flexion and cruciate-retaining models provided higher function scores. In the surgeon-implant combinations, surgeons provided mixed results that often did not reflect findings from other levels; one surgeon's use of a posterior cruciate ligament retaining prosthesis achieved 14.7° greater flexion than the surgeon's use of a corresponding posterior cruciate ligament substituting design.
Posterior cruciate ligament treatment is confounded by other variables, including the operating surgeon. The arthroplasty surgeon should choose a prosthesis based, not only on outside results, but also on personal experience and comfort.
Electronic supplementary material
The online version of this article (doi:10.1007/s11420-014-9389-5) contains supplementary material, which is available to authorized users.
PMCID: PMC4071471  PMID: 25050092
posterior cruciate ligament retention; posterior cruciate ligament substitution; total knee arthroplasty; surgeon effect
20.  The association between the sagittal femoral stem alignment and the resulting femoral head centre in total hip arthroplasty 
International Orthopaedics  2010;35(7):981-987.
Adequate stem alignment is essential for the success of Total Hip Arthroplasty (THA) to avoid dislocation and impingement. One factor that has not been sufficiently investigated so far is the stem tilting in the sagittal plane, which has an influence on the position of the centre of the femoral head and thus also on prosthesis torsion. We aimed to evaluate sagittal stem position using 3D-CTs in patients with THA and to develop a mathematical-geometrical model to simulate the functional correlation between sagittal stem tilting and the influence on functional anteversion. Thirty patients with THA underwent a CT-scan. By 3D-reconstruction of the CT-data, femoral-/prosthesis-axis, torsion and sagittal tilt were determined. In accordance with the position of the femoral and prosthesis axes, the rotatory (rAV) (surgically adjusted) and functional (depending on sagittal tilt) anteversion (fAV) was measured. A three dimentional-coordinate transformation was also performed using the Euler-angles to derive a mathematical-geometrical correlation between sagittal stem tilting and corresponding influence on anteversion. The mean rAV was 8° (-11.6 - 26°), the fAV 18° (6.2 - 37°), and the difference 10° (8.8 - 18°). The mean degree of stem tilting was 5.2° (0.7 - 9°) anterior towards the femoral axis. The individually measured parameters are reflected in the mathematical-geometrical model. Depending on the extent of the sagittal deviation, a clear influence on the torsion emerges. For example, a stem implanted at a 15° anteverted angle with a sagittal tilt by two degrees towards anterior results in a fAV of 20°. A clear association between the sagittal stem alignment and the impact on the fAV was demonstrated. Hence, the rotatory anteversion intended by the surgeon may be functionally significantly different. This might pose an increased risk of dislocation or impingement. The sagittal tilt of the prosthesis should therefore be considered in the context of impingement and dislocation diagnosis. In this respect, we recommend a 3D-analysis of stem alignment.
PMCID: PMC3167395  PMID: 20549502
21.  The LP-ESP® lumbar disc prosthesis with 6 degrees of freedom: development and 7 years of clinical experience 
The viscoelastic lumbar disk prosthesis-elastic spine pad (LP-ESP®) is an innovative one-piece deformable but cohesive interbody spacer providing 6 full degrees of freedom about the 3 axes, including shock absorption. A 20-year research program has demonstrated that this concept provides mechanical properties very close to those of a natural disk. Improvements in technology have made it possible to solve the problem of the bond between the elastic component and the titanium endplates and to obtain an excellent biostability. The prosthesis geometry allows limited rotation and translation with resistance to motion (elastic return property) aimed at avoiding overload of the posterior facets. The rotation center can vary freely during motion. It thus differs substantially from current prostheses, which are 2- or 3-piece devices involving 1 or 2 bearing surfaces and providing 3 or 5 degrees of freedom. This design and the adhesion-molding technology differentiate the LP-ESP prosthesis from other mono-elastomeric prostheses, for which the constraints of shearing during rotations or movement are absorbed at the endplate interface. Seven years after the first implantation, we can document in a solid and detailed fashion the course of clinical outcomes and the radiological postural and kinematic behavior of this prosthesis.
PMCID: PMC3567327  PMID: 23412443
Disc arthroplasty; Disc replacement biomechanics; Motion preservation; Disc degeneration; Low back pain; Spinal alignment
22.  Seventeen-millimeter St. Jude Medical Regent valve in patients with small aortic annulus: dose moderate prosthesis-patient mismatch matter? 
The study was designed to evaluate the effects of moderate prosthesis-patient mismatch (defined as 0.65 cm2/m2 < indexed effective orifice area ≤ 0.85 cm2/m2) on midterm outcomes after isolated aortic valve replacement with a 17-mm St. Jude Medical Regent valve in a large series of patients, and to determine if these effects are influenced by patient confounding variables.
One-hundred and six patients with and without moderate prosthesis-patient mismatch early after implantation of a 17-mm Regent valve at aortic position were included. Both clinical and echocardiographic assessments were performed preoperatively, at discharge and during follow-up period (mean follow-up time 52.6 ± 11.9 months).
The prevalence of moderate prosthesis-patient mismatch was documented in 46 patients (43.4%) at discharge. During the follow-up period, no difference in the regression of left ventricular mass, decrease of transvalvular pressure gradients, mortality and prosthesis-related complications was observed between patients with and without moderate prosthesis-patient mismatch. After adjustment for several risk factors, moderate prosthesis-patient mismatch was associated with increased midterm mortality in patients with baseline left ventricular ejection fraction < 50% (HR: 1.80, p = 0.02), but with normal prognosis in those with preserved LV function. Younger age (cut off value = 65 years) was not an independent predictor of increased midterm mortality and valve-related complications in patients with moderate prosthesis-patient mismatch.
Moderate prosthesis-patient mismatch after aortic valve replacement with a small mechanical prosthesis is associated with increased mortality and adverse events in patients with pre-existing left ventricular dysfunction. Selected patients with small aortic annulus can experience satisfactory clinical improvements and midterm survival after aortic valve replacement with a 17-mm Regent valve.
PMCID: PMC3896805  PMID: 24438101
Prosthesis-patient mismatch; 17-mm Regent valve; Aortic valve replacement; Clinical outcome
23.  Differences in External and Internal Cortical Strain with Prosthesis in the Femur 
The contact between a femoral stem prosthesis and the internal surface of the cortical bone with the stress in the interface is of crucial importance with respect to loosening. However, there are no reports of strain patterns at this site, and the main aim of the current study was to investigate differences of internal and external cortical strain in the proximal femur after insertion of a stem prosthesis. The external cortical strain of a human cadaveric femur was measured with strain gauges before and after implantation of a stem prosthesis. By use of optical fibres embedded longitudinally in the endosteal cortex, deformations at the implant–internal cortex interface could also be measured. The main external deformation during loading of the intact femur occurred as compression of the medial cortex; both at the proximal and distal levels. The direction of the principal strain on the medial and lateral aspects was close to the longitudinal axis of the bone. After resection of the femoral neck and insertion of a stem prosthesis, the changes in external strain values were greatest medially at the proximal level, where the magnitude of deformation in compression was reduced to about half the values measured on the intact specimen. Otherwise, there were rather small changes in external principal strain. However, by comparing vertical strain in the external and internal cortex of the proximal femur, there were great differences in values and patterns at all positions. The transcortical differences in strain varied from compression on one side to distraction on the other and vice versa in some of the positions with a correlation coefficient of 0.07. Our results show that differences exist between the external and internal cortical strain when loading a stem prosthesis. Hence, strain at the internal cortex does not correspond and can not be deducted from measured strain at the external cortex.
PMCID: PMC3253998  PMID: 22235237
Deformation; femur; hip; optical fibre; prosthesis; strain.
24.  Airway stenting with the LT-Mold™ for severe glotto-subglottic stenosis or intractable aspiration: experience in 65 cases 
The purpose of this study was to assess the safety and efficacy of stenting in upper airway reconstructions for benign laryngotracheal stenosis (LTS) with a newly designed prosthesis, the LT-Mold™. The LT-Mold and its proper use during open surgery and endoscopy are described, and the experience gathered from a prospectively collected database on 65 patients treated for complex LTS or severe aspiration is reported. This series is compared to the results of other stenting methods. All patients were available for evaluation. In all but one case, the prosthesis was removed at the end of the study. The new prosthesis did not induce any stent-related trauma to the supraglottis, glottis and subglottis. Before adding a distal round-shaped silicone cap to the LT-Mold, granulation tissue was usually seen at the stent-mucosal interface at the tracheostoma level. In 14 cases, there has been a spontaneous extrusion of the prosthesis through the mouth; this problem was solved by fixing the prosthesis through the reinforced portion of the prosthesis at the cap level and by adding one fixation stitch in the supraglottis. We have to document the loss of the silicone cap in three cases. This problem was resolved by designing a new prototype with an integrated cap, glued with a slow hardening silicone glue. Fifty-four (83 %) of 65 patients were decannulated after a mean duration of stenting of 3 months (range 1–12 months). The mean follow-up after decannulation was 23 months (range 1 month to 10 years). The experience gathered with the LT-Mold shows that long-term stenting for complex LTS is safely achieved when the prosthesis is used with its distal integrated silicone cap. The softness and smoothness of the prosthesis with a round-shaped configuration of both extremities help avoid ulceration and granulation tissue formation in the reconstructed airway. Adequate fixation is mandatory to avoid extrusion.
PMCID: PMC3491198  PMID: 22722945
Laryngotracheal stenosis; Airway stenting; LT-Mold; Laryngotracheal reconstruction; Partial cricotracheal resection; Intractable aspiration
25.  Arterial stiffness identification of the human carotid artery using the stress-strain relationship in vivo 
Ultrasonics  2011;52(3):402-411.
Arterial stiffness is well accepted as a reliable indicator of arterial disease. Increase in carotid arterial stiffness has been associated with carotid arterial disease, e.g., atherosclerotic plaque, thrombosis, stenosis, etc. Several methods for carotid arterial stiffness assessments have been proposed. In this study, in-vivo noninvasive assessment using applanation tonometry and an ultrasound-based motion estimation technique was applied in seven healthy volunteers (age 28 ± 3.6 years old) to determine pressure and wall displacement in the left common carotid artery (CCA), respectively. The carotid pressure was obtained using a calibration method by assuming that the mean and diastolic blood pressures remained constant throughout the arterial tree. The regional carotid arterial wall displacement was estimated using a 1D cross-correlation technique on the ultrasound radio frequency (RF) signals acquired at a frame rate of 505–1010 Hz. Young’s moduli were estimated under two different assumptions: (i) a linear elastic two-parallel spring model and (ii) a two-dimensional, nonlinear, hyperelastic model. The circumferential stress (σθ) and strain (εθ) relationship was then established in humans in vivo. A slope change in the circumferential stress-strain curve was observed and defined as a transition point. The Young’s moduli of the elastic lamellae (E1), elastin-collagen fibers (E2) and collagen fibers (E3) and the incremental Young’s moduli before (E0≤εθ<ε0T) and after the transition point (EεθT≤εθ) were determined from the first and second approach, respectively, to describe the contribution of the complex mechanical interaction of the different arterial wall constituents. The average E1, E2 and E3 from seven healthy volunteers were found to be equal to 0.15 ± 0.04, 0.89 ± 0.27 and 0.75 ± 0.29 MPa, respectively. The average E0≤εθ<εθTInt and EεθT≤εθInt of the intact wall (both the tunica adventitia and tunica media layers) were found to be equal to 0.16 ± 0.04 MPa and 0.90 ± 0.25 MPa, respectively. The average E0≤εθ<εθTAd and EεθT≤εθAd of the tunica adventitia were found to be equal to 0.18 ± 0.05 MPa and 0.84 ± 0.22 MPa, respectively. The average EεθT≤εθMe and EεθT≤εθMe of the tunica media were found to be equal to 0.19 ± 0.05 MPa and 0.90 ± 0.25 MPa, respectively. The stiffness of the carotid artery increased with strain during the systolic phase of cardiac cycle. In conclusion, the feasibility of measuring the regional stress-strain relationship and stiffness of the normal human carotid artery noninvasively was demonstrated in human in vivo.
PMCID: PMC4009743  PMID: 22030473
Arterial stiffness; Carotid artery; Collagen; Elastin; Motion estimation; Tonometry; Ultrasound

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