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1.  Biomechanical comparison of three stand-alone lumbar cages — a three-dimensional finite element analysis 
For anterior lumbar interbody fusion (ALIF), stand-alone cages can be supplemented with vertebral plate, locking screws, or threaded cylinder to avoid the use of posterior fixation. Intuitively, the plate, screw, and cylinder aim to be embedded into the vertebral bodies to effectively immobilize the cage itself. The kinematic and mechanical effects of these integrated components on the lumbar construct have not been extensively studied. A nonlinearly lumbar finite-element model was developed and validated to investigate the biomechanical differences between three stand-alone (Latero, SynFix, and Stabilis) and SynCage-Open plus transpedicular fixation. All four cages were instrumented at the L3-4 level.
The lumbar models were subjected to the follower load along the lumbar column and the moment at the lumbar top to produce flexion (FL), extension (EX), left/right lateral bending (LLB, RLB), and left/right axial rotation (LAR, RAR). A 10 Nm moment was applied to obtain the six physiological motions in all models. The comparison indices included disc range of motion (ROM), facet contact force, and stresses of the annulus and implants.
At the surgical level, the SynCage-open model supplemented with transpedicular fixation decreased ROM (>76%) greatly; while the SynFix model decreased ROM 56-72%, the Latero model decreased ROM 36-91%, in all motions as compared with the INT model. However, the Stabilis model decreased ROM slightly in extension (11%), lateral bending (21%), and axial rotation (34%). At the adjacent levels, there were no obvious differences in ROM and annulus stress among all instrumented models.
ALIF instrumentation with the Latero or SynFix cage provides an acceptable stability for clinical use without the requirement of additional posterior fixation. However, the Stabilis cage is not favored in extension and lateral bending because of insufficient stabilization.
PMCID: PMC3852219  PMID: 24088294
ALIF; Anterior lumbar interbody fusion; Stand-alone cage; Finite element analysis
2.  A free vascularized tibia-fibular composite graft for the traumatic femoral bony defect of a 6-year-old boy with 10-year follow up: a case report 
Free vascularized fibular grafts have been widely used for the reconstruction of long bone defects. However, the use of a vascularized tibial graft is precluded by its weight-bearing function and unacceptable donor site morbidity.
Case presentation
We present a rare case of using a vascularized tibia-fibular composite graft taken from a 6-year-old Chinese boy’s ipsilateral lower leg to reconstruct a large bony defect of his traumatic femur. Hypertrophy of the tibial graft, good remodeling of the femoral shaft, and atrophy of the unloaded fibular graft were noted at the 10-year follow up. He was able to participate in outdoor activities such as basketball while wearing his prosthesis.
The 10-year follow up demonstrates the feasibility of this salvage procedure for a floating knee injury with neurovascular compromise.
PMCID: PMC3680008  PMID: 23714102
Pediatrics; Traumatic bony defect; Vascularized tibia-fibular graft
3.  Biomechanical comparison of unilateral and bilateral pedicle screws fixation for transforaminal lumbar interbody fusion after decompressive surgery -- a finite element analysis 
Little is known about the biomechanical effectiveness of transforaminal lumbar interbody fusion (TLIF) cages in different positioning and various posterior implants used after decompressive surgery. The use of the various implants will induce the kinematic and mechanical changes in range of motion (ROM) and stresses at the surgical and adjacent segments. Unilateral pedicle screw with or without supplementary facet screw fixation in the minimally invasive TLIF procedure has not been ascertained to provide adequate stability without the need to expose on the contralateral side. This study used finite element (FE) models to investigate biomechanical differences in ROM and stress on the neighboring structures after TLIF cages insertion in conjunction with posterior fixation.
A validated finite-element (FE) model of L1-S1 was established to implant three types of cages (TLIF with a single moon-shaped cage in the anterior or middle portion of vertebral bodies, and TLIF with a left diagonally placed ogival-shaped cage) from the left L4-5 level after unilateral decompressive surgery. Further, the effects of unilateral versus bilateral pedicle screw fixation (UPSF vs. BPSF) in each TLIF cage model was compared to analyze parameters, including stresses and ROM on the neighboring annulus, cage-vertebral interface and pedicle screws.
All the TLIF cages positioned with BPSF showed similar ROM (<5%) at surgical and adjacent levels, except TLIF with an anterior cage in flexion (61% lower) and TLIF with a left diagonal cage in left lateral bending (33% lower) at surgical level. On the other hand, the TLIF cage models with left UPSF showed varying changes of ROM and annulus stress in extension, right lateral bending and right axial rotation at surgical level. In particular, the TLIF model with a diagonal cage, UPSF, and contralateral facet screw fixation stabilize segmental motion of the surgical level mostly in extension and contralaterally axial rotation. Prominent stress shielded to the contralateral annulus, cage-vertebral interface, and pedicle screw at surgical level. A supplementary facet screw fixation shared stresses around the neighboring tissues and revealed similar ROM and stress patterns to those models with BPSF.
TLIF surgery is not favored for asymmetrical positioning of a diagonal cage and UPSF used in contralateral axial rotation or lateral bending. Supplementation of a contralateral facet screw is recommended for the TLIF construct.
PMCID: PMC3503692  PMID: 22591664
Transforaminal lumbar interbody fusion; Pedicle screw fixation; Contralateral facet screw; Finite element analysis
4.  Lateral fixation of AO type-B2 ankle fractures: the Acutrak plus compression screw technique 
International Orthopaedics  2010;34(6):903-907.
The Acutrak plus compression screw (APCS) (Acumed Inc., Beaverton, OR, USA) is an intramedullary implant which can achieve stable fixation with minimum soft tissue dissection. The characteristics of the APCS include fully-threaded length, headless, cannulated, and variable thread pitch. Twenty-three patients with AO type-B2 ankle fractures treated with lateral fixation by an APCS were retrospectively reviewed. Evaluation of postoperative roentgenograms for adequacy of reduction revealed a good reduction in 22 of 23 (95.7%) patients. The average wound incision was 4.1 cm. The operative time was 25.3 minutes. All the ankle fractures showed radiographic evidence of healing within four months. At the final follow-up, the ankle scores of the patients were evaluated for functional outcomes. Good to excellent results were obtained in 21 (91.3%) patients. No patient complained of symptomatic hardware. In conclusion, lateral fixation of AO type-B2 ankle fractures by APCS offers several advantages including stable fixation, a small surgical wound, less dissection of soft tissue, no palpable hardware, and easy application with a short operating time.
PMCID: PMC2989028  PMID: 20177893
6.  Stabilisation of the fractured fibula plays an important role in the treatment of pilon fractures: a retrospective comparison of fibular fixation methods 
International Orthopaedics  2008;33(3):695-699.
Ninety-eight pilon fractures associated with ipsilateral distal fibular fracture were included in this study. The pilon fractures were treated by open reduction and plating. The 98 fractures were divided into three groups based on the treatment method of fractured fibula. Group A was composed of 50 fibular fractures treated by open reduction and plate fixation. Group B was composed of 23 fibular fractures treated by open reduction and pin fixation. Group C was composed of 25 fibular fractures treated conservatively by closed reduction. The radiographs were reviewed for adequacy of fracture reduction and posttraumatic arthrosis. At the end of follow-up, the clinical outcomes were evaluated using a rating scale. The three groups were similar in respect to Ruedi type, open fracture grade, and demographics (all p values >0.25). Group A showed a decreasing trend of malunion and ankle arthrosis compared to group C (p = 0.091 and p = 0.099, respectively). Group A had a better clinical outcome than group C (p = 0.008). In addition, group A showed an increasing trend of satisfactory outcome compared to group B (p = 0.096). In conclusion, for pilon fractures associated with ipsilateral fibular fractures, stabilisation of the fractured fibula plays an important role in the decrease of distal tibial malunion and post-traumatic ankle arthrosis as well as improvement of clinical outcomes.
PMCID: PMC2903122  PMID: 18931843
7.  Spontaneous infective spondylitis and mycotic aneurysm: incidence, risk factors, outcome and management experience 
European Spine Journal  2007;17(3):439-444.
Infective spondylitis occurring concomitantly with mycotic aneurysm is rare. A retrospective record review was conducted in all cases of mycotic aneurysm from January 1995 to December 2004, occurring in a primary care and tertiary referral center. Spontaneous infective spondylitis and mycotic aneurysm were found in six cases (10.3% of 58 mycotic aneurysm patients). Neurological deficit (50% vs. 0; P < 0.001) is the significant clinical manifestation in patients with spontaneous infective spondylitis and mycotic aneurysm. The presence of psoas abscess on computed tomography (83.3% vs. 0; P < 0.001) and endplate destruction on radiography (50% vs. 0; P < 0.001) are predominated in patients with spontaneous infective spondylitis and mycotic aneurysm. Of these six patients, four with Salmonella infection received surgical intervention and all survived. Another two patients (one with Streptococcus pyogenes, another with Staphylococcus aureus) received conservative therapy and subsequently died from rupture of aneurysm or septic shock. Paravertebral soft tissue swelling, presence of psoas abscess and/or unclear soft tissue plane between the aorta and vertebral body in relation to mycotic aneurysm may indicate a concomitant infection in the spine. In contrast, if prevertebral mass is found in the survey of spine infection, coexisting mycotic aneurysm should be considered.
PMCID: PMC2270374  PMID: 18046585
Infective spondylitis; Mycotic aneurysm; Psoas abscess
8.  Biomechanical comparison of a new stand-alone anterior lumbar interbody fusion cage with established fixation techniques – a three-dimensional finite element analysis 
Initial promise of a stand-alone interbody fusion cage to treat chronic back pain and restore disc height has not been realized. In some instances, a posterior spinal fixation has been used to enhance stability and increase fusion rate. In this manuscript, a new stand-alone cage is compared with conventional fixation methods based on the finite element analysis, with a focus on investigating cage-bone interface mechanics and stress distribution on the adjacent tissues.
Three trapezoid 8° interbody fusion cage models (dual paralleled cages, a single large cage, or a two-part cage consisting of a trapezoid box and threaded cylinder) were created with or without pedicle screws fixation to investigate the relative importance of the screws on the spinal segmental response. The contact stress on the facet joint, slip displacement of the cage on the endplate, and rotational angle of the upper vertebra were measured under different loading conditions.
Simulation results demonstrated less facet stress and slip displacement with the maximal contact on the cage-bone interface. A stand-alone two-part cage had good slip behavior under compression, flexion, extension, lateral bending and torsion, as compared with the other two interbody cages, even with the additional posterior fixation. However, the two-part cage had the lowest rotational angles under flexion and torsion, but had no differences under extension and lateral bending.
The biomechanical benefit of a stand-alone two-part fusion cage can be justified. This device provided the stability required for interbody fusion, which supports clinical trials of the cage as an alternative to circumferential fixations.
PMCID: PMC2442839  PMID: 18559117
9.  Staged arthroplasty as salvage procedure for deep hip infection following intertrochanteric fracture 
International Orthopaedics  2006;30(4):228-232.
Deep hip infection is a rare complication of intertrochanteric fractures and an optimal treatment has not yet been reported. Twenty-seven patients who contracted deep hip sepsis following the failed primary treatment of an intertrochanteric fracture were treated with two-stage hip arthroplasty. Antibiotic-impregnated cement beads were implanted following resection arthroplasty in the first 15 patients, and a temporary cement spacer prosthesis was used in the other 12 hips. There was only one recurrence of infection at an average follow-up of 4.8 years. Complications included non-union of the greater trochanter in four patients, intraoperative femoral fracture in two and fracture of the cement prosthesis in one. The use of an interim spacer was associated with better hip function in the interim period; a decreased operative time and less blood loss at the time of arthroplasty; and a higher hip score at final follow-up. Staged arthroplasty is an effective salvage procedure for deep hip infection after the failed treatment of an intertrochanteric fracture. The use of a temporary spacer maintains hip function between stages, makes arthroplasty less complicated, and improves the clinical outcome.
PMCID: PMC2532121  PMID: 16673103
10.  Biomechanical effects of polyaxial pedicle screw fixation on the lumbosacral segments with an anterior interbody cage support 
Lumbosacral fusion is a relatively common procedure that is used in the management of an unstable spine. The anterior interbody cage has been involved to enhance the stability of a pedicle screw construct used at the lumbosacral junction. Biomechanical differences between polyaxial and monoaxial pedicle screws linked with various rod contours were investigated to analyze the respective effects on overall construct stiffness, cage strain, rod strain, and contact ratios at the vertebra-cage junction.
A synthetic model composed of two ultrahigh molecular weight polyethylene blocks was used with four titanium pedicle screws (two in each block) and two rods fixation to build the spinal construct along with an anterior interbody cage support. For each pair of the construct fixed with polyaxial or monoaxial screws, the linked rods were set at four configurations to simulate 0°, 7°, 14°, and 21° lordosis on the sagittal plane, and a compressive load of 300 N was applied. Strain gauges were attached to the posterior surface of the cage and to the central area of the left connecting rod. Also, the contact area between the block and the cage was measured using prescale Fuji super low pressure film for compression, flexion, lateral bending and torsion tests.
Our main findings in the experiments with an anterior interbody cage support are as follows: 1) large segmental lordosis can decrease the stiffness of monoaxial pedicle screws constructs; 2) polyaxial screws rather than monoaxial screws combined with the cage fixation provide higher compression and flexion stiffness in 21° segmental lordosis; 3) polyaxial screws enhance the contact surface of the cage in 21° segmental lordosis.
Polyaxial screws system used in conjunction with anterior cage support yields higher contact ratio, compression and flexion stiffness of spinal constructs than monoaxial screws system does in the same model when the spinal segment is set at large lordotic angles. Polyaxial pedicle screw fixation performs nearly equal percentages of vertebra-cage contact among all constructs with different sagittal alignments, therefore enhances the stabilization effect of interbody cages in the lumbosacral area.
PMCID: PMC1829160  PMID: 17349057
11.  Multiple parallel skin markers for minimal incision lumbar disc surgery; a technical note 
Spinal surgery depends on accurate localization to prevent incorrect surgical approaches. The trend towards minimally invasive surgery that minimizes surgical exposure and reduces postoperative pain increasingly requires surgeons to accurately determine the operative level before an incision is made. Preoperative localization with a C-arm image intensifier is popular, but the exposure of both patients and theatre staff to radiation is a disadvantage, as well as being time-consuming.
We describe a simple surgical tool developed to help localize exact spinal levels in conjunction with a simple AP X-ray film immediately before surgery. Multiple parallel skin markers were made using a circular oven rack comprising multiple 1.5 cm spaced parallel wires attached to a circular outside rim. The longest line was placed on the line of the postero-superior iliac spine (PSIS) over the junction of the L5-S1 region.
Results and conclusions
Based on the film taken, the incision can be accurately made at the intended level. The incision wound can be minimized to 3.0 cm even when using conventional disc surgery instruments.
PMCID: PMC394334  PMID: 15113431

Results 1-11 (11)