A potential effective treatment for prevention of osteoporotic hip fractures is augmentation of the mechanical properties of the femur by injecting it with agents such as (PMMA) bone cement – femoroplasty. The operation, however, is only in research stage and can benefit substantially from computer planning and optimization. We report the results of computational planning and optimization of the procedure for biomechanical evaluation. An evolutionary optimization method was used to optimally place the cement in finite element (FE) models of seven osteoporotic bone specimens. The optimization, with some inter-specimen variations, suggested that areas close to the cortex in the superior and inferior of the neck and supero-lateral aspect of the greater trochanter will benefit from augmentation. We then used a particle-based model for bone cement diffusion simulation to match the optimized pattern, taking into account the limitations of the actual surgery, including limited volume of injection to prevent thermal necrosis. Simulations showed that the yield load can be significantly increased by more than 30%, using only 9ml of bone cement. This increase is comparable to previous literature reports where gross filling of the bone was employed instead, using more than 40ml of cement. These findings, along with the differences in the optimized plans between specimens, emphasize the need for subject-specific models for effective planning of femoral augmentation.
Femoroplasty; PMMA Cement; Finite Element; Optimization; Planning
Le Fort-based face–jaw–teeth transplantation (FJTT) attempts to marry bone and teeth geometry of size-mismatched face–jaw–teeth segments to restore function and form due to severe mid-facial trauma. Recent development of a computer-assisted planning and execution (CAPE) system for Le Fort-based FJTT in a pre-clinical swine model offers preoperative planning, and intraoperative navigation. This paper addresses the translation of the CAPE system to human anatomy and presents accuracy results.
Single-jaw, Le Fort-based FJTTs were performed on plastic models, one swine and one human, and on a human cadaver. Preoperative planning defined the goal placement of the donor’s Le Fort-based FJTT segment on the recipient. Patient-specific navigated cutting guides helped achieve planned osteotomies. Intraoperative cutting guide and donor fragment placement were compared with postoperative computed tomography (CT) data and the preoperative plan.
Intraoperative measurement error with respect to postoperative CT was less than 1.25 mm for both mock transplants and 3.59 mm for the human cadaver scenario. Donor fragment placement (as compared to the planned position) was less accurate for the human model test case (2.91 mm) compared with the swine test (2.25 mm) and human cadaver (2.26 mm).
The results indicate the viability of the CAPE system for assisting with Le Fort-based FJTT and demonstrate the potential in human surgery. This system offers a new path forward to achieving improved outcomes in Le Fort-based FJTT and can be modified to assist with a variety of other surgeries involving the head, neck, face, jaws and teeth.
Face–jaw–teeth transplantation; Face transplant; Le Fort-based transplant; Surgical cutting guide; Navigation; Preoperative planning
The paper addresses the coupled motion of a 6 degree of freedom robot and a snake-like dexterous manipulator (SDM) designed for the treatment of bone defects behind the implant during total hip arthroplasty revision surgery. We have formulated the problem as a weighted, multi-objective constraint, linear optimization. A remote center of motion (RCM) acts as a virtual constraint for the robot. The coupled robot kinematics does not assume piecewise-constant curvature for the SDM. We have evaluated our method by simulating the coupled system inside a potential lesion area.
2-D-to-3-D registration is critical and fundamental in image-guided interventions. It could be achieved from single image using paired point correspondences between the object and the image. The common assumption that such correspondences can readily be established does not necessarily hold for image guided interventions. Intraoperative image clutter and an imperfect feature extraction method may introduce false detection and, due to the physics of X-ray imaging, the 2-D image point features may be indistinguishable from each other and/or obscured by anatomy causing false detection of the point features. These create difficulties in establishing correspondences between image features and 3-D data points. In this paper, we propose an accurate, robust, and fast method to accomplish 2-D–3-D registration using a single image without the need for establishing paired correspondences in the presence of false detection. We formulate 2-D–3-D registration as a maximum likelihood estimation problem, which is then solved by coupling expectation maximization with particle swarm optimization. The proposed method was evaluated in a phantom and a cadaver study. In the phantom study, it achieved subdegree rotation errors and submillimeter in-plane (X –Y plane) translation errors. In both studies, it outperformed the state-of-the-art methods that do not use paired correspondences and achieved the same accuracy as a state-of-the-art global optimal method that uses correct paired correspondences.
2-D–3-D registration; feature-based registration; image-guided interventions (IGIs); particle swarm optimization (PSO)
The aim of this study was to provide a fast and accurate finite element (FE) modeling scheme for predicting bone stiffness and strength suitable for use within the framework of a computer-assisted osteoporotic femoral bone augmentation surgery system. The key parts of the system, i.e. preoperative planning and intraoperative assessment of the augmentation, demand the finite element model to be solved and analyzed rapidly. Available CT scans and mechanical testing results from nine pairs of osteoporotic femur bones, with one specimen from each pair augmented by polymethylmethacrylate (PMMA) bone cement, were used to create FE models and compare the results with experiments. Correlation values of R2 = 0.72–0.95 were observed between the experiments and FEA results which, combined with the fast model convergence (~3 min for ~250,000 degrees of freedom), makes the presented modeling approach a promising candidate for the intended application of preoperative planning and intraoperative assessment of bone augmentation surgery.
Femoroplasty; Finite element analysis; Biomechanics; Bone cement
This paper presents and validates a computer-navigated system for performing periacetabular osteotomy (PAO) to treat developmental dysplasia of the hip. The main motivation of the biomechanical guidance system (BGS) is to plan and track the osteotomy fragment in real time during PAO while simplifying the procedure for less-experienced surgeons. The BGS aims at developing a platform for comparing biomechanical states of the joint with the current gold standard geometric assessment of anatomical angles. The purpose of this study was to (1) determine the accuracy with which the BGS tracks the hip joint through repositioning and (2) identify improvements to the workflow.
Nineteen cadaveric validation studies quantified system accuracy, verified system application, and helped to refine surgical protocol. In two surgeries, navigation and registration accuracy were computed by affixing fiducials to two cadavers prior to surgery. All scenarios compared anatomical angle measurements and joint positioning as measured intraoperatively to postoperatively.
In the two cases with fiducials, computed fragment transformations deviated from measured fiducial transformations by 1.4 and 1.8 mm in translation and 1.0° and 2.2° in rotation, respectively. The additional seventeen surgeries showed strong agreement between intraoperative and postoperative anatomical angles, helped to refine the surgical protocol, and demonstrated system robustness.
Estimated accuracy with BGS appeared acceptable for future surgical applications. Several major system requirements were identified and addressed, improving the BGS and making it feasible for clinical studies.
Periacetabular osteotomy; Developmental dysplasia; Computer-assisted surgery; Orthopedics
Snake-like manipulators with a large, open lumen can offer improved treatment alternatives for minimally- and less-invasive surgeries. In these procedures, surgeons use the manipulator to introduce and control flexible tools in the surgical environment. This paper describes a predictive algorithm for estimating manipulator configuration given tip position for nonconstant curvature, cable-driven manipulators using energy minimization. During experimental bending of the manipulator with and without a tool inserted in its lumen, images were recorded from an overhead camera in conjunction with actuation cable tension and length. To investigate the accuracy, the estimated manipulator configuration from the model and the ground-truth configuration measured from the image were compared. Additional analysis focused on the response differences for the manipulator with and without a tool inserted through the lumen. Results indicate that the energy minimization model predicts manipulator configuration with an error of 0.24 ± 0.22mm without tools in the lumen and 0.24 ± 0.19mm with tools in the lumen (no significant difference, p = 0.81). Moreover, tools did not introduce noticeable perturbations in the manipulator trajectory; however, there was an increase in requisite force required to reach a configuration. These results support the use of the proposed estimation method for calculating the shape of the manipulator with an tool inserted in its lumen when an accuracy range of at least 1mm is required.
Medical Robots and Systems; Kinematics; Underactuated Robots
A novel algorithm is presented to segment and reconstruct injected bone cement from a sparse set of X-ray images acquired at arbitrary poses. The sparse X-ray multi-view active contour (SxMAC—pronounced “smack”) can 1) reconstruct objects for which the background partially occludes the object in X-ray images, 2) use X-ray images acquired on a noncircular trajectory, and 3) incorporate prior computed tomography (CT) information. The algorithm’s inputs are preprocessed X-ray images, their associated pose information, and prior CT, if available. The algorithm initiates automated reconstruction using visual hull computation from a sparse number of X-ray images. It then improves the accuracy of the reconstruction by optimizing a geodesic active contour. Experiments with mathematical phantoms demonstrate improvements over a conventional silhouette based approach, and a cadaver experiment demonstrates SxMAC’s ability to reconstruct high contrast bone cement that has been injected into a femur and achieve sub-millimeter accuracy with four images.
Active contour; bone cement; deformable models; intra-operative imaging; reconstruction; segmentation
Intraoperative patient registration may significantly affect the outcome of image-guided surgery (IGS). Image-based registration approaches have several advantages over the currently dominant point-based direct contact methods and are used in some industry solutions in image-guided radiation therapy with fixed X-ray gantries. However, technical challenges including geometric calibration and computational cost have precluded their use with mobile C-arms for IGS. We propose a 2D/3D registration framework for intraoperative patient registration using a conventional mobile X-ray imager combining fiducial-based C-arm tracking and graphics processing unit (GPU)-acceleration. The two-stage framework 1) acquires X-ray images and estimates relative pose between the images using a custom-made in-image fiducial, and 2) estimates the patient pose using intensity-based 2D/3D registration. Experimental validations using a publicly available gold standard dataset, a plastic bone phantom and cadaveric specimens have been conducted. The mean target registration error (mTRE) was 0.34 ± 0.04 mm (success rate: 100%, registration time: 14.2 s) for the phantom with two images 90° apart, and 0.99 ± 0.41 mm (81%, 16.3 s) for the cadaveric specimen with images 58.5° apart. The experimental results showed the feasibility of the proposed registration framework as a practical alternative for IGS routines.
C-arm pose tracking; GPU-acceleration; image-guided surgery; intraoperative 2D/3D registration
Current protocols for facial transplantation include the mandatory fabrication of an alloplastic “mask” to restore the congruency of the donor site in the setting of “open casket” burial. However, there is currently a paucity of literature describing the current state-of-the-art and available options.
During this study, we identified that most of donor masks are fabricated using conventional methods of impression, molds, silicone, and/or acrylic application by an experienced anaplastologist or maxillofacial prosthetics technician. However, with the recent introduction of several enhanced computer-assisted technologies, our facial transplant team hypothesized that there were areas for improvement with respect to cost and preparation time.
The use of digital imaging for virtual surgical manipulation, computer-assisted planning, and prefabricated surgical cutting guides—in the setting of facial transplantation—provided us a novel opportunity for digital design and fabrication of a donor mask. The results shown here demonstrate an acceptable appearance for “open-casket” burial while maintaining donor identity after facial organ recovery.
Several newer techniques for fabrication of facial transplant donor masks exist currently and are described within the article. These encompass digital impression, digital design, and additive manufacturing technology.
3-dimensional printing; scanning; computer design; AMT; additive manufacturing; craniofacial; binder jetting; materials jetting; mask; donor mask
Gender-specific anthropometrics, skin texture/adnexae mismatch, and social apprehension have prevented cross-gender facial transplantation from evolving. However, the scarce donor pool and extreme waitlist times are currently suboptimal. Our objective was to: 1) perform and assess cadaveric facial transplantation for each gender-mismatch scenario employing virtual panning with cutting guide fabrication and 2) review the advantages/disadvantages of cross-gender facial transplantation.
Cross-gender facial transplantation feasibility was evaluated through two mock, double-jaw, Le Fort-based cadaveric allotransplants, including female donor-to-male recipient (T1-FM) and male donor-to-female recipient (T2-MF). Hybrid facial-skeletal relationships were investigated using cephalometric measurements, including sellion-nasion-A point (SNA) and sellion-nasion-B point (SNB) angles, and lower-anterior-facial-height to total-anterior-facial-height ratio (LAFH/TAFH). Donor and recipient cutting guides were designed with virtual planning based on our team’s experience in swine dissections and used to optimize the results.
Skeletal proportions and facial-aesthetic harmony of the transplants [n=2] were found to be equivalent to all reported experimental/clinical gender-matched cases by using custom guides and Mimics technology. Cephalometric measurements are shown in Table 1 relative to Eastman Normal Values.
Based on our results, we believe that cross-gender facial transplantation can offer equivalent, anatomical skeletal outcomes to those of gender-matched pairs using pre-operative planning and custom guides for execution. Lack of literature discussion of cross-gender facial transplantation highlights the general stigmata encompassing the subject. We hypothesize that concerns over gender-specific anthropometrics, skin texture/adnexae disparity, and increased immunological resistance have prevented full acceptance thus far. Advantages include an increased donor pool with expedited reconstruction, as well as size-matched donors.
Face Transplant; Craniomaxillofacial; Vascularized Composite Allotransplantation (VCA); Gender; Cross-gender; Intraoperative Cutting Guide
Facial transplantation represents one of the most complicated scenarios in craniofacial surgery because of skeletal, aesthetic, and dental discrepancies between donor and recipient. However, standard off-the-shelf vendor computer-assisted surgery systems may not provide custom features to mitigate the increased complexity of this particular procedure. We propose to develop a computer-assisted surgery solution customized for preoperative planning, intraoperative navigation including cutting guides, and dynamic, instantaneous feedback of cephalometric measurements/angles as needed for facial transplantation.
We developed the Computer-Assisted Planning and Execution (CAPE) workstation to assist with planning and execution of facial transplantation. Preoperative maxillofacial computed tomography (CT) scans were obtained on 4 size-mismatched miniature swine encompassing 2 live face-jaw-teeth transplants. The system was tested in a laboratory setting using plastic models of mismatched swine, after which the system was used in 2 live swine transplants. Postoperative CT imaging was obtained and compared with the preoperative plan and intraoperative measures from the CAPE workstation for both transplants.
Plastic model tests familiarized the team with the CAPE workstation and identified several defects in the workflow. Live swine surgeries demonstrated utility of the CAPE system in the operating room, showing submillimeter registration error of 0.6 ± 0.24 mm and promising qualitative comparisons between intraoperative data and postoperative CT imaging.
The initial development of the CAPE workstation demonstrated integration of computer planning and intraoperative navigation for facial transplantation are possible with submillimeter accuracy. This approach can potentially improve preoperative planning, allowing ideal donor-recipient matching despite significant size mismatch, and accurate surgical execution.
Computer-assisted planning; computer-integrated surgery; cutting guides; maxillofacial transplant; swine facial transplant; craniofacial; craniomaxillofacial surgery; swine study; face transplant
Le Fort-based, maxillofacial allotransplantation is a reconstructive alternative gaining clinical acceptance. However, the vast majority of single-jaw transplant recipients demonstrate less-than-ideal skeletal and dental relationships with suboptimal aesthetic harmony. The purpose of this study was to investigate reproducible cephalometric landmarks in a large animal model, where refinement of computer-assisted planning, intra-operative navigational guidance, translational bone osteotomies, and comparative surgical techniques could be performed.
Cephalometric landmarks that could be translated into the human craniomaxillofacial skeleton, and would remain reliable following maxillofacial osteotomies with mid-facial alloflap inset, were sought on six miniature swine. Le Fort I-and Le Fort III-based alloflaps were harvested in swine with osteotomies, and all alloflaps were either auto-replanted or transplanted. Cephalometric analyses were performed on lateral cephalograms pre- and post-operatively. Critical cephalometric data sets were identified with the assistance of surgical planning and virtual prediction software, and evaluated for reliability and translational predictability.
Several pertinent landmarks and human analogues were identified including pronasale (PRN), zygion (Zy), parietale (PA), gonion (GO), gnathion (GN), lower incisior base (LIB), and alveolare (ALV). PA-PRN-ALV and PA-PRN-LIB were found to be reliable correlates of SNA and SNB measurements in humans, respectively.
There is a set of reliable cephalometric landmarks and measurement angles pertinent for utilization within a translational large animal model. These craniomaxillofacial landmarks will allow us to develop novel navigational software technology, improve our cutting guide designs, and explore new avenues for investigation and collaboration.
Level of Evidence
N/A (Large Animal Study)
Maxillofacial Transplant; Swine Facial Transplant; Cephalometrics; Cephalomtetric landmark; Craniofacial; Craniomaxillofacial surgery; Swine study; Face transplant; Allotransplantation; Computer assisted; Computer enhanced surgery; Cutting guides
Femoroplasty is a potential preventive treatment for osteoporotic hip fractures. It involves augmenting mechanical properties of the femur by injecting Polymethylmethacrylate (PMMA) bone cement. To reduce the risks involved and maximize the outcome, however, the procedure needs to be carefully planned and executed. An important part of the planning system is predicting infiltration of cement into the porous medium of cancellous bone. We used the method of Smoothed Particle Hydrodynamics (SPH) to model the flow of PMMA inside porous media. We modified the standard formulation of SPH to incorporate the extreme viscosities associated with bone cement. Darcy creeping flow of fluids through isotropic porous media was simulated and the results were compared with those reported in the literature. Further validation involved injecting PMMA cement inside porous foam blocks — osteoporotic cancellous bone surrogates — and simulating the injections using our proposed SPH model. Millimeter accuracy was obtained in comparing the simulated and actual cement shapes. Also, strong correlations were found between the simulated and the experimental data of spreading distance (R2 = 0.86) and normalized pressure (R2 = 0.90). Results suggest that the proposed model is suitable for use in an osteoporotic femoral augmentation planning framework.
Objective: This study addresses the effects of cartilage thickness distribution and compressive properties in the context of optimal alignment planning for periacetabular osteotomy (PAO).
Background: The Biomechanical Guidance System (BGS) is a computer-assisted surgical suite assisting surgeon’s in determining the most beneficial new alignment of a patient’s acetabulum. The BGS uses biomechanical analysis of the hip to find this optimal alignment. Articular cartilage is an essential component of this analysis and its physical properties can affect contact pressure outcomes.
Methods: Patient-specific hip joint models created from CT scans of a cohort of 29 dysplastic subjects were tested with four different cartilage thickness profiles (one uniform and three non-uniform) and two sets of compressive characteristics. For each combination of thickness distribution and compressive properties, the optimal alignment of the acetabulum was found; the resultant geometric and biomechanical characterization of the hip were compared among the optimal alignments.
Results: There was an average decrease of 49.2 ± 22.27% in peak contact pressure from the preoperative to the optimal alignment over all patients. We observed an average increase of 19 ± 7.7° in center-edge angle and an average decrease of 19.5 ± 8.4° in acetabular index angle from the preoperative case to the optimized plan. The optimal alignment increased the lateral coverage of the femoral head and decreased the obliqueness of the acetabular roof in all patients. These anatomical observations were independent of the choice for either cartilage thickness profile, or compressive properties.
Conclusion: While patient-specific acetabular morphology is essential for surgeons in planning PAO, the predicted optimal alignment of the acetabulum was not significantly sensitive to the choice of cartilage thickness distribution over the acetabulum. However, in all groups the biomechanically predicted optimal alignment resulted in decreased joint contact pressure and improved acetabular coverage.
periacetabular osteotomy; preoperative planning; articular cartilage thickness; cartilage compressibility; biomechanical analysis
Current assessment techniques for focal acetabular overcoverage are neither consistent nor quantitatively accurate.
We propose: (1) a method to precisely quantify the amount of focal acetabular overcoverage in a patient’s pincer deformity based on CT data; (2) to evaluate the consistency of this method; and (3) to compare the method with conventional radiographic assessments.
We developed a method to assess focal acetabular overcoverage using points selected from CT scans along the acetabular rim after realigning the pelvis into a neutral position. Using four resampled and segmented pelvic CT scans of cadaveric specimens with virtually induced impingement, two observers independently tested the algorithm’s consistency. Our algorithm assessed the amount of focal acetabular overcoverage using CT data and projected data from reconstructed radiographs.
(1) We successfully showed the feasibility of the software to produce consistent, quantitative measurements. (2) Testing showed the average difference between observers in aligning the pelvis was 0.42°, indicative of a consistent approach. (3) Differences between measurements on three-dimensional (3-D) CT and simulated radiographs were significant.
The proposed method represents a new avenue in consistently quantifying focal acetabular overcoverage using CT models while correcting for pelvic tilt and rotation. Our analysis confirms AP hip radiograph simulations overestimate the amount of overhanging acetabular rim in a pincer deformity.
This technique has potential to improve preoperative diagnostic accuracy and enhance surgical planning for correction of a pincer deformity resulting from focal acetabular overcoverage.
Osteotomies around hip acetabulum have become a routine surgical intervention in cases with constant pain without joint degeneration in adult dysplasia. However, it remains a challenge to plan and realign optimally the joint after osteotomy to reach best function and longevity in the clinical outcome. Tool tracking navigation systems have been available for many years but they have not become popular among surgeons because they extend operation time, require preoperative CT scan and, on the other hand, produce only marginal advantage in hands of an experienced surgeon. Real-time biomechanical assessment, based on computer analysis using preoperative CT-scanning, has become an interesting means to adjust the acetabular reorientation during surgery according to the patient’s individual structure and loading conditions. Further, real-time feedback allows the surgeon to foresee radiographic angles while performing fixation of the osteotomized fragment. Assessment of peak pressure and potential weight bearing area in real-time allows prospective and retrospective systematic biomechanical studies of patient outcomes. To conclude, a major development in navigation software is under way and we have so far seen a spectrum of new features like loading condition assessment in real time for osteotomies. This is, however, merely the start of a revolutionary change in operative planning in orthopaedics with the help of computer aided guiding and bioengineering.
Due to wide variations in acetabular structure of individuals with hip dysplasia, the measurement of the acetabular orientation may not be sufficient to predict the joint loading and pressure distribution across the joint. Addition of mechanical analysis to preoperative planning, therefore, has the potential to improve the clinical outcome.
We analyzed the effect of periacetabular osteotomy on hip dysplasia using computer-aided simulation of joint contact pressure on regular AP radiographs. The results were compared with the results of surgery based on realignment of acetabular angles to the normal hip.
Patients and methods
We studied 12 consecutive periacetabular osteotomies with no femoral head deformity. The median age of patients, all females, was 35 (20−50) years. The median follow-up was 2 years (1.3−2.2). Patient outcome was measured with the total score of a self-administered questionnaire (q-score) and with the Harris hip score. The pre- and postoperative orientation of the acetabulum was defined using reconstructed 3D CT-slices to measure angles in the three anatomical planes. Peak contact pressure, weight-bearing area, and the centroid of the contact pressure distribution (CP-ratio) were calculated.
While 9 of 12 cases showed decreased peak pressure after surgery, the mean changes in weight-bearing area and peak contact pressure were not statistically significant. However, CP-ratio changed (p < 0.001, paired t-test) with surgery. For the optimal range of CP-ratio (within its mid-range 40−60%), the mechanical outcome improved significantly.
Verifying the correlation between the optimal CP-ratio and the outcome of the surgery requires additional studies on more patients. Moreover, the anatomically measured angles were not correlated with the ranges of CP-ratio, suggesting that they do not always associate with objective mechanical goals of realignment osteotomy. Mechanical analysis, therefore, can be a valuable tool in assessing two-dimensional radiographs in hip dysplasia.
Periacetabular osteotomy (PAO) is intended to treat a painful dysplastic hip. Manual radiological angle measurements are used to diagnose dysplasia and to define regions of insufficient femoral head coverage for planning PAO. No method has yet been described that recalculates radiological angles as the acetabular bone fragment is reoriented. In this study, we propose a technique for computationally measuring the radiological angles from a joint contact surface model segmented from CT-scan data. Using oblique image slices, we selected the lateral and medial edge of the acetabulum lunate to form a closed, continuous, 3D curve. The joint surface is generated by interpolating the curve and the radiological angles are measured directly using the 3D surface. This technique was evaluated using CT data for both normal and dysplastic hips. Manual measurements made by three independent observers showed minor discrepancies between the manual observations and the computerized technique. Inter-observer error (mean difference±standard deviation) was 0.04±3.53° Observer 1; −0.46±3.13° for Observer 2; and 0.42±2.73° for Observer 3. The measurement error for the proposed computer method was −1.30±3.30°. The computerized technique demonstrates sufficient accuracy compared to manual techniques, making it suitable for planning and intraoperative evaluation of radiological metrics for periacetabular osteotomy.
Periacetabular osteotomy; inter-observer error; radiographic angles; preoperative planning; acetabular coverage; cartilage segmentation
Background and purpose
Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment.
Patients and methods
We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years.
The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis.
The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.
Background and purpose Because of the varying structure of dysplastic hips, the optimal realignment of the joint during periacetabular osteotomy (PAO) may differ between patients. Three-dimensional (3D) mechanical and radiological analysis possibly accounts better for patient-specific morphology, and may improve and automate optimal joint realignment.
Patients and methods We evaluated the 10-year outcomes of 12 patients following PAO. We compared 3D mechanical analysis results to both radiological and clinical measurements. A 3D discrete-element analysis algorithm was used to calculate the pre- and postoperative contact pressure profile within the hip. Radiological angles describing the coverage of the joint were measured using a computerized approach at actual and theoretical orientations of the acetabular cup. Quantitative results were compared using postoperative clinical evaluation scores (Harris score), and patient-completed outcome surveys (q-score) done at 2 and 10 years.
Results The 3D mechanical analysis indicated that peak joint contact pressure was reduced by an average factor of 1.7 subsequent to PAO. Lateral coverage of the femoral head increased in all patients; however, it did not proportionally reduce the maximum contact pressure and, in 1 case, the pressure increased. This patient had the lowest 10-year q-score (70 out of 100) of the cohort. Another hip was converted to hip arthroplasty after 3 years because of increasing osteoarthritis.
Interpretation The 3D analysis showed that a reduction in contact pressure was theoretically possible for all patients in this cohort, but this could not be achieved in every case during surgery. While intraoperative factors may affect the actual surgical outcome, the results show that 3D contact pressure analysis is consistent with traditional PAO planning techniques (more so than 2D analysis) and may be a valuable addition to preoperative planning and intraoperative assessment of joint realignment.