Statistical-Shape Prediction of Lower Limb Kinematics During Cycling, Squatting, Lunging, and Stepping-Are Bone Geometry Predictors Helpful?

Purpose: Statistical shape methods have proven to be useful tools in providing statistical predications of several clinical and biomechanical features as to analyze and describe the possible link with them. In the present study, we aimed to explore and quantify the relationship between biometric features derived from imaging data and model-derived kinematics. Methods: Fifty-seven healthy males were gathered under strict exclusion criteria to ensure a sample representative of normal physiological conditions. MRI-based bone geometry was established and subject-specific musculoskeletal simulations in the Anybody Modeling System enabled us to derive personalized kinematics. Kinematic and shape findings were parameterized using principal component analysis. Partial least squares regression and canonical correlation analysis were then performed with the goal of predicting motion and exploring the possible association, respectively, with the given bone geometry. The relationship of hip flexion, abduction, and rotation, knee flexion, and ankle flexion with a subset of biometric features (age, length, and weight) was also investigated. Results: In the statistical kinematic models, mean accuracy errors ranged from 1.60° (race cycling) up to 3.10° (lunge). When imposing averaged kinematic waveforms, the reconstruction errors varied between 4.59° (step up) and 6.61° (lunge). A weak, yet clinical irrelevant, correlation between the modes describing bone geometry and kinematics was observed. Partial least square regression led to a minimal error reduction up to 0.42° compared to imposing gender-specific reference curves. The relationship between motion and the subject characteristics was even less pronounced with an error reduction up to 0.21°. Conclusion: The contribution of bone shape to model-derived joint kinematics appears to be relatively small and lack in clinical relevance.

Accurate Arthroscopic Cam Resection Normalizes Contact Stresses in Patients With Femoroacetabular Impingement.

BACKGROUND: Femoroacetabular impingement (FAI) is increasingly recognized as a cause of hip pain in young adults. The condition leads to chondrolabral separation and chondral delamination and eventually predisposes to osteoarthritis of the hip. FAI that inflicts cartilage damage has been observed in hips with abnormal morphological characteristics and is related to a long-term evolution toward osteoarthritis. Arthroscopic surgery, which allows for correction of morphological characteristics and restores impingement-free motions, is the current standard of treatment. HYPOTHESIS: Arthroscopic cam resection can restore the normal mechanical environment of the hip joint in cam-type FAI. STUDY DESIGN: Descriptive laboratory study. METHODS: Patient-specific discrete element models from 10 patients with cam-type FAI (all male; age, 18-40 years) were defined based on preoperative computed tomography scans and postoperative magnetic resonance imaging (MRI) scans. Complete cam resection postoperatively on MRI was confirmed with alpha angles <55°. The preoperative and postoperative peak contact stress findings during impingement testing were compared against a matched control group. RESULTS: Peak contact stress was significantly elevated in patients with cam-type FAI during impingement testing, with increasing amounts of internal hip rotation (26.6 ± 11.64 MPa in cam patients preoperatively, 12.1 ± 4.62 MPa in those same patients postoperatively, and 11.4 ± 1.72 MPa in the virtual control group during impingement testing at 20° of internal hip rotation; P < .01). This effect was normalized after arthroscopic cam resection and loading patterns matched those of the control group. CONCLUSION: Accurate arthroscopic cam resection restored the normal peak joint contact stresses in the hip joint. This highlights the importance of early and complete cam resections in the face of a positive diagnosis of cam-type FAI. CLINICAL RELEVANCE: Treatment of cam-type FAI effectively normalizes hip joint contact mechanics.

A Combined Geometric Morphometric and Discrete Element Modeling Approach for Hip Cartilage Contact Mechanics.

Finite element analysis (FEA) provides the current reference standard for numerical simulation of hip cartilage contact mechanics. Unfortunately, the development of subject-specific FEA models is a laborious process. Owed to its simplicity, Discrete Element Analysis (DEA) provides an attractive alternative to FEA. Advancements in computational morphometrics, specifically statistical shape modeling (SSM), provide the opportunity to predict cartilage anatomy without image segmentation, which could be integrated with DEA to provide an efficient platform to predict cartilage contact stresses in large populations. The objective of this study was, first, to validate linear and non-linear DEA against a previously validated FEA model and, second, to present and evaluate the applicability of a novel population-averaged cartilage geometry prediction method against previously used methods to estimate cartilage anatomy. The population-averaged method is based on average cartilage thickness maps and therefore allows for a more accurate and individualized cartilage geometry estimation when combined with SSM. The root mean squared error of the population-averaged cartilage geometry predicted by SSM as compared to the manually segmented cartilage geometry was 0.31 ± 0.08 mm. Identical boundary and loading conditions were applied to the DEA and FEA models. Predicted DEA stress distribution patterns and magnitude of peak stresses were in better agreement with FEA for the novel cartilage anatomy prediction method as compared to commonly used parametric methods based on the estimation of acetabular and femoral head radius. Still, contact stress was overestimated and contact area was underestimated for all cartilage anatomy prediction methods. Linear and non-linear DEA methods differed mainly in peak stress results with the non-linear definition being more sensitive to detection of high peak stresses. In conclusion, DEA in combination with the novel population-averaged cartilage anatomy prediction method provided accurate predictions while offering an efficient platform to conduct population-wide analyses of hip contact mechanics.

Personalized hip joint kinetics during deep squatting in young, athletic adults.

The goal of this study was to report deep squat hip kinetics in young, athletic adults using a personalized numerical model solution based on inverse dynamics. Thirty-five healthy subjects underwent deep squat motion capture acquisitions and MRI scans of the lower extremities. Musculoskeletal models were personalized using each subject's lower limb anatomy. The average peak hip joint reaction force was 274 percent bodyweight. Average peak hip and knee flexion angles were 107° and 112° respectively. These new findings show that deep squatting kinetics in the younger population differ substantially from the previously reported in vivo data in older subjects.

Defining the shape of the scapulothoracic gliding surface.

PURPOSE: The aim of the study is to evaluate the difference in shape of the upper part and lower part of the Scapulothoracic Gliding Surface (STGS). METHODS: 3D-CT images of the thoracic cage of 50 patients were created in MIMICS ®. Three anatomical landmarks (insertion m. serratus anterior on 5th rib; transverse process of 2th and 7th vertebra) were used as an anteroposterior cutting plane to define the STGS. The upper part of the STG was defined as rib 2-5 and the lower part as 5-8. Next, in MATLAB ®, a script was used to create the sphere with best fit for upper and lower parts of STGS. The Root-Square-Mean Error (RSME) (mm) between two closest points on the fitted sphere and the STGS of both parts were calculated to determine the goodness-of-fit. RESULTS: The RSME was found to be significantly lower for the area ribs 2-5 (mean 7.85 mm, SD 1.86) compared the area of ribs 5-8 (mean 10.08 mm, SD 1.90). CONCLUSION: The STGS of the upper thoracic wall (2-5) is more spherical shaped than the STGS of the lower thoracic wall (rib 5-8).

Cascaded statistical shape model based segmentation of the full lower limb in CT.

Image segmentation has become an important tool in orthopedic and biomechanical research. However, it greatly remains a time-consuming and laborious task. In this manuscript, we propose a fully automatic model-based segmentation pipeline for the full lower limb in computed tomography (CT) images. The method relies on prior shape model fitting, followed by a gradient-defined free from deformation. The technique allows for the generation of anatomically corresponding surface meshes, which can subsequently be applied in anatomical and mechanical simulation studies. Starting from an initial, small (n ≤ 10) sample of manual segmentations, the model is continuously updated and refined with newly segmented training samples. Validation of the segmentation pipeline was performed by comparing the automatic segmentations against corresponding manual segmentations. Convergence of the segmentation pipeline was obtained in 250 cases and failed in three samples. The average distance error ranged from 0.53 to 0.76 mm and maximal error ranged from 2.0 to 7.8 mm for the 7 different osteological structures that were investigated. The accuracy of the shape model-based segmentation gradually increased as the number of training shapes in the updated population also increased. When optimized with the free form deformation, however, average segmentation accuracy rapidly plateaued from already as little as 20 training samples on. The maximum segmentation error plateaued from 100 training samples on.

Morphologic variations of the scapula in 3-dimensions: a statistical shape model approach.

BACKGROUND: Morphologic variations of the scapula and acromion have been found to be associated with shoulder pathology. This study used statistical shape modelling to quantify these variations in healthy shoulders. MATERIALS AND METHODS: A statistical shape model of the scapula was created using 3-dimensional computed tomography reconstructions of 108 survey-confirmed nonpathologic shoulders of 54 patients. The mean shape and the 95% confidence interval were calculated and analyzed in the first 5 shape modes. RESULTS: The first 5 shape modes consisted of consecutively sized (72% of total variation), rotation of the coracoacromial complex (5%), acromial shape and slope (4%), shape of the scapular spine (2%), and acromial overhang (2%). DISCUSSION AND CONCLUSION: In healthy shoulders, a certain variation in rotation of the coracoacromial complex and in acromial shape and slope was observed. These new parameters might be correlated with shoulder pathology such as glenohumeral osteoarthritis or rotator cuff tears.

Accuracy of navigated cam resection in femoroacetabular impingement: A randomised controlled trial.

BACKGROUND: The main cause for revision hip arthroscopy surgery is incomplete bony resection of femoroacetabular impingement (FAI). This study aimed to compare the cam resection accuracy via the conventional hip arthroscopy technique with the navigation technique. METHODS: Two prospectively randomized groups were recruited: navigated (n = 15) and conventional (n = 14). A pre-operative CT and post-operative MRI scan were obtained in all cases to compare alpha angle, range of motion simulation and determine a pre-operative 3D surgical resection plan. RESULTS: Post-operatively, the mean maximal alpha angle improved significantly in the navigated group compared with the conventional group (55°vs.66°; P = 0.023), especially in the 12 o' clock position (45°vs.60°; P = 0.041). However, positioning time and radiation exposure were significantly longer in the navigated group. CONCLUSION: Navigated surgery is effective for patients with cam type FAI in helping restore normal anatomy, however, not without drawbacks. Larger studies will be required to validate our results.

Patient-specific assessment of dysmorphism of the femoral head-neck junction: a statistical shape model approach.

BACKGROUND: Objective quantification of anatomical variations about the femur head-neck junction in pre-operative planning for surgical intervention in femoro-acetabular impingement is problematic, as no clear definition of average normal anatomy for a specific subject exists. METHODS: We have defined the normal-equivalent of a subject's anatomy by using a statistical shape model and geometric shape optimization for finding correspondences, while excluding the femoral head-neck junction during the fitting procedure. The presented technique was evaluated on a cohort of 20 patients. RESULTS: Difference in α-angle measurement between the actual morphology and the predicted normal-equivalent, averaged 1.3° (SD 1.7°) in the control group versus 8° (SD 7.3°) in the patient group (p < 0.05). CONCLUSIONS: Defining normal equivalent anatomy is effective in quantifying anatomical dysmorphism of the femoral head-neck junction and as such can improve presurgical analysis of patients diagnosed with femoro-acetabular impingement. Copyright © 2016 John Wiley & Sons, Ltd.

Prevalence of radiographic parameters predisposing to femoroacetabular impingement in young asymptomatic Chinese and white subjects.

BACKGROUND: Osteoarthritis of the hip is five to ten times more common in white people than in Chinese people. Little is known about the true prevalence of femoroacetabular impingement or its role in the development of osteoarthritis in the Chinese population. A cross-sectional study of both white and Chinese asymptomatic individuals was conducted to compare the prevalences of radiographic features posing a risk for femoroacetabular impingement in the two groups. It was hypothesized that that there would be proportional differences in hip anatomy between the white and Asian populations. METHODS: Pelvic computed tomography scans of 201 subjects (ninety-nine white Belgians and 102 Chinese; 105 men and ninety-six women) without hip pain who were eighteen to forty years of age were assessed. The original axial images were reformatted to three-dimensional pelvic models simulating standardized radiographic views. Ten radiographic parameters predisposing to femoroacetabular impingement were measured: alpha angle, anterior offset ratio, and caput-collum-diaphyseal angle on the femoral side and crossover sign, ischial spine projection, acetabular anteversion angle, center-edge angle, acetabular angle of Sharp, Tönnis angle, and anterior acetabular head index on the acetabular side. RESULTS: The white subjects had a less spherical femoral head than the Chinese subjects (average alpha angle, 56° compared with 50°; p<0.001). The Chinese subjects had less lateral acetabular coverage than the white subjects, with average center-edge angles of 35° and 39° (p<0.001) and acetabular angles of Sharp of 38° and 36° (p<0.001), respectively. A shallower acetabular configuration was predominantly present in Chinese women. CONCLUSIONS: Significant differences in hip anatomy were demonstrated between young asymptomatic Chinese and white subjects. However, the absolute size of the observed differences appears to contrast with the reported low prevalence of femoroacetabular impingement in Chinese individuals compared with the high prevalence in white populations.

Range of motion in femoroacetabular impingement.

Recent epidemiological studies have demonstrated that radiographic features specific to femoroacetabular impingement appear far more frequently in healthy and asymptomatic cohorts than previously anticipated. It remains unclear how incidental findings should be interpreted clinically. In addition, several authors have suggested that a decreased range of motion is part of the clinical presentation of femoroacetabular impingement. The purpose of the present study was to describe and analyze differences in range of motion between femoroacetabular impingement patients, asymptomatic individuals with incidental radiographic findings and healthy controls, using a validated electromagnetic tracking system. Furthermore, it was evaluated which motions were clinically relevant and could be used to differentiate between these three groups. We found all evaluated motions to differ significantly between patients and controls. The anterior impingement test showed a significant difference between patients and asymptomatic cases. In conclusion, functional evaluation of the range of motion appeared in this study as a useful tool in the diagnostic work-up of femoracetabular impingement.