The anterior center edge angle has limited ability to predict three-dimensional coverage of the femoral head in patients with developmental dysplasia of the hip undergoing curved periacetabular osteotomy.

INTRODUCTION: Femoral head coverage in patients with hip dysplasia (DDH) is typically quantified using 2D measurements of the lateral center edge angle (LCEA) and anterior center edge angle (ACEA). However, as the morphology of DDH is complex and varies between patients, 2D measurements may not predict the true 3D femoral head coverage. Herein, 2D and 3D coverage were quantified before and after curved periacetabular osteotomy (CPO) and their relationships were assessed. MATERIALS AND METHODS: Forty-three hips that underwent CPO for DDH were analyzed. For 2D evaluation, LCEA was quantified from X-rays and CT images. The ACEA was measured from CT images (CT-ACEA) and digitally reconstructed radiographs generated from CT images (DRR-ACEA). Three-dimensional coverage was quantified from CT reconstructions of the hip and evaluated in the anterior, superior, posterior, and inferior regions of the femoral head. Two-dimensional measurements were correlated to 3D coverage to assess their relationships. RESULTS: The median preoperative 3D percent coverage was 17.7, 36.1, 56.1, and 14.6% for the anterior, superior, posterior, and inferior region, respectively. After CPO, all LCEAs and ACEAs increased significantly (all p < 0.001). For the 3D coverage, anterior and superior coverage significantly increased while the posterior and inferior coverage decreased (all p < 0.001). Moderate to strong correlations were detected between the two LCEAs and the 3D superior coverage in both the preoperative and postoperative period. For the correlation between 3D anterior coverage, no significant correlation was found between the CT-ACEA while a moderate correlation was found between the DRR-ACEA (rs = 0.41, p = 0.023). CONCLUSIONS: Our results indicate that the LCEA can be used to predict 3D coverage in the superior region of the femoral head. However, as the CT-ACEA or DRR-ACEA had no or only moderate correlation between the 3D anterior coverage, these measurements are not recommended for evaluating/estimating the 3D anterior coverage in patients with DDH.

How Does Chondrolabral Damage and Labral Repair Influence the Mechanics of the Hip in the Setting of Cam Morphology? A Finite-Element Modeling Study.

BACKGROUND: Individuals with cam morphology are prone to chondrolabral injuries that may progress to osteoarthritis. The mechanical factors responsible for the initiation and progression of chondrolabral injuries in these individuals are not well understood. Additionally, although labral repair is commonly performed during surgical correction of cam morphology, the isolated mechanical effect of labral repair on the labrum and surrounding cartilage is unknown. QUESTION/PURPOSES: Using a volunteer-specific finite-element analysis, we asked: (1) How does cam morphology create a deleterious mechanical environment for articular cartilage (as evaluated by shear stress, tensile strain, contact pressure, and fluid pressure) that could increase the risk of cartilage damage compared with a radiographically normal hip? (2) How does chondrolabral damage, specifically delamination, delamination with rupture of the chondrolabral junction, and the presence of a chondral defect, alter the mechanical environment around the damage? (3) How does labral repair affect the mechanical environment in the context of the aforementioned chondrolabral damage scenarios? METHODS: The mechanical conditions of a representative hip with normal bony morphology (characterized by an alpha angle of 37°) and one with cam morphology (characterized by an alpha angle of 78°) were evaluated using finite-element models that included volunteer-specific anatomy and kinematics. The bone, cartilage, and labrum geometry for the hip models were collected from two volunteers matched by age (25 years with cam morphology and 23 years with normal morphology), BMI (both 24 kg/m2), and sex (both male). Volunteer-specific kinematics for gait were used to drive the finite-element models in combination with joint reaction forces. Constitutive material models were assigned to the cartilage and labrum, which simulate a physiologically realistic material response, including the time-dependent response from fluid flow through the cartilage, and spatially varied response from collagen fibril reinforcement. For the cam hip, three models were created to represent chondrolabral damage conditions: (1) "delamination," with the acetabular cartilage separated from the bone in one region; (2) "delamination with chondrolabral junction (CLJ) rupture," which includes separation of the cartilage from the labrum tissue; and (3) a full-thickness chondral defect, referred to throughout as "defect," where the acetabular cartilage has degraded so there is a void. Each of the three conditions was modeled with a labral tear and with the labrum repaired. The size and location of the damage conditions simulated in the cartilage and labrum were attained from reported clinical prevalence of the location of these injuries. For each damage condition, the contact area, contact pressure, tensile strain, shear stress, and fluid pressure were predicted during gait and compared. RESULTS: The cartilage in the hip with cam morphology experienced higher stresses and strains than the normal hip. The peak level of tensile strain (25%) and shear stress (11 MPa) experienced by the cam hip may exceed stable conditions and initiate damage or degradation. The cam hip with simulated damage experienced more evenly distributed contact pressure than the intact cam hip, as well as decreased tensile strain, shear stress, and fluid pressure. The peak levels of tensile strain (15% to 16%) and shear stress (2.5 to 2.7 MPa) for cam hips with simulated damage may be at stable magnitudes. Labral repair only marginally affected the overall stress and strain within the cartilage, but it increased local tensile strain in the cartilage near the chondrolabral junction in the hip with delamination and increased the peak tensile strain and shear stress on the labrum. CONCLUSION: This finite-element modeling pilot study suggests that cam morphology may predispose hip articular cartilage to injury because of high shear stress; however, the presence of simulated damage distributed the loading more evenly and the magnitude of stress and strain decreased throughout the cartilage. The locations of the peak values also shifted posteriorly. Additionally, in hips with cam morphology, isolated labral repair in the hip with a delamination injury increased localized strain in the cartilage near the chondrolabral junction. CLINICAL RELEVANCE: In a hip with cam morphology, labral repair alone may not protect the cartilage from damage because of mechanical overload during the low-flexion, weightbearing positions experienced during gait. The predicted findings of redistribution of stress and strain from damage in the cam hip may, in some cases, relieve disposition to damage progression. Additional studies should include volunteers with varied acetabular morphology, such as borderline dysplasia with cam morphology or pincer deformity, to analyze the effect on the conclusions presented in the current study. Further, future studies should evaluate the combined effects of osteochondroplasty and chondrolabral treatment.

Which Two-dimensional Radiographic Measurements of Cam Femoroacetabular Impingement Best Describe the Three-dimensional Shape of the Proximal Femur?

BACKGROUND: Many two-dimensional (2-D) radiographic views are used to help diagnose cam femoroacetabular impingement (FAI), but there is little consensus as to which view or combination of views is most effective at visualizing the magnitude and extent of the cam lesion (ie, severity). Previous studies have used a single image from a sequence of CT or MR images to serve as a reference standard with which to evaluate the ability of 2-D radiographic views and associated measurements to describe the severity of the cam lesion. However, single images from CT or MRI data may fail to capture the apex of the cam lesion. Thus, it may be more appropriate to use measurements of three-dimensional (3-D) surface reconstructions from CT or MRI data to serve as an anatomic reference standard when evaluating radiographic views and associated measurements used in the diagnosis of cam FAI. QUESTIONS/PURPOSES: The purpose of this study was to use digitally reconstructed radiographs and 3-D statistical shape modeling to (1) determine the correlation between 2-D radiographic measurements of cam FAI and 3-D metrics of proximal femoral shape; and 2) identify the combination of radiographic measurements from plain film projections that were most effective at predicting the 3-D shape of the proximal femur. METHODS: This study leveraged previously acquired CT images of the femur from a convenience sample of 37 patients (34 males; mean age, 27 years, range, 16-47 years; mean body mass index [BMI], 24.6 kg/m, range, 19.0-30.2 kg/m) diagnosed with cam FAI imaged between February 2005 and January 2016. Patients were diagnosed with cam FAI based on a culmination of clinical examinations, history of hip pain, and imaging findings. The control group consisted of 59 morphologically normal control participants (36 males; mean age, 29 years, range, 15-55 years; mean BMI, 24.4 kg/m, range, 16.3-38.6 kg/m) imaged between April 2008 and September 2014. Of these controls, 30 were cadaveric femurs and 29 were living participants. All controls were screened for evidence of femoral deformities using radiographs. In addition, living control participants had no history of hip pain or previous surgery to the hip or lower limbs. CT images were acquired for each participant and the surface of the proximal femur was segmented and reconstructed. Surfaces were input to our statistical shape modeling pipeline, which objectively calculated 3-D shape scores that described the overall shape of the entire proximal femur and of the region of the femur where the cam lesion is typically located. Digital reconstructions for eight plain film views (AP, Meyer lateral, 45° Dunn, modified 45° Dunn, frog-leg lateral, Espié frog-leg, 90° Dunn, and cross-table lateral) were generated from CT data. For each view, measurements of the α angle and head-neck offset were obtained by two researchers (intraobserver correlation coefficients of 0.80-0.94 for the α angle and 0.42-0.80 for the head-neck offset measurements). The relationships between radiographic measurements from each view and the 3-D shape scores (for the entire proximal femur and for the region specific to the cam lesion) were assessed with linear correlation. Additionally, partial least squares regression was used to determine which combination of views and measurements was the most effective at predicting 3-D shape scores. RESULTS: Three-dimensional shape scores were most strongly correlated with α angle on the cross-table view when considering the entire proximal femur (r = -0.568; p < 0.001) and on the Meyer lateral view when considering the region of the cam lesion (r = -0.669; p < 0.001). Partial least squares regression demonstrated that measurements from the Meyer lateral and 90° Dunn radiographs produced the optimized regression model for predicting shape scores for the proximal femur (R = 0.405, root mean squared error of prediction [RMSEP] = 1.549) and the region of the cam lesion (R = 0.525, RMSEP = 1.150). Interestingly, views with larger differences in the α angle and head-neck offset between control and cam FAI groups did not have the strongest correlations with 3-D shape. CONCLUSIONS: Considered together, radiographic measurements from the Meyer lateral and 90° Dunn views provided the most effective predictions of 3-D shape of the proximal femur and the region of the cam lesion as determined using shape modeling metrics. CLINICAL RELEVANCE: Our results suggest that clinicians should consider using the Meyer lateral and 90° Dunn views to evaluate patients in whom cam FAI is suspected. However, the α angle and head-neck offset measurements from these and other plain film views could describe no more than half of the overall variation in the shape of the proximal femur and cam lesion. Thus, caution should be exercised when evaluating femoral head anatomy using the α angle and head-neck offset measurements from plain film radiographs. Given these findings, we believe there is merit in pursuing research that aims to develop the framework necessary to integrate statistical shape modeling into clinical evaluation, because this could aid in the diagnosis of cam FAI.

Do Your Routine Radiographs to Diagnose Cam Femoroacetabular Impingement Visualize the Region of the Femoral Head-Neck Junction You Intended?

PURPOSE: To use computer models and image analysis to identify the position on the head-neck junction visualized in 10 radiographic views used to quantify cam morphology. METHODS: We generated 97 surface models of the proximal femur from computed tomography scans of 59 control femurs and 38 femurs with cam morphology-a flattening or convexity at the femoral head-neck junction. Each model was transformed to a position that represents the anteroposterior, Meyer lateral, 45° Dunn, modified false-profile, Espié frog-leg, modified 45° Dunn, frog-leg lateral, cross-table, 90° Dunn, and false-profile views. The position on the head-neck junction visualized from each view was identified on the surfaces. This position was then quantified by a clock face generated on the plane of the head-neck junction, in which the 12-o'clock position indicated the superior head-neck junction and the 3-o'clock position indicated the anterior head-neck junction. The mean visualized clock-face position was calculated for all subjects. Analysis was repeated to account for variability in femoral version. A general linear model with repeated measures was used to compare each radiographic view and anteversion angle. RESULTS: Each radiographic view provided visualization of the mean clock-face position as follows: anteroposterior view, 12:01; Meyer lateral view, 1:08; 45° Dunn view, 1:40; modified false-profile view, 2:01; Espié frog-leg view, 2:14; modified 45° Dunn view, 2:35; frog-leg lateral view, 2:45; cross-table view, 3:00; 90° Dunn view, 3:13; and false-profile view, 3:44. Each view visualized a different position on the clock face (all P < .001). Increasing simulated femoral anteversion by 10° changed the visualized position of the head-neck junction to a more clockwise position (range, 0:07 to 0:29; all P < .001), whereas decreasing anteversion by 10° visualized a more counterclockwise position (range, -0:23 to -0:08; all P < .001). CONCLUSIONS: Ten common radiographic views used to identify cam morphology visualized different clock-face positions of the head-neck junction. Our data will help clinicians to understand the position of the head-neck junction visualized for each radiographic view and make educated decisions in the selection of radiographs acquired in the clinic. CLINICAL RELEVANCE: Our findings will aid clinicians in choosing a set of radiographs to capture cam morphology in the assessment of patients with hip pain.

Assessment of Acetabular Morphology Using the Acetabular Anterior Center-Edge Angle on Modified False-Profile Radiographs.

PURPOSE: To compare radiographic parameters of acetabular morphology between standard and modified false-profile (FP) radiographs. METHODS: Standard and modified FP radiographs were obtained in 225 hips in 200 consecutive patients evaluated for hip pain and suspected femoroacetabular impingement. Radiographs were retrospectively reviewed by 2 readers to determine the anterior center-edge angle (ACEA), as assessed to the sourcil and to the bone edge. Inter-rater reliability of radiographic measurements was assessed using the intraclass correlation coefficient. Measurements were evaluated for normality with the Shapiro-Wilk test, averaged between the 2 readers, and compared between views using the paired Wilcoxon test. RESULTS: The intraclass correlation coefficient values for standard and modified FP views were 0.923 and 0.932, respectively, measuring to the sourcil and 0.867 and 0.896, respectively, measuring to the lateral bone edge. The median difference in ACEA measurements to the sourcil was 1° between the standard and modified FP view (45° vs 44°, P < .001). The median difference in ACEA measurements to the bone edge was 2° (34° vs 32°, P < .001). CONCLUSIONS: Thirty-five degrees of femoral internal rotation for a modified FP hip radiographic view provides similar clinical information regarding acetabular morphology to that of the standard FP view. Given that the modified FP view also provides better visualization of the anterosuperior head-neck junction cam lesion, the modified FP view may be preferred over the standard FP view in evaluation of hip pain in the young patient. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Modified False-Profile Radiograph of the Hip Provides Better Visualization of the Anterosuperior Femoral Head-Neck Junction.

PURPOSE: The purpose of this study was to quantify the amount of internal femur rotation required to visualize the 12 to 3 o'clock positions of the femoral head-neck junction as seen on the false-profile radiograph. METHODS: Computed tomography (CT) images of the femur were retrospectively reviewed from control subjects and cam femoroacetabular impingement (FAI) patients. Using an automatically determined clockface, the positions between 12 and 3 o'clock were determined. The optimal femoral rotation angle to visualize each clockface position on the femoral head-neck junction was calculated based on the CT surface data. RESULTS: Fifty-nine control subjects and 38 cam FAI patients were evaluated for this study. The mean (95% confidence interval) internal femur rotation needed to optimally visualize the clockface positions of the femoral head-neck junction on the modified false-profile radiograph were 0.9° (0.8°-1.0°) for 3:00, 10.3° (10.0°-10.6°) for 2:30, 21.6° (21.0°-22.1°) for 2:00, 34.3° (33.6°-35.1°) for 1:30, 49.6° (48.6°-50.4°) for 1:00, 68.4° (67.7°-69.0°) for 12:30, and 90.1° (89.9°-90.4°) for 12:00. CONCLUSIONS: Internal femur rotation of 35° during the false-profile radiograph may better visualize the femoral head-neck junction in the anterosuperior (1 to 2 o'clock) region commonly associated with the cam lesion. From this view, rotation angles between 0° and 90° can be used to visualize other regions of the anterosuperior femoral head-neck junction. CLINICAL RELEVANCE: The internal rotation of the affected femur for a modified false-profile radiograph may provide a new radiographic view that can be used to quantify anterosuperior femoral head-neck morphology.

Three-dimensional femoral head coverage in the standing position represents that measured in vivo during gait.

Individuals with over- or under-covered hips may develop hip osteoarthritis. Femoral head coverage is typically evaluated using radiographs, and/or computed tomography (CT) or magnetic resonance images obtained supine. Yet, these static assessments of coverage may not provide accurate information regarding the dynamic, three-dimensional (3-D) relationship between the femoral head and acetabulum. The objectives of this study were to: (1) quantify total and regional 3-D femoral head coverage in a standing position and during gait, and (2) quantify the relationship between 3-D femoral head coverage in standing to that measured during gait. The kinematic position of the hip during standing and gait was measured in vivo for 11 asymptomatic morphologically normal subjects using dual fluoroscopy and model-based tracking of 3-D CT models. Percent coverage in the standing position and during gait was measured overall and on a regional basis (anterior, superior, posterior, inferior). Coverage in standing was correlated with that measured during gait. For total coverage, very little change in coverage occurred during gait (range: 35.0-36.7%; mean: 36.2%). Coverage at each time point of gait strongly correlated with coverage during standing (r = 0.929-0.989). The regions thought to play an important role in weight bearing (i.e. anterior, superior, posterior) were significantly correlated with coverage in standing during the stance phase. Our results suggest that coverage measured in a standing position is a good surrogate for coverage measured during gait. Clin. Anat. 31:1177-1183, 2018. © 2018 Wiley Periodicals, Inc.

Does Removal of Subchondral Cortical Bone Provide Sufficient Resection Depth for Treatment of Cam Femoroacetabular Impingement?

BACKGROUND: Residual impingement resulting from insufficient resection of bone during the index femoroplasty is the most-common reason for revision surgery in patients with cam-type femoroacetabular impingement (FAI). Development of surgical resection guidelines therefore could reduce the number of patients with persistent pain and reduced ROM after femoroplasty. QUESTIONS/PURPOSES: We asked whether removal of subchondral cortical bone in the region of the lesion in patients with cam FAI could restore femoral anatomy to that of screened control subjects. To evaluate this, we analyzed shape models between: (1) native cam and screened control femurs to observe the location of the cam lesion and establish baseline shape differences between groups, and (2) cam femurs with simulated resections and screened control femurs to evaluate the sufficiency of subchondral cortical bone thickness to guide resection depth. METHODS: Three-dimensional (3-D) reconstructions of the inner and outer cortical bone boundaries of the proximal femur were generated by segmenting CT images from 45 control subjects (29 males; 15 living subjects, 30 cadavers) with normal radiographic findings and 28 nonconsecutive patients (26 males) with a diagnosis of cam FAI based on radiographic measurements and clinical examinations. Correspondence particles were placed on each femur and statistical shape modeling (SSM) was used to create mean shapes for each cohort. The geometric difference between the mean shape of the patients with cam FAI and that of the screened controls was used to define a consistent region representing the cam lesion. Subchondral cortical bone in this region was removed from the 3-D reconstructions of each cam femur to create a simulated resection. SSM was repeated to determine if the resection produced femoral anatomy that better resembled that of control subjects. Correspondence particle locations were used to generate mean femur shapes and evaluate shape differences using principal component analysis. RESULTS: In the region of the cam lesion, the median distance between the mean native cam and control femurs was 1.8 mm (range, 1.0-2.7 mm). This difference was reduced to 0.2 mm (range, -0.2 to 0.9 mm) after resection, with some areas of overresection anteriorly and underresection superiorly. In the region of resection for each subject, the distance from each correspondence particle to the mean control shape was greater for the cam femurs than the screened control femurs (1.8 mm, [range, 1.1-2.9 mm] and 0.0 mm [range, -0.2-0.1 mm], respectively; p < 0.031). After resection, the distance was not different between the resected cam and control femurs (0.3 mm; range, -0.2-1.0; p > 0.473). CONCLUSIONS: Removal of subchondral cortical bone in the region of resection reduced the deviation between the mean resected cam and control femurs to within a millimeter, which resulted in no difference in shape between patients with cam FAI and control subjects. Collectively, our results support the use of the subchondral cortical-cancellous bone margin as a visual intraoperative guide to limit resection depth in the correction of cam FAI. CLINICAL RELEVANCE: Use of the subchondral cortical-cancellous bone boundary may provide a method to guide the depth of resection during arthroscopic surgery, which can be observed intraoperatively without advanced tooling, or imaging.

In Vivo Kinematics of the Tibiotalar and Subtalar Joints in Asymptomatic Subjects: A High-Speed Dual Fluoroscopy Study.

Measurements of joint kinematics are essential to understand the pathomechanics of ankle disease and the effects of treatment. Traditional motion capture techniques do not provide measurements of independent tibiotalar and subtalar joint motion. In this study, high-speed dual fluoroscopy images of ten asymptomatic adults were acquired during treadmill walking at 0.5 m/s and 1.0 m/s and a single-leg, balanced heel-rise. Three-dimensional (3D) CT models of each bone and dual fluoroscopy images were used to quantify in vivo kinematics for the tibiotalar and subtalar joints. Dynamic tibiotalar and subtalar mean joint angles often exhibited opposing trends during captured stance. During both speeds of walking, the tibiotalar joint had significantly greater dorsi/plantarflexion (D/P) angular ROM than the subtalar joint while the subtalar joint demonstrated greater inversion/eversion (In/Ev) and internal/external rotation (IR/ER) than the tibiotalar joint. During balanced heel-rise, only D/P and In/Ev were significantly different between the tibiotalar and subtalar joints. Translational ROM in the anterior/posterior (AP) direction was significantly greater in the subtalar than the tibiotalar joint during walking at 0.5 m/s. Overall, our results support the long-held belief that the tibiotalar joint is primarily responsible for D/P, while the subtalar joint facilitates In/Ev and IR/ER. However, the subtalar joint provided considerable D/P rotation, and the tibiotalar joint rotated about all three axes, which, along with translational motion, suggests that each joint undergoes complex, 3D motion.

Accuracy of 3D dual echo steady state (DESS) MR arthrography to quantify acetabular cartilage thickness.

PURPOSE: To deploy and quantify the accuracy of 3D dual echo steady state (DESS) MR arthrography with hip traction to image acetabular cartilage. Clinical magnetic resonance imaging (MRI) sequences used to image hip cartilage often have reduced out-of-plane resolution and may lack adequate signal-to-noise to image cartilage. MATERIALS AND METHODS: Saline was injected into four cadaver hips placed under traction. 3D DESS MRI scans were obtained before and after cores of cartilage were harvested from the acetabulum; the two MRIs were spatially aligned to reference core positions. The thickness of cartilage cores was measured under microscopy to serve as the reference standard. 3D reconstructions of cartilage and subchondral bone were generated using automatic and semiautomatic image segmentation. Cartilage thickness estimated from the 3D reconstructions was compared to physical measurements using Bland-Altman plots. RESULTS: As revealed by the automatic segmentation mask, saline imbibed the joint space throughout the articulating surface, with the exception of the posteroinferior region in two hips. Locations where air bubbles were introduced and regions of suspected low density bone disrupted an otherwise smooth automatic segmentation mask. Automatic and semiautomatic segmentation yielded a bias ± repeatability coefficient (95% limits of agreement) of 0.10 ± 0.51 mm (-0.41 to 0.61 mm) and 0.06 ± 0.43 mm (-0.37 to 0.49 mm), respectively. CONCLUSION: Cartilage thickness can be estimated to within ∼0.5 mm of the physical value with 95% confidence using 3D reconstructions of 3D DESS MR arthrography images. Manual correction of the automatic segmentation mask may improve reconstruction accuracy.

Subject-specific patterns of femur-labrum contact are complex and vary in asymptomatic hips and hips with femoroacetabular impingement.

BACKGROUND: Femoroacetabular impingement (FAI) may constrain hip articulation and cause chondrolabral damage, but to our knowledge, in vivo articulation and femur-labrum contact patterns have not been quantified. PURPOSE: In this exploratory study, we describe the use of high-speed dual-fluoroscopy and model-based tracking to dynamically measure in vivo hip articulation and estimate the location of femur-labrum contact in six asymptomatic hips and three hips with FAI during the impingement examination. We asked: (1) Does femur-labrum contact occur at the terminal position of impingement? (2) Could range of motion (ROM) during the impingement examination appear decreased in hips with FAI? (3) Does the location of femur-labrum contact coincide with that of minimum bone-to-bone distance? (4) In the patients with FAI, does the location of femur-labrum contact qualitatively correspond to the location of damage observed intraoperatively? METHODS: High-speed dual-fluoroscopy images were acquired continuously as the impingement examination was performed. CT arthrogram images of all subjects were segmented to generate three-dimensional (3-D) surfaces for the pelvis, femur, and labrum. Model-based tracking of the fluoroscopy images enabled dynamic kinematic observation of the 3-D surfaces. At the terminal position of the examination, the region of minimal bone-to-bone distance was compared with the estimated location of femur-labrum contact. Each patient with FAI underwent hip arthroscopy; the location of femur-labrum contact was compared qualitatively with damage found during surgery. As an exploratory study, statistics were not performed. RESULTS: Femur-labrum contact was observed in both groups, but patterns of contact were subject-specific. At the terminal position of the impingement examination, internal rotation and adduction angles for each of the patients with FAI were less than the 95% confidence intervals (CIs) for the asymptomatic control subjects. The location of minimum bone-to-bone distance agreed with the region of femur-labrum contact in two of nine hips. The locations of chondrolabral damage identified during surgery qualitatively coincided with the region of femur-labrum contact. CONCLUSIONS: Dual-fluoroscopy and model-based tracking provided the ability to assess hip kinematics in vivo during the entire impingement examination. The high variability in observed labrum-femur contact patterns at the terminal position of the examination provides evidence that subtle anatomic features could dictate underlying hip biomechanics. Although femur-labrum contact occurs in asymptomatic and symptomatic hips at the terminal position of the impingement examination, contact may occur at reduced adduction and internal rotation in patients with FAI. Use of minimum bone-to-bone distance may not appropriately identify the region of femur-labrum contact. Additional research, using a larger cohort and appropriate statistical tests, is required to confirm the findings of this exploratory study.

Accuracy and feasibility of dual fluoroscopy and model-based tracking to quantify in vivo hip kinematics during clinical exams.

Accurate measurements of in-vivo hip kinematics may elucidate the mechanisms responsible for impaired function and chondrolabral damage in hips with femoroacetabular impingement (FAI). The objectives of this study were to quantify the accuracy and demonstrate the feasibility of using dual fluoroscopy to measure in-vivo hip kinematics during clinical exams used in the assessment of FAI. Steel beads were implanted into the pelvis and femur of two cadavers. Specimens were imaged under dual fluoroscopy during the impingement exam, FABER test, and rotational profile. Bead locations measured with model-based tracking were compared with those measured using dynamic radiostereometric analysis. Error was quantified by bias and precision, defined as the average and standard deviation of the differences between tracking methods, respectively. A normal male volunteer was also imaged during clinical exams. Bias and precision along a single axis did not exceed 0.17 and 0.21 mm, respectively. Comparing kinematics, positional error was less than 0.48 mm and rotational error was less than 0.58°. For the volunteer, kinematics were reported as joint angles and bone-bone distance. These results demonstrate that dual fluoroscopy and model-based tracking can accurately measure hip kinematics in living subjects during clinical exams of the hip.

Subject-specific analysis of joint contact mechanics: application to the study of osteoarthritis and surgical planning.

Advances in computational mechanics, constitutive modeling, and techniques for subject-specific modeling have opened the door to patient-specific simulation of the relationships between joint mechanics and osteoarthritis (OA), as well as patient-specific preoperative planning. This article reviews the application of computational biomechanics to the simulation of joint contact mechanics as relevant to the study of OA. This review begins with background regarding OA and the mechanical causes of OA in the context of simulations of joint mechanics. The broad range of technical considerations in creating validated subject-specific whole joint models is discussed. The types of computational models available for the study of joint mechanics are reviewed. The types of constitutive models that are available for articular cartilage are reviewed, with special attention to choosing an appropriate constitutive model for the application at hand. Issues related to model generation are discussed, including acquisition of model geometry from volumetric image data and specific considerations for acquisition of computed tomography and magnetic resonance imaging data. Approaches to model validation are reviewed. The areas of parametric analysis, factorial design, and probabilistic analysis are reviewed in the context of simulations of joint contact mechanics. Following the review of technical considerations, the article details insights that have been obtained from computational models of joint mechanics for normal joints; patient populations; the study of specific aspects of joint mechanics relevant to OA, such as congruency and instability; and preoperative planning. Finally, future directions for research and application are summarized.

A Correspondence-Based Network Approach for Groupwise Analysis of Patient-Specific Spatiotemporal Data.

Methods for statistically analyzing patient-specific data that vary both spatially and over time are currently either limited to summary statistics or require elaborate surface registration. We propose a new method, called correspondence-based network analysis, which leverages particle-based shape modeling to establish correspondence across a population and preserve patient-specific measurements and predictions through statistical analysis. Herein, we evaluated this method using three published datasets of the hip describing cortical bone thickness of the proximal femur, cartilage contact stress, and dynamic joint space between control and patient cohorts to evaluate activity- and group-based differences, as applicable, using traditional statistical parametric mapping (SPM) and our proposed spatially considerate correspondence-based network analysis approach. The network approach was insensitive to correspondence density, while the traditional application of SPM showed decreasing area of the region of significance with increasing correspondence density. In comparison to SPM, the network approach identified broader and more connected regions of significance for all three datasets. The correspondence-based network analysis approach identified differences between groups and activities without loss of subject and spatial specificity which could improve clinical interpretation of results.

Patients with cam-type femoroacetabular impingement demonstrate increased change in bone-to-bone distance during walking: A dual fluoroscopy study.

Cam-type femoroacetabular impingement (FAI) syndrome is a painful, structural hip disorder. Herein, we investigated hip joint mechanics through in vivo, dynamic measurement of the bone-to-bone distance between the femoral head and acetabulum in patients with cam FAI syndrome and morphologically screened controls. We hypothesized that individuals with cam FAI syndrome would have larger changes in bone-to-bone distance compared to the control group, which we would interpret as altered joint mechanics as signified by greater movement of the femoral head as it articulates within the acetabulum. Seven patients with cam FAI syndrome and 11 asymptomatic individuals with typical morphology underwent dual fluoroscopy imaging during level and inclined walking (upward slope). The change in bone-to-bone distance between femoral and acetabular bone surfaces was evaluated for five anatomical regions of the acetabulum at each timepoint of gait. Linear regression analysis of the bone-to-bone distance considered two within-subject factors (activity and region) and one between-subjects factor (group). Across activities, the change in minimum bone-to-bone distance was 1.38-2.54 mm for the cam FAI group and 1.16-1.84 mm for controls. In all regions except the anterior-superior region, the change in bone-to-bone distance was larger in the cam group than the control group (p ≤ 0.024). An effect of activity was detected only in the posterior-superior region where larger changes were noted during level walking than incline walking. Statement of clinical significance: Patients with cam FAI syndrome exhibit altered hip joint mechanics during the low-demand activity of walking; these alterations could affect load transmission, and contribute to pain, tissue damage, and osteoarthritis.

Statistical multi-level shape models for scalable modeling of multi-organ anatomies.

Statistical shape modeling is an indispensable tool in the quantitative analysis of anatomies. Particle-based shape modeling (PSM) is a state-of-the-art approach that enables the learning of population-level shape representation from medical imaging data (e.g., CT, MRI) and the associated 3D models of anatomy generated from them. PSM optimizes the placement of a dense set of landmarks (i.e., correspondence points) on a given shape cohort. PSM supports multi-organ modeling as a particular case of the conventional single-organ framework via a global statistical model, where multi-structure anatomy is considered as a single structure. However, global multi-organ models are not scalable for many organs, induce anatomical inconsistencies, and result in entangled shape statistics where modes of shape variation reflect both within- and between-organ variations. Hence, there is a need for an efficient modeling approach that can capture the inter-organ relations (i.e., pose variations) of the complex anatomy while simultaneously optimizing the morphological changes of each organ and capturing the population-level statistics. This paper leverages the PSM approach and proposes a new approach for correspondence-point optimization of multiple organs that overcomes these limitations. The central idea of multilevel component analysis, is that the shape statistics consists of two mutually orthogonal subspaces: the within-organ subspace and the between-organ subspace. We formulate the correspondence optimization objective using this generative model. We evaluate the proposed method using synthetic shape data and clinical data for articulated joint structures of the spine, foot and ankle, and hip joint.

Acetabular labrum and cartilage contact mechanics during pivoting and walking tasks in individuals with cam femoroacetabular impingement syndrome.

Femoroacetabular impingement syndrome (FAIS) is a motion-related pathology of the hip characterized by pain, morphological abnormalities of the proximal femur, and an elevated risk of joint deterioration and hip osteoarthritis. Activities that require deep flexion are understood to induce impingement in cam FAIS patients, however, less demanding activities such as walking and pivoting may induce pain as well as alterations in kinematics and joint stability. Still, the paucity of quantitative descriptions of cam FAIS has hindered understanding underlying hip joint mechanics during such activities. Previous in silico studies have employed generalized model geometry or kinematics to simulate impingement between the femur and acetabulum, which may not accurately capture the interplay between morphology and motion. In this study, we utilized models with participant-specific bone and articular soft tissue anatomy and kinematics measured by dual-fluoroscopy to compare hip contact mechanics of cam FAIS patients to controls during four activities of daily living (internal/external pivoting and level/incline walking). Averaged across the gait cycle during incline walking, patients displayed increased strain in the anterior joint (labrum strain: p-value = 0.038, patients: 11.7 ± 6.7 %, controls: 5.0 ± 3.6 %; cartilage strain: p-value = 0.029, patients: 9.1 ± 3.3 %, controls: 4.2 ± 2.3). Patients also exhibited increased average anterior cartilage strains during external pivoting (p-value = 0.039; patients: 13.0 ± 9.2 %, controls: 3.9 ± 3.2 %]). No significant differences between patient and control contact area and strain were found for level walking and internal pivoting. Our study provides new insights into the biomechanics of cam FAIS, including spatiotemporal hip joint contact mechanics during activities of daily living.