Effect of sagittal pelvic tilt on joint stress distribution in hip dysplasia: A finite element analysis

Periacetabular Osteotomy Improves Hip Microinstability Between Supine and Standing Radiographs in Symptomatic Hip Dysplasia

Background

Whether periacetabular osteotomy (PAO) improves hip microinstability in patients with symptomatic hip dysplasia remains poorly understood.

Purpose

To assess the femoral head translation with static postural change, considered a potential indicator of hip microinstability, comparing dysplastic hips before and after PAO with normal hips.

Study Design

Descriptive laboratory study.

Methods

A total of 26 patients (30 hips) with hip dysplasia underwent PAO, and 18 healthy individuals (18 hips) were eligible. Using a 3-dimensional-to-2-dimensional registration technique, femoral head translation before and after PAO was quantified as the displacement of the center of the femoral head relative to the center of the acetabulum between supine and standing positions. Morphological factors on supine anteroposterior pelvic radiographs before and after PAO correlated with the femoral head translation, particularly lateral translation, were examined.

Results

Femoral head translation decreased after PAO (1.5 ± 0.4 mm vs 1.0 ± 0.4 mm; P < .001) but remained larger than in controls (1.0 ± 0.4 mm vs 0.7 ± 0.3 mm; P = .01). The more severe the hip dysplasia before PAO was, the greater the femoral head translation. However, the femoral head translation improved after PAO with sufficient acetabular correction. The acetabular roof obliquity (ARO) showed the strongest correlation with lateral translation of the femoral head from the supine to standing position before PAO. In contrast, no correlation was found after PAO.

Conclusion

This study demonstrates that the severity of hip dysplasia influences hip microinstability, that PAO mitigates hip microinstability with adequate acetabular correction, and that PAO does not normalize hip stability because of residual joint incongruity. In patients with a larger ARO, the femoral head has more lateral translation in the standing position. Therefore, weightbearing postural radiographs are crucial for understanding hip biomechanics in hip dysplasia and refining surgical corrections during PAO.

Clinical Relevance

PAO can make the hip more stable in hip dysplasia, but not as stable as the normal hip. In hip dysplasia, pre-PAO standing radiographs should be evaluated due to their accurately representing the femoral head position relative to the acetabulum.

Posterior Pelvic Tilt Allows for Increased Hip Motion, While Anterior Pelvic Tilt Decreases Joint Stress: A Systematic Review of Biomechanical and Motion Analyses

PURPOSE

The purpose of this systematic review was to evaluate the effect of pelvic tilt on hip joint contact forces and range of motion in patients with femoroacetabular impingement (FAI) and acetabular dysplasia.

METHODS

A literature review querying the U.S. National Library of Medicine (PubMed/MEDLINE), EMBASE, SCOPUS, and Cochrane Databases using the key words ("Femoroacetabular Impingement" OR "Hip Dysplasia") AND ((((("Pelvic Tilt") OR (Joint Contact) OR (Kinetics) OR ("Pelvic Incidence") OR (Lumbar Lordosis)))). 14 studies were included in the review with methodological quality evaluated through the Methodological Index for Non-Randomized Studies (MINORS) and Risk of Bias in Non-Randomized Studies- of Interventions (ROBINS-I) criteria.

RESULTS

There were 474 total patients (577 hips) in the 14 studies reviewed. Two studies focused on hip joint contact forces and femoral head coverage in acetabular dysplasia. These found that posterior pelvic tilt was associated with decreased hip joint contact area (range: 490-581 mm2 vs 919-1094 mm2), increased joint contact pressure (range: 3.9-7.3 mPa vs 1.8-3.5 mPa), and decreased femoral head coverage (range: 30.2-43.4% vs 38.9-50.3%) in dysplastic subjects compared to control populations. Twelve studies evaluated the range of hip motion in FAI populations undergoing different functional maneuvers. Posterior pelvic tilt in FAI patients was found to increase hip range of motion to impingement on supine testing and biomechanical modeling (Internal rotation in flexion range: -6.5° to 15.5° with anterior tilt, 12.9° to 31.4° with posterior tilt). With dynamic maneuvers, FAI patients had decreased pelvic mobility (range: 7.2°-14.7° vs 12.7°-24.2°) and decreased posterior pelvic tilt (range: 3.4°-15.9° vs 9.8°-21.1°) compared to patients without FAI.

CONCLUSIONS

Hip joint stress is increased with posterior pelvic tilt in dysplastic patients, while increasing posterior pelvic tilt increases hip range of motion to impingement in patients with FAI. During weight-bearing exercises, the ability for FAI patients to posteriorly tilt the pelvis is restricted compared to a control population.

CLINICAL RELEVANCE

Spinopelvic kinematics and alignment affect composite hip motion and play a critical role in bipedal locomotion. The influence of spinopelvic parameters on treatment outcomes for acetabular dysplasia and FAI is controversial and currently limited by an imperfect understanding of the hip-spine relationship as it relates to nonarthritic hip disease. The present systematic review provides a summary of the results of biomechanical studies investigating pelvic tilt in this population.

Biomechanical evaluation for bone arthrosis morphology based on reconstructed dynamic kinesiology

A biomechanical evaluation method for bone arthrosis morphology based on reconstructed dynamic kinesiology (RDK) is proposed. The hip joint is a ball-and-socket joint, morphologically characterized by an acetabulum with a nearly spherical concavity and uniform curvatures, where Gaussian curvature exhibits negative characteristic. Subsequently, RDK of bone joint morphology is developed, offering detailed anatomical and kinematic insights. The hip joint is taken as a verification instance, where a precise biomechanical evaluation of bone arthrosis morphology is simulated through finite element analysis (FEA). Latin Hypercube sampling (LHS) with the criterion of maximizing the minimum distance enhances uniformity and representation. The response surface is subsequently constructed by Kriging interpolation, significantly enhancing computational efficiency and FEA accuracy. Innovatively, a stress contour statistical histogram of load transfer is presented to quantitatively analyze the stress lines, supplying support for biomechanical evaluation, which is essential for accurate hip replacement planning. The instance indicates that the proposed RDK facilitates accurate biomechanical evaluations for bone arthrosis morphology, providing a critical theoretical foundation for conceptual design of ergonomic wearable devices, as well as optimization of replacement surgeries.

Acetabular osteophyte formation in dysplastic hip osteoarthritis

The growth of periacetabular osteophytes with developmental dysplasia of the hip (DDH) remains unclear. This study aimed to perform a three-dimensional assessment of periacetabular osteophytes and the effects of superiorization (SP) and lateralization (LT) of the femoral head on osteophyte formation. Female (n = 105) with unilateral hip osteoarthritis due to DDH who underwent total hip arthroplasty between 2016 and 2022 were included. The SP and LT of the femoral head were assessed using anteroposterior radiographs. We measured the periacetabular osteophyte using computed tomography. The correlation coefficient between SP or LT and the length of each osteophyte were investigated. Furthermore, multiple regression analyses with SP and LT as explanatory variables and each osteophyte as an objective variable were performed to evaluate the effect of SP and LT on osteophyte formation. The longest osteophyte was the anterior osteophyte (20.48 mm ± 11.8 mm). Acetabular osteophytes correlated with LT as follows: anterior (r = 0.55), posterosuperior (r = 0.51), and inferior (r = 0.48). Multiple regression analysis showed that all acetabular osteophytes were influenced by LT (p < 0.05 for all factors). Hip surgeons may need to be aware that cases with marked lateralization of the femoral head require treatment of the periacetabular osteophytes.

A Computer Modeling-Based Target Zone for Transposition Osteotomy of the Acetabulum in Patients with Hip Dysplasia

BACKGROUND

This study aimed to determine the acetabular position to optimize hip biomechanics after transposition osteotomy of the acetabulum (TOA), a specific form of periacetabular osteotomy, in patients with hip dysplasia.

METHODS

We created patient-specific finite-element models of 46 patients with hip dysplasia to simulate 12 virtual TOA scenarios: lateral rotation to achieve a lateral center-edge angle (LCEA) of 30°, 35°, and 40° combined with anterior rotation of 0°, 5°, 10°, and 15°. Joint contact pressure (CP) on the acetabular cartilage during a single-leg stance and simulated hip range of motion without osseous impingement were calculated. The optimal acetabular position was defined as satisfying both normal joint CP and the required range of motion for activities of daily living. Multivariable logistic regression analysis was used to identify preoperative morphological predictors of osseous impingement after virtual TOA with adequate acetabular correction.

RESULTS

The prevalence of hips in the optimal position was highest (65.2%) at an LCEA of 30°, regardless of the amount of anterior rotation. While the acetabular position minimizing peak CP varied among patients, approximately 80% exhibited normalized peak CP at an LCEA of 30° and 35° with 15° of anterior rotation, which were the 2 most favorable configurations among the 12 simulated scenarios. In this context, the preoperative head-neck offset ratio (HNOR) at the 1:30 clock position (p = 0.018) was an independent predictor of postoperative osseous impingement within the required range of motion. Specifically, an HNOR of <0.14 at the 1:30 clock position predicted limitation of required range of motion after virtual TOA (sensitivity, 57%; specificity, 81%; and area under the receiver operating characteristic curve, 0.70).

CONCLUSIONS

Acetabular reorientation to an LCEA of between 30° and 35° with an additional 15° of anterior rotation may serve as a biomechanics-based target zone for surgeons performing TOA in most patients with hip dysplasia. However, patients with a reduced HNOR at the 1:30 clock position may experience limited range of motion in activities of daily living postoperatively.

CLINICAL RELEVANCE

This study provides a biomechanics-based target for refining acetabular reorientation strategies during TOA while considering morphological factors that may limit the required range of motion.

Hip joint stress distribution changes depending on three-dimensional pelvic orientation: Finite-element analysis

BACKGROUND

Pelvis experiences changes in its orientation due to the alignment of the hip joint and spine, and its orientation might affect both joints. Pelvic tilt on the sagittal plane has been widely discussed; however, the pelvis is oriented also on the coronal and horizontal planes. This study aimed to examine how stress distribution on intact hip joint changes under the three-dimensional pelvic orientation.

METHODS

Computed tomography data of five patients with unilateral pelvic girdle were analyzed. Thirteen models were evaluated by the MECHANICAL FINDER: neutral position at 0°; 10° and 20° anterior and posterior pelvic tilt; 10° and 20° pelvic hike and drop; 10° and 20° pelvic forward and backward rotation. Stress assessment was performed in four parts of the acetabulum: anterosuperior, posterosuperior, posteroinferior, and central parts.

RESULTS

Compared with the neutral position, the mean value of the equivalent stress and maximum principal stress in the anterosuperior part significantly increased by 1.51 times and 1.57 times at 20° posterior tilt, respectively. The maximum principal stress in the anterosuperior part significantly increased by 1.44 times at 20° hike. A significant increase of 1.45 times was found in the maximum principal stress in the anterosuperior part at 20° forward rotation.

CONCLUSIONS

Local stress accumulated in the anterosuperior acetabulum at the posterior pelvic tilt, pelvic hike, and pelvic forward rotation, which might lead to hip overload. The effect of posterior pelvic tilt appears to be greater for the hip joint than at the pelvic hike or forward rotation.

Females with hip pain walk with altered kinematics at peaks and throughout the gait cycle

BACKGROUND

Females with acetabular dysplasia and/or labral tears (hip pain) exhibit altered walking kinematics, with studies reporting mixed results in sagittal and frontal planes compared to pain-free controls, often conducting only discrete analyses and warranting further investigation. The objective of this study was to investigate discrete and continuous hip and pelvic kinematics between females with and without hip pain in two walking conditions.

METHODS

We collected kinematic walking data from 69 females (35 with hip pain, 34 controls) using motion capture and an instrumented treadmill in two conditions: preferred and fast (125% preferred). We used a general linear model and one-dimensional statistical parametric mapping to conduct discrete and continuous analyses comparing kinematics between groups, with and without adjustment for gait speed.

FINDINGS

The hip pain group walked with reduced peak hip extension (Preferred: P = .046, Cohen's d = 0.41; Fast: P = .028, d = 0.48) and greater peak anterior pelvic tilt (Preferred: P = .011, d = 0.57; Fast: P = .012, d = 0.58) compared to controls. From continuous analyses, the hip pain group walked with reduced hip extension during terminal stance (Fast: P = .040), greater anterior pelvic tilt throughout (Preferred: P = .007; Fast: P = .004), and greater contralateral pelvic drop (Preferred: P = .045) during midstance. Adjusting for speed slightly affected p-values, but significance was retained for all prior variables except pelvic drop.

INTERPRETATION

Kinematic differences between individuals with and without hip pain may provide insight into potential predisposing factors for hip pathology and/or compensations for pain or pathological processes. This work furthers understanding of altered movement patterns in individuals with hip pain and may inform physical therapy treatments.

Biomechanical analysis of load distribution in porcine hip joints at different acetabular coverages

BACKGROUND

Developmental dysplasia of the hip causes secondary osteoarthritis. Finite element analysis suggests high hip joint contact pressure in patients with hip dysplasia and a reduction in contact pressure after periacetabular osteotomy. However, few biomechanical studies have examined the load distribution in the hip joint. This study aimed to investigate the biomechanical properties of load distribution in porcine hip joints at different acetabular coverages.

METHODS

Six porcine hip joints were analyzed using three models: 1) neutral coverage, 2) 15° under-coverage (defined as dysplasia model), and 3) 15° over-coverage created by varying the acetabular coverage. The load distribution was assessed using a pressure-mapping sensor system after applying a loading force of 100 N to the hip joint.

RESULTS

In the dysplasia model, the load was concentrated at the acetabular rim; in the neutral and over-coverage models, it was dispersed. The average contact pressure was significantly higher in the dysplasia model than in the neutral coverage model ([0.42 vs. 0.3 MPa]; p = 0.004). The contact area was significantly smaller in the dysplasia model than in the neutral coverage model ([250.7 vs. 345.0 mm2]; p = 0.004). No significant differences were observed in contact pressure or area between the neutral and over-coverage models.

CONCLUSIONS

Insufficient acetabular coverage in the dysplasia model demonstrated higher contact pressure and smaller contact area than the neutral model. Conversely, the contact pressure and area in the over-coverage model did not differ significantly from those in the normal model. Therefore, surgeons should note that acetabular coverage overcorrection has limited effect; normalization is crucial during periacetabular osteotomy.

Impact of sagittal and coronal pelvic tilt on hip subluxation in non-ambulatory flaccid neuromuscular scoliosis patients following spinal correction

PURPOSE

To evaluate the actual change in clinical hip pain and hip migration after operation for non-ambulatory flaccid neuromuscular (NM) scoliosis and investigate whether there is an association between hip migration and coronal/sagittal pelvic tilt (CO-PT/SA-PT).

PATIENTS AND METHODS

This retrospective, single-center, observational study evaluated a total of 134 patients with non-ambulatory flaccid neuromuscular scoliosis who underwent surgery performed by a single surgeon between 2003 and 2020, with at least 2 years of follow-up period. Operation procedures were conducted in two stages, beginning with L5-S1 anterior release followed by posterior fixation. Radiologic parameters were measured at preoperative, immediate postoperative, and last follow-up periods with clinical hip pain and clinical hip dislocation events.

RESULTS

The significant improvements occurred in various parameters after correction surgery for NM scoliosis, containing Cobb's angle of major curve and CO-PT. However, Reimer's hip migration percentage (RMP) was increased on both side of hip (High side, 0.23 ± 0.16 to 0.28 ± 0.21; Low side, 0.20 ± 0.14 to 0.23 ± 0.18). Hip pain and dislocation events were also increased (Visual analog scale score, 2.5 ± 2.3 to 3.6 ± 2.6, P value < 0.05; dislocation, 6-12). Logistic regression analysis of the interactions between ΔRMP(High) and the change of sagittal pelvic tilt (ΔSA-PT) after correction reveals a significant negative association. (95% CI 1.003-1.045, P value = 0.0226).

CONCLUSIONS

In cases of non-ambulatory flaccid NM scoliosis, clinical hip pain, and subluxation continued to deteriorate even after correction of CO-PT. There was a relationship between the decrease in SA-PT, and an increase in hip migration percentage on high side, indicating the aggravation of hip subluxation.

Hip-spine relationship: clinical evidence and biomechanical issues

The hip-spine relationship is a critical consideration in total hip arthroplasty (THA) procedures. While THA is generally successful in patient, complications such as instability and dislocation can arise. These issues are significantly influenced by the alignment of implant components and the overall balance of the spine and pelvis, known as spinopelvic balance. Patients with alteration of those parameters, in particular rigid spines, often due to fusion surgery, face a higher risk of THA complications, with an emphasis on complications in instability, impingement and dislocation. For these reasons, over the years, computer modelling and simulation techniques have been developed to support clinicians in the different steps of surgery. The aim of the current review is to present current knowledge on hip-spine relationship to serve as a common platform of discussion among clinicians and engineers. The offered overview aims to update the reader on the main critical aspects of the issue, from both a theoretical and practical perspective, and to be a valuable introductory tool for those approaching this problem for the first time.

Which Acetabular Measurements Most Accurately Differentiate Between Patients and Controls? A Comparative Study

BACKGROUND

Acetabular morphology is an important determinant of hip biomechanics. To identify features of acetabular morphology that may be associated with the development of hip symptoms while accounting for spinopelvic characteristics, one needs to determine acetabular characteristics in a group of individuals older than 45 years without symptoms or signs of osteoarthritis. Previous studies have used patients with unknown physical status to define morphological thresholds to guide management.

QUESTIONS/PURPOSES

(1) To determine acetabular morphological characteristics in males and females between 45 and 60 years old with a high Oxford hip score (OHS) and no signs of osteoarthritis; (2) to compare these characteristics with those of symptomatic hip patients treated with hip arthroscopy or periacetabular osteotomy (PAO) for various kinds of hip pathology (dysplasia, retroversion, and cam femoroacetabular impingement); and (3) to assess which radiographic or CT parameters most accurately differentiate between patients who had symptomatic hips and those who did not, and thus, define thresholds that can guide management.

METHODS

Between January 2018 and December 2018, 1358 patients underwent an abdominopelvic CT scan in our institution for nonorthopaedic conditions. Of those, we considered 5% (73) of patients as potentially eligible as controls based on the absence of major hip osteoarthritis, trauma, or deformity. Patients were excluded if their OHS was 43 or less (2% [ 28 ]), if they had a PROMIS less than 50 (1% [ 18 ]), or their Tönnis score was higher than 1 (0.4% [ 6 ]). Another eight patients were excluded because of insufficient datasets. After randomly selecting one side for each control, 40 hips were left for analysis (age 55 ± 5 years; 48% [19 of 40] were in females). In this comparative study, this asymptomatic group was compared with a group of patients treated with hip arthroscopy or PAO. Between January 2013 and December 2020, 221 hips underwent hip preservation surgery. Of those, eight were excluded because of previous pelvic surgery, and 102 because of insufficient CT scans. One side was randomly selected in patients who underwent bilateral procedure, leaving 48% (107 of 221) of hips for analysis (age 31 ± 8 years; 54% [58 of 107] were in females). Detailed radiographic and CT assessments (including segmentation) were performed to determine acetabular (depth, cartilage coverage, subtended angles, anteversion, and inclination) and spinopelvic (pelvic tilt and incidence) parameters. Receiver operating characteristics (ROC) analysis was used to assess diagnostic accuracy and determine which morphological parameters (and their threshold) differentiate most accurately between symptomatic patients and asymptomatic controls.

RESULTS

Acetabular morphology in asymptomatic hips was characterized by a mean depth of 22 ± 2 mm, with an articular cartilage surface of 2619 ± 415 mm 2 , covering 70% ± 6% of the articular surface, a mean acetabular inclination of 48° ± 6°, and a minimal difference between anatomical (24° ± 7°) and functional (22° ± 6°) anteversion. Patients with symptomatic hips generally had less acetabular depth (20 ± 4 mm versus 22 ± 2 mm, mean difference 3 mm [95% CI 1 to 4]; p < 0.001). Hips with dysplasia (67% ± 5% versus 70% ± 6%, mean difference 6% [95% CI 0% to 12%]; p = 0.03) or retroversion (67% ± 5% versus 70% ± 6%, mean difference 6% [95% CI 1% to 12%]; p = 0.04) had a slightly lower relative cartilage area compared with asymptomatic hips. There was no difference in acetabular inclination (48° ± 6° versus 47° ± 7°, mean difference 0.5° [95% CI -2° to 3°]; p = 0.35), but asymptomatic hips had higher anatomic anteversion (24° ± 7° versus 19° ± 8°, mean difference 6° [95% CI 3° to 9°]; p < 0.001) and functional anteversion (22° ± 6° versus 13°± 9°, mean difference 9° [95% CI 6° to 12°]; p < 0.001). Subtended angles were higher in asymptomatic at 105° (124° ± 7° versus 114° ± 12°, mean difference 11° [95% CI 3° to 17°]; p < 0.001), 135° (122° ± 9° versus 111° ± 12°, mean difference 10° [95% CI 2° to 15°]; p < 0.001), and 165° (112° ± 9° versus 102° ± 11°, mean difference 10° [95% CI 2° to 14°]; p < 0.001) around the acetabular clockface. Symptomatic hips had a lower pelvic tilt (8° ± 8° versus 11° ± 5°, mean difference 3° [95% CI 1° to 5°]; p = 0.007). The posterior wall index had the highest discriminatory ability of all measured parameters, with a cutoff value of less than 0.9 (area under the curve [AUC] 0.84 [95% CI 0.76 to 0.91]) for a symptomatic acetabulum (sensitivity 72%, specificity 78%). Diagnostically useful parameters on CT scan to differentiate between symptomatic and asymptomatic hips were acetabular depth less than 22 mm (AUC 0.74 [95% CI 0.66 to 0.83]) and functional anteversion less than 19° (AUC 0.79 [95% CI 0.72 to 0.87]). Subtended angles with the highest accuracy to differentiate between symptomatic and asymptomatic hips were those at 105° (AUC 0.76 [95% CI 0.65 to 0.88]), 135° (AUC 0.78 [95% CI 0.70 to 0.86]), and 165° (AUC 0.77 [95% CI 0.69 to 0.85]) of the acetabular clockface.

CONCLUSION

An anatomical and functional acetabular anteversion of 24° and 22°, with a pelvic tilt of 10°, increases the acetabular opening and allows for more impingement-free flexion while providing sufficient posterosuperior coverage for loading. Hips with lower anteversion or a larger difference between anatomic and functional anteversion were more likely to be symptomatic. The importance of sufficient posterior coverage was also illustrated by the posterior wall indices and subtended angles at 105°, 135°, and 165° of the acetabular clockface having a high discriminatory ability to differentiate between symptomatic and asymptomatic hips. Future research should confirm whether integrating these parameters when selecting patients for hip preservation procedures can improve postoperative outcomes.Level of Evidence Level III, prognostic study.

Incorporating patient-specific hip orientation from weightbearing computed tomography affects discrete element analysis-computed regional joint contact mechanics in individuals treated with periacetabular osteotomy for hip dysplasia

Computational models of the hip often omit patient-specific functional orientation when placing imaging-derived bony geometry into anatomic landmark-based coordinate systems for application of joint loading schemes. The purpose of this study was to determine if this omission meaningfully alters computed contact mechanics. Discrete element analysis models were created from non-weightbearing (NWB) clinical CT scans of 10 hip dysplasia patients (11 hips) and oriented in the International Society of Biomechanics (ISB) coordinate system (NWB-ISB). Three additional models were generated for each hip by adding patient-specific stance information obtained via weightbearing CT (WBCT) to each ISB-oriented model: (1) patient-specific sagittal tilt added (WBCT-sagittal), (2) coronal and axial rotation from optical motion capture added to (1; WBCT-combo), and (3) WBCT-derived axial, sagittal, and coronal rotation added to (1; WBCT-original). Identical gait cycle loading was applied to all models for a given hip, and computed contact stress and contact area were compared between model initialization techniques. Addition of sagittal tilt did not significantly change whole-joint peak (p = 0.922) or mean (p = 0.871) contact stress or contact area (p = 0.638). Inclusion of motion-captured coronal and axial rotation (WBCT-combo) decreased peak contact stress (p = 0.014) and slightly increased average contact area (p = 0.071) from WBCT-sagittal models. Including all WBCT-derived rotations (WBCT-original) further reduced computed peak contact stress (p = 0.001) and significantly increased contact area (p = 0.001). Variably significant differences (p = 0.001-1.0) in patient-specific acetabular subregion mechanics indicate the importance of functional orientation incorporation for modeling applications in which local contact mechanics are of interest.

Gait pattern analysis before and after periacetabular osteotomy in unilaterally affected dysplastic patients

BACKGROUND

Patients with acetabular dysplasia have an abnormal acetabular geometry which results in insufficient coverage of the femoral head. This coverage deficiency reduces contact surfaces within the joint, accelerating the wear of the articular cartilage and predisposing patients to early osteoarthritis. Periacetabular osteotomy is a surgical treatment of acetabular dysplasia that aims to reorient the acetabulum relative to the femoral head, increasing coverage.

METHODS

Pelvic kinematics and lower limbs joint kinematics and kinetics during the stance phase of gait were recorded using a 3D motion capture system and force plates, then compared pre- to post- and between limbs with a repeated measures 2-way ANOVA. Radiographic measurements and gait parameters were compared pre- to post-surgery using a t-test for dependant samples. To identify predictors of pelvic symmetry improvements during gait, a multivariate analysis was performed using a forward stepwise linear regression.

FINDINGS

Radiographic measurements improved for all participants while gait parameters remained unchanged. Hip flexion symmetry was improved following surgery. The external rotation moment of the healthy hip was reduced after surgery (-29%) resulting in increased asymmetry. Pelvic tilt was significantly greater on the affected side (+0.5°) during the loading response, and the difference tended to be greater after surgery (+0.8°).

INTERPRETATION

Unilaterally affected dysplastic patients have an asymmetrical gait pattern that is only partially corrected by periacetabular osteotomy even when radiographic and clinical targets are met. Differences between the limbs could be explained in part by a learned antalgic pattern and muscle weaknesses leading to complex compensation mechanisms.

Investigating sagittal spinopelvic alignment and equivalent stress on the femoral head in patients with rapidly destructive coxarthrosis

PURPOSE

Rapidly destructive coxarthrosis (RDC) is a rare syndrome of unknown etiology. This study evaluated sagittal spinopelvic alignment (SSPA) in patients with RDC and compared it with that in patients with hip osteoarthritis (HOA). In addition, finite element analysis (FEA) was performed to investigate the distribution of stress on the femoral head in RDC versus HOA.

METHODS

This retrospective study included patients who had undergone primary total hip arthroplasty for RDC (n = 33) and HOA (n = 99; age- and sex-matched to patients with RDC) at three hospitals from June 2014 to September 2020. Preoperative SSPA parameters and inflammatory blood markers were compared between the two groups. FEA on the computed tomography data was performed for four patients from each group with similar pelvic tilt (PT) and lateral center-edge angle (LCEA). The distribution of Drucker-Prager equivalent stress was assessed at the loaded area of the femoral head.

RESULTS

Patients with RDC had significantly higher PT, lower sacral slope, decreased lumbar lordosis (LL), higher sagittal vertical axis, and higher pelvic incidence minus LL than patients with HOA, indicating sagittal spinal imbalance. Blood test revealed patients with RDC had higher levels of inflammation markers than patients with HOA. FEA revealed no statistically significant difference in the degree of stress concentration or the maximum equivalent stress between the two groups when PT and LCEA were comparable.

CONCLUSION

Patients with RDC tend to have sagittally imbalanced spine. Decreased acetabular coverage of the femoral head may heighten mechanical load of the hip joint in patients with RDC.

Effects of bone mineral density at the lateral sclerotic boundary on the femoral head collapse onset in osteonecrosis of the femoral head: A preliminary study

BACKGROUND

In the natural course of osteonecrosis of the femoral head, sclerotic changes at the boundary of necrotic lesion gradually occur until femoral head collapse. This study aims to examine the effects of bone mineral density at the lateral boundary of necrotic lesion on a subsequent femoral head collapse.

METHODS

We developed patient-specific finite element models of 9 hips with subsequent collapse and 10 hips without subsequent collapse. Cubic regions of interest were selected at both subchondral areas of the lateral boundary and the adjacent necrotic lesion. Bone mineral density values of the regions of interest were quantitatively measured, and a ratio of bone mineral density values (lateral boundary/necrotic lesion) was calculated. Stress values at the lateral boundary were also evaluated.

FINDINGS

The ratio of bone mineral density values was significantly higher in hips with subsequent collapse than that without subsequent collapse (p = 0.0016). The median equivalent stress and shear stress were significantly higher in hips with subsequent collapse than that without subsequent collapse (p = 0.0071, and p = 0.0143, respectively). The ratio of bone mineral density values showed a promising value in predicting the occurrence of subsequent femoral head collapse (AUC = 0.97).

INTERPRETATION

Our results indicated that bone mineral density value at the lateral boundary of necrotic lesion may be associated with the occurrence of subsequent femoral head collapse in pre-collapse stage osteonecrosis of the femoral head.

The sourcil roundness index is a useful measure for quantifying acetabular concavity asphericity

This study aimed to clarify the clinical utility of the sourcil roundness index (SRI), a novel index for quantifying the asphericity of the acetabular concavity, by determining (1) the difference in the SRI between dysplastic and normal hips and (2) the correlation between the SRI and radiographic parameters of hip dysplasia. We reviewed standing anteroposterior pelvic radiographs of 109 dysplastic and 40 normal hips. The SRI was determined as the ratio of the distance from the medial edge of the sourcil to the most concave point of the acetabular sourcil (A) to the distance from the medial to the lateral edge of the sourcil (B). The formula for SRI is (A/B) × 100-50 (%), with an SRI of 0% indicating a perfectly spherical acetabulum, and higher SRI values indicating a more aspherical shape. The median SRI was greater in patients with hip dysplasia than in normal hips (5.9% vs. - 1.4%; p < 0.001). Furthermore, the median SRI was greater in the severe dysplasia subgroup (18.9%) than in the moderate (3.5%) and borderline-to-mild (- 1.3%) dysplasia subgroups (p < 0.05). Quantification of acetabular concavity asphericity by the SRI showed that dysplastic hips had a more lateral acetabular concave point than normal hips, and that the severity of hip dysplasia had an effect on the acetabular concavity asphericity.

Revealing the Effect of Spinopelvic Alignment on Hip Disorders

Background

Hip osteoarthritis (HOA) is a growing burden and one of the leading causes of hip pain. The relationship between the HOA and the alignment of the spinopelvic region has been intensively studied, however the issue remains controversial. Spinopelvic imbalance, HOA, and dysplasia were investigated in relation to sagittal spinopelvic parameters in this study.

Methods

We collected computerized tomography (CT) topograms of the pelvis or abdomen from 380 patients. In antero-posterior (AP) topograms, Tonnis grading, center-edge angle (CEA) and Sharp's acetabular angle (AA) measurements were performed on each patient. Lateral topograms were used to evaluate the following spinopelvic parameters for each patient: pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), sacral table angle (STA), lumbar lordosis (LL), proximal lumbar lordosis (PLL), distal lumbar lordosis (DLL), and PI-LL difference. Initially, the cohort was divided into two subgroups based on whether or not they had HOA. Then, they were divided into two subgroups based on whether or not they had dysplasia. Ultimately, it was divided in half based on the PI-LL imbalance. Statistical analyses were conducted to determine the likely correlations between the spinopelvic parameters of these subgroups. In addition, the correlations between spinopelvic parameters were investigated.

Results

There were 380 patients evaluated. We found no association between HOA or dysplasia and spinopelvic parameters. In addition, there was no association between PI-LL imbalance and HOA or dysplasia.

Conclusion

There was no difference in constant PI and STA angle, besides other variable parameters, between groups having HOA and dysplasia or not. PI-LL imbalance has no effect on HOA and dysplasia.

Hip Pain and Movement Dysfunction Associated With Nonarthritic Hip Joint Pain: A Revision

The Academy of Orthopaedic Physical Therapy (AOPT), formerly the Orthopaedic Section of the American Physical Therapy Association (APTA), has an ongoing effort to create evidence-based practice guidelines for orthopaedic physical therapy management of patients with musculoskeletal impairments described in the World Health Organization's International Classification of Functioning, Disability, and Health (ICF). This is an update to the 2014 Clinical Practice Guideline (CPG) for Hip Pain and Movement Dysfunction Associated with Nonarthritic Hip Joint Pain. The goals of the revision were to provide a concise summary of the contemporary evidence since publication of the original guideline and to develop new recommendations or revise previously published recommendations to support evidence-based practice. This current CPG covers pathoanatomical features, clinical course, prognosis, diagnosis, examination, and physical therapy interventions in the management of nonarthritic hip joint pain. J Orthop Sports Phys Ther 2023;53(7):CPG1-CPG70. doi:10.2519/jospt.2023.0302.

[Progress in diagnosis and hip arthroscopic treatment of borderline developmental dysplasia of hip with Cam-type femoroacetabular impingement]

OBJECTIVE

To summarize the biomechanical characteristics, diagnosis, and hip arthroscopic treatment of borderline developmental dysplasia of hip (BDDH) with Cam-type femoroacetabular impingement (Cam FAI).

METHODS

The literature on BDDH with Cam FAI at home and abroad in recent years was extensively reviewed and analyzed.

RESULTS

In patients with BDDH and Cam FAI, the femoral neck anteversion angle and femoral neck shaft angle increase, the pelvis tilts, and the acetabulum rotates, resulting in instability of the hip joint. In order to maintain the stability of the hip joint, the direction of biomechanical action of the hip joint has changed, which further affects the anatomical structures such as the proximal femur and acetabular morphology. BDDH with Cam FAI can be diagnosed clinically by combining lateral center edge angle, anterior center edge angle, and acetabular index. BDDH with Cam FAI can be effectively treated through arthroscopic polishing of the edges of the acetabular proliferative bone, excision of Cam malformations, and minimally invasive repair of the glenoid lip and cartilage of the hip joint.

CONCLUSION

Currently, there is no unified standard for the diagnosis and treatment of BDDH with Cam FAI. Minimally invasive treatment of the hip under arthroscopy can achieve good early- and medium-term effectiveness, and has certain advantages in repairing and maintaining the integrity of the glenoid lip and suturing/compression joint capsule. However, the long-term effectiveness needs to be further followed up to determine. The timing of surgery, intraoperative bone edge depth polishing, and joint capsule suturing/compression techniques also need to be further explored.

T1 pelvic angle is associated with rapid progression of hip arthrosis

PURPOSE

To evaluate the association between global spinal malalignment and rapid progression of hip arthrosis.

METHODS

This was a retrospective, case-control study including 90 patients, contributing 90 hips, who underwent hemi- or total hip arthroplasty at our institution. For analysis, hips were classified into a rapid progression group, defined as ≥ 2 mm destruction of the femoral head or loss of the hip joint space within a 12-month period (n = 30), and a non-rapid progression group, defined by no observable hip disease progression over a period more than 12 months (n = 60). Logistic regression analysis identified factors that predicted rapid progression, with a receiver operating characteristic curve analysis used to confirm factors.

RESULTS

Significant between-group differences were identified for the following parameters: pelvic tilt (P = 0.002, PT), sagittal vertical axis (P = 0.002, SVA), and T1 pelvic angle (P < 0.001, TPA). On multiple logistic regression, PT (P = 0.002), SVA (P = 0.002), and TPA (P < 0.001) were predictive of a rapid progression on hip arthrosis, with the area under the curve being greater for TPA than PT (P = 0.035).

CONCLUSION

Global spinal alignment is associated with rapid progression of hip arthrosis. TPA could assist in identifying patients at risk for rapid progression of hip arthrosis, allowing for time management.

Influence of femoral bowing on stress distribution of the proximal femur: a three-dimensional finite element analysis

BACKGROUND

Whether femoral bowing or its direction has a mechanical effect on the proximal femur is unclear. This study aimed to define the changes in stress distribution in the proximal femur associated with femoral bowing using finite element analysis.

METHODS

We created four femoral models: original, entire lateral bowing, entire anterior bowing, and the middle of both (50% anterolateral bowing) from computed tomography data of women with standard bowing. Each model's stress distribution was compared by two-layering the stress distribution under loading conditions during walking. We also evaluated displacement vectors.

RESULTS

In all directions of femoral bowing, the stress increased in the femoral neck and the femoral trochanter in the 50% anterolateral bowing. The direction of deformation of the vector for the femoral head increased anteroinferiorly in the 50% anterolateral bowing.

CONCLUSIONS

This study showed that the stress distribution at the proximal femur shifted laterally. The high-stress area increased at the femoral neck or trochanter due to increasing femoral bowing. Femoral bowing also increases the anteroinferior vector in the femoral head. This study provides valuable insights into the mechanism of proximal femoral fractures in older adults.

Posterior Pelvic Tilt in the Standing Position Might Be Associated with Collapse Progression in Post-Collapse Stage Osteonecrosis of the Femoral Head

OBJECTIVE

Excessive pelvic tilt has been reported to impair the biomechanical loading of the hip joint. However, the influence of pelvic tilt in osteonecrosis of the femoral head (ONFH) remains unclear. This study aims to assess whether sagittal pelvic posture in the standing position correlates with progression of femoral head collapse in post-collapse stage ONFH.

METHODS

This is a single-center retrospective study. We investigated 107 patients (107 hips; 73 males and 34 females; mean age, 48 years) diagnosed with Association of Research Circulation Osseous (ARCO) stage III ONFH at the first visit and who subsequently underwent surgical treatment in our institution from July 2016 to December 2020. The sagittal pelvic posture in the standing position before surgery was quantified as the angle formed by the anterior pelvic plane and the vertical z-axis in the sagittal view (APP angle). An APP angle <0° indicated posterior pelvic tilt. Progression of femoral head collapse was calculated as collapse speed. The following factors potentially associated with collapse speed were evaluated by exploratory data analysis followed with multiple linear regression analysis: sex, age, BMI, etiology, pelvic incidence, contralateral hip condition, time interval between the first visit and surgery, size of necrotic lesion, location of necrotic lesion, and APP angle.

RESULTS

As ONFH progressed from ARCO stage IIIA to stage IV, APP angle decreased significantly and continuously (stage IIIA, -0.2° ± 5.5°; stage IIIB, -3.7° ± 5.8°; stage IV, -7.1° ± 6.4°). The factors significantly associated with collapse speed were size of necrotic lesion (p = 0.0079), location of necrotic lesion (p = 0.0190), and APP angle (p < 0.0001). APP angle showed a negative correlation with collapse speed (r = -0.40, p < 0.0001). After stratifying by size of necrotic lesion (<50% and ≥50% involvement) and location of necrotic lesion (JIC type C1 and C2), a significant negative correlation was observed between APP angle and collapse speed in each group (JIC type C1 with <50% involvement, r = -0.69, p < 0.0001; JIC type C1 with ≥50% involvement, r = -0.58, p = 0.0475; JIC type C2 with <50% involvement, r = -0.51, p = 0.0124; JIC type C2 with ≥50% involvement, r = -0.39, p = 0.0286).

CONCLUSIONS

Our results suggest that posterior pelvic tilt in the standing position occurred as ONFH progressed from ARCO stage IIIA to stage IV, which might be associated with progression of femoral head collapse in ONFH.

Factors Associated With Abnormal Joint Contact Pressure After Periacetabular Osteotomy: A Finite-Element Analysis

BACKGROUND

Identifying factors associated with poor hip contact mechanics after periacetabular osteotomy (PAO) may help surgeons optimize acetabular corrections in individual patients. We performed individual-specific finite-element analyses to identify preoperative morphological and surgical correction factors for abnormal contact pressure (CP) after PAO.

METHODS

We performed finite-element analyses before and after PAO with reference to the standing pelvic position on individual-specific 3-dimensional hip models created from computed tomography images of 51 dysplastic hips. Nonlinear contact analyses were performed to calculate the joint CP of the acetabular cartilage during a single-leg stance.

RESULTS

The maximum CP decreased in 50 hips (98.0%) after PAO compared to preoperative values, and the resulting maximum CP was within the normal range (<4.1 MPa) in 33 hips (64.7%). Multivariate analysis identified the roundness index of the femoral head (P = .002), postoperative anterior center-edge angle (CEA; P = .004), and surgical correction of lateral CEA (Δlateral CEA; P = .003) as independent predictors for abnormal CP after PAO. A preoperative roundness index >54.3°, a postoperative anterior CEA <36.3°, and a Δlateral CEA >27.0° in the standing pelvic position predicted abnormal CP after PAO.

CONCLUSION

PAO normalized joint CP in 64.7% of the patients but was less likely to normalize joint CP in patients with aspheric femoral heads. Successful surgical treatment depends on obtaining adequate anterior coverage and avoiding excessive lateral correction, while considering the physiological pelvic tilt in a weight-bearing position.

Changes in hip joint contact stress during a gait cycle based on the individualized modeling method of "gait-musculoskeletal system-finite element"

OBJECTIVE

To construct a comprehensive simulation method of "gait-musculoskeletal system (MS)-finite element (FE)" for analysis of hip joint dynamics characteristics and the changes in the contact stress in the hip throughout a gait cycle.

METHODS

Two healthy volunteers (male and female) were recruited. The 3D gait trajectories during normal walking and the CT images including the hip and femur of the volunteers were obtained. CT imaging data in the DICOM format were extracted for subjected 3D hip joint reconstruction. The reconstructed 3D model files were used to realize the subject-specific registration of the pelvis and thigh segment of general musculoskeletal model. The captured marker trajectory data were used to drive subject-specific musculoskeletal model to complete inverse dynamic analysis. Results of inverse dynamic analysis were exported and applied as boundary and load settings of the hip joint finite element in ABAQUS. Finally, the finite element analysis (FEA) was performed to analyze contact stress of hip joint during a gait cycle of left foot.

RESULTS

In the inverse dynamic analysis, the dynamic changes of the main hip-femoral muscle force with respect to each phase of a single gait cycle were plotted. The hip joint reaction force reached a maximum value of 2.9%BW (body weight) and appeared at the end of the terminal stance phase. Twin peaks appeared at the initial contact phase and the end of the terminal stance phase, respectively. FEA showed the temporal changes in contact stress in the acetabulum. In the visual stress cloud chart, the acetabular contact stress was mainly distributed in the dome of the acetabulum and in the anterolateral area at the top of the femoral head during a single gait cycle. The acetabular contact area was between 293.8 and 998.4 mm², and the maximum contact area appear at the mid-stance phase or the loading response phase of gait. The maximum contact stress of the acetabulum reached 6.91 MPa for the model 1 and 6.92 MPa for the model 2 at the terminal stance phase.

CONCLUSIONS

The "Gait-MS-FE" technology is integrated to construct a comprehensive simulation framework. Based on human gait trajectories and their CT images, individualized simulation modeling can be achieved. Subject-specific gait in combination with an inverse dynamic analysis of the MS provides pre-processing parameters for FE simulation for more accurate biomechanical analysis of hip joint.

Lumbar Fusion including Sacroiliac Joint Fixation Increases the Stress and Angular Motion at the Hip Joint: A Finite Element Study

Introduction

Adult spinal fusion surgery improves lumbar alignment and patient satisfaction. Adult spinal deformity surgery improves saggital balance not only lumbar lesion, but also at hip joint coverage. It was expected that hip joint coverage rate was improved and joint stress decreased. However, it was reported that adjacent joint disease at hip joint was induced by adult spinal fusion surgery including sacroiliac joint fixation on an X-ray study. The mechanism is still unclear. We aimed to investigate the association between lumbosacral fusion including sacroiliac joint fixation and contact stress of the hip joint.

Methods

A 40-year-old woman with intact lumbar vertebrae underwent computed tomography. A three-dimensional nonlinear finite element model was constructed from the L4 vertebra to the femoral bone with triangular shell elements (thickness, 2 mm; size, 3 mm) for the cortical bone's outer surface and 2-mm (lumbar spine) or 3-mm (femoral bone) tetrahedral solid elements for the remaining bone. We constructed the following four models: a non-fusion model (NF), a L4-5 fusion model (L5F), a L4-S1 fusion model (S1F), and a L4-S2 alar iliac screw fixation model (S2F). A compressive load of 400 N was applied vertically to the L4 vertebra and a 10-Nm bending moment was additionally applied to the L4 vertebra to stimulate flexion, extension, left lateral bending, and axial rotation. Each model's hip joint's von Mises stress and angular motion were analyzed.

Results

The hip joint's angular motion in NF, L5F, S1F, and S2F gradually increased; the S2F model presented the greatest angular motion.

Conclusions

The average and maximum contact stress of the hip joint was the highest in the S2F model. Thus, lumbosacral fusion surgery with sacroiliac joint fixation placed added stress on the hip joint. We propose that this was a consequence of adjacent joint spinopelvic fixation. Lumbar-to-pelvic fixation increases the angular motion and stress at the hip joint.

Effect of coronal plane acetabular correction on joint contact pressure in Periacetabular osteotomy: a finite-element analysis

Background

The ideal acetabular position for optimizing hip joint biomechanics in periacetabular osteotomy (PAO) remains unclear. We aimed to determine the relationship between acetabular correction in the coronal plane and joint contact pressure (CP) and identify morphological factors associated with residual abnormal CP after correction.

Methods

Using CT images from 44 patients with hip dysplasia, we performed three patterns of virtual PAOs on patient-specific 3D hip models; the acetabulum was rotated laterally to the lateral center-edge angles (LCEA) of 30°, 35°, and 40°. Finite-element analysis was used to calculate the CP of the acetabular cartilage during a single-leg stance.

Results

Coronal correction to the LCEA of 30° decreased the median maximum CP 0.5-fold compared to preoperatively (p <  0.001). Additional correction to the LCEA of 40° further decreased CP in 15 hips (34%) but conversely increased CP in 29 hips (66%). The increase in CP was associated with greater preoperative extrusion index (p = 0.030) and roundness index (p = 0.038). Overall, virtual PAO failed to normalize CP in 11 hips (25%), and a small anterior wall index (p = 0.049) and a large roundness index (p = 0.003) were associated with residual abnormal CP.

Conclusions

The degree of acetabular correction in the coronal plane where CP is minimized varied among patients. Coronal plane correction alone failed to normalize CP in 25% of patients in this study. In patients with an anterior acetabular deficiency (anterior wall index < 0.21) and an aspherical femoral head (roundness index > 53.2%), coronal plane correction alone may not normalize CP. Further studies are needed to clarify the effectiveness of multiplanar correction, including in the sagittal and axial planes, in optimizing the hip joint’s contact mechanics.

Is Anterior Rotation of the Acetabulum Necessary to Normalize Joint Contact Pressure in Periacetabular Osteotomy? A Finite-element Analysis Study

BACKGROUND

Inappropriate sagittal plane correction can result in an increased risk of osteoarthritis progression after periacetabular osteotomy (PAO). Individual and postural variations in sagittal pelvic tilt, along with acetabular deformity, affect joint contact mechanics in dysplastic hips and may impact the direction and degree of acetabular correction. Finite-element analyses that account for physiologic pelvic tilt may provide valuable insight into the effect of PAO on the contact mechanics of dysplastic hips, which may lead to improved acetabular correction during PAO.

QUESTIONS/PURPOSES

We performed virtual PAO using finite-element models with reference to the standing pelvic position to clarify (1) whether lateral rotation of the acetabulum normalizes the joint contact pressure, (2) risk factors for abnormal contact pressure after lateral rotation of the acetabulum, and (3) whether additional anterior rotation of the acetabulum further reduces contact pressure.

METHODS

Between 2016 and 2020, 85 patients (92 hips) underwent PAO to treat hip dysplasia. Eighty-two patients with hip dysplasia (lateral center-edge angle < 20°) were included. Patients with advanced osteoarthritis, femoral head deformity, prior hip or spine surgery, or poor-quality images were excluded. Thirty-eight patients (38 hips) were eligible to participate in this study. All patients were women, with a mean age of 39 ± 10 years. Thirty-three women volunteers without a history of hip disease were reviewed as control participants. Individuals with a lateral center-edge angle < 25° or poor-quality images were excluded. Sixteen individuals (16 hips) with a mean age of 36 ± 7 years were eligible as controls. Using CT images, we developed patient-specific three-dimensional surface hip models with the standing pelvic position as a reference. The loading scenario was based on single-leg stance. Four patterns of virtual PAO were performed in the models. First, the acetabular fragment was rotated laterally in the coronal plane so that the lateral center-edge angle was 30°; then, anterior rotation in the sagittal plane was added by 0°, 5°, 10°, and 15°. We developed finite-element models for each acetabular position and performed a nonlinear contact analysis to calculate the joint contact pressure of the acetabular cartilage. The normal range of the maximum joint contact pressure was calculated to be < 4.1 MPa using a receiver operating characteristic curve. A paired t-test or Wilcoxon signed rank test with Bonferroni correction was used to compare joint contact pressures among acetabular positions. We evaluated the association of joint contact pressure with the patient-specific sagittal pelvic tilt and acetabular version and coverage using Pearson or Spearman correlation coefficients. An exploratory univariate logistic regression analysis was performed to identify which of the preoperative factors (CT measurement parameters and sagittal pelvic tilt) were associated with abnormal contact pressure after lateral rotation of the acetabulum. Variables with p values < 0.05 (anterior center-edge angle and sagittal pelvic tilt) were included in a multivariable model to identify the independent influence of each factor.

RESULTS

Lateral rotation of the acetabulum decreased the median maximum contact pressure compared with that before virtual PAO (3.7 MPa [range 2.2-6.7] versus 7.2 MPa [range 4.1-14 MPa], difference of medians 3.5 MPa; p < 0.001). The resulting maximum contact pressures were within the normal range (< 4.1 MPa) in 63% of the hips (24 of 38 hips). The maximum contact pressure after lateral acetabular rotation was negatively correlated with the standing pelvic tilt (anterior pelvic plane angle) (ρ = -0.52; p < 0.001) and anterior center-edge angle (ρ = -0.47; p = 0.003). After controlling for confounding variables such as the lateral center-edge angle and sagittal pelvic tilt, we found that a decreased preoperative anterior center-edge angle (per 1°; odds ratio 1.14 [95% CI 1.01-1.28]; p = 0.01) was independently associated with elevated contact pressure (≥ 4.1 MPa) after lateral rotation; a preoperative anterior center-edge angle < 32° in the standing pelvic position was associated with elevated contact pressure (sensitivity 57%, specificity 96%, area under the curve 0.77). Additional anterior rotation further decreased the joint contact pressure; the maximum contact pressures were within the normal range in 74% (28 of 38 hips), 76% (29 of 38 hips), and 84% (32 of 38 hips) of the hips when the acetabulum was rotated anteriorly by 5°, 10°, and 15°, respectively.

CONCLUSION

Via virtual PAO, normal joint contact pressure was achieved in 63% of patients by normalizing the lateral acetabular coverage. However, lateral acetabular rotation was insufficient to normalize the joint contact pressure in patients with more posteriorly tilted pelvises and anterior acetabular deficiency. In patients with a preoperative anterior center-edge angle < 32° in the standing pelvic position, additional anterior rotation is expected to be a useful guide to normalize the joint contact pressure.

CLINICAL RELEVANCE

This virtual PAO study suggests that biomechanics-based planning for PAO should incorporate not only the morphology of the hip but also the physiologic pelvic tilt in the weightbearing position in order to customize acetabular reorientation for each patient.

Association between global sagittal malalignment and increasing hip joint contact force, analyzed by a novel musculoskeletal modeling system

Patients with adult spinal deformity have various standing postures. Although several studies have reported a relationship between sagittal alignment and exacerbation of hip osteoarthritis, information is limited regarding how spinopelvic sagittal alignment changes affect hip joint loading. This study aimed to investigate the relationship between sagittal spinopelvic-lower limb alignment and the hip joint contact force (HCF) using a novel musculoskeletal model. We enrolled 20 women (78.3±6.7 years) from a single institution. Standing lateral radiographs were acquired to measure thoracic kyphosis, lumbar lordosis, the pelvic tilt, sacral slope, sagittal vertical axis (SVA), femur obliquity angle, and knee flexion angle. In the model simulation, the Anybody Modeling System was used, which alters muscle pathways using magnetic resonance imaging data. Each patient’s alignment was entered into the model; the HCF and hip moment in the standing posture were calculated using inverse dynamics analysis. The relationship between the HCF and each parameter was examined using Spearman’s correlation coefficient (r). The patients were divided into low SVA and high SVA groups, with a cutoff value of 50 mm for the SVA. The HCF was 168.2±60.1 N (%BW) and positively correlated with the SVA (r = 0.6343, p<0.01) and femur obliquity angle (r = 0.4670, p = 0.03). The HCF were 122.2 and 214.1 N (75.2% difference) in the low SVA and high SVA groups, respectively (p<0.01). The flexion moment was also increased in the high SVA group compared with that in the low SVA group (p = 0.03). The SVA and femur obliquity angle are factors related to the HCF, suggesting an association between adult spinal deformity and the exacerbation of hip osteoarthritis. Future studies will need to assess the relationship between the hip joint load and sagittal spinopelvic parameters in dynamic conditions.

Does Patient-specific Functional Pelvic Tilt Affect Joint Contact Pressure in Hip Dysplasia? A Finite-element Analysis Study

BACKGROUND

Although individual and postural variations in the physiologic pelvic tilt affect the acetabular orientation and coverage in patients with hip dysplasia, their effect on the mechanical environment in the hip has not been fully understood. Individual-specific, finite-element analyses that account for physiologic pelvic tilt may provide valuable insight into the contact mechanics of dysplastic hips, which can lead to further understanding of the pathogenesis and improved treatment of this patient population.

QUESTION/PURPOSE

We used finite-element analysis to ask whether there are differences between patients with hip dysplasia and patients without dysplasia in terms of (1) physiologic pelvic tilt, (2) the pelvic position and joint contact pressure, and (3) the morphologic factors associated with joint contact pressure.

METHODS

Between 2016 and 2019, 82 patients underwent pelvic osteotomy to treat hip dysplasia. Seventy patients with hip dysplasia (lateral center-edge angle ≥ 0° and < 20° on supine AP pelvic radiographs) were included. Patients with advanced osteoarthritis, femoral head deformity, prior hip or supine surgery, or poor-quality imaging were excluded. Thirty-two patients (32 hips) were eligible to this finite-element analysis study. For control groups, we reviewed 33 female volunteers without a history of hip disease. Individuals with frank or borderline hip dysplasia (lateral center-edge angle < 25°) or poor-quality imaging were excluded. Sixteen individuals (16 hips) were eligible as controls. Two board-certified orthopaedic surgeons measured sagittal pelvic tilt (the angle between the anterior pelvic plane and vertical axis: anterior pelvic plane [APP] angle) and acetabular version and coverage using pelvic radiographs and CT images. Intra- and interobserver reliabilities, evaluated using the kappa value and intraclass correlation coefficient, were good or excellent. We developed individual-specific, finite-element models using pelvic CT images, and performed nonlinear contact analysis to calculate the joint contact pressure on the acetabular cartilage during the single-leg stance with respect to three pelvic positions: standardized (anterior pelvic plane), supine, and standing. We compared physiologic pelvic tilt between patients with and without dysplasia using a t-test or the Wilcoxon rank sum test. A paired t-test or the Wilcoxon signed rank test with a Bonferroni correction was used to compare joint contact pressure between the three pelvic positions. We correlated joint contact pressure with morphologic parameters and pelvic tilt using the Pearson or the Spearman correlation coefficients.

RESULTS

The APP angle in the supine and standing positions varied widely among individuals. It was greater in patients with hip dysplasia than in patients in the control group when in the standing position (3° ± 6° versus -2° ± 8°; mean difference 5° [95% CI 1° to 9°]; p = 0.02) but did not differ between the two groups when supine (8° ± 5° versus 5° ± 7°; mean difference 3° [95% CI 0° to 7°]; p = 0.06). The mean pelvic tilt was 6° ± 5° posteriorly when shifting from the supine to the standing position in patients with hip dysplasia. The median (range) maximum contact pressure was higher in dysplastic hips than in control individuals (in standing position; 7.3 megapascals [MPa] [4.1 to 14] versus 3.5 MPa [2.2 to 4.4]; difference of medians 3.8 MPa; p < 0.001). The median maximum contact pressure in the standing pelvic position was greater than that in the supine position in patients with hip dysplasia (7.3 MPa [4.1to 14] versus 5.8 MPa [3.5 to 12]; difference of medians 1.5 MPa; p < 0.001). Although the median maximum joint contact pressure in the standardized pelvic position did not differ from that in the standing position (7.4 MPa [4.3 to 15] versus 7.3 MPa [4.1 to 14]; difference of medians -0.1 MPa; p > 0.99), the difference in the maximum contact pressure varied from -3.3 MPa to 2.9 MPa, reflecting the wide range of APP angles (mean 3° ± 6° [-11° to 14°]) when standing. The maximum joint contact pressure in the standing position was negatively correlated with the standing APP angle (r = -0.46; p = 0.008) in patients with hip dysplasia.

CONCLUSION

Based on our findings that individual and postural variations in the physiologic pelvic tilt affect joint contact pressure in the hip, future studies on the pathogenesis of hip dysplasia and joint preservation surgery should not only include the supine or standard pelvic position, but also they need to incorporate the effect of the patient-specific pelvic tilt in the standing position on the biomechanical environment of the hip.

CLINICAL RELEVANCE

We recommend assessing postural change in sagittal pelvic tilt when diagnosing hip dysplasia and planning preservation hip surgery because assessment in a supine or standard pelvic position may overlook alterations in the hip's contact mechanics in the weightbearing positions. Further studies are needed to elucidate the effect of patient-specific functional pelvic tilt on the degeneration process of dysplastic hips, the acetabular reorientation maneuver, and the clinical result of joint preservation surgery.

Preoperative Rather Than Postoperative Intra-Articular Cartilage Degeneration Affects Long-Term Survivorship of Periacetabular Osteotomy

PURPOSE

To determine whether intra-articular lesions changed in short-term follow-up after periacetabular osteotomy (PAO) and whether the intra-articular lesion changes impacted the long-term survivorship of PAO.

METHODS

We reviewed patients with hip dysplasia who underwent PAO with arthroscopic observation between 1990 and 2001. Patients who underwent second-look arthroscopy were included. The correlations between the intra-articular lesion changes and the long-term outcome of PAO were analyzed for patients with >10 years of follow-up. The possible risk factors included demographic factors (age, sex, and body mass index), radiographic factors (Tönnis grade, lateral center-edge angle, Tönnis angle, acetabular head index, crossover sign, posterior wall sign, and joint congruity), and arthroscopic findings (full-thickness lesions at the time of PAO and lesions changes at the time of second-look arthroscopy).

RESULTS

A total of 64 patients (72 hips) were studied. Second-look arthroscopy was performed at a median of 1.4 years after PAO. Intra-articular lesions were observed in 93% in the acetabulum, 81% in the femoral head, and 97% in the labrum, respectively. These lesions unchanged in 74% in the acetabulum, 76% in the femoral head, and 79% in the labrum, respectively. Cartilage repair was observed in the acetabulum and the femoral head in 24% and 17% of hips, respectively. Labral repair occurred in 10%. Intra-articular lesion changes were not a predictor of failure. Multivariate analysis identified International Cartilage Repair Society grade 4 lesion in the femoral head as an independent risk factor for failure.

CONCLUSIONS

Our results suggest that PAO prevents further deterioration in mild cartilage lesions and results in cartilage repair in some cases with advanced cartilage degenerations in the short term. However, these postoperative changes were not associated with long-term survivorship. Thus, appropriate surgical indications based on the preoperative intra-articular cartilage degeneration is paramount to achieving long-term success in PAO.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Automated segmentation of an intensity calibration phantom in clinical CT images using a convolutional neural network

PURPOSE

In quantitative computed tomography (CT), manual selection of the intensity calibration phantom's region of interest is necessary for calculating density (mg/cm³) from the radiodensity values (Hounsfield units: HU). However, as this manual process requires effort and time, the purposes of this study were to develop a system that applies a convolutional neural network (CNN) to automatically segment intensity calibration phantom regions in CT images and to test the system in a large cohort to evaluate its robustness.

METHODS

This cross-sectional, retrospective study included 1040 cases (520 each from two institutions) in which an intensity calibration phantom (B-MAS200, Kyoto Kagaku, Kyoto, Japan) was used. A training dataset was created by manually segmenting the phantom regions for 40 cases (20 cases for each institution). The CNN model's segmentation accuracy was assessed with the Dice coefficient, and the average symmetric surface distance was assessed through fourfold cross-validation. Further, absolute difference of HU was compared between manually and automatically segmented regions. The system was tested on the remaining 1000 cases. For each institution, linear regression was applied to calculate the correlation coefficients between HU and phantom density.

RESULTS

The source code and the model used for phantom segmentation can be accessed at https://github.com/keisuke-uemura/CT-Intensity-Calibration-Phantom-Segmentation . The median Dice coefficient was 0.977, and the median average symmetric surface distance was 0.116 mm. The median absolute difference of the segmented regions between manual and automated segmentation was 0.114 HU. For the test cases, the median correlation coefficients were 0.9998 and 0.999 for the two institutions, with a minimum value of 0.9863.

CONCLUSION

The proposed CNN model successfully segmented the calibration phantom regions in CT images with excellent accuracy.