The biomechanical disadvantage of dysplastic hips

The Amputated Limb Gluteus Medius is Biomechanically Disadvantaged in Patients with Unilateral Transfemoral Amputation

Patients with transfemoral amputation (TFA) are at an increased risk of secondary musculoskeleteal comorbidities, primarily due to asymmetric joint loading. Amputated limb muscle weakness is also prevalent in the TFA population, yet all factors that contribute to muscle strength and thus joint loading are not well understood. Our objective was to bilaterally compare gluteus medius (GMED) muscle factors (volume, fatty infiltration, moment arm) that all contribute to joint loading in patients with TFA. Quantitative magnetic resonance (MR) images of the hip were collected from eight participants with unilateral TFA (2M/6F; age: 47.3 ± 14.7 y/o; BMI: 25.4 ± 5.3 kg/m2; time since amputation: 20.6 ± 15.0 years) and used to calculate normalized GMED muscle volume and fatty infiltration. Six participants participated in an instrumented gait analysis session that collected whole-body kinematics during overground walking. Subject-specific musculoskeletal models were used to calculate bilateral GMED (anterior, middle, posterior) moment arms and frontal plane hip joint angles across three gait cycles. Differences in volume, fatty infiltration, hip adduction-abduction angle, and peak moment arms were compared between limbs using paired Cohen's d effect sizes. Volume was smaller by 36.3 ± 18.8% (d = 1.7) and fatty infiltration was greater by 6.4 ± 7.8% (d = 0.8) in the amputated limb GMED compared to the intact limb. The amputated limb GMED abduction moment arms were smaller compared to the intact limb for both overground walking (anterior: d = 0.9; middle: d = 0.1.2) and during normal range of motion (anterior: d = 0.8; middle: d = 0.8) while bilateral hip adduction-abduction angles were similar during overground walking (d = 0.5). These results indicate that in patients with TFA, the amputated limb GMED is biomechanically disadvantaged compared to the intact limb, which may contribute to the etiology of secondary comorbidities. This population might benefit from movement retraining to lengthen the amputated limb GMED abduction moment arm during gait.

Pediatric Hip Dysplasia Surgery Outcomes by Pediatric Versus Nonpediatric Orthopedists

Objectives Developmental dysplasia of the hip (DDH) encompasses a spectrum of abnormalities in the immature hip. Surgical intervention is indicated if conservative management fails. Despite the increased supply of pediatric orthopedic surgeons (POSs) over the last few decades, there continues to be a maldistribution of surgeons. The purpose of this study is to determine outcomes following surgical management of hip dysplasia by POSs compared to non-pediatric orthopedic surgeons. Methods Pediatric patients who underwent surgical treatment for hip dysplasia from 2012 to 2019 were identified using a large national database. Patient demographics, comorbidities, and postoperative complications were compared by pediatric versus nonpediatric-trained orthopedic surgeons. Bivariate and multivariable regression analyses were performed. Results Of the 10,780 pediatric patients who underwent hip dysplasia surgery, 10,206 patients (94.7%) were operated on by a POS, whereas 574 (5.3%) were operated on by a non-pediatric orthopedic surgeon. POSs were more likely to operate on patients with a higher American Society of Anesthesiologists class (p<0.001) and those with a greater number of medical comorbidities, including cardiac (p=0.001), gastrointestinal (p=0.017), and neurological (p<0.001). Following analysis using multivariable regression models to control for patient baseline characteristics, there were no differences in any postoperative complications between patients treated by pediatric-trained and nonpediatric-trained orthopedic surgeons. Conclusions Compared to non-pediatric orthopedic surgeons, POSs were more likely to operate on younger patients with increased medical comorbidities. However, there were no differences in postoperative complications following surgical management for DDH in patients treated by nonpediatric and pediatric orthopedic surgeons.

Femoral neck shortening as a sequela of internal fixation for femoral neck fractures and its effect on the coronal alignment of the limb: a pilot study

INTRODUCTION

Femoral neck shortening is a common phenomenon following osteosynthesis for femoral neck fractures, which was shown to have a negative effect on hip function. There is paucity of literature on the effect of shortening on the ipsilateral limb mechanical axis and knee coronal alignment. We hypothesized that postoperative femoral neck shortening can alter the limb's mechanical axis into valgus.

METHODS

Of 583 patients screened, 13 patients with severe neck shortening (< 10 mm) following femoral neck fracture fixation, were found eligible and agreed to participate. A full-length lower limb radiographs were obtained and radiographic parameters (offset, neck-shaft angle, HKA, mLPFA, mDLFA, mMPTFA, MAD, MAD-r) as well as functional scores were obtained.

RESULTS

Statistically significant differences in mechanical axis deviation ratio (MAD-r) were found between the ipsilateral and the contralateral extremities (0.41 ± 0.16 versus 0.55 ± 0.11, p = 0.03). A correlation between femoral neck length differences and MAD was not statistically significant although a tendency towards lateral deviation of the mechanical axis was noted (r = - 0.5, p = 0.077). A negative correlation was found between a greater difference in the femoral neck length and the SF12 score, both in the physical and the mental parts (r = - 0.69, p = 0.008; r = - 0.58, p = 0.035, respectively).

CONCLUSION

We found a more lateralized mechanical axis in limbs that demonstrated post-operative ipsilateral femoral neck severe shortening. These findings may provide a possible explanation and rationale for knee pain and perhaps for the development of knee osteoarthritis as a sequalae of femoral neck shortening. Further investigation and larger cohort, long-term studies are needed to further explore this hypothesis.

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.

Are Abnormal Muscle Biomechanics and Patient-reported Outcomes Associated in Patients With Hip Dysplasia?

BACKGROUND

Developmental dysplasia of the hip (DDH) is a major risk factor for the early development of hip osteoarthritis. Recent studies have demonstrated how DDH alters hip muscle moment arms and elevates muscle-induced biomechanical variables such as joint reaction forces and acetabular edge loads. Understanding the link between abnormal biomechanics and patient-reported outcome measures (PROMs) is important for evidence-based clinical interventions that improve patient symptoms and functional outcomes. To our knowledge, there are no reports of the relationships between muscle-induced biomechanics and PROMs.

QUESTIONS/PURPOSES

(1) Are there associations between PROMs and muscle-induced hip biomechanics during gait for patients with DDH and controls? (2) Are there associations among PROMs and separately among biomechanical variables?

METHODS

Participants in this prospective cross-sectional comparative study included 20 female patients with DDH who had no prior surgery or osteoarthritis and 15 female individuals with no evidence of hip pathology (controls) (age: median 23 years [range 16 to 39 years]; BMI: median 22 kg/m 2 [range 17 to 27 kg/m 2 ]). Muscle-induced biomechanical variables for this cohort were reported and had been calculated from patient-specific musculoskeletal models, motion data, and MRI. Biomechanical variables included joint reaction forces, acetabular edge loads, hip center lateralization, and gluteus medius muscle moment arm lengths. PROMs included the Hip Disability and Osteoarthritis Outcome Score (HOOS), the WOMAC, International Hip Outcome Tool-12, National Institutes of Health Patient-Reported Outcome Measure Information System (PROMIS) Pain Interference and Physical Function subscales, and University of California Los Angeles activity scale. Associations between PROMs and biomechanical variables were tested using Spearman rank-order correlations and corrected for multiple comparisons using the Benjamini-Yekutieli method. For this study, associations between variables were considered to exist when correlations were statistically significant (p < 0.05) and were either strong (ρ ≥ 0.60) or moderate (ρ = 0.40 to 0.59).

RESULTS

Acetabular edge load impulses (the cumulative acetabular edge load across the gait cycle), medially directed joint reaction forces, and hip center lateralization most commonly demonstrated moderate or strong associations with PROMs. The strongest associations were a negative correlation between acetabular edge load impulse on the superior acetabulum and the HOOS function in daily living subscale (ρ = -0.63; p = 0.001), followed by a negative correlation between hip center lateralization and the HOOS pain subscale (ρ = -0.6; p = 0.003), and a positive correlation between hip center lateralization and the PROMIS pain subscale (ρ = 0.62; p = 0.002). The University of California Los Angeles activity scale was the only PROM that did not demonstrate associations with any biomechanical variable. All PROMs, aside from the University of California Los Angeles activity scale, were associated with one another. Although most of the biomechanical variables were associated with one another, these relationships were not as consistent as those among PROMs.

CONCLUSION

The associations with PROMs detected in the current study suggest that muscle-induced biomechanics may have wide-reaching effects not only on loads within the hip, but also on patients' perceptions of their health and function. As the treatment of DDH evolves, patient-specific joint preservation strategies may benefit from targeting the underlying causes of biomechanical outcomes associated with PROMs.

LEVEL OF EVIDENCE

Level III, prognostic study.

Derotational femoral osteotomy locations and their influence on joint reaction forces in dysplastic hips

Femoral version (FV) deformities are common in patients with developmental dysplasia of the hip (DDH) and may contribute to cartilage damage due to abnormal joint loading. Derotational femoral osteotomy (DFO) surgery corrects FV deformities. However there is little consensus about the femoral transection location for DFO, and its influence on joint loads is unknown. The purpose of this study was to compare the effects of two common DFO locations on muscle forces and hip joint reaction forces (JRFs) in patients with DDH. DFO was simulated in nine patients with DDH and abnormal FV using patient-specific musculoskeletal models. Femoral transection for DFO was separately simulated proximal and distal to the lesser trochanter and FV values were corrected to an idealized 15°. JRFs during early and late stance of gait were compared between the two simulated transection locations. Most changes to JRFs were similar between proximal and distal DFO, however, statistically significant differences were found for the medial JRF component during late stance among patients with femoral anteversion (p = 0.01). Force changes from five hip muscles were significantly different between DFO locations, however, changes were minimal. Most changes after DFO in patients with femoral retroversion were opposite of those with femoral anteversion, with anteroposterior and superior JRFs increasing after retroversion correction. After DFO correction, superior and medial JRFs in DDH patients remained elevated compared to controls. Understanding the influence of DFO location on muscle-generated hip forces can help surgeons justify decisions and potentially standardize surgical correction of FV deformities in patients with DDH.

Arthritis Foundation/HSS Workshop on Hip Osteoarthritis, Part 2: Detecting Hips at Risk: Early Biomechanical and Structural Mechanisms

Far more publications are available for osteoarthritis of the knee than of the hip. Recognizing this research gap, the Arthritis Foundation (AF), in partnership with the Hospital for Special Surgery (HSS), convened an in-person meeting of thought leaders to review the state of the science of and clinical approaches to hip osteoarthritis. This article summarizes the recommendations gleaned from 5 presentations given in the "early hip osteoarthritis" session of the 2023 Hip Osteoarthritis Clinical Studies Conference, which took place on February 17 and 18, 2023, in New York City. It also summarizes the workgroup recommendations from a small-group discussion on clinical research gaps.

Relationships between self-perceived and clinical expression of pain and function differ based on the underlying pathology of the human hip

BACKGROUND

Patient-reported outcomes are commonly used to assess patient symptoms. The effect of specific hip pathology on relationships between perceived and objectively measured symptoms remains unclear. The purpose of this study was to evaluate differences of function and pain in patients with FAIS and DDH, to assess the correlation between perceived and objective function, and to determine the influence of pain on measures of function.

METHODS

This prospective cross-sectional study included 35 pre-operative patients (60% female) with femoroacetabular impingement syndrome (FAIS) and 37 pre-operative patients (92% female) with developmental dysplasia of the hip (DDH). Objectively measured function (6-min walk [6MWT], single leg hop [SLHT], Biodex sway [BST], hip abduction strength [HABST], and STAR excursion balance reach [STAR] tests), patient-reported function (UCLA Activity, Hip Outcome Score [HOS], Short Form 12 [SF-12], and Hip Disability and Osteoarthritis Outcome Score [HOOS]), and patient-reported pain (HOOS Pain, visual analogue scale (VAS), and a pain location scale) were collected during a pre-surgical clinic visit. Between-group comparisons of patient scores were performed using Wilcoxon Rank-Sum tests. Within-group correlations were analyzed using Spearman's rank correlation coefficients. Statistical correlation strength was defined as low (r =  ± 0.1-0.3), moderate (r =  ± 0.3-0.5) and strong (r >  ± 0.5).

RESULTS

Patients with DDH reported greater pain and lower function compared to patients with FAIS. 6MWT distance was moderately-to-strongly correlated with a number of patient-reported measures of function (FAIS: r = 0.37 to 0.62, DDH: r = 0.36 to 0.55). Additionally, in patients with DDH, SLHT distance was well correlated with patient reported function (r = 0.37 to 0.60). Correlations between patient-reported pain and objectively measured function were sparse in both patient groups. In patients with FAIS, only 6MWT distance and HOOS Pain (r = -0.53) were significantly correlated. In patients with DDH, 6MWT distance was significantly correlated with VAS Average (r = -0.52) and Best (r = -0.53) pain.

CONCLUSION

Pain is greater and function is lower in patients with DDH compared to patients with FAIS. Moreover, the relationship between pain and function differs between patient groups. Understanding these differences is valuable for informing treatment decisions. We recommend these insights be incorporated within the clinical continuum of care, particularly during evaluation and selection of surgical and therapeutic interventions.

Greater hip abductor size in prearthritic patients with developmental dysplasia of the hip versus femoroacetabular impingement

Developmental dysplasia of the hip (DDH) and femoroacetabular impingement (FAI) are common hip pathologies and important risk factors for osteoarthritis, yet the disease mechanisms differ. DDH involves deficient femoral head coverage and a shortened abductor moment arm, so this study hypothesized that the cross-sectional area (CSA) of the gluteus medius/minimus muscle complex and the stabilizing iliocapsularis muscle would be larger in DDH versus FAI, without increased fatty infiltration. A longitudinal cohort identified prearthritic patients with DDH or FAI who underwent imaging before surgery. Patients with DDH and FAI (Cam, Pincer, or Mixed) were 1:1 matched based on age, sex, and body mass index. Magnetic resonance imaging was used to measure the gluteus medius/minimus complex and iliocapsularis in two transverse planes. Amira software was used to quantify muscle and noncontractile tissue. Paired samples t-tests were performed to compare muscle size and composition (p < 0.05). There were no differences in the iliocapsularis muscle. Patients with DDH had significantly larger CSA of the gluteus medius/minimus complex at both transverse planes, and the noncontractile tissue proportion did not differ. The mean difference in overall muscle CSA at the anterior inferior iliac spine was 4.07 ± 7.4 cm² (p = 0.005), with an average difference of 12.1%, and at the femoral head this was 2.40 ± 4.37 cm² (p = 0.004), with an average difference of 20.2%. This study reports a larger CSA of the gluteus medius/minimus muscle complex in DDH compared to FAI, without a difference in noncontractile tissue, indicating increased healthy muscle in DDH.

Above knee socket prosthesis use changes proximal femur morphology

Patients with transfemoral amputation (TFA) are up to six times more likely to develop hip osteoarthritis (OA) in either or both the intact and residual limb, which is primarily attributed to habitually altered joint loading due to compensatory movement patterns. However, joint loading patterns differ between limbs, which confounds the understanding of loading-induced OA etiology across limbs. It remains unknown if altered loading due to amputation results in bony shape changes at the hip, which is a known etiological factor in the development of hip OA. Retrospective computed tomography images were collected of the residual limb for 31 patients with unilateral TFA (13F/18M; age: 51.7 ± 9.9 y/o; time since amputation: 13.7 ± 12.4 years) and proximal femur for a control group of 29 patients (13F/16M; age: 42.0 ± 12.27 years) and used to create 3D geometries of the proximal femur. Femoral 3D geometric variation was quantified using statistical shape modeling (SSM), a computational tool which placed 2048 corresponding particles on each geometry. Independent modes of variation were created using principal component analysis. 2D radiographic measures of the proximal femur, including common measures such as α-angle, head neck offset, and neck shaft angle, were quantified on digitally reconstructed radiographs (DRRs). SSM results were then compared to 2D measures using Pearson correlation coefficients (r). Two-sample t-tests were used to determine if there were significant differences between the TFA and control group means of 2D radiographic measurements (p < 0.05). Patients with TFA had greater femoral head asphericity within the SSM, which was moderately correlated to head-neck offset (r = -0.54) and α-angle (r = 0.63), as well as greater trochanteric torsion, which was strongly correlated to the novel radiographic measure of trochanteric torsion (r = -0.78), compared to controls. For 2D measures, the neck-shaft angle was smaller in the TFA group compared to the control group (p = 0.01) while greater trochanter height was larger in the TFA group compared to the control group (p = 0.04). These results indicate altered loading from transfemoral prosthesis use changes proximal femur bony morphology, including femoral head asphericity and greater trochanter changes. Greater trochanter morphologic changes, though not a known factor to OA, affect moment arm and line of action of the primary hip abductors, the major muscles which contribute to joint loading and hip stability. Thus, chronic altered loading of the amputated limb hip, whether under- or overloading, results in bony changes to the proximal femur which may contribute to the etiological progression and development of OA.

Patient-Reported Outcomes are Similar in the First Two Years after Staged versus Combined Hip Arthroscopy and Periacetabular Osteotomy for Hip Dysplasia

PURPOSE

The purpose of this study was to compare early patient reported outcomes after staged versus combined hip arthroscopy and periacetabular osteotomy for hip dysplasia.

METHODS

A prospective database was retrospectively reviewed to identify patients that underwent combined or staged hip arthroscopy and PAO from 2012-2020. Patients were excluded if they were >40 years of age, had prior ipsilateral hip surgery, or did not have at least 12-24 month postoperative PRO data. PROs included the Hip Outcomes Score (HOS) Activities of Daily Living (ADL) and Sports Subscale (SS), Non-Arthritic Hip Score (NAHS), and the Modified Harris Hip Score (mHHS). Paired t-tests were used to compare preoperative to postoperative scores for both groups. Outcomes were compared using linear regression adjusted for baseline characteristics including age, obesity, cartilage damage, acetabular index, and procedure timing (early vs. late practice).

RESULTS

Sixty-two hips were included in this analysis (39 combined, 23 staged). The average length of follow up was similar between the combined and staged groups (20.8 vs. 19.6 months, p=0.192). Both groups reported significant improvements in PROs at final follow up compared to preoperative scores (p<0.05 for all). There were no significant differences in HOS-ADL, HOS-SS, NAHS, or mHHS scores between groups preoperatively or at 3, 6, or 12 months postoperatively (p>0.05 for all). There was no significant difference in PROs between the combined and staged groups at the final postoperative time point: HOS-ADL (84.5 vs. 84.3, p=0.77), HOS-SS (76.0 vs. 79.2, p=0.68), NAHS (82.2 vs. 84.5, p=0.79), mHHS (71.0 vs. 71.0, p=0.75) respectively.

CONCLUSION

Staged hip arthroscopy and PAO for hip dysplasia leads to similar PROs at 12-24 months compared to combined procedures. This suggests that with careful and informed patient selection, staging these procedures is an acceptable option for these patients and does not change early outcomes.

LEVEL OF EVIDENCE

Level III Retrospective Comparative.

A minimally invasive periacetabular osteotomy improves the radiographic parameters and functional outcomes in the treatment of developmental dysplasia of the hip in adolescents and adults: surgical technique and early results

PURPOSE

To introduce West China Hospital periacetabular osteotomy (WCH PAO) for acetabular dysplasia in adolescent and young adult patients and evaluate the early clinical results of WCH PAO.

METHODS

A retrospective analysis of 34 patients with developmental dysplasia of the hip was performed from October 2019 to April 2021. Baseline data with surgical time and perioperative blood-loss volume were retrieved from medical record systems. The lateral center-to-edge angle (LCEA), acetabular inclination (AI), hip disability and osteoarthritis outcome score (HOOS), University of California Los Angeles (UCLA), and modified Harris hip score (mHHS) were compared preoperatively and postoperatively.

RESULTS

All patients had significant postoperative radiology improvements, including LCEA and AI. The LCEA was improved from 12.9 to 33.2°, and the AI was decreased from 27.2 to 8.5°. In addition, hip functional outcomes, including HOOS, UCLA and mHHS, were improved. The UCLA was improved from 3.9 to 6.3, and the HOOS was decreased from 71.0 to 10.5. The Harris hip score improved from 50.8 before surgery to 87.4 after surgery. The mean operative time was 155 min (range 120 to 190 min), and the mean intra-operative blood loss was 580.2 ± 285.5 ml. Furthermore, no major complications, including nerve injury or bone nonunion, occurred in the cohort study.

CONCLUSION

WCH PAO is a minimally invasive surgical method for acetabular dysplasia in adolescent and young adult patients who that simplifies the surgical procedure and decreases the incidence of complications related to osteotomy.