Radiographic predictors of hip pain in femoroacetabular impingement

Intertrochanteric curved varus osteotomy for subchondral fracture of the femoral head: a case series

Although favorable results have been reported with total hip arthroplasty, joint-preserving treatment should be the first choice for subchondral fracture of the femoral head (SFF) in young patients. This study reviewed four young male patients with SFF who underwent intertrochanteric curved varus osteotomy (CVO). The patients had a mean age of 32.3 years (range: 18-49 years). Conservative treatment was initially attempted in all cases, but failed to alleviate the pain, leading to surgical intervention at an average time of 6 months (range: 4-10 months) after symptom onset. As the fracture sites were located medial to the lateral edge of the acetabulum in all cases, CVO was performed to achieve a postoperative intact ratio of ≥ 34% in the weight-bearing region of the femoral head. The average follow-up period after surgery lasted 4.3 years (range: 2-7 years). Clinical and radiographic assessments were performed pre- and postoperatively. At the latest follow-up, the mean Harris hip score improved from 67.3 preoperatively to 99.5 postoperatively. The average preoperative intact ratio of the weight-bearing region of the femoral head was 12.3%, which increased to 44.3% postoperatively. No progression to femoral head collapse or joint space narrowing was observed on the plain radiographs. CVO is a simple, less-invasive, and beneficial approach for treating SFF in young patients whose fractures occur medial to the lateral edge of the acetabulum.

Does femoroacetabular impingement syndrome affect range of motion? A systematic review with meta-analysis

BACKGROUND

It is unclear whether femoroacetabular impingement syndrome (FAIS) affect hip range of motion (ROM).

SOURCES OF DATA

We performed a systematic review with meta-analysis searching six electronic databases from inception to March 21, 2022. We included studies assessing hip ROM in FAIS, FAI morphology without symptoms (FAIm), and healthy controls. Mean differences between groups were measured in ROM degrees with 95% confidence interval (CI).

AREAS OF AGREEMENT

A total of 17 studies (1702 hips) were included. Comparison of FAIS patients versus healthy controls showed that hip ROM was clinically and statistically reduced in FAIS for internal rotation (90° hip flexion, -8.01°, 95% CI: -11.21, -4.90; 0° hip flexion -6.38°, 95% CI: -9.79, -2.97); adduction (90° hip flexion, -4.74°, 95% CI: -8.13, -1.34); flexion (-5.41°, 95% CI: -7.05, -3.49), abduction (0° hip flexion, -5.76°, 95% CI: -8.38, -3.23), and external rotation (90° hip flexion, -3.5°, 95% CI: -5.32, -1.67) ranging from low to high certainty of evidence. Comparison of FAIm versus healthy controls showed no statistically significant differences in any direction of movement, albeit with uncertainty of evidence.

AREAS OF CONTROVERSY

The certainty of evidence was unclear, particularly for asymptomatic FAIm.

GROWING POINTS

Hip ROM may be reduced in all directions except extension in FAIS compared to controls. Hip ROM may not be restricted in asymptomatic FAIm.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further studies are needed to resolve the uncertainty of evidence about ROM restrictions in asymptomatic FAIm compared to healthy controls.

Which hip morphology measures and patient factors are associated with age of onset and symptom severity in femoroacetabular impingement syndrome?

BACKGROUND

Bony morphology is central to the pathomechanism of femoroacetabular impingement syndrome (FAIS), however isolated radiographic measures poorly predict symptom onset and severity. More comprehensive morphology measurement considered together with patient factors may better predict symptom presentation. This study aimed to determine the morphological parameter(s) and patient factor(s) associated with symptom age of onset and severity in FAIS.

METHODS

99 participants (age 32.9 ± 10.5 years; body mass index (BMI 24.3 ± 3.1 kg/m²; 42% females) diagnosed with FAIS received standardised plain radiographs and magnetic resonance scans. Alpha angle in four radial planes (superior to anterior), acetabular version (AV), femoral torsion, lateral centre-edge, anterior centre-edge (ACEA) and femoral neck-shaft angles were measured. Age of symptom onset (age at presentation minus duration of symptoms), international Hip Outcome Tool-33 (iHOT-33) and modified UCLA activity scores were recorded. Backward stepwise regression assessed morphological parameters and patient factors (age, sex, BMI, symptom duration, annual income, private/public healthcare system accessed) to determine variables independently associated with onset age and iHOT-33 score.

RESULTS

Earlier symptom onset was associated with larger superoanterior alpha angle (p = 0.007), smaller AV (p = 0.023), lower BMI (p = 0.010) and public healthcare system access (p = 0.041) (r² = 0.320). Worse iHOT-33 score was associated with smaller ACEA (p = 0.034), female sex (p = 0.040), worse modified UCLA activity score (p = 0.010) and public healthcare system access (p < 0.001) (r² = 0.340).

CONCLUSIONS

Age of symptom onset was chiefly predicted by femoral and acetabular bony morphology measures, whereas symptom severity predominantly by patient factors. Factors measured explained a small amount of variance in the data; additional unmeasured factors may be more influential.

Arthroscopic Femoral and Acetabular Osteoplasties Alter the In Vivo Hip Kinematics of Patients With Femoroacetabular Impingement

Purpose

Three-dimensional (3D)-two-dimensional (2D) fluoroscopic image registration was used to measure 3D hip kinematics before and after hip arthroscopy in patients with femoroacetabular impingement (FAI).

Methods

In total, 24 subjects diagnosed with FAI (21 unilateral, 3 bilateral) were prospectively recruited. A clinical impingement test was performed on both hips while the patient was awake and then while anaesthetized, and in the operative hip after arthroscopic osteoplasties and labral repair. Fluoroscopy was used to image the hip during the impingement tests. Images were analyzed using 3D-2D image registration to calculate joint kinematics. The examiner's hand was instrumented with a glove to measure internal rotation torque applied to the hip during each test.

Results

Internal rotation increased by 3.7° (standard error [SE] 0.95°) after surgery (P = .001). Maximum displacement of the femoral head out of the acetabulum was 4.0 mm (SE 0.5 mm) in the operative group before surgery and 1.8 mm (SE 0.3 mm) after surgery (P < .001). This was due to a decrease in lateral displacement by 1.3 mm (SE 0.4 mm, P = .002) and proximal displacement by 0.8 mm (SE 0.3 mm, P = .013). Internal rotation torque was greater in the operative hips when anaesthetized compared with when awake, by 5 Nm (SE 1.2 Nm, P < .001), and greater in the contralateral hips than the operative hips when awake by 8.4 Nm (SE 1.4 mm, P < .001).

Conclusions

Arthroscopic osteoplasty and labral repair increased hip range of motion and reduced femoral head displacement from the acetabulum during the IR90 provocation test (i.e., hip flexion to 90°, maximum internal rotation) in patients with FAI. This suggests that the impinging acetabular rim acted as a fulcrum before surgery and may have caused edge loading that was reduced after surgery.

Level of Evidence

Level IV case series, therapeutic study.

Anthropometric measurements of the pediatric hip using CT-based simulated anteroposterior radiographs of the pelvis

Normal anatomical variants and pathological deformities of the pediatric hip can only be differentiated after a prior definition of normal ranges for anthropometric parameters with increasing age. Aim of the present study was to provide reliable reference values of the pediatric hip morphometry, using computed tomography (CT)-based rotation-corrected summation images of the pelvis that simulate the widely available plain radiograph-based measurements, but offer the higher precision of the CT technique. This retrospective study included 85 patients (170 hips) under 15 years of age (0-15). The measured anthropometric parameters included femur head extrusion index, lateral center-edge angle, acetabular inclination, Tönnis angle, and femoral neck-shaft angle. Mean values, range, SD, P values, intra-rater, and inter-rater reliability were calculated. All measurements correlated with age. None of the measurements correlated with gender or side. Rapid growth phases were noted in all measurements at the age of 12 (14 in males and 11 in females). The inter-rater and intra-rater reliability was high (range inter/intraclass correlation coefficient 0.926-0.998 Cronbach's alpha 0.986-0.998). The present work provides age- and gender-related normative values of the classically used hip measurements as well as growth phases describing pediatric hip morphology in a broad age range. A discrepancy was noted between the values measured in the current study and the classical X-ray-based reference values in the literature especially for the Tönnis angle and LCEA values. This suggests that the rotation and inclination correction in the CT-based techniques might have the advantage of compensating for a possible overestimation in the conventional X-ray-based methods.

Correlation of the Imaging Features of Femoroacetabular Impingement Syndrome With Clinical Findings and Patient Functional Scores

The relationship among the severity of the imaging features of femoroacetabular impingement syndrome (FAIS), patient symptoms, and function has not been elucidated. Understanding this relationship helps to improve the prognostic value of imaging. The goal of this study was to examine the correlation of clinical findings, patient pain, and function with severity, as measured with radiographic and 3-dimensional magnetic resonance imaging (3D-MRI). Data collected prospectively through a longitudinally maintained hip database were reviewed, and 37 hips from 31 patients were included. All patients were examined by an experienced orthopedic surgeon, and preoperative radiographs and 3D-MRI were obtained. Preoperatively, the patients completed validated patient-reported outcome measures (PROMs). Mean±SD alpha angles were 69.4°±10.3°, 70.0°±10.3°, 70.6°±8.4°, and 74.8°±9.2° at 12 o'clock, 1 o'clock, 2 o'clock, and 3 o'clock, respectively. Mean lateral center edge angle was 30.1°±5.3°. The authors did not observe a statistically significant correlation between PROMs and the features measured by radiographs and 3D-MRI (P>.05). In this subset of prospectively imaged patients with FAIS, the authors did not find a correlation between the severity of symptoms measured by PROMs and features on radiographs and 3D-MRI. The severity of dysfunction is multifactorial, and anatomic severity, as measured radiographically and with 3D-MRI, may not correlate with symptoms. Further investigation is necessary to address the sources of patient pain. [Orthopedics. 2021;44(4):e577-e582.].

Analysis of morphological parameters in pelvic radiography and hip MRI : a practical reporting recommendation

Although numerous criteria have been proposed to define abnormal hip morphology, mostly used in the diagnosis of femoroacetabular impingement, it is not a practical approach to measure all of these parameters in all cases without clinical suspicion. In this study, our aim was to develop an evaluating and reporting standardization for routine hip examinations to define both hip morphology and impingement. A total of 108 patients with routine hip magnetic resonance imaging (MRI) and antero-posterior pelvic radiograph (PR) were included in this retrospective study. Alpha angle (AA), acetabular depth (AD), acetabular protrusion, acetabular anteversion, collo- diaphyseal angle (CDA), lateral center-edge angle (LCEA) and Tönnis angle (TA) were measured. The differences and associations between these parameters were evaluated according to imaging modality or plane, and sex. Although a significant difference has been found between the axial AA and the coronal AA mean values measured on MRI, there was also a strong correlation. Coronal measurements were significantly higher. AA values measured in PR and coronal MRI were comparable. Males had higher AA in both planes as compared to females. There were no significant differences between CDA values in MRI and PR. There was a significant difference and a moderate correlation between AD values in MRI and PR. We suggest that routine reports should include a measurement of AA in two planes, and measurement of CDA in PR or MRI. Due to the difference in AD between MRI and radiography, LCEA or TA may represent better alternatives. Checking for a negative Tönnis sign would represent a practical approach.

Sex differences in the prevalence of radiographic findings of structural hip deformities in patients with symptomatic femoroacetabular impingement

The purpose of this study was to determine the sex differences in the overall prevalence of radiographic femoroacetabular impingement (FAI) deformity patients presenting with hip pain and to identify the most common radiographic findings in male and female patients. A geographic database was used to identify patients between the age of 14 and 50 years with hip pain from 2000 to 2016. A chart and radiographic review was performed to identify patients with cam, pincer and mixed-type FAI. A total of 374 (449 hips) out of 612 (695 hips) male patients and 771 (922 hips) out of 1281 (1447 hips) female patients had radiographic features consistent with FAI. Ninety-four male hips (20.9%) and 45 female hips (4.9%) had cam type, 20 male hips (4.5%) and 225 female hips (24.4%) had pincer type and 335 male hips (74.6%) and 652 female hips (70.7%) had mixed type. The overall prevalence of radiographic findings consistent with FAI in male and female patients with hip pain was 61.1% and 60.2%, respectively. Mixed type was the most prevalent. The most common radiographic finding for cam-type FAI was an alpha angle >55°, and the most common radiographic finding for pincer-type FAI was a crossover sign. Male patients were found to have a higher prevalence of cam-type deformities, whereas female patients were found to have a higher prevalence of pincer-type deformities.

Prevalence of Morphological Variations Associated With Femoroacetabular Impingement According to Age and Sex: A Study of 1878 Asymptomatic Hips in Nonprofessional Athletes

Background:

Radiographic findings related to the cam and pincer variants of femoroacetabular impingement (FAI) include measurements of the alpha angle and lateral center-edge angle (LCEA). The function of these radiographic findings has been put into question because of high heterogeneity in reported studies.

Purpose:

The aim of this study was 3-fold: (1) to determine the prevalence of cam and pincer variants according to sex and age on anteroposterior (AP) pelvic radiographs from an asymptomatic nonathletic population, (2) to identify the most common radiographic signs of cam- and pincer-type variants, and (3) to determine if there are variations in the prevalence of these radiographic signs according to sex and age.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

There were 3 independent observers who retrospectively analyzed the 939 AP pelvic radiographs (1878 hips) of patients aged 18 to 50 years who did not have hip symptoms and who were not professional athletes. The prevalence of the cam and pincer variants according to the alpha angle and LCEA, respectively, and the presence of other radiographic signs commonly associated with these variables were determined in the overall population and by subgroup according to sex and age group (18-30, 31-40, and 41-50 years). Descriptive and inferential statistics were used to analyze the study sample.

Results:

The mean age of the included population was 31.0 ± 9.2 years, and 68.2% were male. The prevalence of the cam-type variant was 29.7% (558/1878), and that of the pincer-type variant was 24.3% (456/1878). The radiographic signs that were most associated with the cam and pincer variants were a pistol-grip deformity and the crossover sign, respectively. Significant differences (P < .001) in the prevalence of these variants were identified between men and women in both variants. No differences were observed in the alpha angle or LCEA according to sex or age.

Conclusion:

Radiographic findings suggestive of FAI had significant variations with respect to sex and age in this study sample. This study provides information to determine the prevalence of these anatomic variants in the general population.

The prevalence of femoroacetabular impingement anatomy in Division 1 aquatic athletes who tread water

Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes. Increased stress on the hip during development has been associated with increased risk of cam morphology. The specific forces involved are unclear, but may be due to continued rotational motion, like the eggbeater kick. The goal of this prospective cohort study was to use magnetic resonance imaging (MRI) to identify the prevalence of FAI anatomy in athletes who tread water and compare it to the literature on other sports. With university IRB approval, 20 Division 1 water polo players and synchronized swimmers (15 female, 5 male), ages 18-23 years (mean age 20.7 ± 1.4), completed the 33-item International Hip Outcome Tool and underwent non-contrast MRI scans of both hips using a 3 Tesla scanner. Recruitment was based on sport, with both symptomatic and asymptomatic individuals included. Cam and pincer morphology were identified. The Wilcoxon Signed-Rank/Rank Sum tests were used to assess outcomes. Seventy per cent (14/20) of subjects reported pain in their hips yet only 15% (3/20) sought clinical evaluation. Cam morphology was present in 67.5% (27/40) of hips, while 22.5% (9/40) demonstrated pincer morphology. The prevalence of cam morphology in water polo players and synchronized swimmers is greater than that reported for the general population and at a similar level as some other sports. From a clinical perspective, acknowledgment of the high prevalence of cam morphology in water polo players and synchronized swimmers should be considered when these athletes present with hip pain.

The Prevalence of Radiographic Findings of Structural Hip Deformities for Femoroacetabular Impingement in Patients With Hip Pain

BACKGROUND

Radiography is the initial imaging modality used to evaluate femoroacetabular impingement (FAI), and diagnostic radiographic findings are well-established. However, the prevalence of these radiographic findings in patients with hip pain is unknown.

PURPOSE

The purpose was 3-fold: (1) to determine the overall prevalence of radiographic FAI deformities in young patients presenting with hip pain, (2) to identify the most common radiographic findings in patients with cam-type FAI, and (3) to identify the most common radiographic findings in patients with pincer-type FAI.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A geographic database was used to identify patients aged 14 to 50 years with hip pain between the years 2000 to 2016. The following were evaluated on radiographs: cam type: typical pistol grip deformity, alpha angle >55°; pincer type: crossover sign (COS), coxa profunda or protrusio acetabuli, lateral center edge angle (LCEA) ≥40°, Tönnis angle <0°; and mixed type: both cam- and pincer-type features. Posterior wall sign (PWS) and ischial spine sign (ISS) were also evaluated. The prevalence of each was determined. Descriptive statistics were performed on all radiographic variables.

RESULTS

There were 1893 patients evaluated, and 1145 patients (60.5%; 1371 hips; 374 male and 771 female; mean age, 28.8 ± 8.4 years) had radiographic findings consistent with FAI. Of these hips, 139 (10.1%) had cam type, 245 (17.9%) had pincer type, and 987 (72.0%) had mixed type. The prevalence of a pistol grip deformity and an alpha angle >55° was 577 (42.1%) and 1069 (78.0%), respectively. The mean alpha angle was 66.9°± 10.5°. The prevalence of pincer-type radiographic findings was the following: COS, 1062 (77.5%); coxa profunda, 844 (61.6%); ISS, 765 (55.8%); PWS, 764 (55.7%); Tönnis angle <0°, 312 (22.8%); LCEA ≥40°, 170 (12.4%); and protrusio acetabuli, 7 (0.5%).

CONCLUSION

The overall prevalence of radiographic findings consistent with FAI in young patients with hip pain was 60.5%. Radiographic findings for mixed-type FAI were the most prevalent. The most common radiographic finding for cam-type FAI was an alpha angle >55°. The most common radiographic finding for pincer-type FAI was the COS.

An automated workflow based on hip shape improves personalized risk prediction for hip osteoarthritis in the CHECK study

OBJECTIVE

To design an automated workflow for hip radiographs focused on joint shape and tests its prognostic value for future hip osteoarthritis.

DESIGN

We used baseline and 8-year follow-up data from 1,002 participants of the CHECK-study. The primary outcome was definite radiographic hip osteoarthritis (rHOA) (Kellgren-Lawrence grade ≥2 or joint replacement) at 8-year follow-up. We designed a method to automatically segment the hip joint from radiographs. Subsequently, we applied machine learning algorithms (elastic net with automated parameter optimization) to provide the Shape-Score, a single value describing the risk for future rHOA based solely on joint shape. We built and internally validated prediction models using baseline demographics, physical examination, and radiologists scores and tested the added prognostic value of the Shape-Score using Area-Under-the-Curve (AUC). Missing data was imputed by multiple imputation by chained equations. Only hips with pain in the corresponding leg were included.

RESULTS

84% were female, mean age was 56 (±5.1) years, mean BMI 26.3 (±4.2). Of 1,044 hips with pain at baseline and complete follow-up, 143 showed radiographic osteoarthritis and 42 were replaced. 91.5% of the hips had follow-up data available. The Shape-Score was a significant predictor of rHOA (odds ratio per decimal increase 5.21, 95%-CI (3.74-7.24)). The prediction model using demographics, physical examination, and radiologists scores demonstrated an AUC of 0.795, 95%-CI (0.757-0.834). After addition of the Shape-Score the AUC rose to 0.864, 95%-CI (0.833-0.895).

CONCLUSIONS

Our Shape-Score, automatically derived from radiographs using a novel machine learning workflow, may strongly improve risk prediction in hip osteoarthritis.

Hip and Knee Injuries

Hip and knee injuries are a common presenting concern for patients to a primary care office. This pathology represents a large differential and it can often be a diagnostic challenge for providers to determine the etiology of a patient's symptoms. This article discusses several of the most common causes for hip and knee pain while providing an evidence based review of physical examination maneuvers, imaging studies and treatment modalities to assist a primary care provider when encountering active patients with underlying hip or knee pain.

Demographic and Radiographic Factors Associated With Intra-articular Hip Cartilage Injury: A Cross-sectional Study of 1511 Hip Arthroscopy Procedures

BACKGROUND

Moderate to severe (grade 3-4) hip joint cartilage injury seems to impair function in patients with femoroacetabular impingement syndrome.

PURPOSE

To investigate whether demographic and radiographic factors were associated with moderate to severe hip joint cartilage injury.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Patients were identified in the Danish Hip Arthroscopy Registry. The outcome variables were acetabular cartilage injury (modified Beck grade 0-2 vs 3-4) and femoral head cartilage injury (International Cartilage Repair Society grade 0-2 vs 3-4). Logistic regressions assessed the association with the following: age (<30 vs 30-50 years); sex; sport activity level (Hip Sports Activity Scale); alpha angle (AA) assessed as normal (AA <55°), cam (55°≤ AA <78°), or severe cam (AA ≥78°); lateral center-edge angle (LCEA) assessed as normal (25°≤ LCEA ≤ 39°), pincer (LCEA >39°), or borderline dysplasia (LCEA <25°); joint space width (JSW) assessed as normal (JSW >4.0 mm), mild reduction (3.1 mm ≤ JSW ≤ 4.0 mm), or severe reduction (2.1 mm ≤ JSW ≤ 3.0 mm).

RESULTS

A total of 1511 patients were included (mean ± SD age: 34.9 ± 9.8 years). Male sex (odds ratio [OR], 4.42), higher age (OR, 1.70), increased AA (cam: OR, 2.23; severe cam: OR, 4.82), and reduced JSW (mild: OR, 2.04; severe: OR, 3.19) were associated (P < .05) with Beck grade 3-4. Higher age (OR, 1.92), increased Hip Sports Activity Scale (OR, 1.13), borderline dysplasia (OR, 3.08), and reduced JSW (mild: OR, 2.63; severe: OR, 3.04) were associated (P < .05) with International Cartilage Repair Society grade 3-4.

CONCLUSION

Several demographic and radiographic factors were associated with moderate to severe hip joint cartilage injury. Most notably, increased cam severity and borderline dysplasia substantially increased the risk of grade 3-4 acetabular and femoral head cartilage injury, respectively, indicating that specific deformity may drive specific cartilage injury patterns in the hip joint.

Cam FAI and Smaller Neck Angles Increase Subchondral Bone Stresses During Squatting: A Finite Element Analysis

BACKGROUND

Individuals with a cam deformity and a decreased (varus) femoral neck-shaft angle may be predisposed to symptomatic femoroacetabular impingement (FAI). However, it is unclear what combined effects the cam deformity and neck angle have on acetabular cartilage and subchondral bone stresses during an impinging squat motion. We therefore used finite element analysis to examine the combined effects of cam morphology and femoral neck-shaft angle on acetabular cartilage and subchondral bone stresses during squatting, examining the differences in stress characteristics between symptomatic and asymptomatic individuals with cam deformities and individuals without cam deformities and no hip pain.

QUESTIONS/PURPOSES

Using finite element analysis in this population, we asked: (1) What are the differences in acetabular cartilage stresses? (2) What are the differences in subchondral bone stresses? (3) What are the effects of high and low femoral neck-shaft angles on these stresses?

METHODS

Six male participants were included to represent three groups (symptomatic cam, asymptomatic cam, control without cam deformity) with two participants per group, one with the highest femoral neck-shaft angle and one with the lowest (that is, most valgus and most varus neck angles, respectively). Each participant's finite element hip models were reconstructed from imaging data and assigned subject-specific bone material properties. Hip contact forces during squatting were determined and applied to the finite element models to examine maximum shear stresses in the acetabular cartilage and subchondral bone.

RESULTS

Both groups with cam deformities experienced higher subchondral bone stresses than cartilage stresses. Both groups with cam deformities also had higher subchondral bone stresses (symptomatic with high and low femoral neck-shaft angle = 14.1 and 15.8 MPa, respectively; asymptomatic with high and low femoral neck-shaft angle = 10.9 and 13.0 MPa, respectively) compared with the control subjects (high and low femoral neck-shaft angle = 6.4 and 6.5 MPa, respectively). The symptomatic and asymptomatic participants with low femoral neck-shaft angles had the highest cartilage and subchondral bone stresses in their respective subgroups. The asymptomatic participant with low femoral neck-shaft angle (123°) demonstrated anterolateral subchondral bone stresses (13.0 MPa), similar to the symptomatic group. The control group also showed no differences between cartilage and subchondral bone stresses.

CONCLUSIONS

The resultant subchondral bone stresses modeled here coincide with findings that acetabular subchondral bone is denser in hips with cam lesions. Future laboratory studies will expand the parametric finite element analyses, varying these anatomic and subchondral bone stiffness parameters to better understand the contributions to the pathomechanism of FAI.

CLINICAL RELEVANCE

Individuals with a cam deformity and more varus neck orientation may experience elevated subchondral bone stresses, which may increase the risks of early clinical signs and degenerative processes associated with FAI, whereas individuals with cam morphology and normal-to-higher femoral neck-shaft angles may be at lesser risk of disease progression that would potentially require surgical intervention.

Hip Joint Torsional Loading Before and After Cam Femoroacetabular Impingement Surgery

BACKGROUND

Surgical management of cam femoroacetabular impingement (FAI) aims to preserve the native hip and restore joint function, although it is unclear how the capsulotomy, cam deformity, and capsular repair influence joint mechanics to balance functional mobility.

PURPOSE

To examine the contributions of the capsule and cam deformity to hip joint mechanics. Using in vitro, cadaveric methods, we examined the individual effects of the surgical capsulotomy, cam resection, and capsular repair on passive range of motion and resistance of applied torque.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Twelve cadaveric hips with cam deformities were skeletonized to the capsule and mounted onto a robotic testing platform. The robot positioned each intact hip in multiple testing positions: (1) extension, (2) neutral 0°, (3) flexion 30°, (4) flexion 90°, (5) flexion-adduction and internal rotation (FADIR), and (6) flexion-abduction and external rotation. Then the robot performed applicable internal and external rotations, recording the neutral path of motion until a 5-N·m of torque was reached in each rotational direction. Each hip then underwent a series of surgical stages (T-capsulotomy, cam resection, capsular repair) and was retested to reach 5 N·m of internal and external torque again after each stage. During the capsulotomy and cam resection stages, the initial intact hip's recorded path of motion was replayed to measure changes in resisted torque.

RESULTS

Regarding changes in motion, external rotation increased substantially after capsulotomies, but internal rotation only further increased at flexion 90° (change +32%, P = .001, d = 0.58) and FADIR (change +33%, P < .001, d = 0.51) after cam resections. Capsular repair provided marginal restraint for internal rotation but restrained the external rotation compared with the capsulotomy stage. Regarding changes in torque, both internal and external torque resistance decreased after capsulotomy. Compared with the capsulotomy stage, cam resection further reduced internal torque resistance during flexion 90° (change -45%, P < .001, d = 0.98) and FADIR (change -37%, P = .003, d = 1.0), where the cam deformity accounted for 21% of the intact hip's torsional resistance in flexion 90° and 27% in FADIR.

CONCLUSION

Although the capsule played a predominant role in joint constraint, the cam deformity provided 21% to 27% of the intact hip's resistance to torsional load in flexion and internal rotation. Resecting the cam deformity would remove this loading on the chondrolabral junction.

CLINICAL RELEVANCE

These findings are the first to quantify the contribution of the cam deformity to resisting hip joint torsional loads and thus quantify the reduced loading on the chondrolabral complex that can be achieved after cam resection.

Pincer-type MRI morphology seen in over a third of asymptomatic healthy volunteers without femoroacetabular impingement

BACKGROUND

In daily routine, pincer femoroacetabular impingement (FAI) findings are often seen without a clinical diagnosis of pincer FAI.

PURPOSE

To assess the presence of pincer FAI MRI findings in asymptomatic volunteers with negative impingement test versus patients with clinically confirmed FAI.

STUDY TYPE

Case-control study.

POPULATION

Sixty-three asymptomatic volunteers and 63 matched patients with FAI were included.

FIELD STRENGTH/ SEQUENCE

A coronal T₁ -weighted turbo spin-echo sequence as well as a 3D oblique transverse water-excitation true fast imaging sequence at 1.5T.

ASSESSMENT

The volunteers underwent standard MRI of the hip, and patients underwent MR arthrography of the symptomatic hip using the same MR sequences. Measurements of cranial acetabular version, acetabular depth, and lateral center-edge angle were performed independently by three fellowship-trained musculoskeletal radiologists.

STATISTICAL TESTS

Descriptive statistics, Mann-Whitney U-test, Unpaired t-test, receiver operating characteristics (ROC), Intraclass correlation coefficient (ICC).

RESULTS

Forty-one percent (26/63, reader 1), 32% and 37% (20 and 23/63, reader 2/3) of asymptomatic volunteers had at least one positive MR finding for pincer-FAI. Patients with pincer or mixed-type FAI had cranial retroversion of the acetabulum of -0.2° ± 7.1 (mean ± standard deviation) for reader 1 and -0.3° ± 5.5/-0.2° ± 4.8 for reader 2 / reader 3, while asymptomatic volunteers had an anteversion of 6.2° ± 6.4 (reader 1) and 3.2° ± 4.9/3.1° ± 6.5 (readers 2/3): This difference was statistically significant (P ≤ 0.002), but there was a large overlap between the groups. Acetabular depth measurements were very similar for patients with either pincer or mixed-type FAI (5.1-5.3 mm ± 3.1) and volunteers (5.2-6.1 mm ± 2.6), without a statistically significant difference (P ≤ 0.50). Lateral center-edge angle was also similar in patients with either pincer or mixed-type FAI (32.1-35.1° ± 9.1) and volunteers (30.7-33.2° ± 6.5), without a statistically significant difference (P ≤ 0.28).

DATA CONCLUSION

There is a large overlap in pincer-type MRI findings between patients with symptomatic FAI and asymptomatic volunteers. More than a third of volunteers exhibited at least one positive pincer-type MRI finding.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1296-1303.

Altered Walking and Muscle Patterns Reduce Hip Contact Forces in Individuals With Symptomatic Cam Femoroacetabular Impingement

BACKGROUND

Cam-type femoroacetabular impingement (FAI) is a causative factor for hip pain and early hip osteoarthritis. Although cam FAI can alter hip joint biomechanics, it is unclear what role muscle forces play and how they affect the hip joint loading. Purpose/Hypothesis: The purpose was to examine the muscle contributions and hip contact forces in individuals with symptomatic cam FAI during level walking. Patients with symptomatic cam FAI would demonstrate different muscle and hip contact forces during gait.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eighteen patients with symptomatic cam FAI were matched for age and body mass index with 18 control participants. Each participant's walking kinematics and kinetics were recorded throughout a gait cycle (ipsilateral foot-strike to ipsilateral foot-off) by use of a motion capture system and force plates. Muscle and hip contact forces were subsequently computed by use of a musculoskeletal modeling program and static optimization methods.

RESULTS

The FAI group walked slower and with shorter steps, demonstrating reduced joint motions and moments during contralateral foot-strike, compared with the control group. The FAI group showed reduced psoas major (median, 1.1 newtons per bodyweight [N/BW]; interquartile range [IQR], 1.0-1.5 N/BW) and iliacus forces (median, 1.2 N/BW; IQR, 1.0-1.6 N/BW), during contralateral foot-strike, compared with the control group (median, 1.6 N/BW; IQR, 1.3-1.6 N/BW, P = .004; and median, 1.5 N/BW; IQR, 1.3-1.6 N/BW, P = .03, respectively), which resulted in lower hip contact forces in the anterior ( P = .026), superior ( P = .02), and medial directions ( P = .038). The 3 vectors produced a resultant peak force at the anterosuperior aspect of the acetabulum for both groups, with the FAI group demonstrating a substantially lower magnitude.

CONCLUSION

FAI participants altered their walking kinematics and kinetics, especially during contralateral foot-strike, as a protective mechanism, which resulted in reduced psoas major and iliacus muscle force and anterosuperior hip contact force estimations.

CLINICAL RELEVANCE

Limited hip mobility not only is attributed to bone-on-bone impingement, caused by cam morphology, but could be attributed to musculature as well. Not only would the psoas major and iliacus be able to protect the hip joint during flexion-extension, athletic conditioning could further strengthen core muscles for improved hip mobility and pelvic balance.

Asymptomatic Participants With a Femoroacetabular Deformity Demonstrate Stronger Hip Extensors and Greater Pelvis Mobility During the Deep Squat Task

Background:

Cam-type femoroacetabular impingement (FAI) is a femoral head-neck deformity that causes abnormal contact between the femoral head and acetabular rim, leading to pain. However, some individuals with the deformity do not experience pain and are referred to as having a femoroacetabular deformity (FAD). To date, only a few studies have examined muscle activity in patients with FAI, which were limited to gait, isometric and isokinetic hip flexion, and extension tasks.

Purpose:

To compare (1) hip muscle strength during isometric contraction and (2) lower limb kinematics and muscle activity of patients with FAI and FAD participants with body mass index–matched healthy controls during a deep squat task.

Study Design:

Controlled laboratory study.

Methods:

Three groups of participants were recruited: 16 patients with FAI (14 male, 2 female; mean age, 38.5 ± 8.0 years), 18 participants with FAD (15 male, 3 female; mean age, 32.5 ± 7.1 years), and 18 control participants (16 male, 2 female; mean age, 32.8 ± 7.0 years). Participants were outfitted with electromyography electrodes on 6 muscles and reflective markers for motion capture. The participants completed maximal strength tests and performed 5 deep squat trials. Muscle activity and biomechanical variables were extrapolated and compared between the 3 groups using 1-way analysis of variance.

Results:

The FAD group was significantly stronger than the FAI and control groups during hip extension, and the FAD group had greater sagittal pelvic range of motion and could squat to a greater depth than the FAI group. The FAI group activated their hip extensors to a greater extent and for a longer period of time compared with the FAD group to achieve the squat task.

Conclusion:

The stronger hip extensors of the FAD group are associated with greater pelvic range of motion, allowing for greater posterior pelvic tilt, possibly reducing the risk of impingement while performing the squat, and resulting in a greater squat depth compared with those with symptomatic FAI.

Clinical Relevance:

The increased strength of the hip extensors in the FAD group allowed these participants to achieve greater pelvic mobility and a greater squat depth by preventing the painful impingement position. Improving hip extensor strength and pelvic mobility may affect symptoms for patients with FAI.

Anatomic Predictors of Sagittal Hip and Pelvic Motions in Patients With a Cam Deformity

BACKGROUND

As there is a high prevalence of patients with cam deformities and no ongoing hip dysfunction, understanding the biomechanical factors predicting the onset of symptoms and degenerative changes is critical. One such variable is how the spinopelvic parameters may influence hip and pelvic sagittal mobility. Hypothesis/Purpose: Pelvic incidence may predict sagittal hip and pelvic motions during walking and squatting. The purpose was to determine which anatomic characteristics were associated with symptoms and how they influenced functional hip and pelvic ranges of motion (ROMs) during walking and squatting.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fifty-seven participants underwent computed tomography and were designated either symptomatic (n = 19, cam deformity with pain), asymptomatic (n = 19, cam deformity with no pain), or control (n = 19, no cam deformity or pain). Multiple femoral (cam deformity, neck angle, torsion), acetabular (version, coverage), and spinopelvic (pelvic tilt, sacral slope, pelvic incidence) parameters were measured from each participant's imaging data, and sagittal hip and pelvic ROMs during walking and squatting were recorded using a motion capture system.

RESULTS

Symptomatic participants had large cam deformities, smaller femoral neck-shaft angles, and larger pelvic incidence angles compared with the asymptomatic and control participants. Discriminant function analyses confirmed that radial 1:30 alpha angle (λ₁ = 0.386), femoral neck-shaft angle (λ₂ = 0.262), and pelvic incidence (λ₃ = 0.213) ( P < .001) were the best anatomic parameters to classify participants with their groups. Entering these 3 parameters into a hierarchical linear regression, significant regressions were achieved for hip ROM only when pelvic incidence was included for walking ( R² = 0.20, P = .01) and squatting ( R² = 0.14, P = .04). A higher pelvic incidence decreased walking hip ROM ( r = -0.402, P = .004). Although symptomatic participants indicated a trend of reduced squatting hip and pelvic ROMs, there were no significant regressions with the anatomic parameters.

CONCLUSION

A cam deformity alone may not indicate early clinical signs or decreased ROM. Not only was pelvic incidence a significant parameter to classify the participants, but it was also an important parameter to predict functional ROM. Symptomatic patients with a higher pelvic incidence may experience limited sagittal hip mobility.

CLINICAL RELEVANCE

Patients with symptomatic femoroacetabular impingement showed a higher pelvic incidence and, combined with a cam deformity and varus neck, can perhaps alter the musculature of their iliopsoas, contributing to a reduced sagittal ROM. With an early and accurate clinical diagnosis, athletes could benefit from a muscle training strategy to protect their hips.

Hip shape is symmetric, non-dependent on limb dominance and gender-specific: implications for femoroacetabular impingement. A 3D CT analysis in asymptomatic subjects

OBJECTIVE

To determine the reference intervals (RefInt) of the quantitative morphometric parameters of femoroacetabular impingement (FAI) in asymptomatic hips with computed tomography (CT) and determine their dependence on age, side, limb dominance and sex.

METHODS

We prospectively included 590 patients and evaluated 1111 hips with semi-automated CT analysis. We calculated overall, side- and sex-specific parameters for imaging signs of cam [omega and alpha angle (α°)] and pincer-type morphology [acetabular version (ACvers), lateral centre-edge angle (LCEA) and cranio-caudal coverage].

RESULTS

Hip shape was symmetrical and did not depend on limb dominance. The 95% RefInt limits were sex-different for all cam-type parameters and extended beyond current abnormal thresholds. Specifically, the upper limits of RefInt for α° at 12:00, 1:30 and 3:00 o'clock positions were 56°, 70° and 58°, respectively, and 45° for LCEA. Acetabular morphology varied between age groups, with a trend toward an LCEA/ACvers increase over time.

CONCLUSION

Our morphometric measurements can be used to estimate normal hip morphology in asymptomatic individuals. Notably they extended beyond current thresholds used for FAI imaging diagnosis, which was most pronounced for cam-type parameters. We suggest the need to reassess α° RefInt and consider a 60° threshold for the 12:00/3:00 positions and 65-70° for other antero-superior positions.

KEY POINTS

• Hip shape is symmetrical regardless of limb dominance. • Pincer/cam morphology is frequent in asymptomatic subjects (20 and 71%, respectively). • LCEA and acetabular version increases with age (5-7° between opposite age groups). • Femoral morphology is stable after physeal closure (in the absence of pathology). • Alpha and omega angle thresholds should be set according to sex.

Comprehensive Clinical Evaluation of Femoroacetabular Impingement: Part 1, Physical Examination

A thorough evaluation of the hip must include a comprehensive medical and surgical history focused on the hip joint, surrounding soft tissues, and the associated structures of the spine, pelvis, and lower extremities. These details can guide the physical examination and provide insight into the cause of the patient's chief complaints. A proper examination includes physical examination while the patient is in the upright, supine, prone, and lateral position, as well as an evaluation of gait. Guided by a thorough history, the physical examination enables the surgeon to distinguish between intra-articular and extra-articular contributors to hip pain, selection of appropriate imaging modalities, and ultimately supports medical decision making.

The Etiology of Cam-type Femoroacetabular Impingement: A Cadaveric Study

BACKGROUND

There is a dearth of literature examining the causes of cam-type femoroacetabular impingement (FAI) and when such morphology appears. The purpose of the current study was to analyze how the ossific portion of the proximal femur develops over time with respect to standard cam-type FAI parameters.

METHODS

A collection of 193 femurs from cadavers aged 4 to 21 years were evaluated. The age, sex, ethnicity, and status of the proximal femoral physes (open or closed) of each were recorded. Each specimen was digitally photographed in standardized anteroposterior and modified axial positions. From these photographs, the anterior offset, anterior offset ratio (AOR), and α-angle were determined. A cam lesion was defined as an α-angle >55 degrees on the lateral view.

RESULTS

The mean age of the specimens was 17.5±4.2 years. The majority were male (69%) and African American (79%) with closed physes (78%). There were significant differences among discrete age groups with respect to α-angle (P=0.01), anterior offset (P<0.01), and AOR (P<0.01). In addition, younger femurs with open physes had a significantly higher mean α-angle (P<0.01), lower mean anterior offset (P<0.01), and higher mean AOR (P<0.01) compared with older ones with closed physes. Specimens defined as having a cam deformity had a statistically higher α-angle (P<0.01) and lower anterior offset (P<0.01), but there was no difference in AOR values compared with specimens without a cam lesion (P=0.1).

CONCLUSIONS

The apparent decline in α-angles as age increases indicates that the traditional α-angle in younger patients measures a different anatomic parameter (ossified femur excluding the cartilaginous portion) than in older patients (completely ossified femur). This suggests that the bony α-angle is inappropriate in the evaluation of cam lesions in the immature physis. The AOR, rather than the anterior offset, may be more accurate in the evaluation of the growing proximal femur.

CLINICAL RELEVANCE

This study provides novel insight into, and enhances the understanding of, the development of cam-type FAI.

Radiographic Diagnosis of Pincer-Type Femoroacetabular Impingement: A Systematic Review

Background:

Femoroacetabular impingement (FAI) is a well-recognized condition that causes hip pain and can lead to early osteoarthritis if not managed properly. With the increasing awareness and efficacy of operative treatments for pincer-type FAI, there is a need for consensus on the standardized radiographic diagnosis.

Purpose:

To perform a systematic review of the evidence regarding imaging modalities and radiographic signs for diagnosing pincer-type FAI.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

A literature review was performed in 2016 using the Cochrane, PubMed, and Embase search engines. All articles focusing on a radiographic diagnosis of pincer-type FAI were reviewed. Each of the included 44 articles was assigned the appropriate level of evidence, and the particular radiographic marker and/or type of imaging were also summarized.

Results:

There were 44 studies included in the final review. Most of the articles were level 4 evidence (26 articles), and there were 12 level 3 and 6 level 2 articles. The crossover sign was the most commonly used radiographic sign (27/44) followed by the lateral center-edge angle (22/44). Anteroposterior (AP) pelvis plain radiographs were the most commonly used imaging modality (33 studies). Poor-quality evidence exists in support of most currently used radiographic markers, including the crossover sign, lateral center-edge angle, posterior wall sign, ischial spine sign, coxa profunda, acetabular protrusion, and acetabular index. There is poor-quality conflicting evidence regarding the use of the herniation pit to diagnose pincer-type FAI. Some novel measurements, such as β-angle, acetabular roof ratio, and acetabular retroversion index, have been proposed, but they also lack support from the literature.

Conclusion:

No strong evidence exists to support a single best set of current radiographic markers for the diagnosis of pincer-type FAI, largely due to the lack of better quality trials (levels 1 and 2) that compare conventional radiographic findings with the gold standard, which is the intraoperative findings. More sophisticated imaging modalities such as computed tomography and magnetic resonance arthrography are often needed to diagnose pincer-type FAI, and these investigations are relatively accurate in assessing labral pathology or cartilage damage.

Increased Hip Stresses Resulting From a Cam Deformity and Decreased Femoral Neck-Shaft Angle During Level Walking

BACKGROUND

It is still unclear why many individuals with a cam morphology of the hip do not experience pain. It was recently reported that a decreased femoral neck-shaft angle may also be associated with hip symptoms. However, the effects that different femoral neck-shaft angles have on hip stresses in symptomatic and asymptomatic individuals with cam morphology remain unclear.

QUESTIONS/PURPOSES

We examined the effects of the cam morphology and femoral neck-shaft angle on hip stresses during walking by asking: (1) Are there differences in hip stress characteristics among symptomatic patients with cam morphology, asymptomatic individuals with cam morphology, and individuals without cam morphology? (2) What are the effects of high and low femoral neck-shaft angles on hip stresses?

METHODS

Six participants were selected, from a larger cohort, and their cam morphology and femoral neck-shaft angle parameters were measured from CT data. Two participants were included in one of three groups: (1) symptomatic with cam morphology; (2) asymptomatic with a cam morphology; and (3) asymptomatic control with no cam morphology with one participant having the highest femoral neck-shaft angle and the other participant having the lowest in each subgroup. Subject-specific finite element models were reconstructed and simulated during the stance phase, near pushoff, to examine maximum shear stresses on the acetabular cartilage and labrum.

RESULTS

The symptomatic group with cam morphology indicated high peak stresses (6.3-9.5 MPa) compared with the asymptomatic (5.9-7.0 MPa) and control groups (3.8-4.0 MPa). Differences in femoral neck-shaft angle influenced both symptomatic and asymptomatic groups; participants with the lowest femoral neck-shaft angles had higher peak stresses in their respective subgroups. There were no differences among control models.

CONCLUSIONS

Our study suggests that the hips of individuals with a cam morphology and varus femoral neck angle may be subjected to higher mechanical stresses than those with a normal femoral neck angle.

CLINICAL RELEVANCE

Individuals with a cam morphology and decreased femoral neck-shaft angle are likely to experience severe hip stresses. Although asymptomatic participants with cam morphology had elevated stresses, a higher femoral neck-shaft angle was associated with lower stresses. Future research should examine larger amplitudes of motion to assess adverse subchondral bone stresses.

Association of clinical and radiographic signs of femoroacetabular impingement in the general population

BACKGROUND

The relationships between the clinical and radiographic signs of femoroacetabular impingement (FAI) are unknown. The purpose of this study was to assess the relationship between hip pain, a positive anterior impingement sign (AIS), and radiographic signs of FAI in a general Japanese population.

METHODS

A total of 616 individuals participated in this study. Hip pain was assessed using the Japanese Orthopaedic Association Hip-Disease Evaluation Questionnaire (JHEQ) pain category score and the AIS was used as a provocation test. Participants were divided into a positive AIS group (at least one positive hip) and a negative AIS group. Radiographs were assessed for the cross-over sign (COS), ischial spine sign (ISS), posterior wall sign (PWS), and pistol grip deformity (PGD). Then, the relationships between the clinical and radiographic signs of FAI were evaluated.

RESULTS

JHEQ pain scores did not differ between men and women. Seven men (3.4%) and 29 women (7.1%) had a least one hip with a positive AIS. The mean JHEQ pain scores were 22.9 ± 7.2 for the positive and 27.3 ± 2.2 for the negative AIS group (P < 0.01). The prevalences of COS, ISS, PWS, and PGD were 8.9%, 17.2%, 21.8%, and 1.9%, respectively. There were no significant associations between degree of hip pain, AIS, and each radiographic finding.

CONCLUSIONS

Radiographic signs of FAI were not associated with the degree of hip pain or a positive AIS, which suggests that radiographic findings may not be important in the clinical diagnosis of FAI.

What is the Prevalence of Radiographic Hip Findings Associated With Femoroacetabular Impingement in Asymptomatic Asian Volunteers?

BACKGROUND

Morphologic features of the proximal femur reminiscent of those seen in patients with femoroacetabular impingement (FAI) have been reported among asymptomatic individuals in Western populations, but whether this is the case in Asian populations is unknown.

QUESTIONS/PURPOSES

The purpose of this study was to determine the prevalence of radiographic findings in the proximal femur that are consistent with FAI in asymptomatic Korean volunteers.

METHODS

Two hundred asymptomatic volunteers with no prior hip surgery or childhood hip problems underwent three-view plain radiographs (pelvis AP view, Sugioka view, and 45° Dunn view) of both hips. There were 146 hips from male volunteers and 254 hips from female volunteers in the study. The mean age of all participants was 34.7 years (range, 21-49 years). Cam-type morphologic features were defined as the presence of the following on one or more of the three views: pistol-grip morphologic features, an osseous bump at the femoral head-neck junction, flattening of the femoral head-neck offset, or alpha angle greater than 55°. Pincer-type morphologic features were determined by radiographic signs, including crossover sign, deficient posterior wall sign, or lateral center-edge angle greater than 40°.

RESULTS

The prevalence of cam-type morphologic features seen on at least one radiograph was 38% (male, 57%; female, 26%). The prevalence of cam-type features (at least one positive cam-type feature) was 2.0% (male, 6%; female, 0%) on the pelvic AP view, 24% (male, 36%; female, 17%) on the Sugioka view, and 30% (male, 47%; female, 20%) on the 45° Dunn view. The prevalence of pincer-type morphologic features (at least one positive pincer-type feature) was 23% (male, 27%; female, 21%) on the pelvic AP view.

CONCLUSION

The prevalence of FAI-related morphologic features in asymptomatic Asian populations was comparable to the prevalence in Western populations. Considering the high prevalence of radiographic hip findings reminiscent of FAI in asymptomatic Asian populations, it will be important to determine whether FAI-related morphologic features are a cause of hip pain when considering surgery in Asian patients.

Midterm Outcomes of Reverse (Anteverting) Periacetabular Osteotomy in Patients With Hip Impingement Secondary to Acetabular Retroversion

BACKGROUND

There is a paucity of data on the results of reverse (anteverting) periacetabular osteotomy (RPAO) for treatment of femoroacetabular impingement (FAI) secondary to acetabular retroversion.

PURPOSE

To evaluate the midterm outcomes of RPAO for FAI secondary to acetabular retroversion in those with and without hip dysplasia.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A retrospective review identified RPAOs performed on patients with acetabular retroversion in isolation or in the setting of dysplasia (lateral center-edge angle [LCEA] ≤19°). Acetabular retroversion with FAI was diagnosed clinically and radiographically, with a positive crossover and posterior wall signs on pelvic radiographs. Twenty-three patients (30 hips) met the inclusion criteria; 20 hips with isolated retroversion and 10 hips with retroversion and hip dysplasia. The average age at the time of the procedure was 26 years (range, 13-45 years). The average length of follow-up was 5 years (range, 2-19 years). Harris Hip Score (HHS) and radiographs were evaluated preoperatively and at last follow-up.

RESULTS

The mean preoperative LCEA was 31° (range, 22°-49°) in the isolated retroversion group and 9° (range, -4° to 17°) in the dysplastic group. Postoperatively, the LCEA in the dysplastic group increased to 35° (range, 15°-46°) (P = .0001). The crossover sign corrected in 55% (11/20) of the isolated retroversion group and 80% (8/10) of the dysplastic group. The acetabular index (mean ± SD) improved from 1.3 ± 0.3 to 1.7 ± 0.6 (P = .0001), indicating improved anteversion. At the latest follow-up, the average HHS in the isolated retroversion group increased from 58 preoperatively (range, 23-77) to 93 (range, 68-100) (P = .0001); the HHS in the dysplastic group improved from 49 (range, 20-74) to 92 (range, 77-100) (P < .0001). Complication rates were similar in both groups. Excluding hardware removal, additional surgeries were performed in 13% (4/30).

CONCLUSION

RPAO performed for FAI in the young patient with isolated acetabular retroversion or retroversion in the setting of dysplasia successfully improved clinical and radiographic results at mid- to long-term follow-up.

Differences in anatomical parameters between the affected and unaffected hip in patients with bilateral cam-type deformities

BACKGROUND

It is still unclear why many individuals with bilateral cam deformities demonstrate only unilateral symptoms of femoroacetabular impingement, thus symptoms may be attributed to additional anatomical parameters. The purpose was to examine patients with bilateral cam deformities, with unilateral symptoms, and compare anatomical hip joint parameters between their affected (symptomatic) hip and their contralateral, unaffected (asymptomatic) hip.

METHODS

Twenty participants (n=20) with unilateral symptoms, but bilateral cam deformities, underwent CT imaging to measure their affected and unaffected hip's: axial and radial alpha angles, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version, center-edge angle; and a physical examination (hip flexion, straight-leg raise, internal rotation, external rotation) to ascertain clinical signs.

FINDINGS

The affected hips demonstrated limited motions during physical examination, compared with unaffected hips (effect size=0.550 to 0.955). The affected hips had significantly lower femoral neck-shaft angles (mean 125° (SD 3)) and lower medial proximal femoral angles (mean 79° (SD 4)), compared with the unaffected hips (mean 127° (SD 3), P=0.001, effect size=0.922; and mean 81° (SD 4), P=0.011, effect size=0.632; respectively). There were no differences in cam deformity parameters (axial and radial alpha angles, femoral head-neck offset), femoral torsion, acetabular version, and center-edge angle, between affected and unaffected hips.

INTERPRETATION

A decreased femoral neck-shaft angle or medial proximal femoral angle can be implemented as a diagnostic predictor, to determine which hip may be at a greater risk of developing early symptoms.

Hip Joint Stresses Due to Cam-Type Femoroacetabular Impingement: A Systematic Review of Finite Element Simulations

Background

The cam deformity causes the anterosuperior femoral head to obstruct with the acetabulum, resulting in femoroacetabular impingement (FAI) and elevated risks of early osteoarthritis. Several finite element models have simulated adverse loading conditions due to cam FAI, to better understand the relationship between mechanical stresses and cartilage degeneration. Our purpose was to conduct a systematic review and examine the previous finite element models and simulations that examined hip joint stresses due to cam FAI.

Methods

The systematic review was conducted to identify those finite element studies of cam-type FAI. The review conformed to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and studies that reported hip joint contact pressures or stresses were included in the quantitative synthesis.

Results

Nine articles studied FAI morphologies using finite element methods and were included in the qualitative synthesis. Four articles specifically examined contact pressures and stresses due to cam FAI and were included in the quantitative synthesis. The studies demonstrated that cam FAI resulted in substantially elevated contact pressures (median = 10.4 MPa, range = 8.5–12.2 MPa) and von Mises stresses (median 15.5 MPa, range = 15.0–16.0 MPa) at the acetabular cartilage; and elevated maximum-shear stress on the bone (median = 15.2 MPa, range = 14.3–16.0 MPa), in comparison with control hips, during large amplitudes of hip motions. Many studies implemented or adapted idealized, ball-and-cup, parametric models to predict stresses, along with homogeneous bone material properties and in vivo instrumented prostheses loading data.

Conclusion

The formulation of a robust subject-specific FE model, to delineate the pathomechanisms of FAI, remains an ongoing challenge. The available literature provides clear insight into the estimated stresses due to the cam deformity and provides an assessment of its risks leading to early joint degeneration.

Femoro-acetabular impingement clinical research: is a composite outcome the answer?

Femoro-acetabular impingement (FAI) is increasingly recognized as an important cause of hip pain in the young adult. However, the methods of evaluating the efficacy of surgical intervention are often not validated and/or inconsistently reported. Important clinical, gait, radiographic and biomarker outcomes are discussed. This article (1) presents the rationale for considering a composite outcome for FAI patients; (2) examines a variety of important end points currently used to evaluate FAI surgery; (3) discusses a strategy to generate a composite outcome by combining these end points; and (4) highlights the challenges and current areas of controversy that such an approach to evaluating symptomatic FAI patients may present.

Imaging prevalence of femoroacetabular impingement in symptomatic patients, athletes, and asymptomatic individuals: A systematic review

BACKGROUND

There is a wide discrepancy in reported prevalence rates for cam, pincer, and mixed femoroacetabular impingement (FAI), particularly among distinct populations, namely asymptomatic or symptomatic subjects and athletes. No systematic analysis to date has yet compared studies among these groups to determine differences in radiographic signs of FAI.

METHODS

A systematic review of existing literature was performed to determine the prevalence of radiographic signs of FAI among athletes, asymptomatic subjects, and symptomatic patients. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were applied to systematically search PubMed, MEDLINE, CINAHL, and Cochrane databases.

RESULTS

We identified 361 studies in our literature search. After considering the exclusion criteria, 60 were included in this systematic review: 15 in athletes, 10 in purely asymptomatic patients, and 35 in symptomatic, non-athlete populations. Cam impingement was significantly (p=0.0003) more common in athletes versus asymptomatic subjects but not compared to symptomatic patients (p=0.107). In addition, cam FAI was significantly more common in symptomatic versus asymptomatic cases (p=0.009). The percentage of patients with cam-type FAI showed significant differences across groups (p=0.006). No significant differences were found between pincer-type FAI morphology prevalence when comparing athletes to symptomatic patients. However, mixed-type FAI was significantly more common in athletes versus asymptomatic subjects (p=0.03) and in asymptomatic versus symptomatic subjects (p=0.015). The percentage of patients with mixed-type FAI showed significant differences across groups (p=0.041). The mean alpha angle was significantly greater in the symptomatic group versus either the asymptomatic or athlete group (p<0.001). Significant differences in mean alpha angles were noted across groups (p=0.0000).

CONCLUSIONS

Imaging suspicion of FAI is common among athletes, asymptomatic, and symptomatic populations. However, significant differences in type and imaging signs of FAI exist among these groups that need to be considered in patients' decision making.

Relationship between the alpha and beta angles in diagnosing CAM-type femoroacetabular impingement on frog-leg lateral radiographs

PURPOSE

Alpha and beta angles are commonly used radiographic measures to assess the sphericity of the proximal femur and distance between the pathologic head-neck junction and the acetabular rim, respectively. The aim of this study was to explore the relationship between these two measurements on frog-leg lateral hip radiographs.

METHODS

Fifty frog-leg lateral hip radiographs were evaluated by two orthopaedic surgeons and two radiologists. Each reviewer measured the alpha and beta angles on two separate occasions to determine the relationship between positive alpha and beta angles and the inter- and intra-observer reliability of these measurements.

RESULTS

There was no significant association between positive alpha and beta angles, [kappa range -0.043 (95 % CI -0.17 to 0.086) to 0.54 (95 % CI 0.33-0.75)]. Intra-observer reliability was high [alpha angle intra-class correlation coefficient (ICC) range 0.74 (95 % CI 0.58-0.84) to 0.99 (95 % CI 0.98-0.99) and beta angle ICC range 0.86 (95 % CI 0.76-0.92) to 0.97 (95 % CI 0.95-0.98)].

CONCLUSIONS

There is no statistical or functional relationship between readings of positive alpha and beta angles. The radiographic measurements resulted in high intra-observer and fair-to-moderate inter-observer reliability. Results of this study suggest that the presence of a CAM lesion on lateral radiographs as suggested by a positive alpha angle does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle and thus may not be the best measure of functional impingement. Understanding the relationship between these two aspects of femoroacetabular impingement improves a surgeon's ability to anticipate potential operative management.

A Computed Tomography Study of Gender Differences in Acetabular Version and Morphology: Implications for Femoroacetabular Impingement

PURPOSE

To assess the prevalence of acetabular retroversion in a large population of patients with asymptomatic hips. Furthermore, we sought to identify gender differences in acetabular morphology to address the current thinking that retroversion and pincer-type femoroacetabular impingement (FAI) are more common in women.

METHODS

We retrospectively reviewed morphologic features of acetabula from a consecutive series of trauma-protocol computed tomography scans of patients without pelvis injury. An automated algorithm determined the acetabular rim profile and center of the femoral head, normalized the frontal plane of the pelvis, and calculated version and coverage. We then compared male and female rim profiles, specifically focusing on version and acetabular wall coverage in the 1-o'clock (anterosuperior), 2-o'clock (central), and 3-o'clock (inferior) positions.

RESULTS

Of 1,088 patients in the database, 878 had complete data (i.e., age, ethnicity, and body mass index) and were therefore included in the final analysis. Of these, 34.3% were women and 65.7% were men. Mean global acetabular version was 19.1° for men and 22.2° for women (P < .001). Mean acetabular version for men and women was 15.5° and 18.3°, respectively, in the 1-o'clock position; 21.5° and 24.0°, respectively, in the 2-o'clock position; and 20.2° and 24.3°, respectively, in the 3-o'clock position (P < .001 for all 3). True retroversion (<0°) was observed only in the 1-o'clock position. The prevalence of true acetabular retroversion in the 1-o'clock position for men and women was 4.3% and 3%, respectively (P = .36).

CONCLUSIONS

Mean global and focal acetabular anteversion was greater in women, and the prevalence of focal cephalad retroversion in the 1-o'clock position was not significantly different compared with men. Acetabular retroversion and anterior overcoverage are not more prevalent in women in the anterosuperior acetabulum, where femoroacetabular impingement most commonly occurs.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Prevalence of Femoroacetabular Impingement Imaging Findings in Asymptomatic Volunteers: A Systematic Review

PURPOSE

The aim of this study was to determine the prevalence of radiographic findings suggestive of femoroacetabular impingement (FAI) in asymptomatic individuals.

METHODS

A systematic review was performed using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies reporting radiographic, computed tomographic, or magnetic resonance imaging (MRI) findings that were suggestive of FAI in asymptomatic volunteers were included. Cam, pincer, and combined pathologic conditions were investigated.

RESULTS

We identified 26 studies for inclusion, comprising 2,114 asymptomatic hips (57.2% men; 42.8% women). The mean participant age was 25.3 ± 1.5 years. The mean alpha angle in asymptomatic hips was 54.1° ± 5.1°. The prevalence of an asymptomatic cam deformity was 37% (range, 7% to 100% between studies)-54.8% in athletes versus 23.1% in the general population. Of the 17 studies that measured alpha angles, 9 used MRI and 9 used radiography (1 study used both). The mean lateral and anterior center edge angles (CEAs) were 31.2° and 30°, respectively. The prevalence of asymptomatic hips with pincer deformity was 67% (range 61% to 76% between studies). Pincer deformity was poorly defined (4 studies [15%]; focal anterior overcoverage, acetabular retroversion, abnormal CEA or acetabular index, coxa profunda, acetabular protrusio, ischial spine sign, crossover sign, and posterior wall sign). Only 7 studies reported on labral injury, which was found on MRI without intra-articular contrast in 68.1% of hips.

CONCLUSIONS

FAI morphologic features and labral injuries are common in asymptomatic patients. Clinical decision making should carefully analyze the association of patient history and physical examination with radiographic imaging.

LEVEL OF EVIDENCE

Level IV, systematic review if Level II-IV studies.

Patient-specific anatomical and functional parameters provide new insights into the pathomechanism of cam FAI

BACKGROUND

Femoroacetabular impingement (FAI) represents a constellation of anatomical and clinical features, but definitive diagnosis is often difficult. The high prevalence of cam deformity of the femoral head in the asymptomatic population as well as clinical factors leading to the onset of symptoms raises questions as to what other factors increase the risk of cartilage damage and hip pain.

QUESTIONS/PURPOSES

The purpose was to identify any differences in anatomical parameters and squat kinematics among symptomatic, asymptomatic, and control individuals and if these parameters can determine individuals at risk of developing symptoms of cam FAI.

METHODS

Forty-three participants (n = 43) were recruited and divided into three groups: symptomatic (12), asymptomatic (17), and control (14). Symptomatic participants presented a cam deformity (identified by an elevated alpha angle on CT images), pain symptoms, clinical signs, and were scheduled for surgery. The other recruited volunteers were blinded and unaware whether they had a cam deformity. After the CT data were assessed for an elevated alpha angle, participants with a cam deformity but who did not demonstrate any clinical signs or symptoms were considered asymptomatic, whereas participants without a cam deformity and without clinical signs or symptoms were considered healthy control subjects. For each participant, anatomical CT parameters (axial alpha angle, radial alpha angle, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version) were evaluated. Functional squat parameters (maximal squat depth, pelvic range of motion) were determined using a motion capture system. A stepwise discriminant function analysis was used to determine which of the parameters were most suitable to classify each participant with their respective subgroup.

RESULTS

The symptomatic group showed elevated alpha angles and lower femoral neck-shaft angles, whereas the asymptomatic group showed elevated alpha angles in comparison with the control group. The best discriminating parameters to determine symptoms were radial alpha angle, femoral neck-shaft angle, and pelvic range of motion (p < 0.001).

CONCLUSIONS

In the presence of a cam deformity, indications of a decreased femoral neck-shaft angle and reduced pelvic range of motion can identify those at risk of symptomatic FAI.

Labral injury: radiographic predictors at the time of hip arthroscopy

PURPOSE

The purpose of this study was to investigate the influence of multiple demographic and radiographic findings on the size of labral tears identified at the time of hip arthroscopy.

METHODS

Data were prospectively collected for patients treated with arthroscopic labral repair or debridement from February 2008 to August 2011. Preoperative radiographic and demographic data were collected for 392 patients during the study period. Exclusion criteria included revision surgery and previous hip conditions. An anteroposterior pelvic view, 45° Dunn view, and false-profile view were used to measure Tönnis grade, neck-shaft angle, alpha angle, lateral center edge angle (LCEA), anterior center edge angle (ACEA), acetabular inclination, and the extent of crossover sign when present. At the time of surgery, labral tear size and location were documented for all patients, using traditional acetabular clock face nomenclature for sizing. A multiple linear regression analysis was then performed to assess the correlation of radiographic and demographic findings with the size of the labral tear.

RESULTS

Regression analysis displayed statistical significance for sex (P < .0001), age (P < .0001), and alpha angle (P = .005) with labral tear size. For female patients, Tönnis grade (P = .0004) and neck-shaft angle (P = .004) correlated with labral tear size. This model accounted for only 26% of variation in labral tear size.

CONCLUSIONS

Preoperative risk factors for the extent of labral tear size are male sex, increasing age, and increasing alpha angle. Labral tears were larger in female patients with higher Tönnis grades and lower neck-shaft angles. Measurements of acetabular coverage and version showed no correlation with labral tear size. The majority of labral tear size variation was not accounted for in this model.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

The role of experience level in radiographic evaluation of femoroacetabular impingement and acetabular dysplasia

Accurate radiographic interpretation is essential for properly diagnosing the etiology of pre-arthritic hip pain such as femoroacetabular impingement (FAI) and acetabular dysplasia (AD); however, radiographic interpretation can be significantly influenced by the observer’s experience level. This study assesses the accuracy and inter- and intraobserver reliability in the radiographic evaluation of FAI and AD based on experience level. Fifty-five patients diagnosed with FAI, AD or normal hip morphology were identified from the principal investigator’s institutional database. Four observers performed an independent and blinded radiographic review, assessing 14 radiographic parameters and an interpretation of a final diagnosis. A second radiographic evaluation of 20 preselected cases was completed 6 weeks after the initial reading to assess intraobserver reliability. Inter- and intraobserver reliability was determined using Cohen’s Kappa Coefficient (κ) and intraclass correlation coefficient (ICC) for continuous parameters in a four-rater design. Interobserver reliability was highest across experience levels for lateral centre edge angle (ICC = 0.92) and alpha angle (ICC = 0.90) and lowest (κ < 0.3, ICC < 0.3) for joint congruency and detection of herniation pits. Intraobserver reliability was highest for acetabular depth (κ = 0.89) and alpha angle (ICC = 0.80) and lowest for head–neck offset ratio and Tönnis grade. Final diagnosis was consistent with the original blinded clinical diagnosis 75–84% of the time across four experience levels. The attending orthopaedic hip surgeon demonstrated greatest diagnostic sensitivity but lowest specificity for making an accurate radiographic diagnosis. Subjective parameters must be redefined, and objective parameters must be further developed to improve the reliability of accurately diagnosing FAI or AD.

What is normal femoral head/neck anatomy? An analysis of radial CT reconstructions in adolescents

BACKGROUND

Cam morphology in femoroacetabular impingement has been implicated in the development of osteoarthritis. The alpha angle and femoral head/neck offset are widely used to determine femoral head asphericity. To our knowledge, no study has evaluated the alpha angle circumferentially using three-dimensional imaging in a population of healthy individuals of adolescent age.

QUESTIONS/PURPOSES

We sought to (1) determine normal values for the alpha angle in adolescents, (2) define the location along the neck with the highest alpha angle, and (3) determine normal femoral head and neck radii and femoral head/neck offset.

METHODS

Fifty CT scans from a database of scans obtained for reasons not related to hip pain were studied. The average age of the subjects was 15 years (range, 14-16 years). Alpha angle and femoral head/neck offset were measured circumferentially.

RESULTS

The alpha angle averaged 40.66 ± 4.46 mm for males and 37.77 ± 5.65 mm for females. The alpha angle generally was highest between the 11:40 and 12:40 o'clock and between the 6:00 and 7:40 o'clock positions. The femoral head radius was 24.53 ± 1.74 mm for males and 21.94 ± 1.13 mm for females, and the femoral neck radius was 16.14 ± 2.32 mm for males and 13.82 ± 2.38 mm for females. The mean femoral head/neck offset was 8.39 ± 1.97 mm for males and 8.13 ± 2.27 mm for females.

CONCLUSIONS

In this healthy population of 14- to 16-year-old subjects, the highest alpha angle was at the superior and inferior aspects of the heads rather than at the anterosuperior aspect. This information will provide benchmark values for distinction between normal and abnormal morphologic features of the femoral head.

Femoroacetabular impingement: a review of diagnosis and management

Hip pain in adults has traditionally been associated with osteoarthritis in the joint. However, many young patients with hip pain do get referred to orthopaedic surgeons without arthritis. Subtle bony and soft tissues abnormalities can present with hip pain in the active young adult. These abnormalities can lead to premature arthritis. With the improvements in clinical examination for hip impingement, radiological imaging using magnetic resonance arthrography (MRA) and or computed tomograms (CT) Scans, these lesions are being detected early. Though the cause of primary osteoarthritis is unknown, it is suggested that femoro-acetabular impingement (FAI) may be responsible for the progression of the disease in these patients. FAI is a pathological condition leading to abutment between the proximal femur and the acetabular rim. Two different mechanisms are described, although a combination of both is seen in clinical practice. Cam impingement is a result of reduced anterior femoral head neck offset. Pincer lesion is caused by abnormalities on the acetabular side. FAI due to either mechanism can lead to chondral lesions and labral pathology. Patients present with groin pain and investigated with radiographs, CT and MRA. Surgery is the treatment of choice. Open or arthroscopic exploration of the hip is undertaken with bony resection to improve the femoral head neck junction with resection or repair of the damaged labrum. This may involve femoral osteochondroplasty for the cam lesion and acetabular rim resection for pincer lesion. There is no difference in outcome between open and arthroscopic surgery for FAI.