Acetabular overcoverage in the horizontal plane: an underdiagnosed trigger of early hip arthritis. A CT scan study in young adults

Association between acetabular coverage over femoral head and rate of joint space narrowing in non-arthritic hips

Aims

This study was performed to investigate the association between the acetabular morphology and the joint space narrowing rate (JSNR) in the non-arthritic hip.

Methods

We retrospectively reviewed standing whole-leg radiographs of patients who underwent knee arthroplasty from February 2012 to March 2020 at our institute. Patients with a history of hip surgery, Kellgren-Lawrence grade ≥ II hip osteoarthritis, or rheumatoid arthritis were excluded. The hip JSNR was measured, and the normalized JSNR (nJSNR) was calculated by calibrating the joint space width with the size of the femoral head in 395 patients (790 hips) with a mean age of 73.7 years (SD 8.6). The effects of the lateral centre-edge angle (CEA) and acetabular roof obliquity (ARO) in the standing and supine positions were examined using a multivariate regression model.

Results

The mean JSNR and nJSNR were 0.115 mm/year (SD 0.181) and 2.451 mm/year (SD 3.956), respectively. Multivariate regressions showed that older age was associated with a larger nJSNR (p = 0.010, standardized coefficient (SC) 0.096). The quadratic curve approximation showed that the joint space narrowing was smallest when the CEA was approximately 31.9°. This optimal CEA was the same in the standing and supine positions. Multivariate regressions were separately performed for joints with a CEA of < 31.9° and > 31.9°. When the CEA was < 31.9°, a smaller CEA was associated with a larger nJSNR (p < 0.001, SC 0.282). When the CEA was > 31.9°, a larger CEA was associated with a larger nJSNR (p = 0.012, SC 0.152). The ARO was not associated with the nJSNR.

Conclusion

Both insufficient coverage and over-coverage of the acetabulum over the femoral head were associated with increased joint space narrowing in hips that were non-arthritic at baseline. The effects of insufficient coverage were stronger than those of overcoverage.

Impact of a Unilateral High Tibial Osteotomy With a Large Correction on Functional Lateral Acetabular Coverage of the Hip Joint

Background

Changes in limb length and coronal pelvic tilt, which occur along with changes in limb alignment, may affect the functional lateral acetabular coverage of the hip joint under weightbearing conditions.

Purpose

To analyze the functional lateral acetabular coverage after unilateral closed-wedge and open-wedge high tibial osteotomies with a large wedge correction of ≥10 mm.

Study Design

Cohort study; Level of evidence, 3.

Methods

A retrospective analysis was conducted for 107 unilateral closed-wedge high tibial osteotomies (CWHTOs) and 100 unilateral open-wedge high tibial osteotomies (OWHTOs) with a wedge correction of ≥10 mm and without correction loss during a 2-year follow-up. Limb length and coronal pelvic tilt were measured. Functional lateral acetabular coverage was evaluated using the lateral center-edge angle (LCEA), acetabular index, sharp angle, and femoral head extrusion index (FHEI) with reference to the ground horizontal line. Appropriate ranges of the LCEA (22° to 40°), acetabular index (-8° to 14°), sharp angle (34° to 43°), and FHEI (11% to 27%) were investigated.

Results

Limb length significantly decreased after CWHTO (-7.2 mm) and increased after OWHTO (11.5 mm). The pelvis of the operative limb tilted downward after CWHTO (-1.0°) and upward after OWHTO (2.1°). The mean parameters for functional lateral acetabular coverage significantly changed toward more coverage after CWHTO and less coverage after OWHTO (change in LCEA, acetabular index, sharp angle, and FHEI = 1.2°, -1.1°, -1.0°, and -0.7%, respectively, in CWHTO and -1.3°, 1.8°, 1.6°, and 2.7%, respectively, in OWHTO). When evaluating the appropriateness of each parameter for coverage, cases of conversions from undercoverage to appropriate coverage (1.9% to 4.7%) and appropriate to overcoverage (0.9% to 5.6%) after CWHTO and from overcoverage to appropriate coverage (0% to 8%) and appropriate to undercoverage (2% to 7%) after OWHTO were observed.

Conclusion

The functional lateral acetabular coverage increased after CWHTO and decreased after OWHTO. Surgeons may want to consider the acetabular coverage of the ipsilateral hip joint when performing a unilateral high tibial osteotomy with a large correction.

ASD with high pelvic retroversion develop changes in their acetabular orientation during walking

Introduction

It was hypothesized that pelvic retroversion in Adult Spinal Deformity (ASD) can be related to an increased hip loading explaining the occurrence of hip-spine syndrome.

Research question

How pelvic retroversion can modify acetabular orientation in ASD during walking?

Methods

89 primary ASD and 37 controls underwent 3D gait analysis and full-body biplanar X-rays. Classic spinopelvic parameters were calculated from 3D skeletal reconstructions in addition to acetabular anteversion, abduction, tilt, and coverage. Then, 3D bones were registered on each gait frame to compute the dynamic value of the radiographic parameters during walking. ASD patients having a high PT were grouped as ASD-highPT, otherwise as ASD-normPT. Control group was divided in: C-aged and C-young, age matched to ASD-hightPT and ASD-normPT respectively.

Results

25/89 patients were classified as ASD-highPT having a radiographic PT of 31° (vs 12° in other groups, p ​< ​0.001). On static radiograph, ASD-highPT showed more severe postural malalignment than the other groups: ODHA ​= ​5°, L1L5 ​= ​17°, SVA ​= ​57.4 ​mm (vs 2°, 48° and 5 ​mm resp. in other groups,all p ​< ​0.001). During gait, ASD-highPT presented a higher dynamic pelvic retroversion of 30° (vs 15° in C-aged), along with a higher acetabular anteversion of 24° (vs 20°), external coverage of 38° (vs 29°) and a lower anterior coverage of 52° (vs 58°,all p ​< ​0.05).

Conclusion

ASD patients with severe pelvic retroversion showed an increased acetabular anteversion, external coverage and lower anterior coverage during gait. These changes in acetabular orientation, computed during walking, were shown to be related to hip osteoarthritis.

Posterior acetabular wall morphology is an independent risk factor that affects the occurrence of acetabular wall fracture in patients with traumatic, posterior hip dislocation

PURPOSE

Smaller posterior acetabular walls have been shown to independently influence the risk for bipolar hip dislocation. We asked whether differences would also be observed in patients with traumatic posterior hip dislocation with and without posterior wall fractures.

METHODS

Between 2012 and 2020 we observed 67 traumatic posterior hip dislocations. Of these, 43 traumatic posterior hip dislocations in 41 patients met the inclusion criteria. Eighteen dislocations were excluded with an acetabular fracture other than posterior wall fracture and six dislocations had insufficient computed tomography (CT) data. The mean age was 41 ± 11 years, 32 males and nine females. We observed 26 traumatic hip dislocations with posterior wall fractures and 17 without. All patients underwent polytrauma CT scans and postoperative/postinterventional pelvic CT scans. On axial CT-scans, posterior wall determining angles were measured.

RESULTS

Patients with posterior wall fractures were not significantly older than patients without posterior wall fractures (42 ± 12 vs. 38 ± 10 years; p = 0.17). Patients without posterior wall fractures had significantly smaller posterior acetabular sector angles (84° ± 10°) than did patients with posterior wall fractures (105° ± 12°) (p < 0.01; OR 1.178). Likewise, the posterior wall angle was significantly smaller in patients without posterior wall fracture (62° ± 9°) than in those with posterior wall fractures (71° ± 8°) (p < 0.01; OR 1.141).

CONCLUSION

Both posterior acetabular sector angle and posterior wall angle are independent factors determining the posterior wall fracture morphology in patients with traumatic posterior hip dislocation. Age and the observed trauma mechanism did not differentiate between traumatic posterior hip dislocations with and without posterior wall fractures.

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.

Multi-landmark environment analysis with reinforcement learning for pelvic abnormality detection and quantification

Morphological abnormalities of the femoroacetabular (hip) joint are among the most common human musculoskeletal disorders and often develop asymptomatically at early easily treatable stages. In this paper, we propose an automated framework for landmark-based detection and quantification of hip abnormalities from magnetic resonance (MR) images. The framework relies on a novel idea of multi-landmark environment analysis with reinforcement learning. In particular, we merge the concepts of the graphical lasso and Morris sensitivity analysis with deep neural networks to quantitatively estimate the contribution of individual landmark and landmark subgroup locations to the other landmark locations. Convolutional neural networks for image segmentation are utilized to propose the initial landmark locations, and landmark detection is then formulated as a reinforcement learning (RL) problem, where each landmark-agent can adjust its position by observing the local MR image neighborhood and the locations of the most-contributive landmarks. The framework was validated on T1-, T2- and proton density-weighted MR images of 260 patients with the aim to measure the lateral center-edge angle (LCEA), femoral neck-shaft angle (NSA), and the anterior and posterior acetabular sector angles (AASA and PASA) of the hip, and derive the quantitative abnormality metrics from these angles. The framework was successfully tested using the UNet and feature pyramid network (FPN) segmentation architectures for landmark proposal generation, and the deep Q-network (DeepQN), deep deterministic policy gradient (DDPG), twin delayed deep deterministic policy gradient (TD3), and actor-critic policy gradient (A2C) RL networks for landmark position optimization. The resulting overall landmark detection error of 1.5 mm and angle measurement error of 1.4° indicates a superior performance in comparison to existing methods. Moreover, the automatically estimated abnormality labels were in 95% agreement with those generated by an expert radiologist.

Hip joint range of motion is restricted by pain rather than mechanical impingement in individuals with femoroacetabular impingement syndrome

INTRODUCTION

Discerning whether range of motion (ROM) is restricted by morphology or other pain sources is challenging in patients with femoroacetabular impingement syndrome (FAIS). Computed tomography (CT) motion simulation provides a hypothetical ROM based on morphology. This study aimed to explore associations between ROM measured using CT motion simulation and maximum passive ROM measured clinically using three dimensional (3D) motion analysis in patients with FAIS, prior to and post arthroscopic hip surgery.

MATERIALS AND METHODS

Eight males with FAIS (in total 12 hip joints) were included in this explorative feasibility study. Participants were examined using CT according to a low-dose protocol prior to and 7-months post arthroscopic surgery. Software was used to simulate at which ROM the impingement would occur. With the hip in 90 degrees' flexion, maximum passive range of internal hip rotation, and maximum passive internal hip rotation coupled with adduction was examined clinically using 3D motion analysis pre- and postoperatively. Spearman rank correlation coefficients and linear regressions examined associations between methods.

RESULTS

Preoperatively, the correlation between maximum internal hip rotation measured using CT motion simulation and 3D motion analysis was strong (r = 0.71, p = 0.009). Linear regressions demonstrated that maximal internal rotation measured using CT motion simulation was predominantly larger than when measured using 3D motion analysis. Postoperatively, and when maximum internal rotation was coupled with adduction, no correlations were found between the two methods.

CONCLUSIONS

The hypothetical morphology restricted ROM is larger than clinically assessed pain restricted ROM, both prior to and post hip arthroscopy. These findings suggest that ROM is restricted by pain rather than mechanical, morphology-based impingement in individuals with FAIS.

Anthropometry of the proximal femur and femoral head in children/adolescents using three-dimensional computed tomography-based measurements

Purpose

Defining normal anthropometric ranges of proximal femur and femoral head for each age group in children/adolescents is a necessity when differentiating normal anatomical variants from pathological deformities. Aim of this study is to define a set of normal anthropometric parameters based on 3D-CT measurements in normal asymptomatic children/adolescents and analyse the variations arising depending on age, side, and/or gender.

Methods

Morphology of the proximal femur was retrospectively assessed in 170 hips (85 children, < 15 years). Measurements included covered femoral head volume (CFHV), femoral head diameter (FHD), femoral head extrusion index (FHEI), coronal alpha angle (CAA), lateral centre-edge angle (LCEA), anterior (AOS) and posterior head-neck offset (POS) and femoral neck-shaft angle (FNSA). Correlation analyses as well as inter- and intra-rater reliability were performed.

Results

CFHV, LCEA, FHD and AOS/POS increased with age and FHEI, CAA, and FNSA decreased with age. None of the measurements correlated with the side. AOS showed a poor correlation with gender. Rapid growth phases were observed at the age of 1, 7 and 11. The inter- and intra-rater reliability was high (range ICC 0.8–0.99 Cronbach alpha 0.86–0.99).

Conclusion

This data delivers a description of growth phases as well as gender and age-correlated reference values of the proximal femoral morphology that could be used by paediatricians and orthopaedic/paediatric surgeons to early diagnose proximal femur deformities and provide guidance in the planning of possible operations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00276-021-02841-3.

Is hip morphology a risk factor for developing hip osteoarthritis? A systematic review with meta-analysis

OBJECTIVE

To appraise the highest evidence on hip morphology as a risk factor for developing hip osteoarthritis (OA).

DESIGN

We searched for studies evaluating the association between radiological hip morphology parameters and the prevalence, incidence or progression of hip OA (based on different radiographic and clinical criteria) in the MEDLINE, EMBASE, Web of Science, Scopus, Cochrane Library and PEDro databases from inception until June 2020. Prospective and cross-sectional studies were separately evaluated. Data are presented as odds ratios (OR) with 95% confidence intervals (CI).

RESULTS

We included 9 prospective and 21 cross-sectional studies in the meta-analysis, and evaluated 42,831 hips from 25,898 individuals (mean age: 59 years). Prospective studies showed that, compared with control hips, hips with cam morphology (alpha angle >60°; OR = 2.52, 95% CI: 1.83 to 3.46, P < 0.001) or hip dysplasia (lateral center-edge angle (LCEA) <25°; OR = 2.38, 95% CI: 1.84 to 3.07, P < 0.001), but not hips with pincer morphology (LCEA >39°; OR = 1.08, 95% CI: 0.57 to 2.07, P = 0.810), were more likely to develop hip OA than hips without these morphologies. Cross-sectional studies showed a greater prevalence of pincer morphology (LCEA >39°, OR = 3.71, 95% CI: 2.98 to 4.61, P < 0.001) and acetabular retroversion (crossover sign; OR = 2.65, 95% CI: 1.17 to 6.03, P = 0.020) in hips with OA than in control hips.

CONCLUSION

Cam morphology and hip dysplasia were consistently associated with the development of hip OA. Pincer morphology was associated with hip OA in cross-sectional but not in prospective studies. The heterogeneous quantification of pincer morphology on radiographs limits a clear conclusion on its association with hip OA.

Primary cam morphology; bump, burden or bog-standard? A concept analysis

BACKGROUND

Cam morphology, a distinct bony morphology of the hip, is prevalent in many athletes, and a risk factor for hip-related pain and osteoarthritis. Secondary cam morphology, due to existing or previous hip disease (eg, Legg-Calve-Perthes disease), is well-described. Cam morphology not clearly associated with a disease is a challenging concept for clinicians, scientists and patients. We propose this morphology, which likely develops during skeletal maturation as a physiological response to load, should be referred to as primary cam morphology. The aim of this study was to introduce and clarify the concept of primary cam morphology.

DESIGN

We conducted a concept analysis of primary cam morphology using articles that reported risk factors associated with primary cam morphology; we excluded articles on secondary cam morphology. The concept analysis method is a rigorous eight-step process designed to clarify complex 'concepts'; the end product is a precise definition that supports the theoretical basis of the chosen concept.

RESULTS

We propose five defining attributes of primary cam morphology-tissue type, size, site, shape and ownership-in a new conceptual and operational definition. Primary cam morphology is a cartilage or bony prominence (bump) of varying size at the femoral head-neck junction, which changes the shape of the femoral head from spherical to aspherical. It often occurs in asymptomatic male athletes in both hips. The cartilage or bone alpha angle (calculated from radiographs, CT or MRI) is the most common method to measure cam morphology. We found inconsistent reporting of primary cam morphology taxonomy, terminology, and how the morphology is operationalised.

CONCLUSION

We introduce and clarify primary cam morphology, and propose a new conceptual and operational definition. Several elements of the concept of primary cam morphology remain unclear and contested. Experts need to agree on the new taxonomy, terminology and definition that better reflect the primary cam morphology landscape-a bog-standard bump in most athletic hips, and a possible hip disease burden in a selected few.

Risk factors for dislocation after bipolar hemiarthroplasty: a retrospective case-control study of patients with CT data

Purpose

Bipolar hemiarthroplasty has been shown to have a lower rate of dislocation than total hip arthroplasty. However, as the influencing risk factors for bipolar hemiarthroplasty dislocation remain unclear, we aimed to analyse patient and surgeon-specific influencing risk factors for bipolar hemiarthroplasty dislocation.

Methods

We retrospectively analysed patients who were operated between 2012 and 2018 and had dislocated bipolar hemiarthroplasty and matched them to patients without a dislocated bipolar hemiarthroplasty, operated between 2018 and 2019. The study was limited to patients who received either a pre- or postoperative pelvic computed tomography. Besides demographic, morphologic, and physiologic data, we analysed duration of surgery; ASA score; Charlson Comorbidity Index; Almelo Hip Fracture Score; Parker Score; and acetabular morphology angles including acetabular anteversion angle, posterior acetabular sector angle, posterior wall angle, and acetabular roofing.

Results

We included nine patients with a dislocated bipolar hemiarthroplasty and 30 with a non-dislocated bipolar hemiarthroplasty. Patient-specific factors prompting a higher risk for dislocated bipolar hemiarthroplasty were longer duration of surgery (min) (115 ± 50 vs. 80 ± 27, p = 0.01); dementia (56% vs. 13%, p < 0.01); smaller posterior acetabular sector angle (°) (96 ± 6 vs. 109 ± 10, p < 0.01); and smaller posterior wall angle (°) (67 ± 6 vs. 77 ± 10, p = 0.02).

Conclusion

Dementia and insufficient posterior wall angle were associated with higher risk of dislocation in bipolar hemiarthroplasty

No association between femoral or acetabular angles and patient-reported outcomes in patients with femoroacetabular impingement syndrome-results from the HAFAI cohort

Patients with femoroacetabular impingement syndrome (FAIS) are diagnosed using imaging, but detailed description especially the acetabular shape is lacking and may help give more insight to the pathogenesis of FAIS. Furthermore, associations between patient-reported outcomes (PROs) and the radiological angles might highlight which radiological angles affect outcomes experienced by the patients. Hence, the aims of this study were (i) to describe computer tomography (CT) acquired angles in patients with FAIS and (ii) to investigate the association between radiological angles and the Copenhagen Hip and Groin Outcome Score (HAGOS) in patients with FAIS. Patients scheduled for primary hip arthroscopic surgery for FAIS were included. Based on CT, following angles were measured before and 1 year after surgery; femoral anteversion, alpha, lateral centre edge, acetabular index, anterior sector, posterior sector and acetabular anteversion. All patients completed the HAGOS. Sixty patients (63% females) aged 36 ± 9 were included. One year after surgery, significant alterations in the alpha angle and the acetabular index angle were found. Neither baseline PROs nor changes in PROs were associated with the radiological angles or changes in angles. Since neither changes in CT angles nor baseline scores were associated with HAGOS, the improvements felt by patients must origin from somewhere else. These findings further underlines that morphological changes seen at imaging should not be treated arthroscopically without a patient history of symptoms and clinical findings.

Labral tears with axial plane disorders

OBJECTIVES

This study aims to determine if there is an axial plane coverage insufficiency in patients with symptomatic labral tears compared to the contralateral asymptomatic side and healthy control subjects.

PATIENTS AND METHODS

This retrospective study was conducted between December 2017 and January 2019. Thirty patients (21 males, 9 females; mean age 28 years; range, 20 to 36 years) operated due to unilateral symptomatic acetabular labral tears secondary to femoroacetabular impingement were evaluated. Twenty asymptomatic patients (13 males, 7 females; mean age 27±9 years; range, 19 to 36 years) were included in the control group. The relationship between acetabular morphology and labral tear was investigated with the comparison of unilateral symptomatic hips with contralateral asymptomatic hips and the control group by using radiological parameters on plain radiographs and computed tomography.

RESULTS

When the patient group symptomatic side was compared to the control group, acetabular anteversion angle (A A A) and alpha (α) angle were higher, while posterior acetabular sector angle and horizontal acetabular sector angle were lower. When the asymptomatic side was compared to the control group, AAA was higher in the patient group. There was no difference between the symptomatic and asymptomatic sides in the patient group; the symptomatic side yielded a higher α; angle.

CONCLUSION

Posterior axial plane coverage deficiency in combination with cam deformity (increased α angle) seems to play a role in the pathogenesis of symptomatic acetabular labral tears, even creating a side-to-side difference in some individuals.

Acetabular posterior wall morphology. A CT-based method to distinguish two acetabular posterior wall types

Background

The anatomy of the posterior wall of the acetabulum is important for the hip stability. We wanted to know whether differences can be observed.

Material and methods

On lateral 3D pelvic CT reconstruction of the pelvis two types were identified. On axial CT-images acetabular angles were determined.

Results

We observed 35 type I acetabular and 61 type II acetabular. Posterior acetabular sector angle was 114° in type I and 94° in type II acetabular (p < 0.01). At an cut-off angle of 100° we could predict the type of acetabulum.

Conclusions

We could describe reference values for the posterior wall to distinguish two morphological types.

Osteoarthritis year in review 2018: imaging

PURPOSE

To provide a narrative review of the most relevant original research published in 2017/2018 on osteoarthritis imaging.

METHODS

The PubMed database was used to recover all relevant articles pertaining to osteoarthritis and medical imaging published between 1 April 2017 and 31 March 2018. Review articles, case studies and in vitro or animal studies were excluded. The original publications were subjectively sorted based on relevance, novelty and impact.

RESULTS AND CONCLUSIONS

The publication search yielded 1,155 references. In the assessed publications, the most common imaging modalities were radiography (N = 708) and magnetic resonance imaging (MRI) (355), followed by computed tomography (CT) (220), ultrasound (85) and nuclear medicine (17). An overview of the most important publications to the osteoarthritis (OA) research community is presented in this narrative review. Imaging studies play an increasingly important role in OA research, and have helped us to understand better the pathophysiology of OA. Radiography and MRI continue to be the most applied imaging modalities, while quantitative MRI methods and texture analysis are becoming more popular. The value of ultrasound in OA research has been demonstrated. Several multi-modality predictive models have been developed. Deep learning has potential for more automatic and standardized analyses in future OA imaging research.

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.