The anterior hip capsule is thinner in dysplastic hips: a study comparing different young adult hip patients

Imaging characteristics of hip joint microinstability: a case-control study of hip arthroscopy patients

OBJECTIVES

Hip microinstability is a clinical entity increasingly recognized and treated but challenging to diagnose with a lack of objective criteria. This study assessed the prevalence and diagnostic accuracy of different imaging findings for hip microinstability on radiograph and MR.

METHODS

A retrospective case-control study of 224 hips treated with arthroscopic surgery by a single orthopedic surgeon, 112 hips with clinical microinstability and 112 controls without. Pre-operative radiograph and MRI/MRA imaging were evaluated by two musculoskeletal radiologists to assess morphological parameters and imaging signs reportedly associated with hip microinstability.

RESULTS

Four imaging features reached significance as predictors of microinstability via three-step logistic regression: labral hyperplasia and decreased lateral center edge angle on MR (OR 2.45 and 0.93, respectively) and the absence of positive ischial spine sign and absence of osteophytes on radiographs (OR 0.47 and 0.28, respectively). Increased acetabular anteversion and absence of cam lesions were more likely in the microinstability group (p = 0.02 and 0.04, respectively), but not independent predictors. Labral tears, chondral loss, abnormal ligamentum teres, anterior capsule thinning, iliocapsularis to rectus femoris ratio, posterior crescent sign, cliff sign, and femoro-epiphyseal acetabular roof (FEAR) index were not associated with microinstabillity.

CONCLUSION

Imaging features may be predictive of hip microinstability in some cases. Decreased LCEA, increased acetabular anteversion, and labral hyperplasia were associated with microinstability in this study, while many other published imaging findings were not. Imaging remains complementary, but not definitive, in the diagnosis of hip microinstability.

Femoral Anteversion Angle as a Predictor of Anterior Hip Labral Length in Patients With Femoroacetabular Impingement Syndrome

Background

The relationship between hip rotational abnormalities and hip labral size has not been fully investigated.

Purposes

To (1) examine the correlation between rotational abnormalities of the hip and labral size, while also identifying other predictive values for hip labral size, and (2) explore whether femoral torsion will lead to increased labral size.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

A total of 180 patients (180 hips) with femoroacetabular impingement syndrome (FAIS) (mean age, 36.81 ± 10.17 years; 67 male, 113 female) who underwent hip arthroscopic surgery between January 2021 and May 2022 were included. The femoral version (FV), acetabular version, and combined version angles were measured on computed tomography, and the labral length and height at the 12-o'clock and 3-o'clock positions were measured on magnetic resonance imaging. The hips were categorized into 3 groups based on FV angle: small (SFV; <10°); moderate (MFV; ≥10° and ≤20°), and large (LFV; >20°), and group comparisons were performed. Linear correlation and regression analysis were employed.

Results

Predictive factors for labral length were FV angle (β = 0.298; P = .02), sex (β = -0.302; P < .001), and age (β = -0.169; P = .016) at 3 o'clock and lateral center-edge angle (LCEA; β = -0.208; P = .005) and age (β = -0.186; P = .011) at 12 o'clock. FV angle was positively correlated with labral length at 3 o'clock (r = 0.267; P < .001) and negatively correlated with age (r = -0.222; P = .003) and female sex (r = -0.202; P = .006). LCEA (r = -0.227; P = .002) and age (r = -0.205; P = .006) were negatively correlated with labral length at 12 o'clock. Labral length at 3 o'clock was significantly different between the LFV (n = 49 hips), MFV (n = 65 hips), and SFV (n = 66 hips) groups (9.85 ± 2.28, 8.89 ± 2.44, and 8.30 ± 2.05 mm, respectively; P = .027 for LFV vs MFV; P < .001 for LFV vs SFV).

Conclusion

Patients with FAIS who exhibited a higher FV angle were at a greater likelihood of having a larger anterior labral length. Increased femoral anteversion and decreased LCEA, male sex, and younger age were significantly associated with longer hip labral length.

Is hip capsule morphology associated with hip pain in patients without another structural correlate?

OBJECTIVE

The goals of this study were (i) to assess the association between hip capsule morphology and pain in patients without any other MRI abnormalities that would correlate with pain and (ii) to investigate whether hip capsule morphology in hip pain patients is different from that of controls.

METHODS

In this study, 76 adults with hip pain who did not show any structural abnormalities on MRI and 46 asymptomatic volunteers were included. Manual segmentation of the anterior and posterior hip capsules was performed. Total and mean anterior hip capsule area, posterior capsule area, anterior-to-posterior capsule area ratio, and medial-to-lateral area ratio in the anterior capsule were quantified. Differences between the pain and control groups were evaluated using logistic regression models.

RESULTS

Patients with hip pain showed a significantly lower anterior-to-posterior area ratio as compared with the control group (p = 0.002). The pain group's posterior hip capsule area was significantly larger than that of controls (p = 0.001). Additionally, the ratio between the medial and lateral sections of the anterior capsule was significantly lower in the pain group (p = 0.004).

CONCLUSIONS

Patients with hip pain are more likely to have thicker posterior capsules and a lower ratio of the anterior-to-posterior capsule area and thinner medial anterior capsules with a lower ratio of the medial-to-lateral anterior hip capsule compartment, compared with controls.

CLINICAL RELEVANCE STATEMENT

During MRI evaluations of patients with hip pain, morphology of the hip capsule should be assessed. This study aims to be a foundation for future analyses to identify thresholds distinguishing normal from abnormal hip capsule measurements.

KEY POINTS

• Even with modern image modalities such as MRI, one of the biggest challenges in handling hip pain patients is finding a structural link for their pain. • Hip capsule morphologies that correlated with hip pain showed a larger posterior hip capsule area and a lower anterior-to-posterior capsule area ratio, as well as a smaller medial anterior capsule area with a lower medial-to-lateral anterior hip capsule ratio. • The hip capsule morphology is correlated with hip pain in patients who do not show other morphology abnormalities in MRI and should get more attention in clinical practice.

Magnetic Resonance Imaging and Magnetic Resonance Arthrography Are Both Reliable and Similar When Measuring Hip Capsule Thickness in Patients With Femoroacetabular Impingement Syndrome

Purpose

To propose an accurate method of measuring hip capsular thickness in patients with femoroacetabular impingement syndrome and to compare the reliability of these measurements between magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRA).

Methods

A previously established database of patients with femoroacetabular impingement syndrome (FAIS) was used to identify candidates with preoperative MRI or MRA from November 2018 to June 2021. Two reviewers independently examined preoperative imaging for 85 patients. Capsular thickness was measured in 12 standardized locations. Intraclass correlation coefficients (ICCs) were calculated using an absolute-agreement, 2-way random-effects model. Using the same method, 30 patients were randomly selected for repeat measurements by 1 reviewer following a washout period. Ten additional patients with preoperative MRI and MRA of the same hip were identified to compare measurements between modalities using paired samples t test.

Results

ICCs for measurements on MRIs and MRAs using these proposed measurements to compare inter-rater reliability were 0.981 and 0.985. ICCs calculated using measurements by a single reviewer following a washout period for intrarater reliability were 0.998 and 0.991. When comparing MRI and MRA measurements in the same patient, t test for all pooled measurements found no difference between modality (P = .283), and breakdown of measurements by quadrant found no difference in measurements (P > .05), with the exception of the inferior aspect of the capsule on coronal sequences (P = .023).

Conclusions

In patients with FAIS, both MRI and MRA have excellent reliability for quantifying hip capsular thickness. A difference in capsular thickness was found only when comparing MRI and MRA on inferior coronal aspects of the hip capsule, indicating interchangeability of these imaging modalities when measuring the clinically important aspects of the hip capsule.

Level of Evidence

Level IV, diagnostic case series.

Association Between Anterior Hip Capsule Thickening and Sagittal Pelvic Alignment Among Patients With Developmental Dysplasia of the Hip

INTRODUCTION

The pathogenesis and pathology of secondary osteoarthritis (OA) of the hip, which is mainly due to developmental dysplasia of the hip (DDH), in Japan are obscure. There are some reports on the thickening of the hip capsule, but the relationship between the thickness of the hip capsule and the pelvic alignment due to hip deformity is not well known. This research investigated whether the capsular thickness of female DDH patients was related to pelvic alignment.

METHODS

This single-center cross-sectional study included female patients aged 50-79 years (n=13) who had undergone primary total hip arthroplasty (THA) due to secondary hip OA with a background of DDH. The part of the hip capsule including the iliofemoral ligament was resected and measured directly with a digital caliper. The Sharp angle, center-edge (CE) angle, sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), and lumbar lordosis angle (LLA) were measured with an X-ray image to investigate the relationship between the capsular thickness and the pelvic posture.

RESULTS

Pearson's correlation coefficient showed a negative correlation between hip capsular thickness and Sharp angle (r=-0.57, p>0.05). No significant correlation was found between the thickness of the hip capsule and the sagittal X-ray parameters including SS, PT, PI, LLA, and CE angle in the coronal plane.

CONCLUSION

The thickness of the hip capsule is moderately associated with the Sharp angle on the coronal plane. The results of this study suggest that the thickness of the joint capsule does not necessarily relate to the degenerative process among patients with DDH and the process can be complex to apply two-dimensional postural indices for the explanation.

Ultrasound had high accuracy in measuring hip joint capsule thickness

BACKGROUND

The hip joint capsule is an essential component of hip joint function and stability, and its thickness is closely associated with certain medical conditions, surgical outcomes, and rehabilitation treatments. Currently, in clinical practice, hip joint capsule thickness is predominantly measured using magnetic resonance imaging (MRI), with limited utilization of ultrasound examinations for this purpose.

METHODS

We retrospectively evaluated patients who visited our Sports Medicine Department between February 2017 and March 2023 and underwent both hip joint MRI and ultrasound imaging on the same side. All patients had undergone preoperative hip joint MRI and ultrasound examinations, with the time gap between the two examinations not exceeding three months. Measurements of hip joint capsule thickness were taken on both MRI and ultrasound images for the same patients to analyze their consistency. Additionally, we measured the alpha angle, lateral center-edge angle, acetabular anteversion angle, and femoral anteversion angle of the patients' hip joints and analyzed their correlation with hip joint capsule thickness measure by ultrasound.

RESULTS

A total of 307 patients were included in this study, with hip joint capsule thickness measured by MRI and ultrasound being 5.0 ± 1.2 mm and 5.0 ± 1.5 mm, respectively. The Bland-Altman analysis demonstrates good agreement or consistency. The paired t-test resulted in a p-value of 0.708, indicating no significant statistical difference between the two methods. The correlation analysis between acetabular anteversion angle and ultrasound-measured capsule thickness yielded a p-value of 0.043, indicating acetabular anteversion angle and capsular thickness may have negative correlation.

CONCLUSIONS

The measurements of joint capsule thickness obtained through ultrasound and MRI showed good consistency, suggesting that ultrasound can be used in clinical practice as a replacement for MRI in measuring hip joint capsule thickness. There was a significant correlation between acetabular anteversion angle and hip joint capsule thickness, indicating potential for further research in this area.

Editorial Commentary: Femoral Version and Capsular Thickness Analysis in Hip Preservation Surgery-Surgical Indications Are as Important as Surgical Technique

Optimal treatment of patients with femoroacetabular impingement syndrome requires both thoughtful decision-making and skillful operative technique. Traditional evidence-based literature and routine clinical practice overemphasize the role of the alpha angle on the femoral side and lateral center edge angle on the acetabular side. Femoral and acetabular version are critical values that influence outcomes and warrant measurement and consideration. Without version analysis, an uniformed, possibly poor, decision may be made. The literature and clinical practice also place dichotomous emphasis on labral (torn/intact) and capsular (torn/intact) integrity, with minimal appreciation of the morphological details of both. Not all capsules are created equal. "Normal" capsule thickness is a nebulous concept, with thinner anterior capsules more prone to anterior instability. Intuitively, it biomechanically stands to reason that excessive femoral anteversion (and excessive anterior cranial and central acetabular version) would place additional stress on the anterior capsule. Excessive femoral anteversion is associated with a thinner anterior capsule. Whether the latter is a reactive process (implies causation) or simply 2 concordant metrics (only correlation) has yet to be determined. In patients with nonarthritic hip pain, comprehensive quantitative consideration of both femoral and acetabular version and capsular thickness determines the optimal hip preservation procedure. Surgical indications are as important as surgical technique.

Femoral Anteversion Is Associated With a Thinner Anterior Capsule in Patients With Femoroacetabular Impingement Syndrome

PURPOSE

To measure femoral torsion on computed tomography images in patients with femoroacetabular impingement syndrome and explore whether femoral torsion was significantly correlated with anterior capsular thickness.

METHODS

Prospectively collected data of surgical patients were retrospectively reviewed. Only patients aged 16 to 55 years who underwent primary hip surgery were included in this study. Patients with a history of revision hip surgery, previous knee surgery, hip dysplasia, hip synovitis, and/or incomplete radiographs and medical records were excluded from the study. Femoral torsion was measured via computed tomography imaging using transcondylar slices of the knee. Anterior capsular thickness was measured using oblique-sagittal sequences on a 3.0-T magnetic resonance imaging system. The association between anterior capsular thickness and related variables, including femoral torsion, was assessed via multiple linear regression. The patients were then divided into 2 groups to further confirm the effect of femoral torsion on capsular thickness: Patients in the study group had hips with moderate (20°-25°) or severe (>25°) antetorsion, whereas patients in the control group had hips with normal torsion (5°-20°) or retrotorsion (<5°). Anterior capsular thickness was also compared between the 2 groups.

RESULTS

A total of 156 patients (89 female patients [57.1%] and 67 male patients [42.9%]) were finally included in the study. The mean age and body mass index of the included patients were 35.8 ± 11.2 years and 22.7 ± 3.5, respectively. The mean femoral torsion for the entire study population was 15.9° ± 8.9°. Multivariable regression analysis showed that femoral torsion (P < .001) and sex (P = .002) were significantly correlated with anterior capsular thickness. Propensity-score matching yielded 50 hips in the study group and 50 hips in the control group on femoral torsion subanalysis. The results showed that anterior capsular thickness was significantly smaller in the study group than in the control group (3.8 ± 0.5 mm vs 4.7 ± 0.7 mm, P < .001).

CONCLUSIONS

Femoral torsion is significantly inversely correlated with anterior capsular thickness.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Femoral neck-shaft angle can predict the anterior capsular thickness in patients with femoracetabular impingement syndrome

PURPOSE

To measure the femoral neck-shaft angle (NSA) on computed tomography (CT) images in femoracetabular impingement syndrome (FAIS) patients and explore its relationship with the anterior capsular thickness (ACT).

METHODS

A retrospective review of prospectively collected data from 2022 was performed. Inclusion criteria included: primary hip surgery, 18 to 55 years of age, and CT imaging of the hips. Exclusion criteria included: revision hip surgery, mild or borderline hip dysplasia, hip synovitis, and incomplete radiographs and medical records. NSA was measured on CT imaging. ACT was measured using magnetic resonance imaging (MRI). Multiple linear regression was performed to assess the association between ACT and related variables, including age, sex, body mass index (BMI), lateral center-edge angle (LCEA), alpha angle, Beighton test score (BTS), and NSA.

RESULTS

A total of 150 patients were included. The mean age, BMI, and NSA were 35.8 ± 11.2 years, 22.8 ± 3.5, and 129.4° ± 7.7°, respectively. Eighty-five (56.7%) patients were females. Multivariable regression analysis revealed that NSA (P = 0.002) and sex (P = 0.001) were significantly negatively correlated with ACT. Age, BMI, LCEA angle, alpha angle, and BTS were not correlated with ACT.

CONCLUSIONS

This study confirmed that NSA significantly predicts ACT. A decrease in the NSA by 1° increases the ACT by 0.24 mm.

LEVEL OF EVIDENCE

Level III.