Capsular laxity of the hip: findings at magnetic resonance arthrography

Utilization trends for MR arthrography of the hip and shoulder: a retrospective cross-sectional analysis of 20-year data from a tertiary care academic medical center

OBJECTIVE

The purpose of this study is to analyze changes in the utilization of MRA of the hip and shoulder at a large tertiary care academic medical center during a period of significant technological advancements over the last 20 years.

MATERIALS AND METHODS

This retrospective cross-sectional analysis identified MRA of the hip and shoulder performed at our institution over a 20-year period (2/2003-2/2023) in relation to the total number of MR hip and shoulder examinations during the same period. Patient characteristics and referring provider demographic information were extracted. Descriptive statistics and trend analysis were performed.

RESULTS

The total number of MRIs of the hip and shoulder increased overall, with small dips in 2020 and 2022. MRA of the hip increased significantly over the first 10 years of the study period (p = 0.0005), while MRA of the shoulder did not change significantly (p = 0.33). The proportion of both MRA of the hip and shoulder declined over the last 10 years (hip, p = 0.0056; shoulder, p = 0.0017). Over the same period, there was significant increase in the proportion of examinations performed at 3 Tesla versus 1.5 (p < 0.0001).

CONCLUSION

Overall, there was a downward trend in MR shoulder and hip arthrogram utilization in the second half of this 20-year study period. However, utilization varied somewhat by referring specialties and credentials. These changes are likely reflective of both improvements in image quality and evolving practice recommendations. Awareness of such trends may be valuable in ensuring appropriate patient care, as well as for anticipating the needs of a musculoskeletal radiology practice.

Capsular and retinaculum thickening in type II mucopolysaccharidosis: a novel MRI finding

Mucopolysaccharidoses (MPS) are a group of inherited lysosomal storage diseases caused by a deficiency of glycosaminoglycan (GAG) catalytic enzymes, resulting in an accumulation of unprocessed or partly degraded GAGs in different tissues, including bones and joints. Notably, skeletal and joint abnormalities may be the first complaint that prompts patients to seek medical attention, especially in the milder forms of the disease. To our knowledge, there are no prior imaging reports that have documented capsuloligamentous thickening in patients with MPS on MRI. In this study, we present four cases of patients with clinically and genetically confirmed diagnosis of type II MPS, encompassing seven MRI examination of different joints, including cervical spine, hip, wrist, knee, and shoulder. All of the patients were male, aged between 14 and 35 years, and exhibited varying degrees of joint stiffness in the clinical examination and carpal tunnel syndrome in cases of the wrist joint was affected. None of the patients had a history of surgical procedures on the affected joint, other metabolic or deposit diseases, or sports activity practice. The MRI revealed significant capsuloligamentous and retinaculum thickening, up to eight times greater than the normal capsular thickness reported in the literature.

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.

Relationship Between Hip Capsular Thickness and Instability After Previous Hip Arthroscopic Surgery: A Matched-Cohort Analysis

Background

Thinner anterior hip capsules are associated with hip laxity, but there is little known about the impact of capsular thickness on the development of instability after primary hip arthroscopic surgery.

Purpose

To investigate the relationship between hip capsular thickness as measured on preoperative magnetic resonance imaging (MRI) and the development of hip instability after hip arthroscopic surgery for femoroacetabular impingement.

Study Design

Case-control study; Level of evidence, 3.

Methods

We reviewed revision hip arthroscopic procedures performed between January 1, 2019, and May 1, 2021, at a single institution. Inclusion criteria were preoperative MRI/magnetic resonance arthrography, completion of the study traction protocol, and asymmetric distraction between the hips of ≥3 mm on examination under anesthesia. A comparison group of patients treated for femoroacetabular impingement with primary hip arthroscopic surgery who did not develop capsular instability were matched 1:1 to the patients with instability. Superolateral hip capsular thickness was measured on MRI before index surgery. Analysis was conducted using independent-samples t tests and multivariable linear regression.

Results

A total of 44 patients were included, with 22 patients each in the instability and no-instability groups. The mean capsular thickness was lower in the patients with hip instability than in those without (1.9 ± 0.6 vs 3.4 ± 1.1 mm, respectively; P < .001). Decreased capsular thickness was significantly associated with hips with instability versus no-instability (β = -1.468 [95% CI, -2.049 to -0.887]; P < .001).

Conclusion

Thinner preoperative hip capsules in the region of the iliofemoral ligament were seen in patients who subsequently underwent revision arthroscopic surgery for hip instability compared to patients who underwent primary hip arthroscopic surgery without subsequent revision. Patients at a higher risk for the development of postoperative hip instability had a superolateral hip capsular thickness of <2 mm.

Hip Capsulolabral Complex: Anatomy, Disease, MRI Features, and Postoperative Appearance

The hip is a uniquely constrained joint with critical static stability provided by the labrum, capsule and capsular ligaments, and ligamentum teres. The labrum is a fibrocartilaginous structure along the acetabular rim that encircles most of the femoral head. Labral tears are localized based on the clock-face method, which determines the extent of the tear while providing consistent terminology for reporting. Normal labral variants can mimic labral disease and can be differentiated by assessment of thickness or width, shape, borders, location, and associated abnormalities. The Lage and Czerny classification systems are currently the most well-known arthroscopic and imaging systems, respectively. Femoroacetabular impingement is a risk factor for development of labral tears and is classified according to bone dysmorphisms of the femur ("cam") or acetabulum ("pincer") or combinations of both (mixed). The capsule consists of longitudinal fibers reinforced by ligaments (iliofemoral, pubofemoral, ischiofemoral) and circular fibers. Capsular injuries occur secondary to hip dislocation or iatrogenically after capsulotomy. Capsular repair improves hip stability at the expense of capsular overtightening and inadvertent chondral injury. The ligamentum teres is situated between the acetabular notch and the fovea of the femoral head. Initially considered to be inconsequential, recent studies have recognized its role in hip rotational stability. Existing classification systems of ligamentum teres tears account for injury mechanism, arthroscopic findings, and treatment options. Injuries to the labrum, capsule, and ligamentum teres are implicated in symptoms of hip instability. The authors discuss the labrum, capsule, and ligamentum teres, highlighting their anatomy, pathologic conditions, MRI features, and postoperative appearance. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

SSR white paper: guidelines for utilization and performance of direct MR arthrography

OBJECTIVE

Direct magnetic resonance arthrography (dMRA) is often considered the most accurate imaging modality for the evaluation of intra-articular structures, but utilization and performance vary widely without consensus. The purpose of this white paper is to develop consensus recommendations on behalf of the Society of Skeletal Radiology (SSR) based on published literature and expert opinion.

MATERIALS AND METHODS

The Standards and Guidelines Committee of the SSR identified guidelines for utilization and performance of dMRA as an important topic for study and invited all SSR members with expertise and interest to volunteer for the white paper panel. This panel was tasked with determining an outline, reviewing the relevant literature, preparing a written document summarizing the issues and controversies, and providing recommendations.

RESULTS

Twelve SSR members with expertise in dMRA formed the ad hoc white paper authorship committee. The published literature on dMRA was reviewed and summarized, focusing on clinical indications, technical considerations, safety, imaging protocols, complications, controversies, and gaps in knowledge. Recommendations for the utilization and performance of dMRA in the shoulder, elbow, wrist, hip, knee, and ankle/foot regions were developed in group consensus.

CONCLUSION

Although direct MR arthrography has been previously used for a wide variety of clinical indications, the authorship panel recommends more selective application of this minimally invasive procedure. At present, direct MR arthrography remains an important procedure in the armamentarium of the musculoskeletal radiologist and is especially valuable when conventional MRI is indeterminant or results are discrepant with clinical evaluation.

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.

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.

Patients With Unhealed or Partially Healed Anterior Capsules After Hip Arthroscopy for Borderline Developmental Dysplasia of the Hips Have Inferior Patient-Reported Outcome Measures

PURPOSE

To evaluate the changes in anterior hip capsular thickness on pre- and postoperative magnetic resonance imaging (MRI) and their associated clinical outcomes in patients with borderline developmental dysplasia of the hip (BDDH).

METHODS

A minimum 2-year follow-up retrospective analysis was performed using data from symptomatic patients with BDDH who underwent hip arthroscopy with routine capsular closure between 2018 and 2020. An available postoperative hip MRI was a prerequisite for study inclusion. Capsular thickness at the capsulotomy zone was measured on MRI. An analysis of the correlations between anterior capsular thickness differences and demographic factors (including age, sex, body mass index, laterality, preoperative alpha angle and lateral center-edge angle, cartilage lesion grade, follow-up time, and capsule management) was performed. Patients with unhealed or partially healed capsules (study group) were propensity-score matched 1:1 to patients with completely healed capsules based on age, sex, body mass index, and follow-up time. Comparisons and analyses of the following parameters were completed for both groups: patient-reported outcomes (Hip Outcome Score-Activities of Daily Living [HOS-ADL], Hip Outcome Score-Sports-Specific Subscale [HOS-SSS], International Hip Outcome Tool 12-component form [iHOT-12], and modified Harris Hip Score), visual analog scale scores, radiographic measures, performed procedures, and complications.

RESULTS

Data were compiled for 59 patients' hips after patient selection. The majority of the repaired hip capsules remained closed (93.2%) at a minimum 2-year follow-up. Propensity-score matching was applied to distribute 25 subjects in the study group and 25 in the control group. The anterior capsule was significantly thinner postoperation in the study group (3.0 ± 1.2 mm vs 4.1 ± 0.6 mm; P < .001). Compared with the control group, patients in the study group had significantly inferior postoperative HOS-ADL (75.1 vs 83.5, P = .007), HOS-SSS (64.5 vs 77.1, P = .005), and iHOT-12 scores (56.1 vs 70.2, P = .006). In addition, patients in the study group were significantly less likely to achieve the minimum clinically important difference for the HOS-ADL score (52% vs 80%, P = .037) score and patient acceptable symptomatic state for the HOS-ADL score (32% vs 60%, P = .047).

CONCLUSIONS

The majority of the repaired hip capsules in patients with BDDH remained closed but not all capsules completely healed at a minimum 2-year follow-up. Patients with an unhealed or partially healed capsule had inferior HOS-ADL, HOS-SSS, and iHOT-12 scores and were less likely to achieve the minimum clinically important difference and patient acceptable symptomatic state for the HOS-ADL score.

LEVEL OF EVIDENCE

III, retrospective comparative prognostic study.

The posterior capsule is distended in dysplastic hips, but the anterior capsule is not

PURPOSE

In the setting of acetabular dysplasia, the increased translational motion of the femur may damage the labrum and cartilage, as well as stretch the capsule. The purpose of the study was to investigate the relationship between the acetabular coverage and the capsular stiffness by assessing the distension of anterior and posterior joint recesses on the hip computed tomography arthrography.

METHODS

One hundred thirty-three patients (138 hips) with a median age of 36 years (range 18-50 years) who received the computed tomography arthrography for evaluation of nonarthritic hip pain in our institute between 2015 and 2017 were retrospectively reviewed. The maximal distance between the anterior/posterior capsule and the anterior femoral head-neck junction/posterior femoral head on the axial imaging of computed tomography arthrography was defined as the width of anterior/posterior joint recess. The width of anterior/posterior joint recess was adjusted with the diameter of the femoral head and was then compared between acetabular dysplasia (lateral center-edge angle < 25°), normal acetabulum (lateral center-edge angle between 25 and 39°), and deep acetabulum (lateral center-edge angle > 39°). In addition, the standard univariate linear regression analysis was used to investigate the relationship between the adjusted width of anterior/posterior joint recess and anterior/posterior coverage of the hip, determined by the anterior/posterior wall index.

RESULTS

The adjusted width of posterior joint recess was significantly greater in the acetabular dysplasia group than the normal acetabulum and deep acetabulum groups (p < 0.01 and p = 0.02, respectively). There was no significant difference of the adjusted width of anterior joint recess between the groups (n.s.). The adjusted width of posterior joint recess had a significant but weak negative correlation with the anterior wall index (r =  - 0.25, p < 0.001), and no correlation with the posterior wall index (r =  - 0.0004, n.s.). There was no significant correlation between the adjusted width of anterior joint recess and the anterior/posterior wall index (r = 0.05, n.s./r = 0.07, n.s.).

CONCLUSIONS

The distension of posterior capsule on the computed tomography arthrography was significantly greater in acetabular dysplasia. In addition, there was a significant but weak negative correlation between the distension of posterior capsule and the anterior coverage of the hip. It indicated a looser posterior capsule was observed in a dysplastic hip. The relevance of posterior capsular laxity to clinical outcomes warrants further investigation. Given the fact that the distension of anterior capsule was not significantly higher in acetabular dysplasia, the need of anterior capsular plication in a dysplastic hip should be carefully evaluated.

LEVEL OF EVIDENCE

Level III.

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

PURPOSE

To investigate the thickness and intra-substance change of anterior capsule of the hip joint, and compare the difference of the capsular features in patients with different statuses of hip stability.

METHODS

A retrospective study was performed to review a hip preservation database. Using the lateral center edge angle(LCEA), patients with borderline dysplasia of the hip (BDH) of 20° ≤ LCEA ≤ 25°, femoracetabular impingement(FAI) with LCEA > 30° and dysplasia of the hip (DH) of LCEA < 20° were enrolled and stratified into different treatment groups. The patients' imaging was reviewed by two experienced musculoskeletal radiologists who were blinded to clinical outcomes. Thickness and intra-substance change of the anterior hip capsule was measured on the sagittal oblique sequences of MRI. A surgeon measured the thickness of the anterior hip capsule during arthroscopy. The capsular thickness and intra-substance change were compared among different groups.

RESULTS

Thirty patients (17 women and 13 men) enrolled in each group (FAI, BDH, and DH) matched by sex and ages were evaluated. There were no significant differences in terms of age, sex, BMI, Alpha angle, and Tönnis grade among all three groups. The mean thickness of the anterior capsule in the DH group was 3.2 ± 0.5 mm, which was significantly thinner than that in the BDH and FAI groups (4.5 ± 0.8 mm and 4.7 ± 0.6 mm), and there was no significant difference in capsular thickness between the BDH and FAI groups. The Median of anterior capsule thickness via arthroscopic measuring was 6 mm and 7 mm in the BDH and FAI groups respectively, which has no statistical difference. The intra-substance change of the anterior capsule shows a significant difference among the three groups, and a higher incidence of delamination of the capsule was found in DH groups (p < 0.001).

CONCLUSIONS

Patients with hip dysplasia have a significantly reduced capsular thickness on MRI and delaminated anterior joint capsule, which could be a sequence of instability. The clinical relevance of this study is that capsular thickness and intra-substance changes of the anterior capsule vary which could alter capsular management strategies.

LEVEL OF EVIDENCE

Level III of evidence, DIAGNOSTIC STUDIES, No consistently applied reference standard.

Diagnosing Hip Microinstability: an international consensus study using the Delphi methodology

PURPOSE

Hip microinstability is a relatively new diagnosis which is increasingly being discussed in the literature and yet there are no clear guidelines for making a diagnosis. Microinstability has generally been defined as persistent excessive hip motion that has become symptomatic especially with pain. This aim of this Delphi study was to seek expert opinion to formulate a diagnostic criteria for hip microinstability.

METHODS

A Delphi methodology was used for this consensus study. A literature search was conducted on PubMed up to March 2019 using the keywords ((hip) and (microinstability)) to identify relevant articles on this topic. All relevant criteria used for diagnosing hip microinstability were collated to create a questionnaire and further criterion suggested by the experts were included as well. Four rounds of questionnaires were delivered via an online survey platform. Between each round the authors acted as administrating intermediaries, providing the experts with a summary of results and synthesising the next questionnaire. The expert panel was comprised of 27 members: 24 (89%) orthopaedic surgeons and 3 (11%) physiotherapists from around the world.

RESULTS

Expert panel participation in rounds 1-4 was: 27 (100%), 20 (74%), 21 (78%) and 26 (96%) respectively. A literature review by the authors identified 32 diagnostic criteria to populate the first questionnaire. Experts suggested amending three criteria and creating five new criteria. The panel converged on ranking 3 (8%) of criteria as "Not important", 20 (54%) as "Minor Factors" and 14 (38%) as "Major Factors". No criteria was ranked as "Essential". Criteria were subcategorised into patient history, examination and imaging. Experts voted for a minimum requirement of four criteria in each subcategory, including at least six "Major factors". The final diagnostic tool was approved by 20 (77%) of the final round panel.

CONCLUSION

This study describes the first known expert consensus on diagnosing hip microinstability. The relative complexity of the final diagnostic tool is illustrative of the difficulty clinicians' face when making this diagnosis.

LEVEL OF EVIDENCE

V.

Female Patients and Decreased Hip Capsular Thickness on Magnetic Resonance Imaging Associated With Increased Axial Distraction Distance on Examination Under Anesthesia: An In Vivo Study

PURPOSE

To investigate the relation of hip capsular thickness as measured on preoperative magnetic resonance imaging (MRI) and intraoperative hip joint axial distraction distance on an examination under anesthesia.

METHODS

A retrospective review of primary arthroscopic hip procedures performed between November 2018 and June 2021 was conducted. The inclusion criteria included a diagnosis of femoroacetabular impingement syndrome and preoperative radiographic imaging and MRI. Fluoroscopic images were obtained at 0 lb and 100 lb of axial traction force. Total distraction distance was calculated by comparing the initial joint space with the total joint space at 100 lb. Hip capsular thickness was measured on MRI. Analysis was conducted using multiple linear regression, independent-samples t tests, and Mann-Whitney U tests.

RESULTS

Eighty patients were included. Bivariable regression showed an association between an increased distraction distance and female sex (β = 4.303, R = 0.561, P < .001), as well as decreased anterior axial (β = -1.291, R = 0.365, P < .001) and superior coronal (β = -1.433, R = 0.501, P < .001) capsular thickness. Multivariable regression (R = 0.645) showed an association between an increased distraction distance and female sex (β = 3.175, P < .001), as well as decreased superior coronal capsular thickness (β = -0.764, P = .022). Independent-samples t tests showed that female patients had significantly decreased superior coronal capsular thickness (2.92 ± 1.14 mm vs 3.99 ± 1.15 mm, P < .001).

CONCLUSIONS

Female sex and decreased hip capsular thickness in the superior aspect of the coronal plane on magnetic resonance scans were found to be predictors of increased hip joint axial distraction distance on examination under anesthesia prior to hip arthroscopy, with anterior axial capsular thickness being a moderate predictor. Poor predictors of distraction distance were posterior axial and inferior coronal capsular thickness, age, body mass index, and lateral center-edge angle. Female patients were also found to have thinner hip capsules in the superior region, which may explain the association between female patients and increased distraction. These findings further characterize the relation between capsular thickness and hip laxity.

LEVEL OF EVIDENCE

Level IV, case series.

Editorial Commentary: Patients With Thin Hip Capsules, Capsular Redundancy, Capsular Defects, Hypermobility, Dysplasia, and Female Patients Are at Increased Risk of Hip Instability

Patients with thin hip capsules, capsular redundancy, capsular defects, hypermobility, dysplasia, and female patients are at increased risk of hip instability. As our understanding of the factors that contribute to hip instability has increased, so too has our ability to identify "at-risk" patients, in whom we should avoid surgery or perform capsular repair or plication following hip arthroscopy to achieve optimal results. We must tailor our surgical planning accord to gender, bony morphology, capsular volume, and properties of the tissue.

Criteria for the Operating Room Confirmation of the Diagnosis of Hip Instability: The Results of an International Expert Consensus Conference

PURPOSE

The purpose of this study was to establish an international expert consensus on operating room findings that aid in the diagnosis of hip instability.

METHODS

An expert panel was convened to build an international consensus on the operating room diagnosis/confirmation of hip instability. Seventeen surgeons who have published or lectured nationally or internationally on the topic of hip instability were invited to participate. Fifteen panel members completed a pre-meeting questionnaire and agreed to participate in a 1-day consensus meeting on May 15, 2021. A review of the literature was performed to identify published intraoperative reference criteria used in the diagnosis of hip instability. Studies were included for discussion if they reported and intraoperative findings associated with hip instability. The evidence for and against each criteria was discussed, followed by an anonymous voting process. For consensus, defined a priori, items were included in the final criteria set if at least 80% of experts agreed.

RESULTS

A review of the published literature identified 11 operating room criteria that have been used to facilitate the diagnosis of hip instability. Six additional criteria were proposed by panel members as part of the pre-meeting questionnaire. Consensus agreement was achieved for 8 criteria, namely ease of hip distraction under anesthesia (100.0% agreement), inside-out pattern of chondral damage (100.0% agreement), location of chondral damage on the acetabulum (93.3% agreement), pattern of labral damage (93.3% agreement), anteroinferior labrum chondral damage (86.7% agreement), perifoveal cartilage damage (97.6% agreement), a capsular defect (86.7% agreement), and capsular status (80.0% agreement). Consensus was not achieved for 9 items, namely ligamentum teres tear (66.7% agreement), arthroscopic stability tests (46.7% agreement), persistent distraction after removal of traction (46.7% agreement), findings of examination under anesthesia (46.7% agreement), the femoral head divot sign (40.0% agreement), inferomedial synovitis (26.7% agreement), drive-through sign (26.7% agreement), iliopsoas irritation (26.7% agreement) and ligamentum teres-labral kissing lesion (13.3% agreement). All experts agreed on the final list of 8 criteria items reaching consensus.

CONCLUSION

This expert panel identified 8 criteria that can be used in the operating room to help confirm the diagnosis of hip instability.

LEVEL OF EVIDENCE

Level V expert opinion.

Evaluation of additional causes of hip pain in patients with femoroacetabular impingement syndrome

Femoroacetabular impingement syndrome (FAIS) is an increasingly prevalent pathology in young and active patients, that has contributing factors from both abnormal hip morphology as well as abnormal hip motion. Disease progression can be detrimental to patient quality of life in the short term, from limitations on sport and activity, as well as the long term through early onset of hip arthritis. However, several concurrent or contributing pathologies may exist that exacerbate hip pain and are not addressed by arthroscopic intervention of cam and pincer morphologies. Lumbopelvic stiffness, for instance, places increased stress on the hip to achieve necessary flexion. Pathology at the pubic symphysis and sacroiliac joint may exist concurrently to FAIS through aberrant muscle forces. Additionally, both femoral and acetabular retro- or anteversion may contribute to impingement not associated with traditional cam/pincer lesions. Finally, microinstability of the hip from either osseous or capsuloligamentous pathology is increasingly being recognized as a source of hip pain. The present review investigates the pathophysiology and evaluation of alternate causes of hip pain in FAIS that must be evaluated to optimize patient outcomes.

"Anterior-shift sign": a novel MRI finding of adult hip dysplasia

INTRODUCTION

In adult hip dysplasia, methods for direct evaluation of hip instability have not been established. The present study aimed to determine findings suggestive of hip instability on magnetic resonance imaging (MRI) and to evaluate their correlations with clinical and radiological factors.

MATERIALS AND METHODS

We retrospectively reviewed 72 hips in 50 patients with hip dysplasia (45 females, 5 males; mean age: 40.0 years; age range: 15-59 years; Kellgren-Lawrence grade: ≤ 2). Hip dysplasia was defined as a lateral center-edge angle < 25°. Among the hips, 50 had pain (symptomatic dysplasia group) and 22 were asymptomatic (asymptomatic dysplasia group). As controls, 12 normal hips in 12 patients who underwent screening for asymptomatic osteonecrosis of the femoral head by MRI were evaluated. Using an oblique axial view on fat-suppressed T2-weighted images, we evaluated the presence of a gap between the posterior part of the femoral head and the corresponding acetabular surface, indicating hip instability (anterior-shift sign). The correlations of anterior-shift sign with clinical and radiographical factors were examined.

RESULTS

Anterior-shift sign was observed in 92.0% in the symptomatic dysplasia group, 9.1% in the asymptomatic dysplasia group, and 0% in the control group. In adult hip dysplasia, cases with anterior-shift sign had significantly more pain and labrum tear occurrence than cases without anterior-shift sign. Anterior-shift sign was correlated with Kellgren-Lawrence grade and degree of acetabular coverage.

CONCLUSIONS

This study suggested that hip instability can be observed as the anterior-shift sign on MRI. This sign is useful when considering indications for periacetabular osteotomy in adult hip dysplasia.

Patients With Generalized Joint Hypermobility Have Thinner Superior Hip Capsules and Greater Hip Internal Rotation on Physical Examination

Purpose

To compare preoperative hip range of motion (ROM), hip capsular thickness on magnetic resonance imaging (MRI), and bony morphology on radiographs and computed tomography (CT) between patients with and without joint hypermobility as measured by the Beighton Test score (BTS), with subanalysis based on sex and age.

Methods

Consecutive patients who underwent hip arthroscopy for a diagnosis of femoroacetabular impingement syndrome with or without dysplasia were retrospectively reviewed. Patient BTS, hip ROM, demographics, surgical data, morphologic measures on radiographs and CT, and MRI findings including hip capsule thickness at various locations were compiled. Multiple statistical tests were performed, including multivariable linear or logistic regression models, while controlling for BTS, age, and sex.

Results

In total, 99 patients were included with a mean age of 29 ± 9.9 years; 62 (62.6%), were female. Forty patients (40.4%) had a BTS ≥4. Female patients (P < .001) and younger patients (26.7 vs 30.9 years, P = .030) were more likely to have a BTS ≥4. Male patients had significantly thicker superior capsules (3.4 mm vs. 2.8 mm, P = .034). BTS was not associated with capsular thickness when controlling for sex. On CT, femoral version (18.9° vs 11.4°, P < .001), and McKibben index (37.8° vs. 28.2°, P < .001) were significantly greater in those with a BTS ≥4. Patients with a BTS ≥4 had more hip internal rotation at 90° of flexion (15.0° vs 10.0°, P < .001), when prone (30.0° vs 20.0°, P = .004), and in extension (10.0° vs. 5.0°, P < .001).

Conclusions

All female patients, regardless of Beighton score, and all patients with a BTS ≥4 indicated for primary hip arthroscopy for femoroacetabular impingement syndrome with or without dysplasia were more likely to have thinner superior hip capsules on MRI and greater hip internal rotation on exam. Bony morphologic differences exist between sexes and between patients with and without hypermobility, likely contributing to differences in ROM.

Level of Evidence

III, retrospective cohort study.

Pre- and intraoperative decision-making challenges in hip arthroscopy for femoroacetabular impingement

There has been a marked increase in the number of hip arthroscopies performed over the past 16 years, primarily in the management of femoroacetabular impingement (FAI). Insights into the pathoanatomy of FAI, and high-level evidence supporting the clinical effectiveness of arthroscopy in the management of FAI, have fuelled this trend. Arthroscopic management of labral tears with repair may have superior results compared with debridement, and there is now emerging evidence to support reconstructive options where repair is not possible. In situations where an interportal capsulotomy is performed to facilitate access, data now support closure of the capsule in selective cases where there is an increased risk of postoperative instability. Preoperative planning is an integral component of bony corrective surgery in FAI, and this has evolved to include computer-planned resection. However, the benefit of this remains controversial. Hip instability is now widely accepted, and diagnostic criteria and treatment are becoming increasingly refined. Instability can also be present with FAI or develop as a result of FAI treatment. In this annotation, we outline major current controversies relating to decision-making in hip arthroscopy for FAI. Cite this article: Bone Joint J 2022;104-B(5):532-540.

Magnetic Resonance Arthrogram Improves Visualization of Hip Capsular Defects in Patients Undergoing Previous Hip Arthroscopy

Purpose

To compare magnetic resonance imaging (MRI) with magnetic resonance arthrogram (MRA) in the identification of hip capsular defects in patients who previously underwent hip arthroscopy.

Methods

Patients who underwent revision hip arthroscopy for capsular insufficiency by a single surgeon between March 2014 and December 2019 were identified by Current Procedural Terminology code. Patients with arthroscopically confirmed capsular defects treated surgically who underwent both MRI and MRA between their primary and revision surgeries were identified. Imaging studies were blinded, randomized, and distributed to two fellowship-trained musculoskeletal radiologists. Radiologists evaluated 14 components of different anatomic structures, including the presence of capsular defect and defect grading, over 2 months, with a 2-week washout period between 4 sets of reads to obtain 2 complete reads from each radiologist. Data were analyzed in R version 4.0.2.

Results

Two hundred thirty patients underwent revision hip arthroscopy between March 2014 and December 2019. Twelve patients had both an MRI and an MRA of the operated hip performed between their primary and revision surgeries. Time between primary and revision hip arthroscopy was 2.0 ± 1.5 years (R: .3-6.3). Time between MRI and MRA was .6 ± .6 years (R: .0-1.6). Sensitivity for detecting hip capsular defects was significantly higher for MRA than for MRI (87.5%, 95% CI: [68,96] vs 50%, 95% CI: [31,69], respectively; P = .008).

Conclusions

This retrospective review demonstrates that MRA has higher sensitivity than MRI in detecting surgically confirmed capsular defects. MRA may be more helpful in identifying capsular defects in patients presenting with hip instability symptoms who have had a previous hip arthroscopy.

Level of Evidence

Level IV, diagnostic case series.

Protocol for a multicenter prospective cohort study evaluating arthroscopic and non-surgical treatment for microinstability of the hip joint

BACKGROUND

Microinstability of the hip joint is a proposed cause of hip pain and reduced function in young individuals. The underlying mechanism is thought to be extraphysiological hip motion due to bony deficiency and/or soft tissue deficiency or decreased soft tissue function. Recently, the condition has gained increased attention, and despite the fact that treatment today includes both non-surgical and surgical approaches, there is limited evidence on diagnostic specificity and treatment effects. The aim of this study is to evaluate clinical outcomes of both non-surgical and surgical treatment for microinstability of the hip joint.

METHODS

A multicenter prospective cohort study is planned to evaluating the outcome of physical therapy aimed at stabilizing the hip joint, as well as arthroscopic plication of the hip joint capsule, if the physical therapy fails. Outcomes will be evaluated using hip-specific patient-reported outcome measures: the short version of the International Hip Outcome Tool and the Copenhagen Hip and Groin Outcome Score, strength and function tests, health-related quality of life as determined using the European Quality of Life-5 Dimensions and the European Quality of Life-Visual Analog Scale, sports activity levels according to the Hip Sport Activity Scale, and reported complications. Patients will be evaluated at 6, 12 and 24 months after each treatment.

DISCUSSION

It is important to evaluate the clinical outcomes of both non-surgical and surgical treatment for suspected microinstability of the hip joint, and the planned prospective evaluation will contribute to the understanding of non-surgical as well as surgical treatment outcomes, including complications.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT04934462 . Registered June 22 2021.

Changes in Hip Capsule Morphology after Arthroscopic Treatment for Femoroacetabular Impingement Syndrome with Periportal Capsulotomy are Correlated With Improvements in Patient-Reported Outcomes

PURPOSE

To assess the correlation between changes in hip capsule morphology with improvements in patient-reported outcome (PRO) scores after arthroscopic surgery for femoroacetabular impingement syndrome (FAIS) using the periportal capsulotomy technique.

METHODS

Twenty-eight patients with cam morphology FAIS (without arthritis, dysplasia, or hypermobility) were prospectively enrolled before arthroscopic labral repair and femoroplasty through periportal capsulotomy (anterolateral/midanterior portals) without closure. Patients completed the Hip Disability and Osteoarthritis Outcomes Score (HOOS) and had nonarthrographic 3T magnetic resonance imaging (MRI) scans of the affected hip before and 1 year after surgery. Anterior capsule thickness, posterior capsule thickness, anterior-posterior capsule thickness ratio, and proximal-distal anterior capsule thickness ratio were measured on axial-oblique MRI sequences. Pearson correlation coefficients were calculated to determine the association between hip capsule morphology and PRO scores.

RESULTS

Postoperative imaging showed that for all 28 patients (12 female), labral repairs and capsulotomies had healed within 1 year of surgery. Analysis revealed postoperative decreases in anterior hip capsule thickness (1395.4 ± 508.4 mm³ vs 1758.4 ± 487.9 mm³; P = .003) and anterior-posterior capsule thickness ratio (0.92 ± 0.33 vs 1.12 ± 0.38; P = .02). Higher preoperative anterior-posterior capsule thickness ratio correlated with lower preoperative scores for HOOS pain (R = -0.43; P = .02), activities of daily living (ADL) (R = -0.43; P = .02), and sport (R = -0.38; P = .04). Greater decrease from preoperative to postoperative anterior-posterior capsule thickness ratio correlated with greater improvement for HOOS pain (R = -0.40; P = .04), ADL (R = -0.45; P = .02), and sport (R = -0.46; P = .02).

CONCLUSIONS

Periportal capsulotomy without closure demonstrates capsule healing by 1 year after arthroscopic FAIS treatment. Changes in hip capsule morphology including decreased anterior-posterior capsule thickness ratio after surgery may be correlated with improvements in patient pain, function, and ability to return to sports.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Hip Capsular Deficiency-A Cause of Post-Surgical Instability in the Revision Setting Following Hip Arthroscopy for Femoroacetabular Impingement

PURPOSE OF REVIEW

To characterize current concepts in capsular repair and hip instability, and examine findings from biomechanical and clinical studies on hip capsular management strategies as they pertain to hip stability, patient outcomes, and hip arthroscopy failure. Further, we discuss the clinical evaluation and treatment of capsular deficiency.

RECENT FINDINGS

There remains debate regarding the optimal capsular management strategies in hip arthroscopy, particularly concerning the necessity of routine capsular repair. A variety of capsulotomy techniques exist and may be used to access the hip joint. Additionally, a wide variety of techniques are employed to repair the hip capsule. Biomechanical evidence supports capsular closure restores hip joint stability to that of the intact, native state. Several clinical studies in both primary and revision hip arthroscopy settings have demonstrated improved pain and functional outcomes in patients who underwent capsular repair or capsular reconstruction. Studies have shown capsular repair may be especially important in patients with ligamentous laxity and hip dysplasia, and in competitive athletes. Post-surgical hip instability secondary to capsular insufficiency is increasingly recognized as a cause of hip arthroscopy failure. Capsular closure restores native biomechanical stability to the hip joint, and several clinical studies report improved pain and functional outcomes following capsular repair or capsular reconstruction in both the primary and revision hip arthroscopy settings. There remains much to learn regarding capsular hip instability as it relates to optimal capsular management surgical technique, intra-operative capsular management decision-making, clinical diagnosis, and related advanced imaging findings.

Three-Dimensional Magnetic Resonance Arthrography of Post-Arthroscopy Hip Instability Demonstrates Increased Effective Intracapsular Volume and Anterosuperior Capsular Changes

Purpose

To quantify the magnetic resonance arthrography (MRA) capsular morphologic findings associated with postarthroscopy hip instability.

Methods

Among patients with clinically significant iatrogenic hip instability at a single center, patients with preindex and postindex surgery MRAs were identified. These MRAs were compared regarding effective intracapsular volume calculated by semi-automated 3-dimensional pixel intensity region segmentation, 2-dimensional anterior proximal intracapsular area in the femoral neck axial plane reconstruction, maximal anterior fluid pocket depth, capsule retraction distance, and capsular instability grade. Morphological measurements were conducted using Horos image processing software. Paired t-test, paired Wilcoxon signed rank test, and the McNemar test were used for identifying statistical significance.

Results

In 42 patients, mean effective intracapsular volume was significantly greater in the postindex surgery MRAs (19.44 cm³ vs 17.26 cm³; P = .006). Proximal anterosuperior (12-3 o'clock) intracapsular area was also significantly greater after index surgery (2.84 cm² vs 1.43 cm²; P < .001. Proximal anteroinferior (3-6 o'clock) intracapsular area (1.34 cm² vs 0.97 cm²; P = .002), capsule deficiency grade (P < .001), anterior capsule retraction distance (4.83 mm vs 0.34 mm; P < .001), and maximum anterior fluid depth (8.33 mm vs 4.90 mm; P <.001) were also significantly increased after index surgery.

Conclusion

In comparison to the preoperative state, iatrogenic hip instability is associated with MRA findings that include increases in total effective intracapsular volume, proximal anterosuperior and anteroinferior intracapsular cross-sectional area, maximum proximal anterosuperior fluid depth, and capsule retraction distance.

Level of Evidence

Level IV, diagnostic case series.

Microinstability of the hip: a systematic review of the imaging findings

OBJECTIVES

To undertake a systematic review of the morphologic features associated with hip microinstability and determine whether there are suggestive or diagnostic imaging findings.

METHODS

Four electronic databases were searched up to September 2019 to identify original research reporting morphologic features in individuals with either a clinical diagnosis of hip microinstability (instability without overt subluxation/dislocation) or those with symptomatic laxity demonstrated on imaging (increased femoral head translation/distraction or capsular volume). Studies focussing on individuals with pre-existing hip conditions (including definite dysplasia (lateral centre edge angle < 20°), significant trauma, previous dislocation or surgery were excluded. Methodological quality was assessed by the Quality Assessment of Diagnostic Accuracy Studies 2 tool.

RESULTS

Twenty-two studies met inclusion criteria (clinical diagnosis of microinstability n = 15 and demonstration of laxity n = 7). Imaging information gathered from the studies includes radiographs (n = 14), MRI (n = 6), MR arthrography (n = 4), CT (n = 1) and intraoperative examination. Most studies exhibited design features associated with an overall high or unclear risk of bias. Some dysplastic features are associated with microinstability or laxity reference measures; however, microinstability is frequently diagnosed in those with a lateral centre edge angle > 25°. Other associated imaging findings reported include impingement morphology, anterior labral tearing, femoral head chondral injury, ligamentum teres tears and capsular attenuation.

CONCLUSIONS

The current literature does not provide strong evidence for imaging features diagnostic of microinstability. In the appropriate clinical context, dysplastic morphology, anterior labral tears and ligamentum teres tears may be suggestive of this condition although further research is needed to confirm this.

PROSPERO REGISTRATION

CRD42019122406.

Capsular thinning on magnetic resonance arthrography is associated with intra-operative hip joint laxity in women

Hip microinstability is a recognized cause of hip pain in young patients. Intra-operative evaluation is used to confirm the diagnosis, but limited data exist associating magnetic resonance arthrography (MRA) findings with hip microinstability. To determine if a difference exists in the thickness of the anterior joint capsule and/or the width of the anterior joint recess on MRA in hip arthroscopy patients with and without an intra-operative diagnosis of hip laxity. Sixty-two hip arthroscopy patients were included in the study. Two musculoskeletal radiologists blinded to surgical results reviewed the MRAs for two previously described findings: (i) anterior joint capsule thinning; (ii) widening of the anterior joint recess distal to the zona orbicularis. Operative reports were reviewed for the diagnosis of joint laxity. In all patients with and without intra-operative laxity, there were no significant differences with either MRA measurement. However, twenty-six of 27 patients with intra-operative laxity were women compared with 11 of 35 patients without laxity (P < 0.001). In subgroup analysis of women, the intra-operative laxity group had a higher rate of capsular thinning compared with the non-laxity group (85% versus 45%; P = 0.01). A 82% of women with capsular thinning also had intra-operative laxity, compared with 40% without capsular thinning (P = 0.01). There were no differences regarding the width of the anterior joint recess. In this study, there was an association between capsular thinning and intra-operative laxity in female patients. Measuring anterior capsule thickness on a pre-operative MRA may be useful for the diagnosis of hip microinstability.

Hip Joint Effusion-Synovitis Is Associated With Hip Pain and Sports/Recreation Function in Female Professional Ballet Dancers

OBJECTIVE

To compare hip joint effusion-synovitis prevalence in professional ballet dancers with nondancing athletes and to evaluate the relationship between effusion-synovitis and clinical measures and cartilage defects.

DESIGN

Case-control study.

SETTING

Elite ballet and sport.

PARTICIPANTS

Forty-nine professional ballet dancers and 49 age-matched and sex-matched athletes.

INDEPENDENT VARIABLES

Group (dancers/athletes), sex, age, years of training, Copenhagen Hip and Groin Outcome Scores (HAGOSs), hip rotation range of motion (ROM), generalized joint hypermobility (GJH), and hip cartilage defect scores.

MAIN OUTCOME MEASURES

Hip joint effusion-synovitis (absent, grade 1 = 2-4 mm, grade 2 = >4 mm) scored with 3-Tesla magnetic resonance imaging.

RESULTS

Hip joint effusion-synovitis was found in 22 (45%) dancers and 13 (26.5%) athletes (P = 0.06). Grade 2 effusion-synovitis was only found in dancers (n = 8, r = 0.31, P = 0.009). The prevalence of effusion-synovitis was similar in men (n = 11, 26%) and women (n = 24, 43%, P = 0.09). Female dancers with effusion-synovitis had lower HAGOS pain (r = 0.63, P = 0.001) and sports/recreation scores (r = 0.66, P = 0.001) compared with those without effusion-synovitis. The HAGOS scores were not related to effusion-synovitis in male dancers or female and male athletes (P > 0.01 for all). Effusion-synovitis was not related to hip ROM, GJH, or cartilage defect scores (P > 0.05 for all).

CONCLUSIONS

Hip joint effusion-synovitis was related to higher levels of pain and lower sports/recreation function in female ballet dancers. Effusion-synovitis was not related to hip rotation ROM, GJH or cartilage defects. Larger sized joint effusion-synovitis was exclusively found in dancers.

Radiographic and clinical characteristics associated with a positive PART (Prone Apprehension Relocation Test): a new provocative exam to elicit hip instability

Hip instability due to mild dysplasia can be a diagnostic challenge. The physical exam is an important adjunct to radiographic evaluation for the clinical diagnosis of hip instability. Herein, we describe a new maneuver to replicate hip instability pain, called the PART (Prone Apprehension Relocation Test). We retrospectively identified patients in our institution’s hip preservation registry who presented for evaluation of hip pain. We divided patients into ‘positive’ or ‘negative’ PART and analyzed associated clinical and radiographic findings. Ninety patients (159 hips) were included, 83 female and 7 male, average age 27.3 ± 9.1 years. Thirty-four hips (21.4%) had a positive PART. There were no significant differences in hip range of motion, lateral center edge angle, or in acetabular depth. There was, however, a significant difference in acetabular version at 3 o’clock between the two test groups (18.5 ± 6.9° in negative, 21.2 ± 4.9° in positive, P = 0.045). There was no association between PART and previously described anterior apprehension testing. Historical methods of diagnosing hip dysplasia may not adequately identify patients with clinical hip instability. We describe a new provocative exam, the PART, which may be helpful in replicating hip instability symptoms in patients with anterior acetabular undercoverage. PART positive patients had significantly more acetabular anteversion at the 3 o’clock position, which is measured on computed tomography and is not visible on standard anteroposterior (AP) pelvis or false profile radiographs. We believe that the PART is a valuable supplement to clinical examination and radiographic measurements to identify patients with symptomatic hip instability.

The dimensions of the hip capsule can be measured using magnetic resonance imaging and may have a role in arthroscopic planning

PURPOSE

The purpose of this study was to systematically evaluate the dimensions and thickness of the hip joint capsule. Secondarily, the study assessed whether there were any described correlations between capsule thickness and stability of the hip joint.

METHODS

Four databases (PubMed, Ovid [MEDLINE], Cochrane Database, and EMBASE) were searched from database inception to May 2018, and two reviewers independently and in duplicate screened the resulting literature. Methodological quality of all included papers was assessed using the Methodological index for non-randomized studies (MINORS) criteria. Mean differences were combined in a meta-analysis using a random effects model when possible.

RESULTS

A total of 14 studies (1 level I, 1 level II, 4 level III, 5 level IV) were identified including 796 patients (1013 hips) with a mean age of 39.5 years (range 2-95). Of the included patients, 55.2% were female and they were followed up for a mean of 7.6 months (range 1-12.5 months). The thickness of the capsule was measured in cadaveric specimens, ultrasound, and magnetic resonance imaging (MRI), with MRI measurements reported most consistently and with the least variation. Mean thickness of the anterior capsule in patients without hip disease on MRI ranged from 4.4 and 4.7 mm. Mean thickness of the anterior capsule in patients with FAI ranged between 4.9 and 5.0 mm. Males had significantly thicker capsules than females (mean difference = 1.92 mm, 0.35-3.49, P = 0.02). Clinical laxity of the hip joint, as well as female gender was correlated with thinner anterior joint capsules.

CONCLUSION

The thickness of the anterior hip capsule can be measured consistently using MRI. A thinner anterior capsule may be associated with clinical laxity of the hip joint. The relevance of capsular thickness on postoperative instability following hip arthroscopy is poorly understood and warrants further investigation. The thickness of the anterior hip capsule, as measured on MRI, has the potential to be used as part of the clinical decision-making in capsular management strategies.

LEVEL OF EVIDENCE

IV.

Contributions of the Capsule and Labrum to Hip Mechanics in the Context of Hip Microinstability

Background

Hip microinstability and labral pathology are commonly treated conditions with increasing research emphasis. To date, there is limited understanding of the biomechanical effects of the hip capsule and labrum on controlling femoral head motion.

Purpose/Hypothesis

The purpose of this study was to determine the relative role of anterior capsular laxity and labral insufficiency in atraumatic hip microinstability. Our hypotheses were that (1) labral tears in a capsular intact state will have a minimal effect on femoral head motion and (2) the capsule and labrum work synergistically in controlling hip stability.

Study Design

Controlled laboratory study.

Methods

Twelve paired hip specimens from 6 cadaveric pelvises (age, 18-41 years) met the inclusion criteria. Specimens were stripped of all soft tissue except the hip capsule and labrum, then aligned, cut, and potted using a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation, while rotating about the mechanical axis of the hip. Labral insufficiency was created with a combined radial and chondrolabral tear under direct visualization. A motion tracking system was used to record hip internal-external rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing variables included baseline, postventing, postcapsular stretching, and postlabral insufficiency.

Results

When comparing the vented state with each experimental pathologic state, increases in femoral head motion were noted in both the capsular laxity state and the labral insufficiency state. The combined labral insufficiency and capsular laxity state produced statistically significant increases (P < .001) in femoral head translation compared with the vented state in all planes of motion.

Conclusion

Both the anterior capsule and labrum play a role in hip stability. In this study, the anterior hip capsule was the primary stabilizer to femoral head translation, but labral tears in the setting of capsular laxity produced the most significant increases in femoral head translation.

Clinical Relevance

This study provides a physiologic biomechanical assessment of the hip constraints in the setting of hip microinstability. It also sheds light on the importance of the hip capsule in the management of labral tears. Our study demonstrates that labral tears in isolation provide minimal changes in femoral head translation, but in the setting of a deficient capsule, significant increases in femoral head translation are seen, which may result in joint-related symptoms.

The Role of Anterior Capsular Laxity in Hip Microinstability: A Novel Biomechanical Model

BACKGROUND

Hip microinstability is an increasingly recognized source of hip pain and disability. Although the clinical entity has been well described, the pathomechanics of this disease remain poorly understood.

PURPOSE/HYPOTHESIS

The purpose of this study was to determine the role of capsular laxity in atraumatic hip microinstability. Our hypothesis was that cyclic stretching of the anterior hip capsule would result in increased hip range of motion and femoral head displacement.

STUDY DESIGN

Controlled laboratory study.

METHODS

In this study, 7 hip specimens met inclusion criteria (age, 18-46 years). Specimens were stripped of all soft tissue, aligned, cut, and potted by use of a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation while rotating about the mechanical axis of the hip. A motion tracking system was used to record hip rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing was conducted at baseline, after venting, and after capsular stretching.

RESULTS

With the hip in anatomic neutral alignment, cyclic stretching of the anterior hip capsule resulted in increased hip rotation ( P < .001). Femoral head displacement significantly increased relative to the vented state in the medial-lateral ( P < .001), anterior-posterior ( P = .013), and superior-inferior ( P = .036) planes after cyclic stretching of the anterior hip capsule.

CONCLUSION

The anterior hip capsule plays an important role in controlling hip rotation and femoral head displacement. This study is the first to display significant increases in femoral head displacement through a controlled cyclic stretching protocol of the anterior hip capsule.

CLINICAL RELEVANCE

This study is directly applicable to the treatment of atraumatic hip microinstability. The results quantitatively define the relative importance of the hip capsule in controlling femoral head motion. This allows for a better understanding of the pathophysiological process of hip microinstability and serves as a platform to develop effective surgical techniques for treatment of this disease.

Capsular plication in the non-deformity hip: impact on post-operative joint stability

Purpose and hypothesis

The aim of this study was to evaluate the hip joint range of motion after different capsular plication. The study hypothesis proposed that capsular plication after hip arthroscopy may reduce hip external rotation and thus prevent the hip joint instability created by arthroscopic capsulotomies.

Methods

Six fresh frozen human cadavers were studied in the intact state (5 males, 1 females) for a total of 12 non-deformity hips tested. They were fixed to the operating room table using a custom-made apparatus. Three Steinman pins were inserted, the first into ASIS, a parallel pin into the distal femur proximal to inter-epicondylar axis and the third pin into the lateral epicondyle. Simulation of arthroscopic capsulotomies was done progressively with simulation of three capsular plication techniques. The first plication technique consisted of a primary plication shift of the antero-lateral capsule. The distal-medial arm of the iliofemoral ligament was shifted toward the proximal-lateral arm. The second plication technique consisted in adding a longitudinal arm to the capsulotomy, between the lateral arm and the medial arm of the iliofemoral ligament, to create a T-shaped capsulotomy. The resulting two triangular capsular flaps were overlaid onto each other by approximately 5 mm, plicated fully and tighly sutured in a double-breast manner. The third plication technique, called redrapping, consisted in excising the inferior capsular triangular flap (previously made in the second technique), and suturing the latero-anterior superior capsular flap to the medial arm of the iliofemoral ligament, superimposing the capsular edges for closure. External rotation of the hip at 0°, 15° and 30° of flexion were obtained after the capsulotomy and each capsular plication technique to quantify the increase in hip stability after plication. Data were assessed using a two-way repeated measure analysis of variance (ANOVAs) and Student’s T-test when necessary to determine if the change in external rotation was significantly different.

Results

After capsulotomy, external rotation averaged 26.3°, 29.1° and 31.1° at 0°, 15° and 30° of flexion. With the primary plication shift, external rotation averaged 24.9°, 30.3° and 34.0°. With the two-triangle technique, external rotation averaged 26.1°, 31.9° and 33.3°. With the re-draping technique, external rotation averaged 25.8°, 30.9° and 32.0°. A significant relationship was found between «Plication Technique» and «Angle of flexion» factors for the measured angle of external rotation (P = 0.04).

A decomposition of the interaction showed that external rotation decreased at 0° of hip flexion and increased as the hip flexion angle increased. The only significant difference found corresponded to the two triangles technique at 15° flexion (mean difference compared to the non-repaired state = 2.8° ± 3.8° or 8.8% increase in external rotation; P = 0.03).

Conclusions

Different techniques of capsular plication result in a non-significant increase in hip external rotation when compared to unrepaired capsulotomies. Therefore, special attention should be paid at the time of capsular plication, which could be disadvantageous when done overzealously aiming to increase postoperative stability.

The Cliff Sign: A New Radiographic Sign of Hip Instability

Background:

The preoperative diagnosis of hip microinstability is challenging. Although physical examination maneuvers and magnetic resonance imaging findings associated with microinstability have been described, there are limited reports of radiographic features. In patients with microinstability, we observed a high incidence of a steep drop-off on the lateral edge of the femoral head, which we have named the “cliff sign.”

Purpose:

(1) To determine the relationship of the cliff sign and associated measurements with intraoperative microinstability and (2) to determine the interobserver reliability of these measurements.

Study Design:

Cohort study (diagnosis); Level of evidence, 2.

Methods:

A total of 115 consecutive patients who underwent hip arthroscopy were identified. Patients with prior hip surgery, Legg-Calve-Perthes disease, fractures, pigmented villonodular synovitis, or synovial chondromatosis were excluded, resulting in the inclusion of 96 patients in the study. A perfect circle around the femoral head was created on anteroposterior pelvis radiographs. If the lateral femoral head did not completely fill the perfect circle, it was considered a positive cliff sign. Five additional measurements relating to the cliff sign were calculated. The diagnosis of microinstability was made intraoperatively by the (1) amount of traction required to distract the hip, (2) lack of hip reduction after initial traction release following joint venting, or (3) intraoperative findings consistent with hip microinstability. Continuous variables were analyzed through use of unpaired t tests and discrete variables with Fisher exact tests. Interobserver reliability (n = 3) was determined for each measurement.

Results:

Overall, 89% (39/44) of patients with microinstability had a cliff sign, compared with 27% of patients (14/52) without instability (P < .0001). Conversely, 74% of patients with a cliff sign had microinstability, while only 12% of patients without a cliff sign had instability (P < .0001). In women younger than 32 years with a cliff sign, 100% (20/20) were diagnosed with instability. No differences were found in any of the 5 additional measurements. Excellent interobserver reliability was found for the presence of a cliff sign and the cliff angle measurement.

Conclusion:

We have identified a radiographic finding, the cliff sign, that is associated with the intraoperative diagnosis of hip microinstability and has excellent interobserver reliability. Results showed that 100% of young women with a cliff sign had intraoperative microinstability. The cliff sign may be useful in the preoperative diagnosis of hip microinstability.

MRI Evaluation of Repaired Versus Unrepaired Interportal Capsulotomy in Simultaneous Bilateral Hip Arthroscopy: A Double-Blind, Randomized Controlled Trial

BACKGROUND

Techniques used in hip arthroscopy continue to evolve, and controversy surrounds the need for capsular repair following this surgical intervention. The purpose of this study was to evaluate the magnetic resonance imaging (MRI) appearance of the hip capsule in patients with femoroacetabular impingement (FAI) who underwent simultaneous bilateral hip arthroscopy through an interportal capsulotomy with each hip randomized to undergo capsular repair or not undergo such a repair.

METHODS

This double-blind, randomized controlled trial included 15 patients (30 hips), with a mean age of 29.2 years, who underwent simultaneous bilateral hip arthroscopy utilizing a small (<3-cm) interportal capsulotomy for the treatment of FAI. The first hip treated in each patient was intraoperatively randomized to undergo capsular repair or no capsular repair. The contralateral hip then received the opposite treatment. MRI was performed at 6 and 24 weeks postoperatively, and the scans were analyzed by 2 musculoskeletal radiologists. The patients and the radiologists were blinded to the treatment performed on each hip. Capsular dimensions were measured at the level of the healing capsulotomy site and, for hips with a persistent defect, at locations both proximal and distal to the defect. These values were then analyzed at both time points to assess the rate and extent of capsular healing.

RESULTS

At 6 weeks postoperatively, a continuous hip capsule (with no apparent capsulotomy defect) was observed in 8 hips treated with capsular repair and 3 hips without such a repair. Of the 19 hips with a discontinuous capsule at 6 weeks, 17 were available for follow-up at 24 weeks postoperatively; all 17 demonstrated progression to healing, with a contiguous appearance without defects and no difference in capsular dimensions between treatment cohorts.

CONCLUSIONS

Arthroscopic repair of a small interportal hip capsulotomy site yields an insignificant increase in the percentage of continuous hip capsules seen on MRI at 6 weeks postoperatively compared with no repair. Repaired and unrepaired capsulotomy sites progressed to healing with a contiguous appearance on MRI by 24 weeks postoperatively.

LEVEL OF EVIDENCE

Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Hip Imaging in Athletes: Sports Imaging Series

Hip or groin pain in athletes is common and clinical presentation is often nonspecific. Imaging is a very important diagnostic step in the work-up of athletes with hip pain. This review article provides an overview on hip biomechanics and discusses strategies for hip imaging modalities such as radiography, ultrasonography, computed tomography, and magnetic resonance (MR) imaging (MR arthrography and traction MR arthrography). The authors explain current concepts of femoroacetabular impingement and the problem of high prevalence of cam- and pincer-type morphology in asymptomatic persons. With the main focus on MR imaging, the authors present abnormalities of the hip joint and the surrounding soft tissues that can occur in athletes: intraarticular and extraarticular hip impingement syndromes, labral and cartilage disease, microinstability of the hip, myotendinous injuries, and athletic pubalgia. (©) RSNA, 2016.

Generalized Joint Hypermobility Is Predictive of Hip Capsular Thickness

Background:

The pathomechanics of hip microinstability are not clearly defined but are thought to involve anatomical abnormalities, repetitive forces across the hip, and ligamentous laxity.

Purpose/Hypothesis:

The purpose of this study was to explore the relationship between generalized joint hypermobility (GJH) and hip capsular thickness. The hypothesis was that GJH would be predictive of a thin hip capsule.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

A prospective study was performed on 100 consecutive patients undergoing primary hip arthroscopy for the treatment of hip pain. A Beighton test score (BTS) was obtained prior to each procedure. The maximum score was 9, and a score of ≥4 was defined as hypermobile. Capsular thickness at the level of the anterior portal, corresponding to the location of the iliofemoral ligament, was measured arthroscopically using a calibrated probe. The presence of ligamentum teres (LT) pathology was also recorded.

Results:

Fifty-five women and 45 men were included in the study. The mean age was 32 years (range, 18-45 years). The median hip capsule thickness was statistically greater in men than women (12.5 and 7.5 mm, respectively). The median BTS for men was 1 compared with 4 for women (P < .001). A statistically significant association was found between BTS and capsular thickness; a BTS of <4 is strongly predictive of having a capsular thickness of ≥10 mm, while a BTS ≥4 correlates with a capsular thickness of <10 mm. There was a statistically greater incidence of LT tears in patients with a capsular thickness of ≤7.5 mm and a BTS of ≥4 (P < .001).

Conclusion:

Measurement of the GJH is highly predictive of hip capsular thickness. A BTS of <4 correlates significantly with a capsular thickness of ≥10 mm, while a BTS ≥4 correlates significantly with a thickness of <10 mm.

The Hip Restoration Algorithm

BACKGROUND

Despite the rapid advancement of imaging and arthroscopic techniques about the hip joint, missed diagnoses are still common. As a deep joint and compared to the shoulder and knee joints, localization of hip symptoms is difficult. Hip pathology is not easily isolated and is often related to intra and extra-articular abnormalities. In light of these diagnostic challenges, we recommend an algorithmic approach to effectively diagnoses and treat hip pain.

METHODS

In this review, hip pain is evaluated from diagnosis to treatment in a clear decision model. First we discuss emergency hip situations followed by the differentiation of intra and extra-articular causes of the hip pain. We differentiate the intra-articular hip as arthritic and non-arthritic and extra-articular pain as surrounding or remote tissue generated. Further, extra-articular hip pain is evaluated according to pain location. Finally we summarize the surgical treatment approach with an algorithmic diagram.

CONCLUSION

Diagnosis of hip pathology is difficult because the etiologies of pain may be various. An algorithmic approach to hip restoration from diagnosis to rehabilitation is crucial to successfully identify and manage hip pathologies. Level of evidence: V.

Does the Hip Capsule Remain Closed After Hip Arthroscopy With Routine Capsular Closure for Femoroacetabular Impingement? A Magnetic Resonance Imaging Analysis in Symptomatic Postoperative Patients

PURPOSE

The purpose of this study was to examine the hip capsule in a subset of symptomatic patients who underwent capsular closure during hip arthroscopy.

METHODS

All patients undergoing primary hip arthroscopy for femoroacetabular impingement (FAI) with routine capsular closure between January 1, 2012, and December 31, 2015, were eligible. Only patients with unilateral surgery and a postoperative magnetic resonance imaging (MRI; ordered for persistent symptoms) were included. Four independent reviewers evaluated each hip capsule for thickness and the absence or presence of defects.

RESULTS

During the study, 1,463 patients had hip arthroscopy for FAI with routine capsular closure, and 53 (3.6%) underwent a postoperative MRI. Fourteen of the 53 were excluded owing to revision status or additional procedures. The final study population included 39 patients (23 female patients and 16 male patients), with an average patient age of 31.7 ± 11.4 years and an average body mass index of 23.3 ± 2.9. There were 3 (7.5%) capsular defects, and the intraclass correlation coefficient (ICC) was 0.82. The operative hip capsule was significantly thicker in the zone of capsulotomy, and subsequent repair as compared with the unaffected, contralateral hip capsule (5.0 ± 1.2 mm vs 4.6 ± 1.4 mm; P = .02), ICC 0.83. Additionally, males had thicker hip capsules as compared with their female counterparts, on the operative side (5.4 ± 1.1 mm vs 4.5 ± 1.2 mm; P = .02) and the nonoperative side (4.8 ± 1.6 mm vs 4.1 ± 0.9 mm; P = .08).

CONCLUSIONS

In a subset of symptomatic patients after hip arthroscopy for FAI, the majority (92.5%) of the repaired hip capsules remained closed at greater than 1 year of follow-up. The hip capsule adjacent to the capsulotomy and subsequent repair is thickened compared with the same location on the contralateral, nonoperative hip. Aside from gender, patient-related and FAI-related factors do not correlate with capsular thickness nor do they seem to correlate with the propensity to develop a capsular defect.

LEVEL OF EVIDENCE

Level IV, prognostic case series.

Microinstability of the hip: a previously unrecognized pathology

BACKGROUND

Hip microinstability is an established diagnosis; however, its occurrence is still debated by many physicians. Diagnosis of hip microinstability is often challenging, due to a lack of specific signs or symptoms, and patients may remain undiagnosed for long periods. This may lead to early manifestation of degenerative joint disease. Consequently, careful patient and family history must be obtained and diagnostic imaging should follow. After a thorough clinical evaluation of the patient with suspected hip microinstability, the physician should focus on how to improve symptoms and functionality in daily and sports activities.

PURPOSE

The purpose of this review article was to give a current update regarding this diagnosis and to provide a complete diagnostic approach in order to effectively treat hip microinstability.

METHODS

We reviewed the literature on the diagnosis, the non-operative and operative indications for the treatment of this complex and often misdiagnosed pathology.

CONCLUSION

Conservative treatment is considered the best initial approach, though, surgical intervention should be considered if symptoms persist or other hip pathology exists. Successful surgical intervention, such as hip arthroscopy, should focus on restoring the normal anatomy of the hip joint in order to regain its functionality. The role of the hip joint capsule has gained particular research interest during the last years, and its repair or reconstruction during hip arthroscopy is considered necessary in order to avoid iatrogenic hip microinstability. Various capsular closure/plication techniques have been developed towards this direction with encouraging results.

LEVEL OF EVIDENCE

V.

Posterior, Lateral, and Anterior Hip Pain Due to Musculoskeletal Origin: A Narrative Literature Review of History, Physical Examination, and Diagnostic Imaging

OBJECTIVE

The purpose of this study was to present a narrative review of the literature of musculoskeletal causes of adult hip pain, with special attention to history, physical examination, and diagnostic imaging.

METHODS

A narrative review of the English medical literature was performed by using the search terms "hip pain" AND "anterior," "lateral," and "posterior." Additionally, specific entities of hip pain or pain referral sources to the hip were searched for. We used the PubMed search engine through January 15, 2016.

RESULTS

Musculoskeletal sources of adult hip pain can be divided into posterior, lateral, and anterior categories. For posterior hip pain, select considerations include lumbar spine and femoroacetabular joint referral, sacroiliac joint pathology, piriformis syndrome, and proximal hamstring tendinopathy. Gluteal tendinopathy and iliotibial band thickening are the most common causes of lateral hip pain. Anterior hip pain is further divided into causes that are intra-articular (ie, labral tear, osteoarthritis, osteonecrosis) and extra-articular (ie, snapping hip and inguinal disruption [athletic pubalgia]). Entrapment neuropathies and myofascial pain should also be considered in each compartment. A limited number of historical features and physical examination tests for evaluation of adult hip pain are supported by the literature and are discussed in this article. Depending on the clinical differential, the gamut of diagnostic imaging modalities recommended for accurate diagnosis include plain film radiography, computed tomography, magnetic resonance imaging, skeletal scintigraphy, and ultrasonography.

CONCLUSIONS

The evaluation of adult hip pain is challenging. Clinicians should consider posterior, lateral, and anterior sources of pain while keeping in mind that these may overlap.

Is the hip capsule thicker in diseased hips?

Objectives

The purpose of this study was to compare the thickness of the hip capsule in patients with surgical hip disease, either with cam-femoroacetabular impingement (FAI) or non-FAI hip pathology, with that of asymptomatic control hips.

Methods

A total of 56 hips in 55 patients underwent a 3Tesla MRI of the hip. These included 40 patients with 41 hips with arthroscopically proven hip disease (16 with cam-FAI; nine men, seven women; mean age 39 years, 22 to 58) and 25 with non-FAI chondrolabral pathology (four men, 21 women; mean age 40 years, 18 to 63) as well as 15 asymptomatic volunteers, whose hips served as controls (ten men, five women; mean age 62 years, 33 to 77). The maximal capsule thickness was measured anteriorly and superiorly, and compared within and between the three groups with a gender subanalysis using student’s t-test. The correlation between alpha angle and capsule thickness was determined using Pearson’s correlation coefficient.

Results

Superiorly, the hip capsule was significantly greater in cam- (p = 0.028) and non-FAI (p = 0.048) surgical groups compared with the asymptomatic group. Within groups, the superior capsule thickness was significantly greater than the anterior in cam- (p < 0.001) and non-FAI (p < 0.001) surgical groups, but not in the control group. There was no significant correlation between the alpha angle and capsule thickness. There were no gender differences identified in the thickness of the hip capsule.

Conclusion

The thickness of the capsule does not differ between cam- and non-FAI diseased hips, and thus may not be specific for a particular aetiology of hip disease. The capsule is, however, thicker in diseased surgical hips compared with asymptomatic control hips.

Cite this article: K. S. Rakhra, A. A. Bonura, R. Nairn, M. E. Schweitzer, N. M. Kolanko, P. E. Beaule. Is the hip capsule thicker in diseased hips? Bone Joint Res 2016;5:586–593. DOI: 10.1302/2046-3758.511.2000495.

A quantitative analysis of hip capsular thickness

PURPOSE

The purpose of this study was to provide a comprehensive quantitative analysis of capsular thickness adjacent to the acetabular rim in clinically relevant locations.

METHODS

Dissections were performed and hip capsular measurements were recorded on 13 non-paired, fresh-frozen cadaveric hemi-pelvises using a coordinate measuring device. Measurements were taken for each clock-face position at 0, 5, 10 and 15 mm distances from the labral edge.

RESULTS

The capsule was consistently thickest at 2 o'clock for each interval from the labrum with a maximum thickness of 8.3 at 10 mm [95 % CI 6.8, 9.8] and 15 mm [95 % CI 6.8, 9.7]. The capsule was noticeably thinner between 4 and 11 o'clock with a minimum thickness of 4.1 mm [95 % CI 3.3, 4.9] at 10 o'clock at the labral edge. Direct comparison between 0 and 5 mm between 9 and 3 o'clock showed that the hip capsule was significantly thicker at 5 mm from the labrum at 9 o'clock (p = 0.027), 10 o'clock (p = 0.032), 1 o'clock (p = 0.003), 2 o'clock (p = 0.001) and 3 o'clock (p = 0.001).

CONCLUSIONS

The hip capsule was thickest between the 1 and 2 o'clock positions for all measured distances from the acetabular labrum and reached its maximum thickness at 2 o'clock, which corresponds to the location of the iliofemoral ligament.

Biomechanical Evaluation of Capsulotomy, Capsulectomy, and Capsular Repair on Hip Rotation

PURPOSE

To determine the effect of different types of capsulotomies on hip rotational biomechanical characteristics.

METHODS

Seven fresh-frozen cadaveric hip specimens were thawed and dissected, leaving the hip capsule and labrum intact. The femur was transected and potted, and each specimen was placed in a custom loading apparatus that allowed for adjustment of flexion, extension, and axial rotation of the femur. Six reflective infrared markers were attached to the specimens to track the motion of the femoral head with respect to the acetabulum in real time, and external rotation was produced by applying a torque of 10 Nm to the hip specimens. Data analysis was performed using the 3-dimensional position of the markers in space. The specimens were tested in neutral flexion and 40° of flexion in the following capsular states: intact, interportal capsulotomy, T-capsulotomy, repaired capsulotomy, and capsulectomy. Paired t tests and analysis of variance were used with an α value of .05 set as significant.

RESULTS

With the hip in neutral flexion, there was increased external rotation with a T-capsulotomy (91.1° ± 20.3°, P = .029) and capsulectomy (91.9° ± 19.6°, P = .015) compared with the intact hip (83.2° ± 20.5°). After complete repair of the T-capsulotomy (87.4° ± 20.6°), there was no significant difference in external rotation compared with the intact hip. No significant differences were seen between groups at 40° of hip flexion.

CONCLUSIONS

A T-capsulotomy showed significantly increased external rotation versus the intact and interportal capsulotomy states. The repaired T-capsulotomy restored the rotational profile back to the native state.

CLINICAL RELEVANCE

Many methods of capsular treatment during hip arthroscopy exist. Capsulotomy and capsulectomy do not restore the external rotation restraint of the hip back to its native state.

Microinstability of the hip-it does exist: etiology, diagnosis and treatment

Symptomatic hip microinstability is now recognized as a potential cause of pain and disability in young patients. Causes of hip microinstability include underlying bony or soft tissue abnormalities and iatrogenic injuries of the hip capsule; however, many patients lack a clear underlying etiology. Treatment usually begins with an extensive course of non-operative management with an emphasis on activity modification and physical therapy. Surgical intervention should focus on treatment of the underlying cause as well as any associated intra-articular pathology. In many cases, arthroscopic suture plication can be considered when bony deficiency is not the cause. In this article, we will review the spectrum of symptomatic hip microinstability with a focus on the relevant anatomy, etiology, diagnosis and various treatment options.

What are the demographic and radiographic characteristics of patients with symptomatic extraarticular femoroacetabular impingement?

BACKGROUND

Extraarticular femoroacetabular impingement (FAI) can result in symptomatic hip pain, but preoperative demographic, radiographic, and physical examination findings have not been well characterized.

QUESTIONS/PURPOSES

The purposes of this study were to (1) define the demographic characteristics of patients with symptomatic extraarticular FAI; and (2) identify relevant radiographic and physical examination findings that are associated with intraoperative locations of extraarticular FAI.

METHODS

For purposes of this study, we defined extraarticular FAI as abnormal contact between the extraarticular regions of the proximal femur (greater trochanter, lesser trochanter, extracapsular femoral neck) and the ilium or ischium. The diagnosis was suspected preoperatively, but it was confirmed at the time of surgery by direct visualization of extraarticular impingement after surgical hip dislocation. A prospective single-center hip preservation registry was used to retrospectively characterize patients presenting between October 2010 and November 2013 with symptomatic hip pain and intraoperative findings of extraarticular FAI (N = 75 patients, 86 hips). Detailed demographic data were recorded. Radiographs, CT, and MRI scans were reviewed for all patients by two of the authors (BFR, ELS). Outcome instruments including modified Harris hip score (mHHS), Hip Outcome Score (HOS), and International Hip Outcome Tool (iHOT-33) were assessed preoperatively. A comparison group of all patients (N = 1690 patients, 1989 hips) undergoing surgery for intraarticular FAI over the study period were included for demographic comparisons. Cases with extraarticular FAI accounted for 4% (75 of 1765 patients) of our cohort over the study time period.

RESULTS

Patients with extraarticular FAI were more likely to be younger (mean ± SD, 24 ± 7 years versus 30 ± 11 years; difference [95% confidence interval {CI}], -7 [-9 to -4]; p < 0.001), female (85% versus 49%; odds ratio [95% CI], 6 [3 to 12]; p < 0.001), to have undergone prior hip surgery (44% versus 10%; odds ratio [95% CI], 9 (6 to 15); p < 0.001), and have lower preoperative outcome scores after adjustment for age, sex, and revision status (mHHS 55 ± 15 versus 63 ± 15; adjusted difference [95% CI], -4 (-8 to -1); p = 0.017; HOS ADL 64 ± 19 versus 73 ± 18; adjusted difference [95% CI], -7 (-11 to -3); p = 0.002) than patients undergoing surgery for intraarticular FAI. Within the extraarticular FAI group, preoperative femoral version on CT was different among patients with anterior versus posterior extraarticular impingement (median [first quartile, third quartile], 8° [2, 18] versus 21° [20, 30], respectively; p = 0.005) and anterior versus complex extraarticular impingement (median [first quartile, third quartile], 8° [2, 18] versus 20° [10, 30], respectively; p = 0.007]. Preoperative external rotation in extension was increased in patients with anterior versus complex extraarticular FAI (median [first quartile, third quartile], 70° [55, 75] versus 40° [20, 60]; p < 0.001).

CONCLUSIONS

Extraarticular FAI is an uncommon source of impingement symptoms. We suspect the diagnosis often is missed, because many of these patients had prior hip surgery before the procedure that diagnosed the extraarticular impingement source. This diagnosis seems more common in younger, female patients. Radiographic and physical examination findings correspond to locations of intraoperative extraarticular impingement. Future studies will need to determine whether surgical treatment of extraarticular impingement pathology improves pain and function in this subset of patients.