The prevalence of synovitis during hip arthroscopy for labral tears – An observational study

INTRODUCTION

Hip pain can significantly affect the quality of life in young adults.^[1] The underlying etiology may include both intraarticular and extra-articular causes, necessitating assessment by orthopedic clinicians with specialized knowledge to ensure that treatable conditions are identified and managed. Labral tears (LTs) are commonly observed during evaluations of young adults presenting with hip pain. These tears may be incidental findings or result from underlying pathologies, most notably femoroacetabular impingement (FAI).^[2] Other frequent causes include acetabular dysplasia, rotational malalignment, femoral head deformity, or a combination of these factors.^[3-5]

Diagnosing the cause of hip pain in young adults can be challenging, with studies indicating that it often takes over 2 years to reach a definitive diagnosis.^[6-8] While magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRA) are crucial for initial imaging, they can yield false positives for LTs or produce inconclusive results.^[6,9,10] In cases with a high suspicion of intra-articular pathology, hip arthroscopy may be performed to provide a definitive diagnosis and address any intra-articular issues.

During hip arthroscopy, synovitis is frequently observed upon initial insertion of the arthroscope, manifesting as inflammation of the synovial membrane lining the hip joint capsule [Figures 1 and 2]. This inflammation can be localized or widespread, with potential causes including hip osteoarthritis, inflammatory conditions, trauma, FAI, or LTs.^[11]

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Figure 1:

Hip synovitis.

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Figure 2:

Hip synovitis during the creation of capsulotomy.

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To date, no studies have investigated the prevalence of synovitis during hip arthroscopy, its potential clinical implications, or its correlation with the presence of LTs. This study aims to elucidate the incidence of synovitis detected during hip arthroscopy in patients with MRI-confirmed LTs.

MATERIALS AND METHODS

We prospectively collected data on 50 consecutive patients who underwent a hip arthroscopy for an MRI-confirmed LT between September 2022 and April 2023 and recorded the presence or absence of global hip synovitis during the initial insertion of the hip scope. In addition, we recorded demographic data, including age and gender, and the grade of LT identified, based on the BARC classification:^[12] (1) labral fraying, (2) LT suitable for repair, and (3) degenerate labrum. To assess potential clinical implications, we collected Visual Analog Scores (VAS pain score) and EQ-5D scores for each patient pre-operatively and performed a comparative analysis between those with and without synovitis. All data collected by the same trained surgeon (AM) for consistency and reliability were input into Microsoft Excel for subsequent analysis.

Data analysis involved simple statistical methods using GraphPad software, including the calculation of descriptive statistics such as means and percentages for data summary. To evaluate the association between VAS and EQ5D pain scores and synovitis, we conducted an analysis of variance (ANOVA) test with a P = 0.05 considered statistically significant. Post hoc analysis using the Tukey test was then performed to strengthen our statistical findings.

Ethical committee approval was not required as it is a retrospective study of anonymous data.

RESULTS

The study cohort of 50 patients included 31 females and 19 males, with a mean age of 33 years (range: 20–54). During hip arthroscopy, 62% (n = 31) of patients were noted to have global hip synovitis, while 38% (n = 19) did not [Tables 1-3]. Among the 31 patients with synovitis, 17 were female and 14 were male. Utilizing the BARC classification for LTs, we observed that the majority of patients (87%, n = 27) had a grade II tear, whereas only 13% (n = 4) had a grade III tear. None of the patients exhibited grade I pathology. Out of this cohort of patients with synovitis, 26 patients had recorded VAS and EQ5D scores, while data were unavailable for the remaining 5 patients. The average VAS score for patients with synovitis was 73.7 (ranging from 40 to 100), and the mean EQ5D score was 0.6 (ranging from 0.32 to 0.8).

Among the total of 19 patients without synovitis, 15 were female and 4 were male. Of these patients, the majority (68%, n = 13) had a grade II LT, while 26% had a grade III tear, and only one patient had grade I labral pathology. Of the 19 patients, 16 patients had recorded VAS and EQ5D scores, while 3 patients had no available scores present. The average VAS score for patients without synovitis was 68.3 (with a range of 20–93) and a mean EQ5D score of 0.5 (ranging from 0.04 to 0.84).

Conducting an ANOVA analysis to compare VAS and EQ5D scores between patients with synovitis and those without, we found no significant difference, with a P = 0.37 for VAS score comparison and 0.15 for EQ5D. These findings were further supported by a post hoc analysis using the Tukey test.

DISCUSSION

This study has demonstrated that the majority (62%) of patients undergoing hip arthroscopy with an MRI confirmed LT had significant synovitis within the hip joint. Despite this, although pathological LTs are thought to be a significant pain generator, the analysis of VAS and EQ5D scores revealed no significant difference between patients with synovitis and those without, indicating that the presence of synovitis may not directly impact pain severity and quality of life in patients with LTs.

The labrum is a triangular-shaped fibrocartilaginous structure that attaches to and surrounds almost the entirety of the acetabular rim, transitioning into the transverse acetabular ligament inferiorly.^[13,14] The anterior part of the labrum is wider and thinner, while the posterior labrum is thicker and has a sulcus formation, which can be mistaken for a pathological feature.^[13,14] The labrum plays an important role in hip joint stability by deepening the joint and maintaining the suction seal of the joint. The negative pressure created by this suction seal helps to maintain the synovial fluid, which lubricates and nourishes the joint and helps distribute contact forces across the articular surfaces.^[13,14]

The location of LT is an important consideration for treatment methods and often corresponds to the area of mechanical conflict between the femur and acetabulum. The most common and simple classification used is based on their location within the labrum, including anterior, posterior, and superolateral tears, of which the latter are the most common.^[15-20] Determining the underlying cause of LTs is essential for determining the most effective treatment approach.^[15-18] This can be challenging, especially when associated with subtle structural abnormalities.

Typically, the first imaging modality used in young adults presenting with anterior hip and groin pain is radiographic evaluation, which can reveal structural abnormalities within the joint, including osteoarthritis, dysplasia, and CAM morphology. However, further evaluation with MRI and/or MRA is often performed to further assess labral and chondral lesions, as well as provide detailed information on the morphology of the acetabulum and proximal femur.^[21,22]

Although MRI is a useful tool for diagnosing LTs, it has limited sensitivity, with reported rates of around 66%,^[23] and can underestimate the severity of labral pathology. Furthermore, recesses (such as the anterior sublabral recess) seen on MRI can often provide false-positive results, further complicating diagnosis on MRI.^[21-24] The current gold standard imaging technique for LTs is MRA.^[21] However, MRA is an invasive procedure with limitations to its sensitivity and specificity found to range from 60% to 100% and 44% to 100%,^[25,26] respectively, compared to diagnostic arthroscopy. Therefore, diagnostic hip arthroscopy may occasionally be used for further evaluation in cases where there is a high degree of clinical suspicion for intra-articular pathology.

Hip arthroscopy is considered the gold standard for the diagnosis and treatment of symptomatic LTs arising from FAI syndrome.^[27] Several studies have suggested that the key cause of pain induced by LT is secondary to synovial inflammation and that labral degeneration is positively correlated with it, especially in patients with FAI.^[28-31] The incidence of synovial inflammation in the presence of LT has not been described previously. Our study found that approximately 62% of patients with LTs also had significant hip synovitis.

CONCLUSION

Our study found that global hip synovitis is present in 62% of patients with an MRI-confirmed diagnosis of LT. If synovitis is present during hip arthroscopy, its presence can guide surgeons to carefully examine the labrum for a tear during hip arthroscopy, particularly in cases where LTs are not initially diagnosed on MRI. Our findings contribute to the evolving body of knowledge regarding hip arthroscopy.