Biochemical and Histologic Evaluation of Pulvinar Synovium Provides Insight Into Osteoarthritis Progression Secondary to Femoroacetabular Impingement

Recent studies have used femoroacetabular impingement (FAI) as a model for hip osteoarthritis, however, the cellular mechanisms underlying disease progression remain unclear. Pulvinar abnormalities within the cotyloid fossa are common findings during hip preservation surgery and total hip arthroplasty (THA). The purpose of this study was to compare histologic inflammation and gene expression of pulvinar synovial tissue in patients with FAI and patients with hip osteoarthritis secondary to FAI (FAI-OA). Patients undergoing hip arthroscopy for FAI and THA for osteoarthritis with FAI morphology (FAI-OA) were included. Macroscopic evaluation of the pulvinar for the FAI cohort was classified through the ligamentum-fossa-fovea complex (LFFC) grading system. RNA was isolated for reverse transcription-polymerase chain reaction to evaluate the expression of inflammatory genes. Synovial samples were graded according to the histologic synovitis scoring system. Twenty-nine patients were included in the study (17 FAI and 12 FAI-OA). FAI patients had a lower pulvinar synovial score (2.3 ± 1.1) compared to FAI-OA patients undergoing THA (3.6 ± 1.7; p = 0.04). Macroscopic pulvinar inflammation in the FAI cohort according to the LFFC classification was associated with worsening histologic synovitis (r = 0.82; p < 0.001). There were no differences in gene expression between the FAI and FAI-OA cohorts, while there was increased expression of IL1β, TGF-β1, and PPARγ in subjects without significant pulvinar synovitis. Increased catabolic gene expression by the pulvinar tissue of patients without histologic synovitis earlier in the disease process may promote the development of worsening synovitis and contribute to articular cartilage degeneration. STATEMENT OF CLINICAL SIGNIFICANCE: Understanding the role of the pulvinar tissue within the hip, both macroscopically and biochemically, can help surgeons understand the complexities of the presentation and progression of osteoarthritis.