Synovitis: a potential predictive factor of structural progression of medial tibiofemoral knee osteoarthritis – results of a 1 year longitudinal arthroscopic study in 422 patients

SummaryObjectiveTo evaluate the prevalence of synovitis in painful medial tibiofemoral knee osteoarthritis (OA) and to evaluate correlation between synovitis and the structural severity and progression of tibiofemoral cartilage damage.DesignStudy: multicenter, longitudinal, 1-year duration. Patients: primary painful knee OA (ACR criteria) of the medial tibiofemoral compartment, with pain of the signal knee on at least 30 days in the past 2 months, medial joint space width ≥2mm, at least 10% of one cartilage surface of the medial compartment affected by superficial fibrillation or worse at baseline arthroscopy. Arthroscopic parameters: knee arthroscopy under local anesthesia was performed and videorecorded at entry and after 1 year. Medial chondropathy was scored by using Société Française d'Arthroscopie (SFA) score (0–100) and reader's overall assessment (VAS score, 100mm). Progression of medial chondropathy was defined by a change in SFA and VAS scores over 4.5 and 8.0mm after 1 year, respectively. Medial perimeniscal synovium was scored as normal (few translucent and slender villi, fine vascular network), reactive (proliferation of opaque villi), or inflammatory (hypervascularization and/or proliferation of hypertrophic and hyperemic villi). Medial chondropathy and synovitis were scored by a single reader blind to chronology of paired videotapes.ResultsFour hundred and twenty-two patients were enrolled (mean age: 61 years, females: 59%, body mass index: 31, mean disease duration: 4 years) and completed the 1-year study. Synovial abnormalities were present in 50% of the patients with reactive and inflammatory aspects in 29% and 21% of the patients, respectively. Patients with a reactive or inflammatory medial synovium had a more severe medial chondropathy. The worsening in medial chondropathy after 1 year was statistically more severe in the group of patients with an inflammatory perimeniscal synovial membrane at baseline compared to patients with normal and reactive aspects, with no difference between these two latter groups. The odds ratio for progression in VAS score after 1 year was 3.11 (95% CI [1.07, 5.69]) for patients with inflammatory synovium at baseline compared to patients with normal synovium.ConclusionsThis study suggests that abnormalities of the medial perimeniscal synovium are a common feature of painful medial knee OA, associated with more severe medial chondropathy. It also suggests that an inflammatory aspect of the medial perimeniscal synovium could be considered as a predictive factor of subsequent increased degradation of medial chondropathy