Introduction

The risk of knee osteoarthritis (OA) is increased after anterior cruciate ligament (ACL) injury due to subchondral, cartilaginous, or meniscal injury sustained at the time of the initial injury or injury recurrence secondary to knee instability. The standards applied for OA diagnosis are usually clinical symptoms and radiographic criteria. However, the disease is initiated long before it can be detected on plain X-rays, and thus when physical or radiographic evidence of OA is established, signi?cant and irreversible disease progression may already have occurred and the optimal time for early treatment is delayed. Therefore, more sensitive techniques for the diagnosis of early OA are needed. Cartilage oligomeric matrix protein (COMP) is a non-collagenous protein related to the thrombospondin family of proteins and is primarily found in the articular cartilage, tendons, and synovium. COMP has utility as a diagnostic marker for OA. COMP may also be able to detect cartilage damage in early knee OA. However, few studies have assessed the reliability of COMP for early OA. The purpose of the present study was to determine the associations of serum COMP with clinical, MRI, and arthroscopic findings in patients with ACL injuries that approximate early knee OA.

Methods

Patients with ACL injury of Kellgren–Lawrence grade 0 or 1 were enrolled after providing informed consent. Serum samples for COMP and matrix metalloproteinase-3 (MMP-3) measurement were obtained before surgery. Correlations of serum COMP with age, body mass index (BMI), duration from injury, Tegner activity scale (TAS), Lysholm knee score, International Knee Documentation Committee score, a side-to-side difference of KT-1000 arthrometer measurements, serum MMP-3, whole-organ magnetic resonance imaging score (WORMS), and MRI T2 relaxation times, and arthroscopic International Cartilage Research Society (ICRS) grade were assessed by calculating Spearman correlation coefficients. We set the regions of interest on the full-thickness cartilage of the medial and lateral femoral condyle (MF/LF) and medial and lateral tibial plateau (MT/LT) and patellofemoral joint (Patella/Trochlea) of the knee and measured the cartilage T2 relaxation times. Associations between intraoperative findings (cartilage, meniscus) and serum COMP were examined by the Mann–Whitney U test. Multiple regression analysis was performed to investigate the correlations between serum biomarker levels and MRI and arthroscopic findings.

Results

Ninety-eight patients were included. The mean age was 23.4 years (range, 12–49 years). The median duration from injury was 3.4 months (range, 0.4–353 months). Higher serum COMP was correlated with higher age, BMI, TAS, serum MMP-3, WORMS, and T2 relaxation times (MF, MT, all regions). Multivariate analysis revealed that serum COMP was an independent factor associated with MRI findings (WORMS) and arthroscopic cartilage findings.

Discussion

The serum COMP level was correlated with age, BMI, TAS score, and MMP-3 level in ACL-deficient knees and was independently correlated with WORMS and ICRS grade. Thus, the serum COMP level can help detect cartilage degeneration even in patients without radiographic osteoarthritic changes.