Among the patients with ACL injury, the T2 relaxation time of some articular cartilage correlated with serum COMP levels. It may indicates that the serum COMP is useful to detect early OA after ACL injury. This biomarker may have a potential to detect early OA and to prevent development and progression of OA after ACL injury.
Objectives:Many previous reports described that anterior cruciate ligament (ACL) injury accelerates the risk of joint degeneration and leads to knee osteoarthritis (OA) and ACL reconstruction does not reliably prevent the development of knee OA. However, radiographic evaluation of OA detects on the presence of joint space narrowing and osteophyte. Magnetic resonance imaging (MRI) is useful to detect early articular cartilage degeneration. Recently, quantitative MRI evaluation have been developed to detect changes within the cartilage matrix in the early stage of OA. T2 mapping has been shown to correlate to collagen orientation in the extracellular matrix of cartilage and T2 relaxation times elevated in patients with knee OA.
On the other hand, cartilage oligomeric matrix protein (COMP) is an extracellular matrix glycoprotein that is released into circulation when cartilage degenerates and therefore is considered a marker of cartilage breakdown. It may be able to detect early OA before radiographic changes become apparent. The aim of this study is to measure serum COMP levels for ACL injured patients and to examine the potential utility of COMP as a diagnostic biomarker, comparing with T2 mapping technique.
47 patients (18 male and 29 female) who underwent ACL reconstruction within 12 months after injury and underwent blood test for serum COMP level were enrolled after providing informed consent. Mean of the age was 22.4 years (13-47), and mean time from injury to operation was 3.8 months (1-11). Serum samples, COMP and matrix metalloproteinase 3 (MMP-3) were obtained before and 1 year after surgery. At follow-up, the patients underwent knee radiograph and MRI (Philips Achieca3.0-T X series). K-L radiographic grade and MRI-T2 mapping were calculated for each patient at baseline and at 1-year follow-up. We set the regions of interest (ROIs) on the full-thickness cartilage of the medial and lateral femoral condyle (MFC/LFC) and medial and lateral tibial plateau (MTP/LTP) and patellofemoral joint (P/F) of the knee and measured the cartilage T2 relaxation times (ms). Relationships between serum COMP levels and age, pre-activity level using Tegner activity scale (TAS), serum MMP-3 levels, K-L grade, T2 relaxation times were assessed by the calculation of Pearson correlation coefficients.
The mean serum COMP level was 151.6ng/ml at baseline. The age, serum MMP-3 level at baseline, KT grade, T2 values of MTP at baseline and T2 values of MFC and P at 1-year follow-up were correlated with the serum COMP level at baseline (r=0.28, 0.34, 0.58, 0.29, 0.32 and 0.33). There was no correlation between any other parameters and serum COMP levels at baseline and 1-year follow-up.
In previous report, serum COMP is elevated patients with age and presence of knee OA and synovitis. Serum COMP and T2 relaxation times are also elevated patients with ACL injury than control subjects, but this is the first study to examine the correlation between serum COMP and T2 relaxation times. The T2 relaxation time of some articular cartilage correlated with serum COMP levels and it may indicate that serum COMP is useful to detect degenerative change of articular cartilage.