Abstract
Purpose: Osteoarthritis (OA) is a non-rheumatoid joint disease characterized by progressive degeneration of extra-cellular cartilage matrix, enhanced subchondral bone remodeling, osteophyte formation and synovial thickening. It has long been speculated and revealed by the recent development of imaging technique that the degeneration and destruction of articular cartilage are started silently and earlier than it hadlong been speculated. Subchondral bone protects cartilage from high peak stresses and possible matrix damage. Animal OA model reduced the subchondral bone thickness and penetrated the subchondral bone in earlystage of the disease, suggesting that subchondral bone remodeling is involved in disease progression. Tartrate-resistant acid phosphatase 5b (TRACP-5b) is the bone-specific acid phosphatase isozyme localized in osteoclasts. The serum levels of TRACP-5b reflect the number and activity of osteoclasts, indicating conditions of bone resorption. The aim of this prospective study was to investigate whether the baseline bone turnover can predict radiographic joint space narrowing (JSN) of the medial knee joint in men in early forties without knee pain.
Methods: This prospective study was conducted by analyzing data of the Sportology Core Study in Juntendo University Graduate School of Medicine, Tokyo, which was started at 2012. Eighty- seven healthy male volunteers (42.9 y in average) who didn’t have any symptoms for knee pain and experience any traumatic episodes for the knee joints were enrolled in this study. A standing, extended antero-posterior view radiograph of both knee was taken at the time of study entry and at three years follow up. Radiological progression of JSN is defined as a 0.3 mm or greater of JSN during 3-years of follow up than in the knee of lower joint space width (JSW) at baseline. The BMD of lumbar spine (L2-L4)(LS-BMD) and femoral neck (H-BMD) were measured using dual X-ray absorptiometry (DXA). The serum levels of TRACP-5b (sTRACP-5b) were measured by ELISA. We examined the relation of tertile groups of sTRACP-5b or BMD to the risk of the radiographic JSN using the logistic regression model. In the multivariable regression model, we adjusted for continuous age and body mass index.
Results: The subjects were divided into two groups by the presence or absence of the radiological progression: the progression during three years of follow-up was observed in twelve of 87 subjects (P group), while it was not observed in the remaining seventy-five subjects (NP group). No significant differences of age and BMI of P group were observed in comparison to those of NP group. The sTRACP-5b were negatively correlated with the LS-BMD at baseline (r: -0.316, p=0.003). The sTRACP-5b of P group at baseline (326.92 mU/dl) were significantly increased in comparison to those of NP group at baseline (280.83 mU/dl, p<0.01). The LS-BMD of P group at baseline (0.931 g/cm2) was significantly lower than those NP group at baseline (1.005 g/cm2, p<0.01). When the subjects were divided into three groups according to the sTRACP-5b at baseline (T1, T2 and T3), the odds ratio (OR) for the JSN after 3-years of follow up in the upper tertile at baseline (T1) was significantly higher than that in the lower tertile (T3) [Odds ratio: 9.0 (95% CI: 1.0 to 78.9), p<0.05]. This risk for the JSN after 3-years of follow up in the upper tertile at baseline (T1) was still observed after adjustment for age and BMI of the subjects [Odds ratio: 10.5 (95% CI: 1.1 to 97.0), p<0.05].
Conclusions: In a three years prospective study, the higher levels of sTRACP-5b were the risk factor for the radiographic medial JSN in men in early forties without knee pain.
