Clinical and biochemical factors associated with risk of total joint replacement and radiographic progression in osteoarthritis: Data from two phase III clinical trials.

OBJECTIVES: Clinical trials of new disease-modifying treatments for osteoarthritis should demonstrate a positive effect on a functional outcome or reduction in joint failure in order to be considered successful. Total joint replacement (TJR) surgery may be considered as joint failure, but great variation in the incidence of TJR complicates its use as a study endpoint. Factors predicting elevated risk of TJR could potentially be used to enrich such outcome-trials. METHODS: Using cumulative data from two phase three clinical trials with urine samples from 1255 knee OA patients followed for two years, we assessed the value of a series of baseline clinical variables including the uCTX-II biomarker, as predictors of joint-space narrowing, Kellgren-Lawrence-grade progression, and total joint replacement. RESULTS: A prediction-model incorporating age, sex, BMI, CTX-II and KL-grade predicted TJR within the two-year period with an AUC of 0.75 (95% CI: 0.72-0.77). The participants with a cumulative KL-grade between knees of 5, 6, or 7 had a more than 3 times higher risk of TJR in the study period compared to lower (HR: 3.03, 95% CI: 1.54 to 5.96, p = 0.001). Age was associated with increased TJR risk (per 5 years of age: HR: 1.28, 95% CI: 1.03-3.79, p = 0.05). Baseline u-CTX-II was associated with elevated risk of radiographic progression in terms of both JSN and KL-grade. CONCLUSIONS: A composite model combining baseline age, sex, BMI, u-CTX-II and KL-grade was able to acceptably predict TJR during a two-year period. In the absence of baseline radiographic OA severity, u-CTX-II independently contributed to prediction of TJR. Baseline urine CTX-II was associated with risk of radiographic progression.

Associations between biomarkers of bone and cartilage turnover, gender, pain categories and radiographic severity in knee osteoarthritis.

BACKGROUND: Excessive cartilage degradation is a known characteristic of osteoarthritis (OA). Biochemical markers, such as uCTX-II, have been shown to be associated with disease severity, yet the tissue origin of CTX-II has been disputed. This analysis investigates the association between OA knee joints at different radiographic stages and pain categories with levels of uCTX-II and biomarkers of bone resorption and formation. METHODS: Baseline data of two randomised clinical trials (NCT00486434 and NCT00704847) in patients with radiographic OA and presence of pain were analysed post hoc. A subgroup with available urine samples and evaluable radiographs for both knees (N = 1241) was analysed. Urine CTX-I, urine CTX-II and serum osteocalcin were analysed for associations with combined Kellgren-Lawrence (KL) scores, gender and pain for both knees to assess the contribution of joints at different stages. RESULTS: Pain, BMI, age, gender and KL grade were all significantly associated with uCTX-II. The association between pain and CTX-II appeared to be driven by weight-bearing pain. The level of uCTX-II incrementally increased with higher radiographic severity of each knee. Levels of bone markers CTX-I and osteocalcin were both significantly associated with BMI and gender, but neither were associated with radiographic severity. Biomarker levels between male or female groups of identical KL scores were found to be higher in females compared to males in some but not all KL score groups. CONCLUSIONS: These results indicate that levels of uCTX-II are independently associated with radiographic severity of OA and pain intensity. CTX-II was associated with weight-bearing pain, but not non-weight-bearing pain, independent of co-variates. Bilateral OA knee joints appear to contribute to uCTX-II levels in an incremental manner according to radiographic severity of single joints. The data suggest that biomarker differences between genders should be taken into account when evaluating these markers in the context of structural features of OA.