Musculoskeletal and biomechanical characteristics are better associated with knee clinical condition than radiographic severity in osteoarthritis patients

Purpose: The diagnosis of knee osteoarthritis (OA) is typically well established with a clinical evaluation and confirmed with an X-Ray assessing the joint’ structural changes and disease progression. Guidelines also recommend taking into account mechanical factors (static and dynamic) to better understand knee function, since they may influence treatment outcomes. However, the relationship between clinical condition of the knee and biomechanical characteristics is not well known, including how such information stands compared to those from other conventional assessments, such as X-ray and physical assessment. The aim of this study is to evaluate the associations between the knee clinical condition assessed by patient-reported outcome measures and parameters from three different types of assessments, namely radiographic, musculoskeletal, and biomechanical assessment in OA patients. Methods: This cross-sectional study was conducted on patients with 1) knee pain ≥ 4/10 on a numeric rating scale in the past 7 days, 2) Kellgren-Lawrence (KL) radiographic OA severity grade higher than KL2, and 3) who were not on a waiting list for knee arthroplasty. Patients’ knee clinical condition was assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire that consists of five subscales: pain, symptoms, function in daily living (ADL), function in sport and recreation (Sport/Rec) and knee-related quality of life (QOL). Twenty musculoskeletal tests were performed by a therapist, including passive flexion and extension ranges of motion (ROM), muscle strength (10 tests assessing hip, knee, and ankle), flexibility (4 tests), swelling measured by the circumference difference between knees, effusion, balance, and functional 30-second chair stand tests (30s_CST). Finally, dynamic mechanical factors were measured during a knee kinesiography exam with the KneeKG™ system (Emovi Inc., QC, Canada) where 70 biomechanical parameters were extracted from 3D knee kinematic curves captured during gait (namely in flexion/extension, adduction/abduction, internal/external tibial rotation). KOOS associations with radiographic severity grades, musculoskeletal tests, and biomechanical parameters were assessed using a canonical correlation analysis (CCA). CCA is a statistical multivariate method for determining the association between two sets of variables measured on the same patients. This method is a multivariate extension of the bivariate approach, where the Pearson’s correlation coefficient r is calculated to quantify the association between two variables. CCA consists of maximizing the Pearson's coefficient between two sets of variables. This allows calculating two distinct types of correlations: the canonical correlations (i.e. ρ coefficients) which quantify the global association between the two sets, and the structural correlations (i.e. Corr coefficients) which estimate the association between a set as a whole and each variable of the other set. This method was used to calculate ρ and Corr coefficients between the KOOS set (i.e. the scores on its five subscales) and all three other data sets (i.e. KL grades, musculoskeletal tests, biomechanical parameters). These coefficients were calculated considering all participants and also sub-groups dividing men and women to assess the impact of sex. Results: 415 participants (251 women and 164 men) were included in this study. The mean (±standard deviation) age and body mass index were 63.3±9.2 years and 30.3±5.6 kg/m2 respectively. The radiographic severity grade was well distributed among patients in the cohort (mild_KL2_n=137, moderate_KL3_n=149, and severe_KL4_n=129). All ρ and Corr coefficients presented indicate a statistically significant correlation (all p0.30). When separating by sex, four of these five parameters were also among the most associated with KOOS in women (Table 2). The remaining parameter (passive flexion ROM) was the second most associated with KOOS for men (after the 30s_CST), followed by a biomechanical parameter (flexion angle ROM during loading) and two additional musculoskeletal parameters (i.e. ankle plantar flexion and hip extension strengths; Table 2). Among these best-associated parameters, the 30s_CST and the flexion angle ROM during loading were the only ones shared between men and women sub-groups. Notably, the radiographic severity grade was more associated with KOOS in men than in women (Corr=-0.261 vs -0.161 respectively). Conclusions: Results suggest that musculoskeletal and biomechanical characteristics are better associated with the patient clinical condition than radiographic severity for knee OA patients. Differences were observed between sexes, as women’s condition was more associated with biomechanical parameters, while men’s condition was similarly associated with musculoskeletal tests results and biomechanical parameters. However, similarities like the performance on the 30s_CST and the role of flexion angle ROM during loading were reported. This study supports the value of adding a biomechanical assessment to the musculoskeletal examination to better understand the clinical state of the knee and to prioritize which mechanical factors to be addressed to improve patient’s condition