Association between altered somatosensation, pain, and knee stability in patients with severe knee osteoarthrosis

Objective: To examine the relationship between knee pain, altered somatosensation, and self-reported instability in individuals with knee osteoarthrosis (OA) during a step-up-and-over task. Methods: Quantitative sensory testing, including mechanical detection threshold (MDT), allodynia, vibration perception threshold, and pressure pain threshold (PPT), was assessed in 16 individuals (mean age, 52±7 y) with knee OA and in 16 age-matched and sex-matched controls. Pain intensity ratings and subjective reports of instability/buckling were recorded at rest and while performing a step-up task, and these findings were correlated with somatosensory measures. Results: In the OA group, all participants reported allodynia on MDT testing. Compared with healthy controls, MDT was significantly increased (P<0.001), and vibration perception threshold was increased (P=0.02) at the medial knee, indicating hypoesthesia. PPT was significantly decreased at the medial joint line (P=0.03) and 12 cm distal (P=0.02). Comparing participants with OA having severe versus mild radiographic changes, PPT was lower at the medial joint line (P<0.01) but not at 12 cm distal. Fourteen (87.5%) participants with knee OA reported pain and instability during the step task as compared with none or 1 (6%) of the controls. On the step task, longer duration of symptoms was associated with increased pain (P=0.02). A moderate correlation between greater self-reported instability and increased vibratory hypoesthesia at the knee (r=-0.633; P=0.01) was demonstrated, suggesting a potential relationship between somatosensory changes and functional deficits. Conclusions: Severe OA may result in both hyperalgesia and hypoesthesia at the affected knee. Perceived instability during functional tasks may be mediated in part by pain in individuals with knee OA.