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.

Heightened flexor withdrawal responses following ACL rupture are enhanced by passive tibial translation.

OBJECTIVE: Hyperexcitability of nociceptive pathways has been demonstrated with several musculoskeletal conditions but not anterior cruciate ligament (ACL) injury. The purpose was to investigate flexor withdrawal reflex (FWR) excitability following ACL rupture and determine if painless stretch of knee joint structures enhanced reflexive responses. METHODS: Ten subjects with and 10 subjects without unilateral ACL rupture were compared. FWRs were induced through sural nerve stimulus in symmetrical stance and recumbent positions, with the knee in relaxed and stressed condition. Latencies and amplitudes of hamstring electromyographic activity were analyzed. RESULTS: FWR thresholds were significantly diminished (p=0.05) on the injured limb (11.8±8 mA) compared to non-injured limb (18.6±13 mA) and controls (22.5±3 mA). Anterior tibial translation resulted in increased (p=0.001) amplitude of EMG hamstring response on the injured limb (70±50%) versus control (-1±20%) and decreased latency (p=0.01) of hamstring activation (82.0±13 ms). CONCLUSIONS: Individuals with ACL rupture demonstrated increased excitability of FWR responses indicated by decreased FWR threshold and reduced hamstring muscle latency. Responses were enhanced by passive stretch of the knee joint. SIGNIFICANCE: Subjects with ACL rupture demonstrated hyperexcitability of nociceptive pathways on the injured limb which may trigger the FWR more readily and promote the sensation of instability at the knee.