Predictors of chronic pain following total knee replacement in females and males: an exploratory study.

AIM: This study explored whether nociceptive (NS) and autonomic nervous system (ANS) dysregulation and psychological distress were predictive of pain 6 months after primary total knee replacement.

PATIENTS & METHODS: ANS and NS regulation, psychological distress and self-reported pain, stiffness and function were evaluated preoperatively in 56 patients. Pain severity measured 6 months after surgery was used as the primary outcome in an analysis of covariance model.

RESULTS: The data of 47 patients (85.5%) could be analyzed. Postoperative pain severity 6 months after surgery was significantly associated with reduced heart rate variability and tended to be related to a lower conditioned pain modulation effect, but the latter only in females.

CONCLUSION: Due to the small sample size the results must be interpreted with caution. A dysregulation of ANS and NS may be predictive of pain severity 6 months after total knee replacement. The impact of the conditioned pain modulation effect could be sex specific.