Facilitated temporal summation of pain correlates with clinical pain intensity after hip arthroplasty

Widespread hyperalgesia has been found in patients with painful hip osteoarthritis (OA) which can be normalized after total hip arthroplasty (THA) if patients have no residual postoperative pain. This study characterized the preoperative somatosensory profiles and provided possible interpretation of underlying pain mechanisms that might influence the development of postoperative pain. Forty hip OA patients with unilateral pain were assessed before and 6 weeks post-THA and compared with 40 asymptomatic control subjects. Hip pain intensity at rest and while walking was assessed on a visual analogue scale (VAS). Bilateral cuff algometry from the thighs was used to assess the cuff pressure pain thresholds, pressure values at VAS scores equal with 6 cm (PVAS6), cuff pressure tolerance, and temporal summation of pain (TSP) quantified by an increase in VAS scores to repeated phasic cuff stimulations. Correlations between hip pain VAS post- THA and preoperative quantitative sensory testing results were analyzed. Post-THA hip pain VAS scores decreased (P, 0.05) compared with pre-THA. The cuff pressure pain threshold, PVAS6, and cuff pressure tolerance were significantly lower bilaterally in both patients with pre-THA and post-THA compared with controls (P < 0.05). Temporal summation of pain was facilitated bilaterally in patients with pre-THA compared with controls and normalized after THA in postoperative pain-free patients (P < 0.05). Postoperative hip pain VAS scores correlated with preoperative ipsilateral TSP (r =0.44, P < 0.05). Bilateral pressure pain hypersensitivity and facilitated TSP were demonstrated in patients with preoperative hip OA. Although persistent postoperative pain is known as multifactorial, greater preoperative TSP was associated with greater pain and less reduction in pain after THA.