A subgroup of patients that undergo TKR surgery have evidence of neuropathic pain and central sensitization that may predispose to severe postoperative pain. This study assesses the correlation of MRI detected bone marrow lesions (BMLs) and synovitis with markers of neuropathic pain and central sensitization in patients undergoing TKR surgery and healthy volunteers.

31 patients awaiting TKR and 5 healthy volunteers were recruited. Each subject underwent a 3-T knee MRI scan that was graded for BMLs (0–45) and synovitis (0–3) using subsets of the MRI Osteoarthritis Knee Score (MOAKS). All subjects were asked to complete the PainDetect questionnaire to identify nociceptive pain (< 13), unclear pain (13–18) and neuropathic pain (>18). Correlation between BMLs and PainDetect score was the primary outcome measure. Secondary outcomes included the correlation of synovitis to PainDetect and temporal summation (TS) a measure of central sensitization to the PainDetect score. TS was determined using a monofilament to evoke pain. Pilot histological analysis of the prevalence of osteoclasts (TRAP⁺) within BMLs versus normal subchondral bone was performed, implying a role in BML pathology.

Increasing BML MOAKS score correlated with neuropathic pain (painDetect), r_s = 0.38, p=0.013 (one-tailed). There was a positive correlation between synovitis and PainDetect score, τ =0.23, p= 0.031 (one-tailed). TS was greater in the neuropathic pain than in nociceptive pain patients, U = 18.0, p=0.003 (one-tailed). TRAP staining identified more osteoclasts within BMLs than contralateral condyle lesion free subchondral bone, z = −2.232, p = 0.026 (Wilcoxon Signed Rank Test, one-tailed).

BMLs and synovitis are more prevalent in neuropathic pain and central sensitization in knee OA. Higher osteoclast prevalence was seen within BMLs which may help explain the association with BMLs and pain in OA.