Post arthroplasty excessive knee pain, could it be neuropathic pain or complex regional pain syndrome type 1? A preliminary study

Abstract

Introduction: Persistent knee pain (PKP) post arthroplasty remains a problem for a subgroup of patients despite serological investigation and diagnostic imaging shown no obvious cause for their signs & symptoms. The infrapatellar branch of the saphenous nerve (IPS) that crosses the inferior knee from medial to lateral and the anterior inferior knee capsule may be injured during surgery. This may potential cause IPS neuropathic pain syndrome or query as Complex Regional Pain Syndrome (CRPS). Preliminary study to differentiate between them. Methodology: Nine PKP patients referred to occupational therapy department for pain management were recruited between October 2017 and May 2018 at Queen Mary Hospital. Budapest Criteria of CRPS, Knee Sensitization Assessment (hot, cold & light touch) & PainDETECT neuropathic pain questionnaire were adopted. Results and Analysis: Nine female patients, mean age 75, post operation 12.5 weeks. Budapest Criteria shown 44% patients were CRPS. Knee Sensitization Assessment results shown hypoalgesia 55%, hyperalgesia 33% & allodynia 33%. Among those sensitization problems, 22% were medial & 78% were lateral to surgical incision & below joint line. PainDETECT on neuropathic pain (NP) with mean score: 13.44. “Unlikely NP” 44%, “May Have NP” 33%, “Definitely NP” 23%. Budapest Criteria CRPS correlated with PainDETECT score (r=0.767, p<.05). Among CRPS patients, 50% had “Definitely NP” & 50% “May have NP”. Discussion and Conclusion: Criteria diagnosed CRPS Type 1 patients highly correlated to NP and from knee sensory assessment revealed the surgical incision injured IPS. Treatment should more focus on IPS neuralgia & function restoration.