Total knee arthroplasty (TKA) is an effective procedure for end-stage osteoarthritis of the knee. Some patients experience persistent unexplained pain post-TKA despite normal investigations. The purpose of this study is to identify which of these patients are likely to improve without any surgical intervention. We hypothesize that patients with unexplained persistent pain and a poor 6-month Oxford knee score (OKS) post-TKA can improve at 2 years.
Prospectively collected data for all primary unilateral TKA performed from June 2004 to January 2012 were analyzed to identify which patients with unexplained pain at 6 months will improve at 2 years. Patients were included if they had persistent pain and an OKS <27 at 6 months; normal radiological and clinical investigations; no infection identified; surgery performed for primary osteoarthritis. Two hundred sixty patients with OKS <27 at 6 months were analyzed. These patients were subdivided into 2 groups (group 1: 6-month OKS 20-26, group 2: 6-month OKS less than 20).
One hundred ninety-one out of 208 (92%) patients in group 1 experienced improvement in pain and outcome at 2 years. Most of the group 1 patients attained a minimal clinically important difference in OKS of at least 5 (P < .001) at 2 years. Group 1 patients also reported better Knee Society Functional Score and Short Form Survey 36 mean scores at 2 years.
In patients with unexplained pain, an OKS of at least 20 at 6 months predicts good functional outcome at 2 years.