Joint Perception After Total Hip Arthroplasty and the Forgotten Joint

Assessing patients' functional outcomes following total hip arthroplasty with traditional scoring systems is limited by their ceiling effects. The Forgotten Joint Score (FJS) has been suggested as a more discriminating option. The actual score in the FJS which constitutes a "forgotten joint," however, has not been defined. The emerging concept of joint perception led to the development of the Patient's Joint Perception question (PJP) to assess the patient's opinion of their prosthetic joint.

Two hundred fifty-seven total hip arthroplasties were assessed at a mean of 68 months of follow-up (range 57-79). Outcomes included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), FJS, and PJP. Correlation of the scores as well as the ceiling effects were analyzed.

The mean FJS was 88.5 (range 27.1-100). PJP was correlated with the FJS and WOMAC (Spearman's rho -0.510 and 0.465, respectively). Fifty-two percent of the patients felt their hip as a natural joint (FJS: 95% confidence interval [CI] 93.3-96.0), 24.1% as an artificial joint with no restriction (FJS: 95% CI 83.1-90.5), and 23.3% as an artificial joint with minor restrictions (FJS: 95% CI 73.8-82.2). Only 0.8% had major restrictions and none reported a non-functional joint. The ceiling effect was high with both the WOMAC and FJS, with 27.2% and 31.9%. In addition, 28.6% of the patients had a WOMAC >10 and 23.4% an FJS <90 while reporting having a natural hip. Furthermore, 21.5% with a perfect WOMAC or 21.9% with a perfect FJS reported having an artificial joint with or without limitation.

A forgotten hip perception corresponds to an FJS >93. In 20%-30% of the cases, the WOMAC and FJS failed to identify the forgotten joint, or reached the maximum score when the patients did not feel their hip was natural. The PJP is a simple and reliable tool that enables identification of patients who feel replaced hip is natural.