Abstract
Background
Assessing patients’ functional outcomes following total knee arthroplasty (TKA) 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.
Methods
101 TKA were assessed at a mean of 41 months of follow-up (range 29=51). 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.
Results
The mean FJS was 79.0 (range 0=100). PJP was correlated with the FJS and WOMAC (Spearman's rho −0.720 and 0.684, respectively). 34% of the patients felt their prosthetic knee as a natural joint (FJS: 95% confidence interval [CI] 92.2–97.9), 15% as an artificial joint with no restriction (FJS: 95% CI 69.6–93.5), and 40% as an artificial joint with minor restrictions (FJS: 95% CI 65.4–78.3). 11% had major restrictions and none reported a non-functional joint. The ceiling effect was high with both the WOMAC and FJS, where 17% and 18% achieved the maximal score respectively. In addition, 13% of the patients had a WOMAC >10 and 22% an FJS < 90 while reporting having a natural knee. Furthermore, 19% with a perfect WOMAC reported having an artificial joint with or without limitation.
Conclusion
With a TKA, a forgotten knee perception corresponds to an FJS >92. In 13%–22% 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 knee was natural. The PJP is a simple and reliable tool that enables identification of patients who feel replaced knee is natural.
