In the absence of consensus over criteria for performing total knee arthroplasty, the variability of symptom burden, and limited resources, some ways to prioritize whether and when to treat would be useful. In the UK, some payers use the New Zealand score to determine access to an orthopaedic surgeon despite limited validation. We tested convergent validity of this score and ascertained its ability to discriminate between groups of patients with high or low disease burden as determined by a validated disease-specific measure. The sample included patients being considered for total knee arthroplasty at one hospital. Convergent validity was tested against the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The ability of the New Zealand score to discriminate between high and low disease burdens was tested by plotting a receiver operating characteristic curve. Correlations between the New Zealand score and WOMAC pain and function were moderate (0.5 and 0.54, respectively). The area under the receiver operating characteristic curve was 0.77, suggesting the New Zealand score was able to discriminate. This study supports the validity of the New Zealand score. However, additional multisite and extended evaluations are needed before we would recommend widespread implementation.
Level of evidence: Level I, economic and decision analyses. See the Guidelines for Authors for a complete description of levels of evidence.