This study is the first in a series to assess the psychometric properties of the HJHS, a promising new measure of joint health in boys with haemophilia.

Objective. Repeated hemarthrosis in hemophilia causes arthropathy with pain and dysfunction. The Hemophilia Joint Health Score (HJHS) was developed to be more sensitive for detecting arthropathy than the World Federation of Hemophilia (WFH) physical examination scale, especially for children and those using factor prophylaxis. The HJHS has been shown to be highly reliable. We compared its validity and sensitivity to the WFH scale. Methods. We studied 226 boys with mild, moderate, and severe hemophilia at 5 centers. The HJHS was scored by trained physiotherapists. Study physicians at each site blindly determined individual and total joint scores using a series of visual analog scales. Results. The mean age was 10.8 years. Sixty-eight percent were severe (93% of whom were treated with prophylaxis), 15% were moderate (24% treated with prophylaxis), and 17% were mild (3% treated with prophylaxis). The HJHS correlated moderately with the physician total joint score (r s ‫؍‬ 0.42, P < 0.0001) and with overall arthropathy impact (r s ‫؍‬ 0.42, P < 0.0001). The HJHS was 97% more efficient than the WFH at differentiating severe from mild and moderate hemophilia. The HJHS was 74% more efficient than the WFH at differentiating subjects treated with prophylaxis from those treated on demand. We identified items on the HJHS that may be redundant or rarely endorsed and could be removed from future versions. Conclusion. Both the HJHS and WFH showed evidence of strong construct validity. The HJHS is somewhat more sensitive for mild arthropathy; its use should be considered for studies of children receiving prophylaxis.