Demographic biases of scoring instruments for the results of total knee arthroplasty

Four knee-scoring systems were used to evaluate 200 adult subjects who had no history of injury, abnormality, or treatment of the knees, hips, lower extremities, or spine. All subjects were in the age-range (fifty to 100 years; average, 65.5 years) typical of candidates for total knee replacement. In addition to a physical examination, complete demographic data were collected for each subject. The knee scores were normalized by dividing the observed score by the maximum possible score. The average normalized total knee score was 91 per cent (range, 22 to 100 per cent) according to the knee score of The Hospital for Special Surgery, 95 per cent (range, 10 to 100 per cent) according to the system of Hungerford and Kenna, 89 per cent (range, - 7.75 to 100 per cent) according to a modification of the scoring system of The Knee Society, and 95 per cent (range, 26.5 to 100 per cent) according to the system of Hofmann et al. Demographic variables that had a significant negative correlation with the knee scores included advanced age (particularly of eighty-five years or more), a family income below the poverty level, and two major medical conditions or more. Observed differences in knee scores between different study groups that have not been matched for various clinically relevant factors are at least as likely to represent differences in the patient populations as they are to represent differences in the operative technique or the design of the implant.