Demographic biases found in scoring instruments of total hip arthroplasty

Four hip scoring systems were used in evaluating 200 adult subjects who had no prior history of injury, pathologic condition, or treatment of the hips, knees, lower extremities, or spine. All subjects were in the age range typical of a total hip arthroplasty candidate (average age, 65 years; range, 50-100 years). In addition to a physical examination, complete demographic data were collected on each subject. Data were recorded on standardized flow sheets so that hip scores could be calculated; scores were normalized by dividing the observed scores by the maximum possible score. The average normalized total hip scores were Harris hip score, 90.8%; modified Harris hip score, 91.9%; Merle D'Aubigne score, 93.9%; and Hospital for Special Surgery hip rating 87.5%. Demographic variables that had a significant negative correlation with hip scores included advanced age (particularly past age 85), an income below the poverty level, and the presence of two or more major medical conditions. Differences in hip scores between different study groups that have not been matched for various clinically relevant factors ("case mix") are at least as likely to represent differences in the patient populations as differences in surgical technique or implant design. Hip scores may decline over the course of a 10- to 20-year follow-up period due to the change in a patient's age and/or medical condition rather than any factor relating to the hip arthroplasty.