The need for a dual rating system in total knee arthroplasty.

The sequential course of the knee score and functional score of the Knee Society rating system of 276 press fit condylar modular unconstrained total knee arthroplasties performed for osteoarthritis between June 1988 and December 1992 was documented prospectively. The knee score increased significantly and stayed on a constant level from 2 years on, whereas the function score reached a maximum at 2 years and declined subsequently. Multiple regression analysis was performed testing the statistical significance and correlation of preoperative predictors with criteria at followup to determine their influence on outcome. Preoperative predictors were knee score and function score, body mass index, age, gender, patient category, and implant factors. Criteria studied were pain, knee score, and function score at 2 years followup. The function score is influenced significantly by the walking distance, age, body mass index, and patient category correlating moderately. The knee score is not affected by any of these factors. Pain was found to correlate low with the walking distance. Rating systems are influenced by numerous factors linked to the patient's general health and condition. Their impact on the overall result can be controlled by separate rating of the knee score and function score as the dual Knee Society rating system does. Scoring systems adding up knee and functional rating to an overall result should not be used. There is a need for additional improvement of total knee arthroplasty rating such as patient based evaluation and establishing reliability and validity.