Rationale of The Knee Society Clinical Rating System

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John N. Insall, MD, Lawrence D. Dorr, MD, Richard D. Scott, MD, and W. Norman Scott, MD

From the Hospital for Special Surgery, affiliated with The New York Hospital and Cornell University Medical College, New York, New York.
Presented at the Fourth Open Scientific Meeting of The Knee Society, Las Vegas, Nevada, February 12, 1989.

(Used with permission by Lippincott Williams & Wilkins. This article originally appeared in Clin Orthop. 1989 Nov;(248):13-14. PMID: 2805470)

A new total knee rating system has been developed by The Knee Society to provide an up-to-date more stringent evaluation form. The system is subdivided into a knee score that rates only the knee joint itself and a functional score that rates the patient's ability to walk and climb stairs. The dual rating system eliminates the problem of declining knee scores associated with patient infirmity.

The variety of knee rating systems used in the past made it difficult to compare the merits of prostheses (for example, to judge between cruciate-substituting and cruciate-retaining designs). The Hospital for Special Surgery Rating System is perhaps the most widely used, but was compiled many years ago at a time when knee arthroplasty was in its infancy and expectations of the result were lower. Also, because the Hospital for Special Surgery system incorporates a functional component, the score tends to deteriorate as patients get older, although the knee remains unchanged.

MATERIALS AND METHODS

The Knee Society considered all the commonly used existing rating systems. By consensus it was agreed that the knee rating and the functional assessment should be separate. With regard to the knee assessment, it was decided that only the three main parameters of pain, stability and range of motion should be judged and that flexion contracture, extension lag and misalignment should be dealt with as deductions. Thus, 100 points will be obtained by a well-aligned knee with no pain, 125 degrees of motion, and negligible anteroposterior and mediolateral instability. Patient function considers only walking distance and stair climbing, with deductions for walking aids. The maximum function score, which is also 100, is obtained by a patient who can walk an unlimited distance and go up and down stairs normally.

The form itself is largely self-explanatory: 50 points are allotted for pain, 25 for stability, and 25 for range of motion. Walking ability is expressed in blocks (approximately 100 meters). Stair climbing is considered normal if the patient can ascend and descend stairs without holding a railing (see Table 1).

DISCUSSION

The Knee Society has proposed this new rating system to be simple but more exacting and more objective. The rating is divided into separate knee and patient function scores. Thus, increasing age or a medical condition will not affect the knee score. It is hoped the rating system will become universally accepted and will be adopted by all authors, even if they wish to report results using a customary scoring method as well.