Knee Arthroplasty and Patellofemoral Rating Systems

Introduction

Many outcome scales and systems have been used to assess the results of total knee arthroplasty (TKA). These include scales specifically designed for this operation, as well as general health measures and outcome instruments that were originally developed for a variety of knee diagnoses. Although some scales only rate levels of physical activity, others are more encompassing in terms of providing a detailed analysis of the knee condition and function. The American Knee Society Scoring System, the University of California Los Angeles (UCLA) Activity-Level Rating Score, and the Oxford Knee Score were devised specifically to determine the outcome of TKA and currently are the most frequently used instruments. The Short Form 36 (SF-36) Health Survey is a common general health measure that is also used in many TKA studies. Disease-specific (osteoarthritis) instruments typically found in TKA investigations are the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Knee Injury and Osteoarthritis Outcome Score (KOOS).

A lack of consensus exists regarding which instrument or rating system should be selected to determine the results of TKA, caused in part by the moderate to poor quality of investigations that determined their psychometric properties. One systematic review found that, of 28 instruments assessed, only three had been studied at length in regard to their measurement properties. These were the WOMAC, the Oxford Knee Score, and the SF-36. Another review of instruments used in hip or knee osteoarthritis studies reported that none of the instruments received positive ratings for all psychometric properties. It is important to note that these reviews were conducted before the publication of the two newest outcome instruments and scales for TKA, the new Knee Society Scoring System and the High-Activity Arthroplasty Score. Some of the more commonly used outcome measures are described below, presented in chronological order of publication. The WOMAC and KOOS outcome assessments are described in Chapter 43 and are not repeated in this chapter.

University of California Los Angeles Activity-Level Rating Score

In 1984, Amstutz and colleagues introduced the UCLA activity rating scale for patients undergoing TKA. The scale has 10 activity levels ranging from “wholly inactive” to “regularly participate in impact sports” ( Table 45-1 ). Subsequently, Zahiri and associates compared this activity score with a quantitative assessment of the walking activity of 100 total joint replacement patients. These investigators found the UCLA score strongly correlated with average steps per day as recorded by a pedometer. The recommendation was made to adjust the score for frequency and intensity of activity to increase its accuracy. Naal and coworkers compared the psychometric properties of the UCLA scale with the Tegner and Marx Sports Activity scales in 105 patients undergoing total hip arthroplasty and 100 patients undergoing TKA. The UCLA scale had the best reliability, the highest completion rate, and the strongest correlations with other measures and was the only scale that discriminated between active and sedentary patients. The score also had no floor effects. These investigators concluded that the UCLA scale appeared to be the most appropriate for assessment of physical activity levels following total joint arthroplasty.

American Knee Society Scoring System

In 1989, the Knee Society (of the American Academy of Orthopaedic Surgeons) published its scoring system, which was intended to quantify the results of TKA. In 2011, an extensive update was performed, and a new system was published in 2012. The goals of the updated version are to better characterize patient expectations and satisfaction of the operation and measure physical activities of younger individuals undergoing TKA. This system consists of an objective knee score completed by the physician ( Table 45-2 ) and several scales completed by the patient that assess satisfaction ( Table 45-3 ), symptoms, expectations ( Table 45-4 ), and knee function ( Table 45-5 ). Noble and associates reported adequate internal consistency, reliability, and construct and convergent validity for the four subscales: objective knee score, satisfaction score, expectation score, and functional activity score. The objective knee score consists of seven items; the satisfaction score, five items; the expectation score; three items; and the functional activity score, 19 items. The questionnaires are available by contacting the Knee Society at knee@aaos.org ; further information, including the user manual, may be found at www.kneesociety.org/web/outcomes.html .