Four Outcome Measures for Patellofemoral Joint Problems: Part 1. Development and validity

Abstract

Background and Purpose This work represents part of a PhD project investigating outcome measures for patellofemoral joint problems – critical angle and angular velocity as measured by video analysis of an eccentric step test, a treadmill test and a Modified Functional Index Questionnaire (MFIQ). This paper describes the development of the outcome measures and provides experimental data to support their validity. Methods A controlled repeated measures study was carried out in the physiotherapy department at Burnley General Hospital, where 88 patients were considered for inclusion. Comparing experimental data collected from the patients with those previously published provided estimates of the validity of the outcome measures. Results Mean critical angle was 57.8° and mean angular velocity was 93°/sec. The eccentric step test was found painful by 74% of patients. Data from the treadmill test were right censored with 49% of patients completing 300 seconds without pain. Cronbach's alpha for the MFIQ was 0.83. Conclusion When comparing video data from this patient group to a previous study of 100 healthy subjects the patients demonstrate an earlier critical angle and faster angular velocity. These data suggest that the measurements of critical angle and angular velocity through video analysis of an eccentric step test are valid measures of patellofemoral joint dysfunction. As treadmill test data are right censored it suggests that the test in the form used in this study is valid for only about 50% of the patients. The high value recorded for Cronbach's alpha suggests that the MFIQ is internally consistent, which in turn suggests it is also a valid measure of patellofemoral dysfunction. This work represents part of a PhD project investigating outcome measures for patellofemoral joint problems – critical angle and angular velocity as measured by video analysis of an eccentric step test, a treadmill test and a Modified Functional Index Questionnaire (MFIQ). This paper describes the development of the outcome measures and provides experimental data to support their validity. A controlled repeated measures study was carried out in the physiotherapy department at Burnley General Hospital, where 88 patients were considered for inclusion. Comparing experimental data collected from the patients with those previously published provided estimates of the validity of the outcome measures. Mean critical angle was 57.8° and mean angular velocity was 93°/sec. The eccentric step test was found painful by 74% of patients. Data from the treadmill test were right censored with 49% of patients completing 300 seconds without pain. Cronbach's alpha for the MFIQ was 0.83. When comparing video data from this patient group to a previous study of 100 healthy subjects the patients demonstrate an earlier critical angle and faster angular velocity. These data suggest that the measurements of critical angle and angular velocity through video analysis of an eccentric step test are valid measures of patellofemoral joint dysfunction. As treadmill test data are right censored it suggests that the test in the form used in this study is valid for only about 50% of the patients. The high value recorded for Cronbach's alpha suggests that the MFIQ is internally consistent, which in turn suggests it is also a valid measure of patellofemoral dysfunction.