MINIMAL DETECTABLE CHANGE IN TWO PATIENT-BASED QUESTIONNAIRES FOR SHOULDER INSTABILITY.

Abstract

To examine the minimal detectable change in two patient –based questionnaires for patients with shoulder instability, managed conservatively.

Oxford Instability Shoulder Score (OISS) and Shoulder Rating Questionnaire (SRQ) were administered to 93 patients (100 shoulders) attending physiotherapy. Scores were transformed to percentages to allow comparison. Questionnaires were collected at nine months with 5 subjective response categories from “much worse” to “much better”. Score changes were related to subjective response categories and data calculated to ascertain minimal detectable change (MDC) using the method of McHorney & Tarlov (1995). Proportion of scores over the minimal detectable change score were then examined.

60 patients (64 shoulders) returned questionnaires at nine months.

34 patients (38 shoulders) reported the shoulder was “much better”. The percentage change scores for these patients were significantly different to all other patients (OISS=26%, p< 0.05 and SRQ =20%, p< 0.05).

The minimal detectable change score was calculated as 14% for OISS and 10.5% for SRQ. Of the 38 ‘much better’ responses, 32 (i.e. 84%) had a change score > 14% for the OISS and 27 (i.e. 71%) > 10.5% for the SRQ. Of those 7 who responded with ‘no change or worse’, 2/7 (29%) scored > 14% for OISS and 1/7 (14.2%) scored > 10.5%

Minimal detectable change scores have been calculated for the OISS and SRQ in patients with shoulder instability. These may help determine change, which is clinically important in outcome research.