Abstract
Introduction Presently, many instruments exist for assessing both patient and surgeon-based satisfaction after joint replacement, including both generic and disease specific measures. Our aim was to derive and assess the validity of a reduced function scale of the WOMAC for patients with osteoarthritis of the hip and knee.
Methods All unilateral data from 12 centres world-wide (UK, US, Canada and Australia) involved in an international, multi-centre outcome study for patients undergoing TKR were included for analysis. The reduced scale was derived from pre-operative and three month postoperative data using a combination of data-driven analysis and purely clinical methods. The reduced WOMAC was then extensively validated in three key areas; validity, reliability and responsiveness using 12 month post-operative data from the study and data from the Medicare Hip Replacement Study. Data from 898 patients pre-operatively and 806 patients at three months was used for the data driven section of analysis. For the clinical section, 30 members of the orthopaedic community were surveyed as to their opinions of which items should be retained in the reduced version of the scale. These results were then combined to produce a reduced function scale of seven items to be used in conjunction with the five item pain scale. This reduced scale was then scrutinised to ensure it’s validity (both construct and content), reliability (both internal consistency and reproducibility) and responsiveness (using Standardised Response Means).
Results The items retained were: ascending stairs, rising from sitting, getting in/out of car, going shopping, rising from bed, taking off socks and sitting. The scales’s construct validity was confirmed by significant positive correlation with the SF-36 physical component score, the knee society function score, the Oxford knee score, and for the hip data, the Harris Hip Score and SF-12 physical component score. Cronbach’s alpha was consistently high (a> 0.85) with the reduced scale, showing it to be reliable.
Conclusions The SRM’s indicated that the reduced scale may even be better at detecting change than the full scale.
The abstracts were prepared by Mr Jerzy Sikorski. Correspondence should be addressed to him at the Australian Orthopaedic Association, Ground Floor, William Bland Centre, 229 Macquarie Street, Sydney NSW 2000, Australia.
None of the authors have received any payment or consideration from any source for the conduct of this study.
