2015 ISAKOS Biennial Congress ePoster #1436

Quality of Life Assessment in Patients with Knee Replacement: Should Aggregate Medical Health Outcomes Study Scores be Used?

Kate E. Webster, PhD, Bundoora, Victoria AUSTRALIA
Julian A. Feller, FRACS, FAOrthA, Melbourne, VIC AUSTRALIA

La Trobe University and Epworth HealthCare, Melbourne, Victoria, AUSTRALIA

FDA Status Not Applicable

Summary: Physical and mental component aggregate scores of the SF-36 and SF-12 may have limitations for use in people with knee replacement.

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Abstract:

Introduction

Health related quality of life is widely accepted as a key outcome measure in chronic illness, including knee osteoarthritis. The Medical Outcomes Study 36-item Short Form Health Survey (SF-36) has become one of the most widely used generic instruments to assess quality of life and has been progressively adopted in orthopaedics. The SF-36 is comprised of eight subscales that can be summarised in two aggregate scores; a physical component score (PCS) and a mental component score (MCS). The shorter version SF-12 can also be summarised by these aggregate scores and its use has recently been recommend in treatment guidelines for knee osteoarthritis. However, the relevance of using these aggregate scores has previously been questioned and has not been investigated in patients with knee replacement. The objective of this study was to assess the relevance of using the aggregate PCS and MCS of both the SF-36 and SF-12 for patients with knee replacement.

Methods

780 patients (317 men, 463 women) completed the SF-36 (from which SF-12 scores were derived) a minimum 12 months following knee replacement surgery. Construct validity of the PCS and MCS for both versions was assessed by convergent and divergent validity and factor analysis. Data were assessed for the sample as a whole and for men and women separately.

Results

PCS and MCS scores were significantly higher for men than women. For both versions, acceptable convergent and divergent validity was observed with the Oxford Knee Score and Knee Society Knee Score, and the correlation between PCS and MCS mean scores was low (SF-36 r=0.05; SF-12 r=-0.04). However, factor analysis performed on the eight subscale scores failed to support the use of PCS and MCS aggregate scores. For both versions two factors were extracted, but these were different than the a priori stratification. For both SF-36 and SF-12, scores for general health, which are usually attributed to PCS were shared between factors. For the SF-12, vitality, social function and role emotional, which are usually attributed to MCS were shared between factors. Gender differences were also found whereby for males, role emotional was attributed to the PCS instead of the MCS.

Discussion

These results suggest that aggregate scores from the PCS and MCS of the SF-36 and particularly the SF-12, as they are currently defined, may have limitations for use in people with knee replacement to assess health related quality of life. These findings are consistent with previous work which has questioned the use of PCS and MCS aggregate scores in people with knee and hip osteoarthritis. Given that it is common practice to report these aggregate scores these results have implications for the routine reporting of quality of life in this patient group.