Relationships between subjective and objective measures after total knee arthroplasty

Total knee arthroplasty (TKA) has proven successful in treating symptomatic arthritis of the knee. Since its development, many and varied outcome measures have been developed to assess outcome. None have been accepted as the universal standard, although some are widely used. Many measures have no data regarding validity, reliability or responsiveness. There is little guidance or consensus in the literature as to which should be used in clinical practice, research or audit. In addition, there is limited research assessing the relationship between subjective clinical outcome scores, patient perceived reports and objective measures such as the timed up and go test (TUG), knee laxity and muscle strength. Establishing relationships between self report and objective measures may aid clinicians in developing more appropriate interventions. Twenty four patients underwent unilateral TKA and were assessed a mean of 27.5 (SD 11.7) months after surgery. Assessment included four patient reported scores (Knee Outcomes and Osteoarthritis Score, Oxford Knee Score, American Knee Society Score and Short Form 12) and three objective outcome scores (knee laxity, quadriceps muscle strength and timed up and go test (TUG). Significant (<0.05) correlations were demonstrated between the four patient reported scores (r=0.410- 0.786) except the MCS portion of the SF12 (r=0.286-0.483). The TUG was the only objective outcome measure to demonstrate a statistically significant (p=0.0001-0.005) correlation with subjective knee outcome scores (OKS, KOOS and 4 items of the KOOS) (r=--0.557 to -0.770). A patient's ability to walk at a certain pace is correlated with patient satisfaction after TKA. There were no 4 observed correlations between knee laxity or quadriceps muscle strength with the four subjective knee scores. Therefore for a comprehensive assessment of outcome after TKA, use of a combination of objective and subjective outcome measures is recommended, as they measure different aspects of outcome.