Objective

Poor functional outcomes post-knee replacement are common, but estimates of its prevalence vary, likely in part because of differences in methods used to assess function. The agreement between improvement in function and absolute good levels of function after knee replacement has not been evaluated. We evaluated the attainment of improvement in function and absolute good function after total knee replacement (TKR) and the agreement between these measures.

Methods

Using data from The Multicenter Osteoarthritis (MOST) Study, we determined the prevalence of achieving a minimal clinically important improvement (MCII, ≥ 14.2/68 point improvement) and Patient Acceptable Symptom State (PASS, ≤ 22/68 post-TKR score) on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) Physical Function subscale at least 6 months after knee replacement. We also assessed the frequency of co-occurrence of the 2 outcomes, and the prevalence according to pre-knee replacement functional status.

Results

We included 228 subjects who had a knee replacement during followup (mean age 65 yrs, mean body mass index 33.4, 73% female). Seventy-one percent attained the PASS for function after knee replacement, while only 44% attained the MCII. Of the subjects who met the MCII, 93% also attained the PASS; however, of subjects who did not meet the MCII, 54% still achieved a PASS. Baseline functional status was associated with attainment of each MCII and PASS.

Conclusion

There was only partial overlap between attainment of a good level of function and actually improving by an acceptable amount. Subjects were more likely to attain an acceptable level of function than to achieve a clinically important amount of improvement post-knee replacement.

Background

Participation is an important, yet seldom studied, outcome after total knee replacement (TKR).

Objective

The purpose of this study was to investigate the extent and predictors of participation and participation restriction among people after TKR.

Materials and methods

This study investigated the changes in pain, function, and participation scores (measured using a subscale of the Late-Life Function and Disability Instrument) from pre-TKR to ≥1 year post-TKR among a subsample of participants from the Multicenter Osteoarthritis Study (MOST) longitudinal cohort (MOST is funded by the National Institutes of Health). The proportions of individuals with participation restriction pre-TKR and ≥1 and ≥2 years post-TKR were calculated for all participants and for important demographic subgroups. The association between demographic and clinical factors and participation was estimated using linear regression. The association between demographic and clinical factors and participation restriction was estimated using logistic regression.

Results

There were 292 individuals with outcome data ≥1 year post-TKR. Of these, 218 (75%) had data pre-TKR and ≥1 year post-TKR and 160 (55%) had data ≥2 years post-TKR. There were mean improvements in pain, function, and participation at ≥1 and 2 years. However, approximately 30% of the study sample had participation restriction pre-TKR and post-TKR, and the proportion decreased significantly only for those <65 years old. Non-whites had a higher proportion of participation restriction than any other subgroup (41% ≥1 year, 48% ≥2 years). Female sex and non-white race were associated with a worse participation score, and several demographic and modifiable factors were associated with participation restriction following TKR.

Limitations

The time between pre-TKR and post-TKR assessment varied across study participants, and data were not available on their rehabilitation utilization.

Conclusions

Although there was a mean increase in participation ≥1 year following TKR, participation restriction was common. The likelihood of low participation was increased among women, non-whites, and those with depressive symptoms, severe pain in either knee, or worse pre-TKR function.