Background/Purpose:

Total knee arthroplasty (TKA) is associated with significant gains in function and pain improvement.  However, decline in function has been noted in patients who have undergone TKA. We were interested in what factors, changing through time, may be associated with this decline in function. In this study, we examined the relationship of the change in comorbidity with the change in SF-36 and WOMAC physical function and pain scores. To our knowledge, none of the previous studies have addressed this question. 

Methods:

We performed a retrospective chart review of veterans who had completed Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short Form-36 (SF36) surveys at regular intervals after primary TKA using structured data abstraction form.  Comorbidity was assessed using a variety of scales: validated Charlson comorbidity score, local musculoskeletal morbidity (back and lower extremity), TKA complications and a novel Medical Comorbidity Severity Index, at multiple time-points post-TKA.  We used  mixed model linear regression to examine the association of worsening comorbidity, with worsening WOMAC and SF36 scores, controlling for age, length of follow-up, and repeated observations.  

Results:

The study cohort consisted of 124 patients with a mean age of 71.7 years (range 58.6-89.2, standard deviation (SD) 6.9) followed for a mean of 4.9 years post-operatively (range 1.3-11.4; SD 2.8). We found that post-operative worsening of the Charlson Index was significantly associated with worsening SF-36 Physical Function (PF) (p<0.0001) and worsening WOMAC PF (p=0.012). Worsening scores on novel medical Comorbidity Severity Index scores were significantly associated with worsening SF-36 PF (p<0.001), and a non-significant trend of association with WOMAC PF (p=0.056). Local comorbidity index was significantly associated with SF-36 PF (p<0.001), WOMAC PF (p<0.001), and WOMAC Pain (p=0.004). TKA complications were not significantly associated with SF-36 or WOMAC domain scores.  

Conclusion:

Worsening medical comorbidity was significantly associated with worsening physical function and worsening lower extremity and spine morbidity with declining physical function as well as worsening pain during intermediate term follow-up after primary TKA.  Further studies should examine which comorbidity had the greatest impact on these outcomes.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/increasing-comorbidity-is-associated-with-worsening-physical-function-during-intermediate-term-follow-up-of-primary-total-knee-arthroplasty/