Background/Purpose: Because total knee (TKR) and total hip (THR) replacement surgery is performed to relieve pain and improve physical function in patients with advanced arthritis, there is growing demand to use patient-reported outcomes (PROs) to assess TKR effectiveness. The UK and others now require PRO assessment after TKR. Thus, a clear understanding of pre-existing clinical factors that influence PROs after surgery is needed before comparing PROs across providers. We evaluated the roles of medical  and musculoskeletal comorbidities in explaining variation in 6 month post-TKR and THR pain relief and functional gain.

Methods: A US cohort of 1,578 TKR and 1,166 THR patients  reported sociodemographic (age, sex, race), BMI, modified Charlson comorbidity, arthritic disease severity (Hip Disability/Knee Injury and Osteoarthritis Outcome Scores (HOOS/KOOS)) in both knees and hips, lumbar disease using the Oswestry Disabiity Index (ODI), emotional health based on the Short Form 36 (SF-36) Mental Component Score (MCS), and physical function (SF-36 PCS). Predictors of change in pre-to-6 month post-TKR and post-THR pain and function were examined using linear mixed models adjusting for clustering within site. 

Results: TKR patients had a mean age of 66 years, mean BMI of 31.5, and were 62% female and 6.8% black. Nine percent (9%) reported Charlson of 2-5, 15% with Charlson of 6, 7% moderate/severe pain in 2-3 knee/hip joints, and 26% moderate/severe lumbar pain. After adjusting for sociodemographic factors, significant predictors of poorer 6 month post-THR pain included poorer emotional health, higher Charlson comorbidities and any lumbar pain at time of THR. These factors also predicted poorer 6 month function.

THR patients had a mean age of 64 years, mean BMI of 29.2, and were 61% female and 4% black. Six percent (6%) reported Charlson of 2-5, 15% with Charlson of 6, 9% moderate/severe pain in 2-3 knee/hip joints, and 34% moderate/severe lumbar pain. After adjusting for sociodemographic factors, significant predictors of poorer 6 month post-THR pain included poorer emotional health, Charlson of 1, and severe lumbar pain at time of THR. These factors also predicted poorer 6 month function, as well as greater BMI and moderate/severe pain in non-operative knees/hips.

Conclusion: Before adopting PROs as a standard measure of TKR or THR effectiveness, a complete understanding of pre-existing clinical factors associated with poorer pain relief and functional gain is needed. These analyses suggest that greater musculoskeletal, as well as medical, comorbid conditions are associated post-operative patient-reported outcomes and should be included in risk-adjustment models.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/important-predictors-of-patient-reported-outcomes-after-tkr-and-thr-are-not-included-in-risk-models-based-on-administrative-data/