Background/Purpose The fastest growing segment of the population undergoing total knee replacements (TKR) are patients younger than <65 years, yet little is known regarding their outcomes as compared to older patients.  We examined, from a national sample of TKR patients, differences in clinical outcomes of pain and function following surgery based on age. 

Methods Patients undergoing primary TKR from 7/1/11 through 8/30/13 for osteoarthritis were identified from a national research consortium which enrolls patients from >130 surgeons across 22 states in the US.  The registry gathers data from patients, surgeons and hospitals on patient demographics, underlying type of arthritis, body mass index, non-arthritis comorbid conditions, arthritis in non-operative hip and knee joints, back pain, global function based on the Short Form 36 Physical Component Score (PCS), and mental health using the SF-36 Mental Component Score (MCS).  We evaluated both change in operative joint pain and function as well as the 6-month post-operative pain and function score based on the estimated Western Ontario and McMaster Universities Arthritis Index (WOMAC) using the Knee Injury and Osteoarthritis Outcome Score (KOOS; range of 0-100 with higher being better).  Descriptive statistics were performed as well as linear and mixed model multivariable regressions examining differences based on age.

Results There were 1164 patients <65 years and 2012 patients ≥ 65 years who underwent primary TKR.  Younger patients were more likely to be nonwhite (8.7% vs. 5.0%, p<0.001), heavier (body mass index 33 vs. 30, p<0.001), with worse emotional health (51.5 vs. 53.9, p<0.001), fewer comorbid conditions (p <0.001), and greater number of non-operative painful hip and knee joints (p<0.03).  At the time of surgery, younger patients had greater pain (50.5 vs. 55.7, p<0.001) and functional impairment (53.2 vs. 54.9).  Overall both younger and older patients had substantial pain relief and functional gain, improvement of 30.4 - 32.6 and 28.7 - 29.4 respectively based on the KOOS.  In adjusted analyses, at 6-months post-operatively younger patients had slightly greater pain (-2.5, p <0.002) and less improvement in function (-2.2, p<0.016). 

Conclusion Both younger and older TKR patients had substantial pain and disability at the time of TKR and achieved substantial pain relief and functional gain following surgery.  However, younger patients had statistically significant less improvement in pain and function, although the clinical significance of this difference is unknown.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/differences-in-total-knee-replacement-outcomes-based-on-age/