Background/Purpose: When knee pain is severe and frequent, or mobility and daily activities become difficult, a total knee replacement (TKR) remains the most effective treatment to relief pain and to improve function. In the US, the annual rate of TKRs in people 65 years or older increased almost 9-fold between 1979 and 2006. The latest US hospital-discharge data indicated a significant increase in use among the younger patients (< 65 years of age). Among the 719,000 TKRs performed in 2010, about 50% were in people < 65. It remains unclear the reasons for such increased TKR use. We examined profiles of patients selected for TKR in a recently established US national registry of total joint replacements (TJR).

Methods: We used data from the Function and Outcomes Research for Comparative Effectiveness in TJR (FORCE-TJR), a national cohort of TJR patients operated by more than 130 surgeons in 22 sites nationwide. The current study included participants with primary and unilateral TKRs that were not indicated by rheumatoid arthritis. Participants were enrolled between April 2011 and Feb 2014, and had completed a pre-operative Knee Injury and Osteoarthritis Outcome Score (KOOS) and Short-Form 36-item (SF-36) functional health survey. Data were also collected on patient demographics, body mass index, general health and comorbid conditions. We classified patients as having high or low pain (KOOS Pain<70 vs. ≥70), and low or high physical function (SF-36 PCS <40 vs. ≥40). We then classified patients into four groups: 1) low pain-high function, 2) high pain-high function, 3) low pain-low function, and 4) high pain-low function. Descriptive statistics including patient demographic and clinical characteristics of the four groups were compared.  

Results: The majority (95%) of patients had high pain and/or low physical function. A small percentage of people (5%), however, had low pain and high function. Many in this latter group reported pain fairly daily (49%) or were aware of their knee problem daily or constantly (85%) despite a very small percentage having experienced severe or extreme pain on stairs (4%) or pain in bed (1%). Moreover, over half had a lot of limitations or difficulties in vigorous activities such as running. Compared with the group with high pain and low function, the group with low pain and high function on average were older, less obese, more highly educated, more likely men, and were generally healthier. Differences for all characteristics by groups were statistically significant at P<0.05, except for race.

Conclusion: The overwhelming majority of TKRs were performed to relieve pain and/or restore physical function. However, a small percent of TKR utilization was in patients with low pre-operative pain and high function, probably for quality of life issues. Further investigation is needed to determine the reasons for TKR use among these patients as this may have an important policy implication.

*All P values were < 0.05, except race