Purpose: Knee osteoarthritis (OA) is not one of the most prevalent conditions leading to disability in the elderly. However, there is also a growing prevalence in younger adults, particularly for obese individuals and those who experience joint injury. Current estimates are that over 710,000 individuals with end-stage knee OA undergo total knee arthroplasties (TKA) annually in the United States, which is an increase of over 40% compared to 2002. The incidence of TKA is projected to exceed 3.5 million by the year 2030. The increases in TKA procedures are not only associated with increases in the population of elderly patients (>70 years), but also to a rise in the number of TKAs performed in a younger population. PURPOSE: The purposes of this study were 1) to compare the preoperative clinical impairments, functional abilities, and self-report measures between subsets of younger and older patients undergoing TKA, and 2) to determine if preoperative predictors of function (clinical impairments and self-reports) are similar between subsets of younger and older patients undergoing TKA. Methods: Subsets of Younger patients, those less than 60 years, and Older patients, those more than 70 years, from our Total Knee Outcome Study were examined. Preoperative testing included impairment-based measures, functional performance tests, and pain. Impairment-based measures included active flexion (Flex) and extension (Ext) range of motion (ROM) and maximal voluntary isometric knee extension strength (MVIC). Functional performance tests included the timed up-and-go (TUG), stair climbing test (SCT), 6-minute walk (6 MW). Pain was assessed on a verbal analog scale, where patients reported average knee pain from 0–10, with 0 equal to no pain and 10 as the worst pain imaginable. Independent t-tests were used to compare the measures between groups. Stepwise linear regression was used to predict functional performance measures (dependent variable) from impairment-based measures and pain (independent variables) separately for the Younger and Older groups. Results: The Younger group was significantly heavier than the Older group (Table 1). No significant differences were observed between groups for the clinical impairments (Flex, Ext or MVIC; p > 0.320) or pain (p = 0.08). Similarly, no significant differences were observed for the TUG (p = 0.927), SCT (p = 0.864), or 6 MW (p = 0.738). Regression analyses revealed that different impairments explained functional performance for the Younger and Older groups (Table 2). For example, the factors the best explained the TUG in the Younger group were Flex ROM and pain (adj. r2 = 0.502, p = 0.001), whereas the in the Older group the factors were Flex ROM and MVIC (adj. r2 = 0.219, p = 0.002). Conclusions: While the Younger group was heavier than the Older group, different factors explained the variance in functional performance measures between the two groups, with Flex ROM consistently an important factor for function in the Younger group and MVIC consistently a factor for the Older group. These findings suggests nonoperative care, preoperative decision making, and postoperative treatment may require differing approaches for younger patients compared to the older patients who are planning or undergo TKA.Tabled 1Table 1. Descriptive statistics.YoungerOlderpN2748Pct. Women7471Height (m)1.7 ± 0.11.7 ± 0.10.737Mass (kg)103.7 ± 23.787.7 ± 20.10.009BMI (kg/mˆ2)37.2 ± 8.931.5 ± 6.40.011Age (yrs)54.1 ± 5.575.9 ± 4.7<0.001 Open table in a new tab Table 2Regression table of factors explaining functional performance measures between the Younger and Older groups. Each lineRadj. R-sqrSign. ChangepModelTUGYounger1Flex ROM0.6160.3490.0020.0022Flex ROM + Pain0.7080.5020.0440.001Older1Ext. Strength0.3970.01380.0070.0072Ext. Strength + Flex0.5050.2190.0240.002SCTYounger1Flex ROM0.6610.4080.0010.001Older1BMI0.4720.2040.0010.0012BMI + Ext. Strength0.620.3550.002<0.0016MWYounger1BMI0.7840.595<0.001<0.0012BMI + Flex ROM0.8560.7040.009<0.001Older1Flex ROM0.5070.239<0.001<0.0012Flex ROM + Pain0.6530.3980.001<0.0013Flex ROM + Pain + Ext. Strength0.710.4670.016<0.0014Flex ROM + Pain + Ext. Strength + BMI0.7570.5290.016<0.001 Open table in a new tab