National joint replacement registries have reported a substantial growth in younger knee osteoarthritic patients (< 55 years old) undergoing total knee replacement, however this younger population is generally understudied. Importantly, studies examining experimentally controlled perturbation have shown age-related differences between younger and older healthy adults, whether similar age-related differences exist among total knee replacement patients is unknown.Methods
A total of 59 participants, including 29 unilateral total knee replacement patients (six-months post-surgery) made up the four experimental groups: 1) younger patient (54.3 (SD 7.9) years), 2) younger control (55.2 (SD 4.0) years), 3) older patient (76.9 (SD 4.7) years), and 4) older control (77.7 (SD 4.1) years). Using a tether-release method to perturb balance and simulate a forward fall, center of mass and stepping characteristics were analyzed.Findings
Younger patients recovered following the perturbation with a significantly smaller center of mass displacement compared to the older patients (14.85 (SD 0.01) v. 18.13 (SD 0.02) %ht, p = 0.02); utilizing a longer (0.43 (SD 0.02) v. 0.39 (SD 0.03) m, p < 0.001) and higher velocity (2.01 (SD 0.2) v. 1.59 (SD 0.2) m/s, p = 0.001) recovery step. Importantly, younger patients did not differ significantly from the younger controls in center of mass displacement or recovery step characteristics (p > 0.05).Interpretation
The younger patients demonstrated superior center of mass control in response to a forward perturbation, suggesting that younger patients would be at a reduced risk of falling when recovering from a forward-directed postural perturbation compared to older patients.