After Total Knee Replacement Younger Patients Demonstrate Superior Balance Control Compared to Older Patients when Recovering from a Forward Perturbation

Abstract

Significant improvements in pain and function have been reported following successful total knee replacement (TKR); however, patients continue to demonstrate persistent balance impairments, increasing the risk of falls and injuries. Data examining experimentally controlled forward perturbation have shown age-related differences between younger and older healthy adults. Recently, national joint replacement registries have reported a substantial growth in younger knee osteoarthritic patients (<55 yrs) undergoing TKR, but this younger TKR population is generally understudied. The age-related differences observed for healthy adults during balance recovery may also distinguish younger TKR patients from the typical, older TKR patients. PURPOSE: To compare the stepping characteristics and centre of mass (COM) control after a postural perturbation between younger and older TKR patients, and their healthy age-matched controls. METHODS: A convenience sample of 59 participants, including 29 unilateral TKR patients six months post-surgery was recruited and consisted of four groups: 1) younger patient (YP) (54.3 ± 7.9 yrs), 2) younger control (YC) (55.2 ± 4.0 yrs), 3) older patient (OP) (76.9 ± 4.7 yrs), and 4) older control (OC) (77.7 ± 4.1 yrs). Using a tether-release method to perturb balance and simulate a forward fall, the following four balance recovery conditions were examined: 1) eyes-open, stepping with right limb, 2) eyes-open stepping with left limb, 3) eyes-closed stepping with left limb, and 4) eyes-closed stepping with left limb. RESULTS: YP recovered following the postural perturbation with a significantly smaller COM displacement compared to that of OP (0.21 ± .03 v. 0.27 ± 0.03 m, p < 0.02), employing a longer (0.43 ± .02 v. 0.39 ± .03 m, p < 0.001) and faster (1.91 ± 0.3 v. 1.74 ± 0.3 m/s, p = 0.001) recovery step. Interestingly, YP did not differ in COM displacement (0.21 ± .03 m) and recovery step length (0.43 ± .02 m) or velocity (2.00 ± 0.3 m/s) from YC (p > 0.05). CONCLUSIONS: YP demonstrated superior COM control in response to a forward perturbation compared to OP. The cause of this superior COM control seems to be based, in part, on stepping characteristics which facilitated a quicker step and larger moment arm associated with the longer step, which helped create an earlier and larger restorative torque.