Balance recovery during induced falls is impaired in people with knee osteoarthritis: Implications for falls prevention

Purpose: Knee osteoarthritis (OA) is a major risk factor for falls with high falls rates reported; 50% in people with knee OA who are over the age of 60. Increased neuromuscular deficits are common in people with knee OA which may further impact on postural control mechanisms and the ability to defend against a fall. Despite the high prevalence of falls in people with knee OA, the mechanism of falling in this group is unclear. This study investigated the biomechanical response of the lower limb joints during a forward induced fall under different task conditions in people with knee OA. Moreover, the balance recovery step responses (single vs multi steps) were also investigated to determine how dynamic postural control would be affected due to the presence of knee OA while undertaking the three task conditions.
Methods: Twenty four participants with knee OA (68.6±6.2 years) and fifteen asymptomatic healthy controls (72.4±4.8 years) participated in the study. Forward fall was induced by releasing participants from a static forward leaning position. Participants were required to recover balance during three conditions: normal, physical dual task (obstacle clearance) and cognitive dual task (counting backwards). Spatiotemporal parameters, lower limb joint kinematics and kinetics of the recovery limb were compared between the two groups and across the three task conditions using two way full factorial Multiple Analyses of Covariate (MANCOVA) with Bonferroni-adjusted post-hoc tests with age as a covariate.
Results: The OA group demonstrated significantly slower spatio-temporal characteristics and reduced hip and knee flexion angles, joint moments/ powers and lower knee and ankle negative works. Cognitive dual task resulted in reduced centre of mass velocity and step length (p=0.03) compared to the physical dual task condition. Reduced knee (p=0.02) and hip powers (p=0.03) were demonstrated in the OA group during the dual task conditions especially obstacle clearance where additional cognitive demand was required. The number of participants who responded with multi steps was similar for both groups during normal balance recovery task (60%; p>0.05). Although not significant, with increased task complexity the number of multi-step responders increased in the OA group compared to the control (75% for OA vs 60% for control during the obstacle task and 83% for OA vs 60% for control during the cognitive task).
Conclusions: When simulating a forward fall, participants with knee OA demonstrated difficulty in absorbing the impact and slowing down the forward momentum of the body during a recovery step. Differences in biomechanical response of the hip and knee were identified which could provide useful and important information regarding the strategies used by people with knee OA to recover balance and avoid a potential fall. Poor dynamic postural control was also demonstrated when required to simultaneously recover balance and attend to a secondary task such as obstacle clearance and cognitive task. As task complexity increased (i.e. use of physical/cognitive dual task), poor recovery strategies (multiple steps) were used more often in the knee OA group. Hence, balance impairment may be further exacerbated by impaired attention dynamics in people with knee OA.