An investigation on the ability in control of static balance and quadriceps muscle activation in patients with knee osteoarthritis

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Huang, LP, Zhou, S, Zhang, LQ, Cao, LJ & Tian, Q 2009, 'An investigation on the ability in control of static balance and quadriceps muscle activation in patients with knee osteoarthritis', paper presented to Motor Control Conference VI: From basic motor control to functional recovery, Varna, Bulgaria, 5-8 October.


Knee Osteoarthritis (KOA) is one of the most prevalent musculoskeletal complaints. Individuals with KOA suffer from loss of function and increased dependency in walking, stair climbing and other lower extremity tasks. Effective control of balance relies not only on accurate sensory input but also on a timely response of neuromuscular control. Examining the impacts of KOA and associated factors on balance control will allow us to elucidate the pathophysiological mechanisms and improve treatment and management of this disease.

AIMS: The purpose of this study was to investigate the ability in control of static standing balance and muscle activation of quadriceps in individuals with KOA, in order to provide the objective and effective evaluation method and rehabilitation treatments for the patients.

METHODS: 20 individuals with known KOA in both knees (61.4±9.8 yrs, 12 males, 8 females) and 10 healthy and age, gender, height and mass matched controls (62.6±8.1 yrs, 6 males, 4 females) were recruited in the study. Static balance function was assessed when the participant stood on a Kistler force platform under four conditions: on a solid or soft surface, and with eyes open or closed. Knee joint proprioception was assessed with a repositioning test on a Cybex dynamometer. The maximal voluntary isometric contraction (MVC) and muscle activation (twitch interpolation) of the quadriceps were measured using a custom-built dynamometer and data acquisition system. Knee pain, stiffness and functional disability of the patients were assessed using a visual analogue scale (VAS) and the Western Ontario and MacMaster University Osteoarthritis Index (WOMAC).

RESULTS: Compared with the control group, the KOA group demonstrated significantly lower MVC (left 62% and right 69% of the control, p<0.05), remarkable deficiency in muscle activation (left 12.45%, right 9.15% lower than the control, p<0.01), significant reduction of knee proprioception (mean error of 77.6% greater than the control, p<0.01) in both legs. When standing on the solid surface with eyes open, there was a near significant difference in body sway in the anterior-posterior (AP) direction (KOA was 29.3% greater, p=0.052), and significant differences in body sway in the medial-lateral (ML) direction (KOA 51.9% greater, p=0.012), and total length of movement (KOA 24.2% greater, p<0.05) between the two groups. When standing on solid surface with eyes closed, the body sway in the AP and ML directions were significantly greater (51% and 44.5% respectively, p<0.01), and total length of movement were remarkably longer (23.4%, p<0.05) in the KOA than those in the controls. There were no significant differences in body sway in the AP or ML direction, and total length of movement between the two groups while standing on soft surface, with eyes open or closed.

CONCLUSIONS: KOA patients showed significantly weaker strength and insufficiency muscle activation of the quadriceps, reduced proprioception, and impaired static balance control. The reduction in proprioception and deficiency in quadriceps activation might be responsible for the impaired static balance in this group of KOA patients. Visual perception could partially compensate for the balance obstacle in the AP direction, but not in the ML direction. It is suggested that greater attention be paid to the proprioception function in rehabilitation interventions for restoring balance control.