Organization of postural responses following a rotational support surface perturbation, after TKA: Sagittal plane rotations William H. Gage a,b, * , James S. Frank b , Stephen D. Prentice b , Peter Stevenson b a Toronto Rehabilitation Institute, 550 University Avenue, Toronto, Ont., Canada M5G 2A2 b University of Waterloo, 200 University Avenue West, Waterloo, Ont., Canada N2L 3G1 Received 15 June 2005; received in revised form 27 September 2005; accepted 14 February 2006 Abstract Proprioceptive dysfunction, related to osteoarthritis and total knee arthroplasty (TKA) may be related to changes in gait, and may result in balance impairment. This study examined the organization of postural responses to rotational support surface perturbations after TKA. Eight TKA patients and nine control participants volunteered. EMG was collected bilaterally from lower limb muscles. Kinematic data were collected using an OPTOTRAK system. The temporal pattern of muscle activation was preserved in both the surgical and sound limbs of the patient groups, while muscle activation amplitude was reduced. Knee joint angular displacement was reduced in both limbs among patients. COM displacement was not different. Patients demonstrated a different method in recovering posture control following a postural perturbation. Bilateral changes appear to reflect a simplification in the organization of the motor response, in response to the needs of the injured, or previously injured limb. # 2006 Elsevier B.V. All rights reserved. Keywords: Total knee arthroplasty; Osteoarthritis; Balance control; Postural perturbation 1. Introduction Total knee arthroplasty (TKA) has become a common surgery in the treatment of severe osteoarthritis. The incidence rate of TKA has grown over the last 20 years, and is projected to continue to grow, in light of changing population demographics [1]. This surgery is performed most often for the dual purpose of reducing pain and improving function. The majority of patients report satisfaction with their surgical outcomes [2]. Despite remarkable pain reduction and functional improvement, previous work has revealed residual functional deficits following surgery; TKA patients have demonstrated reduced walking velocity, and reduced stride length during level walking [3,4], reduced work at the knee joint, with compensatory changes observed at the hip, when ascending a single step [5], and reduced external knee joint moments when climbing stairs [6,7]. These performance deficits may be associated with pre-surgical adaptive gait patterns, alterations in muscle strength, and proprioceptive dysfunction [4]; the preponderance of research to date has not favored one explanation over all others, though these collective results suggest balance impairment following TKA. Translational and rotational support surface perturbation studies have provided good insight into the organization of balance control, and the effect of disease and injury on this organization. Following a disturbance, balance is recaptured and maintained using a flexible set of strategies, which may involve movement at the ankle and hip joints, and changes in base-of-support related to stepping [8,9]. Changes in peripheral sensory function have been shown to alter muscle activity latencies and amplitudes, and scaling of joint torques following a support surface translation [10]. Carpenter and colleagues [11] have described the postural response to sagittal plane rotations of the support surface. The reported changes in ankle, knee, and trunk angular displacement, related to the direction of support surface rotation, with stretch-related and balance-correcting muscle www.elsevier.com/locate/gaitpost Gait & Posture 25 (2007) 112–120 * Corresponding author at: Toronto Rehabilitation Institute, Suite 1209, 550 University Avenue, Toronto, Ont., Canada M5G 2A2. Tel.: +1 416 597 3422x3868. E-mail address: whgage@healthy.uwaterloo.ca (W.H. Gage). 0966-6362/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2006.02.003