ORIGINAL ARTICLE Postural Responses to Dynamic Perturbations in Amputee Fallers Versus Nonfallers: A Comparative Study With Able-Bodied Subjects Natalie Vanicek, MSc, Siobhan Strike, PhD, Lars McNaughton, PhD, Remco Polman, PhD ABSTRACT. Vanicek N, Strike S, McNaughton L, Polman R. Postural responses to dynamic perturbations in amputee fallers versus nonfallers: a comparative study with able-bodied subjects. Arch Phys Med Rehabil 2009;90:1018-25. Objectives: To quantify postural responses in amputee fall- ers versus nonfallers by using computerized dynamic postu- rography. Design: All participants completed standard protocols on the Sensory Organization Test (SOT) and Motor Control Test (MCT) of the NeuroCom Equitest. Setting: Human performance laboratory in a university in the United Kingdom. Participants: Transtibial amputees (n=9) and able-bodied subjects (n=9) (all categorized into fallers and nonfallers ac- cording to their falls history in the previous 9mo). Interventions: Not applicable. Main Outcome Measures: Equilibrium and strategy scores on the SOT. Postural response latency and weight distribution on the MCT. Results: Equilibrium scores were highest when somatosen- sory information was accurate, but there were no differences between the groups. Strategy scores were lower when visual cues and somatosensory information were inaccurate, and the fallers and nonfallers used a combination of ankle and hip strategies to prevent a loss of balance. The amputee nonfallers indicated they had a greater reliance on visual input even when it was inaccurate compared with the amputee fallers, whereas the control fallers used the hip strategy significantly more compared with the control nonfallers (SOT condition 6: 5622 vs 7210, P=.01). Weight distribution symmetry showed that the amputee nonfallers bore significantly more weight through their intact limb compared with the amputee fallers during backward and forward translations (P.05). Conclusions: The SOT and MCT appeared to be population specific and therefore did not reliably identify fallers among transtibial amputees or distinguish between community-dwell- ing control fallers and nonfallers. Amputee and control fallers can prevent a fall during challenging static and dynamic con- ditions by adapting their neuromuscular responses. The results from this study have important implications for amputee gait rehabilitation, falls prevention, and treatment programs. Key Words: Accidental falls; Amputees; Posture; Rehabi- litation. © 2009 by the American Congress of Rehabilitation Medicine P EOPLE WHO HAVE HAD a transtibial amputation ex- hibit similar characteristics compared with the elderly, such as muscle weakness and postural instability, that predis- pose them toward an increased risk of falling. 1,2 Transtibial is the most common level of lower-limb amputation for those aged 65 years and older. 3 Transtibial amputees have joints and muscles replaced with prosthetic components and therefore have reduced joint mobility and muscle strength on the pros- thetic side. 1 There is also a loss of afferent information from receptors in the muscles, tendons, and skin, and, consequently, amputees have altered somatosensory input. If mechanisms responsible for integrating information from different sources are affected by disease, then excessive sway or falls can occur, especially in unusual sensory environments. 4 Therefore, lower- limb amputees are at an increased risk of falling compared with age-matched, able-bodied people, with 52% of transtibial am- putees reporting a fall within a 12-month period. 5 As such, poor balance and falls incidence among this group have be- come a growing concern for rehabilitation specialists. Aging is known to affect the musculoskeletal, visual, ves- tibular, and somatosensory systems that play a vital role in maintaining balance. 6 Older people are at a greater risk of falls, with 30% of those over 65 years of age falling at least once a year. 7 Declines in lower-limb muscle strength and locomotor function have been linked with gait disorders, balance impair- ments, and falls incidence in the elderly. 8 The biomechanical alterations that occur in the elderly are similar to those ob- served among most transtibial amputees. Therefore, similar postural control mechanisms may be evident in the amputee population. Postural control is maintained by keeping the body’s COG over the base of support during static and dynamic balance. Postural control will be compromised if some aspect of the system is disrupted. The inability to realize how far the body’s COM has been displaced or failure to produce the appropriate response because of muscle weakness or insufficient flexibility will likely result in a fall. 9 Depending on the size of the perturbation, 3 postural strategies can be used to reposition the COG. The ankle strategy is typically used in response to slow From the Department of Sport, Health and Exercise Science, University of Hull, Hull, (Vanicek, McNaughton); School of Human and Life Sciences, Roehampton University, London (Strike); and Centre for Applied Sport & Exercise Sciences, University of Central Lancashire, Preston (Polman), UK. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organi- zation with which the authors are associated. Reprint requests to Natalie Vanicek, MSc, Dept of Sport, Health and Exercise Science, University of Hull, Hull, UK HU6 7RX, e-mail: N.Vanicek@hull.ac.uk. 0003-9993/09/9006-00884$36.00/0 doi:10.1016/j.apmr.2008.12.024 List of Abbreviations CDP computerized dynamic posturography COG center of gravity COM center of mass COP center of pressure MCT Motor Control Test SOT Sensory Organization Test 1018 Arch Phys Med Rehabil Vol 90, June 2009