Gait Symmetry and Lower-limb Dominance

Upper-limb asymmetry and limb dominance (handedness) are recognized as normal and taken into consideration when making O&P clinical recommendations. A more significant loss of function is expected following the loss of the dominant upper limb, and out of necessity, dominance transfers to the contralateral side. There is no expectation that tasks will be shared equally by two upper limbs without pathology, and asymmetry is considered an acceptable clinical outcome. However, in lower-limb cases, lower-limb dominance is generally not considered clinically, and asymmetries are viewed as problems to resolve. Symmetry is a common criterion for assessing gait quality and an indication of superior outcomes. Even casual observations of the gait of individuals who have no diagnosed neurological or musculoskeletal pathology highlight the diversity of gait patterns that are considered normal. In many cases, these variations would require correction were they exhibited during prosthetic or orthotic fitting and alignment. Unless unilateral variation is obvious, symmetry of the lower limbs in normal gait is assumed. This assumption persists in research and clinical contexts “for the sake of simplicity in data collection and analysis.” 1 However, Sadeghi et al.’s 2000 review of symmetry and limb dominance in able-bodied gait found that “gait symmetry was actually reported in only a few studies using quantitative biomechanical data, where both lower limbs were evaluated.” 1 Molitor et al. reported that “clinical studies, including those involving unilateral prosthesis users, hemiparetic stroke patients, and others with unilateral limb differences (e.g., anterior cruciate ligament rupture, plantar fasciitis, etc.)…pool data into ‘affected’ and ‘unaffected’ limb categories, without considering the effect of asymmetries present prior to the onset of the condition or injury, where relevant.” 2 Finco et al. reported that for individuals who use a lower-limb prosthesis “symmetry has been associated with increased balance, decreased fall risk, and decreased risk of developing musculoskeletal overuse injuries” and concluded “that symmetry tended to decrease as level of limb loss became more proximal and to increase with prosthetic componentry intended for higher activity levels.” 3 This supports the practice of using symmetry as a clinical goal and outcome measure. However, given that “walking symmetry declines with age,” the mean age of subjects in the studies reviewed ranged from 30-45 years, and most of the prosthetic patients seen in practice have multiple comorbidities, questions remain about the practical relevance of symmetry in clinical decision-making. Additionally, lower-limb orthotic cases often involve highly complex presentations and include neurological factors that may make symmetry a less useful tool for assessing outcomes. The Clinical Limitations of Symmetry In a research context, assuming symmetry and using a normal or average value for a gait parameter is understandable. Clinicians often strive to restore each patient’s gait to the pattern prior to the onset of the condition that requires orthotic or prosthetic intervention. Since in most cases this cannot be observed, the unaffected limb is used as a reference. However, the pathological presentations in highly involved cases are often so significant that restoration of a normal and symmetrical gait is not only impossible but may be inappropriate. Hemiparesis, for example, results in such significant and permanent deviations that restoration of normal and symmetrical gait is not a reasonable expectation, and other goals (such as stability) must be prioritized. More specifically, in cases of recurvatum, allowing some knee hyperextension while preventing maximal hyperextension is often a reasonable compromise to reduce pain and maintain stability. In 1988, Winter and Sienko eloquently described the limited application of symmetry to prosthetic gait: “It is safe to say that any human system with major structural asymmetries in the neuromuscular skeletal system cannot be optimal when the gait is symmetrical. Rather, a new nonsymmetrical optimal is probably being sought by the amputee within the constraints of his residual limb and the mechanics of his prosthesis.” 4 This compromise is starker in many orthotic cases. Clinicians must decide which parameters of gait to assess for symmetry when making clinical decisions. In 2006, Chow et al. investigated “various gait parameters in subjects with unilateral transtibial amputation over a range of acceptable anteroposterior translational and tilt alignments” and examined “if a consistent alignment of highest symmetry can be found.” 5 They reported that not all parameters of gait reach the same level of symmetry when a prosthesis is optimally aligned for a particular patient: “consistently symmetric values for the vertical ground reaction forces…, stance duration…, step length…, and time to maximum flexion during the swing phase…were found, and asymmetry in these parameters may assist the prosthetist in identifying unacceptable alignments.” 5 Of these parameters, only step length can be assessed without the use of specialized instruments not commonly used in a clinical setting. The Asymmetrical Brain Sadeghi et al. point out that “the human body cannot just be viewed from a biomechanical standpoint since movement occurs as a result of the integration of biomechanical and neurophysiological factors.” 1 The functional asymmetry of the brain means that injury to different areas results in different sensory and motor consequences. In 1865, the French physician and anatomist Pierre Broca “was the first to draw attention to and use the term laterality” and identified the left hemisphere as the source of speech and “that motor organization and brain functions of the right and left hemispheres are different.” 1 Subsequent research confirmed that “the left hemisphere is specialized for precise control of fine motor actions on both sides, while the right hemisphere is related to bilateral somatosensory spatial ability, emotional expression, and motor functions.” 1 Some additional research demonstrated that “the asymmetrical behavior of the lower limbs was affected by laterality.” 1 Determining Leg Dominance Limb dominance is an essential element in upper-limb prosthetics decision-making, but generally not considered when addressing the lower limbs. Upper-limb dominance is easily identifiable by patients themselves and through simple observation of them performing activities of daily living. To the extent that lower-limb dominance is considered, most patients and practitioners probably assume that it corresponds to that of the upper limb. Research has demonstrated that there is a difference in lower-limb dominance depending on what type of activity is performed and whether one or both legs is involved in the task. In research testing “the agreement between self-reported and observed leg dominance,” Van Melick et al. found that “the leg used to kick a ball had 100 percent agreement between the self-reported and observed dominant leg for both men and women.” 6 This led to their conclusion that “it is appropriate to ask healthy adults: ‘If you would shoot a ball on a target, which leg would you use to shoot the ball?’ to determine leg dominance in bilateral mobilizing tasks.” 6 These researchers also found “a considerable number of the participants switched the dominant leg in a unilateral stabilizing task.” 6 Overall, their research found that 66.7 percent of men and 85 percent of women “have the same dominant leg when comparing kicking a ball and standing on one leg.” 6 This research is consistent with the results of Sadeghi et al.’s review, which found that “asymmetrical behavior of the lower limbs during able-bodied ambulation…was found to reflect natural functional differences between the lower extremities. These functional differences were probably related to the contribution of each limb in carrying out the tasks of propulsion and control during able-bodied walking.” 1 Sadeghi reported on the results of one study that found “that one lower limb is mainly responsible for support and body weight transfer during walking while the contralateral limb contributes more to propulsion,” “medio-lateral balance was mostly controlled by the left limb,” and that for subjects walking at three different speeds the right limb was responsible for propulsion “while the left limb was found to be responsible for support.” 1 One study included in their review “reported that propulsion was related to the leg with predominantly muscle power generation whereas support and control functions were associated with the limb having predominantly power absorption behavior.” 1 Sadeghi et al. concluded that “able-bodied gait seems to be naturally asymmetrical and this asymmetrical behavior could be associated with the different contributions of the lower limbs in carrying out propulsion and control tasks….” 1 Additionally, “the foot that is used in activities is the preferred foot while the nonpreferred foot provides postural and stabilizing support.” 1 They caution that “although laterality might be considered as one explanation of the existence of functional gait asymmetry in able-bodied gait, it seems that the basic question of foot dominance has not been settled.” 1 This supports Spry et al.’s 1993 conclusion that “right-leg dominant people tended to use the right leg for manipulative skills and the left leg for supportive or weight bearing skills. The reverse was true for the left-leg dominant people." 7 Clinical Implications If normal and symmetrical function is not a reasonable clinical goal, given the asymmetrical nature of normal brain and limb function, what is? For their part, individuals using a prosthesis “consider overall function more important than the presence or degree of gait deviation.” 8 This is consistent with other research demonstrating that in a clinical setting, optimal prosthetic alignment is determined qualitatively by the prosthetist and patient. It is reasonable to assume a similar prioritization and process in orthotic cases. Since a direct relationship between kinetic and kinematic changes should not be assumed, the imposition of kinematic symmetry on patients may impose barriers to function if symmetry is achieved at the added cost of increased energy expenditure or other functional consequences. 9 Sadeghi et al. stated that “although spatiotemporal parameters can provide an overall impression of gait, from another perspective they might not be considered informative parameters since they are only able to provide insight into the effect (e.g. stride length) of the movement and not the cause (e.g. force).” 1 Clinicians must be mindful of which gait parameters are most relevant to support the achievement of broader functional goals rather than focus on improvements in isolated kinematic variables. O&P alignment and gait training appropriately focus on gross functional issues, many of which mask minor variations related to limb dominance. Toward this end, an assessment of symmetry using the contralateral limb as a reference and relevant outcome measures seems appropriate. A greater awareness of the functional implications of limb dominance could provide insight into the function of individuals using a lower-limb orthosis or prosthesis. For example, a 1977 study reported “that lower-limb amputees rehabilitated faster when it was the nondominant limb that had been amputated.” 1 However, assumptions about the effects of limb dominance must be formally investigated, since they may be different than expected. McDonald et al. recently investigated “the effect of adding a toe joint to a passive prosthetic foot” and reported the “unexpected and intriguing observation” that “all participants who wore the prosthesis on their dominant limb preferred the flexible toe joint, and every other participant preferred the locked configuration.” 10 They reported that “between configurations, participants exhibited little change in other gait kinematics or kinetics, and no apparent or consistent difference in the rate of oxygen consumption.... None of the traditional biomechanical or metabolic outcomes seemed to explain user preference.” 10 A 2023 study examining “whether kinematic differences were present between the feet of the dominant and nondominant limb during walking and running on a treadmill” found “no group-level effect of limb dominance” for metatarsophalangeal or medial longitudinal arch range of motion “or heel-rise to toe-off duration.” 2 Additionally, the authors reported that “individual participants did present with notable between-limb differences that were not explained by limb dominance.” 2 As much as we understand about gait, the impact of O&P interventions, and the user experience, there are factors that require additional insight through the collaboration of clinicians and researchers. Until these factors are better understood, limb dominance remains a less important factor than the gross asymmetries commonly used to assess and treat gait abnormalities in clinical practice. John T. Brinkmann, MA, CPO/L, FAAOP(D), is an associate professor at Northwestern University Prosthetics-Orthotics Center. He has over 30 years of experience in patient care and education. References Sadeghi, H., P. Allard, F. Prince, and H. Labelle. 2000. Symmetry and limb dominance in able-bodied gait: A review. Gait & Posture 12(1):34-45. Molitor, S. L., K. E. Zelik, and K. A. McDonald. 2024. Lower-limb dominance does not explain subject-specific foot kinematic asymmetries observed during walking and running. Journal of Biomechanics 162:111877. Finco, M. G., S. C. Moudy, and R. M. Patterson. 2023. Normalized kinematic walking symmetry data for individuals who use lower-limb prostheses: considerations for clinical practice and future research. JPO: Journal of Prosthetics and Orthotics 35(1):e1-e17. Winter, D. A., and S. E. Sienko. 1988. Biomechanics of below-knee amputee gait. Journal of Biomechanics 21(5):361-7. Chow, D. H. K., A. D. Holmes, C. K. L. Lee, and S. W. Sin. 2006. The effect of prosthesis alignment on the symmetry of gait in subjects with unilateral transtibial amputation. Prosthetics and Orthotics International 30(2):114-28. van Melick, N., B. M. Meddeler, T. J. Hoogeboom, M. W. G. Nijhuis-van der Sanden, and R. E. H. van Cingel. 2017. How to determine leg dominance: The agreement between self-reported and observed performance in healthy adults. PloS One 12(12):e0189876. Spry, S., C. Zebas, and M. Visser. 1993. What is leg dominance? In ISBS-Conference Proceedings Archive. Kark, L., and A. Simmons. 2011. Patient satisfaction following lower-limb amputation: the role of gait deviation. Prosthetics and Orthotics International 35(2):225-33. Childers, W. L., and G. F. Kogler. 2014. Symmetrical kinematics does not imply symmetrical kinetics in people with transtibial amputation using cycling model. Journal of Rehabilitation Research & Development 51(8):1243-54. McDonald, K. A., R. H. Teater, J. P. Cruz, J. T. Kerr, G. Bastas, and K. E. Zelik. 2021. Adding a toe joint to a prosthesis: Walking biomechanics, energetics, and preference of individuals with unilateral below-knee limb loss. Scientific Reports 11(1):1924. Image: Hip.hub/stock.adobe.com

Gait Symmetry and Lower-limb Dominance

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