2000 - The Foot Posture Changes in Human Obesity Model

INTRODUCTION: Orthopaedic walking boots are often prescribed to individuals following a variety of musculoskeletal injuries and surgeries.1,2 While walking boots have clear benefits,2 they cause a discrepancy in leg length as it elevates one limb relative to the other.1 Medical professionals anecdotally report that patients prescribed a walking boot often complain of pain up the kinetic chain which has been associated with this difference in leg length combined with altered gait mechanics due to the restricted motion allowed by the boot.3 This study examined the effects of inserting a corrective heel lift on the contralateral limb to correct the leg length discrepancy. We hypothesized that kinematic asymmetries caused by an orthopaedic walking boot would be reduced when worn with a heel lift on the contralateral limb.METHODS: Seventeen healthy adults (25.1u00b14.3 yrs., 1.8u00b10.1 m, 80.5u00b119.7 kg) provided informed consent to participate in this IRB-approved study. A ten-camera motion capture system (Vicon, Oxford, UK) tracked the kinematics of each participant (100 Hz) as they walked across the capture space at a self-selected speed. Three conditions were used; A) two shoes [Shod], B) one shoe and one walking boot (Better Brace, Canada) (Figure 1) [Boot], and C) one shoe with a corrective heel lift and one walking boot [Lift]. Three successful trials were collected for each participant in each condition. The symmetry index (SI) was calculated for the hip and knee angles of one full stride using the method suggested by Nigg et al. (2013)4, and a two-way analysis of variance tested for differences in the SI scores between the conditions. Cohenu2019s D determined the magnitude of effect sizes where >0.5 was considered moderate, and >0.8 was considered large effect.RESULTS: Compared to the shod condition (A), wearing the boot increased the SI score of both the hip and knee in the transverse plane (hip: +35%, p=0.021, D=0.95, and knee: +8%, p=0.176, D=0.61) and the sagittal plane knee motion (+19%, p=0.092, D=0.71) (Figure 2). The heel lift reduced the SI scores for both the hip and knee in the sagittal plane (hip: -35%, p=0.019, D=0.97, and knee: -27%, p=0.038, D=0.94) and the transverse plane (hip: -29%, p=0.062, D=0.58, and knee: -30%, p=0.034, D=0.98) relative to the shod condition. The heel lift also increased the frontal plane hip SI score (+35%, p=0.109, D=0.52).DISCUSSION: This analysis confirmed that walking with an orthopaedic boot increases the asymmetry between the limbs, as suggested by previous analyses.1 It was also shown that adding a heel lift to the contralateral limb did reduce the SI in all motions that were negatively affected by the boot. Interestingly, the introduction of the lift reduced the asymmetry of some motions below what was seen for the shod condition. Since some degree of asymmetry is expected during gait,4 the clinical significance of reduced asymmetry below this base-line (shod) should be considered. The lift also increased the degree of asymmetry in the hip joint frontal motion, which was unaffected by the introduction of the boot. The current understanding of long-term effects of increased asymmetry is limited and so the consequences of these kinematic symmetry changes between the limbs remain unknown. Further, no consensus has been set with regards to what should be considered u2018optimal symmetryu2019 and at which point symmetry or asymmetry becomes undesirable.5 It is also important to consider that although the changes we observed in this study were small, the analysis was limited to one stride. Any differences are likely to grow over an accumulation of many strides, which may lead to pain and discomfort for the patient. It should also be acknowledged that the participants in this study were healthy at the time of testing and did not have any injuries that warranted them wearing the boot. These findings may therefore not apply to individuals prescribed a walking boot as their gait mechanics could be different from the participants in this study due to their injury.SIGNIFICANCE/CLINICAL RELEVANCE: This study showed that adding a corrective heel lift to the contralateral limb may reduce kinematic asymmetries of the lower extremities in healthy adults when walking in an orthopaedic boot. However, clinicians should be aware that the introduction of a corrective heel lift may not restore the degree of asymmetry created by the boot to levels seen during shod walking.

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