How does stiffness of a shockabsorbing prosthetic foot influence the biomechanics of gait?
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To improve shock absorption during gait for individuals with trans-tibial amputation (Ind-TTA), shock-absorbing pylons (SAP) have been designed to replace the rigid pylon of prosthesis. However, it is not known if a viscoelastic rod-air pressure SAP (Ceterus®) improves gait mechanics and/or vertical ground reaction forces (VGRF) during initial contact are attenuated within an optimal range of air pressure settings. Therefore, the purposes of these gait studies were to determine, for Ind-TTA, whether: a) Study 1--- increased air pressure affects kinematic and VGRF and, b) Study 2--- interlimb kinematic symmetry and mechanics are similar to those displayed by controls (CON) without an amputation. Seven Ind-TTA men, (age 20-65 yr) participated in both studies, and seven matched Ind-CON) engaged in Study #2. For both studies, each participant walked across an eight meter walkway while motion and ground reaction force (GRF) signals were collected. For Study #1, seven stiffness settings (0 - 60 psi) were used. Friedman’s 2-way ANOVAs were used to investigate the effect of air pressure (Study #1) and TTA group and limb (Study #2) on GRF and kinematic variables. For Study #1, single-subject analyses also were used. All tests: α = .05. Study #1: No significant group or single-subject differences were found among air-pressure settings for the prosthetic limb (ProsL). Therefore, no consistent mechanical effects or compensatory kinematic strategies were detected. Qualitatively, for first peak VGRF, a U-shaped response to increased air pressure exhibited by three Ind-TTA suggests that an optimal range of air pressures (~10 to 30 psi) existed in which the impact force was attenuated for these participants. Study #2: Compared to Ind CON, Ind-TTA displayed increased interlimb asymmetry for knee flexion displacement occurring during the first double limb stance phase. Furthermore, knee joint displacement, duration of the single limb stance phase and maximum VGRF slope were decreased significantly for the Ind-TTA ProsL compared to the matched CON limb. This allows the user of SAP to increase stability, through decreased knee joint flexion, without losing significant shock absorption on ProsL.