The C-Leg ® (Otto Bock, Duderstadt, Germany) is a microprocessor-controlled prosthetic knee that may enhance amputee gait. This intrasubject randomized study compared the gait biomechanics of transfemoral amputees wearing the C-Leg ® with those wearing a common noncomputerized prosthesis, the Mauch SNS ® (Ossur, Reykjavik, Iceland). After subjects had a 3-month acclimation period with each prosthetic knee, typical gait biomechanical data were collected in a gait laboratory. At a controlled walking speed (CWS), peak swing phase knee-flexion angle decreased for the C-Leg ® group compared with the Mauch SNS ® group (55.2° ± 6.5° vs 64.41° ± 5.8°, respectively; p = 0.005); the C-Leg ® group was similar to control subjects' peak swing knee-flexion angle (56.0° ± 3.4°). Stance knee-flexion moment increased for the C-Leg ® group compared with the Mauch SNS ® group (0.142 ± 0.05 vs 0.067 ± 0.07 N•m, respectively; p = 0.01), but remained significantly reduced compared with control subjects (0.477 ± 0.1 N•m). Prosthetic limb step length at CWS was less for the C-Leg ® group compared with the Mauch SNS ® group (0.66 ± 0.04 vs 0.70 ± 0.06 m, respectively; p = 0.005), which resulted in increased symmetry between limbs for the C-Leg ® group. Subjects also walked faster with the C-Leg ® versus the Mauch SNS ® (1.30 ± 0.1 vs 1.21 ± 0.1 m/s, respectively; p = 0.004). The C-Leg ® prosthetic limb vertical ground reaction force decreased compared with the Mauch SNS ® (96.3 ± 4.7 vs 100.3 ± 7.5 % body weight, respectively; p = 0.0092).

The movement of the center of mass (COM) during human walking has been hypothesized to follow a sinusoidal pattern in the vertical and mediolateral directions. The vertical COM displacement has been shown to increase with velocity, but little is known about the mediolateral movement of the COM. In our evaluation of the mediolateral COM displacement at several walking speeds, 10 normal subjects walked at their self-selected speed and then at 0.7, 1.0, 1.2, and 1.6 m/s in random order. We calculated COM location from a 15segment, full-body kinematic model using segmental analysis. Mediolateral COM displacement was 6.99 +/-1.34 cm at the slowest walking speed and decreased to 3.85 +/-1.41 cm at the fastest speed (p < 0.05). Vertical COM excursion increased from 2.74 +/-0.52 at the slowest speed to 4.83 +/-0.92 at the fastest speed (p < 0.05). The data suggest that the relationship between the vertical and mediolateral COM excursions changes substantially with walking speed. Clinicians who use observational gait analysis to assess walking problems should be aware that even normal individuals show significant mediolateral COM displacement at slow speeds. Excessive vertical COM displacement that is obvious at moderate walking speeds may be masked at slow walking speeds.Abbreviations: ANOVA = analysis of variance, COM = center of mass, fps = frames per second, SS = self-selected.

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