Locomotion on three legs: the tripedal gaits of canine amputees

The gaits of bipedal and quadrupedal animals are well characterized, while, with few naturally occurring tripedal gaits, little is understood regarding locomotion on three legs. Canine amputees provide a unique perturbation into the study of locomotion. This study assesses whether these individuals use distinct limb sequences, with clearly defined kinematics and kinetics, which could be considered discrete gaits. Data for a group of hind- and forelimb canine amputees across a range of speeds show that at higher speeds, three legged dogs use a three beat gallop-like gait: forelimb amputees use a rotary-like gallop; hindlimb amputees use both rotary- and transverse-like sequences. At low speeds, two strategies are observed: (i) maintenance of a three legged gallop with increased stride periods, and (ii) uncoupled walking, with an increased stride period on the 'walking' pair of legs and a constant stride period on the single leg, resulting in decoupling of fore- and hindlimb timings. The single limb is constrained by unsupported aerial time, maintaining a consistent period, striking more than once per cycle at lower speeds. Altered force distributions show high peak vertical forces in the single limb of forelimb amputees, but a relatively even distribution across all limbs in hindlimb amputees.