X-RAY STUDY OF THE CAT HINDLIMB DURING TREADMILL LOCOMOTION

With pulsed X-ray cinematography we have analysed the angular excursio ns of the distal hindlimb joints (proximal interphalangeal, PIP; metat arsophalangeal, MTP; ankle) in cats walking on a treadmill. These dist al joints transmit the body weight and the dynamic forces onto the gro und. We have included the knee and hip joints in the analysis to relat e the angular excursions of the proximal and distal joints and to veri fy the data previously obtained with external markers on the kinematic s of the proximal joints. At the beginning of the stance phase the PIP joints flexed rapidly, the MTP joints extended slowly and the ankle a nd knee yielded under body weight. Whereas the PIP joints maintained a rather constant angular position of similar to 75 degrees throughout the stance phase, extension continued in the MTP joints from similar t o 230 degrees at touch-down to similar to 270 degrees at the end of th e stance phase. Around 50 ms before lift-off the MTP joints flexed rap idly. Early (similar to 30 ms) after lift-off this flexion changed int o a slow extension. The PIP joints extended swiftly at the stance-swin g transition and moderately at the end df the swing phase. During the middle part of the swing phase they flexed slowly. Small rotatory move ments around the long axis of the foot took place in the last 100 ms o f the swing phase. The results of this study on the distal joints are discussed in relation to the placing of the paw, to the translation of forward propulsion into a MTP movement and to the lifting of the paw (conventionally described as toe curling). They show a differentiated mechanical interaction between the different distal limb joints during these different phases, which must be known in detail to interpret th e corresponding electromyographic data and to understand how the hip i s moved forward over the MTP joints which serve as the final pivot dur ing stance.