KINEMATIC ANALYSIS OF THE CAT SHOULDER GIRDLE DURING TREADMILL LOCOMOTION - AN X-RAY STUDY

A quantitative kinematic analysis of the movements of the shoulder gir dle in the three dimensions of space during treadmill locomotion (velo city range 0.33-1.2 m/s) was performed in two cats. Since the movement patterns of the scapula and the humeroscapular joint can only vaguely be estimated through the overlying skin we used implanted metal spher es placed on the scapula in combination with three-dimensional pulsed X-ray cinematography (time resolution 20 ms) to reconstruct the excurs ions of the scapula, the humerus and the elbow and to calculate the re spective angular amplitudes and velocities. The movements of the scapu la relative to the Th4 spinous process consist of four major component s: (i) a monophasic flexion (caudocranial movement of the glenoid foss a during swing)/extension (craniocaudal movement of the glenoid fossa during stance) sequence, the fulcrum for which sequence is situated ne ar the vertebral border of the scapula at the medial elongation of the scapular spine; (ii) a vertical monophasic up/down sequence of the fu lcrum relative to the trunk, the highest vertical position being reach ed during mid-stance and the lowest vertical position during mid-swing ; (iii) a biphasic abduction/adduction sequence during swing and durin g stance respectively; and (iv) small rotations along the scapular spi ne. The trajectory recordings of the scapula indicate that the scapula yields relative to the trunk under the body weight after ground conta ct. The angular excursions of the humeroscapular joint consist of: (i) a flexion/extension sequence during swing, a yield after ground conta ct and a final extension at the end of stance; (ii) an adduction and o utward rotation during the early swing phase flexion; (iii) an abducti on and inward rotation during the late swing phase extension; and (iv) an adduction during the yield with only minor rotations during the wh ole stance phase. The movement patterns are discussed in view of the m uscular synergies necessary to guide the scapula and the humerus durin g stance and swing, and in relation to the implications for the organi zation of these patterns in spinal neuronal systems.