The cat vertebral column: stance configuration and range of motion.

This study examined the configuration of the vertebral column of the cat during independent stance and in various flexed positions. The range of motion in the sagittal plane is similar across most thoracic and lumbar joints, with the exception of a lesser range at the transition region from thoracic-type to lumbar-type vertebrae. The upper thoracic column exhibits most of its range in dorsiflexion and the lower thoracic and lumbar in ventroflexion. Lateral flexion is limited to less than 5 degrees at all segments. The range in torsion is almost 180 degrees and occurs primarily in the midthoracic region, T4-T11. Contrary to the depiction in most atlases, the standing cat exhibits several curvatures, including a mild dorsiflexion in the lower lumbar segments, a marked ventroflexion in the lower thoracic and upper lumbar segments, and a profound dorsiflexion in the upper thoracic (above T9) and cervical segments. The curvatures are not significantly changed by altering stance distance but are affected by head posture. During stance, the top of the scapula lies well above the spines of the thoracic vertebrae, and the glenohumeral joint is just below the bodies of vertebrae T3-T5. Using a simple static model of the vertebral column in the sagittal plane, it was estimated that the bending moment due to gravity is bimodal with a dorsiflexion moment in the lower thoracic and lumbar region and a ventroflexion moment in the upper thoracic and cervical region. Given the bending moments and the position of the scapula during stance, it is proposed that two groups of scapular muscles provide the major antigravity support for the head and anterior trunk. Levator scapulae and serratus ventralis form the lateral group, inserting on the lateral processes of cervical vertebrae and on the ribs. The major and minor rhomboids form the medial group, inserting on the spinous tips of vertebrae from C4 to T4. It is also proposed that the hypaxial muscles, psoas major, minor, and quadratus lumborum could support the lumbar trunk during stance.