CHAPTER 104 Evaluation of Back Pain by Clinical Examination
Back pain is increasingly recognized as a contributing or causative factor in equine lameness. To understand the function of the vertebral column, its attached tissues, and their relationship to the physics of equine locomotion, some basic anatomic and biomechanical knowledge is paramount.
The 260 joints between vertebrae, vertebrae and ribs, sacrum and pelvis, and head and first cervical vertebra contribute to mobility in the entire vertebral column. Because of its connection to the limbs, a major function of the vertebral column and the attached muscles is positioning of the limbs. Some of the muscles controlling limb position have their origin at the vertebral column and their insertion on an extremity; other muscles with both origins and insertions on the vertebral column regulate mobility in the column itself.
Joints of the vertebral column allow flexion dorsally, ventrally, and laterally, and some allow rotation. In specific regions of the column, the vertebrae have specific ranges of motion within the three basic axes. The cervical intervertebral joints allow a relatively large range of flexion dorsoventrally as well as laterally, and the intervertebral joint between the first and second cervical vertebra permits rotation. In the thoracic vertebrae, the mobility is mainly lateral flexion, with some minor dorsoventral motion. In addition, the mobility of the costovertebral joints is necessary for breathing. In the lumbar portion of the column, the main mobility is in dorsoventral flexion with some rotation. In the sacral region, there is a small amount of dorsoventral flexion, and in the tail there is considerable dorsoventral and lateral flexion but no rotation.
The pattern of motion of the vertebral column also is gait specific. The support and the positioning of the column are specific functions of that gait, enhancing the range of motion of the extremities by facilitating optimal positioning of the limb relative to the vertebral column and the other limbs. At the walk, the motion of the column is snakelike with lateral flexion in the thoracic region, some rotation in the lumbar region, and dorsoventral flexion in the cervical region all contributing to support at the walk. At the trot there is only a modest degree of dorsoventral flexion in the thorax and the neck. At the canter there is more lumbar and sacral motion than in any other gait, with lumbar rotation and dorsoventral flexion seen in the lumbar, thoracic, and sacral portions of the vertebral column. An overview of the degrees of mobility and their relationship to the three gaits can be found in Table 104-1.
As in every examination, investigation of the horse with back pain starts with the history. Taking time for a good interview with the client is a first step in better comprehension of the problem. Guiding questions can assist in gaining information about the gait in which the complaints are more evident, whether there are time-related changes in the quality of the gaits, difficulties in keeping the right lead, and other information. Common complaints of owners about horses with back problems are resistance to bending in one direction; not accepting the bridle; kicking and bucking in one gait, most commonly the canter; poor-quality canter; or generalized stiffness. The poor-quality canter may be a no-sound three-beat canter, more bunny hoplike with less separation between the subsequent footfalls of the hind limbs.
Some complaints are specific to the discipline. Complaints indicative of back pain in dressage horses include difficulties in walking and canter pirouettes as well as a poor-quality or lateral walk and unsatisfactory collection and coming under (carriage of the hind quarters). In jumpers, common complaints are unsatisfactory bascule (balance above the fence), lack of propulsion and power, unwillingness to jump or turn, and landing in the wrong lead at the canter. In western pleasure, quite often the quality of the loop is mentioned as being affected in horses with back pain. In racehorses back pain is often localized to the lumbar region. In this location pain can limit dorsoventral flexion, which decreases propulsion and reduces the efficiency of the canter and gallop.
More usual lameness issues also may be mentioned. Forelimb lameness can be a result of thoracic problems because the attachment of the scapula to the thoracic portion of the vertebral column causes painful mobility in the thoracic vertebrae. Reduced stride length in a hind limb or lack of propulsion can be caused by pain in the lumbosacral region, and a lowered hip can be a sign of back pain, not only an indication of hind limb lameness.