Orthopaedics 4. The back and pelvis

Chapter 18


Orthopaedics 4. The back and pelvis




Contents




18.1 Anatomy of the horse’s back


The equine thoracolumbar spine is composed of a complex arrangement of soft-tissue structures supporting a comparatively rigid vertebral column. The equine back has been likened to a ‘bow and string’ arrangement, where the ‘bow’ is the almost rigid vertebral column; the supporting muscles and ligaments act as the ‘string’, maintaining the spine under tension.


There are usually 29 vertebrae in the back (T18, L6, S5); variations in the vertebral back formula are not unusual in clinically normal horses (e.g. 17 thoracic and 7 lumbar vertebrae). The vertebrae are held in place by a series of ligaments (Figure 18.1). The supraspinous ligament is the caudal continuation of the nuchal ligament and inserts at the tip of every thoracolumbar dorsal spinous process. The main muscles of the back include the largest muscle in the body, the longissimus dorsi, and the powerful gluteal muscles (Figure 18.2).




The neck, consisting of seven vertebrae, is most frequently associated with neurological disease and is covered in Chapter 11.



18.2 Diagnostic approach to diseases of the horse’s back


The back of the horse is defined here as the thoracolumbar (T1 to L6) vertebrae, the sacrococcygeal (S1 to Cy2) vertebrae and their associated structures, including the soft tissues. The most common presenting sign of back pain is loss of athletic performance.



History


The history is often of great help in determining whether the clinician is dealing with a genuine case of back pain, or whether factors such as poor behaviour or schooling may be the underlying problem. The history is frequently long and involved; a questionnaire helps to ensure that all relevant details are obtained. Specific aspects include:



• The type of work: the horse may not be suitable for the work expected of it; certain forms of exercise may prove more problematic, e.g. jumping.


• Temperament: owners of horses with a genuine back problem frequently report that the horse has become ill-tempered, fractious or reluctant to work.


• Acute or chronic problem: if the problem has arisen following recent trauma, details of the accident may help to localize the site of pain, although more typically no such incident will have been observed.


• Position of limbs: the horse may no longer straddle when urinating or defecating; there may be reluctance to bear more weight on one hind limb (e.g. during shoeing).


• Bucking: if the history includes episodes of bucking, the safety of any riders should be paramount, regardless of whether the signs are due to pain in the horse’s back or are behavioural; this may limit the clinical investigation, and this should be explained to the owner at the outset.



Examination at rest


Stocks are useful for this part of the investigation, and the horse must be relaxed and bearing weight evenly on all four limbs.








Palpation/manipulation:



• Palpate soft tissues and summits of dorsal spinous processes (DSPs) for pain, heat or swelling.


• Assess flexibility of the back by stimulation reflex extension (dipping), flexion (arching) and lateral bending. This is done by running a blunt probe along the midline of the back from the withers to the sacroiliac region, and laterally from midline. It is important to note that a high range of reflex back movements indicates a normal, pain-free horse, although these movements are often interpreted as a sign of pain. A horse with back pain braces its back rigidly and shows clear signs of resentment.


• Similarly, pressure applied upwards onto the ventral aspect of the sternum should induce a normal horse to arch its back without signs of discomfort.


• Apply pressure to both tubera coxae and tubera sacrale; pain here may indicate fracture of the ilium or a problem in the pelvic or sacroiliac region.


• Poor tail tone may indicate early cauda equina neuritis.



Examination at exercise





In hand:



• The horse is walked and then trotted in-hand for lameness evaluation.


• Overt lameness or gait abnormalities should be identified; many horses with suspected back pain suffer from hind limb lameness. If present, this should be investigated first as described in other chapters.


• Positive hind limb flexion test(s) suggest lameness rather than back pain.


• Back pain often results in a reduced length of stride of the hind limbs and less hock flexion, but the same signs are seen in chronic hind limb lameness.


• Turning the horse tightly in both directions may provoke longissimus dorsi spasm due to pain caused by lateral spinal flexion.


• There may be reluctance to move backwards, with the head being raised and back muscle spasm because this maneuver may provoke spasms of the back muscles.





Aids to diagnosis









Jun 18, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Orthopaedics 4. The back and pelvis
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