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Injury – Effects, Repair and Causes

Common musculoskeletal injuries

Bone damage

Damage to bone equals loss of support in the framework/leverage system. Bone breaks are known as fractures. There are many different types of fracture. In a complete fracture, the line of the break passes through the bone in its entirety; bones may be broken in one or more places, they may also be crushed, or just cracked.

Bone is slow to heal but, provided the ends are approximated – that is, opposite each other – and movement between the bone ends, or between the bone particles/pieces is eliminated, healing will normally occur.

Diagnostic imaging has progressed, whereas previously the density of equine tissue masses meant that only rather poor quality X-rays were available, now with the advancement of technology perfect images can be obtained. In most referral centres there is the capacity to use magnetic resonance imaging, computed tomography, ultrasonography, nuclear scintigraphy, thermography. The advances in technology have expanded diagnostic parameters which have resulted in significant advances in the knowledge of musculoskeletal disease (Fig 2.1).

Images of the neck and back are now possible; problems with or injury to soft tissue, as well as bone and joints, can also be identified, resulting in improved treatments.

Repair phases of the recovery of bone are similar to those of soft tissue. In the case of bone, the end result is probably the most perfect for similarity of original structure. Complete fractures usually need to be immobilised for good repair. In a weight bearing limb this was, in the past, almost impossible but, with the expansion of veterinary orthopaedic surgery, and improvements in anaesthesia, the use of pins and plates are now commonplace. By the use of pins, plates and screws,a great number of horses, whose injuries would formerly have required that they be euthanised are now operated on and saved.

Fig. 2.1 The bones of a foot imaged using a portable radiography system.

Sore shins

Incomplete fractures, such as minute cracks, can be treated without the need for the limb to be immobilised. Of these, the most common condition is that of sore shins. Localised stresses (an occupational hazard of athletic bone) cause minute cracks in the cannon bone. Early radiographs often appear normal but subsequent examination may show callus formation where the tiny cracks are trying to heal. In American terminology, this condition is called bucked shins.

Early lameness denoting this condition may be minimal, but the pain may suddenly rise to a crescendo, with lameness and hypersensitivity to touch. A history of pain and tenderness should lead to at least three weeks of reduced activity. Shock wave therapy has proved beneficial.

Sites of bone inflammation

Other bone sites can cause problems, often giving rise to unexplained lameness in the early stages of bone inflammation. The patella ligament in the horse is the conjunction of three ligaments which are inserted into the tibial tubercle, as in the human model. Irritation of this bone area, described as Osgood-Schlatter’s disease, occurs in teenage human athletes and is considered to be associated with strong muscle traction on immature bone. In the young horse a similar inflammatory response appears to occur, suggesting, as in the teenage athlete, possible skeletal immaturity, with the bone unable to withstand the massive contractile forces of the quadricep muscles.

A curb occurs at the insertion of the extensors of the hock conjoined as the common calcaneal tendon.

Stress fractures which continue to give trouble, however minor, should not be ignored, the state of general maturity, diet, in particular mineral requirement, and exercise protocol, all require consideration, lest a spontaneous, complete fracture occurs.

Damage to the periosteum

The periosteum is the outer covering, or the outer skin, of the bones. Muscles, ligaments and tendons are contiguous with the periosteum at their origins and insertions. Tears, pulls or knocks cause rupture of small blood vessels, with consequent local bleeding. This free blood acts as a chemical irritant and in response to the chemical signals new bone grows, forming small ridges or lumps. These may interfere with normal function if adjacent to a joint or tendon. Bleeding between the bone and the inelastic periosteum also causes severe pain (Fig 2.2).

Damage to the epiphyseal plates

The long bones of the horse have not achieved full development before the age of two; in some breeds growth continues for several years.

Long bones, or limb bones, grow from specialist-type plates called epiphyseal plates. Under certain stress conditions, in particular diet related, and with over-training, these plates become irritated and inflamed. This condition is termed epiphysitis – that is, inflammation of the epiphyseal plate.

Damage to bursae

Bursae are small sacs of fluid, positioned at various points of the body, in areas of possible friction. Their function is to stop the underlying bone rubbing, and so damaging, the under surface of an overlying muscle or tendon. Bursae can become inflamed. If this occurs, they swell, causing severe pain and restricted movement.

The navicular bursa is the culprit in some cases of foot related lameness.

Fig. 2.2 Periosteal bruising to front of cannon hind right. Action in the fetlock joint of the injured side was severely compromised.

Fluid contained in the supraspinous bursa, positioned at the highest point of the withers, and damaged, in earlier times by ill fitting tack, tracked down between the posterior thoracic spines, with no available exit route often becoming infected and causing the condition described as wither fistula. The condition can occur following wither fracture.

There are two bursae sited at the poll, the cranial and caudal nuchal bursae, a horse which pulls back may damage either or both of these if the restraint tie does not break. Bruising results in discomfort to pressure and the horse may become bridle shy and/or head shy.

Damage to joints

The terminology to denote joint damage is arthritis (arth = joint, itis = inflammation). An inflamed joint is an arthritic joint. Unless the word arthritis has a descriptive adjective attached, the term does not necessarily mean that there will be irreversible joint changes.

One irreversible joint change is called osteoarthritis. In this case, areas of bone or the bones involved in the formation of a joint have formed irregularities on their circumference. These areas of irregular bone growth impede the normal movement of the joint. Unfortunately, the inflammatory processes in this condition are not confined to bone alone; the synovial fluid (joint oil) and the hyaline cartilage, coating the articular surfaces of the joint in question, may also be affected. Other types of arthritis may be described as traumatic, septic or infective.

Joints are sprained when put through a range of motion greater than they were anatomically designed to perform. This excessive movement may damage the supporting ligaments and surrounding muscle tissue.

Damage to ligament

Ligaments support joints. Overstretched ligaments therefore lead to loss of stability in their joint. In the case of the suspensory ligament stability is lost at the fetlock joint and below.

Damage to inter-osseous ligaments

These ligaments lie between two adjacent bones (inter = between, osseous = bone); for example, between the splint and the cannon bone. Tears of an inter-osseous ligament cause pain in the first instance and development of new bone in the second; depending on the position of the new growth, interference with normal function may occur. Some degree of pain is usually present in the early active stage of injury.

Damage to muscle

Muscle damage causes ineffective, incorrect and unbalanced movement patterns. Fatigue, bruising, loss of nerve communication and a variety of conditions, for example motor neurone disease and polysaccharide storage myopathy all damage muscle.

Muscle atrophy (loss of muscle tissue) occurs as a result of disuse, loss of communication due to damage to motor nerves or damage to the joint or joints which the muscle influences.

Damage to tendon

Damage to a tendon at the area where the structure inserts to bone or at the muscular tendon junction, occurs in the most part, due to over stretch forces associated with a weak or fatigued parent muscle.

The deep and superficial digital flexor tendons of the limbs may be damaged as a result of impact or more commonly appear to break down as a result of strain, following excessive loading.

To date, no treatment method or chemical stimulant has stimulated the components of the digital flexor tendons in a manner which has caused the original fibre type to reform following damage.

Very recent research looks more promising because considerable advances have been made in the understanding of the factors involved in tendon physiology at molecular level. It is also possible that stem cell therapy may turn out to be of benefit.

Damage to nerve

All body functions are dependent on a normal nerve supply. Any form of damage involving the specialist nerve tissues of the brain or spinal cord, the central nervous system (CNS), results in paralysis. The extent of the paralysis is determined by the area or level at which the damage has occurred, and it is the function of the body parts distal to the...