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Lameness in the hock region
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Summary
Lameness originating from the hock (tarsus) is a common cause of hind limb lameness and morbidity in horses of all age, breed, sex and occupations. The hock has a complex anatomy, consisting of several separate joints and bones. The reciprocal apparatus enables horses to stand for extended periods of time without expending energy and is an important part of the passive ‘stay apparatus’.
Lameness in the hock region may or may not be associated with obvious localising signs (heat, swelling etc.) and special diagnostic aids such and radiography, local anaesthesia, ultrasonography and scintigraphy may be necessary to make a diagnosis.
Management of hock disorders depends entirely on the specific diagnosis/diagnoses and can vary from medical to surgical. This presentation will outline to common causes of lameness in the hock region and focus on their appropriate treatments.
Keywords: Hock, Tarsus, Spavin
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After the foot, the hock region is the most common site of hind limb lameness in horses of all ages, breeds, sexes and occupations.
The Hock (Tarsus) is a complex structure consisting of five separate joints:
- Tarsocrural
- Talocaneal
- Proximal intertarsal
- Distal intertarsal
- Distometatarsal (tarsometatarsal)
The Tarsocrural joint provides most of the range of motion of the hock. Flexion of the hock and stifle are synchronous because of the reciprocal apparatus which consists of the flexor tendons (SDFT) and the extensor tendons (peroneus tertius & extensors).
Disorders of the hock can lameness can be broadly classified as:
- Developmental
- Osteochondrosis Dissecans
- Distal intermediate Ridge of the tibia
- Lateral trochlear ridge
- Medial trochlear ridge
- Medial malleolus
- Lateral malleolus
Osteochondrosis Dissecans (OCD) of the tarsocrural joint commonly occurs in many breeds and as part of ‘developmental orthopaedic disease’ syndrome. The condition may or may not be associated with obvious joint distention (bog) spavin and is associated with variable lameness. Lesions most commonly occur at the distal intermediate ridge of the tibial but can also occur on the trochlear ridges and malleoli. Lateral malleolar OCD lesions are rare and most osteochondral lesions at this site are actually traumatic fractures.
- Degenerative
- Osteoarthritis of the small tarsal joints (Bone Spavin)
- Osteoarthritis of the Talocaneal joint
Osteoarthritis of the small tarsal joints (distal tarsal joint pain/ ‘bone spavin’) is common in horses of all occupations and is often associated with osteoarthritis and lameness which varies from mild to moderate to severe. Clinical signs include lameness and often there are no localising signs. Occasionally there may be bony enlargement over the medial aspect of the distal tarsal joints but swelling is most often absent. Diagnosis is confirmed by lameness examination and intraarticular analgesia (nerve block). Treatment includes intraarticular medication with corticosteroids, regular consistent exercise and remedial farriery. Alcohol facilitated ankylosis may be indicated in some cases and surgical arthrodesis is sometimes performed. Osteoarthritis of the talocaneal joint is rare and carries a poor prognosis.
- Athletic Injury
- Proximal suspensory ligament desmitis
- Collateral ligament strain
- Plantar ligament strain (curb)
- Superficial Digital Flexor Tendon (SDFT) luxation
Proximal suspensory ligament desmitis is a common and important cause of hind limb lameness in the proximal metatarsal region. The lameness is localised to the region by local anaesthesia and diagnosis is confirmed with ultrasound & radiography or occasionally MRI. Conservative medical management is generally unsuccessful and surgical neurectomy/fasciotomy offers better outcomes in selected patients.
Collateral ligament strain is uncommon and the medial ligaments are more commonly affected. Medical management is indicated and outcomes vary from good to fair. Plantar ligament strain occurs most commonly in harness horses and diagnosis is based on clinical examination, localised swelling, palpation and ultrasound. Medical management is generally rewarding.
SDFT luxation is uncommon (lateral luxation is more common than medial) and most commonly treated medically.
- Traumatic
- Fracture (lateral malleolar fracture in particular)
- Wounds
- Rupture of the peroneus tertius
- ‘Capped’ hocks (calcaneal bursitis)
- Lesions of the sustentaculum tali
Fractures of the tarsal bones occur uncommonly and fracture of the lateral malleolus is probably the most common. Wounds of the hock are common and may or not involve synovial structures and can therefore be life threatening. Rupture of the peroneus tertius is uncommon and is characterised by an ability to extend the hock whilst the stifle is flexed (failure of the reciprocal apparatus). Capped hocks are usually caused by self-inflicted trauma and often results in cosmetic disturbance of the point of the hock. Lesions of the sustentaculum tali and the DDFT are generally traumatic and best managed surgically with arthroscopy/tenoscopy.
- Infective
- Joint sepsis (Septic arthritis – haematogenous or wound related)
- Peri-tarsal cellulitis
Joint infection of the tarsocrural joint may be the result of ‘joint ill’ (foals) or traumatic wounds (adults) and is like threatening, usually requiring emergency surgery and antibiotic therapy. Peritarsal cellulitis most commonly affects adults and is secondary to innocuous small distal limb wounds or abrasions.
References
The Tarsus, (Dyson & Ross) Diagnosis and Management of Lameness in the Horse: Ross MW, Dyson SJ, editors; Saunders/Elsevier, St Louis, Missouri; 2003, pp 508-525.
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