Equis ISSN 2398-2977

MC/MT 3: dorsal metacarpal disease

Synonym(s): Bucked shins, shin splints, shin soreness, dorsal metacarpal periostitis, dorsal metacarpal disease/syndrome

Contributor(s): Prof Gary M Baxter, Graham Munroe, Chris Whitton

Introduction

  • Periostitis of dorsal cortex of third metacarpal bone. Most common cause of lameness in 2 year old Thoroughbred horses in their first year of training.
  • Cause: stress periostitis and fractures in young horses introduced to fast exercise.
  • Signs: acute pain on palpation of dorsal metacarpus; failure to perform to optimum level.
  • Diagnosis: palpation   Musculoskeletal: physical examination - adult  , radiography   Forelimb: radiography  , scintigraphy   Bone: scintigraphy  .
  • Treatment: depending on severity and chronicity - rest, anti-inflammatories   Therapeutics: anti-inflammatory drugs  , reduced exercise, altered training program, surgery - forage drilling of dorsal cortex, screw fixation   Bone: internal fixation - screws  .
  • Prognosis: depends on type.

Pathogenesis

Etiology

  • Biomechanical stress results in rapid modeling.

Predisposing factors

General
  • Fast exercise.

Specific

  • Running on hard tracks.
  • Traditional training methods, eg increasing speed and distance run simultaneously.

Pathophysiology

  • Fast exercise   →   acute stress on dorsal cortex of metacarpus   →   loss of stiffness   →   rapid production of periosteal bone/ microfractures   →   pain.
  • If stress continues   →   fatigue fracture of dorsal cortex.
  • Incidence increased on harder surfaces, eg dirt vs firm track and long periods of fast work.
  • Important cause of wastage due to lost training time and poor performance.
  • Cross-section of young metacarpus is symmetric medially and laterally, with a thicker dorsal cortex (experiences more compressive forces).
  • Type I: cyclic loading (repeated stress)   →   loss of stiffness   →   rapid production of periosteal bone   →   periostitis.
  • Type II: with continued track exercise medial side of forelimb suffers more stress, therefore experiences more modeling   →   callus formation.
  • Type III: fracture of the dorsolateral cortex (weaker relative to the dorsomedial cortex) at the junction of the middle and distal thirds of MCIII.

Timecourse

  • Acute - Type I, III.
  • Chronic - Type II, unrecognized Type III.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Griffiths J B et al (2000) Improving the predictability of performance by prerace detection of dorsal metacarpal disease in Thoroughbred racehorses. Aust Vet J 78, 466-467 PubMed.
  • Pilsworth R C (1992) Incomplete fracture of the dorsal aspect of the proximal cortex of the third metatarsal bone as a cause of hindlimb lameness in the racing Throughbred - a review of three cases. Equine Vet J 24, 147-150 VetMedResource.
  • Moyer W, Spencer P A & Kallish M (1991) Relative incidence of dorsal metacarpal disease in young Thoroughbred racehorses training on two different surfaces. Equine Vet J 23, 166-168 PubMed.


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