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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • Commonly referred to as “bucked shin complex”
  • Stress-related bone injury to the dorsal aspect of MCIII resulting in dorsal metacarpal periostitis (“bucked shins”) and dorsal cortical stress fracture (“saucer fracture”)
  • High-strain cyclic fatigue of MCIII causes decreased bone stiffness and the bone responds by adding new bone.
  • Common racehorse disease in the USA and Australia
  • Musculoskeletal—dorsal MCIII, occasionally MTIII

Signalment!!navigator!!

  • Young (2- and 3-year-olds) racehorses
  • Thoroughbreds, Quarter Horses, Arabians, and uncommonly Standardbreds

Signs!!navigator!!

  • Acute soreness, tenderness, swelling of dorsal MCIII after high-speed workout (“breeze”) or race
  • Associated lameness, bilateral stiff or short, choppy forelimb gait
  • Distinct dorsal convexity of MCIII when viewed from the lateral side
  • “Saucer fractures” occur mostly in the left forelimb; focal swelling or bony knot in the dorsal or dorsolateral aspect of mid-MCIII

Causes and Risk Factors!!navigator!!

  • Racing and race training
  • Classically trained racehorses
  • Racing/training on dirt tracks
  • Counterclockwise racing
  • Most racehorses with “saucer fracture” had previous “bucked shins”

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Incomplete, longitudinal MCIII cortical fracture—rule out with radiography
  • Suspensory avulsion fracture—rule out with radiography, nuclear scintigraphy, ultrasonography
  • Periostitis due to direct trauma

Imaging!!navigator!!

Radiography

  • “Bucked shins”—periosteal thickening of dorsal, dorsomedial MCIII diaphysis
  • “Saucer fracture”—short, oblique unicortical fracture in dorsal or dorsolateral MCIII diaphysis

Nuclear Scintigraphy

  • “Bucked shins”—diffuse increased radiopharmaceutical uptake along dorsal MCIII
  • “Saucer fracture”—focal increased radiopharmaceutical uptake (“hot spot”) in dorsal MCIII

Other Diagnostic Procedures!!navigator!!

Diagnostic analgesia—generally not necessary; high palmar analgesia with dorsal proximal MCIII ring block confirms the location of the pain.

Pathologic Findings!!navigator!!

Microradiographic evaluation reveals appositional new bone formation on the dorsomedial periosteal surface of MCIII.

Treatment ⬆ ⬇

TREATMENT

  • Cold water hosing, icing, poultice, or antiphlogistic dressing for several days
  • “Bucked shins”—stall confinement and hand-walking for 2–8 weeks
  • “Saucer fracture”—stall confinement and hand-walking for 4–6 weeks followed by controlled exercise (small paddock or light jogging) for another 6–8 weeks
  • Surgery—osteostixis (fenestration), screw fixation, or both for “saucer fracture”
  • Additional therapies:
    • Thermocautery (“pin firing”)
    • Cryotherapy (“freeze firing”)
    • Periosteal picking—percutaneous periosteum irritation with needle
    • Extracorporeal shockwave therapy

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • NSAIDs (phenylbutazone 2.2–4.4 mg/kg every 12–24 h) for a few days
  • Counterirritants (“paints” and “blisters”)—topical medications

Contraindications/Possible Interactions!!navigator!!

Long-term NSAID use is contraindicated owing to resultant impaired bone healing and risk of catastrophic fracture after “saucer fracture.”

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • For acute mild disease, return to soundness within several days to weeks
  • For severe disease, return to soundness in months. Radiographic evaluation at monthly intervals for “saucer fracture”

Prevention/Avoidance!!navigator!!

  • Revised training regimens to stimulate cyclic bone loading that is similar to those when racing, i.e. train at racing speeds. Horses are worked at or near racing speeds at least twice weekly, initially at very short distances and increased gradually. With each incremental increase in training speed, distance is decreased
  • Avoid slow jogging and long gallops

Possible Complications!!navigator!!

  • Variable proportion of horses experience repeated or chronic episodes
  • Prolonged or incomplete bony healing of a “saucer fracture” with conservative treatment
  • Catastrophic fracture in unrecognized “saucer fracture”

Expected Course and Prognosis!!navigator!!

  • Prognosis for most horses with “bucked shins” is very good after early recognition and strict adherence to revised training protocol
  • The majority of horses with “saucer fractures” treated with osteostixis, screw fixation, or both will return to racing

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Most horses with “saucer fractures” had previous episode of “bucked shins.”

Age-Related Factors!!navigator!!

Young (<4 years of age) racehorses.

Zoonotic Potential!!navigator!!

None

Abbreviations!!navigator!!

  • MCIII = third metacarpal bone
  • MTIII = third metatarsal bone
  • NSAID = nonsteroidal anti-inflammatory drug

Suggested Reading ⬆ ⬇

Nunamaker DM. The bucked shin complex: etiology, pathogenesis, and conservative management. In: Ross MW, Dyson SJ, eds. Diagnosis and Management of Lameness in the Horse. St. Louis, MO: Elsevier Saunders, 2003:847–853.

Author(s) ⬆

Author: Elizabeth J. Davidson

Consulting Editor: Elizabeth J. Davidson