Equis ISSN 2398-2977

Carpus: fracture - slab

Introduction

Pathogenesis

Predisposing factors

Pathophysiology

  • Slab fractures are defined as fractures that involve the proximal and distal articular surfaces and transverse the entire depth of the bone. This differentiates them from the smaller osteochondral fragments that only involve one articular surface Carpus: fracture - chip.
  • Slab fractures of the third carpal bone, usually in the frontal (dorsal) plane are by far the most common.
    • This usually involves the radial fossa (87% of cases in a large survey of Thoroughbred and Standardbred racehorses).
    • Occasionally the intermediate fossa is involved alone or in combination with the radial fossa.
    • Radial fossa fractures may involve the entire width of the fossa, or any part thereof, with range in dorsal-to-palmar depth from 8-10 mm (most common) to 20-25 mm. These very large fragments may be difficult to see on skyline radiographs and can be L-shaped.
  • Slab fractures of the radial, fourth, ulnar and intermediate bones occur uncommonly.
    • Those of the radial facet occurring simultaneously with C3 frontal slab fractures result in carpal instability and are called comminuted carpal fractures.
    • Repair of both fractures by lag screws under arthroscopic guidance is considered the only useful treatment.
    • The other fractures are often not diagnosed promptly and the delay in treatment leads to a poor prognosis.
  • Slab fractures in other planes, including sagittally, are uncommon, and usually involve the medial radial fossa in a direction parallel to that between the 2nd and 3rd bones. Intermediate fossa and bilateral fractures are even less common.
  • A combination of slab fractures occurs rarely and may lead to carpal instability.
  • The majority of slab fractures are a terminal event to nonadaptive or maladaptive bone remodeling changes in the affected bones. Lack of adaptation leads to subchondral bone sclerosis, weakening biomechanically, and fracture during strenuous exercise. Other forms of carpal bone disease may be present concurrently. 
  • Slab fractures in unusual locations may be subsequent to one-off traumatic events.

Timecourse

  • Usually present as an acute forelimb lameness but lower grade and subtle prodromal lameness may have been present chronically. Previous carpal disease, including osteochondral fragmentation, may be present in the history.

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.
  • Garvican E & Clegg P (2007) Clinical aspects of the equine carpal joints. UK Vet 12 (1), 5-10 VetMedResource.
  • Rutherford D J, Bladon B & Rogers C W (2007) Outcome of lag-screw treatment of incomplete fractures of the frontal plane of the radial facet of the third carpal bone in horses. N Z Vet J 55 (2), 94-9 PubMed.
  • Hirsch J E et al (2007) Clinical evaluation of a titanium, headless variable-pitched tapered cannulated compression screw for repair of frontal plane slab fractures of the third carpal bone in Thoroughbred racehorses. Vet Surg 36 (2),178–184 PubMed.
  • Kraus B M, Ross M W & Boston R C (2005) Surgical and nonsurgical management of sagittal slab fractures of the third carpal bone in racehorses: 32 cases (1991-2001). JAVMA 226 (6), 945-950 PubMed.
  • Stephens P R, Richardson D W & Spence P A (1988) Slab fractures of the third carpal bone in Standardbreds and Thoroughbreds: 155 cases (1977–1984) J Am Vet Med Assoc 193 (3), 353–358 PubMed.
  • Martin G S, Haynes P F & McClure J R (1988) Effect of third carpal slab fracture and repair on racing performance in Thoroughbred horses: 31 cases (1977–1984). JAVMA 193 (1), 107–110 PubMed.
  • Richardson D W (1986) Technique for arthroscopic repair of third carpal bone slab fractures in the horse. JAVMA 188 (3), 288–291 PubMed.


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