Third metatarsal bone

Abstract: Objective To determine type, distribution, and radiographic appearance of condylar fractures of the third metacarpal bone (MC-3) or third metatarsal bone (MT-3) in Thoroughbreds (TB), Standardbreds (SB), and Arabians, to assess long-term outcome of horses in which fractures were repaired surgically, and to identify variables associated with prognosis for return to racing. Design Retrospective study. Animals 224 horses with 233 fractures. Procedure Medical records and radiographs obtained before and after treatment were reviewed. Racing performance before and after treatment was determined by reviewing race records. Results TB were overrepresented and SB were underrepresented, compared with the hospital population. Thoroughbreds had significantly more lateral condylar fractures and significantly more forelimb fractures than did SB. Thoroughbreds were less likely to race after treatment if they had complete, rather than incomplete, lateral condylar fracture or had concurrent proximal sesamoid bone fracture. Convalescent time for TB with medial condylar fractures of MT-3 was significantly longer than that for TB with lateral condylar fractures of MT-3. Clinical implications Horses with condylar fractures of MC-3 and MT-3 that had minimal pathologic changes in the involved joint had a favorable prognosis for returning to racing after surgical treatment. Prognosis for horses with complete condylar fractures, particularly those with substantial pathologic changes in the involved joint, was worse.

Abstract: Objective— To examine the fracture failure surfaces from Thoroughbred horses that had sustained a catastrophic condylar fracture. Sample Population— Bone specimens from the failure surface were obtained from 12 Thoroughbred racehorses with catastrophic injury and 2 non-racing horses with accidental long bone fracture. Methods— Bone specimens from the failure surface of each fracture were incubated with gold microspheres to label microcracks before examination at ×50 to ×60,000 using scanning electron microscopy. Microcracking at the failure surface was assessed using a visual analog scale. Results— Branching arrays or clusters of microcracks were seen over a range of magnifications in adapted subchondral bone in the distal end of the MC3/MT3 bone from racing Thoroughbreds with a catastrophic displaced condylar fracture. In the palmar/plantar region, microcracking was associated with the formation of an array of macroscopic cracks in the condylar groove. A different pattern of microcracking was seen in specimens of bone from distal metaphyseal and diaphyseal MC3/MT3 failure surfaces from Thoroughbred racehorses with catastrophic fracture and non-racing horses with an accidental diaphyseal long bone fracture. Few microcracks were seen and typically did not form branching arrays. Conclusion— These data suggest that propagation of condylar fracture in Thoroughbred racehorses is initiated by the formation of nanoscale microcracks in adapted subchondral bone that form during exercise-induced bone adaptation. Clinical Relevance— Accumulation and coalescence of branching microcracks into arrays or clusters appears to eventually lead to the development of macroscopic subchondral cracks in the condylar groove and initiation of a condylar fracture.

Abstract: Fifteen longitudinal fractures involving the medial condyle of the third metatarsal bone were diagnosed in racing Thoroughbreds and Standardbreds. Twelve were repaired surgically with lag screws placed through stab incisions. Two of the horses suffered catastrophic fracture of the third metatarsal bone during recovery from anesthesia, and 3 more sustained complete fractures within 4 days of the repair. Of 3 horses with fractures treated without surgery, 2 healed without complication. Preoperative radiography did not demonstrate a nonlongitudinal fracture component in any of the horses that sustained complete fractures. The complete fractures were uniformly "Y" shaped. Horses in which the fractures healed had a good prognosis for return to racing.