Macroscopic changes in the distal ends of the third metacarpal and metatarsal bones of Thoroughbred racehorses with condylar fractures

Abstract

Results suggest that condylar fractures in horses are pathologic fatigue or stress fractures that arise from a preexisting, branching array of cracks in the condylar groove of the distal end of MCIII or MTIII.

Scanning Electron Microscopic Examination of Third Metacarpal/Third Metatarsal Bone Failure Surfaces in Thoroughbred Racehorses with Condylar Fracture

“…2-4 MC3/MT3 condylar fracture is significantly associated with the development of an array of macroscopic cracks in the palmar/plantar subchondral bone of the condylar groove, which eventually leads to development of a parasagittal linear defect in the subchondral bone and the overlying articular cartilage. 3,4 We have extended these observations by determining that the macroscopic cracks previously observed in the palmar/plantar subchondral bone of the condylar groove 4 arise from a fractal array of branching microcracks that originate at a nanoscale level, with initiation of a microcrack probably occurring at the level of the collagen fiber or below. 14 The branching arrays of microcracks we have observed are site-specific and are principally associated with the adaptive response to racing and training that leads to the formation of a thickened subchondral bone plate in the dorsal and palmar/plantar regions of the condyle from modeling and remodeling of trabecular bone.…”

“…4 After thawing to room temperature, the MC3/MT3 bone was transected just proximal to the proximal end of the condylar fracture and the distal end of the MC3/MT3 bone was dissected from the surrounding soft tissues. The articular cartilage and attached soft tissues were removed by incubating the bone specimen in 0.1-0.2 M NaOH, 10 and the specimen was then fixed in 70% ethanol.…”

“…In particular, how structural failure of bone may be influenced by microdamage accumulation and the consequent remodeling response that is targeted to the removal and replacement of damaged bone are not understood. In an earlier study, 4 we determined that the development of a macroscopic parasagittal array of cracks in the palmar/plantar region of the condylar grooves was significantly associated with the presence of condylar fracture in Thoroughbred racehorses, and that this pathologic cracking of the subchondral bone was increased in the lateral condylar groove, when compared with the medial condylar groove. Because the morphology of a fracture surface may provide important information about the bone failure mechanism, including determination of nanoscale architectural features, 7,9 we have extended these observations by undertaking a fractographic examination of the failure surfaces of condylar fractures in Thoroughbred racehorses that had sustained a catastrophic racetrack injury, using scanning electron microscopy (SEM).…”

“…2 Condylar fractures have the following characteristics: (1) structural failure usually occurs during high-speed exercise, 2 and appears to precede any associated fall; (2) the fracture has a site-specific parasagittal location in the condylar grooves of the distal end of MC3/MT3, usually the lateral groove; 3,4 (3) fracture occurs in adapted bone; 3,4 and (4) the critical fracture line that leads to structural failure arises from an array of cracks in the subchondral bone of the condylar groove, with associated development of a parasagittal linear subchondral bone defect and erosion of overlying articular cartilage. 3,4 Taken together, these findings suggest that condylar fractures arise because of bone fatigue. Similar types of fracture are common in the racing greyhound, [5][6][7] and in human running athletes.…”

Calcified tissue structure in the distal condyle of the third metacarpal bone in young Thoroughbred horses

“…Stepnik, Radtke and Scollay (2004) claim to have observed branching arrays of microcracks at the failure surface of catastrophic Mc3 fractures by scanning electron microscopy (SEM) (Radtke, Danova, Scollay, Santschi, Markel, Da Costa Gomez and Muir 2003;Stepnik, Radtke, Scollay, Oshel, Albrecht, Santschi, Markel and Muir 2004). A thin layer of ACC was reported to overlay remodelled, dense subchondral bone in which branching arrays of microcracks were seen.…”