The horse leg is a fascinating display of integrated biomechanics. Certainly there's ample evidence that some condylar fractures are the final culmination of previous small, cumulative microfractures. Failure of one small component leads to disaster of the whole. Barbaro's bones didn't all shatter in one stride.

In the end, the only people able to knowledgably search their hearts about a possible prior warning of a problem would be the man that rode the horse daily and felt every movement and breath, and the trainer who afterwards ran his hands over every tendon and joint. Matz has been the man on the back of 1100 pounds landing on one coffin bone after clearing a 6-foot wide oxer.

We're armchair quarterbacks <g> that can emotionally walk away. They are the only folks having to bear forever the "what if?" self-doubts. My heart goes out to them for that.

Scanning electron microscopic examination of third metacarpal/third metatarsal bone failure surfaces in thoroughbred racehorses with condylar fracture.
Vet Surg 33[1]:2-10 2004 Jan-Feb Stepnik MW, Radtke CL, Scollay MC, Oshel PE, Albrecht RM, Santschi EM, Markel MD, Muir P
Comparative Orthopaedic Research Laboratory, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA.
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 x50 to x60,000 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.

Macroscopic changes in the distal ends of the third metacarpal and metatarsal bones of Thoroughbred racehorses with condylar fractures.
Am J Vet Res 64[9]:1110-6 2003 Sep Radtke CL, Danova NA, Scollay MC, Santschi EM, Markel MD, Da Costa Gomez T, Muir P
Comparative Orthopaedic Research Laboratory, Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA. OBJECTIVE: To determine changes in the distal ends of the third metacarpal and metatarsal bones (MCIII and MTIII) of Thoroughbred racehorses that had sustained a catastrophic condylar fracture during high-speed exercise. SAMPLE POPULATION: Fractured and contralateral MCIIIs and MTIIIs from 11 Thoroughbred racehorses that sustained a displaced condylar fracture during racing, both MCIIIs from 5 Thoroughbred racehorses euthanized because of a catastrophic injury other than a condylar fracture, and both MCIIIs from 5 horses of other breeds that had not been professionally trained or raced. PROCEDURE: Macroscopic observations were made of the distal ends of the bones before and after digestion of the articular cartilage with NaOH. RESULTS: In all 11 racehorses with a displaced condylar fracture, the fracture was associated with a branching array of cracks in the condylar groove. In this region, fracture margins were smooth, and there was loss of subchondral bone. Comminution of the dorsal cortex was also seen. Parasagittal linear wear lines in the articular cartilage, erosions in the articular cartilage of the condyles, loss of the underlying subchondral bone, and cracking of condylar grooves were all more severe in the Thoroughbred racehorses than in the horses that had not been professionally trained or raced. ***CONCLUSIONS AND CLINICAL RELEVANCE: 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.

Biomechanical investigation of the association between suspensory ligament injury and lateral condylar fracture in thoroughbred racehorses.
Vet Surg 32[6]:585-97 2003 Nov-Dec Le Jeune SS, Macdonald MH, Stover SM, Taylor KT, Gerdes M Veterinary Medical Teaching Hospital, Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA. Objective-To determine whether partial transection of the medial branch of the suspensory ligament (MBSL) alters equine third metacarpal bone (MC3) condylar surface strains and forelimb, distal joint angles in a manner consistent with promotion of lateral condylar fracture. Study Design-In vitro biomechanical experiment. Sample Population-Right forelimbs from 7 Thoroughbred horse cadavers. Methods-Lateral and medial MC3 condylar, dorsal and abaxial, bone surface strains and distal joint angles were measured both before and after partial transection of the MBSL during in vitro axial limb compression. Dorsal, principal bone strains and abaxial, uniaxial, and proximodistal strains were compared before and after MBSL partial transection at 1,400-, 3,000-, and 5,600-N loads. Results-Bone strains increased in all locations with increasing axial load. All lateral condylar bone strains were significantly higher, and abaxial surface medial condylar bone strain was significantly lower, after partial transection of the MBSL. Respective distal joints became more flexed or extended as axial load increased but were not significantly different after partial transection of the MBSL. Conclusions-Partial transection of the MBSL increases in vitro MC3 lateral condylar bone surface strains. ***Clinical Relevance-Loss of integrity of the medial branch of the suspensory ligament could increase the risk for lateral condylar fracture in Thoroughbred horses by amplifying bone strain in the lateral condyle.