Prevalence of carpal fractures in thoroughbred and standardbred racehorses

The prevalence of carpal fractures was determined for 211 thoroughbred and 75 standardbred racehorses. Statistically significant differences were found in the location of fractures between the 2 breeds. In the thoroughbred and standardbred groups, total fractures (460) were distributed nearly equally between the left (224) and right (236) carpi. The most common site of fracture in the thoroughbred group was the distal aspect of the radiocarpal bone (112), whereas the most common site of fracture in standardbred horses was the proximal surface of the third carpal bone (61). Slab fractures were more common in the right carpus of thoroughbred horses (29 right/11 left), but were distributed equally between the left (11) and right (11) carpi of the standardbred group. Fractures of the distal border of the radius and intermediate carpal bone were more common in the left carpi of the thoroughbred group and were relatively uncommon among standardbred horses. Fractures within the intercarpal joints (313) were more common than those within the radiocarpal joints (147) in thoroughbred and standardbred horses.     

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

OBJECTIVE: To report clinical evaluation of third carpal bone (C3) frontal plane slab fracture repair with the Acutrak screw system. STUDY DESIGN: Prospective case series. SAMPLE POPULATION: Racing Thoroughbreds (n=17) with frontal C3 slab fractures. METHODS: C3 slab fractures in Thoroughbred racehorses (1999-2004) were repaired by use of the Acutrak screw system. Data collected were (1) preoperative variables--gender, age at injury, limb involved, injury occurrence, fracture thickness, complexity, and displacement, race starts and earnings and (2) postoperative variables were: surgical complications, days to first start, race starts, and earnings. A Wilcoxon signed-rank test was used to compare pre- and postoperative starts and earnings; significance was set at P<.05. RESULTS: Seventeen Thoroughbred racehorses (12 females, 3 males, 2 geldings) were enrolled. Mean (+/-SD) age at injury was 3.3+/-1.0 years. Right carpi (10) were affected more than left (7). Ten injuries occurred during training, 7 during racing. Twelve of 15 horses that raced before injury returned to racing. Average days to first start was 349.3+/-153.9 days. Horses that returned to racing had more starts after repair (median, 6.5 versus 3.5; P=.04) and did not have decreased earnings per start (median, $2452 versus $3061; P=.30). CONCLUSION: The Acutrak screw system is a useful repair technique for frontal C3 slab fractures in Thoroughbred racehorses. CLINICAL RELEVANCE: Adequate reduction and stability of C3 slab fractures can be achieved with the Acutrak screw system, decreasing the likelihood of fragment splitting and screw head impingement on carpal soft tissues.     

Surgical and nonsurgical management of sagittal slab fractures of the third carpal bone in racehorses: 32 cases (1991-2001)

OBJECTIVE: To compare results (ie, return to racing and earnings per race start) of surgical versus nonsurgical management of sagittal slab fractures of the third carpal bone in racehorses. DESIGN: Retrospective study. ANIMALS: 32 racehorses (19 Thoroughbreds, 11 Standardbreds, and 2 Arabians). PROCEDURE: Medical records and radiographs were reviewed to obtain information regarding signalment and treatment. Follow-up information was obtained from race records. Robust regression analysis was performed to evaluate earnings per start in horses that raced at least once before and after injury. RESULTS: 22 (69%) horses raced at least once after treatment of the fracture. All 7 horses treated by means of interfragmentary compression raced after treatment, and horses that underwent interfragmentary compression had significantly higher earnings per start after the injury than did horses treated without surgery. Eight of 9 horses treated by means of arthroscopic debridement of the damaged cartilage and bone raced after treatment, but only 7 of 16 horses treated without surgery (ie, stall rest) were able to return to racing after treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that racehorses with sagittal slab fractures of the third carpal bone have a favorable prognosis for return to racing after treatment. Horses treated surgically were more likely to race after treatment than were horses treated without surgery.     

Technique for arthroscopic repair of third carpal bone slab fractures in horses

A technique involving internal fixation guided by arthroscopy was used to repair third carpal slab fractures in 23 horses. The technique allowed good reduction and compression of the fractures, with minimal surgical trauma. Ten of 17 horses with a 6-month or longer follow-up have returned to race successfully.     

Survey of arthroscopic surgery for carpal chip fractures in thoroughbred racehorses in Japan

Medical and racing records of 155 Thoroughbred racehorses that underwent arthroscopic surgery for carpal chip fractures were investigated. Articular damage for 98.4% of the fractures was classified as G1 or G2 using McIlwraith's criteria. The rate of return to racing after surgery was 82.6%. Evaluation of racing performance after surgery was attempted using a placing index (PI) based on race finish position. There was no significant difference in the PI distribution between horses that underwent surgery and other healthy horses.     

Surgical repair of radial carpal bone fractures in two racehorses

A 3-year-old Standardbred gelding (Case 1) and a 2-year-old Thoroughbred gelding (Case 2) were referred for surgical evaluation of a left radial carpal bone (RCB) fracture, sustained during training. Clinical findings at the time of initial examination included a palpable effusion within the left middle carpal joint in both horses and marked signs of pain and reduced range of motion on flexion of the affected carpus. In both horses, the RCB fracture was evident on the following radiographic views of the carpus: dorsolateral–palmaromedial oblique (30° off lateromedial) and flexed lateromedial. An additional loose wedge-shaped osteochondral fragment at the proximal articular surface of the RCB could be seen in Case 2. Both horses underwent surgical reduction and repair of the fracture between 1 and 2 days following the initial injury, which consisted of arthroscopic removal of any intra-articular osteochondral fragments, and arthroscopic assisted-interfragmentary compression via a standard dorsomedial and dorsolateral approach to the antebrachiocarpal joint (ACJ) and middle carpal joints (MCJ). The two horses returned to function as racehorses, 6 months (Case 1) and 16 months (Case 2) after surgery. The RCB is a relatively uncommon site for large carpal fractures in horses. The clinical presentation and findings from this report were similar to that of third carpal bone (C3) slab fractures, confirming that surgical repair is indicated in selected cases of RCB fractures.     

Metabolic response to racing and fiber properties of skeletal muscle in standardbred and thoroughbred horses

Muscle biopsies were obtained from 17 Standardbred trotters (S) and 22 Thoroughbred racehorses (T) after races which varied in length from 1200 to 2840 m. Biopsies were taken between 2 and 14 minutes from the conclusion of the race. Histochemical and biochemical analyses were performed on all muscle samples. Standardbred horses possessed fewer Type II fibers, especially Type IIB fibers, and demonstrated a higher oxidative and lower glycolytic capacity in muscle than Thoroughbred horses. Intramuscular glycogen and lac-tate concentrations were lower in Standardbred horses after racing (mean 420 and 82 mmol/kg d.w. respectively) com-pared to Thoroughbred horses (mean 545 and 148 mmol/kg d.w. respectively). Low levels of intramuscular adenosine triphosphate (ATP) (mean S 17, T 15 mmol/kg d.w.) and creatine phosphate (mean S 28, T 42 mmol/kg d.w.) were recorded in both breeds after racing. Differences in muscle enzyme activities and metabolic response to exercise between breeds were related to the different muscle fiber compositions of Standardbred and Thoroughbred horses. Within both breeds, a high percentage of Type IIB fibers was associated with a low oxidative and high glycolytic capacity in muscle and a greater lactate accumulation after racing. In Standardbred horses low intramuscular ATP concentrations post-race were associated with a high percentage of Type IIB fibers and high lactate levels. No relationship was found between placing or speed of racing and intramuscular lactate and ATP concentrations post-race. This may have been due to many other factors which affected the outcome of a race and also due to the fact that it was not known when during a race lactate accumulation and ATP depletion occurred. Since the properties of fiber types appeared to be very different, the metabolic response within individual fiber types may be more closely related to fatigue than the metabolic response measured in whole muscle.     

Outcome and racing performance after internal fixation of third and central tarsal bone slab fractures in horses. A review of 20 cases

Twenty horses with central and third tarsal bone slab fractures, were treated internal fixation. Eighteen of the 20 cases were Standardbred trotters, one was a Thoroughbred racehorse and one a Swedish Warmblood. The central tarsal bone (CT) was involved in 12 cases and the third tarsal bone (T3) in 8 cases. The fractures were treated by lag screw fixation with one (18 cases) or two (2 cases) 3.5 or 4.5 mm cortical screws. Horses were confined to stall rest for one month and then put on a gradually increasing exercise programme. Convalescence time was 3-8 months until the fracture had healed and training could be resumed. Fifteen of the horses regained athletic soundness. Thirteen of the horses (72%) raced after surgery (12 Standardbreds and 1 Thoroughbred). Nine (69%) of these 13 horses won races after surgery.     

Scanning electron microscopic examination of third metacarpal/third metatarsal bone failure surfaces in thoroughbred racehorses with condylar fracture

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.     

Surgical treatment of dorsal cortical fractures of the third metacarpal bone in thoroughbred racehorses: 53 cases (1985-1989).

Between January 1985 and May 1989, 53 Thoroughbred horses (mean age 3.2 years) were surgically treated for dorsal cortical fractures of the third metacarpal bone (MC III). All horses were treated with cortical drilling through the fracture line (osteostixis). Diagnosis of the fractures was confirmed by xeroradiography. Lifetime racing records were obtained for all horses. Forty-seven horses returned to racing after surgery (89%). The mean time between surgery and the first race was 6.8 months. Horses had a mean of 10.9 starts before surgery and 16.1 starts after surgery. The mean earnings per start before surgery was $6,459 and after surgery was $5,685. Of the 47 horses that raced after surgery, 70% raced at the same class or improved. Complications related to surgery were seen in 10 horses. Two horses had a second fracture of MC III at the same site, and were again treated by osteostixis, after which both horses returned to competition. Fractured drill bits were left in the MC III of 4 horses. One of these horses had catastrophic failure of MC III. Two horses developed subcutaneous infections and 2 horses had catastrophic failure of MC III in the surgically treated limb. Osteostixis appears to be an effective treatment for returning horses affected with dorsal cortical fractures to racing.     

Luxation and/or fracture of the first carpal bone in thoroughbred horses and its surgical resolution

A syndrome involving luxation and/or fracture of the first carpal bone is described. Affected horses have a grade 1-3 lameness, which responds to intra-articular anesthesia of the intercarpal joint. Medical treatment has not be successful in relieving lameness, and the treatment of choice is surgical removal of the first carpal bone.     

Subchondral lucency of the third carpal bone in Standardbred racehorses: 13 cases (1982-1988)

Thirteen Standardbreds had subchondral lucency of the third carpal bone (C3), described as single or multiple central areas of C3 bone loss in the radial fossa. Sclerosis of the radial fossa was also detected. The mean age of 9 stallions, 3 mares, and 1 gelding was 4.1 years (range, 3 to 7 years). All horses had an acute moderate to severe lameness referable to the middle carpal joint. A dorsoproximal dorsodistal (skyline) radiographic projection was most useful and identified mild (3 horses), moderate (6 horses), and severe (4 horses) subchondral lucency and sclerosis of the radial fossa. The margin of C3 was intact dorsal to the lucent areas in all horses. In 12 horses, arthroscopic surgical evaluation and curettage of the lesion were performed. Of the 9 horses monitored long enough to allow racing, 8 horses (89%) returned to racing, although only 6 (75%) raced at the same degree of competition. Subchondral lucency of C3 resulted from chronic damage to C3 with subsequent osteochondral collapse or acute C3 proximal surface osteochondral fracture.     

Lag screw fixation of dorsal cortical stress fractures of the third metacarpal bone in 116 racehorses

Reasons for performing study: The effectiveness and best method to manage dorsal cortical stress fractures is not clear. This study was performed to evaluate the success of lag screw fixation of such fractures in a population of Thoroughbred racehorses. Hypothesis: Lag screw fixation of dorsal cortical stress fractures is an effective surgical procedure allowing racehorses to return to their preoperative level of performance. Methods: The records of 116 racehorses (103 Thoroughbreds) admitted to Equine Medical Centre, California between 1986 and 2008 were assessed. Information obtained from medical records included subject details, limb(s) affected, fracture configuration, length of screw used in repair and presence of concurrent surgical procedures performed. Racing performance was evaluated relative to these factors using Fisher's exact test and nonparametric methods with a level of significance of P<0.05. Results: Of 92 Thoroughbred horses, 83% raced preoperatively and 83% raced post operatively, with 63% having ≥5 starts. There was no statistically significant association between age, gender, limb affected, fracture configuration or presence of concurrent surgery and likelihood of racing post operatively or of having 5 or more starts. The mean earnings per start and the performance index for the 3 races following surgery were lower compared to the 3 races prior to surgery; however, 29 and 45% of horses either improved or did not change their earnings per start and performance index, respectively. Conclusions and potential relevance: Data show that lag screw fixation is successful at restoring ability to race in horses suffering from dorsal cortical stress fractures.