Racing prognosis of horses following surgically repaired olecranon fractures

Abstract

Olecranon fracture is a common orthopedic problem in juvenile horses. Prognosis for complete fracture healing when various methods of internal fixation are used is good; however, the impact of olecranon fracture stabilization on the likelihood that foals will start on a racecourse is unknown. Medical records of foals undergoing internal fixation for an olecranon fracture were reviewed. The dam’s foaling records were obtained and lifetime racing records were then retrieved for both the affected foals and 1 of their siblings. Twenty-two of 24 repaired fractures healed completely, subsequently, 16 of the foals started in at least 1 race. Statistical calculations suggest that when compared with their siblings, the occurrence of olecranon factures requiring internal fixation in juvenile racehorses will not significantly reduce the likelihood that they will race; however, the siblings had significantly more lifetime race starts and higher career earnings.

Introduction

Fracture of the olecranon is common in foals and weanlings presented for forelimb lameness (1). Olecranon fractures usually result from traumatic injuries and have a characteristic presentation that should readily be differentiated from a shoulder injury or a neurological deficit. Olecranon disruption prevents horses from extending the elbow, diminishing their ability to bear weight on the forelimb (2,3). The ulna acts like a lever arm, helping to maintain the leg in extension by placing proximad forces on the olecranon through the triceps brachii muscle (3). Foals with an olecranon fracture or triceps brachii muscle apparatus disruption present with a “dropped elbow” and a nonweightbearing lameness; however, radiographic findings are the most definitive and supportive evidence. Depending upon fracture configuration and the degree of lameness, several different management options are available.

Following internal fixation of juvenile olecranon fractures, most foals regain use of the triceps brachii muscle tension apparatus and walk with minimal evidence of pain or lameness. The most common methods of olecranon fracture internal fixation in foals include the narrow dynamic compression plate (nDCP), tension band wire (TBW), and the Association for Osteosynthesis/Association for the Study of Internal Fixation (AO/ASIF) hook plate (AAHP) (3–5). Surgical stabilization is based on the tension band method, which counteracts the distracting forces of the triceps brachii muscle, allowing adequate compression on the fracture while maintaining articular surface continuity of the elbow joint (2). In 2 previous studies, when an nDCP was used, olecranon fracture healing in foals was reported to be 75% and 78%, respectively (3,7). When the TBW technique was used, olecranon fracture healing in foals was reported to be 82%, with a 76% success rate in returning horses back to their intended use (4). When the AAHP was used, olecranon fracture healing in foals was reported to be 60% (5). Nonsurgical management is a viable option, if there is no displacement, the horse is able to bear weight, and a minimal degree of lameness is observed (2). Conservative management of displaced or articular olecranon fractures, or both, that warrant internal fixation has been reported to result in only a 33% fracture healing rate and a poor return to athletic soundness (8).

There are multiple publications reporting on the successful outcome of olecranon fracture repair after various methods of internal fixation have been used in horses of all ages. Previous authors have deemed the outcome as acceptable if the horses survived surgery and were sound at the time of follow-up (3–5,7). Racing prognosis for foals undergoing internal fixation of olecranon fractures has not been evaluated, nor have there been any previous studies in which outcome was compared with a control population. Sixty-nine percent of Thoroughbred (TB) and 66% of standardbred (SB) foals born annually in the United States start on a racecourse at least once (personal communication, the Jockey Club Information Systems, Lexington, Kentucky, and United States Trotting Association, Columbus, Ohio). We hypothesized that the occurrence of an olecranon fracture would not significantly reduce the likelihood of a foal starting to race when compared with its siblings, so the primary goal of this study was to establish the racing prognosis of foals that had undergone surgical repair of an olecranon fracture (principals), and to compare it with that of maternal siblings (controls). A subsidiary goal was to compare the lifetime race starts and career earnings of the 2 groups.

Materials and methods

Study subjects

Complete medical records of all foals admitted to Hagyard Equine Medical Institute between January 1, 1996, and December 31, 2001, with a diagnosis of an olecranon fracture were reviewed. Only TB and SB foals with primary olecranon fractures of the ulna that were repaired with open reduction and internal fixation were included in the study. Horses with fractures of the radius and secondary fracture of the ulna were excluded, because they represent a different clinical entity. Information obtained from the medical records included signalment, radiographic findings, fracture classification, stabilization method, and outcome.

Olecranon fractures were arranged according to the AO/ASIF classifications, which are based on their radiographic appearance. Type-1a fractures involved the proximal olecranon physis, and adjacent metaphysis; the apophysis was usually displaced to some degree (9). Type-1b fractures involved the proximal olecranon physis, extending through the metaphysis, and entering into the elbow joint (9). Type-2 fractures were articular fractures involving the olecranon mid body (9). Type-3 fractures included any simple nonarticular, nonphyseal fracture (9). Type-4 fractures were comminuted fractures involving the articular surface and olecranon body (9). Type-5 fractures were oblique fractures of the distal olecranon involving the elbow joint (9).

All fractured olecranons had been repaired under general anesthesia utilizing 1 of the 3 aforementioned methods of internal fixation devices, based on fracture classification and the surgeons’ preference. The duration of treatment was determined, beginning on the date of fracture repair and extending through the date of implant removal. Complications were determined, based on notations recorded in the medical record, radiographic findings, and communication with owners and trainers. Radiographs were evaluated immediately after surgery and every 21 to 28 d to determine the degree of fracture healing. In some foals, the ulna had been transfixed to the radius, which had necessitated more frequent serial radiographic monitoring for signs of ulnar dysplasia. The effects of radioulnar fixation and an objective measurement of ulnar dysplasia were determined by using the growth disparity equation reported by Clem et al (10).

Controls

The foaling history of each foal’s dam was reviewed in order to obtain registration details of the affected foal, along with details of 1 maternal sibling. When records of 2 siblings immediately preceding and following the principal were available, the matched control was randomly selected from the 2 available controls by a coin toss. Cases in which mares failed to produce another live foal of racing age in the study period (n = 1), no control was available for comparison.

Outcome

Surgical treatment was considered successful, if the fracture had healed completely and allowed the horse to maintain athletic soundness and start a race. Outcome was considered unsuccessful, if the horse had never started a race or had been euthanized. Follow-up information was obtained through reevaluation of foals on farms, telephone conversations with owners or trainers, and lifetime race records retrieved from the Jockey Club and the United States Trotting Association. Race records were also retrieved for all controls. Race records were obtained when foals were ≥ 2 y until December 31, 2003.

Statistical evaluation

The principal’s number of lifetime race starts and career earnings were compared with those of the control that was sequentially closest in birth order by using a Wilcoxon signed-rank test; the starting status and categorized earnings were binomially derived from this assessment. In this analysis, race starts were stratified as ≤ 8, or>8, and career earnings were stratified as ≤US$1000 or > US$1000. These cutpoints were chosen to insure a minimum of at least 5 observations/cell. Comparisons of discreet data among starting status and categorized earning groups were made by using univariate analyses of odds ratio (OR), 95% confidence intervals (CI), and P-values as determined by a chi-square test. Odds ratios greater than 2 with a P-value < 0.05 were considered significant (11). Means (± standard deviation [s]) were calculated.

Results

Twenty-four foals (TB, n = 20, SB, n = 4) had olecranon fractures reduced by internal fixation, including 15 colts and 9 fillies, ranging in age from 2 wk to 11 mo. The left olecranon was affected in 13 horses, the right in 11 horses.

Fracture types represented were 1a (n = 4), 1b (n = 1), 2 (n = 3), 4 (n = 10), and 5 (n = 6). The most commonly used method of repair was an nDCP (n = 22). Two TBWs were used in 1 foal, and an AAHP in another. All plates were secured by using either 4.5-mm cortical bone screws alone or a combination of 4.5-mm cortical and 6.5-mm cancellous bone screws. In 14 foals, the ulna was transfixed to the proximal part of the radial metaphysis.

Complications had been detected in 5 foals (21%). Three foals with radioulnar transfixation developed ulnar dysplasia. The growth disparity as a percentage of the radial epiphyseal width in these 3 foals was 8%, 22%, and 44%, respectively. The age at time of fracture repair and the duration of the implantation were inversely related to the amount of growth disparity. Foals with 8% and 22% growth disparity pursued a racing career, while the remaining foal became a broodmare. Moderate meta-carpophalangeal joint contraction, along with delayed bone union, prevented removal of the nDCP in 1 foal. One of the foals with a TBW acquired an incision infection, which resolved after prolonged antimicrobial therapy and local wound treatment.

Twenty-two of 24 (92%) repaired fractures healed completely and long-term follow-up was possible for 22 of the principals. Two colts (8%) were euthanized for reasons related to the fracture: 1 foal had implant failure in which the screws pulled out of the olecranon, and because of the multitude of fragments and immaturity of the bone, it was destroyed 12 d after surgery. The other colt had an AAHP that became unstable 2 d after surgery, resulting in apophysis displacement and disruption of the triceps brachii muscle tension apparatus. In 20 horses, the nDCPs were removed after complete fracture healing was radiographically and clinically determined. Overall, mean duration of implant fixation was 88 d, s = 24 d. Mean duration of time before implant removal in radioulnar transfixed foals was 85 d, s = 25 d. Mean duration of implant fixation was 93 d, s = 25 d in foals that did not have radioulnar transfixation. Sixteen of 22 (73%) principals maintained athletic soundness and subsequently started in ≥ 1 race, while 14 of 23 (61%) controls started in ≥1 race. Of the 6 principals that failed to race and for which long-term follow-up was available, 3 developed musculoskeletal injuries not associated with the fracture repair, 1 developed significant ulnar dysplasia, 1 acquired metacarpophalangeal joint contracture and delayed bone union, and 1 was euthanized because of gastrointestinal disease during training. Ten foals with radioulnar fixation were capable of pursuing a racing career.

The calculated odds ratios for starting status and categorized career earnings were 1.8 (95% CI [0.3, 11.4], P = 0.533) and 1.96 (95% CI [0.4, 8.9], P = 0.385), respectively. Lifetime race starts differed significantly between principals and controls (P < 0.001); overall, the controls had more lifetime starts (Figure 1). The principals represented in this study started in a mean of 7.3 races, s = 14.7, whereas the controls started in a mean of 11.6 races, s = 19.9. In both populations, there were individual horses that were capable of starting beyond the average number of starts in a healthy racehorse.

Figure 1.

The relative frequency of lifetime race starts in horses requiring olecranon fracture internal fixation and their matched maternal siblings. The principal (73%) and control (61%) starting status can be extrapolated by inversely correlating the relative frequency in the “0 starts” column.

Career earnings differed significantly between principals and controls (P < 0.001); overall, the controls had higher career earnings (Figure 2). The principals represented in this study earned a mean of US$28 322, s = $99 695, whereas the controls earned a mean of US$68 868, s = $230 656. Because data were nonparametrically distributed, Wilcoxon signed-rank test rather than Student’s t-test was used to calculate the P-values associated with these comparisons.

Figure 2.

The relative frequency of upper class limit career earnings in horses requiring olecranon fracture internal fixation and their matched maternal siblings.

Discussion

The success rate for fracture healing reported here in foals treated with olecranon fracture stabilization is higher than in other reports (3–6), which may be the result of early recognition and surgical intervention. All foals were resident at surrounding farms where strict management regimes are implemented.

Despite the large number of publications on olecranon fractures, no objective data is available on racing prognosis. Many studies have examined the efficacy of different treatments for managing olecranon fractures; however, no study has focused on racing prognosis, or compared long-term outcome following surgical treatment for juvenile olecranon fractures with a suitable group. The purpose of this study was not to compare specific internal fixation methods used and their effect on long-term prognosis, but to assess whether foals treated successfully for olecranon fracture would be as likely to race as their siblings. External influences and their effects on racing are multifactorial and difficult to control. Genetic traits, such as speed and racing, are external influences that can be minimized and somewhat controlled by comparing maternal siblings (12). Genetic comparison among horses is generally evaluated by purchasers to assess the value of unproven horses; therefore, we used it as an assessment of the horses’ athletic potential. Statistics published by the Jockey Club and the United States Trotting Association indicate that over the past 10 y, 69% of TB and 66% of SB foals born in a given year start at least once on a racecourse. Although TB and SB horses race in a different manner, performance expectations are no different. In this study, 61% of controls started successfully in at least 1 race, whereas 73% of all principals determined to have had complete fracture healing started in at least 1 race.

The nDCP can be used to repair any olecranon fracture configuration and continues to be the most commonly employed method of internal fixation in equine olecranon fracture repair. It can be easier and more efficient to repair fracture types 2 to 5 because of the orientation of the fracture and ease of placing the plate along the caudal aspect of the ulna. Fracture types 1a and 1b are more difficult to repair, because, usually, the apophysis has to be reduced and the plate contoured around the olecranon. The TBW technique is advantageous when small proximal apophyseal fragments may split if screws are inserted (4). This method of fracture repair can be successfully applied to juvenile horses, but limited application in adult horses has been reported. Case selection should be limited to simple elbow fractures in horses weighing less than 250 kg; surgical repair of type 4 olecranon fractures using tension band wires is not recommended (4).

Primary implant complications usually occur as a consequence of a disturbance within the implant system itself, resulting in implant instability, failure, and an undesirable outcome. It is important to record in the early postoperative period whether the foal has regained its ability to maintain weightbearing forces on the affected limb (5). Triceps brachii muscle tension apparatus disruption after surgery is usually a good indicator of primary implant complications. These catastrophic failures can be attributed to screws and plates loosening, plate bending, wires breaking, refracturing of the ulna, intra-articular screw placement, and implant infections. Factors associated with the primary implant failures include unsatisfactory recoveries from anesthesia, rambunctious stall activity, poor soft tissue coverage over the caudal aspect of the elbow, and hygienic considerations after surgery. Although not encountered in this retrospective study, it can be hypothesized that in foals that have primary implant complications and in which a second repair is attempted, the outcome may result in a poorer prognosis for athletic soundness and a greater chance for developing surgical complications. Common surgical complications include forelimb contracture, incision dehiscence and drainage, forelimb muscle atrophy, and ulnar dysplasia.

Ulnar dysplasia, humeroulnar subluxation, or both are the consequence of radius and ulna fixation. After transfixing the ulna to the proximal part of the radial metaphysis, continued longitudinal growth at the proximal radial physis produces a disparity in radial to ulnar growth, ultimately leading to subluxation (10). The magnitude of ulnar dysplasia is inversely related to the patient’s age at the time of fixation. The proximal physis of the radius contributes approximately 40% of the total elongation of the radius, with 53% of its growth occurring by 3 mo of age and subsequently declining over time until the physis closes at 2 y of age (10). When this technique is applied to skeletally immature individuals, fixation appliances should be removed as early as possible (10). It is important to note that when there has been radioulnar fixation by an orthopedic implant, removal of the implant cannot be relied on to effect resolution of any acquired subluxation, especially when synostosis has formed (10). Disparity between the radius and ulna should be quantified radiographically. Radioulnar fixation is not advocated; however, foals do have the potential to develop into athletically sound racehorses, if the ulnar dysplasia is not severe.

Starting status and categorized earnings were binomially derived while assessing lifetime race starts and career earnings, allowing chi-square testing and odds ratio determination to be performed. The Wilcoxon signed-rank procedure allowed for overall comparison of lifetime race starts and career earnings. Odds ratio determinations between principals and controls helped the authors to conclude whether principals were more or less likely to have ≤ 8 starts and earn ≤ US$1000. The odds ratios concerning starting status and categorized earnings were not relevant, nor were they statistically significant, as none were greater than 2 or had a P-value less than 0.05. This was interpreted to mean that subjects with olecranon fractures are not more likely than their age matched counterparts to start ≤ 8 races or earn ≤ US$1000. Although controls had more lifetime race starts and higher career earnings, this could be explained by an owners’ or trainers’ reluctance to aggressively pursue a racing career in a horse with a previous musculoskeletal injury. On the contrary, owners and trainers should not be averse to pursue race training in horses that have sustained an olecranon fracture as a juvenile. Juvenile olecranon fractures can be very responsive to open reduction and internal fixation, allowing horses to enter race training within 1 y after surgery. An olecranon fracture itself is not going to prevent these juvenile race-horses from developing into a sound horse, but the ensuing degenerative osteoarthritis associated with articular fractures or ulnar dysplasia may be a significant factor.

The longevity of a racing career and potential earnings are difficult to interpret objectively. Although a favorable percentage of TB or SB horses have the athletic potential to race, too many external factors can alter the athletic outcome prior to or during training. Musculoskeletal injuries that result in shortened racing careers and lowered career earnings are commonly encountered in racing horses. In addition, gender may play a major role. Valuable and productive fillies and colts may be retired for breeding purposes at an earlier age and before catastrophic injury occurs.

Despite the number of foals included, this retrospective study design precludes any conclusions being drawn regarding the relative efficacy of olecranon fracture internal fixation. However, the aim of the study was not to compare the relative success associated with internal fixation, but to look at the long-term prognosis of foals and whether the occurrence of olecranon fractures requiring stabilization as a juvenile would affect the likelihood of starting on a racecourse. Studies adopting a case-controlled design would be required to be able to draw any conclusions on the efficacy of specific treatment regimens. Attempts to examine and draw conclusions from the effects of fracture configuration and gender on survival and long-term prognosis were not evaluated, because the low number of foals in each category would have had insufficient power to detect significant differences.

The results of this study should allow equine surgeons to provide a favorable racing prognosis to owners, farm managers, and trainers who intend to pursue juvenile olecranon fracture stabilization; therefore, owners should not hesitate to pursue surgical intervention. Overall, more than 2/3 of the foals that were operated on started in at least 1 race, suggesting that horses of racing breeds undergoing olecranon fracture stabilization as juveniles have an equivalent prognosis for maintaining athletic soundness and the ability to race in comparison with their siblings. CVJ