Retrospective performance-indexed analysis of Thoroughbred racehorses undergoing surgical management of proximal sesamoid bone fractures.

Abstract

BACKGROUND: Proximal sesamoid bone fractures (PSBFs) are a leading cause of economic losses. Post-operative racing prognosis is multi-factorial; however, recent studies are lacking. OBJECTIVES: To provide an update on racing outcomes for horses undergoing surgical management of PSBFs, analyse variables affecting performance and compare post-operative racing performance with pre-operative data and case-matched controls. STUDY DESIGN: Retrospective case series. METHODS: Thoroughbred racehorses that underwent PSBF repair (2008-2022) were included. Data retrieved included fracture type, limb, axiality, treatment, age, sex, suspensory ligament branch (SLB) injury, surgical date, date of racing return, and pre- and post-operative starts and places (1-3), which generated a performance index (PI) and PI per start (PI/S). Chi-squared assessed the effect of categorical variables (sex, limb, fracture type, axiality, SLB injury and pre-surgical racing experience) on racing outcome. Wilcoxon signed-rank test compared pre- and post-operative performance indices. Kruskal-Wallis and Mann-Whitney U tests assessed significance between categorical variables and numerical variables (age, recovery, number of starts (Nstarts), and performance indices). Binary logistical regression performed multivariable analysis. Change in PI and PI/S, and Nstarts were compared between matched controls and cases using Mann-Whitney U tests. RESULTS: Overall, 86/168; 51.2% (confidence interval (CI): 43.5%-58.9%) horses raced post-operatively. Of the 113 horses that raced pre-operatively, 57 raced post-operatively (50.4%, CI: 41.8%-59.3%). Forelimb fracture cases (42.3%) were less likely to race post-operatively compared with hindlimb cases (65.6%, p = 0.003). In univariable analysis, horses that underwent surgical management of mid-body fractures (15.8%) were less likely to race compared with other fracture types (apical 56.1%, abaxial 60.5% and basal 25%, p = 0.001). Horses undergoing screw-fixation were less likely to race compared with fragment-removal (17.4% vs. 56.6%, p = 0.001). Axiality, pre-operative racing and SLB injury did not affect return-to-racing. No significance was observed for post-operative Nstarts, change in PI, change in PI/S or the return-to-racing proportion between cases and controls. MAIN LIMITATION: The retrospective nature and drop-out rate limited post-operative analysis. CONCLUSION: Surgical management of apical and abaxial PSBFs via fragment removal is associated with improved post-operative outcomes compared with PSBFs necessitating internal fixation. Limb is a significant determining factor for return to racing. Post-operative racers have good longevity, although reduced PI/S compared with pre-operative performance.