Comparison of treatment outcomes for superficial digital flexor tendonitis in National Hunt racehorses

S Witte,C Dedman,F Harriss,G Kelly,Y.-M Chang,T.H Witte

doi:10.1016/j.tvjl.2016.08.003

Abstract

Superficial digital flexor (SDF) tendonitis is a common injury in Thoroughbred racehorses. Injuries require prolonged rehabilitation, with unpredictable outcomes and a high incidence of re-injury. This observational case–control study aimed to compare race outcomes after commonly advocated treatments for tendon healing. Clinical and racing records were evaluated for 127 National Hunt racehorses treated between 2007 and 2011 for an SDF tendon injury. Two age- and sex-matched control horses were selected for each case horse to analyse the effect on post-injury racing outcomes of pre-injury data, lesion severity and treatment group [controlled exercise alone, bar firing, intralesional platelet-rich plasma (PRP), tendon splitting, tendon splitting combined with bar firing]. Control horses raced more often than case horses, with higher maximum racing post rating (RPRmax) and longer racing distances. Pre-injury racing performance was not associated with treatment group. Rate of return to racing was not associated with lesion severity or treatment group. Number of races, total distance raced post-injury and RPRmax were not associated with lesion severity or treatment group. Controlled exercise alone offered similar post-injury racing outcomes in National Hunt racehorses with SDF tendonitis to the other treatment options examined. Bar firing, either alone or in conjunction with tendon splitting, provided no additional benefit in rate of return to racing and race performance.

Highlights

Superficial digital flexor (SDF) tendonitis is the most common cause of lameness in National Hunt racehorses, with prevalences as high as 24% (Lam et al, 2007; Avella et al., 2009; Dyson et al, 2011), or 1.71 per 100 horse months in training (Ely et al, 2009)
Immediate treatment of SDF tendonitis targets a reduction in inflammation (Ross et al, 2011; Avella and Smith, 2012), and thereafter various interventions are advocated to improve tendon healing
We hypothesised that lesion severity would be correlated with racing performance post-injury; that horses treated with PRP would more frequently return to racing, and at a higher standard than horses treated by bar firing, controlled exercise, tendon splitting or bar firing combined with tendon splitting; and that bar firing alone or in conjunction with tendon splitting would provide no additional benefit for racing performance post-injury

Summary

Introduction

Superficial digital flexor (SDF) tendonitis is the most common cause of lameness in National Hunt racehorses, with prevalences as high as 24% (Lam et al, 2007; Avella et al., 2009; Dyson et al, 2011), or 1.71 per 100 horse months in training (Ely et al, 2009). Tendon splitting to release the pressure of haemorrhage and promote vascularisation in the injured area has yielded mixed results (Stromberg.B et al, 1974; Henninger et al, 1990; Ross et al, 2011). Desmotomy of the accessory ligament of the superficial digital flexor tendon produced favourable rates of return to racing and number of races completed but resulted in increased suspensory ligament strain experimentally and higher incidence of suspensory ligament desmitis clinically (Bramlage, 1986; Bramlage, 2012). Isolated exogenous growth factors such as insulin-like growth factor 1 and transforming growth factor-β can be administered intra-lesionally (Dowling et al, 2000; Witte et al, 2011), more recently mixed endogenous cytokines have been delivered

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Conclusion