EQUINE VETERINARY EDUCATION / AE / JANUARY 2017


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developed a reinjury (22%) and the diagnosis was confirmed by the local trainer’s veterinarian; both were lateral lesions. A local thickening similar to what was noted at the time of the diagnosis was present in 4 horses (44%), a reduced local thickening was present in 2 horses (22%) and no abnormality was noted at physical examination in 3 horses (33%).


Performance outcome The performance outcome was available for all horses. The mean time between injury and first start ± s.d. was 302 ± 142 days (range: 140–677). Fourteen horses out of 15 returned to racing (93%). The overall performance outcome is presented in the Table 1. For all horses, the number of starts, number of shows,


number of wins and earnings were not significantly different before and after injury (P = 0.77, 0.63, 0.92, 0.48, respectively). Performance outcome for horses with a lateral lesion and


horses with a medial lesion are presented in Table 2. In horses with a lateral lesion, the number of starts, number of shows, number of wins and earnings were not significantly different before and after injury (P = 0.4, 0.37, 0.71, 0.89, respectively). Number of starts, number of shows, number of wins and earnings were not significantly different before and after injury for horses with a medial lesion (P = 0.17, 0.58, 0.37, 0.25, respectively). Number of starts, number of shows, number of wins and earnings were not significantly different after injury for horses with a lateral lesion compared with a medial lesion (P = 0.94, 0.82, 0.87, 0.6, respectively).


Discussion


Fig 1: Ultrasonographic images of tendonitis of the lateral branch of SDFT. a) The arrow shows an enlargement and heterogeneity of the lateral branch. b) The arrow shows an enlargement and a diffuse hypoechoic region of the lateral branch. SDFT: superficial digital flexor tendon, DDFT: deep digital flexor tendon, SDSL: straight distal sesamoidean ligament oblique, ODSL: oblique distal sesamoidean ligament, P1: proximal phalanx.


were affected bilaterally. The lateral branch was involved in 12 horses (80%) and the medial branch in 3 horses (20%). None of the horses were affected biaxially. A local thickening was present in 100% of cases at the time


of the injury. The thickening was positive on pressure in 67% of cases (10/15). All horses were lame. Mean lameness grade ± s.d. was 1.3 ± 0.5 (range: 1–2). The distal limb flexion test was positive in 67% (10/15) and negative in 23% (5/15) of cases. Ultrasonographic examination showed an enlargement of the affected branch in 87% (13/15), a diffuse hypoechoic region in 73% (11/15) and a heterogenic region in 27% of cases (4/15) (Fig 1).


Treatment, rehabilitation and professional trainer’s evaluation All horses were treated conservatively. The typical suggested rehabilitation protocol was 3 weeks of stall rest with limited hand walking followed by 4 months of small paddock turn out. This protocol was adapted based on severity of the lesion. The trainers were asked to pay particular attention to the leg (swelling and pain) and specifically to the pastern region during the rehabilitation phase. The professional trainer’s evaluation was only available for 9 horses and follow-up was lost for 6 horses. Two horses


In a previous study, the forelimbs and lateral SDFT branches were more commonly injured in Thoroughbred racehorses (Gibson et al. 1997). The same observation could be made in our study regarding an exclusive front limb and the lateral branch distribution in Standardbred racehorses. Although no predisposing factors were identified in our case series, conformation was not specifically recorded in our medical files. Undesirable conformation such as long pastern, under-run heel or axially displaced heel should be managed as they may predispose to a SDFT branch injury (Gibson et al. 1997; Reef and Genovese 2011). The left forelimb was more commonly involved in our case series whereas the horses were trained and raced almost equally on both reins. The SDFT supports the metacarpophalangeal and proximal interphalangeal joints during the stance phase and actively and passively flex these joints and the carpus during the swing phase (Denoix 1994). Injuries to the branches of SDFT are less common than injuries to the mid-metacarpal region (Reef and Genovese 2011). In an epidemiological study of musculoskeletal injuries in 356 Standardbred racehorses in training, 76 lesions of SDFT were found (Bertuglia et al. 2014). Sixty-three were in the metacarpal region, 4 in the metatarsal region and 9 at the level of the pastern (Bertuglia et al. 2014). The cross-sectional area of the SDFT is smallest in the mid-metacarpal region and this has been suggested as a reason for susceptibility to injury (Riemersma and Schamhardt 1985). It has also been suggested that blood supply to the mid-metacarpal region is deficient during exercise (Stromberg 1971; Kraus-Hansen et al. 1992). However, although the cross-sectional area of the SDFT is smallest in the mid- metacarpal region, it is not significantly weaker than the proximal end and manica flexoria region of the tendon (Birch et al. 2002).


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