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different probes and the capability to adjust the number of shocks (pulses), depth, and energy settings. Because the settings and machines used in the studies in this paper vary, the information for settings used in each article are provided so that clinicians can compare these settings to their own machine. Table 1 provides a list of some commonly used extracorporeal and radial shock wave machines in equine veterinary medicine.


Review of ESWT and specific soft tissue injuries


Research surrounding specific soft tissue injuries and response to ESWT in horses is limited. The following section provides a review of ESWT in soft tissue injuries based on current literature.


Suspensory ligament desmitis Suspensory ligament injuries can occur at various points along the length of the ligament; however, racehorses have more injuries of the mid body and/or branches, while sport horses have more injuries of the proximal suspensory ligament and/ or branches (Hinchcliff et al. 2004). Horses used for dressage, having a straight hock conformation, or exhibiting hyperextension of the metatarsophalangeal joint, have been found to have a higher incidence of hindlimb PSD (Dyson 2007). Lameness due to hindlimb PSD tends to be more severe and more persistent than lameness caused by forelimb PSD, which is likely related to a compartment syndrome developing in the hindlimbs and subsequent compression on the plantar metatarsal nerves (Dyson and Ross 2003). This may help explain why the prognosis for hindlimb PSD remains worse than in the forelimb. Lameness in horses with hindlimb PSD improved faster and


a greater percentage of horses improved when treated with RPWT, compared to a similar study where RPWT was not used (Crowe et al. 2004). In this study, 41% of horses with chronic hindlimb PSD returned to their previous level of work 6 months after treatment with RPWT. In a separate study, only 12.5% of horses treated with rest and controlled exercise returned to full work for a year or more without recurrent lameness (Dyson 1994). In the RPWT group, all horses had ultrasonographic evidence of PSD and 24% of horses had radiographic abnormalities of the proximoplantar aspect of the third metatarsal bone. There was no reported correlation between these findings and outcome (Crowe et al. 2004). In the study evaluating rest alone, 97% of horses had ultrasonographic evidence of PSD and 54% of horses had radiographic abnormalities (Dyson 1994). Because there was no correlation between outcome of RPWT and radiographic findings, it is unlikely that this played a role in the differences between the two studies. It should also be noted that the Crowe et al. (2004) study used RPWs, which, as stated previously, are not focused shock waves, are superficial in penetration (the machine used in this study had a 15 mm penetration depth), and so, although the horses improved, it is unclear if they would have had greater improvement with focused ESWT treatment. Crowe et al. (2004) also reported that 53% of horses with


chronic forelimb lameness (lame for 3 months or more) associated with suspensory ligament lesions were sound and in full work 6 months after treatment with RPWT. Lischer et al. (2007) reported that 61.8% of horses treated with ESWT for forelimb PSD returned to full work 6 months after diagnosis,


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and 55.9% were still in full work one year after diagnosis. However, this same study showed that only 40.9% of horses treated with ESWT for hindlimb PSD returned to full work 6 months after diagnosis, and that only 18.2% of horses were still in full work one year after diagnosis. These results may indicate that ESWT and RPWT can return horses with forelimb PSD to work faster than rest alone; however, the overall prognosis for hindlimb PSD remains poorer than the prognosis for forelimb PSD. In four horses with collagenase-induced forelimb


suspensory ligament desmitis, ESWT resulted in faster filling of the defects and improved fibre alignment when examined ultrasonographically, compared to untreated limbs (McClure et al. 2004). This study did not have a blinded ultrasonographer, which could have altered the interpretation of the ultrasonographic findings. Caminoto et al. (2005) used a hindlimb collagenase-induced PSD model and showed increased production of TGF-b1, greater


decrease in proportion of the affected ligament, and faster filling of the defects in those limbs treated with ESWT, compared to untreated limbs. It is possible that collagenase- induced lesions do not respond the same as naturally occurring lesions, so these studies may not provide an accurate representation of lesions seen in clinical practice. Each of these studies used similar, yet slightly different ESWT energy settings, which could cause differing results, and suggests that specific parameters for ESWT studies need to be established.


Superficial digital flexor tendonitis Superficial digital flexor tendon lesions can be located within the central portion of the tendon, anywhere along the length of the metacarpal/metatarsal region and, less commonly in the region of the digital tendon sheath (Hinchcliff et al. 2004). Kersh et al. (2006) showed increased capillary formation in


collagenase-induced SDFT tendonitis treated with ESWT. Histologically, the treated limbs had increased numbers of capillaries, but there were no ultrasonographic differences between treated and untreated limbs. Bathe (2006) anecdotally reported faster ultrasonographic resolution of naturally occurring lesions and more rapid development of a longitudinal fibre pattern when ESWT was used in the treatment of mild or chronic SDFT tendonitis. Anecdotal evidence is not critically reviewed, and has no control groups, so should be interpreted cautiously.


Accessory ligament of the deep digital flexor tendon Damage to the accessory ligament of the deep digital flexor tendon (ALDDFT/inferior check ligament) is often related to SDFT injuries, but can occur as an isolated injury (Hinchcliff et al. 2004). Using an ALDDFT collagenase-induced model, no significant ultrasonographic or ligament microstructure changes were seen in ESWT treated limbs compared to controls (Waguespack et al. 2011). Based on the limited studies surrounding treatment of ALDDFT lesions with ESWT, it is unknown if this is an appropriate treatment.


Back pain Based on anecdotal evidence, McClure and Weinberger (2003) found up to 100% improvement in pain and rider satisfaction in horses with mild pain along the dorsal spinous processes (DSPs), but only 65% improvement in severely painful/affected horses. Bathe (2006) reported analgesic


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