Complete SDFT Rupture in Horses: Long-Term Outcomes Show Favorable Prognosis with Prolonged Rehabilitation

Long-Term Prognosis of Complete Rupture of the Superficial Digital Flexor Tendon in 25 Horses – A Retrospective Study

T. Stäubli, F. Theiss, A. Bischofberger

Background

Complete rupture of the superficial digital flexor tendon (SDFT) in horses is uncommon and most often associated with percutaneous trauma, although overstrain-induced rupture has been reported. Published data on prognosis and long-term outcomes after complete SDFT rupture are limited and inconsistent, ranging from euthanasia to successful return to use. The objective of this study was to describe clinical and ultrasonographic findings as well as short- and long-term outcomes in horses with overstrain-induced complete rupture of the SDFT, with the aim of providing a more accurate long-term prognosis.

Methods

Medical records of horses referred to the Equine Hospital, Vetsuisse Faculty, University of Zurich, between 1993 and 2017 were retrospectively reviewed. Horses with unilateral or bilateral overstrain-induced complete rupture of the SDFT were included, while cases with lacerations or partial ruptures were excluded. Diagnosis was based on characteristic ultrasonographic findings. Long-term follow-up was obtained via a structured telephone questionnaire conducted with owners of 25 horses at a mean of 5.9 years after injury. Outcomes assessed included survival, soundness, return to intended use, rehabilitation duration, recurrence of SDF tendonitis, complications, and rupture-specific mortality.

Results

Forty-eight horses met the inclusion criteria, most of which were older Warmblood geldings with forelimb involvement. Of these, 25 horses were available for long-term follow-up. The rupture-associated long-term mortality rate was 12.0%. Recurrent SDF tendonitis did not occur in 76.0% of horses, while 24.0% experienced at least one recurrence, sometimes years after the initial injury. Rehabilitation time was prolonged, lasting approximately one year or longer in most cases. Among horses that completed rehabilitation, 81.0% returned to light ridden exercise and 14.0% achieved pasture soundness. Only a minority returned fully to their intended pre-injury use.

Limitations

This study was retrospective and relied on historical medical records, some of which were incomplete. Long-term outcomes were based on owner-reported information obtained by telephone, introducing potential recall and information bias. Objective follow-up examinations, including ultrasonography and veterinary lameness assessments, were largely unavailable. Nine horses were lost to follow-up, which may have introduced selection bias.

Conclusions

Horses with overstrain-induced complete rupture of the SDFT can have a favorable long-term prognosis when treated, with most achieving soundness for light ridden exercise or pasture use. Rehabilitation is prolonged, typically lasting at least one year, and recurrence of SDF tendonitis occurs in approximately one quarter of cases, even several years after injury. These findings support treatment rather than immediate euthanasia and highlight the importance of long-term monitoring for recurrence.

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