Ruptured Deep Digital Flexor Tendon
(Forelimb or Hindlimb)
The deep digital flexor muscle has three heads of origin; the humeral head arising from the medial epicondyle of the humerus, the radial head arising from the centre of the medial radius and the ulnar head arising from the proximal ulna at the caudal aspect. The tendons of these heads fuse at the carpus (Colville and Bassert, 2009), passes through the carpal canal continuing down the palmar side of the limb to insert on the palmar aspect of the distal phalanx (Dyce et al., 2010). Distal to the carpus, the deep digital flexor tendon (DDFT) is joined by the accessory ligament (Colville and Bassert, 2009) arising from the palmar aspect of the carpal joint capsule (Dyce et al., 2010). The DDFT is composed of two oval-shaped lobes divided by a thin, fibrous, sagittal septum containing an artery. At the level of the palmar tuberosity of the middle phalanx, the DDFT has two layers; dorsally a hypoechogenic fibrocartilaginous pad and on the palmar side an echogenic fibrous segment. Distally, the tendon becomes lateromedially wider and thinner (Seignour et al., 2011). Rupture of the DDFT within the pastern region or the hoof capsule is most often seen after palmar digital neurectomy (Ross and Dyson, 2003). Palmar digital neurectomy involves severing the palmar digital nerves of the pastern to desensitise the caudal third to half of the hoof, in addition to corrective trimming and shoeing, to slow the advancement of navicular disease (Stashak and Hill, 2006). The navicular bone sits in between the distend end of the second phalanx (P2), and a small articular zone on the palmar border of the third phalanx (P3), the navicular bone’s palmar surface faces the DDFT (Dyce et al., 2010). Following neurectomy the horse will return to a normal gait, adhesions between the DDFT and navicular bone are worn and a weakened DDFT (Stashak and Hill, 2006), especially with pre-existing lesions (Ross and Dyson, 2003), may rupture. Rupture may result from advanced navicular disease even without neurectomy, or may trail chronic suppurative navicular bursitis (Stashak and Hill, 2006). Fracture fragments and subsequent change in weightbearing after a P2 fracture that produced numerous bone splinters (comminuted) can also lead to rupture of the DDFT (Elce and Goodrich, 2015).
Clinical Signs & Diagnosis
- Lameness may be progressive or have a sudden onset, and there is intense swelling of the pastern region (Ross and Dyson, 2003).
- During weightbearing the toe of the affected hoof will rotate dorsally (Hoegaerts et al., 2005) [Figure 1].
- Radiographical evidence of subluxation of the distal interphalangeal joint [Figure 2] is visible, the degree of subluxation is dependent on the integrity of the DDFT (Ross and Dyson, 2003).
Treatment & Prognosis
- Injuries to the DDFT have a poor prognosis for return to athletic function (Lavoie and Hinchcliff, 2008), rupture of the DDFT results in no return to athletic function (Elce and Goodrich, 2015).
- Development of peritendonous fibrosis supports the limb adequately for activities that are not athletic such as breeding, as long as the opposite limb can support the body in the meantime (Ross and Dyson, 2003).
Figure 2. Lateromedial radiograph of a horse 3 months post P2 fracture operation, exhibiting subluxation of the distal interphalangeal joint which is indicative of deep digital flexor tendon rupture (Elce and Goodrich, 2015).
References
BOLDIZAR, M. 2015, BoldiVetTV: Rupture of DDFT and SDFT after 8 month, right hind, Youtube, 19/06/2015, viewed 31/07/2017, http://www.youtube.com/watch?v=aXFOf_G1l9I.
COLVILLE, T. P. & BASSERT, M. J. 2009. Clinical Anatomy and Physiology Laboratory Manual for Veterinary Technicians Missouri, USA, Mosby Elsevier.
DYCE, K. M., SACK, W. O. & WENSING, C. J. G. 2010. Textbook of Veterinary Anatomy, Missouri, Saunders.
ELCE, Y. A. & GOODRICH, L. 2015. Deep digital flexor tendon rupture in two horses: A potential complication of comminuted second phalangeal fractures. Equine Veterinary Education, 27, 65-70.
HOEGAERTS, M., PILLE, F., DE CLERCQ, T., FULTON, I. C. & SAUNDERS, J. H. 2005. COMMINUTED FRACTURE OF THE DISTAL SESAMOID BONE AND DISTAL RUPTURE OF THE DEEP DIGITAL FLEXOR TENDON. Veterinary Radiology & Ultrasound, 46, 234-237.
LAVOIE, J.-P. & HINCHCLIFF, K. W. 2008. Blackwell's Five-Minute Veterinary Consult: Equine, USA, John Wiley & Sons.
ROSS, W. M. & DYSON, J. S. 2003. Diagnosis and Management of Lameness in the Horse, Missouri, Saunders.
SEIGNOUR, M., PASQUET, H., COUDRY, V. & DENOIX, J. M. 2011. Ultrasonographic diagnosis of injuries to the deep digital flexor tendon and associated structures in the equine foot (suprasesamoidean area). Equine Veterinary Education, 23, 369-376.
STASHAK, T. S. & HILL, C. 2006. Practical Guide to Lameness in Horses, Iowa, USA, Blackwell Publishing.
Figure 1. Distal limb of a horse showing the toe flipped upward due to subluxation of the distal interphalangeal joint caused by rupture of the deep digital flexor tendon. Thickening of the pastern region is visible as a result of peritendonous fibrosis (Ross and Dyson, 2003).
(Boldizar, 2015)