Ruptured Peroneus Tertius Tendon
The peroneus tertius is a muscular band of tissue which is situated between the tibialis cranialis muscle and the long digital extensor in the hindlimb (Stashak, 2002). It originates from the lower end of the femur with the long extensor and is mostly recessed into the deep surface of the long extensor. The peroneus tertius bifurcates at the hock [Figure 1.] with the dorsal branch inserting on the proximal area of the third tarsal and third metatarsal bones and the lateral branch inserting on the fourth tarsal bone and calcaneus (Dyce et al.,2010). It is very strong. It is part of the reciprocal apparatus which links the action of the hock and stifle joints and works to flex the hock as the stifle joint is flexed (Dyce et al., 2010; Stashak, 2002). The peroneus tertius with the superficial digital flexor forms the cranial part of the reciprocal apparatus (Koenig et al., 2005; Pasquini et al., 2005; Reeves & Trotter, 1991). The peroneus tertius can rupture at any place along its course. A rupture can lead to an avulsion fracture at the extensor fossa (its origin) (Blikslager & Bristol, 1994; Stashak, 2002).
The condition is caused by trauma, overextension of the hock or exertion of a fast start or if a limb becomes caught and the horse struggles to free itself, during barrel racing or after being placed in a full cast (Pasquini et al., 2005; Stashak, 2002). Prognosis is guarded to good, healing will occur in most cases if stable rested with healing. If no signs of healing evident after four weeks prognosis is unfavourable and if no signs of healing after four months, prognosis is poor (Pasquini et al., 2005; Stashak, 2002).
Figure 2. Horse with ruptured peroneus tertius, displaying the characteristic ability to straighten the hock without extension of the stifle (Dyce et al., 2010).
References
Blikslager, A. T. and Bristol, D. G. 1994, ‘Avulsion of the origin of the peroneus tertius tendon in a foal’, Journal of the American Veterinary Medical Association, vol. 204, no. 9, pp. 1483-1485.
Dyce, K. M., Sack, W. O. and Wensing, C. J. G. 2010, Textbook of Veterinary Anatomy, 4th ed., Missouri, Saunders Elsevier.
Koenig, J., Cruz, A., Genovese, R., Fretz, P. and Trostle, S. 2005, 'Rupture of the peroneus tertius tendon in 27 horses', The Canadian Veterinary Journal, vol. 46, no. 6, pp. 503-506.
Pasquini, C., Jann, H., Pasquini, S. & Bahr, R. 2005, Guide to Equine Clinics Lameness, 2nd ed., Texas, Sudz Publishing.
Reeves, M. J. and Trotter, G. W. 1991, 'Reciprocal apparatus dysfunction as a cause of severe hind limb lameness in a horse', Journal of the American Veterinary Medical Association, vol. 199, no. 8, pp. 1047-1048.
Stashak, T. S. 2002, Adam’s Lameness in Horses, 5th ed., Maryland, Lippincott Williams & Wilkins.
Figure 1. The flexors of the hock in the horse. 1 on the illustration depicts peroneus tertius and its bifurcation into the dorsal and lateral branches (Dyce et al., 2010).
- Horse presents with abnormal gait with reduced flexion of the hock when moving and the distal limb hangs limp (Pasquini , 2005).
- Rupture of the peroneus tertius is evident as the stifle joint flexes as the limb moves forward and the hock joint is protracted with minimal flexion. The limb distal to the hock hangs limp as it is protracted. When the hoof is placed onto the ground the horse is able to bear weight and shows minimal signs of pain. During the walk and when the hindlimb is lifted and the hock extended, dimpling in the Achilles tendon is evident (Stashak, 2002).
- The hock can be extended without extending the stifle [Figure 2.] (Koenig 2005; Reeves & Trotter, 1991; Stashak, 2002).
- Bone spavin can also result from the condition (Pasquini , 2005).
- If the origin of the peroneus tertius detaches from the femur, femoropatella effusion occurs (Stashak, 2002).
- A ruptured peroneus tertius can be diagnosed by lifting the limb to flex the hock and then manually extending the hock as an intact peroneus tertius would not allow for full extension. Dimpling of the Achillies tendon should also be noted. An ultrasound can also be used to diagnose the condition looking for anechoic lesions and disruption of parallel fibres (Koenig 2005; Pasquini , 2005).
Clinical Signs & Diagnosis
Treatment & Prognosis
- Treatment consists of stable confinement for four to nine months (minimum of two months) followed by hand walking for 2 months (Pasquini , 2005).
- If conditioned well, horses are usually able to return to full work (Stashak, 2002).
- Surgery is not recommended or conducted as sutures will not hold the muscle together (Pasquini , 2005; Stashak, 2002).
(Herbert, 2011)