Page 403 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

378 CHAPTER 1

VetBooks.ir Management Aetiology/pathophysiology
Calcaneal tendon disease is probably due to repeated
The horse should be box rested for 2–3 months and
work gradually resumed over a further 2–3 months.
Surgical repair is unnecessary and conservative strain or to a single event causing hyperflexion of
the hock while the stifle is extended, although this
management nearly always provides full functional remains unclear. Spontaneous rupture has not been
recovery. described, but wounds to the caudal aspect of the crus
can cause partial to complete laceration of the vari-
Prognosis ous components of the common calcaneal tendon.
The prognosis is good in most cases. Chronic cases
may take longer to heal because of scarring and Clinical presentation
functional lengthening of the fibularis tertius ten- Tendonitis of the deep tarsal tendons is very rare.
don, but gradual fibrosis usually provides eventual It is characterised by moderate hindlimb lameness,
recovery. with or without focal enlargement of the distal part
of the common calcaneal tendon, and distension of
INJURIES TO THE COMMON the calcaneal and gastrocnemius bursae. The gas-
CALCANEAL (‘ACHILLES’) TENDON trocnemius tendons are most commonly affected,
usually in the distal part of the tendon. There may
Definition/overview be associated partial avulsion. Focal swelling may
The common calcaneal (‘Achilles’) tendon is a be visible and there is usually associated calcaneal
complex structure that comprises the two tendons bursa distension. This produces a diffuse enlarge-
of insertion of the gastrocnemius muscles on the ment of the area proximal to the point of the hock
tuber calcis of the calcaneus, the SDFT and the (see Fig. 1.743). Lameness is variable and a specific
deep tarsal tendons, two ligamentous branches that gait abnormality, characterised by lateral rotation of
arise from the fascial reinforcement of the tendon the tuber calcis during the stance phase of the stride,
and receive fibres from the soleus, biceps femoris, shortened caudal phase and reduced foot flight arc,
gracilis, semitendinosus and semimembranosus has been described. Lesions in the tendon of origin
muscles. They insert on the tuber calcis, dorsal to of the gastrocnemius muscles do not give rise to spe-
the gastrocnemius tendons. Although initially deep cific signs and the diagnosis can be a real challenge,
to the gastrocnemius muscles, the SDFT, whose as the muscular heads lie deep in the distal caudal
muscular head is largely atrophied in the hindlimb, thigh.
twists around the medial aspect of the gastroc- Partial laceration usually involves an obvious
nemius tendons to pass superficial to them in the wound. Lameness is generally severe, but close
distal crus. Strain injuries are rare but have been inspection and ultrasonography are often neces-
described in the gastrocnemius and in the deep tar- sary to confirm the partial rupture. Laceration of
sal tendons. The former may be injured at its origin the SDFT disrupts the stay apparatus and causes
on the femur, but the tendons of insertion are most the hock to partially collapse during weight bearing.
commonly affected near the calcaneus. Rupture is Lameness is therefore severe and characterised by a
always traumatic and usually associated with a sharp partial flexion of the hock during the stance phase.
or blunt wound to the caudal aspect of the crus. This Complete laceration of the common calcaneal ten-
structure is part of the reciprocal apparatus and is don is associated with a total inability to bear weight
essential for the animal to bear weight on the limb. on the limb.
It locks the hock into extension when the stifle is
extended, either actively during locomotion or pas- Differential diagnosis
sively through locking of the patella on the medial For tendonitis of the deep tarsal or gastrocnemius
femoral trochlear ridge. tendons: bursitis of the calcaneal and/or gastrocne-
A common condition in man, it is relatively rare mius bursae (‘deep capped hock’); acquired subcuta-
in horses. neous bursa (‘capped hock’).