Page 731 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 697

Acute Tenosynovitis of Extensor Tendons
The long digital extensor tendon (LoDET) lies on the
VetBooks.ir cranial aspect of the crus and courses over the dorsum
of the tarsus just lateral to the MTR of the talus. A prox-
imal, middle, and distal extensor retinaculum cover the
LoDET at the level of the tarsus. The tendon courses
over the tarsus within a synovial sheath from approxi-
mately the level of the LM and continues coverage
through the distal retinaculum almost to the junction
with the lateral digital extensor tendon (LDET). At this
level, the conjoined tendons of the LoDET and LDET
muscles continue distally similarly to the common digi-
tal tendon of the front limb. The LDET of the hindlimb
courses distally across the lateral surface of the tarsus.
Direct trauma is the most likely cause of tenosynovi-
tis of the extensor tendons of the tarsus. Blunt trauma to
the dorsal and lateral surface of the tarsus can create
acute tenosynovitis of extensor sheaths, particularly the
LDET. The LDET sometimes develops idiopathic or
acute tenosynovitis. The swelling within the synovial
sheath may protrude proximally and distally to the reti-
naculum of the lateral digital extensor. Lameness when
it occurs is sudden in onset and moderate in severity.
Mild distension of the sheath may occur initially. These Figure 5.100. Rupture of the peroneus tertius disrupts the
effusions often persist in spite of appropriate treatment. reciprocal apparatus allowing extension of the tarsus and fetlock
The LoDET is rarely affected. The distal aspect of the PT with the stifle flexed. Source: Courtesy of Dr. Gary Baxter.
tendon can be injured as well. Diagnostic US should be
utilized to assess the tendon for damage. Treatment is Careful monitoring of the healing process with US is
determined based on the specific structure(s) involved. If necessary to prevent reinjury.
the tendon appears to be normal, then the treatment Complete rest is the best treatment. The horse should
may be directed at the synovial sheath. be placed in a stall and kept quiet for at least 4–6 weeks,
and then limited exercise should be given for the next
Rupture/Tendonitis of the Peroneus Tertius 2 months. Most cases heal and show normal limb action,
and if properly conditioned, most horses can return to
(Fibularis Tertius) normal work. After rupture of the PT tendon, 71% of
The PT muscle is tendinous over its entire length. It horses returned to their previous level of exercise with a
arises from the extensor fossa of the lateral femoral con- mean rehabilitation period of 41.5 weeks. If a horse was
dyle and inserts with two distinct tendons to the tarsus. a performance horse at the time of injury, it was 11 times
Rupture of the PT is uncommon with trauma being the less likely to return to its intended use. Furthermore, if an
most common cause. 78,86,117,132 The muscle or tendon can additional structure was injured at the time of rupture of
rupture anywhere along its course and can result in an the PT, the horse was 14.6 times less likely to return to its
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avulsion fracture at its origin in the extensor fossa. intended use. Prognostic indicators previously reported
When this muscle is ruptured, the stifle flexes, but the for this type of injury include location and degree of rup-
hock does not. Rupture of the PT is usually due to over- ture. Prognosis has been reported to be favorable when
extension of the hock joint (Figure 5.100). Entrapment rupture occurs in the tibial region and poor if the rupture
of a limb with violent struggles can cause this condition. occurs at the point of origin from the extensor fossa of
Rupture also may occur during the exertion of a fast the lateral femoral condyle with any associated fracture.
start causing overextension of the tarsus such as in Performance horses have a decreased prognosis to return
jumping. It can also occur after a full‐limb cast is applied to their intended use after rupture of the PT.
to the hindlimb. PT injury in adult horses may cause
swelling of the distal cranial aspect of the crus near the
TC joint (usually between the trochlear ridges), but PERIARTICULAR TARSAL CELLULITIS
lesions in the mid‐crus seem to be more common and
often are not associated with significant swelling. If the Spontaneous cellulitis can develop around the tarsus
PT is ruptured, the tarsal joint can be extended while the that can present as an unusual cause of an acute‐onset,
stifle is flexed, indicating loss of the reciprocal appara- severe non‐weight‐bearing lameness. One report
tus function. There is often a dimpling that occurs within described this condition in a series of TB racehorses.
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the common calcaneal tendon. If the origin of the PT Skin abrasions were identified in some horses some-
fractures from the femur, femoropatellar effusion is a where in the more distal part of the limb, and the onset
prominent feature, and the gait deficit is similar. On US, of swelling usually began on the dorsal aspect of the
the acute ruptured PT is enlarged and shows multiple hock. The cellulitis was quite painful to palpation. These
small focal anechoic to hypoechoic lesions. On a longi- clinical signs were associated with a fever, neutrophilia,
tudinal scan, the normal fiber orientation disappears. and hyperfibrinogenemia. Prompt, aggressive treatment