Page 592 - Adams and Stashak's Lameness in Horses, 7th Edition

558 Chapter 4

fractures associated with the collateral ligament may horses. Although all breeds and uses of horses can be
warrant internal fixation to reconstruct the joint surface affected, sport horses, racehorses, Paso Fino horses, and
VetBooks.ir fully. However, prior to immobilization, thorough report desmitis of the fetlock annular ligament was diag-
Warmblood horses appear to be at a greater risk. In one
and improve the prognosis.
Acute open luxations can also be managed success-
nosed mainly in sport horses and less frequently in race-
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debridement of all devitalized soft tissues, bone, and car- horses. In an unpublished report on 49 horses, Paso
tilage should be performed. The joint should be thor- Fino horses and Warmblood types were overrepresented
oughly lavaged, and antimicrobials placed within the compared with the normal hospital population. In
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synovial cavity. IV regional perfusion also is warranted. another study, middle‐aged to older general‐purpose rid-
If the joint is minimally contaminated and was treated ing horses predominated, and PAL desmopathy occurred
immediately, a primary suture apposition of the soft tis- more frequently in the hindlimb than in the forelimbs. 65
sues is recommended. A distal limb cast is then applied
and removed when deemed appropriate based on the
horse’s progress. However, cast immobilization is usu- Etiology
ally required for 6 weeks minimum. Constriction of or by the fetlock annular ligament
usually occurs as a result of trauma and/or infection.
The injury may involve the annular ligament, primarily
Prognosis
resulting in inflammation and thickening (desmitis) of
The prognosis for simple luxation of the fetlock is the structure and thus producing constriction without
good for breeding soundness but guarded for athletic abnormalities in other structures within the fetlock
performance. In one report, 7 of 10 horses, some with canal. Alternatively, the condition may be associated
open luxations, could be used for breeding, and 1 horse with distal superficial digital flexor tendon (SDFT) tend-
was riding sound. Often the final prognosis cannot be initis or longitudinal tears in the deep digital flexor ten-
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accurately assessed until follow‐up radiographs are don (DDFT). Due to the fact that the PAL is minimally
101
taken at 2–3 months after injury. Immediate stabiliza- elastic, swelling of the digital flexor tendons caused by
tion of the joint usually permits healing without the fibrosis and associated tenosynovitis can cause the signs
development of significant OA. Lack of stabilization or of constriction of the annular ligament. Inflammation
unrecognized luxation often results in OA in horses and subsequent scar tissue enlargement often associated
allowed exercise. 81 with a low flexor tendinitis (“low bowed tendon”) may
Acute open luxations exposing the fetlock joint also extend to involve the PAL, also resulting in desmitis.
respond well to early therapy as described. However, Adhesions may form between the SDFT and the annular
one must always be reserved in giving a good prognosis ligament, further restricting motion. Tendinitis of the
until joint infection and OA from direct trauma have DDFT within the fetlock canal also enlarges the tendon
been ruled out as complications. The long‐term outlook within the canal and induces a tenosynovitis and pro-
for return to serviceability is often dependent on the duces the signs of annular ligament constriction. Wounds
degree of initial trauma sustained by the bone and the such as wire cuts or nail punctures can occur in the
severity of secondary OA. region of the palmar/plantar aspect of the fetlock, pro-
ducing thickening, tenosynovitis, and constriction. One
report revealed that primary desmitis of the annular
CONSTRICTION OF OR BY THE FETLOCK ligament was the cause in 55% of the cases, tendinitis
PALMAR/PLANTAR ANNULAR LIGAMENT was the cause in 31%, and sepsis was the cause in 14%
of the cases. Synovial masses within the DFTS may
96
The palmar/plantar annular ligament (PAL) is a also produce a constriction of the annular ligament and
tough, fibrous, thickened, relatively inelastic part of the signs of tenosynovitis. 33
digital flexor tendon sheath (DFTS) strategically located
to support the tendons as they course around the pal-
mar/plantar aspect of the fetlock joint. The PAL together Clinical Signs
with the sesamoid bones provides a canal for the ten- Horses often present with a history of lameness that
dons to glide through. The PAL is lined with synovia and increases with exercise, resolves with rest, and returns
acts to prevent displacement of the tendon, which when put back into performance. The most notable fea-
reduces its mechanical efficiency. Tendons within any ture of annular ligament constriction is swelling of the
tendon sheath and supported by an annular ligament palmar/plantar soft tissues of the distal limb around the
can become enlarged from injury or infection. The fetlock and a characteristic observable proximal border
chronic tendon enlargement/inflammation within the of the annular ligament (“notching”). In nearly all cases,
sheath can also create adjacent PAL thickening. Primary there is distension of the DFTS proximal and distal to
injury to the PAL can also occur, resulting in thickening the PAL.
(desmitis) and a subsequent reduction of the diameter of The lameness is characterized by its persistence, pain
the canal. Compression of the tendon and pressure on fetlock flexion, and worsening with exercise because
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within the canal subsequently restricts the free gliding of inflammation and increased constriction. In the most
function of the tendon, inducing pain and possibly severe cases the horse is reluctant to place the heel on
ischemia to the tissues within the canal, analogous to the ground and will accentuate the cranial phase of the
carpal tunnel disease in people. stride to compensate. The continual external pressure on
Constriction of or by the fetlock PAL can be a cause the tendons may produce abnormalities in the digital
of lameness in performance and general‐purpose riding flexor tendons. 55