Page 554 - Adams and Stashak's Lameness in Horses, 7th Edition

520 Chapter 4

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Figure 4.97. Subluxation of the pastern due to avulsion of the SDFT insertions and the straight distal sesamoidean ligament insertion
that occurred at 1 month of age and was treated by pastern arthrodesis. Source: With permission EVE 2007.

hyperextension of the metacarpo(tarso)phalangeal joint.
Although considered to be uncommon, subluxation/lux-
ation of the PIP joint represented 21% of horses that
underwent a PIP joint arthrodesis in a one report. 31

Etiology
Lateral/medial luxations or subluxations are often
caused by severe trauma resulting in joint capsule and
ligamentous tearing (e.g. distal limb caught in something
and the horse struggles and/or falls) or lacerations that
transect the collateral ligament. Palmar/plantar subluxa-
tion/luxation generally occurs from acute trauma result-
ing in overextension of the PIP joint and tearing of the
soft tissue support structures (joint capsule, straight DSL,
and the insertion of the SDFT). Bilateral palmar/plantar
eminence fractures of P2 may cause the same effect due
to complete loss of the palmar/plantar supporting soft
tissues. Palmar/plantar subluxation can also be seen in
foals and weanlings that have jumped from heights and
in foals with flexor tendon laxity that overexert them-
selves during free exercise. 26,73 Loss of the ligamentous
support of the palmar/plantar aspect of the PIP joint
results in subluxation/luxation and severe lameness. 8
Dorsal subluxations are thought to be secondary to
flexural deformities or limb contracture and may be seen
in foals/weanlings that are rapidly growing with an upright
conformation (Figure 4.98). A form of DDFT contracture
was responsible for dorsal subluxation of the pastern in
63
the pelvic limbs of three horses. Dorsal subluxation may
also be seen in horses after traumatic disruption of the
suspensory apparatus and arthrodesis of the fetlock joint,
or progressive, severe suspensory desmitis. 8 Figure 4.98. A young horse with bilateral dorsal subluxation of the
PIP joints. Dorsal swellings over both rear pastern joints can be seen.
Clinical Signs
pastern associated with the ligament injury, and a limb
The clinical signs associated with complete medial/ deformity may be present. Instability and pain may be
lateral luxation due to tearing of the collateral ligament identified with rotation or medial/lateral movement of
are usually obvious. These horses are often non‐weight the phalanges. In acute cases, heat, pain, and swelling of
bearing or lame at the walk and have swelling of the the pastern region are usually evident.