Page 388 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.8 Soft-tissue injuries 363

VetBooks.ir nosis. In chronic hypertrophic tenosynovitis, the 1.719
Large or deep tendon tears also carry a poor prog-

prognosis is guarded to poor. The prognosis is gen-
erally poorer in the forelimb than in the hindlimb.

PALMAR/PLANTAR ANNULAR
LIGAMENT SYNDROME

Definition/overview
The palmar/plantar annular ligament of the fetlock
(PAL), or palmar/plantar metacarpo(metatarso)-
phalangeal flexor retinaculum, is a focal thickening
of the fascia forming a thin, transverse ligamentous
band that restrains the digital flexor tendons on the
palmar/plantar aspect of the fetlock during flexion.
It extends from the periosteum on the abaxial aspect
of the PSBs and lies superficial to the digital sheath.
It measures approximately 1 mm in thickness.
PAL syndrome is characterised by thickening of this
ligament, which allegedly induces compression of
the tendons and digital sheath, with associated pain Fig. 1.719 Notched appearance over the palmar
and inflammation (tenosynovitis). There is consid- fetlock (arrow), sometimes wrongly attributed to
erable controversy on this point as ultrasonography annular ligament thickening but actually due to
has revealed that the ligament is rarely affected and distension of the proximal recesses of the digital
when it is, thickening tends to be centrifugal. The sheath proximal to the non-elastic, palmar annular
typical notched appearance often associated with ligament of the fetlock.
the syndrome is actually due to the proximal sheath
pouch bulging proximal to the ligament due to syno-
vial distension, regardless of whether the ligament thickened as a result of chronic inflammation and
is affected or not (Fig. 1.719). Thickening of the synovial hyperplasia.
ligament is more frequently associated with chronic It is questionable whether these conditions actu-
tenosynovitis, in which case adhesions and synovial ally involve a compressive syndrome, as histology
thickening are the actual cause of restriction of ten- has not shown any local necrosis and no major nerves
don motion and sheath cavity space. traverse the sheath, unlike in the carpal canal. PAL
syndrome is most often a feature of chronic digital
Aetiology/pathophysiology tenosynovitis.
A true PAL syndrome is characterised by thick-
ening of the PAL, most often as a result of direct Clinical presentation
trauma to the palmar aspect of the fetlock. It may Typically, the sign most commonly reported is
also be due to spontaneous injury, possibly as a result ‘constriction’ of the palmar aspect of the fetlock,
of overextension of the digit with tension on both causing the sheath to bulge proximal and palmar to
PSBs. The condition is relatively rare and largely the ligament. This is not due to PAL thickening,
overdiagnosed. but solely to sheath distension or synovial thicken-
Apparent thickening of the tissues palmar to the ing. PAL thickening may cause diffuse thickening
SDFT is most often due to thickening and fibro- over the whole palmar (or plantar) aspect of the
sis of the subcutaneous tissues. In tenosynovitis fetlock region, but in most cases, there are no spe-
the visceral and parietal sheath layers may also be cific morphological signs. There may be local pain