SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
Tendon and Ligament Abnormalities in the Pastern
Lameness is common in horses with soft tissue injuries in the pastern. Swelling, heat
and sensitivity are frequently present on palpation of this area. When the swelling is
localized to the palmaro/plantarolateral or palmaro/plantaromedial aspects of the
pastern, parallel to the long axis of the pastern, injury of the superficial digital flexor
tendon (SDFT) branches should be suspected. The swelling will be more localized at
the base of either proximal sesamoid bone, extending towards the midline of the
palmar/plantar aspects of the pastern when the middle distal sesamoidean ligament
(MDSL) is affected. Swellings along the center of the palmar/plantar aspect of the
pastern would indicate injury to the deep digital flexor tendon (DDFT) or straight distal
sesamoidean ligament (SDSL). When the DDFT is affected, distension of the digital
sheath is frequently seen. Swellings along the medial or lateral aspect of the mid
pastern occur with injuries to the collateral ligaments of the PIP joint or the
palmar/plantar ligaments of this joint; the latter are slightly more palmar/plantar than
swellings associated with the collateral ligaments and extend more distally.
Superficial digital flexor tendon
The injury to the SDFT in the pastern often occurs in isolation, without an injury to
the SDFT in the metacarpal region. Some SDFT injuries in the distal metacarpal
region extend through the region of the annular ligament into the proximal pastern
region and, less frequently, into the mid and distal pastern. The characteristic
swelling is usually a longitudinal swelling, which extends in a proximal to distal
direction along the lateral and/or medial aspect of the pastern throughout its length.
Focal heat and sensitivity usually accompany this swelling and lameness at the
onset of this injury is common. Lameness is more common with SDFT injuries in the
pastern and may persist longer than for injuries in the metacarpal region, lasting for 1
- 4 weeks. Dropping of the fetlock joint and/or subluxation of the PIP joint can occur
in horses with severe injury to or complete rupture of the SDFT in the pastern.
Horses with SDFT injuries in the pastern may have a poorer prognosis than those in
the metacarpal region for returning to racing and the recurrence of these injuries is
not uncommon. However, successful return to performance does occur for horses
with SDFT branch injuries.
In the proximal pastern the homogeneously echogenic SDFT has a thin, half moon
shape in the transverse plane. In normal horses it is difficult to distinguish the annular
ligament from the digital sheath and the palmar or plantar border of the SDFT. On
sagittal sonograms the SDFT has a triangular shape along the midline as its thickness
decreases distally. The body of the SDFT ranges in thickness (palmar - to - dorsal) in
the proximal pastern region from 2 - 6 mm to 1 - 4 mm over the middle of P1. The
teardrop shaped medial and lateral SDFT branches in the mid pastern are similarly
homogeneously echogenic with a parallel fiber pattern throughout their length. The
branches become more triangular distally over the lateral and medial aspects of distal
P1 and proximal P2. The branches of the SDFT range in thickness from 4 - 7 mm in the
proximal pastern to 7 - 12 over distal P1.
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