Page 124 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 99

VetBooks.ir 1.171 1.172

Fig. 1.171 Subchondral cyst-like lesion. Radiograph Fig. 1.172 T1-weighted MR image of an osseous
demonstrating a circular area of demineralisation of cyst-like lesion in the distal phalanx (arrow) that was
the subchondral bone of the distal phalanx immediately not visible on radiographs.
distal to the extensor process. A narrow communication
with the distal interphalangeal joint can be observed.

in the extensor process are better observed on lat- Prognosis
eromedial projections. Small subchondral cyst-like The prognosis is good for centrally located cyst-
lesions are usually not visible on radiographs, espe- like lesions in young horses that can be debrided
cially those located close to the palmar border of the arthroscopically. The prognosis is guarded for all
distal phalanx, and cross-sectional imaging modali- other lesions that are associated with lameness.
ties (CT or MRI) may be required to identify them
(Fig. 1.172). Scintigraphy may be useful to identify SIDEBONE
increased bone turnover around radiographically
invisible cysts, but not all cyst-like lesions result in Definition/overview
increased radionuclide uptake. Ossification of the ungual (collateral) cartilages.

Management Aetiology/pathophysiology
Conservative management with stall rest and intra- The precise aetiology of sidebone is unknown, but
articular medication may be successful in a small it is associated with concussion in heavy horses and
percentage of cases. As the majority of horses remain is more common in older horses. Uneven loading of
lame, surgical debridement of cyst-like lesions has the heels in imbalanced feet may also be a factor. The
been advocated, either through a dorsal arthroscopic progressive ossification of the ungual cartilages usu-
approach or extra-articularly. The latter approach ally occurs in a distal to proximal direction, although
through the hoof may result in complications of ossification may occur concurrently from a separate
infection and is rarely used. Not all cyst-like lesions proximal centre. In horses with biaxial ossification
can be reached arthroscopically, but a highly success- of the cartilages of the foot, the lateral sidebone is
ful outcome has been reported for accessible cysts in usually larger than the medial one. Ossification
young horses following arthroscopic-guided debride- of the ungual cartilages has been associated with
ment. Alternatively, direct injection of the cyst cav- increased incidence of collateral ligament desmitis
ity and its fibrous tissue content with corticosteroids, of the DIP joint. Moderate to severe ossification of
under arthroscopic control, may also be successful. the ungual cartilage predisposes to stress-induced