Page 728 - Adams and Stashak's Lameness in Horses, 7th Edition

694 Chapter 5

signs of calcaneal osteitis or sequestrum formation may Because of the severe swelling over the point of the
take several days or weeks to appear, and thus sequen- hock, an inaccurate diagnosis of capped hock or calca-
VetBooks.ir graphic appearance of calcaneal osteitis depends on the pletely luxated (stable luxation) or can reduce and then
neal bursitis may be made. The tendon may remain com-
tial radiographic evaluation is recommended. The radio-
displace while walking (unstable luxation). Most com-
duration of infection before treatment and if other
structures are involved. Ultrasonography can be useful mon is a tearing of the medial retinaculum with a lateral
to assess synovial structure involvement and provide displacement, but medial displacement does rarely occur.
direct visualization of needle placement into a pocket of One case report described a situation where the tendon
fluid for the aspiration of synovial fluid for analysis. fibers of the SDFT split near its center over the point of
Acute injuries to the TC with minimal contamination the hock (one‐half of the SDFT displacing medially and
may resolve with local wound management without the the remaining half laterally). 127
development of bony lesions. Osteitis of the TC is best Luxation of the SDFT tends to be an injury that
addressed by curettage of the affected bone. occurs in horses that compete at speed or due to trauma.
Sequestrectomy is indicated if a sequestrum develops. Initially, affected horses appear quite uncomfortable
Secondary sepsis of the ICB or TS should be treated after the injury. In the acute to subacute injury, diffuse
aggressively similar to any synovial infection. More swelling around the point of the hock can make it diffi-
complex surgical intervention may be required in more cult to accurately define what is injured. However, an
traumatic injuries with heavy contamination and devi- unstable luxation of the SDFT tendon allows the tendon
talized and infected soft tissue and/or bone. The progno- to move back into its original position only to luxate
sis for horses with calcaneal osteitis depends on the again when the horse walks off. Typically, the tendon
structures involved and the duration of infection before tends to luxate when the tarsus is flexed. The position of
treatment. In one study, 9 of 18 horses with infection of the tendon can become more easily appreciated as the
the TC were used as broodmares, and 9 horses returned swelling subsides. On palpation, the luxation of the
to athletic function. 87 SDFT can often be appreciated. Horses with actively
luxating tendons may become quite distressed. If the
tendon remains permanently luxated, the horse’s dis-
Dislocation of the Superficial Digital Flexor Tendon (SDFT)
tress diminishes quickly. Horses with a permanently lux-
The SDFT contains very little muscular tissue and ated tendon (usually laterally) can, with conservative
consists almost entirely of a strong tendon forming part management, return to useful work. By contrast, those
of the stay apparatus in the hindlimb. Its action is to flex with unstable subluxations, in which the tendon sponta-
the digit and extend the hock, but this is considered neously reduces and then displaces, often remain perma-
largely to be a mechanical effect resulting from the nently compromised frequently with continued anxiety.
action of other muscles of the stifle joint. A wide, flat, There have been rare cases of horses that have had the
fibrous bundle arising from the SDFT attaches the ten- SDFT luxate bilaterally.
don to the calcaneus laterally and medially. This struc- A definitive diagnosis is usually made by visualizing
ture, called the retinaculum, stabilizes the tendon at that the displacement of the tendon. However, radiographs
level of the TC. The dislocation occurs when one of the and US examination should be performed to more accu-
fascial attachments (usually the medial retinaculum) of rately define the extent of injury. Radiographs are taken
the SDFT to the calcaneus ruptures with displacement to rule out the possibility of a fracture or other associ-
laterally (Figure 5.97). 118,127,128,135,149 ated bony disorders of this area. US can assist in the
diagnosis by defining the structures that are involved
and the degree of damage. Most often the medial reti-
naculum is torn completely. However, partial tears of
the retinaculum exist with subluxation of the SDFT
occurring rather than complete luxation. Because the
retinaculum exists within the ICB, fraying and tears of
this structure can create moderate effusion of the calca-
neal bursa. Partial tears could easily be misdiagnosed as
a simple capped hock.
The literature would suggest that the treatment of
choice for luxated tendons (unstable displacements) is
surgical correction with postoperative immobilization
in a cast for 4–6 weeks. There have been a number of
surgical procedures recommended, all of which include
open reduction with some form of suture of the torn
retinaculum, some of which had a retinacular reinforce-
ment with or without imbrication and some using a syn-
thetic (polypropylene) mesh. There are only a few
reports of reduction representing a total of nine docu-
mented cases, but the results have often been disap-
Figure 5.97. Caudal view of the tarsi in a horse with severe pointing. Recovery in a full‐limb cast and the possibility
swelling within the right calcaneal bursa and evidence of lateral of cast complications are always a concern.
luxation of the right SDFT from the tuber calcanei (arrows). Source: Endoscopy of the CB may provide another alternative
148
Courtesy of Gary Baxter. approach to luxation of the SDFT. Exploratory