Page 135 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

110 CHAPTER 1

VetBooks.ir 1.190 abnormalities include periarticular osteophytes,
joint capsule entheseophytes, loss of joint space,
subchondral bone sclerosis and subchondral bone
lysis (Figs. 1.191–1.194). Chronic synovitis may
result in enlargement of the synovial invaginations
of the distal border of the navicular bone as they
communicate directly with the synovial space of the
DIP joint. Capsulitis may result in pallisading new
bone on the dorsal surface of the diaphysis of the
middle phalanx and is usually associated with lame-
ness. This should be differentiated from the mature
smooth new bone that is seen commonly at this site
as an incidental radiological finding. The shape of
the extensor process of the distal phalanx is highly
variable between horses and care should be taken
with the interpretation of osteophytes or entheseo-
phytes at the level of the extensor process. OA tends
to result in osteophyte formation at the dorsodistal
Fig. 1.190 This horse has a distended distal and palmarodistal aspects of the middle phalanx and
interphalangeal joint visible as a swelling just above the the dorsoproximal margin of the navicular bone, as
dorsal coronary band. (Photo courtesy Graham Munroe) well as at the level of the extensor process, and these
areas should be assessed in concert. In horses with-
out radiographic evidence of disease, scintigraphy
is generally painful, but this is a variable finding and may show increased radiopharmaceutical uptake at
early-stage low-grade joint disease may not be pain- the level of the DIP joint in horses with subchon-
ful on flexion. Regional analgesia is not very helpful dral bone injury rather than OA. MRI is the most
in localising pain to the DIP joint. A palmar digi- comprehensive imaging modality for diagnosis of
tal nerve block performed immediately proximal to joint disease as it can identify focal or generalised
the ungual cartilages will result in improvement in cartilage loss, focal or generalised subchondral bone
the majority of horses with lameness caused by pain change including abnormal fluid, osteolysis or den-
in the DIP joint as well as lameness caused by the sification, and soft-tissue changes that are not visible
majority of other injuries in the foot. Intra-articular radiographically (Figs. 1.195, 1.196).
analgesia of the DIP joint is also non-specific and
may desensitise many structures in the navicular Management
region. The only diagnostic analgesic technique The first line of therapy for horses with confirmed
that can distinguish podotrochlear pain from DIP DIP joint pain should be to correct any foot imbal-
joint pain is intrasynovial analgesia of the navicu- ance. Additionally, shoes that ease breakover and pads
lar bursa because 3 cc of mepivacaine injected into that diminish the concussion associated with weight
the navicular bursa does not alleviate pain arising bearing may be helpful. Oral NSAIDs may offer the
from the DIP joint. Therefore, a horse with lame- simplest solution where lameness is mild and com-
ness that is abolished by intra-articular analgesia petition rules permit. The choice of intra-articular
of the DIP joint but not by intrabursal analgesia is medication for DIP joint pain depends on the sever-
most likely to suffer from primary DIP joint pain. In ity of the joint disease. Horses with mild synovitis
one large retrospective study, only 6% of horses pre- or capsulitis, without degenerative changes of the
sented for examination of foot lameness fitted this cartilage or subchondral bone, may respond to intra-
profile. Horses with synovitis, capsulitis or early OA articular injection of hyaluronic acid, polysulphated
of the DIP joint may or may not have radiographic glycosaminoglycan or autologous conditioned serum
changes. In horses with radiographic changes, the (ACS/interleukin 1-receptor-antagonist [IRAP]) and