Page 497 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 463

COFFIN JOINT AND DISTAL PHALANX

VetBooks.ir gaRy M. BaxtER

OSTEOARTHRITIS (OA) OF THE DISTAL Clinical Signs
INTERPHALANGEAL (DIP) JOINT Effusion of the DIP joint is usually present in most
Osteoarthritis (OA) of the distal interphalangeal horses with OA or synovitis/capsulitis of the DIP joint
(DIP) joint, or “low ringbone,” is a common cause of (Figure 4.25). However, effusion can be present in nor-
forelimb lameness in horses. It can be a primary cause of mal horses, so this finding is not always indicative of
17
lameness, but more commonly, it occurs concurrently problems within the DIP joint. However, sound horses
with other lameness conditions of the foot. Synovitis/ usually have less DIP joint effusion that lame horses and
capsulitis of the DIP joint is considered to be a less severe the effusion is often symmetrical from right to left. Most
form of OA that may occur in some horses in the early times significant effusion of the DIP joint can be seen as
stages of the disease process. Although advanced low a slight bulging just above the coronary band. The fluid
ringbone can be associated with dorsal exostosis of the can usually be balloted from medial to lateral along the
extensor process of P3, contributing to an enlargement dorsal midline of the joint. With chronic or advanced
at the coronary band and pyramidal distortion of the disease, the joint capsule may become thickened, result-
5
hoof, this occurs uncommonly. Distortion of the hoof ing in a firm swelling just above the dorsal aspect of the
leading to pyramidal disease or buttress foot is most coronary band. Digital pressure over the swelling may
5
likely associated with large extensor process fractures of elicit a painful response. The joint may be painful to
the distal phalanx. 15 flexion and rotation, but this is uncommon unless the
OA is advanced or secondary to another problem in
the joint. Lameness is variable and often depends on the
Etiology severity of the disease, whether it is primary or second-
17
Primary OA of the DIP joint can be due to acute or ary, and whether one or both limbs are affected. The
repetitive trauma to the joint comparable to any articu- lameness is often worse on hard ground, when circled,
lation in the horse. Horses with a broken pastern axis and after distal limb or phalangeal flexion.
(forward or backward) and other types of hoof imbal- Lameness associated with the DIP joint is often
ances appear particularly prone to repetitive trauma to improved and sometimes alleviated completely with a
the DIP joint and development of OA. Acute or repeti- PD nerve block. 16,55 However, anesthesia at the base of
tive trauma may cause tearing of the joint capsule (cap- the sesamoid bones or a pastern ring block may be
sulitis) and/or direct damage to the articular cartilage required for complete resolution of the lameness. Intra‐
and subchondral bone. Excessive strain of the attach- articular (IA) anesthesia of the DIP joint is not specific
ments of the long or common digital extensor tendon for problems within the joint, but using a small volume
to the extensor process may also occur and contribute of anesthetic (6 mL or less) and observing for a change
to periostitis and enthesophyte formation along the in lameness very soon after the injection (within 10 minutes)
dorsal aspect of the joint. Primary OA of the DIP joint
5
not associated with trauma, conformational defects, or
developmental abnormalities of the joint has also been
50
reported. This condition was characterized as a
chronic condition with a slow onset of cartilage degen-
eration and reactive changes within the DIP joint of a
single front limb. The diagnosis of this condition was
challenging with radiographs alone, and low‐field
standing MRI was necessary to make the diagnosis. 50
Secondary OA can occur from other lameness condi-
tions that involve the DIP joint, either directly or indi-
rectly. These include navicular disease, complete
navicular bone fractures, articular fractures of the distal
phalanx, subchondral cystic lesions (SCLs) of the distal
phalanx, osteochondral fragmentation within the joint,
and desmitis of the collateral ligaments (CLs) of the DIP
joint. 5,18,19,21,47 These abnormalities are thought to
directly or indirectly cause pathology to the DIP joint,
which leads to the development of OA over time.
Prevention of DIP joint OA is often an important aspect
of treatment for many of these conditions. See the dis-
cussion of each of these conditions in this chapter for
more information. Figure 4.25. Effusion within the DIP joint can be seen and
palpated as swelling just above the coronary band (arrow).