Page 548 - Adams and Stashak's Lameness in Horses, 7th Edition

514 Chapter 4

VetBooks.ir

Figure 4.88. Transverse and sagittal STIR MR images with a large bone bruise of the dorsodistal P2. Because this lesion does not involve
the subchondral bone, it healed without long‐term consequences with rest alone.

OA, the severity of lameness often correlates with the
severity of the OA within the PIP joint, especially when
there is joint space narrowing. The lameness is usually
exacerbated at a trot, at exercise on an uneven surface (e.g.
slope), or by circling at a trot. Except in early cases where
there is focal medial injury, increased lameness is usually
seen when the affected limb is on the inside of the circle. In
some cases during foot flight, an exaggerated extension of
the toe may be seen prior to foot placement. 68
Pastern joint‐associated lameness should not improve
with a PD nerve block if performed very low in the pas-
tern (just above collateral cartilages) with a small vol-
ume of anesthetic (1.5 mL). However, some PD nerve
62
blocks may desensitize the PIP joint. Most horses
improve with a basisesamoid or high PD nerve block
but may not become completely sound, especially if the
disease process is severe. Response to IA analgesia varies
depending on the injury, but improvement of lameness
by 50% or more usually implicates the PIP joint as the
site of the problem. The authors prefer the palmar/plan-
tar approach to block and inject the PIP joint when there
is dorsal bony proliferation, which can make the dorsal
approaches more difficult. 45

Figure 4.89. Typical enlargement of the pastern that may be Diagnosis
visible in horses with OA of the PIP joint. This was a 9‐year‐old
Warmblood show jumper that was presented for pastern arthrodesis. A tentative diagnosis of OA of the PIP joint is often
made based on physical examination findings combined
with the responses to local anesthesia and radiographs.
horses there is pain on flexion and rotation of the The most common radiographic findings in a study per-
pastern region, unless the joint has undergone ankylosis. formed on 196 horses (262 joints) with chronic OA of
Obvious enlargement of the pastern and/or varus the PIP joint were (1) joint space narrowing or collapse,
deformity of the phalanges may be present in horses (2) osteophyte formation, (3) subchondral bone sclero-
with advanced disease. Horses with mild or early disease sis, (4) periosteal/periarticular bony proliferation, (5)
may have no visual or palpable abnormalities in the pas- deformity/collapse of the joint space, and (6) subchon-
tern region. dral lysis (Figure 4.90). Other radiographic features
15
Lameness severity is variable depending on the severity that may be identified include SCLs (Figure 4.86) or
of the disease. When there is radiographically apparent OC lesions, and chronic eminence fractures of P2.
71