Page 203 - Canine Lameness

13.3 ­FractFres ofctrf rFrral reg o 175

13.2.1 Immune-Mediated Polyarthritis
The carpus is a common site of IMPA including erosive (i.e. radiographic evidence of bone lysis) and
nonerosive (i.e. lack of erosive radiographic changes) forms of the disease. In contrast to other dif-
ferential diagnoses (e.g. septic arthritis, neoplasia, and degenerative joint disease), immune-medi-
ated diseases generally affect multiple joints, most frequently the distal joints (i.e. carpi and tarsi).
Treatment consists of immunosuppressive drug therapy or carpal arthrodesis, if pain is severe.

Non-erosive polyarthritis can occur in all breeds but tends to affect middle-aged large-breed dogs
(Johnson and Mackin 2012). It can be idiopathic (Type I), which is the most common form, or
secondary to amyloidosis (Shar-Peis), to receiving sulfa drugs (Doberman Pinschers), or to the
presence of neoplasia (Type IV), enterohepatic disease (Type III), or other chronic diseases,
particularly infectious diseases (Type II). The clinical signs of polyarthritis vary but may include CARPAL REGION
reluctance to walk, stiffness, vocalizing, exercise intolerance, and systemic signs such as inap-
petence and pyrexia. In one study, 40% of dogs with fever of unknown origin were diagnosed
with polyarthritis (Lunn 2001). Lameness may be mild to severe and shift from one leg to another
but frequently affects both thoracic limbs. Loss of carpal joint flexion secondary to carpal effu-
sion, and pain response may be present; however, in one study, only 40% of dogs showed joint
pain (Jacques et al. 2002). Besides joint effusion, the diagnosis of nonerosive polyarthritis relies
on the lack of radiographic changes (Figure 13.3) and arthrocentesis showing suppurative
inflammation without evidence of infection (Chapter 9). The most commonly affected joints are
the tarsi, carpi, and the stifle. Aspiration of these joints is generally recommended (Johnson and
Mackin 2012) since some dogs with polyarthritis do not have palpable carpal effusion or show
signs of pain, so it is important to collect joint fluid when polyarthritis is suspected, even if effu-
sion is not detected. It is also important to collect joint fluid to evaluate the response to therapy
regardless of the presence or absence of effusion.
Erosive polyarthritis, also termed rheumatoid arthritis, tends to occur in smaller dogs and is rare.
In one study, all dogs with erosive polyarthritis had erosive lesions of the carpal joint
(Shaughnessy et al. 2016). The diagnosis of erosive polyarthritis relies on radiographs (to diag-
nose erosive lesions) in combination with joint fluid analysis. Carpal joint instability and hyper-
extension may occur secondarily. A juvenile form of polyarthritis has been reported in Akitas
(Dougherty et al. 1991).

13.3 Fractures of the Carpal Region

Fractures of the carpal region (Figure 13.4) include fractures of the distal aspect of the radius and
ulna, particularly Salter-Harris (SH) fractures of the distal radial and ulnar physes, as well as frac-
tures of the carpal bones. Physeal fractures of the distal radial and ulnar physes appear to be the
most common physeal fractures in dogs (Marretta and Schrader 1983). These fractures are generally
classified using the SH classification system (Figure 13.5). In the radius, fractures across the distal
radial physis without (SH Type I) or with a metaphyseal bone fragment (SH Type II) and asymmetric
compressive lesions leading to premature physeal closure (described as SH Type VI) are most com-
mon. Physeal distal radial fractures that involve the articular surface without (SH Type III) or with
a metaphyseal bone fragment (SH Type IV) rarely occur. In the ulna, the distal physis is cone-shaped
and excessive bending leads to a compressive injury on one side of the cone and secondary prema-
ture closure (SH Type V). Since these distal ulna fractures frequently lead to angular limb deformity
due to premature growth plate closure, their identification prior to the development of deformities