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Ectrodactyly (split-hand or lobster claw deformity) is one of several congenital bone abnormalities uncommonly seen in the dog and cat. It is characterized by a soft tissue and boney split between metacarpal bones and the radius and ulna, along with deformities of the carpal bones. A case of surgically managed ectrodactyly in a Siberian husky is presented.
Tikanni, an 8-week-old male Siberian husky was presented for evaluation of a deformity of the left forelimb. The dog bore limited weight on the dorsal aspect of the carpus and held the paw in flexion (Figure 1). A decision was made to monitor the condition and consider surgery once the dog had grown larger.
The dog was presented for radiography and surgery at 7 kg body weight and 15 wk of age. Radiography showed a cleft between the 2nd and 3rd metacarpal bones as well as the radius and ulna. Several carpal bones were hypoplastic and deformed (Figure 2). The ulna was shorter than normal but there did not appear to be any incongruity of the elbow joint (Figure 3). There was flexor contracture of the digits laterally which prevented full extension of digits 3, 4, and 5. This was deemed to be primarily related to the shortened ulna.
Surgery consisted of a distal ulnar ostectomy including the styloid process which allowed extension of the contracted digits. A pancarpal arthrodesis was performed using a 2.7/2.0 pancarpal arthrodesis plate (Jorgensen, Loveland, Colorado, USA) centered on the hypoplastic radial-carpal bone and the second metacarpal bone. In most cases the plate is centered on the 3rd metacarpal bone; however, the 3rd metacarpal bone in this dog was much thinner than the 2nd. After curettage of articular cartilage, a cancellous bone graft from the ipsilateral proximal humerus was packed into the joint spaces. Two 2.7-mm cortical bone screws were used to span the proximal aspect of the metacarpal bones from lateral to medial (Figure 4). A v-shaped incision between the divided 2nd and 3rd metacarpals was created and sutured to join the soft tissues. The 3rd phalanx of the 2nd digit was found to be subluxated due to weight-bearing but was not treated. The limb was placed in a mason metasplint for 5 wk. Some moist dermatitis between digits was treated at the time of bandage changes. Twelve weeks after surgery the dog was bearing weight on the limb and using it when playing with other animals (Figure 5).
Intrinsic malformation or disruption of the development of mesenchymal bone cells between 23 and 35 d of gestation results in limb abnormalities including ectrodactyly (1). Genetic mutations and environmental factors including maternal disease or diet, drugs and vaccines, or radiation have been proposed as causative factors (1). Cadmium has been shown to produce the defect in laboratory species (2). Genetic inheritance of the trait, by various means, has been demonstrated in cats and in humans; however, no such data exist for dogs (1,2). Ectrodactyly is frequently associated with other congenital abnormailities in humans, specifically cleft palate. There is no such connection in the dog; however, one report described cleft palate in a littermate of a dog that had ectrodactyly (2).
Ectrodactyly is characterized by the presence of a cleft between metacarpal bones, most commonly between the 1st and 2nd metacarpal bones but any of the other metacarpals can be involved. Carpal bones may be abnormally formed, hypoplastic, or absent. One or more metacarpal-phalanges groupings may be absent. The ulna is generally shorter than normal and this may produce elbow incongruity to the point of subluxation or luxation (1). The radius and ulna are seen to be separated radiographically. The condition has always been reported to be unilateral involving a forelimb. The degree of deformity may be mild to severe and accordingly, function may vary from mild disability to complete non-weight bearing.
Reports of limb-sparing surgical treatment of ectrodactyly are few (2,3). The surgical plan is tailored to the severity and specifics of the deformity in a particular case but can include ulnar osteotomy or ostectomy, partial or pancarpal arthrodesis, and connection of the boney and soft tissue clefts in the paw. Perhaps the most difficult issue to determine in this case, and others in the literature, was the appropriate timing of the surgery. While the disability can become a significant issue as soon as the puppy becomes ambulatory, there is reluctance to perform surgery that might have an impact on growing bones, especially in large breed dogs. Specifically, the spanning of growth plates by surgical implants, in this case the pancarpal arthrodesis plate, was certain to affect bone growth. However, there are several reports of compensatory growth from other physes, both at the proximal radius and especially the proximal humerus, which makes up for the lost growth in the distal radius (2). When considering the flexural contracture of this dog’s digits and the extremely limited use of the limb, the decision was made to proceed with surgery at 15 wk of age. Post-operatively, while the antebrachium appeared grossly to be shorter in the left forelimb, the dog was able to place the paw on the ground and bear weight on the limb suggesting that compensatory overgrowth, especially of the humerus, had taken place.
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