In dogs and domestic cats, ectrodactyly has been considered a highly heterogeneous disorder with different sites of soft tissue separation and a variety of abnormalities [7
]. The radiographic and macroscopic features noted in this tiger were compatible with some reported cases of ectrodactyly [7
]. A study of 14 dogs with ectrodactyly found that the soft tissue separation extended up to the proximal metacarpal level in 85.7% of the cases and mainly between metacarpal bones one and two [10
]. The same was noted in the present case, but the separation occurred between metacarpal bones two and three. Absence or hypoplasia of metacarpal and carpal bones may be present in cases of ectrodactyly [10
]. In the present case, the second metacarpal bone was also hypoplastic. The luxation between this bone and the proximal phalanx could be congenital since the phalanx was malformed. There was also a traumatic component since the tiger was constantly striking his second digit on the ground. Differences in bone length such as decreased or increased length of both radius and ulna, or decreased ulna or increased radius have also been described [10
]. In the present case both the radius and ulna were shorter in the affected limb. The radius and ulna physes appeared normal, implying that premature closure was not the cause of the shortened bones.
A supernumerary digit constituted only by the distal phalanx and connected to the fourth digit by cutaneous tissue was observed in a dog with ectrodactyly [11
]. In the present case an extra claw was observed and presented no osseous connection to the third metacarpal bone.
In the majority of the reported canine ectrodactyly cases, the cause was unknown [5
]. However, in domestic cats a mode of inheritance due to a heterozygous gene with variable expression has been demonstrated [14
]. Except for hemivertebra [15
], other detectable congenital abnormalities have not been found in most of the reported cases of ectrodactyly in dogs and cats [4
]. In the present case, the tiger was the first of his species to show such a deformity, and no other abnormality was observed.
There is no specific management or treatment strategy for congenital anomalies, but the primary goals are to prevent progression of the condition and to improve quality of life. In case of minor lesions of ectrodactyly that do not affect limb function no treatment is required; however, reconstruction is necessary in severe cases [5
]. In the present case the malposition of the digit was inducing lameness, because of the constant trauma of the digit on the ground as confirmed by the worn nail and luxation between the metacarpal bone and proximal phalanx. In addition, infrared thermography showed difference in heat radiation between the second and third digits. Since the second digit had decreased heat radiation, the lesion may be characterized as not inflammatory. Infrared thermography can be helpful to detect the source of lameness in wild animals, as observed in the present case [16
]. Furthermore, no temperature differences were observed between right and left shoulder. Probably the small bone fragment at the caudal border of the glenoid cavity on the left shoulder was an incidental incomplete ossification of the glenoid rim.
Ulnar osteotomy or ostectomy, partial or pancarpal arthrodesis, use of orthopedic wire around adjacent bones, bone lengthening and soft tissue reconstruction are some procedures reported in dogs for treatment of ectrodactyly [5
]. Surgical decision making and selection of the appropriate procedure depends on the species being treated, the type of deformity, the timing of surgery and the possible risk of physeal arrest [7
]. A few cases have been managed by amputation [6
]. In the present study, a soft tissue reconstruction of the cleft with excision of both the second digit and a portion of the second metacarpal bone was considered the best option. The third and fourth digits are considered the most important in dogs and cats because they are the primary weight-bearing digits, and no lameness is expected as a result of second digit removal [17
]. Therefore, the low degree of lameness still present in the tiger is probably associated with the discrepancy in length between the thoracic limbs.