Degenerative Osteoarthropathy in Laboratory Housed Xenopus (Silurana) tropicalis

Abstract

In this case study, 15 adult laboratory Xenopus (Silurana) tropicalis (7 adult males and 8 adult females) were examinedfor nodular enlargements of the clawed digits (digits 0, I, II, and III) on the hind feet. Radiographs showed smoothly margined,rounded, peripherally mineralized lesions arising from the distal phalanges of digits 0-III with osteoproductive and osteolytic components in all frogs. Micro computed tomography (microCT) scans further revealed interphalangeal (IP),metacarpophalangeal (MCP), and metatarsophalangeal (MTP) joint osteoarthritis characterized by periarticular new bone formation, rounded mineral foci both peripherally and centrally within the joints, and more rarely, linear mineralizationpalmar/plantar to the joints in the flexor tendons. In the nonclawed digits, the shape of the distal phalanx was variablydistorted and both subluxation and malangulation of IP joints were identified. Histologically, nodules corresponded to aperipheral rim of mature cortical bone surrounding central adipose tissue, scattered hematopoietic elements, and residualbone of the distal phalanx. Occasionally, the peripheral rim of cortical bone extended proximally to encompass the distalaspect of adjacent phalanx. MCP, MTP and IP joint spaces of most digits exhibited widespread osteoarthritis characterizedby periarticular cartilaginous or osseous metaplasia, bony remodeling, and less frequently, granulomatous osteomyelitis.Nutritional analyses of the feed did not indicate imbalances nor were the lesions consistent with metabolic bone disease.The exact etiopathogenesis of these lesions is unknown; however, we hypothesize that the osteoarthritic changes are due toa combination of the frogs’ mature age, the unique structure of the Xenopus spp. claw, genetics and biomechanical forces onthe digits and distal phalanges of the hind feet.