Abstract

Arthritis involving the joints of the legs is a common problem in captive cranes.^1,4 Trauma is the most common etiologic factor; infectious arthritis and arthritis secondary to congenital or developmental deformities have also been documented.¹ Here, we report on bilateral progressive degenerative osteoarthritis involving the intertarsal (hock) joints and seen uniquely in one species of cranes, the Siberian crane (Grus leucogeranus). The International Crane Foundation (ICF) maintains a breeding population of 15 Siberian cranes to produce eggs and chicks for release programs in Asia. The Siberian crane is the third rarest species of crane, and there is intensive international work to conserve the endangered wild populations.³ Siberian cranes are relatively rare in captivity.

Lameness was first noted in two of ICF's adult Siberian cranes at 15 yr and 21 yr of age, respectively. In both cases, the lameness was associated with bilateral firm enlargement of the intertarsal joints. Radiographically, there was both significant soft tissue swelling and periarticular bone proliferation. No bacteria were found on aerobic culture of synovial fluid aspirated from the joints; cytology of joint fluid was compatible with mild chronic inflammation. In both cases, the severity of the joint changes and the lameness progressed over the next 5 yr. Non-steroidal anti-inflammatory drugs (Table 1) initially appeared to help maintain the birds' mobility, but later in the course of the disease these drugs were no longer palliative. Inter-articular and IM injections of polysulfated glycosaminoglycans (Adequan®) had no observable effect. One bird was euthanatized when it became so debilitated that it was considered inhumane to prolong its life; it was still producing eggs that year. Gross and histopathologic examination of its hock joints showed replacement of the articular cartilage by dense fibrocartilaginous tissue with many areas of erosion. The joint capsule was thickened with chondroid metaplasia, but little inflammation. There was marked periarticular bony reorganization. In the second case, replacement of the more severely affected hock with a human digit artificial joint was attempted; this surgical treatment will be reported by Bennett et al. at this meeting.

The other Siberian cranes in the ICF flock were screened radiographically for evidence of osteoarthritis in the hock joints. All the cranes 13 yr and older (seven birds) had degenerative changes in at least one hock. The consistent early change was a small osteophyte (“chip”) anterior to the hock joint, apparently associated with the joint capsule. A survey requesting information on occurrence of hock arthritis and husbandry practices was mailed to the 17 zoos world-wide known to house Siberian cranes. Affected Siberian cranes were identified at two other institutions.

Table 1. Non-steroidal anti-inflammatory drugs used orally in arthritic cranes

^aFlunixin meglumine has been shown to be nephrotoxic, even at very low doses, in several species of birds, including cranes.² It is no longer used at ICF.

Because this degenerative osteoarthritis is bilateral, not known to be associated with trauma, occurs regularly in young adults, and is seen in Siberian cranes but not the other 14 crane species at ICF, we investigated species-specific biology and husbandry practices as possible causal factors. Siberian cranes are the most aquatic of the cranes, exclusively using wetlands for roosting and feeding in both their breeding and wintering ranges.³ It is probable that their leg joint anatomy is adapted to “mushy” substrates. At ICF, and at both of the two other centers that have affected Siberian cranes, the cranes have generally been housed in dirt pens without ponds, with access to concrete-floored buildings. We hypothesize that the chronic joint stress associated with standing and walking on packed dirt and concrete may precipitate the osteoarthritis seen in this species. ICF is working on modifying its husbandry of Siberian cranes, primarily through seasonally providing ponds with mud substrates. The Siberian cranes will be monitored radiographically to see if these husbandry changes reduce the incidence and progression of progressive degenerative hock arthritis in the flock.

Literature Cited

1.  Curro, T.G., J. Langenberg, and J. Paul-Murphy. 1992. A review of lameness in long-legged birds. Proc. Annu. Conf. Assoc. Avian Vet., Pp. 265–269.

2.  Klein, P.N., K. Charmatz and J. Langenberg. 1994. The effect of flunixin meglumine (Banamine®) on the renal function in northern bobwhite (Colinus virginianus): an avian mode. Proc. Amer. Assoc. Zoo Vets, Pp 128–131.

3.  Meine, C.D. and G.W. Archibald. 1996. The Cranes: Status Survey and Conservation Action Plan. IUCN, Gland, Switzerland, Pp. 88–102.

4.  Olsen, G.H. 1994. Orthopedics in cranes: pediatrics and adults. Seminars in Avian and Exotic Pet Medicine. 3:73–80.