Discarthrosis is defined as the structural and functional failure of the discal joint, combining degeneration of the intervertebral disc and accompanied or followed by bone changes. The condition starts as degeneration of the disc, followed by vertically disposed marginal osteophytes, disrupture of the vertebral endplate, and changes in the subchondral bone in the form of sclerosis, erosions, and eburnation. Osteoarthrosis of the zygapophyseal joints is called zygarthrosis (François et al., 1995). Features of discarthrosis were found in all three bear skeletons examined. However, ankylosis of two or more vertebrae is uncommon in discarthrosis.
Reiter’s syndrome and psoriatic arthritis are members of the spondyloarthropathy (synonyms: spondyloarthritis, spondarthritis) network. The cause of spondyloarthropathy is probably the combination of genetic and environmental factors (e.g. infections elsewhere). Reiter’s syndrome has often an infectious ‘trigger’ (e.g. Chlamydia, Shigella, Yersinia, Salmonella, Campylobacter, Mycoplasma). There is often asymmetrical peripheral nonpurulent arthritis in more than five joints. Sacroiliac fusion is evident in this condition.
Unquestionably the dominant axial pathology in all three cases described here can be diagnosed as spondyloarthropathy. The (nonmarginal) syndesmophytes (all cases), zygapophyseal joint involvement (case 1 and 2) and fusion (case 2), smoothly formed ankylosis (case 2), and sacroiliac fusion (all cases) are diagnostic for this condition. Based on these features, other vertebral conditions like advanced discarthrosis and Diffuse Idiopathic Skeletal Hyperostosis (DISH) can be ruled out. In all cases discarthrosis is present in the vertebral column as well.
Discarthrosis has been diagnosed in the Pleistocene Ursus spelaeus (cf. Fischer, 1995; Tasnádi-Kubacska, 1962), but among these fossil cases are most probably those in which the pathological changes are characteristic for spondyloarthropathy (fused zygapophyseal joints, smoothly formed ventrally disposed ankylosis, nonmarginal syndesmophytes). Wallach & Boever (1983) illustrated a case of arthritis in an old Grizzly bear, Ursus arctos horribilis. Klöppel (1991) described a case of vertebral deformation in a 40 year old Kodiak bear, Ursus arctos middendorfii. He diagnosed the pathology as osteodystrophia deformans (Paget’s disease) or as a severe case of infectious spondylitis. Rothschild & Turnbull (1987) described a case of a treponemal infection in an Indiana Pleistocene bear, Arctodus simus, resulting in an erosive spondylitis of thoracic vertebrae.
Osteoarthrosis (synonyms: osteoarthritis, arthrosis deformans, discarthrosis) is found in fossil and contemporary bears. Tasnádi-Kubacska (1935, 1962) illustrated some good examples of this condition in Ursus spelaeus. This material can, however, include cases of inflammatory erosive arthritis (called by the author ‘arthritis deformans’ and ‘arthritis erosiva’. We likewise found classic features of osteoarthrosis, especially in the skeletons of Ursus ursinus and Ursus thibetanus. In other carnivores (e.g. Hyaenidae and Felidae), osteoarthrosis is rare and inflammatory erosive arthritis is more common (Rothschild & Rothschild, 1994; Rothschild et al., 1998).
Rothschild et al. (1993) found in 86 % of 243 adult bear skeletons (all species) calcification of the annulus fibrosus, forming syndesmophytes, zygapophysial joint fusion and sacroiliac joint fusion as features of spondyloarthropathy. They concluded that it is most plausible to consider Reiter’s syndrome as the cause of these deformations. In another article, Rothschild (1997) mentions 25 % occurrence of type B rheumatoid arthritis and spondyloarthropathy in contemporary bears. In Hyaenidae, Rothschild & Rothschild (1994) found axial involvement in 57 % of the material examined. Spondyloarthropathy was documented in 3.7 % of 386 large Felidae (Rothschild et al., 1998).
It is not completely clear which factor triggered the development of the spondyloarthropathy in the three ursids described. Seen the form and distribution of the nonmarginal syndesmophytes found in the first two cases, Reiter’s syndrome or reactive arthritis is most likely in these cases. In man, the classical reactive arthritis is triggered by two major types of bacterial infection: in the first place, sexually transmitted infection (mostly by Chlamydia trachomatis) and in the second place a gastroenteritis due to, e.g., Salmonella ssp., Shigella ssp., Yersinia ssp., or Campylobacter ssp. Infection with parasites of the genus Ascaris can cause reactive arthritis in man (Khan, 1995).
Rothschild et al. (1993) concluded that the sexually transmitted variant was most likely, seen the high frequency of fractured bacula in Ursidae. However, these fractured penis bones are especially known in Ursus spelaeus (Tasnádi-Kubacska, 1933; 1962), and are less common (less described) in recent bears. Unfortunately, Rothschild et al. (1993) gave no percentages of fractured bacula in the 280 bears examined by them. Tasnádi-Kubacska (1933) mentioned only 15 known cases of fractured bacula in Ursus spelaeus. Furthermore, the relationship between fractured penis bones and sexually transmitted diseases is not completely clear to us. In our understanding, a bear can fracture his baculum without transmitting or obtaining bacterial or viral diseases.
The ‘bullhorn’ shaped nonmarginal syndesmophytes that are visible on the radiographs made of the vertebral column in the examined Ursus ursinus (case 1) are characteristic of Reiter’s syndrome (Dihlmann, 1986). On the macerated bones bulky syndesmophytes are found, also more often found in Reiter’s syndrome than in other variants of spondyloarthropathy (Kerr & Resnick, 1985). The sacroiliac involvement is persistent in this case, but appears to be asymmetrical and not complete. This Sloth bear was suffering from a (chronic) colitis, which made the enteropathic variant of Reiter’s syndrome plausible.