Ossification pattern of the unusual pisiform in two-toed (Choloepus) and three-toed sloths (Bradypus)
Creator
Lia M Gavazzi
Kelsey M Kjosness
Philip L Reno
Date
2022
Description
Two-toed (Choloepus sp.) and three-toed (Bradypus sp.) sloths possess short, rounded pisiforms that are rare among mammals and differ from other members of Xenarthra like the giant anteater (Myrmecophaga tridactyla) which retain elongated, rod-like pisiforms in common with most mammals. Using photographs, radiographs, and μCT, we assessed ossification patterns in the pisiform and the paralogous tarsal, the calcaneus, for two-toed sloths, three-toed sloths, and giant anteaters to determine the process by which pisiform reduction occurs in sloths and compare it to other previously studied examples of pisiform reduction in humans and orangutans. Both extant sloth genera achieve pisiform reduction through the loss of a secondary ossification center and the likely disruption of the associated growth plate based on an unusually porous subchondral surface. This represents a third unique mechanism of pisiform reduction among mammals, along with primary ossification center loss in humans and retention of two ossification centers with likely reduced growth periods in orangutans. Given the remarkable similarities between two-toed and three-toed sloth pisiform ossification patterns and the presence of pisiform reduction in fossil sloths, extant sloth pisiform morphology does not appear to represent a recent convergent adaptation to suspensory locomotion, but instead is likely to be an ancestral trait of Folivora that emerged early in the radiation of extant and fossil sloths.
SYNOVITIS EQUIVALENT TO EROSIONS IN RHEUMATOID-ARTHRITIS - IMPLICATIONS OF SKELETAL ANALYSIS FOR THE CLINICAL MANAGEMENT OF CONTEMPORARY RHEUMATOID-ARTHRITIS
Creator
Rothschild B M; Woods R J
Publisher
Clinical and Experimental Rheumatology
Date
1992
1992-03
Description
Examination of a contemporary skeletal collection revealed a rheumatoid subgroup with parameters mirroring those of contemporary clinical populations. This rheumatoid population was also indistinguishable from contemporary (live) clinical populations, on the basis of the actual distribution of radiologically detectable erosions, thus validating its representativeness. Gross examination of these defleshed skeletons allowed assessment of the significance of erosive disease in rheumatoid arthritis. As anticipated, the frequency of visibly detectable erosions exceeded that detectable radiologically. The frequency of visibly detectable erosions, however, was indistinguishable from the frequency of synovitis in clinical populations. The excellent correlation of the gross and clinical distribution of disease suggests that some degree of erosive disease is integral to all lesions of rheumatoid arthritis and that only the relative insensitivity of radiologic techniques precludes universal recognition of those erosions. This work suggests that any therapeutic intervention which settles for only partial synovitis control will not prevent the progression of erosive disease; and perhaps explains the difficulty of demonstrating alterations in erosion progression in studies of disease modifying agents.