Articular cartilage in the knee joint of the African elephant, Loxodonta africana, Blumenbach 1797

Abstract

Knee joints of one adult and three juvenile African elephants were dissected. The specific features of the articular cartilage with particular reference to matrix components were studied by light and electron microscopy and immunohistochemistry. The elephant knee joint cartilage contains an unusually low concentration of proteoglycans resulting in rather eosinophilic staining properties of the matrix. The very thick collagen fibers of the cartilage possibly represent collagen I. Except for the different thickness of cartilage at the weight-bearing surfaces of femur (approximately 6.7 mm) and tibia (approximately 11.2 mm) in juvenile elephants, light and electron microscopy did not reveal distinct topographical differences in cartilage structure, perhaps because of the high congruency of the articulating surfaces and resulting uniform load distribution in the knee. The number of cell profiles per section area of both femoral (approximately 950 cell profiles/mm(2)) and tibial cartilage (approximately 898 cell profiles/mm(2)) was low, indicating excessive matrix production by the chondrocytes during cartilage development. These unique properties could be a result of the enormous compressive load resting on the elephant knee. Maintenance of the equilibrium between biological function and resistance to compression seems to be crucial in the elephant knee joint cartilage. Any disturbance that interferes with this equilibrium appears to lead to arthrotic alterations, as particularly seen in captive elephants.

The movements of limb segments and joints during locomotion in African and Asian elephants

“…We expected that there would be no major size/species differences in elephant kinematics (as in Hutchinson et al, 2006;Ren and Hutchinson, 2008) but here search for any previously overlooked differences within limbs, as earlier studies have focused on wholebody or whole-limb kinematics. Another subsidiary goal of our analysis was to quantify how 'normal' elephant limbs move in order to establish a comparative dataset for identifying foot, joint or other limb pathologies, which are a major concern for elephant keepers (Csuti et al, 2001;Egger et al, 2008). Table 1 lists the animals we worked with and the zoos/parks where they were held.…”

Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs

“…This scaffold of cartilage cells forms a thin lamina of calcified cartilage that persists as an evenly curved surface on the end of the bone [20]. Despite our understanding of skeletal tissue biology, few studies have attempted to quantify how much of an epiphyseal cartilaginous cap is present, particularly in reptiles [22]–[24].…”

What Lies Beneath: Sub-Articular Long Bone Shape Scaling in Eutherian Mammals and Saurischian Dinosaurs Suggests Different Locomotor Adaptations for Gigantism

“…For mammals articular cartilage remains relatively thin across all size ranges (a few millimeters in thickness), even for elephants [48], [49]. In fact, the relative thickness of articular cartilage decreases with increasing size in eutherian mammals [48].…”

“…That is, the load or force being imposed on a joint is best dispersed by having closely articulating surfaces that spread stress over much of the epiphysis [55], [56] and into the underlying subchondral bone. Moreover, congruent joints ensure that the articular cartilage is loaded in predictable patterns which may limit shear stresses or inhibit peak, focused pressure points [49], [57]. In fact, enhanced joint congruence in eutherian mammals such as dogs [57] and elephants [49] is well-documented, and typically joint congruence increases with increasing size [58].…”

“…Moreover, congruent joints ensure that the articular cartilage is loaded in predictable patterns which may limit shear stresses or inhibit peak, focused pressure points [49], [57]. In fact, enhanced joint congruence in eutherian mammals such as dogs [57] and elephants [49] is well-documented, and typically joint congruence increases with increasing size [58]. Furthermore, the amount of joint congruence varies inversely with cartilage thickness in eutherian mammals.…”