The elephant knee joint: morphological and biomechanical considerations

Abstract

Elephant limbs display unique morphological features which are related mainly to supporting the enormous body weight of the animal. In elephants, the knee joint plays important roles in weight bearing and locomotion, but anatomical data are sparse and lacking in functional analyses. In addition, the knee joint is affected frequently by arthrosis. Here we examined structures of the knee joint by means of standard anatomical techniques in eight African ( Loxodonta africana ) and three Asian elephants ( Elephas maximus ). Furthermore, we performed radiography in five African and two Asian elephants and magnetic resonance imaging (MRI) in one African elephant. Macerated bones of 11 individuals (four African, seven Asian elephants) were measured with a pair of callipers to give standardized measurements of the articular parts. In one Asian and three African elephants, kinematic and functional analyses were carried out using a digitizer and according to the helical axis concept. Some peculiarities of healthy and arthrotic knee joints of elephants were compared with human knees. In contrast to those of other quadruped mammals, the knee joint of elephants displays an extended resting position. The femorotibial joint of elephants shows a high grade of congruency and the menisci are extremely narrow and thin. The four-bar mechanism of the cruciate ligaments exists also in the elephant. The main motion of the knee joint is extension-flexion with a range of motion of 142 ° .In elephants, arthrotic alterations of the knee joint can lead to injury or loss of the cranial (anterior) cruciate ligament.

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

“…Elephants smoothly adducted their upper arm and thigh from midswing through late-stance phase, then abducted. The elbow tended to be fairly static in adduction during stance, then abducted and adducted in swing, whereas the knee showed a similar motion to the upper arm and thigh but with markedly large swing-phase abduction [note that the knee joint's helical axis passively contributes to this motion (Weissengruber et al, 2006)]. The wrist remained quite static (more so than the elbow) in slight abduction during stance (much like its stasis in extension) and then quickly abducted, then adducted during swing.…”

“…As humans have a similar hindlimb design to elephants (Weissengruber et al, 2006) (e.g. long femur and short tibia, large functionally plantigrade foot) despite their bipedalism, it is interesting to compare their limb motions.…”

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

“…In contrast to the half-bent posture of knee joints of other mammals, the elephant knee exhibits an extended resting position. The angle between femur and tibia is close to 1808 (Weissengruber et al, 2006). This posture resembles that in humans.…”

“…Therefore, correct interpretation of both morphology and composition of articular cartilage requires in-depth knowledge of joint morphology. Surprisingly, there is no information on the morphology of articular cartilage in the elephant, although in elephants of higher age, disorders of the locomotory apparatus including osteoarthritis, degenerative joint disease or arthrosis frequently occur (Ruthe, 1961;Salzert, 1972;Hittmair and Vielgrader, 2000;Forstenpointner et al, 2001;Hittmair et al, 2001;Weissengruber et al, 2006).…”

Macroanatomy of the Bones of Thoracic Limb of an Asian Elephant (Elephas maximus)

“…Elephant can move slowly to quite fast, and elephants can out run most humans and can remain standing for long periods with the support of bones and limbs. Both in structure and in kinematic patterns (Muybridge, 1899;Howell, 1944;Gambaryan & Hardin, 1974;Hildebrand & Hurley, 1985;Hutchinson et al, 2003;Weissengruber & Forstenpointner, 2004;Weissengruber et al, 2006) the limbs of elephants reveal many peculiarities. A column-shaped, extended limb integrates all structures of the locomotor apparatus (Howell; Gambaryan & Hardin).…”