Cruciate ligaments of the avian knee: Insight into a complex system

The avian cruciate ligaments were examined in Gallus domesticus, Anas platyrhynchos, Meleagris gallopavo, and Struthio camelus australis. The ligaments proved to be deviated around the intercondylar groove (cranial cruciate) and around the medial femoral condyle (caudal cruciate). Four functionally different fiber groups could be differentiated: fibers taut only in maximal extension, fibers taut only in maximal flexion, fibers taut in ranges from an intermediate position to an extreme position, and fibers taut throughout the entire range of motion (guiding bundles). Hence the cruciates serve the guiding of the joint and the restriction of motion, whereby the majority of the cranial cruciate fibers are taut in extension while those of the caudal cruciate are in flexion. No differences were found between the species examined with respect to fiber arrangement and function. The avian mechanical model proved to be more complex than the relatively simple mammalian four-bar link model as the avian guiding bundles change their shape due to deflection during motion. © 1992 Wiley-Liss, Inc.