Paper 111: Comparative Anatomy of the Knee and the ACL

Abstract

The function of knee is determined by its complex anatomy. Anterior cruciate ligament (ACL) is an important structure of knee and controls the stability of knee, whereas the sizes and shapes of condyles determine the anterior-posterior and rotational motion of the knee. A comparison of the basic anatomy of modern human knee to ancestral human knees, and to those of other animals (mostly primates) can provide novel insights into the natural history of human knee structure and function. This study will help surgeons to better understand the correlation between anatomy and function. 1 - Review ACL anatomy and osseous landmarks in human and different animals, and correlate the anatomy of the ACL with knee function. 2 - Measure and compare the sizes and shapes of the medial and lateral femoral condyles. 1 - Animals in greater need of rotation of the knee will present with a larger ACL, more specifically of the PL bundle. 2 - The size of the overall medial femoral condyle contact area will be bigger than the size of lateral femoral condyle contact area. Animals with greater rotation will have a larger ratio between condyle sizes. 3 - The size of the distal femoral contact area of both condyles (contact area in extension) will be different than the posterior femoral contact area of condyles (contact area in flexion). Animal anatomy was studied on freshly frozen specimens. The ACL anatomy was studied by MR imaging, followed by dissection. Bones from different species were studied by using three-dimensional laser photography and 3D CT scans and measurements were done on specific software. We have found a large variety of ACL anatomy in the Animal Kingdom. The Nubian goat (Capra hircus), the springbok (Antidorcas marsupialis), the pig (Sus scrofa domestica) and the Rhesus monkey (Macaca mulatta) have three ACL bundles (AM, IM, PL). Human (Homo sapiens) has 2 bundles. The ostrich (Struthio camelus) and the chicken (Gallus gallus) have only one bundle. By studying the complexities of functional morphologic features of the knee in different animal species we can help surgeons better understand knee kinematics and the role of each ACL bundle in human being and this knowledge will help surgeons reconstruct anatomy more accurately and therefore perform a more precise knee surgery.