105 - Collagen Fiber Orientation of the ACL and PCL at the Distal Femoral Entheses: A Human Cadaveric Study

Poster Board Number: 105
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Abstract Body : Ligaments play an important role in body mechanics and are responsible for force distribution and mobility at a joint. The specific region where the ligament embeds into the bone is known as the enthesis. Here, we microscopically investigate the collagen fiber orientation of the ligaments at the entheses of the distal femur of humans. Specifically, we examine the anterior and posterior cruciate ligaments (ACL and PCL, respectively). Tendon and ligament enthesis in other regions, such as at the rotator cuff or the insertion of the flexor digitorum profundus muscle, have shown variability in the degree of collagen fiber orientation as these structures embed into the bone. We hypothesize that similar variability may be present at the distal femoral ACL and PCL entheses.

Three cadaveric knees were extracted following a routine medical dissection at Northeast Ohio Medical University. All individuals were over 75 years of age. The distal femur was cut and prepared in Osteobed using hard tissue embedding techniques. Sagittal sections were cut from medial to lateral and ground to a thickness of 50-100 micrometers. Sections were photographed and analyzed using quantitative polarized light microscopy (qPLM). QPLM images were realigned to a volume rendering generated from the µCT scan (using Avizo software).

Preliminary results suggest differing collagen fiber orientation at the enthesis between and sometimes within sagittal cross-sections of the ACL and PCL. This indicates that the collagen fibers of these ligaments embed into the bone at various angles. Orientation variability may reflect the cortical bone structure at the distal femur and could correlate with the likelihood of a ligament tear at this point. This information is important because cruciate ligaments are often injured in exercise, sports, and even non-contact biomechanical movements. Many of these injuries occur at the distal femur especially when considering the ACL. PCL injuries are less common, however, they are still known to cause discomfort and altered knee kinematics. Increased understanding of collagen fiber orientation at the sites of ligament may lead to injury prevention and improved therapy interventions. Lastly, from an anthropological standpoint, it may provide an increased understanding of how embedded ligament orientation relates to stance during life.