The use of a laser micrometer system to determine the cross-sectional shape and area of ligaments: a comparative study with two existing methods.

Determination of the tensile stresses in ligaments and tendons during uniaxial loading depends on accurate measurement of the cross-sectional area. In this study, a laser micrometer system was employed to evaluate the cross-sectional shape and area of the medial collateral ligament (MCL) at three locations and anterior cruciate ligament (ACL). In a New Zealand White (NZW) rabbit, morphologic sections of the ligaments were made to verify the cross-sectional shape reconstructed by the laser micrometer system. The areas obtained by the laser micrometer system from ten additional NZW rabbits were compared with those obtained by two other methods commonly used to measure the cross-sectional area of ligaments and tendons: one method uses digital calipers and the other a constant pressure (0.12 MPa) area micrometer. For the MCL, the digital calipers yielded results very similar to those of the laser micrometer, but the constant pressure area micrometer yielded values 20 percent lower. The area measured at the proximal site of the MCL was 13 percent greater than the area measured at the joint line and distal line. For the ACL, the values obtained by the digital calipers and constant pressure area micrometer were 16 and 20 percent lower, respectively. Because of the irregular shape exhibited by the rabbit ACL, the digital calipers could not accurately measure the cross-sectional area. The constant pressure area micrometer yielded lower values for the cross-sectional area of both the MCL and ACL, presumably due to the applied pressure which caused changes in both the cross-sectional shape and area.