Effect of ACL deficiency on MCL strains and joint kinematics.

The knee joint is partially stabilized by the interaction of multiple ligament structures. This study tested the interdependent functions of the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) by evaluating the effects of ACL deficiency on local MCL strain while simultaneously measuring joint kinematics under specific loading scenarios. A structural testing machine applied anterior translation and valgus rotation (limits 100 N and 10 N m, respectively) to the tibia of ten human cadaveric knees with the ACL intact or severed. A three-dimensional motion analysis system measured joint kinematics and MCL tissue strain in 18 regions of the superficial MCL. ACL deficiency significantly increased MCL strains by 1.8% (p<0.05) during anterior translation, bringing ligament fibers to strain levels characteristic of microtrauma. In contrast, ACL transection had no effect on MCL strains during valgus rotation (increase of only 0.1%). Therefore, isolated valgus rotation in the ACL-deficient knee was nondetrimental to the MCL. The ACL was also found to promote internal tibial rotation during anterior translation, which in turn decreased strains near the femoral insertion of the MCL. These data advance the basic structure-function understanding of the MCL, and may benefit the treatment of ACL injuries by improving the knowledge of ACL function and clarifying motions that are potentially harmful to secondary stabilizers.

Effect of dermatan sulfate glycosaminoglycans on the quasi-static material properties of the human medial collateral ligament.

The glycosaminoglycan of decorin, dermatan sulfate (DS), has been suggested to contribute to the mechanical properties of soft connective tissues such as ligaments and tendons. This study investigated the mechanical function of DS in human medial collateral ligaments (MCL) using nondestructive shear and tensile material tests performed before and after targeted removal of DS with chondroitinase B (ChB). The quasi-static elastic material properties of human MCL were unchanged after DS removal. At peak deformation, tensile and shear stresses in ChB treated tissue were within 0.5% (p>0.70) and 2.0% (p>0.30) of pre-treatment values, respectively. From pre- to post-ChB treatment under tensile loading, the tensile tangent modulus went from 242+/-64 to 233+/-57 MPa (p=0.44), and tissue strain at peak deformation went from 4.3+/-0.3% to 4.4+/-0.3% (p=0.54). Tissue hysteresis was unaffected by DS removal for both tensile and shear loading. Biochemical analysis confirmed that 90% of DS was removed by ChB treatment when compared to control samples, and transmission electron microscopy (TEM) imaging further verified the degradation of DS by showing an 88% reduction (p<.001) of sulfated glycosaminoglycans in ChB treated tissue. These results demonstrate that DS in mature knee MCL tissue does not resist tensile or shear deformation under quasi-static loading conditions, challenging the theory that decorin proteoglycans contribute to the elastic material behavior of ligament.