The Entheses of the Medial Meniscns and Ligaments of the Knee Joint : Descriptive and Experimental Studies

• Meniscal injuries are common in sports. Surgical removal of the meniscus to relieve symptoms is associated with a high risk for late knee joint osteoarthrosis and pain. Meniscal repair or replacement has therefore been advocated. In meniscal replacement procedures proper fixation of the substitute to bone is decisive to guarantee normal meniscal load transmitting function and prevention of osteoarthrosis. Secure fixation of the graft is also essential for the success of ligament reconstruction. Thus, this thesis concentrates on exploration of normal morphology of the insertions of the medial meniscus and other knee ligaments, their ultimate strength and failure mode, and finally the capacity of the meniscal insertion for repair and reconstruction in a rabbit animal model.Extreme mechanical demands are posed on the insertion which connects highly loaded and mobile ligamentous tissue to bone. The abrupt change in tissue stiffness in the insertion is made more gradual by interposition of uncalcified and calcified fibrocartilage tissues of intermediate stiffness between the soft ligament and the hard bone. The thickness of calcified fibrocartilage in an insertion seems to be related to the amount of bending at this site. The interface between calcified fibrocartilage and bone is irregular thereby increasing the contact area between these 2 mechanically different tissues and their resistance to separation; its configuration is individual in each ligament and seems adapted to the loads to which the insertion is subjected. During mechanical testing failures through insertional structures were rare, which confirmed the effectiveness of this tissue configuration. Presence of nerve fibres in meniscal insertional structures suggests sensory function beside the mechanical ones. Hence, all of these specific features need to be reestablished after a reconstructive procedure to ensure adequate insertional function.Transection of meniscal insertions without refixation resulted in repair which after 12 weeks showed tissue differentiation and maturation according to local loading conditions. The repair tissue in the anterior insertion which is mainly loaded in tension acquired ligament-like appearance; in the posterior insertion, which is subjected to compressive, shear and tensile loading, fibrocartilage-like tissue had formed. Calcified and uncalcified fibrocartilages mimicing insertional tissue formed after refixation of the insertion into a bone channel, but a nonnal collagen matrix, interface to bone and mechanical strength did not reestablish.A meniscal insertion healed in prolongated position after transection, and in a case with refixation, it was found partially pulled out. This resulted in both instances in a displacement of the meniscus to the joint periphery and signs for osteoarthrosis similar to what has been found after removal of the meniscus. Thus, despite some capacity of the repair tissue to differenciate and mature to insertionspecific tissue after transection or reconstruction a normal load transmission function of the meniscus probably did not reestablish, and osteoarthrosis was common. Further studies are necessary to improve the fixation of meniscal or ligament substitutes to bone.

Nyckelord

knee joint

meniscus

ligaments

insertion

enthesis

quantitative morphology

fibrocartilage

cement line

collagens

proteoglycans

nerve fibres

tensile strength

failure mode

transection

refixation

repair

healing

osteoarthrosis

histology

immunohistochemistry

biomechanics

rabbit model

MEDICINE

MEDICIN

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