Ligament-bone Interface Research Articles

Biochemical Analysis of Collagens at the Ligament–Bone Interface Reveals Presence of Cartilage-Specific Collagens

The collagen fibrils of some ligaments attach to bone by passing through a zone that consists of nonmineralized and mineralized fibrocartilages. Very little, however, is known about the cells, the biochemical composition, the extracellular matrix organization, and function of these fibrocartilages. In this study, the collagens present in the fibrocartilages of the bovine medial collateral and anterior cruciate ligaments femoral attachments to bone were isolated, characterized, and their distribution at these sites was assessed by laser confocal microscopy. Types II, IX, and XI collagens were identified after pepsin digestion of the tissues in addition to the types I and V collagens. Immunoblotting using specific polyclonal antibodies confirmed the presence of types II and IX collagens at these sites. Immunofluorescence using confocal microscopy showed that type II collagen was prominent in the nonmineralized area and to a lesser extent in the mineralized zone of the insertion. Type IX collagen showed similar distribution as type II collagen. Type II collagen isolated from the ligament–bone interface contained half hydroxypyridinium cross-linking residues when compared to type II collagen isolated from articular cartilage of the same animals. These data indicate that the fibrocartilaginous zones at the ligament–bone interface are cartilaginous in nature. The cartilage collagens may play a role of anchoring the ligament to bone or the cartilage-like tissue may participate in the modulation of the mechanical stresses which are known to exist at the soft tissue–hard tissue interface.

Collagens in an adult bovine medial collateral ligament: immunofluorescence localization by confocal microscopy reveals that type XIV collagen predominates at the ligament-bone junction.

To understand the structure and function of medial collateral ligament, collagens present in an adult bovine ligament were determined. The mid-section of the ligament was powdered and extracted with 4M guanidinium hydrochloride, and the residue was digested with pepsin to solubilize the collagens. Type I collagen was the major fibril collagen recovered in the pepsin solubilized fraction, with types III and V each representing about 5% and 2%, respectively. Type VI collagen was the major collagen present in the guanidinium hydrochloride extract, and it accounted for about 40% of the proteins in the extract or 4% of the tissue dry weight. Type XII and XIV collagens were also detected in the guanadinium hydrochloride extract as minor components. Immunofluorescence localization using confocal microscopy showed that type XII and XIV collagens are associated with the ligament fibrillar network and that type XIV collagen was prominent at the ligament-bone junction. These data reinforce the notion that these collagens are associated with the type I collagen fibrillar network in connective tissues. In view of high mechanical stresses that exist at the ligament-bone interface, presence of type XIV collagen in high concentration at this junction may contribute to the modulation of the biomechanical properties of this tissue.

Variations in rupture site and surface strains at failure in the maturing rabbit medial collateral ligament.

The relationship between the pattern of surface strain and the site of failure in maturing rabbit ligaments was studied in vitro. Bone-medial collateral ligament (MCL)-bone complexes of 24 female New Zealand White rabbits at 3, 6, 9 and 12 months of age (n = 6 rabbits, 12 MCLs per group) were tested in tension to failure. A video dimension analysis (VDA) system was used to map the surface strain at failure across the width and along the length of the medial side of each MCL during testing. Results showed that the highest strains were consistently located at the femoral insertion decreasing towards the midsubstance, with the highest strain occurring in the anterior portion of the MCL immediately adjacent to the femoral insertion. Strains of the complex at failure increased with rabbit maturation. The strain distribution however, did not change dramatically, even though the locations of MCL failure changed from exclusively tibial avulsion in the three month old rabbits to predominantly midsubstance failures in the 12 month old rabbits. In the six month old rabbits, there was a particular dissociation with all MCLs failing near the tibial insertion while femoral strains were apparently the highest. These results suggest two possibilities beyond that of some unknown artifacts of optical strain measurement. First, since failure sites rarely correlated with areas of maximum surface strain in this study, it seems possible that higher strains could exist deeper in the tissue, particularly at the bone-ligament interface of the tibial insertion in immature animals and somewhere within the midsubstance of the MCL in the adult. Secondly, it is possible that the ligament material may be heterogeneous.

Mechanical properties of the human anterior cruciate ligament

The aim was to measure the stiffness and strength of the femur-anterior cruciate ligament-tibia complex tested in a physiological manner with a force exerted anteriorly on the tibia, at knee joint flexion angles of 0 °, 10 ° and 30 ° and at speeds of 50 and 500 mm/min. Ligaments were preconditioned by cycling five times, with data from the fifth cycle used to determine the stiffness of the ligament in a low-load range. The ligaments were then tested to failure with the knee at 30 ° flexion. The specimens were divided into two groups, middle-aged (40–60) and old (>60). For each group no statistical difference was observed between stiffness of the ligament at different joint flexion angles or speeds. Seven of the 21 specimens in the older age group failed by avulsion at the bone-ligament interface. All the other specimens failed by tears in the substance of the ligament. Ultimate failure load was found to have a significant correlation with bodyweight. It was 1.6 and 1.3 times bodyweight for the middle-aged and older age groups respectively. This study has highlighted the importance of identifying different modes of failure, of making corrections for bodyweight and testing in a physiological manner. The results allow a better understanding of the mechanical behaviour of the anterior cruciate ligament and provide design data for anterior cruciate ligament grafts and prostheses.

A Bioabsorbable Polymer for Collateral Ligament Repair in the Pig

SummaryA bioabsorbable internal fixation device of a poly-L-isomer of lactic acid (PLLA) was used to repair the proximal attachment of the medial femorotibial collateral ligament (MCL) in six miniature Yucatan pigs and compared with metal screw fixation in four pigs. Healing was evaluated by physical examination, gross dissection of surgical sites and histological evaluation of bone ligament interface. Chemical stress analysis of the tack was also evaluated.The absorbable PLLA tack induced minimal tissue reaction and maintained sufficient apposition for healing of the MCL in the miniature Yucatan pigs. No postsurgical complications were noted in the experimental or control groups. All surgical implant procedures were considered successful in maintaining MCL apposition. This study suggests future potential for utilization of the PLLA tack for bioabsorbable implants in soft tissue or bone.A bioabsorbable internal fixation device of a poly-L-isomer of lactic acid was used to repair the proximal attachment of the medial femorotibial collateral ligament in pigs, and compared with metal screw fixation. No postsurgical complications were noted in either group. All surgical implant procedures were successful. This study suggests future potential for utilization of the tack for bioabsorbable implants in soft tissue or bone.

The Effect of Physical Activity on Ligamentous Strength: An Overview

A brief review of the literature pertaining to the strengthening of ligamentous tissue through physical activity is presented. Although literature exists supporting both sides of the question, the predominence of evidence seems to be in favor of improved ligamentous strength following physical activity. Despite the general agreement, the exact mechanism involved is unclear. It is also unclear whether the ligament or the ligament-bone interface is the site of increased strength. A review of the possible mechanisms involved, as well as a discussion of the influence of immobility on the validity of the experimental results, is presented. J Orthop Sports Phys Ther 1984;5(5):275-277.