Means of accelerating tendon graft healing after ACL reconstructions

Rupture of the anterior cruciate ligament (ACL) is one of the most common sport-related injuries. As the ACL is unable to repair itself, reconstructive surgery, using a tendon graft, remains the number one option for the restoration of the joint function. This thesis has explored solutions capable of shortening the healing process along four lines. First, the tissue-regenerative properties of the tendon graft compared to the native ligament was evaluated. Using an in vitro analysis of the phenotype of cells derived from each tissue it was identified that the cells lack regenerative properties. The consequent task has been to find cells that do have these properties and can be used in ACL reconstruction practice. These properties are found in bone marrow cells. Secondly, the possibility of sourcing bone marrow cells proximal to the knee joint would be optimal for ACL reconstruction. However, our comparative study of different bone marrow cell sources has shown that bone marrow cells derived from the ilium offer the strongest regenerative properties. To enhance these properties further, this research has also investigated different priming methods, such as acoustic stimulation and selection of cells through different isolation methods. Thirdly, using an in vitro indirect co-culture system, the crosstalk between different cell types that contribute to the development of tendons and ligaments during embryogenesis was studied. This has revealed that myoblast-derived signals are capable of upregulating classical tendon/ligament gene expression markers on tendon-derived cells, which can contribute to ACL graft healing. Using a rat model of ACL reconstruction, we demonstrated that muscle-derived signals accelerate femoral tunnel closure and can be employed to improve ACL graft healing in a clinical setting. Finally, modulation of BMP-2 and TGF-β1 signalling pathways is essential during tendon/ligament healing. Unfortunately, growth factor delivery in situ is far from trivial and, in many cases, the necessary growth factors are not approved for clinical use. This research has screened a library of small molecules, which has led to the identification of modulators of both signalling pathways. The dissertation concludes with a brief reflection on the field of musculoskeletal tendon and ligament research.