Enhancement of Tendon Graft Osteointegration Using Mesenchymal Stem Cells in a Rabbit Model of Anterior Cruciate Ligament Reconstruction

Lim JK, Hui J, Li L, Chong SW, Chan J, Thambyah A, Goh J, Lee EH
Department of Orthopaedic Surgery, National University of Singapore

Introduction

Mesenchymal stem cells (MSCs) are under investigation as potential agents
to enhance bone and cartilage healing in a variety of orthopaedic disorders. We hypothesized that the application of MSCs at the tendon-bone junction during ACL reconstruction might result in both acceleration and enhancement of osteointegration of the tendon graft to the bone tunnel.

Methods

Bilateral ACL reconstructions with hamstring tendon autografts were performed in 30 adult rabbits. The graft was coated with allogenous MSCs in a fibrin glue carrier in one limb, while the contralateral limb served as control with no application of MSCs. The reconstructions were assessed at 2, 4 and 8 weeks. Histological analysis was performed using
hematoxylin/eosin and safranin-O staining. Biomechanical testing of the ACL grafts for stress, strain and elastic modulus was performed with cyclical loading followed by load-to-failure.

Results

Histologic analysis of controls revealed fibroblasts and granulation tissue with development of some collagen fibres resembling Sharpey’s fibres by 8 weeks. The tendon-bone interfaces of the MSC enhanced reconstructions, consistently demonstrated large areas of fibrocartilage between tendon and bone as early as 4 weeks. On biomechanical testing, the MSC enhanced grafts had significantly higher load-to-failure than did controls at all time frames.

Conclusions

The application of mesenchymal stem cells at the tendon-bone interface during ACL reconstruction results in the development of an intervening zone of fibrocartilage (resembling the chondral enthesis of normal ACL insertions) rather than collagen fibres and scar tissue. The resultant ACL reconstructions perform significantly better on biomechanical testing. The use of MSCs to enhance tendon graft osteointegration is a novel method offering the potential of more physiological, earlier healing and biomechanically stronger ligament reconstructions.