Abstract
Intra-synovial tendon injuries affect compressed tendon within a synovial environment (eg Rotator cuff tears of the shoulder) and frequently demonstrate ‘failed healing'. Current therapeutic methods for tendon tears (intra-synovial corticosteroid medication and surgical debridement) offer poor outcomes and new strategies for enhancing repair are needed. We have therefore evaluated two different approaches involving the use of mesenchymal stem cells and scaffolds. Bone marrow- and synovial-derived stem cells were capable of adhering to cut surfaces of tendon in vitro and modulating the release of extracellular matrix into the media. However, when administered in vivo into the digital flexor tendon sheath in naturally-occurring deep digital flexor tendon tears in horses and in an experimental model in sheep, neither cell type was capable of healing the tendon defect. Superparamagnetic iron oxide particle labelling of the implanted cells imaged using MRI and histologically revealed that cells only engraft into the synovium. In contrast a non-cellularised bilayered electrospun and woven polydioxanone scaffold, when used in the same experimental sheep model via a modified open approach and sutured over the created defect resulted in no local or systemic signs of excessive inflammation 3 months after implantation. All the tendon lesions healed with only a mild local inflammatory reaction and minimal-to-mild adhesion formation. Significant proliferative fibroblast infiltration was observed within and immediately adjacent to the implanted scaffold. The cellular infiltrate was accompanied by an extensive network of new blood vessel formation within the new tissue. In conclusion, the use of a scaffold to cover the defect appears to be a more successful strategy to repair intra-synovial tendon defects than intra-synovially injected mesenchymal stem cells. It remains to be tested whether the combination of the two techniques might offer an even better healing response.
