Enhancement of Tendon-to-Bone Healing: Choose a Monophasic or Hierarchical Scaffold?

To enhance the healing of tendon to bone, various biomimetically hierarchical scaffolds have been proposed. However, the fabrication of such scaffolds is complicated. Furthermore, the most significant result after a routine repair is loss of the transition zone between the tendon and bone, whose main components are similar to fibrocartilage.To compare tendon-to-bone healing results in a rabbit model using a monophasic graft (decellularized fibrocartilage graft; DFCG) and hierarchical graft (decellularized tendon-to-bone complex; DTBC) that contain the native hierarchical enthesis.Controlled laboratory study.DFCG and DTBC were harvested from allogenic rabbits. A rabbit model of a chronic rotator cuff tear was established, and 3 groups were assessed: direct repair or repair with DFCG or DTBC fixed between the tendon and bone. Hierarchical evaluations of the repaired tendon-to-bone interface were performed with regard to the tendon zone, transition zone, and bone zone using histological staining and micro-computed tomography scanning. Biomechanical analysis was performed to evaluate the general healing strength.The healing results in the tendon zone exhibited no significant difference among the 3 groups at any time point. In the transition zone, the grade in the direct repair group was significantly lower than that in the DFCG and DTBC groups at 4 weeks, and the grade in the DFCG group was significantly lower than that in the DTBC group at this time point. However, any significant difference between the DFCG group and DTBC group could no longer be detected at 8 and 16 weeks, which was inconsistent with the results of the biomechanical analysis. Micro-computed tomography analysis showed no significant difference among the 3 groups with regard to bone mineral density at 16 weeks.A monophasic DFCG was able to achieve enhanced tendon-to-bone healing similar to that with hierarchical DTBC over the long term, with regard to both histological and biomechanical properties.Fabrication of a monophasic scaffold instead of a hierarchical scaffold to promote regeneration and remodeling of a transition zone, which was mainly composed of fibrocartilaginous matrix between the tendon and bone, may be sufficient to enhance tendon-to-bone healing.