Poster 105: Rotator cuff healing using demineralised bone fibers in ovine infraspinatus tendon models

OBJECTIVES: Rotator cuff tears are a common cause of shoulder pain and functional deficits. Although surgical repair is often able to restore function and resolve pain, high rates of postoperative structural failures have been reported. To improve the outcomes and reduce re-tear rates biologic tissue scaffolds have been used to augment and reinforce the primary tendon repair by providing mechanical support of the initial repair and ideally improving the rate and/or quality of biological healing at the tendon-bone interface. Demineralised bone fibers (DBF) are bone collagen and can be formed into a patch providing a scaffold and inductive bone morphogenetic proteins known to facilitate healing. This study evaluated the in vivo response of human DBF Patches (hDBF-P) as an onlay over the infraspinatus tendon (IST) and at the tendon-bone interface in an ovine model. METHODS: The hDBF-P was characterised using stereozoom (Figure 1A) and environment electron microscopy (Figure 1B). The osteoinductivity (OI) was evaluated in the standard nude rat intramuscular implantation (IM) model at 28 days using mCT and paraffin histology. A bilateral model of an onlay or an enthesis repair was performed in 12 adult wethers following ethical approval. Four groups were evaluated at 6 and 12 weeks (n=3 per time point): Onlay control and hDBF treated; Enthesis repair control and hDBF treated. The onlay model simulated a tendon injury by 4 longitudinal slits along the IST and lateral drill holes in the proximal humerus in the onlay control group [1]. In the onlay treated group the hDBF-P was hydrated in saline and secured to the IST with interrupted 2-0 non-resorbable sutures (Figure 2A). On contralateral side, the central third of the IST was sharply dissected, the footprint burred, and 2 medial row anchors inserted. The sutures were passed through the IST in the enthesis repair control group. In the enthesis repair treatment group, the sutures were passed through the hDBF-P which was placed at the tendon bone interface followed by sutures through the IST. Two lateral push lock anchors were used for a suture bridge (Figure 2B) in the control and treated groups. Endpoints included clinical recovery, macroscopic dissection, 3T MRI, radiographs, mCT and paraffin histology processing, H&E staining, and light microscopic evaluations to assess local cell and tissue responses and healing. RESULTS: OI was confirmed on IM implantation in nude rats. The sheep recovered uneventfully with no adverse events macroscopically or radiographically. MRI in the onlay control group revealed little response and no increase in tendon thickness which was confirmed histologically. In contrast the onlay hDBF-P treated demonstrated increased tendon thickness and hDBF resorption with time. Histology showed some initial inflammatory cells that decrease with time in the onlay group. MRI in the hDBF-P treated enthesis group supported increased activity at the bone interface at 6 and 12 weeks compared to controls. Histology at the interface with hDBF-P showed evidence of new bone formation at 6 weeks that matured with time support enthesis reformation. CONCLUSIONS: hDBF-P is a collagen graft composed of demineralized bone fibers that have osteoconductive and osteoinductive potential. When formed into a patch, this implant provides a scaffold that can participate with the local biology. hDBF-P used as on-lay in a tendon injury model increased tendon thickness. hDBF-P when used at the interface between the tendon and bone facilitated enthesis reformation through its conductive and inductive potential as well as scaffold architecture. DBF patches represent an exciting allograft implant with the potential to address the clinical problems in rotator cuff surgery. Literature cited 1. Van Kampen, C., et al. (2013). Tissue-engineered augmentation of a rotator cuff tendon using a reconstituted collagen scaffold: a histological evaluation in sheep. Muscles, ligaments and tendons journal, 3(3), p.229.