We used demineralised bone matrix (DBM) to augment re-attachment of tendon to a metal prosthesis in an in vivo ovine model of reconstruction of the extensor mechanism at the knee. We hypothesised that augmentation of the tendon-implant interface with DBM would enhance the functional and histological outcomes as compared with previously reported control reconstructions without DBM. Function was assessed at six and 12 weeks postoperatively, and histological examination was undertaken at 12 weeks.

A significant increase of 23.5% was observed in functional weight-bearing at six weeks in the DBM-augmented group compared with non-augmented controls (p = 0.004). By 12 weeks augmentation with DBM resulted in regeneration of a more direct-type enthesis, with regions of fibrocartilage, mineralised fibrocartilage and bone. In the controls the interface was predominantly indirect, with the tendon attached to the bone graft-hydroxyapatite base plate by perforating collagen fibres.

Research in to tendon-bone healing techniques focus on increasing bone growth at the interface such as cell or growth factor (e.g. BMP-2) augmentation. Demineralised bone matrix (DBM) is osseoinductive and is in use clinically.

Hypothesis: DBM augmentation of a healing tendon-bone interface will result in improved function at 3, 6, 9 and 12 weeks, and a morphology that more closely resembles that of a normal enthesis at 12 weeks.

Materials and methods: An ovine patellar tendon model was used. 19 skeletally mature ewes were allocated to the control group or DBM group. In both groups the patellar tendon was detached, and following tibial tubercle osteotomy, was re-attached using 3 suture anchors. In the DBM group a piece of DBM was placed between the tendon and bone. 2 animals were sacrificed at 6 weeks and 6 animals at 12 weeks. Animals underwent force plate analysis at 3, 6, 9 and 12 weeks. The tendon-bone interface length which was fibrous or fibrocartilaginous, and the area of fibrocartilage, mineralised fibrocartilage and new bone was quantified.

Results: 3 control group animals (33%) failed within 6 weeks. None failed in the DBM group. The DBM group was significantly better than the control at all time points (p< 0.05). DBM produced a significantly more fibrocartilaginous enthesis than the control group (p< 0.05). Controls were significantly more fibrous than the DBM group (p< 0.05). DBM produced significantly more fibrocartilage (p< 0.05), and mineralised fibrocartilage (p< 0.05).

Discussion: 33% of the control group failed within 6 weeks, whilst no failures were observed in the DBM group. DBM animals mobilised earlier and had significantly better function at all time points. Histologically, the DBM group showed a more mature direct type enthesis at earlier time points.

Conclusion: DBM augmentation of a healing tendon-bone interface enhances functional and morphological recovery at earlier time points.

We used an in vivo model to assess the use of an autogenous cancellous bone block and marrow graft for augmenting tendon reattachment to metallic implants. We hypothesised that augmentation of the tendon-implant interface with a bone block would enable retention of the graft on the implant surface, enhance biological integration, and result in more consistent functional outcomes compared with previously reported morcellised graft augmentation techniques.

A significant improvement in functional weight-bearing was observed between six and 12 weeks. The significant increase in ground reaction force through the operated limb between six and 12 weeks was greater than that reported previously with morcellised graft augmented reconstructions. Histological appearance and collagen fibre orientation with bone block augmentation more closely resembled that of an intact enthesis compared with the morcellised grafting technique. Bone block augmentation of tendon-implant interfaces results in more reliable functional and histological outcomes, with a return to pre-operative levels of weight-bearing by 24 weeks.

We examined the mechanical properties of Vicryl (polyglactin 910) mesh in vitro and assessed its use in vivo as a novel biomaterial to attach tendon to a hydroxyapatite-coated metal implant, the interface of which was augmented with autogenous bone and marrow graft. This was compared with tendon re-attachment using a compressive clamp device in an identical animal model. Two- and four-ply sleeves of Vicryl mesh tested to failure under tension reached 5.13% and 28.35% of the normal ovine patellar tendon, respectively. Four-ply sleeves supported gait in an ovine model with 67.05% weight-bearing through the operated limb at 12 weeks, without evidence of mechanical failure.

Mesh fibres were visible at six weeks but had been completely resorbed by 12 weeks, with no evidence of chronic inflammation. The tendon-implant neoenthesis was predominantly an indirect type, with tendon attached to the bone-hydroxyapatite surface by perforating collagen fibres.