Bone marrow concentrates are being used to augment soft tissue healing. However, only 0.01% of these cells meet the criteria of a mesenchymal stem cell (MSC), which likely accounts for the variability in reported results. Previous studies using an established rat rotator cuff repair model have demonstrated that bone marrow-derived MSCs had no effect on healing. In this study we evaluated the effect of purified human MSCs on rotator cuff healing in an athymic rat model. Hypothesis: Purified human MSCs added to the repair site will improve biomechanical strength and fibrocartilage formation of the healing tendon.

Fifty-two athymic rats underwent unilateral detachment and repair of the supraspinatus tendon with either fibrin glue (control) or fibrin glue with 106 hMSCs (experimental) applied at the repair site. Flow cytometry verified the stem cell phenotype of the cells as CD73+, CD90+, CD105+, CD14-, CD34- and CD45-. Rats were sacrificed at 2 and 4 weeks, with 10 used for biomechanical testing and 3 for histologic analysis from each group.

Biomechanical testing revealed a significant increase in failure load (11.5±2.4N vs. 8.5±2.4N, p=0.002) and stiffness (7.1±1.2 N/mm vs. 5.7±2.1 N/mm, p0.17).

These data demonstrate the potential for stem cells to augment tendon healing. This is the first study to use purified stem cells, rather than simple bone marrow concentrate. In the future, cell sorting techniques and culture expansion could be used to select and expand the small population of true stem cells in bone marrow. Furthermore, healing could potentially be improved with repeat cell injection at an additional post-operative time point.

Introduction and Aims: The usefulness of bone graft substitutes and growth factors to promote bone graft incorporation and prosthesis fixation in hip replacement should be examined in a loaded model, as results from cortical defect models may not apply. This paper reviews the results of femoral impaction grafting using these materials in an ovine hip replacement model.

Method: At cemented hemiarthroplasty, sheep femurs were impacted with allograft bone (control group n=23) or with allograft mixed with: 1) corglaes bioglass (n=12); 2) a synthetic hydroxyapatite (HA) (n=6) or the bone morpohogenetic protein OP-1 (n=6) (study groups) and implanted with a cemented double taper femoral stem. Sheep were sacrificed at between six and 26 weeks. The primary outcome was femoral stem subsidence, as determined more recently by the development of clinical radiostereometric analysis (RSA) in this model. Femoral fixation, as assessed by ex-vivo mechanical testing, and bone graft incorporation, as assessed by histological review and histoquantitation, were also key outcomes.

Results: In the control groups, there was a consistent response with bone graft incorporation by new bone advancing proximal to distally in the femur and advancing from the endocortex towards the cement mantle. Mineralised bone apposition occurred by six weeks and this was preceeded by partial resorption of the graft. Complete graft incorporation, with subsequent remodelling of bone, was evident proximally by 26 weeks. Bone graft incorporation in femurs impacted with a 1:1 allograft: bioglass mix was minimal and there was often partial or complete resorption of the graft with replacement by fibrous tissue, resorption of endocortical bone and instability of the femoral prosthesis. Supplementation of allograft with OP-1 promotes initial graft resorption, thus hastening bone graft incorporation and remodelling but one case of stem subsidence, that may have been associated with early resorption seen in the OP-1 group, reinforces the need for further studies examining dose response. There was excellent incorporation of the allograft and HA, with new woven bone directly apposing the HA surface and integrated into the larger porous spaces of the HA. There was no adverse response to the HA and there was minimal to no subsidence of the stem at the cement-bone interface, as determined by RSA.

Conclusion: This model is extremely valuable for investigating new biological approaches to reconstruction of major bone deficiency at revision hip replacement and demonstrates clear differences between materials used to supplement allograft, with HA and OP-1 giving encouraging results. RSA is an essential outcomes tool for this model.

Introduction: New biological approaches to reconstruction of major bone deficiency such as the use of bone substitutes and growth factors are being developed. This paper reports on the adverse response to the Bioglass in comparison to allograft alone.

Aim: To compare the biological response to femoral impaction grafting and a cemented femoral stem when using allograft bone versus allograft bone plus a synthetic bone graft substitute, Bioactive glass.

Methods: Eighteen merino wethers underwent a left cemented hemi-arthroplasty and were randomised to have impaction allografting of the femur using either allograft alone (allograft group) or a 50:50 mix of allograft and Bioactive glass (Bioglass group). After sacrifice at 12 weeks, histological analysis of the femora at the levels of the proximal, mid and distal femoral stem and distal to the stem was undertaken.

Results: In the allograft group, there was a consistent response with bone graft incorporation being greatest in the proximal femur and occurring progressively less, more distally. Mineralised bone apposition in the graft occurred post-operatively after eight weeks. In contrast, in the Bioglass group, the response was inconsistent. Bone graft incorporation was either minimal, or there was partial or complete resorption of the bone graft with replacement by particulate-laden fibrous tissue and resorption of endocortical bone. Inflammation of the capsule tissue was noted in some cases.

Conclusion: In comparison to allograft alone, the use of Bioglass to supplement allograft for use in impaction grafting in ovine hip arthroplasty gave inferior results.