11. Utilisation des allogreffes, substituts osseux et cellules souches pour la fixation du cotyle dans les révisions de PTH - Allografts, bone substitute and stem cells for hip revision

Ph Hernigou, Y Homma, A Poignard, CH Flouzat- Lachaniette (Créteil)

Deficiencies of acetabular bone stock at revision hip replacement are usually reconstructed with allograft using impaction bone grafting and a reinforcement metal device. We have used in 20 patients a standard frozen irradiated bone allograft vitalised with autologous marrow prepared with concentration by centrifugation and compared the results with those of 20 other patients who received standard frozen irradiated bone allograft without stem cells. We looked also the results of patients operated with hip dysplasia and received an autograft associated to their total hip arthroplasty. With a follow-up of ten years hips that received allograft vitalised with autologous marrow showed evidence of trabeculation and incorporation of the allograft with no acetabular loosening, compared with 7 failures in the other group with allograft without stem cells and 4 failures (graft resorption) in the group of patients with autograft. These results suggest that the use of an acetabular reinforcement ring and a living composite of sterile allograft and autologous marrow concentrate appear to be a method of reconstructing acetabular deficiencies which gives better results than allograft alone or autograft of the femoral head, at least in our experience. The question is how to improve the preparation of such a bone allograft vitalised with stem cells.

Material and methods: Femoral heads were obtained from patients with hips fractures. The allograft head was prepared using bone marrow aspirated from the iliac crest. Marrow was aspirated from both anterior iliac crests, concentrated on a cell separator, and then injected into the femoral head. The marrow was injected into the allograft several times until the bone block was saturated. Several tests were done with 10 cc, 20 cc, 40 cc. The aim of this study was to evaluate how many stem cells can be charged in an allograft femoral head during surgery and to provide indications of the number of these stem cells according to the method of concentration used for the preparation of the bone marrow. The number of progenitors cells that was transplanted was estimated by counting the Fibroblast Colony-Forming Units (FCFUs).

Results: In a normal femoral head the mean number of FCFUs is 33.5 (SD 21.7) per 10^6 bone-marrow cells. The volume of a femoral head is average 60 cubic centimetres. The number of progenitor cells is average 50 FCFUs per cubic centimeter, and the total number of FCFUs is average 3000 FCFUs in an autograft femoral head. In an allograft there are no stem cells before injection of bone marrow. The average volume of bone marrow that we were able to load in the allograft was 6 cc (range 4 to 8), whatever the number of bone marrow we injected in the femoral head and whatever was the method of injection (closing or not the femoral cut). Because bone marrow obtained by aspiration without concentration only contains a mean of approximately 600 progenitors per cubic centimeters (range 12 to 1224 per cubic centimeter, injection of 6 cc of bone marrow in an allograft femoral head will give an allograft with average 3600 progenitor cells, so the same number as in an autograft femoral head (50 FCFUs per cubic centimetre). If we consider that the gold standard for a graft is a piece of bone coming from the iliac crest (600 FCFUs per cubic centimeter), and that our best results were obtained with allograft with bone marrow concentrate, femoral head allograft and perhaps also femoral head autograft should be loaded with bone marrow concentration than can increase the number of stem cells 5 or 10 times according to the device system used for concentration.

Discussion and conclusion: Autograft has been shown to be better than allograft in restoring bone stock because of its osteoconductive, osteoinductive and osteogenic properties. However, because autograft is of poorer quality in elderly patients and postmenopausal women, allograft is used extensively not least because of its ready availability and lack of donor site morbidity. However, allograft does have a number of disadvantages (lack of osteogenic cells and reduced osteoinductive factors). This study has shown that a sterile allograft-autologous marrow composite gives an identical clinical and radiological outcome, and can content after preparation more or an identical number of stem cells as an autograft. The allograft used in impaction grafting is not vascularised; it is therefore unclear how successful incorporation is achieved. Bone ingrowth can be encouraged by osteoinduction, osteoconduction and mechanical loading.

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