Autograft Versu Allograft

Autograft versus allograft with or without demineralized bone matrix in posterolateral lumbar fusion in rabbits.

Julio Urrutia M.D.

Daniel Apablaza M.D.

Felipe Pizarro M.D.

Nicolás Thumm M.D.

Alejandro Zylberberg M.D.

Rodrigo Mardones M.D.




* Department of Orthopaedics Surgery Pontificia Universidad Católica de Chile.


Abstract


Introduction: Posterolateralspinal fusion is performed to treat different spinal diseases. Autograft continues to be the gold standard graft on healing rate. However it is associated with donor side morbidity and limited source. Allograft has been used for spinal fusion, although lower fusion rates have been reported. Demineralized bone matrix (DBM) has been used to increase the fusion rate in different critical defect models.Different forms demineralized bone matrixes available are a potential clinical alternative in achieving this goal. Our goal was to evaluate the effect of a specific DBM presentation when added to allograft in the healing rate of spine posterolateral fusion in a rabbit model. We compared it with allograft alone and autograft.


Method: Forty-five New Zealand male rabbits underwent a bilateral,one level (L4-L5) intertransverse process fusion. Bilateral iliac crest bone graft was harvested from each rabbit, in order to obtain corticocancellous graft. The rabbits where randomly divided in three groups: Group I: Autograft 15 rabbits, Group II: Allograft 15 rabbits and Group III: Allograft plus paste demineralized bone matrix (Dynagraft®). The animals where euthanized eight weeks aftersurgery. The fusion was analyzed radiographically and by manual palpation by two independent observers. Fusion was defined when both criteria where present. The rate of fusion in each group was compared using Fisher’s exact test and Chi-square test.


Results: The fusion rate was 45% (7 of 15 rabbits) in the autograft group, 33% (5 of 15 rabbits) in the allograft group and 33% (5 of 15 rabbits) inthe allograft plus past DBM group. No significant difference was found among the three groups (p>0.05).


Discussion: A demanding criteria to define fusion and the variables related with a challenged surgical model may explain in part the low rate of fusion observed with autograft. However this correlated with clinical and previous experimental findings in this model. A trend toward betterfusion rate with autograft compared to allograft was observed. Because the limited sizes of the samples no significant difference was shown between autograft and allograft. By power analysis a study group of at least 300 rabbits would be needed when the same fusion criteria are applied to find a significant difference between this two groups with this model (Autograft v/s Allograft alone). Theaddition of DBM to allograft in a paste presentation (Dynagraft®) did not increase the fusion rate in this model when compared to allograft alone.


Introduction

Posterolateral spinal fusion is performed to treat different spinal diseases, such as deformities, infections, traumatic, tumoral, and degenerative conditions. This spinal surgery has been associated to high non union rates(1,2);instrumentation has partially diminished this complication (3,4).
Autograft, usually harvested from the iliac crest, is the gold standard to reach fusion, even when it is associated with donor site morbidity (local pain, infection, bleeding, etc.) and limited supply (5-9).
There are many clinical situations which make grafts alternatives desirable, like long spinal fusions and patientsin whom iliac crest bone graft has already been harvested.
Allograft has been used for spinal fusion as an autograft extender or substitute. Allograft is highly osteoconductive, poorly osteoinductive and does not contribute with osteogenic cells (10). There is also the possibility of disease transmission and immune response (11,12). It has lower fusion rates than autograft when used for...