Determination of mechanical properties of impacted human morsellized cancellous allografts for revision joint arthroplasty

Efficient use of a limited resource femoral head allograft: A comparison of allograft preparation methods

PURPOSE

The purpose of the study was to compare the yield and compressed volume of femoral head allograft prepared by either hand morselization or a bone mill.

METHODS

Twenty human femoral head allografts were donated from a bone bank and morselized by two different methods. The heads were divided in half and split into two sample groups. One group underwent hand morselization with large bone nibblers, while the other was prepared using a bone mill. The volume of graft produced was measured. Ten-gram aliquots of each sample then underwent 30 impactions in a contained cavity, with the volume of graft compression measured.

RESULTS

Bone milling yielded approximately 31% more usable graft than hand morselization (81% to 50%; p = 0.0001). There was no difference between the compressed volume of graft prepared by either method ( p = 0.14).

CONCLUSION

This study demonstrates the efficacy of preparation of allograft with a bone mill and assists the clinician in determining the yield of graft by the weight of femoral head, thereby potentially minimizing excessive ordering and wastage.

A novel technique for impaction bone grafting in acetabular reconstruction of revision total hip arthroplasty using an ex vivo compaction device

BACKGROUND

Impaction bone grafting allows restoration of the acetabular bone stock in revision hip arthroplasty. The success of this technique depends largely on achieving adequate initial stability of the component. To obtain well-compacted, well-graded allograft aggregates, we developed an ex vivo compaction device to apply it in revision total hip arthroplasty on the acetabular side, and characterized mechanical properties and putative osteoconductivity of allograft aggregates.

METHODS

Morselized allograft bone chips were compacted ex vivo using the creep technique and subsequent impaction technique to form the bone aggregates. Impaction allograft reconstruction of the acetabulum using an ex vivo compaction device was performed on eight hips. The mechanical properties and three-dimensional micro-CT-based structural characteristics of the bone aggregates were investigated.

RESULTS

In clinical practice, this technique offered good reproducibility in reconstructing the cavity and the segmental defects of the acetabulum, with no migration and no loosening of the component. In vitro analysis showed that the aggregates generated from 25 g fresh-frozen bone chips gained compression stiffness of 13.5-15.4 MPa under uniaxial consolidation strain. The recoil of the aggregates after compaction was 2.6-3.9%. The compression stiffness and the recoil did not differ significantly from those measured using a variety of proportions of large- and small-sized bone chips. Micro-CT-based structural analysis revealed average pore sizes of 268-299 μm and average throat diameter of pores in the bone aggregates of more than 100 μm. These sizes are desirable for osteoconduction, although large interconnected pores of more than 500 μm were detectable in association with the proportion of large-sized bone chips. Cement penetration into the aggregates was related to the proportion of large-sized bone chips.

CONCLUSION

This study introduces the value of an ex vivo compaction device in bone graft compaction in clinical applications. In vitro analysis provided evidence that compaction of sequential layers of well-compacted, well-graded bone aggregates, i.e., the aggregates comprising smaller sized chips at the host bone side and larger sized chips at the component side, may have the advantages of initial stability of the acetabular component and biological response of the grafted aggregates.

Influence of cement penetration and graft density on stem stability in impaction allografting: a finite element study

BACKGROUND

Excessive stem migration is often problematic after impaction allografting. The mechanisms responsible for migration are not known, but achieving a dense graft bed has traditionally been believed to be essential for stem stability. When the stem is cemented into the allograft bed, however, the graft becomes infiltrated with bone cement. Extensive cement penetration into the graft has been observed in previous studies, resulting in regions of cement-endosteum contact.

METHODS

This study explored the effects of graft density and cement penetration on stem motion using a finite element model that was validated against experimental data.

FINDINGS

Cement penetration has a considerable stabilizing effect on stem motion, whereas graft density is important only when there is no cement-endosteum contact. Stem migration can be attributed primarily to slippage at the endosteum and stem-cement interfaces rather than to shear failure within the graft.

INTERPRETATION

Partial cement penetration to the endosteum increases the likelihood of meeting clinical requirements of early implant stability, particularly when a dense graft bed cannot be achieved.