The Initial Stability of Femoral Impaction Grafting

Abstract

Aseptic loosening is the major cause of failure in primary total hip replacements. Loss of bone stock occurs in both cementless and cemented implants. Impaction of morsellised allograft represents a major advance in the restoration of bone loss at revision hip surgery. This study was designed to test the early stability of the femoral impaction construct. Polished double tapered stems were inserted into neomedullary canals within impacted allograft in fibreglass femora. Subsidence was measured during cyclical loading. Four methods of impaction grafting were tested: allograft alone; allograft and heparinised blood; allograft/cement/heparinised blood; allograft/cement/clotted blood. Uncemented impaction grafting failed at low loads and few cycles. The cemented technique supported higher loads. Heparinised blood reduced the strength of the composite. Initial stability was achieved with allograft, cement and clotted blood. There is need for caution in the early post-operative period due to the wide variation in initial stability of the allograft composite. The reliability of this technique has been increased by the use of specialised instruments. Experimental studies and clinical experience suggest that this approach to revision surgery is technique dependent.

Factors affecting the cohesion of impaction bone graft

“…21,22 Our clinical practice is to add 5 ml of clotted blood to each 50 g of morsellised femoral head during impaction grafting procedures. 19 We used samples of approximately 5 g and therefore used 0.5 ml of blood per sample. In order to induce clotting, 60 µ l of 1 mol calcium chloride was added to each 0.5 ml sample of blood, which was thoroughly mixed and then left to stand for six minutes in order to activate.…”

“…12 Additional variables, identified as important for stability in laboratory studies, include the presence of clotted blood and bone cement. 19 Many surgeons remain reluctant to use bone-graft extenders because of the different handling and mechanical properties compared with those of allograft. One particular problem in terms of handling is that during the impaction procedure, a large number of extender particles are removed each time the impactors are withdrawn.…”

Impaction bone grafting in revision hip surgery: past, present and future

“…Comparative studies of cemented versus uncemented femoral implants following impaction bone grafting have demonstrated that uncemented femoral implants have inferior mechanical stability (Smith et al 1996). Unfortunately, this biomechanical data is supported by both published reports and results from the Norwegian arthroplasty register, both of which demonstrate poorer outcomes for uncemented femoral components when used in conjunction with impaction grafting.…”

A Hydroxyapatite Graft Substitute Reduces Subsidence in a Femoral Impaction Grafting Model

“…The higher levels of subsidence may have been because blood was not added to the graft material, as this substantially affects graft behavior. 25 Alternatively, it may have been from the use of cadaveric rather than synthetic bones, differences in impaction technique or measurement methods (mechanical rather than RSA), or other differences in the precise experimental design.…”