Mechanical considerations in impaction bone grafting

Abstract

In impaction grafting of contained bone defects after revision joint arthroplasty the graft behaves as a friable aggregate and its resistance to complex forces depends on grading, normal load and compaction. Bone mills in current use produce a distribution of particle sizes more uniform than is desirable for maximising resistance to shear stresses.We have performed experiments in vitro using morsellised allograft bone from the femoral head which have shown that its mechanical properties improve with increasing normal load and with increasing shear strains (strain hardening). The mechanical strength also increases with increasing compaction energy, and with the addition of bioglass particles to make good the deficiency in small and very small fragments. Donor femoral heads may be milled while frozen without affecting the profile of the particle size. Osteoporotic femoral heads provide a similar grading of sizes, although fewer particles are obtained from each specimen. Our findings have implications for current practice and for the future development of materials and techniques.

Influence of water and fat content on compressive stiffness properties of impacted morsellized bone: An experimental ex vivo study on bone pellets

“…In this study, the physical properties of the loose unmodified bone were comparable to findings in corresponding studies (Brodt et al 1998, Brewster et al 1999, Bavadekar et al 2001, Verdonschot et al 2001. Mechanically, the bone pellets were characterized by their axial stiffness.…”

“…Extracting water chemically could change the character of proteins, as might temperatures above 40°C. Centrifuging the bone mass could change the size and distribution, with unpredictable effects on mechanical behavior (Brewster et al 1999). Granulate moisture influences mechanical behavior (Giesen et al 1999, Ullmark and Nilsson 1999, Voor et al 2000, Dunlop et al 2003.…”

“…Early axial subsidence and torsion may disturb the geometry of the implant system and hence reduce the durability of the revised prosthesis (Franzén et al 1995, Eldridge et al 1997, Brodt et al 1998, Ornstein et al 2002. Various factors influence the mechanical stability of impacted bone: particle size and grading (Brewster et al 1999, Ullmark 2000, moisture (Voor et al 2000, Dunlop et al 2003, addition of bone substitutes (Verdonschot et al 2001), and impaction energy (Ullmark 2000, Fosse et al 2004. Despite extensive application, the significance and function of several of these factors is obscure.…”

Factors Influencing the Stability of Stems Fixed with Impaction Graft in Vitro

“…Several studies experimentally investigated the mechanical properties of impacted bone particles [5,6], but the bone particles were compacted into the cylindrical camber; thus, these conditions are different from those when bone particles are impacted in the femoral canal. In fact, the size distribution of bone particles depends on the type of bone mill.…”

Biological and mechanical changes of the bone graft–cement interface after impaction allografting

“…Extensive reseaxch has focused on characterizing the allograft layer in vitro [5,6,17], allograft incorporation [25,34,41], and the evaluation of bone graft substitutes [3,19,43]. Although important for the success of any THR, the interface between the host cortex and the graft material has not been addressed for impaction allografting.…”