For millions of patients world-wide, primary total hip replacement (THR) is
an effective way to improve quality of life. Failed THRs are often associated with
extensive bone loss which makes the revision difficult. An established technique
uses impacted morsellized allograft bone to reconstruct the proximal femur and
ensure a rigid accommodation of the cemented revision component. There
remains a fundamental lack of understanding of the impaction allografting
procedure and its complications, particularly with its morphology and
biomechanical characteristics.
The objectives of this thesis were to i) describe the morphology after
impaction allografting in the femur, ii) incorporate a computer simulation that
should help the orthopaedic surgeon to control the morphology during surgery, iii)
determine how the morphology affects the immediate strength of the host bone
interface, and iv) develop an animal model to investigate the changes in
composite morphology and strength with postoperative healing.
Around the middle third of the stem, virtually the entire femoral canal was
filled with cement, thereby forming a cement-allograft composite, whereas in
other locations a pure allograft-host bone interface was found. The computer
simulation suggested that cement penetration could be controlled by varying graft
impaction and limiting cement volume injection. Cement penetration up to the
endosteal surface significantly enhanced the host bone interface strength. In the animal study, the strength of the composite-host bone interface increased
significantly at 3 weeks and was higher than the pure allograft construct. In
contrast to the composite, the pure allograft construct failed at the cement-allograft
interface. At 6 weeks the interface strength of the composite decreased,
presumably due to cortical cancellation caused by damaged endosteal
circulation.
Cement penetration to the endosteal surface appears to be important for
immediate postoperative clinical stability. However, the presence of the cement
does not allow reconstitution of the host bone stock. Cortical cancellisation and
medullary canal widening caused by a damaged endosteal circulation may be
responsible for clinically unstable implants postoperatively. These findings
suggest that the optimal reconstruction provide clinical stability without the
, cement reaching the endosteal surface, thereby enabling revascularisation and
subsequent bone remodelling.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat