Effects of femoral bone defect morphology on initial polished tapered stem stability in massive defect model: a biomechanical study

BackgroundGood outcomes have been reported in revision total hip replacement with massive segmental defects using impaction bone grafting with circumferential metal meshes. However, the morphology of defects that require a mesh is poorly defined. The purpose of this study was to evaluate the effects of a variety of segmental defects on load transmission to the proximal femur under both axial and rotational loads.MethodsInitial stability of the Exeter stem was investigated in a composite bone model using three medial bone defect morphologies: Long (length 5cmxwidth 2cm), Short (2.5cmx2cm), Square (3.2cmx3.2cm), Square with mesh (3.2cmx3.2cm defect covered with metal mesh), and with no defect as control. Specimens (5 per group) were axially loaded and internally rotated up to 20 degrees or to failure. Strain distributions of the femora were measured using a strain gauge.ResultsAll Square group specimens failed while rotation was increasing. In the other four groups, failure was not observed in any specimens. Mean torsional stiffness in the Long (4.40.3Nm/deg.) and Square groups (4.3 +/- 0.3Nm/deg.) was significantly smaller than in the Control group (4.8 +/- 0.3Nm/deg.). In the medio-cranial region, the magnitude of the maximum principal strain in the Square group (1176.4 +/- 100.9) was significantly the largest (Control, 373.2 +/- 129.5, p<0.001; Long, 883.7 +/- 153.3, p=0.027; Short, 434.5 +/- 196.8, p<0.001; Square with mesh, 256.9 +/- 100.8, p