Changes in proximal femoral strain after insertion of uncemented standard and customised femoral stems

Abstract

We have compared the changes in the pattern of the principal strains in the proximal femur after insertion of eight uncemented anatomical stems and eight customised stems in human cadaver femora. During testing we aimed to reproduce the physiological loads on the proximal femur and to simulate single-leg stance and stair-climbing.The strains in the intact femora were measured and there were no significant differences in principal tensile and compressive strains in the left and right femora of each pair. The two types of femoral stem were then inserted randomly into the left or right femora and the cortical strains were again measured. Both induced significant stress shielding in the proximal part of the metaphysis, but the deviation from the physiological strains was most pronounced after insertion of the anatomical stems.The principal compressive strain at the calcar was reduced by 90% for the anatomical stems and 67% for the customised stems. Medially, at the level of the lesser trochanter, the corresponding figures were 59% and 21%. The anatomical stems induced more stress concentration on the anterior aspect of the femur than did the customised stems. They also increased the hoop strains in the proximomedial femur. Our study shows a consistently more physiological pattern of strain in the proximal femur after insertion of customised stems compared with standard, anatomical stems. [Br] 2001;83-B:921-9. J Bone Joint Surg

Internal fixation of fragility fracturesof the femoral neck

“…Our laboratory has traditionally used fresh frozen femurs for biomechanical experiments (Aamodt et al 2001, Wik et al 2010) and fresh frozen femurs were chosen accordingly. During the course of our study embalmed femurs were shown to provide similar mechanical properties to fresh frozen ones and could have been an alternative (Topp et al 2012).…”

“…Although it is possible to apply torque in constrained femurs (Brandt et al 2006), more degrees of freedom in the hip-jig make a separate application of torque possible. The torque can then be applied to the femoral head (Deneka et al 1997) or the distal diaphysis (Aamodt et al 2001).…”

The effect of a lateral flare feature on implant stability

“…Femoral components that engage the metaphysis and load the femur both medially and laterally are inherently more stable [1,4,12]. The stem does not need to be 'press-fitted' into the femur or driven distally (interference fit) in the diaphysis to achieve initial stability.…”

Differences in stability and bone remodeling between a customized uncemented hydroxyapatite coated and a standard cemented femoral stem A randomized study with use of radiostereometry and bone densitometry

“…Our findings of the Unique stem are in agreement with this. Thus, the 2 year bone remodeling around the custom-made stem does not seem to reflect the retention of the postoperative cortical strains that has been demonstrated experimentally [3]. Two studies of stems with reduced stiffness have shown either a reduced loss in BMD or a gain of BMD [8,18].…”