Search

Physical exercise is widely recommended to promote bone health and mitigate the detrimental effect of osteoporosis. However, contrasting bone responses to different physical exercise interventions have been shown. The current study hypothesized that different muscle groups have the potential to load the femoral neck to varying levels. A validated finite-element (FE) model of the femur was used in conjunction with a validated musculoskeletal model from the same donor. Maximal isometric contractionsof the hip-spanning muscle groups were simulated for a set of static postures spanning physiological rangesof motion. Strain energy and peak tensile strain in the femoral neck were calculated to evaluatethe influence of hip muscle activity on femoral neckbone mechanics. The hip extensorsinduced the highest levels ofpeak strain and strain energydue to theirsize and location relative to the hip joint. Our results suggest that hip extensor muscle activitymaybe used in exercise interventions designed to maximally stimulate bone growth in the femoral neck.

Background Total hip arthroplasty carried out using cemented modular-neck implants provides the surgeon with greater intra-operative flexibility and allows more controlled stem positioning. Methods In this study, finite element models of a whole femur implanted with either the Exeter or with a new cemented modular-neck total hip arthroplasty (separate, neck and stem components) were developed. The changes in bone and cement mantle stress/strain were assessed for varying amounts of neck offset and version angle for the modular-neck device for two simulated physiological load cases: walking and stair climbing. Since the Exeter is the gold standard for polished cemented total hip arthroplasty stem design, bone and cement mantle stresses/strains in the modular-neck finite element models were compared with finite element results for the Exeter. Findings For the two physiological load cases, stresses and strains in the bone and cement mantle were similar for all modular-neck geometries. These results were comparable to the bone and cement mechanics surrounding the Exeter. These findings suggest that the Exeter and the modular neck device distribute stress to the surrounding bone and cement in a similar manner. Interpretation It is anticipated that the modular-neck device will have a similar short-term clinical performance to that of the Exeter, with the additional advantages of increased modularity.

Hybrid hip resurfacing arthroplasty (HRA), with uncemented acetabular and cemented femoral fixation is increasingly popular as an alternative to total hip replacement. There is concern about femoral neck fractures and long term survival has not yet been demonstrated. Thermal necrosis may be an important factor for neck fracture and will affect the viability of the femoral bone. This cadaveric study investigated the thermal effect of thick (1.5mm, n=3) and thin (0.5mm, n=3) cement mantles; five thermocouples were used to record temperature at the femoral bone/cement interface during HRA. The maximum recorded temperatures were significantly higher when a thick cement mantle is used (45.4 C), compared to a thin cement mantle (32.7 C). In order to reduce the potential for thermal necrosis, the thin cement mantle technique is recommended.