A small but significant fraction of screw placement in the proximal femur for hip fractures results in iatrogenic fractures associated with the screw hole [1]. There is evidence that the failure occurs under fatigue, and it is likely that those individuals experiencing failure have greater stresses in the proximal femur as dictated by key morphometric variables, such as cortical thickness and bone size. Finite element analysis (FEA) could greatly facilitate fracture risk assessment in the presurgical phase by predicting the local stresses, however, executing FEM in a patient customized fashion would be costly, time consuming, and technically difficult for surgeons to perform.

Hip fractures are among the most common types of osteoporotic fractures that affect one in three women and one in six men over the age of 50 [1]. It is well known that loss of bone mass, quantified by bone mineral density using Dual-energy X-ray Absorptiometry (DXA), is associated with the increasing risk of bone fractures. However, bone mineral density (BMD) alone cannot fully explain changes in fracture risks [2, 3]. In particular, BMD is not able to predict fracture risks for women with osteopenia, in which a BMD T-score is between −1.0 and −2.5. This suggests additional factors (i.e., bone quality) should be considered in predicting fracture risks [4].

Osteoporotic and age-related fractures are a significant public health problem. One of the most common osteoporotic fracture sites in the aging population is distal radius. There is evidence in the literature that distal radius fractures (Colles’ fracture) are an indicative of increased risk of future spine and hip fractures [1]. Therefore, developing new methods for accurate evaluation of human radius fracture risk is necessary. The previous studies showed that geometrical properties of the radius correlate with its fracture load [2]. However, the combined effect of geometrical and material properties on fracture load has not been studied.

Despite the central role of femoral strength in the etiology of osteoporotic hip fractures [1], the associated micromechanical basis of femoral strength remains poorly understood. Cadaver studies [2] using biomechanical testing have established that both the cortical and trabecular bone contribute to the structural integrity of the proximal femur but these studies did not address mechanisms. Addressing mechanisms, theoretical and finite element continuum analyses have assessed cortical-trabecular load sharing and have described stress and strain distributions throughout the proximal femur [1,3]. However, the regions of the bone at highest risk of initial failure remain unclear, in part because the continuum nature and low spatial resolution of these previous analyses render them incapbable of capturing load transfer associated with the microstructure of the trabecular bone and the sometimes thin cortex. Overcoming this limitation, micro-CT-based finite element analysis has recently been applied to the entire proximal femur [4], but so far only two femurs have been analyzed and thus reported trends are difficult to generalize. To extend this recent work and provide further insight into the microstructural basis of femoral strength, we applied micro-CT based finite element analysis to investigate femoral micro-mechanics in a cohort of elderly human proximal femurs.

Annually, in the United States there are roughly 352,000 incidents of hip fractures [1], 300,000 total hip replacements, and 270,000 total knee replacements, most of which are in adults over age 50 [2]. During rehabilitation, patients who have undergone total knee or hip replacement, cartilage cell transplant, cruciate ligament replacement, meniscus debridement, or complex fracture repairs may be instructed to restrict weight bearing. Partial weight bearing (PWB) includes everything from toe-touch to strict PWB (10–50% of the patients’ body weight), to full weight bearing as tolerated [3]. The restrictions following a hip replacement with a cement-less implant typically require a 6-week PWB regimen [4].

Acetabular fractures present a clinical challenge due to the complicated anatomy and difficulty of exposure, reduction, and fixation. There are several indications for surgery including any fracture which is displaced more than 2mm, failure to maintain reduction by closed means, or, for transverse fractures, a roof-arc angle less than 45 degrees (1,2). The last indication was determined by a cadaver model that only evaluated hip stability in the single leg stance phase of the gait cycle (3). Kinesiological models have well established that the magnitude and direction of the joint contact force can deviate substantially from the mechanics of gait loading, particularly for such activities of daily living as sit-to-stand maneuvers and climbing stairs (4,5). Thus, the criteria for fracture stability established using gait-only loading conditions may be inadequate for other activities of daily living. Basic engineering principles would dictate that the most conservative estimate of dislocation potential be used in managing these cases clinically; and it is therefore important to re-evaluate fracture management criteria in alternative loading conditions that have a high potential for dislocation.