Atypical subtrochanteric femoral shaft fractures: role for mechanics and bone quality

Bisphosphonates are highly effective agents for reducing osteoporotic fractures in women and men, decreasing fracture incidence at the hip and spine up to 50%. In a small subset of patients, however, these agents have recently been associated with ''atypical femoral fractures'' (AFFs) in the subtrochanteric region or the diaphysis. These fractures have several atypical characteristics, including occurrence with minimal trauma; younger age than typical osteoporotic fractures; occurrence at cortical, rather than cancellous sites; early radiographic appearance similar to that of a stress fracture; transverse fracture pattern rather than the familiar spiral or transverse-oblique morphologies; initiation on the lateral cortex; and high risk of fracture on the contralateral side, at the same location as the initial fracture. Fracture is a mechanical phenomenon that occurs when the loads applied to a structure such as a long bone exceed its load-bearing capacity, either due to a single catastrophic overload (traumatic failure) or as a result of accumulated damage and crack propagation at sub-failure loads (fatigue failure). The association of AFFs with no or minimal trauma suggests a fatigue-based mechanism that depends on cortical cross-sectional geometry and tissue material properties. In the case of AFFs, bisphosphonate treatment may alter cortical tissue properties, as these agents are known to alter bone remodeling. This review discusses the use of bisphosphonates, their effects on bone remodeling, mechanics and tissue composition, their significance as an effective therapy for osteoporosis, and why these agents may increase fracture risk in a small population of patients.     

Pathological fractures of the femoral neck

In a review of subcapital fractures due to metastases in the femoral neck it was found that in the majority of cases pain in the region of the hip developed a few days prior to fracture. While the majority of subcapital fractures are sustained as the result of a single incident of trauma, in cases with metastases trabecular stress fractures occur in increasing numbers until finally femoral neck fracture occurs. It would seem that once a critical number of trabecular stress fractures has been reached the patient develops pain. Immediate radiologic examination should be performed, and if there is evidence of bone destruction approaching 50% of the cortex, prophylactic hip pinning is strongly indicated.     

Metabolic syndrome: a brain disease

Recent research indicates an association between brain dysfunction and the pathogenesis of metabolic syndrome. To investigate this, we created a Medline search (up to December 2011) of articles in PubMed. The results indicated that refined carbohydrates, saturated and total fat, high levels of ω-6 fatty acids, and low levels of ω-3 fatty acids and other long chain polyunsaturated fatty acids (PUFA), all in conjunction with sedentary behaviour and mental stress can predispose to inflammation. Increased sympathetic activity, with increased secretion of catecholamine, cortisol, and serotonin can cause oxidative stress, which may damage the arcuate nucleus as well as the hypothalamus and macrophages, and the liver may release pro-inflammatory cytokines. These, in conjunction with an underlying deficiency in long chain PUFA, may damage the arcuate nucleus as well as neuropeptide-Y and pro-opiomelanocortin neurons and insulin receptors in the brain, especially during fetal life, infancy, and childhood, resulting in their dysfunction. Of the fatty acids in the brain, 30%-50% are long chain PUFA, which are incorporated in the cell membrane phospholipids. Hence, ω-3 fatty acids, which are also known to enhance parasympathetic activity and increase the secretion of anti-inflammatory cytokines interleukin (IL)-4 and IL-10 as well as acetylcholine in the hippocampus, may be protective. Therefore, treatment with ω-3 fatty acids may be applied for the prevention of metabolic syndrome.     

Regional survey of femoral neck fractures.

In the South-west Thames Region 2619 patients (2105 women and 514 men) were discharged with a diagnosis of femoral neck fracture in 1974. The equivalent of a 250-bedded hospital was occupied throughout the year. The incidence, average length of stay, and mortality rate rose with increasing age and there were differences in these indices in the five health areas. These results confirm the enormous burden placed on the hospital service by patients with fracture of the femoral neck but suggest that differences in practice in the five areas may contribute to the size of the problem.     

Metabolic bone disease resembling osteosarcoma in a wooly monkey (Lagothrix lagotricha).

A female pet wooly monkey with metabolic bone disease initially presented with a proliferating bony mass in the left humerus which had many features of osteosarcoma. At necropsy, parathyroid hyperplasia, osteoclastic resorption, proliferative osteoid deposition in the calvarium and cortex of long bones, and fibrous proliferation of the marrow indicated the presence of generalized osteodystrophia fibrosa. The dietary history of deficient vitamin D3 and protein and minimal exposure to sunlight supported this diagnosis, as did depressed levels of serum calcium and elevated levels of serum parathyroid hormone, alkaline phosphatase, and acid phosphatase.     

Linear and nonlinear analyses of femoral fractures: Computational/experimental study

This paper describes two new methods for computational fracture analysis of human femur using Quantitative Computed Tomography (QCT) voxel-based finite element (FE) simulation. The paper also reports comprehensive mechanical testing for validation of the methods and evaluation of the required material properties. The analyses and tests were carried out on 15 human femurs under 11 different stance-type loading orientations. Several classical forms of subcapital, transcervical, basicervical, and intertrochanteric fractures plus a specific type of subtrochanteric fracture were created and analyzed. A new procedure was developed for prediction of the strengths and the fracture initiation patterns using a FE-based linear scheme. The predicted and observed fracture patterns were in correspondence, and the FE predictions of the fracture loads were in very good agreement with the experimental results. Moreover, the crack initiation and growth behaviors of two subtrochanteric fractures were successfully simulated through a novel implementation of the cohesive zone model (CZM) within a nonlinear FE analysis scheme. The CZM parameters were obtained through a series of experimental tests on different types of specimens and determination of a variety of material properties for different anatomic regions and orientations. The presented results indicated that the locations and patterns of crack initiation, the sequences of crack growth on different paths, and the compatibility of growth increments agreed very well with the observed specifications. Also, very good agreements were achieved between the measured and simulated fracture loads.