Elsevier

Bone

Volume 49, Issue 4, October 2011, Pages 600-604
Bone

Perspective
Investigation of differences between hip fracture types: A worthy strategy for improved risk assessment and fracture prevention

https://doi.org/10.1016/j.bone.2011.07.022Get rights and content

Introduction

The clinical assessment of hip fracture risk is still to a large extent based on areal bone mineral density (BMD) measured by dual X-ray absorptiometry (DXA). According to the definition of osteoporosis, however, architectural deterioration of bone tissue also contributes to increases in bone fragility and susceptibility to fracture [1]. This may be one reason why the majority of fractures occur among individuals with BMD in the non-osteoporotic range [2], [3]. Consequently, the paradigm for fracture risk assessment had to be broadened to comprehensive risk assessment, covering “the sum total of characteristics of the bone that influence the bone's resistance to fracture” [4]. A WHO Scientific Group has recently recommended using an individual's 10-year fracture risk to guide therapy decisions. The fracture risk assessment tool (FRAX®) developed for this purpose takes into account selected clinical risk factors (age, sex, weight, previous fractures, the parents' history of hip fractures, current smoking, using of glucocorticoids, rheumatoid arthritis, secondary osteoporosis and alcohol consumption) with or without BMD [5]. However, we have already evidence that even FRAX is not sufficient to capture the complexity of factors affecting fracture risk [6], [7], [8], [9], [10], [11]. In fact it is a drawback of generic fracture risk assessment tools that they are optimized for the population and thus have limitations for risk assessment in individuals with more unusual combinations of risk factors. The fact that clinical risk factors, whether included or not included in FRAX, independently contribute to fracture risk provides a strong indication that our diagnostic techniques do not yet succeed to measure bone fragility in a sufficiently comprehensive and thus accurate way. How could we improve this situation? For example, finite element techniques permit modeling of different loading conditions and such analyses would provide improved insight into fracture mechanics and guide the development of refined techniques, e.g. based on computed tomography.

Hip fractures are the most problematic outcome of osteoporosis. In this perspective, we suggest that one potential reason for the current limits of hip fracture risk assessment may relate to the neglect of etiological and pathophysiological diversity of (a minimum of two) different types of hip fractures. We suggest that we can improve risk assessment and fracture prevention if we tailor diagnostic techniques according to the specific type of hip fracture to be predicted. For example, mechanical indices that reflect fracture type specific fragility aspects should be tested for their predictive power in prospective studies that monitor hip fracture type.

Section snippets

Cervical and trochanteric hip fractures

Hip fractures can be classified into two main categories, cervical (intracapsular) and trochanteric (extracapsular) fractures. These may further be divided into subgroups depending on the level of the fracture and the presence or absence of displacement and comminution [12]. Orthopedic surgeons and other experts in osteoporosis are well cognizant not only of the different phenotypes of these subgroups of hip fractures, but also that their clinical treatment differs [12] and that they also

Differences in skeletal density and structure

Cervical and trochanteric fractures show substantial differences both in morphology and structure. Bone composition in the trochanteric region is rather similar to that of vertebra, involving about 70% to 90% trabecular bone [13], [19]. Indeed, it has been demonstrated that previous vertebral fractures are twice as common in patients with trochanteric fracture compared to those with cervical fracture [13]. It has also been shown that women with trochanteric fractures have a more severe and

Differences in risk factors

Not only skeletal characteristics but also clinical risk factors, general health status, functional outcome as well as mortality have been shown to differ between patients with different fracture types [35], [36], [37]. Age is a major clinical risk factor for hip fracture and recent epidemiological data suggests that differences in the age-related increase in risk reflect the differing pathophysiological processes of cervical and trochanteric fractures. In a review of 15 published reports,

Falling mechanisms may also influence fracture types

It has been suggested that the strongest risk factor for a fracture is falling and the type and severity of falling are crucial in determining whether a fracture occurs [49], [50], [51], [52], [53], [54], [55]. In persons over 65 years of age, falls are the main etiological factor in over 90% of hip fractures, and a history of falls is associated with an increased risk of hip fractures [56], [57], [58], [59]. A sideways fall increases the risk of hip fracture three to five times, and the risk is

Diagnostic potential

Recent improvements in imaging technology may allow to noninvasively measure several of the aforementioned aspects of density and structure. Quantitative Computed Tomography (QCT) permits separate evaluation of trabecular and cortical bone envelopes, as well as specific subsections of these, e.g. of those segments of the femoral neck shown to have particular relevance for bone fragility. Advanced image processing approaches permit accurate assessment of cortical thickness at the proximal femur

Potential for prevention and therapy

Recognition of the differing etiologies of hip fracture types may also open up improved strategies for prevention and therapy. Bone is able to adapt to different loading conditions, as Julius Wolff presented as early as 1892 [71] and thus there is potential for tailored physical exercise to specifically target the weakest structures. Indeed, the study of Grahn Kronhed et al. announces urgent needs for targeted site-specific exercises [72]. In this study, the impact of community-based

Summary

There is ample evidence that etiology and pathophysiology differ between cervical and trochanteric hip fractures and as a consequence substantial differences in density patterns, structure and risk factors are observed. With QCT we now have a diagnostic tool to non-invasively measure several of these characteristics. Recognition of hip fracture type specific features is likely to improve patient-specific risk assessment. Given the differing treatment effects of current and forthcoming

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