Bo ne Fractal Analysis Gian Pietro Feltrin, MD*, Roberto Stramare, MD, Diego Miotto, MD, Dario Giacomini, MD, and Claudio Saccavini, PhD Address *Radiology Section, D epartment Medical D iagnostic Sciences and Special Therapies, Padua University, Policlinico University H., via Giustiniani, 2, 35128 Padova, Italy. E-mail: giampietro.feltrin@ unipd.it Current Osteoporosis Reports 2004, 2: 53–58 Current Science Inc. ISSN 1544-1873 Copyright © 2004 by Current Science Inc. Introduction The primary aim to evaluate the status o f bo ne metabo lism is to determine the increased fracture risk under several circum- stances. The evaluation of bone fragility is achieved by mea- suring the bo ne mass ( ie, the mineral co ntent thro ugho ut the systems assessing the bone mineral density [BMD]) [1–5]. Unfortunately, BMD does not usually assure the prediction fo r fracture risk because o f a large o verlap o f results in gro ups with or without fractures [6–8]. Multiple methods were pro- posed to evaluate bone fragility and consequently, the risk fo r fracture is substantially arranged o n mineral density o r, in absolute, on the content of calcium [4,6,8,9]. Bone density is evaluated by the attenuation of x-ray by dual energy x-ray absorptiometry (DXA) or by quantitative computed tomography (QCT). The difficulties were assessed and the correct limit was distinguished by the high or low risk for fractures, and were overcome by ade- quately choosing a selection of patient groups, sorted by age, diseases, and history to obtain the best separation between the two groups [2,10,11]. The fragility of bones, physically conceived as a reduction in bone calcium con- tent, may be independent from those aforementioned characteristics and also by a threshold of calcium content. A choice of 108 mg of calcium was used in an attempt to separate the fragile or not fragile bones, and therefore it appears to be completely arbitrary compared with the more realistic values likely defined by age and density. In fact, all patients beyond a certain age ( ie, 65 years) should experience fragility and bone fracture only because they are under the horizontal line of 108 mg of calcium [12]. Ultrasounds are also used to achieve a reliable evalua- tion of bone fragility and as a method to study a complex structure by measuring ultrasound transmission through- out the bone and particularly to determine the acoustic impedance of bone [13–15]. However, the spatial complexity of the cancellous mor- phology determines the impedance of ultrasound. How- ever, the exam most used among bone ultrasound does not directly indicate the architecture, but only the resistance to ultrasound transmission. The parameters obtained by the ultrasound bone studies are speed of sound (SOS) and broadband ultrasound attenuation (BUA) which represent the velocity and the resistance to the sound waves trans- mission. However, they are not directly determined by morphologic bone assessment in images of the studies [16]. Effectively it may be considered that the cortex and cancellous morphology can influence the sound transmis- sion defined by the probe of the machine only by a numer- ical value [17]. Therefore, these considerations could explain the value of the diffuse experiences limited to dis- tinguish normal and osteoporotic patients but not to indi- cate the risk fo r fracture. For many of these reasons, the only measurement of the calcium content achieved questionable results to define the fracture risk, utilizing only numerical values instead of the morphology obtained by some diagnostic means of imaging. In other words the studies of anatomic morphol- ogy of bone seem more adequate to define the architectural constitution of cancellous bones as the most sensitive com- ponent to indicate the metabolism and rearrangement of the bone under aging or disease factors [18,19]. Attempts to assess bone fragility are significantly increased in number, changing the evaluation from mea- surable entity to a morphologic analysis of bones Fractal analysis is a quantitative method used to evaluate complex anatomic findings in their elementary component. Its application to biologic images, particularly to cancellous bones, has been well practiced within the past few years. The aims of these applications are to assess changes in bone and the loss of spongious architecture, indicate bone fragility, and to show the increased risk for fracture in pri- mary or secondary osteoporosis. The applications are very promising to help complete the studies that can define bone density (bone mineral density by dual energy x-ray absorptiometry or quantitative computed tomography), and also have the capacity to distinguish the patients with a high or low risk for fracture. Their extension to the clinical fields, to define a test for fracture risk, is still limited by dif- ficult application to the medical quantitative imaging of bones, between correct application at superficial bones and unreliable application to deep bones. The future evolution and validity do not depend upon fractal methods but upon well-detailed imaging of the bones in clinical conditions.