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Journal of Orthopaedic Research
Journal of Orthopaedic Research 23 (2005)1035-1046
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Pulsed electromagnetic field treatments enhance the healing of fibular osteotomies Ronald J. Midura Michael 0. Ibiwoye Kimerly A. Powell Yoshitada Sakai a, Todd Doehring a, Mark D. Grabiner Thomas E. Patterson ', Maciej Zborowski a, Alan Wolfman
a,
Department of Biomedical Engineering, The Orthopaedic Research Center. Lerner Research Institute of The Cleveland Clinic Foundation, Cleveland, OH 44195, USA Department of Movement Sciences, University of Illinois at Chicago, Chicago, IL 60608, USA ' Department of Cell Biology, Lerner Research Institute of The Cleveland Clinic Foundation, Cleveland, OH 44195, USA a
Received 16 August 2004; accepted 14 March 2005
Abstract
This study tested the hypothesis that pulsed electromagnetic field (PEMF) treatments augment and accelerate the healing of bone trauma. It utilized micro-computed tomography imaging of live rats that had received bilateral 0.2 mm fibular osteotomies (-0.5% acute bone loss) as a means to assess the in vivo rate dynamics of hard callus formation and overall callus volume. Starting 5 days post-surgery, osteotomized right hind limbs were exposed 3 h daily to Physio-Stim@PEMF, 7 days a week for up to 5 weeks of treatment. The contralateral hind limbs served as sham-treated, within-animal internal controls. Although both PEMF- and sham-treatment groups exhibited similar onset of hard callus at -9days after surgery, a 2-fold faster rate of hard callus formation was observed thereafter in PEMF-treated limbs, yielding a 2-fold increase in callus volume by 13-20 days after surgery. The quantity of the new woven bone tissue within the osteotomy sites was significantly better in PEMF-treated versus sham-treated fibulae as assessed via hard tissue histology. The apparent modulus of each callus was assessed via a cantilever bend test and indicated a 2-fold increase in callus stiffness in the PEMF-treated over sham-treated fibulae. PEMF-treated fibulae exhibited an apparent modulus at the end of 5-weeks that was -80% that of unoperated fibulae. Overall, these data indicate that Physio-Stim@PEMF treatment improved osteotomy repair. These beneficial effects on bone healing were not observed when a different PEMF waveform, Osteo-Stim@,was used. This latter observation demonstrates the specificity in the relationship between waveform characteristics and biological outcomes. 0 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Introduction
Abbreviations: PEMF, pulsed electromagnetic field; Micro-CT, micro-computed tomography; ROI, region of interest. * Corresponding author. Address: Department of Biomedical Engineering, ND20, Lerner Research Institute of The Cleveland C h i c Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA. Tel.: +1 216 445 3212; fax: + I 216 445 4383. E-mail address:
[email protected] (R.J. Midura). These authors contributed equally to this work.
'
Approximately 2 million cases of delayed and nonunion fractures OCCUr annually [161, and this prevalence drives continuing research to develop more effective treatments to help heal these recalcitrant fractures. several published studies have reported on the successful use of non-invasive, pulsed electromagnetic field (PEMF) tfeatments for improving bone healing in delayed- and non-union fractures [7,43,6,9,40,21,18,11,
0736-02666- see front matter 0 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved doi: 10.1016/j.orthres.2005.03.0l5
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R.J. Miduru et al. I Journal of Orrhopaedir Research 23 (2005) 1035-1046
2,34,13]. Nevertheless, even when comparing separate randomized, double-blinded, prospective studies involving large numbers of test subjects [28,36], there are conflicting interpretations of whether PEMF exhibits clinically significant improvements in new bone tissue production. Thus, despite its FDA approval for clinical use, PEMF treatment has not been widely accepted within the orthopaedic community because of this continuing debate regarding its clinically beneficial effects [7,43,36,28,5]. Better-defined studies using animal models have also been used to evaluate the effectiveness of PEMF on bone healing, but here again the interpretations are conflicting [32,12,39,22,19]. Four limitations are apparent in the research designs of these previous studies, which may have influenced their outcome interpretations. Firstly, most previous studies based their interpretations on only one quantitative outcome measure (e.g., mechanical strength testing), with the remaining outcome measures being of a more qualitative nature (e.g., observer-based clinical and radiological scoring, patients’ responses to pain questionnaires, or evaluation of 2D histological sections). The inability to measure values from these qualitative parameters and correlate them with the values obtained from the quantitative parameters seems to have contributed to some ambiguity in the overall interpretations. One technical limitation apparent in this literature, the use of planar X-ray image scoring, can be rectified by the use of in vivo micro-computed tomography (micro-CT) to achieve a quantitative assessment of newly formed bone tissue volumes during fracture healing in vivo. Secondly, there has been a general lack in the documentation of standardized bone trauma in several previous experimental fracture studies [4], which may have resulted in technical variations and further difficulties with comparison and interpretation of the observed PEMF effects. A review of the literature indicates that the degree of damage to bone and soft tissue during a fracture, and the mechanical stability of the fracture, have great influences on the quality and quantity of callus subsequently formed and on the healing pattern of the fracture [3,4,16,30,31,26,27,37,38]. Thus, without adequate documentation to establish similar levels of bone trauma, the bone healing responses would inherently exhibit a large variation in the measured outcome parameters that could only be accounted for by using extremely large test populations. A third limitation relevant to many of these animal studies is whether PEMF treatments began shortly after fracture or osteotomy, or whether the bone trauma was allowed to progress to a quiescent state, modeling a delayed or non-union phenotype before PEMF treatments were initiated. Little is known about this aspect, but it has been reported that both human bone fractures and osteotomies in animal models responded more vigor-
ously to PEMF treatments when treatment began soon after trauma [32], than when treatments began well after the bone trauma had progressed to a quiescent state [25]. Thus, variation in the time after bone trauma of when PEMF treatments were initiated may have contributed to some of the reported variability in healing effectiveness. The fourth limitation relates to whether the quality of the PEMF treatments with respect to their spectral characteristics and energy output are additional factors that need to be considered when assessing the efficacy of PEMF treatments. In this regard, previous studies have generally used a single PEMF waveform, and did not take into account the possibility that the specific waveform characteristics may have been outside a spectral and energy range necessary for imparting biological effects. Thus, a side-by-side comparison of distinct PEMF waveform treatments on bone healing within the same study would be an important contribution to this question, in particular, and this field of study, in general. Given the current uncertainty as to whether PEMF treatments extend beneficial effects to the healing of bone fractures, the purpose of the present study was to test the hypothesis that PEMF treatments would augment and accelerate healing of a substantial-sized bone trauma. Its experimental design circumvented the previously mentioned limitations via four combined approaches. First, it used standardized bilateral fibular osteotomies, thereby providing a sham-treated control limb within each animal to reduce the influences of between-animal variability in natural physiology. Second, it employed longitudinal in vivo micro-CT imaging to quantitate the dynamic changes in hard callus volume during in vivo bone healing after exposure to daily PEMF therapy or sham-treatments. These volumetric measures as a function of healing time were used to calculate rates of hard callus formation. Both the measured bone volumes and the calculated rates of hard callus formation were correlated with a quantitative assessment of the relative bending strength of the fibulae after 5-weeks of healing. Third, in contrast to our earlier study in which PEMF treatments began well after the bone trauma had progressed to a non-united state [25], the current study started PEMF treatments relatively soon after osteotomy surgery. This approach enabled us to assess directly whether bone trauma in the same animal model would respond more vigorously to the same PEMF treatments when treatment began soon after trauma. Finally, we explored a side-by-side comparison of two distinct PEMF waveform treatments on the healing response of the same type of bone trauma. This approach was used to test the hypothesis that the spectral characteristics and energy output of PEMF waveforms would influence their bone healing effectiveness.
R J. Midura et al. I Journal of Orthopaedic Research 23 (2005) 1035-1046
Materials and methods Animals and operative techniques
All animal procedures used in this study were reviewed and approved by the Institutional Animal Care and Use Committee. A total of 15 adult male Sprague Dawley rats (Harlan, USA) weighing 500600 g were used in this study: 8 animals were assigned to Physio-Stim@ and 7 were assigned to Osteo-Stim@experiments. The rats were housed in individual cages in the Central Animal Fac identical conditions and allowed access to food and water ad libitum. We selected a 0.2 mm fibula diaphyseal osteotomy as a model of standardized bone trauma, representing an acute bone volume loss of close to 0.5%. The unique anatomical arrangement of the rodent tibidfibula unit enables the larger and stronger tibia to provide natural stability against the mechanical effects of the animal's weight and locomotor activities on the healing of fibular osteotomies without applying external splinting or intramedullary fixation [lo]. Such a model isolates and accentuates the natural healing processes in the absence of the known influences of external or internal fixators on bone repair [17,35]. Bilateral fibular osteotomies were performed using a modification of a previously described procedure [25]. A small portion of bone was removed (0.20 ? 0.04 mm), complete with the periosteal covering, from the fibula approximately at the junction between the middle and lower third of the diaphysis using a high-speed rotary saw-toothed blade pre-cooled to 4 "C with sterile physiological saline containing Gentamicin (Sigma, USA 50 pg/ml) and Fungizone (Life Technologies, USA: 2.5 pg/ml). Care was taken to avoid damaging the surrounding soft tissues. Marcaine in isotonic saline (Abbott Laboratories, USA; 0.5%) was applied to the osteotomy site as a local anesthetic, and the skin was closed with 2-0 silk interrupted sutures (Ethicon Inc., USA). Bacitracin ointment (Clay Park Laboratories, USA; 500 units) was applied to the closed surgical wound. Rats were allowed unrestricted cage activities and were examined daily and weighed twice weekly. Two rats in this study exhibited only minor weight loss (
