Diffusion Tensor Imaging To Assess Triceps Surae After Achilles Tenotomy In Rats.

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1 Diffusion Tensor Imaging To Assess Triceps Surae After Achilles Tenotomy In Rats. Yusuke Hara 1, Kazuya Ikoma, MD, PhD 1, Tsuyoshi Sukenari 1, Yuji Arai 1, Yasuo Mikami 1, Hiroyoshi Fujiwara 1, Takashi Yoshida 1, Yoshinobu Oka 1, Mitsuhiro Kawata 2, Toshikazu Kubo 1. 1 Department of Orthopaedics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan, 2 Department of Anatomy and Neurobiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan. Disclosures: Y. Hara: None. K. Ikoma: None. T. Sukenari: None. Y. Arai: None. Y. Mikami: None. H. Fujiwara: None. T. Yoshida: None. Y. Oka: None. M. Kawata: None. T. Kubo: None. Introduction: The treatment following Achilles tendon rupture, it has been reported that the function of triceps surae muscle declines with a load-free orthosis (1). This decline is considered to be a dysfunction of the triceps surae associated with stretching of the tendon, and assessing the function of the triceps surae is important for re-acquiring motor function in the course of treatment for the Achilles tendon. Recently, diffusion tensor imaging (DTI) is considered a useful technique for the structural and pathological assessment of muscle tissue. DTI measures the diffusion anisotropy of water molecules in tissue along multiple directions and it was suitable for the fibrous tissues (2, 3). Our hypothesis was that the muscle power of triceps surae was decrease after Achilles tendon rupture because of macro and micro morphological changes, and DTI might detect the anisotropic change involoved in that. The aim of this study was to examine the usefulness of DTI for evaluating dysfunctional muscles with performing DTI parameters, histological changes, and macro-measurements in the triceps surae following Achilles tendon rupture in rats. Methods: The subjects were six 12-week-old, male Sprague-Dawley (SD) rats. Achilles tenotomy was performed on the right hind leg, while the left hind leg served as the unaffected control. The animal experimental protocols for this study were approved by the university. A 7.0-T high-field MRI device was used at two and four weeks after the tenotomy to capture proton density-weighted images and diffusion tensor images of the triceps surae of both hind legs. The eigenvalues (λ) and fractional anisotropy (FA) of the triceps surae muscle belly were calculated from the resulting images, and their values at each imaging time were examined statistically. The regions of interest were set at four points, namely, the anterior, posterior, medial and lateral points of the triceps surae, in the slices of the axial images which the muscle belly was largest. The valus of all parameters were average of those points. The DTI results were studied to determine whether there were significant differences in the eigenvalues and FA values for the triceps surae between the controls two weeks and four weeks after surgery. ANOVA was performed and p<0.05 indicates a significant difference. Histological preparations of the triceps surae were created with hematoxylin and eosin stain, and Azan stain after the MRI. The longitudinal axis length and maximum section area of the muscle belly of the triceps surae were measured in six 12-week-old SD rats that were treated similarly at two weeks after treatment. In the macro-measurement, Student s t-test was performed, and p<0.05 indicates a significant difference. Results: λ1 was ± on the control, ± at two weeks after tenotomy, and ± at four weeks after tenotomy. λ2 was ± on the control, ± at two weeks after tenotomy, and ± at four weeks after tenotomy. λ3 was ± on the control, ± at two weeks after tenotomy, and ± at four weeks after tenotomy. There was a significant increase in λ1 (p=0.04), while no significant differences were observed in λ2 or λ3 at two and four weeks after tenotomy (p=0.75). (Figure 1a, b and c) The FA value was ± for the control, ± at two weeks after tenotomy, and ± at four weeks after tenotomy. The FA values were significantly higher in the two-week group and the four-week group than in the control group (p=0.04). (Figure 1d) The histological images showed atrophy of the triceps surae and disappearance of normal construction of connective tissue around the endomysium after treatment. In the macro-measurement, the muscle belly lengths were significantly shortened (p<0.001), and the cross-sectional areas were not different (p=0.19). (Figure 2a, b) Discussion: In this study, we found that FA and eigenvalue of the long axis of triceps surae was increase and muscle length was decrease. The muscle power depends heavily on muscle length and some muscle fibers tend to be atrophied in histological result. We thought triceps surae become into dysfunctional muscle. Some papers were studied about damaged or denervated atrophic muscle using DTI, it is clear that the DTI parameters were related to morphological change (3, 4). Adding the functional testing, DTI could be an indicator of muscle function about a statement of tendon rupture. Significance: The muscle functional examination is depends on the examiner, then it is less objective in the serial assessment and inter-rater reliability. DTI has a possibility of assessing dysfunctional muscle. Acknowledgments: none References: (1) Kearney RS, Costa ML. Current concepts in the rehabilitation of an acute rupture of the tendo Achillis. J Bone

2 Joint Surg Br 2012; 94, 1: (2) Heemskerk AM, Damon BM. Quantitative assessment of DTI-based muscle fiber tracking and optimal tracking parameters. Magn Reson Med 2009; 61: (3) Zhang J, Sheikh KA. Magnetic resonance imaging of mouse skeletal muscle to measure denervation atrophy. Experimental Neurology 2008; 212: (4) Zaraiskaya T, Noseworthy MD. Diffusion tensor imaging in evaluation of human skeletal muscle injury. J Magn Reson Imaging 2006; 24:

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4 ORS 2014 Annual Meeting Poster No: 1941

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