PURPOSE

To investigate acute muscle tears affecting the lower limb of football players with Stimulated Echo Diffusion Tensor Imaging (STEAM-DTI).

METHODS

Football players with clinically diagnosed acute muscle tear of the lower limb were investigated on a 3T TIM Trio MRI Scanner (Siemens Healthcare, Erlangen, Germany) using an 8-channel knee coil or a combination of 4-channel matrix array coil/12-channel spine coil.For the morphological assessment, axial, coronal and sagittal proton density fat-sat and axial T1-weighted TSE sequences were applied. Both limbs were also investigated using a prototype ss-EPI STEAM-DTI sequence: diffusion time 200ms, GRAPPA-2, FatSat, b-values 0 and 500s/mm2, 6 averages, 12 directions; 30 adjacent axial slices of 3.5mm thickness.Since STEAM-DTI images are affected by random artifacts due to involuntary muscle contraction, we applied a previously tested correction method based on the weighted mean of voxels’ signal intensity[1]. Each injury was rated according to the Munich Consensus classification[2] using morphological images. DSI Studio (http://dsi-studio.labsolver.org) was used for the DTI analyses. DTI metrics (i.e.,fractional anisotropy (FA), mean-(MD), radial-(RD) and axial (AD) diffusivity, number, length and volume of fiber tracks) were collected, after manual segmentation, from the entire injured muscle and from the healthy contralateral corresponding muscle and then compared (Student’s t-test). Freehand ROIs were drawn along the borders of each muscle tear (ROI_tear) and the same ROI was applied on the corresponding healthy contralateral muscle (ROI_{hc_t}).Additionally, two other ROIs were drawn to rule out any physiological difference between right and left limb:one on a healthy area ipsilateral to the injury (ROI_hi) and one on a corresponding contralateral area (ROI_{hc_i}). To evaluate possible changes in DTI metrics due to the tear or laterality even in healthy tissue, all ROIs were compared using one-way ANOVA test Greenhouse-Geisser post-hoc Bonferroni corrected. Ratios of DTI metrics of the injured side (ROI_tear/ROI_hi) and of the corresponding contralateral healthy areas (ROI_{hc_t}/ROI_{hc_i}) were performed and compared (Student’s t-test).

RESULTS

Eight patients with acute muscle tear were examined (all males, age range 20-36 years).Five showed an injury of the thigh and three of the calf. Seven lesions affected the right side and one the left.According to the Munich Consensus classification, two tears were rated as minor partial and six as moderate. No significant differences occurred comparing the entire injured muscle with the contralateral (p>0.05, each) except for higher AD values (+3.76%;p=0.048)(Fig. 1). No differences in DTI metrics occurred among all ROIs placed in healthy areas (p>0.05, each). ROI_tear showed higher MD (+10.32%, +12.31% respectively) and AD values (+6.60%, +9.08%, respectively)(p<0.05, each) than ROI_{hc_}t and ROI_{hc_i} but no differences emerged with ROI_hi (all p>0.05). FA was lower in ROI_tear than in ROI_{hc_t} and ROI_hi (-11.49%, -19.81%;p<0.05, each) but no differences emerged with ROI_{hc_i} (p>0.05). RD was higher in ROI_tear than in all other healthy areas (+13.14%, +10.46%, +14.73%;p<0.05) whereas no differences emerged for fibers’ number, length and volume (p>0.05). Greater differences occurred after normalizing the data.The comparison of the ratios (i.e., ROI_tear/ROI_hi and ROI_{hc_t}/ROI_{hc_i}) revealed higher MD and RD (+6.02% and +8.69%) and lower FA (-19.51%) as well as a reduced number and length of fibers on the injured side (-55.65% and -39.47%) (p<0.05, each).No significant changes emerged for AD and fibers’ volume (p>0.05,each)(Fig. 2).

DISCUSSION

Acute muscle injuries are very common in elite and non-elite athletes[3,4] but the prevalent MRI-based classification is still based on a rough quantification of the amount of torn fibers[5]. DTI already demonstrated to be highly suitable for the anatomical assessment of muscles but only a few studies investigated muscle tears. Indeed, Zaraiskaya et al.[6] showed lower FA and higher MD but only in two patients with acute lesions of the gastrocnemius whereas Froeling et al.[7] successfully evaluated muscle changes in marathon runners. For the first time, we used STEAM-based DTI to investigate muscle tears in athletes using the contralateral healthy side as reference and applying a normalization of the data.Indeed, physiological differences between right and left muscles may occur and affect DTI metrics but the application of a ratio provided robust results demonstrating that structural changes, affecting not only MD, FA and RD but also fibers’ number and length, occur in the tears and are quantifiable using DTI.

CONCLUSIONS

STEAM-based DTI allowed a robust characterization and quantification of the injured fibers in athletes especially when a ratio between the injured and the contralateral muscles was applied. Aiming to improve the current imaging-based classification of muscle tears as well as to increase the accuracy of the therapeutic and prognostic management of injured athletes, future studies including a larger population and evaluating muscle tears also during the follow-up, are necessary.

Acknowledgements

No acknowledgement found.