Healing of the Achilles tendon in rabbits—evaluation by magnetic resonance imaging and histopathology

BACKGROUND Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) could provide valuable findings for tendon regeneration. A non-invasive image method that can effectively evaluate the quality of the scar tissue has not yet been employed. METHODS Thirteen New Zealand rabbits were divided into two groups: group 1--non-treated control (n = 4); group 2--surgical intervention (n = 9). The central portion of the Achilles tendon was resected, and after 30 days, DCE-MRI was performed. Contrast enhancement methods were applied using the region of interest (ROI) technique. In the medium third of the Achilles tendon, the intra-substantial signal intensity and the presence of hyper-intense intra-tendon focus points and of signal heterogeneity were evaluated. Antero-posterior and transversal diameters of the tendon were measured. The Achilles tendon was removed and dissected free from other tissues. Sections from the central part of the tendon were stained for histological analysis. RESULTS The difference between the contrast enhancement curves of the control and surgical groups (p < 0.0001) was observed. The surgical group had an intense contrast enhancement in the contrast sequences, enlargement of the diameter and intra-substantial signal intensity alteration, with hyper-signal focus points and widening of the tendon sheath, which presented irregular contours and intense contrast enhancement. On histology, the Achilles tendon presented diffuse widening of the tendon sheath and wedge-shaped areas with scarring tissue rich in disordered collagen fibres. These findings were related to alteration in the intra-substantial signal intensity, with hyper-signal focus points in the DCE-MRI. CONCLUSIONS MRI with perfusion could be a useful technique for evaluating tissue and fibrous scarring in tendons.