Restoration of Strength Despite Low Stress and Abnormal Imaging after Achilles Injury

TRUDEL. G. G P DOHERTY, Y KOIKE. N RAMACHANDRAN, M. LECOMPTE, L DINH. and H K UHTHOFF Restoration of Strength Despite Low Stress and Abnormal Imaging after Achilles Injury Med Sci Sports Exerc, Vol 41. No 11, pp 2009-2016, 2009 Purpose To determine the usefulness of clinical imaging in predicting the mechanical properties of rabbit Achilles tendons after acute injury Methods. We created a 2 x 7-mm full-thickness central tendon defect in one Achilles tendon of healthy rabbits. Rabbits in groups of 10 were killed immediately and 4 and 8 wk after surgery (n = 30) We then performed magnetic resonance (MR) imaging, ultrasonography (US), bone mineral densitometry (BMD), and mechanical testing to failure using a dual-cryofixation assembly on experimental and contralateral tendons The main outcome measures included tendon dimensions, optical density (OD) of T(1)-weighted, proton density (PD), and T(2)-weighted MR sequences, US focal abnormalities, BMD of the calcaneus, and stress and peak load to failure Results. On MR imaging and US, all dimensions of the injured tendons after 2 wk and more were greater than those of the contralateral tendons (P < 0.05) The mean T(1)-weighted OD was greater at 4 wk (256 +/- 53) and 8 wk (184 +/- 24) than immediately after surgery (149 +/- 15) Mechanical stress was markedly lower in the experimental than in the contralateral tendons at both 4 wk (39 +/- 9 vs 77 +/- 16 N mm(-2)) and 8 wk (58 +/- 6 vs 94 +/- 26 N mm(-2). P < 0.05) Mean peak load to failure was significantly lower immediately after surgery (332 +/- 128 N) than at 4 and 8 wk (712 +/- 106 and 836 +/- 90 N, respectively) Both high T(1)-weighted OD (r = -0.73) and PD OD (r = -0.69) correlated with lower mechanical stress (P < 0.05) In the experimental tendons. higher T(1)-weighted OD Correlated With lower peak load (r = -0.46 P < 0.05) Conclusions Normal peak loads 4 wk after injury were withstood by an enlarged tendon of lower stress. These findings support progressive physical loading 4 wk after an Achilles tendon injury T(1)-weighted OD constituted a marker of tendon mechanical recovery