Mechanical Alterations of Rabbit Achilles’ Tendon After Immobilization Correlate With Bone Mineral Density But Not With Magnetic Resonance or Ultrasound Imaging

Abstract

Trudel G, Koike Y, Ramachandran N, Doherty G, Dinh L, Lecompte M, Uhthoff HK. Mechanical alterations of rabbit Achilles’ tendon after immobilization correlate with bone mineral density but not with magnetic resonance or ultrasound imaging. Objective To assess the usefulness of magnetic resonance imaging (MRI), ultrasound (US) imaging, or bone mineral density (BMD) in predicting the mechanical properties of immobilized rabbit Achilles’ tendons. Design Experimental study. Setting Basic university laboratory. Animals Twenty-eight rabbits. Interventions Twelve rabbits had 1 hindlimb casted for 4 weeks and 10 rabbits were casted for 8 weeks. Contralateral legs and 12 normal hindlimbs served as controls. Main Outcome Measures Achilles’ tendon dimensions on MRI and US, T1- and T2-signal intensities on MRI, classification of abnormalities on MRI and US; BMD of the calcaneus with dual-energy x-ray absorptiometry. Biomechanic measures consisted of peak load, stiffness, and stress. Imaging variables were correlated with biomechanic alterations. Results Immobilized Achilles’ tendons were weaker and showed decreased mechanical stress compared with their contralateral legs and controls (all P<.05). MRI and US revealed larger Achilles’ tendons after immobilization. However, neither increased MRI nor US signal abnormality was found. BMD was lower in immobilized calcanei and larger in contralateral legs than controls. Only BMD correlated with both the decreased peak load ( R 2=.42, P<.05) and stress ( R 2=.54, P<.05) of immobilized Achilles’ tendon. Conclusions This study established weakened mechanical properties of immobilized Achilles’ tendons. BMD of the calcaneus, but not MRI and US, was predictive of the mechanical alterations in immobilized Achilles’ tendons. BMD may be a useful biomarker to monitor disease and recovery in Achilles’ tendons.