Rehabilitating Tendons: Can Elastography Help?

Elastography is a new ultrasonographic technique that allows an evaluation of the mechanical properties of tissues. This technique estimates tissue strain, where strain is defined as the fractional change in length of a tissue when an external force is applied. Elastography evaluates tissue motion as compression is applied, using manual compression with the ultrasound transducer, internal organ movement during respiration, or low frequency vibrations. Tissue displacement causes measureable displacement of the ultrasound waves. Soft, deformable structures, such as damaged or disrupted tissues, cause greater displacement of sound waves than hard, rigid structures. Elastography therefore can provide information about the behaviour of internal structures when under load. Since pathological tissues often exhibit altered mechanical properties, elastography allows the differentiation between normal and diseased tissues due to the differences in these elastic properties. This is in contrast to conventional ultrasonography which only evaluates tissue morphology and the differences between acoustic impedance of adjacent structures. Elastography is used in humans for differentiating benign from malignant nodules in breast, prostate, thyroid, liver, and lymph tissue, and for evaluating hepatic fibrosis. Recently, elastography has been investigated as an imaging modality for musculoskeletal injuries, primarily the Achilles tendon. It correlated strongly with clinical examination and greyscale ultrasonography and enabled detection of more alterations in injured tendons than with conventional ultrasound imaging. Evaluation of acute injuries revealed significantly increased softness in areas of haematoma and fibre disruption that became progressively stiffer with healing. These studies suggest potential application of elastography for the diagnosis and monitoring of rehabilitation of musculoskeletal injuries in the horse. [...]