Noninvasive magnetic resonance-guided focused ultrasound for tendon disruption: an in vivo Animal study

Surgical resection of the tendon is an effective treatment for severe contracture. Magnetic Resonance-guided Focused Ultrasound (MRgFUS) is a non-invasive ultrasonic therapy which produces a focal increase in temperature, subsequent tissue ablation and disruption. We evaluated MRgFUS as a clinically translatable treatment modality to non-invasively disrupt in vivo porcine tendons.

In vivo Achilles tendons (n = 28) from 15-20kg Yorkshire pigs (n = 16) were randomly assigned to 4 treatment groups of 600, 900, 1200 and 1500 J. Pretreatment range of motion (ROM) of the ankle joint was measured with the animal under general anesthesia. Following MRgFUS treatment, success of tendon rupture, ROM increase, temperature, thermal dosage, skin burn, and histology analyses were performed.

Rupture success was found to be 29%, 86%, 100% and 100% for treatment energies of 600, 900, 1200 and 1500 J respectfully. ROM difference at 90^° flexion showed a statistically significant change in ROM between 900 J and 1200 J from 16^° to 27^°. There was no statistical significance between other groups, but there was an increase in ROM as more energy was delivered in the treatment. For each of the respective treatment groups, the maximal temperatures were 58.4 °C, 63.3 °C, 67.6 °C, and 69.9 °C. The average areas of thermal dose measured were 24.3mm², 53.2mm², 77.8mm² and 91.6mm². The average areas of skin necrosis were 5.4mm², 21.8mm², 37.2mm², and 91.4mm². Histologic analysis confirmed tissue ablation and structural collagen fiber disruption.

This study demonstrated that MRgFUS is able to disrupt porcine tendons in vivo without skin incisions.