The effects of low-intensity ultrasound on medial collateral ligament healing in the rabbit model

Background: Ruptured medial collateral ligaments are capable of healing over time, but biomechanical and biochemical properties remain inferior to normal tissue. Low-intensity ultrasound may improve healing. Hypothesis: Medial collateral ligaments treated with ultrasound will demonstrate superior healing. Study Design: Controlled laboratory study. Methods: Twenty-one late-adolescent male rabbits underwent bilateral ligament transection. One ligament from each rabbit received ultrasound treatment every other day for 6 total treatments. Contralateral ligaments received sham treatments. After 3 or 6 weeks, ligaments were evaluated biomechanically and assayed for collagen concentration and the relative proportions of types I and III collagen. Results: Areas of sonicated specimens were significantly larger (10.6% +/- 4.90%) at 6 weeks. Ultimate load (39.5% +/- 17.0%), ultimate displacement (24.5% +/- 8.0%), and energy absorption (69.1% +/- 22.0%) were significantly higher for sonicated specimens at 6 weeks. No significant biomechanical differences were observed at 3 weeks. The relative proportion of type I collagen was significantly higher in sonicated ligaments at 3 weeks (8.61% +/- 4.0%) and 6 weeks (6.91% +/- 3.0%). No significant differences in collagen concentration were observed at either 3 or 6 weeks. Conclusion: Subtle improvement with ultrasound treatment may be apparent by 3 weeks after injury, suggested by increased proportion of type I collagen. Ultrasound appears to improve some structural properties and to modestly increase scar cross-sectional area and type I collagen present at 6 weeks after injury in this model. Clinical Relevance: Ultrasound treatments after ligament injury may facilitate earlier return to activities and decrease risk of reinjury.