The Effects of Low-Intensity Ultrasound on Medial Collateral Ligament Healing in the Rabbit Model

Sparrow, Karen J. PT, PhD
Finucane, Sheryl D. PT, PhD
Owen, John R. PE
Wayne, Jennifer S. PhD

^†Department of Physical Therapy, Virginia Commonwealth University, Richmond, Virginia
^‡Orthopaedic Research Laboratory, Departments of Biomedical Engineering and Orthopaedic Surgery, Virginia Commonwealth University, Richmond, Virginia

^*Address correspondence to Karen J. Sparrow, PT, PhD, Virginia Commonwealth University, Department of Physical Therapy, School of Allied Health, 1200 East Broad Street, PO Box 980224, Richmond, VA 23298-0224.

No potential conflict of interest declared. See Acknowledgment for funding information.

American Journal of Sports Medicine 33(7):p 1048-1056, July 2005.

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.