Therapeutic Ultrasound for the Healing of Tendons and Ligaments
Sound is made up of vibrations that are audible to the human ear at a frequency of 18,000 cycles per second. Frequencies that are above this range cannot be heard by the human ear and are called ultrasonic. In addition to the well known heating effects of therapeutic ultrasound, a non-thermal effect known as acoustical streaming and micro-massage has been shown to increase protein synthesis for improved wound healing. Non-thermal ultrasound enhances alignment of collagen fibers and increases the collagen content there by increasing the tensile strength of tendons and ligaments. Therefore, the treatment of acute sport injuries suh as tendinitis, ligamentous strain and synovitis of joints should be performed as soon as possible after injury. Effectiveness of the treatment is dependent on early referral, good technique and an accurate diagnosis. Low doses of pulsed ultrasound have been reported to clear fibrous adhesions and soften scar tissues associated with tendon and ligament injury.
The treatment protocol and timeline for healing utilizing pulsed ultrasound therapy for tendons and ligaments in the horse can be illustrated in the following case study.
A 3 year old standard-bred filly was diagnosed post-race with a lesion in the proximal superficial tendon of the right foreleg. Therapeutic pulsed ultrasound was initiated in the acute stage to eliminate the swelling and alleviate the pain. Also pulsed ultrasound at the early stages prevents the fibrous adhesions and scaring from forming in the lesion area. The settings utilized were 20% pulse (5:1), 1 MHz and 0.5 intensity (w/cm²). Daily treatments were performed for 10 min over the lesion site and 5 min on each side of the full tendon area. The filly was stalled except for 2x/day walking for 15 min on an equine exercise machine. Non-steroidal drugs were not used and are contraindicated due to their supression of proteoglycan synthesis. Instead, the horse was given a product, Conquer™ (oral sodium hyaluronate) on a daily basis, at 10 cc per dose per day.
In one month, new diagnostic ultrasound scans revealed the lesion area to have over 50% fiber production. Treatment with pulsed ultrasound was continued 4 to 5x per week for the next 2 mo with exerise the same except at the 3rd month the filly was jogging 15 min per day. Following the 2nd mo of treatment, the diagnostic ultrasound scans revealed complete fiber infiltration of the lesion. Fibers at this time were short and stubby on longitudinal view indicating remodeling of the tendon lesion was still occurring. Care has to be taken when such structural configuration is noted, as fibers are friable and easily re-damaged. When fibers elongate and have normal cross-linking structure, the horse may return to work. Riding at the walk for 1 to 2 wk, then jogging for at least 3 wk before increasing the workload on the tendon is recommended.
In conclusion, over the last 18 years I have treated performance horses with tendon and ligament injury with great success utilizing pulsed ultrasound. Utilizing this technique decreases healing time by half and the tensile strength of the tendon or ligament is 95% of the original state.