Ultrasound-Guided Lower Leg Muscle Compressibility Before and After a Standard Treadmill Test in Healthy Volunteers

Military personnel on duty or engaged in sports activities may experience exercise-induced lower leg pain (ELP). If history and physical examination suggest chronic exertional compartment syndrome (CECS) and conservative treatments prove ineffective, a muscle compartment pressure measurement is advised. However, this test is invasive with suboptimal test characteristics. Aim of this study is to determine whether a novel noninvasive soft tissue compressibility analysis using ultrasound can detect changes in anterior tibial muscle (ATM) compartment thickness and compressibility following a standardized treadmill test.

Healthy volunteers without ELP underwent serial ultrasound measurements of the ATM during rest and after treadmill walking (5.5 km/h, slope 15%). Compartment thickness, defined as the distance between the superficial fascia and two different deep landmarks (interosseous membrane (IM), or transition zone IM to tibia (TZIT)) was measured with 10 mmHg (d10) and 80 mmHg (d80) external probe pressure. Compartment compressibility was calculated as a ratio (d10-d80)/d10*100%.

Healthy volunteers (n = 70, males n = 28, age 19-72 years) were included (IM n = 35; TZIT n = 35). Compartment thickness (d80) during rest, 1- and 5-minutes post-exercise with IM as internal landmark was 25.9mm (±2.7), 27.0mm (±3.1; p < .01), and 26.5mm (±2.7; p < .01), respectively. Using TZIT as landmark, these values were 22.2 mm (±3.1), 23.8 mm (±3.7; p <  .01) and 23.0 mm (±3.7; p < .07). Compartment compressibility with the IM as landmark during rest was 9.5% (±2.5) and did not significantly change post-exercise (p = 0.45). Using TZIT, compressibility was 15.0% (±4.2) at rest, and decreased to 13.1% (±3.8; p =  .02) and 14.1% (±4.5; p =  .21) 1- and 5 min post-exercise, respectively.

Soft tissue compressibility analysis using ultrasound successfully detected changes in ATM compartment thickness following a standard treadmill test. Changes in muscle compressibility depended on type of internal anatomical landmark used. Future research focuses on lower leg muscle compressibility in individuals with exercise-induced leg pain.