Ultrasound monitoring of patients with leg muscle atrophy

Background. So far, the description of muscle atrophy in humans has been mostly based on changes in anatomical cross-sectional area (ACSA) measured at specific sites along the muscle belly by imaging techniques. However, there is experimental evidence of regional differences in muscle atrophy and therefore changes in the internal architecture of the muscle could go undetected on the basis of ACSA calculations. Skeletal muscles can be divided into roughly two categories: parallel muscles, whose muscle fibres are parallel to the tendon attached to the bone and are therefore on the traction axis of the muscle, and pennated muscles, whose fibres are connected to the tendinous sheet with an angle defined as the 'pennation angle'. In a previous study, we demonstrated that muscle atrophy led to a decrease in pennation angle and fibre length. The present study aimed demonstrate that to ultrasound may represent a simple, disposable non-invasive method to be used in rehabilitation medicine to assess muscle atrophy and monitoring changes in muscle architecture after rehabilitation. Methods. Ten patients (6 males, 4 females, 21-41 yrs.) with unilateral muscle atrophy were admitted to this study. Maximum anatomical CSA of the gastrocnemius medians (GM) was determined with CT scans of both legs. GM muscle fiber pennation angle and fiber length were measured in both legs in the same region of maximum CSA by real-time ultrasound with a 7.5 MHz, 4 cm long, linear probe. Maximal voluntary and electrically evoked torque of the plantar flexor muscles were measured. The twitch interpolation technique was also used. The measurements were repeated after a one month rehabilitation period in all of subject. Results. The mean pre-rehabilitation CSA was 17.8 cm2 in the unaffected limb and 16.7 cm2 in the affected limb; the post-rehabilitation values were 19.8 cm2 in the unaffected limb and 18.2 cm2 in the affected limb. Mean pennation angles differed by 11% (25.5% in the unaffected limb and 22.8% in the affected limb, p<0.02) at pre-rehabilitation, while no significant differences were observed at post-rehabilitation. No changes in fiber length were observed at pre- and post-rehabilitation. Affected to unaffected differences in maximal voluntary strength varied from 32.4% at pre- rehabilitation to 9.6% at postrehabilitation. Conclusions. This study showed that US provides a simple non-invasive means of quantify muscle atrophy and monitoring changes following rehabilitation. Structural changes in CSA and pennation angle as monitored by US, and functional changes in muscle maximal strength provide an 'up to date' profile of the muscular architecture and performance capacity. US represents a sensitive-to-change method to evaluate the degree of muscle atrophy in rehabilitation patients.