Quantitative evaluation of the echo intensity of the median nerve and flexor muscles of the forearm in the young and the elderly

Objectives

Musculoskeletal structures often appear brighter on imaging in the elderly, which makes it difficult to accurately delineate a peripheral nerve during ultrasound-guided regional anaesthetic procedures. The echo intensity of skeletal muscles is significantly increased in the elderly. However, there are no data comparing the echo intensity of peripheral nerves in the young and the elderly, which this study was designed to evaluate.

Methods

13 healthy, young volunteers (aged <30 years) and 11 elderly patients (aged >60 years) who were scheduled to undergo orthopaedic lower limb surgery were recruited. The settings of the ultrasound system were standardised and a high-frequency linear array transducer was used for the scan. A transverse scan of the median nerve (MN) and the flexor muscles (FMs) at the left mid-forearm was performed and three video loops of the ultrasound scan were recorded for each subject. Still images were captured from the video loops and normalised. Computer-assisted greyscale analysis was then performed on these images to determine the echo intensity of the MN and the FMs of the forearm.

Results

The echo intensity of the MN and FMs of the mid-forearm was significantly increased in the elderly (p<0.005). There was also a reduction in contrast between the MN and the adjoining FM in the elderly (p=0.04).

Conclusion

Under the conditions of this study, the MN and the FMs in the forearm appeared significantly brighter than those in the young, and there was a loss of contrast between these structures in sonograms of the elderly.Recently, there has been an increase in interest in the use of ultrasound to guide peripheral nerve blocks [1-3]. We have observed during such procedures that musculoskeletal structures often appear significantly brighter and that there is loss of contrast between the nerve and its adjoining muscles in the elderly, which often makes it difficult to accurately delineate a peripheral nerve using ultrasound in this age group. There are published data showing that the echo intensity (EI) of skeletal muscles is significantly increased in the elderly [4]. However, there are no data comparing the EI of a peripheral nerve in the young and the elderly, which this study was designed to evaluate.