Procedure-oriented torsional anatomy of the proximal arm for spasticity injection

This is the first in a series of papers related to the new concept of "torsional" anatomy. The objective of this article is to provide musculoskeletal ultrasound (MSKUS) anatomy of the upper arm in the position of hemispastic flexion as a reference relevant to needle procedures.

The MSKUS images were obtained in a healthy human subject. A pair of MSKUS images was recorded for each level: the first in anatomic neutral and second in hemispastic position.

At the proximal 1/3 level of the upper arm, the pectoralis major rotated out of view. At the middle of the upper arm, the biceps rotated medially, and the brachialis rotated from far lateral to the middle of the screen. At the distal 1/3 level of the upper arm, the radial nerve rotated more anteriorly. At the distal 1/6 level of the upper arm, the biceps shifted and was replaced by the brachialis and brachioradialis. The radial nerve also rotated more anteriorly and superficially.

With torsion, it is possible that intended muscle targets, such as the pectoralis, are missed, and unintended targets, such as the radial nerve, are accidentally injected in the upper arm.

It is hoped that this series of images will increase the accuracy and safety of needle placement for spasticity and nerve block injections in the proximal upper arm.