AB041. The morphological changes of paraspinal muscles in adult brachial plexus injury.

Background: Traumatic brachial plexus injury (BPI) is a debilitating injury that has a devastating impact. However, management of BPI remains a complex challenge, not only in diagnosis but also in treatment strategies for reconstructive microsurgeons. The aim of this study was to develop an additional assessment tool for root avulsion based on the volume of paraspinal muscle (PM) prior to surgical intervention, making the preoperative diagnosis more precise.

Methods: This retrospective study was centered on adult patients with BPI who underwent surgical exploration and treatment, postoperative follow-up at the Chang Gung Hospital. Labeling of PMs was aided by semi-automated segmentation using 3D Slicer 5.2.2. Slices spanning from the lower end of the upper vertebral body endplate to the upper end of the lower vertebral body. The ratio of muscle volume on the lesion side to that on the normal side (L/N ratio), indicating the volume proportion between the injured and healthy areas, serves as the primary parameter for assessing the relationship in root avulsion.

Results: The L/N ratio for the deepest layers of PMs consistently predicted the level of root injury across C4 to C7 levels, with all reaching statistical significance. In terms of partial and total root avulsion, the L/N ratio of layer 4th at 0.78 significantly outperforms other methods. Concerning the timing of MRI, both partial avulsion (PA) and total avulsion (TA) groups of merge roots showed a statistically significant decrease in the L/N ratio over time.

Conclusions: In conclusion, the L/N volume ratio of 4th layer in PMs reliably predicts the functional severity of avulsed roots and surpasses the performance of traditional diagnostic tools under specific conditions.