Cervical nerve root contribution to diaphragm motor innervation revisited via intraoperative clinical and...

Classical descriptions state that diaphragmatic motor innervation arises predominantly from the fourth cervical nerve root (C4), with additional contributions from C3 and C5. However, clinical evidence supporting the functional involvement of C3 and C5 remains limited. Study aimed to reassess cervical root contribution to diaphragmatic innervation through intraoperative observations.

Eighteen consecutive patients undergoing dorsal root entry zone (DREZ) lesioning for refractory pain in upper-limb mostly due to brachial plexus injury were included. The procedure allowed intradural exposure of the C4 and C5 roots. During surgery, cervical roots were evaluated for anatomical integrity, and electrical stimulation of the ventral roots of C4 and C5 was performed to assess their functional contribution to diaphragmatic activation. The functional role of the C3 ventral root, not directly exposed, was not explored.

Stimulation of an intact C4 ventral root (n = 10) or damaged but with preserved responsiveness (n = 2) constantly produced diaphragmatic contraction; when C4 was avulsed or unresponsive (n = 6), diaphragmatic paralysis was present in all but one patient (p < 0.001); Stimulation of an intact C5 ventral root (n = 6) never elicited diaphragmatic contraction (p > 0.05). In one patient with normal C5 but avulsed C4, diaphragm was paralyzed.

Intraoperative observations support C4 as the critical contributor to diaphragmatic motor innervation. No functional contribution of C5 was identified.

These findings, harvested in clinical conditions, refine the functional anatomy of the phrenic motor pathways and may assist neurological evaluation, and surgical planning in cervical and brachial plexus pathologies.