Channel-Assisted Microscopy for Contralateral C7 Nerve Transfer Through Posterior Cervical Keyhole Approach: An Anatomical Study

BACKGROUND: This study was designed to investigate the anatomical feasibility and operative safety of contralateral C7 nerve transfer through a posterior keyhole approach assisted by a tubular retractor under microscopy. METHODS: Microsurgical dissection was performed on 10 fresh adult head and neck specimens. With the specimens positioned in a prone neck-flexed posture, bilateral 2 cm incisions were simulated for the insertion of the operative channel. Stepwise dissection was carried out to expose and mobilize the contralateral and ipsilateral C7 nerve roots. A laminar-underlying epidural corridor was established to achieve direct end-to-end neurorrhaphy. RESULTS: Tension-free coaptation of bilateral C7 nerves was successfully achieved in all specimens. Measurements revealed that the prone neck-flexed position significantly increased the area of zone V by 20.73 ± 8.12 mm2, thereby improving surgical exposure. The nerve transposition distance was 30.30 ± 4.20 mm, while the obtainable length of the contralateral C7 nerve was 52.40 ± 3.10 mm, which permitted direct anastomosis without the need for nerve grafting. Furthermore, the distance from point V to the C7 nerve root was 2.45 ± 0.72 mm, and the distance from the medial edge of the facet joint to the nerve root was 2.28 ± 0.98 mm, indicating that adequate nerve root exposure could be attained without facetectomy, thus preserving cervical stability. The diameter of the mobilized contralateral C7 nerve stump was 3.60 ± 0.45 mm, and the width of the transposition pathway was 4.12 ± 0.41 mm, suggesting no risk of nerve compression by the lamina. CONCLUSION: The posterior keyhole approach is demonstrated to be anatomically sound and technically reliable for contralateral C7 nerve transfer. Its advantages-minimal invasiveness, short trajectory, favorable operative space, and elimination of nerve grafting-provide a robust anatomical foundation for clinical application.