Introduction: C1-2 polyaxial screw-rod fixation is a relatively new technique. While recognising the potential for inadvertent vertebral artery injury there have been few reports in the literature outlining all the possible complications.

Aim:To review all cases of C1 lateral mass screw insertion with emphasis on the evaluation of the potential structures at risk during the procedure.

Methods: We retrospectively reviewed all patients in our unit who has C1 lateral mass screw insertion over a 2 year period. The C1 lateral mass screw was inserted as part of an atlantoaxial stabilisation or incorporated into a modular occiput/subaxial construct. Outcome measures included clinical and radiological parameters. Clinical indicators included age, gender, neurologic status, surgical indication and the number of levels stabilised. Intraoperative complications including blood loss, vertebral artery injury or dural tears were recorded. Radiological indicators included post-operative plain radiographs to assess sagittal alignment and to check for screw malposition or construct failure.

Results: A total of 18 C1 lateral mass screws were implanted in 9 patients. There were 3 male and 6 female patients who had C1 lateral mass screws inserted in this tertiary referral centre. Two patients had atlantoaxial stabilisation of a C2 odontoid fracture. There were 4 patients with rheumatoid arthritis whose C1 lateral mass screws were inserted as part of an occipitocervical or subaxial cervical stabilisation. The other pathologies included trauma and spinal tumours.

There was no vertebral artery injury and no cerebrospinal fluid leak. Three patients developed post operative occipital neuralgia. This neuralgia was transient in one of the patients having settled at 6-week follow up. In the other 2 patients the neuralgia was unresolved at the time of latest follow up but was adequately controlled with appropriate pain management. Post operatively no patient had radiographic evidence of construct failure and all demostrated excellent sagittal alignment.

Conclusion: It has been reported that the absence of threads on the upper portion of the long shank screw may protect against neural irritation. However insertion of the C1 lateral mass screw necessitates careful caudal retraction of the C2 dorsal root ganglion. The insertion point for the C1 lateral mass screw is at the junction of the C1 posterior arch and the midpoint of the posterior inferior part of the C1 lateral mass. Two patients in our series suffered occipital neuralgia post insertion of the C1 lateral mass screws. This highlights the potential for C2 nerve root irritation during and after the insertion of the C1 lateral mass screw.