Posterior Occipitocervical Approach

What it exposes. The posterior occipitocervical approach is the dorsal midline exposure of the entire occiput, the posterior arch of the atlas (C1) and the elements of the axis (C2), extended caudally as far as required. It gives direct, extensile access to the dorsal surface of the occipital squama, the C1 lateral masses and the C2 pedicle and isthmus - the screw start points for the common craniocervical constructs. Primary indications: - Craniocervical and atlantoaxial instability requiring posterior fixation and fusion

• Occipitocervical fusion for rheumatoid craniocervical disease, basilar invagination, occipitocervical trauma, tumour or congenital instability
• Atlantoaxial (C1-C2) fusion for unstable odontoid fractures unsuitable for anterior fixation, transverse ligament rupture, rotatory subluxation, or rheumatoid atlantoaxial instability
• Posterior decompression of the foramen magnum and upper cervical canal (foramen magnum stenosis, Chiari, extradural tumour)
• Revision of failed anterior upper cervical fixation Why this approach is chosen. A single midline incision gives extensile access to the whole occiput, C1 and C2. The midline raphe (ligamentum nuchae) is relatively avascular, and the plane between the paraspinal muscle columns does not cross a major nerve, which limits bleeding and avoids denervation. It is the workhorse exposure for occipitocervical and atlantoaxial fixation because the dorsal surfaces reached are the screw start points for the standard constructs, and it is the only practical route for an occiput-to-cervical construct. Contraindications: - Medical unfitness for prone positioning and prolonged anaesthesia
• Local posterior skin infection or soft-tissue compromise
• An anomalous vertebral artery course (a high-riding or medially grooved C2 isthmus, or a persistent first intersegmental artery) that makes the planned screws unsafe on pre-operative imaging
• Where an anterior approach (anterior odontoid screw fixation or transoral decompression) better addresses the single pathology Alternative approaches: - Anterior odontoid screw fixation for a reducible type II odontoid fracture in a young patient with favourable fracture geometry
• Transoral or endoscopic endonasal approach for irreducible anterior craniocervical compression (retro-odontoid pannus, displaced odontoid) requiring decompression rather than fixation alone
• Lateral transcondylar or far-lateral approach for lateral mass and foramen magnum pathology
• Posterior subaxial approach (a caudal extension of this same midline exposure) for pathology below C2 Position, landmarks and incision. The patient is prone on a radiolucent table (Jackson, Wilson or Relton-Hall frame) with the chest supported parallel, and the head rigidly fixed in Mayfield skull tongs (or a Gardner-Wells clamp on a Mayfield adapter, or a padded horseshoe headrest). Mayfield pins are placed in the temporal squamosa, avoiding the temporalis muscle and the temporal artery. A slight amount of neck flexion opens the posterior C1-C2 interval for exposure, but the final head position must reproduce the desired craniocervical alignment, because the patient is fused in roughly this position; confirm reduction on fluoroscopy before instrumentation. Reverse Trendelenburg tilt reduces venous bleeding and engorgement of the epidural and suboccipital venous plexus. Arms are tucked and padded at the sides with the shoulders taped down gently to improve lateral imaging. Pad every pressure point and confirm the eyes are entirely free of pressure (posterior visual loss is a recognised prone complication), and record baseline motor and somatosensory evoked potentials for instability cases. Key bony landmarks: the external occipital protuberance (inion) marking the superior extent of the exposure; the superior nuchal line curving laterally from the inion (the upper limit for safe occipital fixation); the mastoid processes; the large often bifid spinous process of C2 (the first large spinous process felt below the occiput, with the small C1 posterior tubercle deep and superior to it); and the C3 to C7 spinous processes for distal extension. Key soft-tissue landmarks: the ligamentum nuchae (the fibrous midline raphe from the inion to C7 - the dissection plane), and the greater occipital nerve (sensory branch of C2) and occipital artery ascending subcutaneously alongside the midline in the suboccipital region. Incision planning. A straight midline longitudinal incision centred on the spinous processes, from just above the inion to the lowest level required. A short incision from the occiput to C2 suits a pure C1-C2 fusion; a longer incision suits an occipitocervical or occiput-to-subaxial construct; a cephalad extension over the occipital squama reaches the foramen magnum for suboccipital decompression. Staying strictly in the midline keeps the wound in the avascular raphe and gives the most extensile exposure.

The dissection is performed strictly down the avascular midline raphe, then subperiosteally over the occipital squama, the C1 posterior arch and the C2 elements, working layer by layer to the screw start points while protecting the vertebral artery and the C2 nerve root.

Bony anatomy you will encounter. The occipital squama is a broad curved plate above the foramen magnum; the thick midline occipital crest (external and internal occipital protuberance) is the strongest occipital fixation purchase. The posterior arch of C1 is a thin curved bar with a small posterior tubercle in the midline and a wide superior sulcus on its posterosuperior surface for the vertebral artery. The axis (C2) has a large often bifid spinous process, large laminae, a broad isthmus (pars interarticularis) connecting the pedicle to the body, and superior facets that face upward and slightly laterally to receive the C1 lateral masses. Muscular layers stripped from superficial to deep (each supplied segmentally by its own posterior rami): | Layer | Muscle | Innervation | Role in the approach | |-------|--------|-------------|----------------------| | Superficial | Trapezius | Spinal accessory (motor), C3-C4 (proprioception) | Split in the midline at its aponeurosis | | Intermediate | Splenius capitis, semispinalis capitis | Segmental posterior rami | Stripped subperiosteally off the occiput | | Deep suboccipital | Rectus capitis posterior major and minor, obliquus capitis superior and inferior | Suboccipital nerve (C1 dorsal ramus) | Stripped off the occiput and C1-C2 for exposure | | Cervical paraspinal | Multifidus, semispinalis cervicis, erector spinae | Segmental posterior rami | Swept laterally off the laminae and spinous processes | Neurovascular anatomy of the craniocervical junction: | Structure | Course | Clinical significance | |-----------|--------|----------------------| | Vertebral artery (V3 segment) | Exits the C2 transverse foramen, enters the C1 transverse foramen, then turns medially in the sulcus on the superior surface of the C1 posterior arch, pierces the posterior atlanto-occipital membrane and enters the foramen magnum | THE key danger: injured on the C1 arch or at the C1-C2 facet; bleeding is torrential and stroke is possible | | Suboccipital venous plexus | Engorged venous network around the vertebral artery between C1 and C2 | Profuse venous bleeding when disturbed | | C2 nerve root and ganglion | Emerges between the C1 and C2 laminae and arches, crosses the posterior aspect of the C1-C2 facet joint, gives off the greater occipital nerve | At risk around the C1-C2 joint and the C1 lateral mass screw start point; injury causes occipital numbness or neuralgia | | Third occipital nerve | Sensory branch of the C3 dorsal ramus, crosses the midline over the C2-C3 joint | Encountered in the superficial subcutaneous layer | | Spinal cord and dura | Lie immediately anterior to the C1 and C2 laminae | At risk during decompression and during any wire, hook or screw that breaches the canal | | Occipital and marginal sinuses | Venous channels around the foramen magnum | May bleed during occipital exposure near the foramen magnum | The internervous plane. Unlike a limb approach with a named intermuscular plane between two muscles of different nerves, the posterior cervical midline approach runs down the fibrous ligamentum nuchae between the right- and left-sided paraspinal columns. Because the posterior rami supply the muscles segmentally on each side, the midline raphe is both avascular and internervous: a dissection kept strictly in it does not cross a nerve and does not denervate muscle. The cardinal rule of the exposure is therefore simple - stay exactly in the midline. Brisk bleeding means the dissection has wandered off the midline into muscle.

Structures at risk, by layer, and how to protect them:

Intra-operative complications: | Complication | Prevention | Management | |--------------|------------|------------| | Vertebral artery injury | Pre-operative CT for anomalies; stay within the C1 safe zone; abandon an unsafe screw | Immediate tamponade, expose and control, vascular surgery input, post-operative imaging for posterior circulation stroke | | Dural tear or CSF leak | Careful subperiosteal work; no blind instrumentation in the canal | Primary watertight dural repair, fascial overlay, bed rest, lumbar drain if needed | | C2 nerve root injury | Gentle mobilisation of the C2 root at the C1 lateral mass | Expectant; occipital neuralgia managed medically; rare re-exploration | | Spinal cord injury | Neuromonitoring, careful reduction, avoid canal instrumentation | Steroid protocol per local policy, urgent imaging, maintain perfusion | Post-operative complications: | Complication | Incidence | Prevention | Treatment | |--------------|-----------|------------|-----------| | Occipital neuralgia | Variable | Protect the C2 root and greater occipital nerve | Neuropathic analgesia, nerve blocks | | Wound infection or dehiscence | A few percent | Meticulous layered closure, drains, antibiotics | Debridement, antibiotics, plastic cover if needed | | CSF leak or pseudomeningocoele | Low | Watertight dural and fascial closure | Lumbar drain, re-exploration and repair | | Non-union | Low with modern constructs | Rigid fixation, decortication, autograft | Revision fixation and grafting | | Posterior visual loss (prone) | Rare but devastating | Eyes free of pressure, avoid prolonged hypotension, limit operative time | Urgent ophthalmology; largely irreversible |

Extensile options. Extend proximally (cephalad) over the occipital squama to the foramen magnum for suboccipital and foramen magnum decompression (foramen magnum stenosis, Chiari, extradural tumour), limited laterally by the venous sinuses and the occipital condyles and with the vertebral artery at risk where it enters the foramen magnum. Extend distally (caudad) along the cervical and upper thoracic spinous processes to expose the subaxial spine (C3-C7) or upper thoracic levels for a long occipitocervical or occipitothoracic construct; the midline raphe persists to C7, keeping the plane avascular throughout. Lateral extension is strictly limited at every level by the vertebral artery: on the C1 arch the safe zone is confined to roughly 1.5 cm from the midline, and further lateral exposure requires formal identification and protection of the artery. Closure. Achieve meticulous haemostasis with particular attention to the suboccipital and epidural venous plexus. Reapproximate the paraspinal muscles and the ligamentum nuchae in layers over the construct and graft to restore the posterior cervical extensor mechanism. If the dura was opened or a CSF leak is present, close the dura and overlying fascia in a watertight fashion to prevent CSF leak and pseudomeningocoele. A subfascical drain is used for 24 to 48 hours in selected cases, and the fascia, subcutaneous tissue and skin are closed in layers. Post-operative care. Neurological monitoring (including occipital sensation via the C2 and greater occipital nerve and long-tract signs), with monitoring for wound haematoma and airway compromise (consider keeping the patient intubated overnight after prolonged prone upper cervical surgery). A rigid or semirigid cervical orthosis is worn for 6 to 12 weeks depending on construct rigidity and bone quality, with longer protection for wiring-only constructs. Wound check and suture or staple removal at 2 weeks, then standing lateral and AP cervical radiographs at 6 weeks, 3 months, 6 months and 12 months, with flexion-extension views at 3 months if instability or non-union is suspected.

Atlantoaxial (C1-C2) fixation options performed through this exposure:

Occipitocervical fixation. The occiput is fixed with an occipital plate seated on the midline occipital crest (the thickest bone) or with occipital wiring. Rods link the occipital fixation to cervical pedicle, lateral mass or isthmus screws. The head is positioned in the intended craniocervical alignment because the construct holds the patient in this position. All procedures performed through this approach: - Occipitocervical fusion - occipital plate (or occipital wiring) linked by rods to subaxial cervical screws for craniocervical instability

• Goel-Harms atlantoaxial fixation - polyaxial C1 lateral mass screws and C2 pedicle, pars or isthmus screws joined by rods; allows intra-operative reduction
• Magerl transarticular screw fixation - one screw on each side crossing the C2 isthmus and the C1-C2 facet into the C1 lateral mass, combined with posterior bone graft and wiring (Gallie or Brooks)
• Posterior wiring and bone-graft techniques - Gallie (single midline wire around the C1 arch and C2 spine with a corticocancellous graft) and Brooks-Jenkins (sublaminar wires at C1 and C2 with paired wedge grafts)
• Posterior decompression - occipital or C1 laminectomy and foramen magnum decompression

Guidelines, registries and global practice. Craniocervical and atlantoaxial instability is managed by spinal and trauma surgeons worldwide, and the principles of the posterior occipitocervical approach are convergent across examination systems (advanced orthopaedic practice and advanced orthopaedic practice, DNB and MS, MRCS, SICOT). Pre-operative cross-sectional imaging to define the bony anatomy and the vertebral artery course before any C1 or C2 screw is now universal, as is intra-operative fluoroscopy or imaging to confirm screw trajectory and reduction. Side-by-side principles (where guidance converges): | Body | Position on posterior craniocervical fixation | |------|-----------------------------------------------| | AO Foundation | Segmental screw-rod fixation (C1 lateral mass and C2 pedicle or isthmus) is the standard dorsal fixation of the craniocervical junction; rigid internal fixation with autograft and meticulous technique gives high fusion rates; pre-operative imaging of the vertebral artery is mandatory | | NICE and NHS (UK specialist spinal commissioning) | Complex craniocervical fixation is concentrated in specialist spinal centres; posterior fixation is preferred for instability where anterior decompression is not the primary need | | AAOS, AANS and CNS (US) | Occipitocervical and atlantoaxial fixation indicated for traumatic, inflammatory, congenital and neoplastic instability; image-guided screw placement reduces malposition | Global practice variation. In high-resource settings, intra-operative CT, navigation and neuromonitoring are standard for upper cervical screw placement. In resource-limited settings, the same dorsal midline approach and wiring-based techniques (Gallie, Brooks) achieve fusion without implants that depend on imaging, and fluoroscopy is used where available. The core surgical principle - the midline avascular plane and protection of the vertebral artery - is unchanged. Consent (globally applicable): discuss vertebral artery injury (bleeding, stroke, fistula), spinal cord injury and paralysis, C2 nerve injury and occipital neuralgia, CSF leak and dural injury, wound infection and dehiscence, non-union, and the risks of prone positioning including posterior visual loss.