Posterior Cervical Foraminotomy (Keyhole)

Surgical Indications

Absolute Indications

• Unilateral cervical radiculopathy from a posterolateral soft disc herniation with concordant symptoms and imaging, failing at least 6-12 weeks of conservative treatment (physiotherapy, NSAIDs, activity modification)
• Unilateral foraminal stenosis from an uncovertebral joint (Luschka) osteophyte compressing the exiting nerve root, with dermatomal pain and/or motor weakness
• Recurrent radiculopathy after prior ACDF at an adjacent level, where further anterior surgery is undesirable and the recurrent compression is posterolateral

Relative Indications

• Patient preference for motion-preserving surgery over fusion (avoids adjacent segment disease, preserves cervical range of motion, no graft or plate-related complications)
• Young patient (under 50) with a soft lateral disc where long-term fusion-related adjacent segment degeneration is a concern
• Prior anterior cervical surgery (scarring makes repeat anterior approach harder) where the new pathology is posterolateral and accessible posteriorly
• Contraindication to anterior surgery (prior irradiation, tracheostomy, severe cervical kyphosis precluding anterior exposure)

Contraindications

Absolute:

• Myelopathy from central canal stenosis or anterior cord compression — posterior foraminotomy decompresses only the lateral foramen and cannot address ventral cord compression
• Significant cervical kyphosis — posterior decompression removes posterior tension band elements and can worsen the kyphotic deformity
• Segmental instability on dynamic flexion-extension radiographs (greater than 3.5 mm translation or greater than 11 degrees angular motion)
• Pathology requiring resection of more than 50 percent of the facet joint — proceed to laminectomy with fusion or ACDF instead

Relative:

• Central disc herniation — ACDF provides direct anterior decompression and disc space restoration
• Bilateral radiculopathy — requires bilateral foraminotomies or alternative approach
• Predominant axial neck pain without radiculopathy — posterior foraminotomy targets the nerve root, not the disc or facet joint as pain generators; facet injection or medial branch blocks should be considered first
• Obesity with a thick posterior cervical soft tissue envelope — limits visualisation and increases retraction pressure in the minimally invasive tubular approach
• Prior posterior cervical surgery with scar tissue — increases difficulty of dissection and nerve root identification

Pathology and Rationale

Why Posterior and Not Anterior?

Posterior cervical foraminotomy accesses the nerve root from behind, drilling the lamina-facet junction to decompress the lateral foramen and remove a posterolateral disc fragment or foraminal osteophyte. The key advantage is that NO fusion is performed — the facet joint, disc, and motion segment are preserved.

This matters because:

• Adjacent segment disease: ACDF eliminates motion at the operated level and transfers biomechanical stress to adjacent segments, accelerating degeneration above and below the fusion over 10-20 years
• Fusion morbidity: ACDF carries risks of graft subsidence, plate/screw complications, dysphagia, dysphonia (recurrent laryngeal nerve injury), and pseudarthrosis
• Recovery: Foraminotomy patients typically return to work faster than ACDF patients because no bone graft healing or fusion is required

The posterior approach is ideal when the compressive pathology is posterolateral (lateral to the cord) and the compression can be reached by removing bone at the lamina-facet junction without violating the disc space anteriorly.

Best Pathology for Keyhole Foraminotomy

• Soft posterolateral disc herniation: the most common indication. A herniated nucleus pulposus fragment that has migrated postero-laterally into the neural foramen, compressing the exiting root. The fragment is accessible through the keyhole corridor and can be removed with pituitary forceps after bone decompression.
• Foraminal osteophyte: an uncovertebral joint (Luschka) osteophyte encroaching on the neural foramen from the anterior-lateral direction. These are harder than soft discs and may require more bone removal, increasing the risk of facet over-resection.

Pathology Better Suited to ACDF

• Central or paracentral disc herniation with cord compression or myelopathy
• Disc space collapse with loss of height and foraminal narrowing anteriorly
• Reversal of cervical lordosis or fixed kyphosis
• Discogenic axial neck pain (discography-positive) — foraminotomy does not address the disc

Evidence

Outcomes of Posterior Cervical Foraminotomy

Multiple case series and comparative studies report excellent outcomes for posterior cervical foraminotomy in appropriately selected patients:

• Clinical success rate: 85-97 percent good-to-excellent outcomes at short-to-medium term follow-up in appropriately selected patients with unilateral radiculopathy
• Arm pain relief: complete or near-complete resolution of radiculopathy in 85-95 percent of patients
• Nerve root recovery: motor strength recovery in patients with preoperative weakness is seen in 80-90 percent of cases within 6-12 months
• Return to work: median return to work 2-6 weeks (compared with 6-12 weeks after ACDF in most series)
• Reoperation rate: 5-10 percent at 5-10 years (primarily for recurrent disc herniation or persistent symptoms)
• Adjacent segment disease: NOT a concern (no fusion performed) — this is a long-term advantage over ACDF

Key Evidence

Posterior Cervical Anatomy — Key Structures

Surface Anatomy and Level Identification

• Spinous processes: C2 (bifid, prominent), C7 (most prominent non-bifid spinous process — vertebra prominens). In the subaxial spine, C3-6 spinous processes are bifid and overlapped.
• Midline: palpable from the external occipital protuberance to the C7 spinous process. The nuchal ligament runs in the midline and is the key landmark for the midline incision.
• Level localisation: preoperative lateral cervical radiograph with a metallic marker taped to the posterior neck confirms the operative level. Intraoperative lateral fluoroscopy confirms the target level before bone removal.
• Junction of lamina and lateral mass (facet joint): the V-shaped trough between the lamina and the facet is the surgical entry point for the keyhole. This junction lies approximately 1.5-2 cm lateral to the midline spinous process at the subaxial levels.

Subaxial Cervical Facet (Lateral Mass) Anatomy

• The cervical facet joint (lateral mass) is oriented 45 degrees to the sagittal plane — this oblique orientation means the lateral mass has a medial wall (facing the lamina) and a lateral wall (facing the posterior elements).
• Medial facet-lamina junction: the surgical keyhole is created at this junction. The lamina slopes downward and the facet joint slopes upward; the junction forms a V or trough that guides the initial burr entry.
• Facet joint size: the cervical facet is relatively small. At C5-6 (the most commonly operated level), the facet is approximately 10-12 mm in width and 12-15 mm in height. Resecting more than half of this small area significantly compromises stability.
• Superior and inferior articular processes: the superior facet of the lower vertebra and the inferior facet of the upper vertebra form the facet joint. The keyhole foraminotomy removes bone from the inferior edge of the superior facet (above) and the superior edge of the inferior facet (below).

Cervical Nerve Root Course

• The cervical nerve root exits ABOVE its corresponding pedicle (at C5-6, the C6 root exits above the C6 pedicle).
• After exiting the dural sac, the root angles obliquely infero-laterally through the neural foramen — approximately 45 degrees to the horizontal in the subaxial spine.
• Anterior: root lies on the posterior longitudinal ligament, the disc, and the uncovertebral joint (Luschka).
• Posterior: root lies against the superior articular process (facet) and the ligamentum flavum.
• Foramen boundaries: roof = superior pedicle, floor = inferior pedicle, anterior = uncovertebral joint and disc, posterior = facet and ligamentum flavum.

Vascular Anatomy

• Vertebral artery: lies anterior to the transverse foramen at each cervical level, lateral to the uncovertebral joint. At risk if bone removal extends too far laterally past the lateral mass.
• Posterior epidural venous plexus: prominent in the lateral recess; bleeds readily during bone removal and must be controlled before nerve root manipulation.
• Posterior cervical (segmental) spinal artery: small branches that enter the spinal canal through the intervertebral foramen; rarely a clinical issue during foraminotomy but can cause bleeding.

Muscles of the Posterior Cervical Spine

• Superficial layer: trapezius.
• Intermediate layer: splenius capitis and cervicis, levator scapulae.
• Deep layer (paraspinal): semispinalis cervicis and capitis, multifidus, rotatores.
• Key principle: in the open approach, the paraspinal muscles are elevated subperiosteally off the laminae and lateral masses — take care to preserve the facet capsule where possible, especially at levels adjacent to the decompression.
• Minimally invasive approach: a tubular retractor is docked on the lamina-facet junction using serial dilators, splitting (not stripping) the paraspinal muscle fibres — this preserves muscle attachments and reduces postoperative pain.

Ligamentum Flavum

• The ligamentum flavum connects the laminae, forming the posterior boundary of the spinal canal.
• At the lateral edge, the ligamentum flavum continues laterally and forms part of the posterior capsule of the facet joint.
• During foraminotomy, the lateral ligamentum flavum is removed to expose the nerve root and epidural space. This is a key step — the ligament must be removed carefully to avoid tearing the underlying dura.

Positioning and Preparation

Patient position: Prone on a Jackson spinal table or Wilton frame, with the head in a Mayfield three-point pin fixation or a padded skull clamp. The neck is maintained in a NEUTRAL or SLIGHTLY FLEXED position (not extended — extension closes the foramen and makes decompression harder).

Why neutral or slight flexion: slight flexion opens the interlaminar space and the neural foramen, making the laminofacet junction more accessible. Excessive flexion strains the posterior ligamentous complex and risks iatrogenic kyphosis. Extension closes the interlaminar interval and must be avoided.

Anaesthesia: General endotracheal anaesthesia with the patient prone. Intraoperative neuromonitoring (somatosensory evoked potentials [SSEP] and motor evoked potentials [MEP]) is strongly recommended — it provides real-time warning of nerve root or cord compromise during bone removal and retraction.

Antibiotic prophylaxis: single dose of IV cefazolin 2 g (or alternative based on allergies) at induction. Redose if the procedure exceeds 4 hours.

Intraoperative imaging: lateral cervical fluoroscopy confirms the operative level before incision and before bone removal. Use a radiopaque marker on a spinal needle placed on the appropriate spinous process.

Consent: counsel specifically regarding risk of nerve root injury (less than 1 percent permanent), spinal cord injury (rare but catastrophic), CSF leak/durotomy (1-3 percent), postoperative instability requiring secondary fusion, recurrence (5-10 percent), infection (less than 1 percent), and postoperative neck pain.

Open Technique — Step-by-Step

Step 1: Incision and Exposure

Make a midline posterior cervical incision centred on the spinous processes at the operative level(s). For a single-level foraminotomy at C6-7, the incision extends from the C5 to C7 spinous processes (approximately 3-4 cm).

In the subaxial spine, the spinous processes are bifid — dissect in the midline nuchal ligament. Subperiosteally elevate the paraspinal muscles (semispinalis and multifidus) off the laminae using Cobb elevators, working laterally to expose the medial facet-lamina junction (the V-shaped trough).

Place self-retaining retractors (Taylor or Adson) to maintain exposure. Ensure the facet capsule at adjacent levels is preserved — do not strip muscle off facet joints at levels not being operated on.

Step 2: Identify the Operative Level

Confirm the operative level with lateral fluoroscopy. Place a needle on the target spinous process before incision, or confirm with an intraoperative lateral radiograph after exposure.

Identify the lamina of the vertebrae above and below the target foramen. For a C6-7 foraminotomy (decompressing the C7 root), the operative corridor is at the lateral margin of the C6 and C7 laminae, centred on the C6-7 facet joint.

Step 3: Create the Keyhole — Initial Bone Removal

Using a high-speed pneumatic burr with a diamond or round burr tip, begin bone removal at the medial facet-lamina junction on the symptomatic side. The V-shaped trough between the lamina and the facet is the starting point.

Direction of bone removal: drill in a slightly lateral and cephalad direction, removing the medial edge of the inferior facet (of the vertebra above) and the superior edge of the superior facet (of the vertebra below). This opens the lateral recess and the medial edge of the neural foramen.

Depth control: the burr should remove cortical bone until the underlying cancellous bone is visible, then continue to thin the cortical bone of the lateral mass until the ligamentum flavum is encountered. Do NOT drill through the ligamentum flavum into the epidural space — remove the ligamentum flavum separately with Kerrison rongeurs.

Step 4: Remove the Ligamentum Flavum and Expose the Root

Once the cortical bone is thinned, carefully remove the ligamentum flavum at the lateral margin using Kerrison rongeurs (2 mm and 3 mm). Work from medial to lateral.

As the ligamentum flavum is removed, the epidural fat and the exiting nerve root become visible. The root lies laterally and is often draped with epidural veins.

Control epidural bleeding with bipolar diathermy and thrombin-soaked Gelfoam patties before proceeding.

Identify the exiting nerve root — it is a white, slightly shiny structure (resembling a strand of thick cotton) running infero-laterally through the foramen.

Step 5: Complete Foraminal Decompression

Now that the root is visualised, continue bone removal with the burr (and Kerrison rongeurs for thinner bone) to enlarge the foramen sufficiently for root decompression. The goal is to remove all compressive bone: the medial facet edge, foraminal osteophytes, and the posterior lip of the superior pedicle (if it contributes to foraminal narrowing).

Decompression endpoint: the nerve root is fully decompressed when it is visibly free of bony compression throughout its course through the foramen, and a nerve hook can be passed freely around the root proximally and distally without encountering bony obstruction.

At this stage, any soft disc fragment that has migrated posterolaterally into the foramen may be visible through the keyhole. Remove it gently with micropituitary rongeurs, retracting the root medially with a Penfield 4 dissector. Do NOT enter the disc space anteriorly.

Check the superior pedicle (roof of the foramen) and the lateral mass (posterior wall) — any residual osteophyte compressing the root is removed with the burr or Kerrison.

Step 6: Haemostasis and Closure

Achieve meticulous haemostasis. Irrigate the wound with warm saline. Perform a Valsalva manoeuvre (anaesthetist increases intrathoracic pressure) to check for any occult epidural venous bleeding.

If a durotomy occurred during the case ( recognised intraoperatively), repair with 6-0 Prolene suture, cover with a small fat graft harvested from the wound, and apply fibrin sealant. Consider a lumbar drain for 24-48 hours for larger tears.

Place a small drain (Hemovac or Jackson-Pratt) in the paraspinal muscle bed — NOT in the epidural space.

Close the deep fascia and nuchal ligament with 0 Vicryl sutures. Close subcutaneous tissue with 2-0 Vicryl. Close skin with staples or 3-0 nylon subcuticular suture.

Apply a soft cervical collar for comfort in the immediate postoperative period (optional — many surgeons do not collar patients after foraminotomy). The collar is NOT for stability (the facet is preserved) — it simply reduces neck pain from muscle splitting.

Minimally Invasive Tubular Technique

Differences from the Open Approach

• Incision: a 16-22 mm paramedian incision, approximately 12-15 mm lateral to the midline, centred on the lamina-facet junction.
• Muscle dissection: serial muscle-splitting dilators are passed through the paraspinal muscles (splitting, not stripping) to dock the tubular retractor on the lamina-facet junction. The retractor is then attached to the table-mounted arm.
• Visualization: an operating microscope or endoscope is used through the tubular retractor.
• Bone removal: identical principles — drill the medial facet-lamina junction, remove the lateral ligamentum flavum, decompress the root. The corridor is narrower, so incremental bone removal and irrigation are even more critical.

Advantages of the Tubular Approach

• Reduced paraspial muscle stripping and denervation
• Lower postoperative neck pain scores compared with open technique
• Shorter hospital stay (many patients go home the same day)
• Smaller scar and reduced wound morbidity

Disadvantages

• Narrower working corridor — loss of tactile feedback compared with open surgery
• Steeper learning curve — the surgeon must adapt to operating through a tube with microscopic or endoscopic visualisation
• Limited ability to extend the decompression if unexpected pathology is encountered (e.g., a more medial disc herniation)
• Cannot treat bilateral pathology through a single tube (requires two separate incisions)

Post-operative Protocol

Immediate Post-operative Phase (Day 0-1)

• Neurological observations: hourly motor and sensory checks in the recovery area for the first 6 hours, then 2-4 hourly for 24 hours. Document any change in preoperative deficits. Check for new radicular symptoms or myelopathic signs.
• Pain management: regular paracetamol and NSAIDs; oral opioids as required for the first 24-48 hours. Muscle relaxants (cyclobenzaprine or diazepam) are often helpful for paraspinal muscle spasm.
• Mobilisation: sit out of bed on the evening of surgery or the following morning. Walk with assistance initially. No collar is required in most patients — a soft collar may be used for comfort for the first few days if neck pain is significant.
• Drain removal: if a wound drain was placed, remove at 24-48 hours when output is less than 30 mL per 8-hour shift.

Early Recovery Phase (Week 1-2)

• Activity: walking as tolerated from day 1. Avoid heavy lifting (nothing heavier than 5 kg), repetitive neck extension, and vigorous overhead activity for the first 4 weeks.
• Wound care: staples or sutures removed at 10-14 days. Keep the wound dry for the first 5-7 days, then shower with a waterproof dressing.
• Driving: resume when neck pain is controlled, cervical range of motion is adequate for shoulder checks, and the patient is off opioid analgesia — typically 2-3 weeks.
• Physiotherapy: gentle active range-of-motion exercises for the cervical spine begin at 1-2 weeks postoperatively. Focus on restoring cervical flexion, extension, rotation, and lateral bending.
• Neck pain: some posterior neck pain and paraspinal muscle soreness is expected for 2-4 weeks, especially after the open approach. NSAIDs and gentle mobilisation are the mainstays of treatment.

Return to Function

• Office/sedentary work: 2-3 weeks
• Light manual work: 4-6 weeks
• Heavy manual work/contact sports: 8-12 weeks
• Full unrestricted activity: 12 weeks (including heavy lifting, contact sports, and high-impact activities)

Formal Physiotherapy Programme

• Weeks 1-4: gentle active cervical ROM exercises, isometric neck strengthening, postural re-education (especially for patients with pre-existing cervical lordosis loss)
• Weeks 4-8: progressive dynamic strengthening of the cervical and scapular stabilisers, proprioceptive training, functional movement retraining
• Weeks 8-12: sport-specific or work-specific rehabilitation, return-to-activity progression

Long-term Follow-up

• 6 weeks: clinical review with neurological examination; assess radiculopathy resolution, motor recovery, neck pain, and wound healing. Flexion-extension radiographs if there is any concern about stability.
• 3 months: repeat clinical assessment; most patients have returned to full activity by this stage. Persistent weakness at 3 months warrants nerve conduction studies and repeat MRI.
• 12 months: final clinical review; assess for recurrence. Long-term: educate the patient that recurrence of radiculopathy (new disc herniation or foraminal osteophyte progression) occurs in 5-10 percent of patients over 10 years.

Special Cases

Young Patient with Soft Lateral Disc

Posterior cervical foraminotomy is particularly well-suited to young patients (under 50) with a soft posterolateral disc herniation. These patients benefit most from the motion-preserving nature of the procedure because:

• Fusion at a young age commits the patient to decades of adjacent segment stress
• The soft disc fragment is easily removed through the posterior keyhole corridor
• The facet is typically normal, so adequate decompression with facet preservation is straightforward
• Long-term outcomes in this group are excellent with high patient satisfaction

Recurrent Radiculopathy After ACDF

When radiculopathy recurs at a level adjacent to a prior ACDF, a posterior foraminotomy may be the preferred approach because:

• The anterior approach is complicated by scar tissue from the prior fusion
• The new compression (typically foraminal osteophyte or lateral disc) is often accessible posteriorly
• The foraminotomy does not disturb the prior anterior fusion

Minimally Invasive Approach — When to Choose It

• Patient preference for smaller incision and same-day discharge
• Single-level unilateral radiculopathy with a favourable body habitus (BMI less than 35)
• No significant central stenosis or unexpected pathology expected
• Surgeon experience with tubular retractor systems — the learning curve is significant and outcomes correlate with case volume

C7-T1 Foraminotomy — Anatomical Considerations

The C7-T1 level requires special attention because:

• The C8 nerve root (exiting at C7-T1) supplies the intrinsic hand muscles — a root injury here has profound functional consequences
• The T1 vertebral artery lies closer to the surgical field than at higher subaxial levels
• The thoracic laminae are oriented differently from cervical laminae at this transitional level, and the facet orientation is slightly different
• The surgical corridor is narrower at C7-T1 than at C5-6, making facet preservation technically more demanding