Transforaminal Lumbar Interbody Fusion (TLIF) Approach

Transforaminal lumbar interbody fusion (TLIF) is a posterior lumbar fusion technique that accesses the disc space through a unilateral facetectomy and transforaminal corridor (through the neural foramen), inserting a single interbody cage from ONE side (right or left) while preserving the CONTRALATERAL facet and posterior tension band. TLIF was popularised by Harms and Rolinger as a modification of PLIF (posterior lumbar interbody fusion) to reduce neurological morbidity: the transforaminal approach mobilises only ONE nerve root (the exiting root) and avoids the BILATERAL thecal sac and traversing-root retraction required for PLIF.

The critical anatomic concept is Kambin's triangle (the transforaminal "safe working zone") - a triangular corridor in the posterolateral foramen bounded by: (1) the exiting nerve root (the superior, oblique hypotenuse - e.g., the L4 nerve root crossing the upper L4-5 foramen), (2) the traversing nerve root / dural sac (the medial, vertical border - e.g., the L5 nerve root descending to exit at L5-S1), and (3) the superior endplate of the caudal vertebra (the inferior border/base). A trapezoidal "safe zone" lies immediately superior to the caudal pedicle and is free of nerve roots; this is the target for disc access. Kambin's transforaminal access principle was first described clinically by Kambin and Sampson (1986), and the working-triangle dimensions have since been quantified in cadaveric studies (mean working-triangle area approx 1.8 cm², largest at L5-S1 - Hardenbrook 2016).

The TLIF approach offers ADVANTAGES over PLIF: (1) Unilateral facetectomy - preserves the contralateral facet and posterior tension band, theoretically reducing adjacent-segment stress compared with the bilateral facetectomy of PLIF; (2) Single-root mobilisation - only the exiting root is retracted rather than the thecal sac and both traversing roots, with comparative series showing a TREND to fewer durotomies (approx 9% TLIF vs approx 17% PLIF) and less iatrogenic nerve-root dysfunction (approx 2% vs approx 8%), all transient in that series (Mehta 2010); (3) Equivalent fusion - TLIF and PLIF achieve comparable interbody fusion rates, both higher than instrumented posterolateral fusion alone (Makanji 2018).

The CRITICAL structures at risk are: (1) Exiting nerve root (1-8% injury risk - MOST COMMON neurological complication), which lies in the superior foramen deep to the superior articular process and crosses above the caudal pedicle; injured during facetectomy/SAP resection, by a too-lateral or too-superior upper pedicle screw, or by aggressive lateral retraction during disc/cage work, (2) Dura/thecal sac and traversing root (durotomy approx 3-9%), forming the medial wall of the corridor and injured during ligamentum flavum removal, medial retraction, or disc access, (3) Anterior great vessels (RARE, less than 0.5%, but CATASTROPHIC), at risk if an interbody instrument, anteriorly oversized cage, or an anteriorly breaching pedicle screw violates the anterior longitudinal ligament/anterior vertebral cortex. Note that the vertebral artery is NOT relevant in the lumbar spine - it terminates in the cervical/upper thoracic region and is not a structure at risk during lumbar TLIF.

Lumbar Facet Joint and Neural Foramen Anatomy

The lumbar facet joint (also called zygapophyseal joint) is formed by the superior articular process (SAP) of the caudal vertebra (e.g., L5 SAP at L4-5 level) and the inferior articular process (IAP) of the cephalad vertebra (e.g., L4 IAP). The facet joint is a synovial joint oriented at ~45° in the sagittal plane (vertical), providing resistance to anterior translation and rotation. The ligamentum flavum attaches to the anterior surface of the superior facet (medial border) and extends medially to cover the interlaminar space.

Neural Foramen Boundaries:

The neural foramen is the exit canal for spinal nerve roots, with boundaries:

• Anterior: Posterior vertebral body and intervertebral disc (anterior 1/3), superior endplate of inferior vertebra (middle 1/3), inferior endplate of superior vertebra (posterior 1/3)
• Posterior: Pars interarticularis and facet joint (ligamentum flavum covers medial aspect)
• Superior: Pedicle of cephalad vertebra (e.g., L4 pedicle forms superior border of L4-5 foramen)
• Inferior: Pedicle of caudal vertebra (e.g., L5 pedicle forms inferior border of L4-5 foramen)

Foramen Dimensions:

• Height: 18-22mm (L1-L5, decreases caudally)
• Width: 8-12mm (narrowest at mid-foramen where nerve root transitions from vertical to horizontal)
• Depth: 10-15mm (anterior-posterior distance)

The foramen is SMALLEST at the mid-level (where facet joint is located posterolaterally), creating a "waist" where nerve root impingement occurs in degenerative disease (facet hypertrophy, disc herniation, osteophytes reduce foraminal diameter).

Kambin's Triangle - The "Safe Zone" for TLIF

Kambin's triangle is the right-angled triangular working corridor in the posterolateral foramen that provides a relatively nerve-free zone for transforaminal disc access. The most widely used description of its boundaries is:

1. Hypotenuse (superior/oblique border): Exiting nerve root (e.g., the L4 nerve root at the L4-5 foramen) - crosses above the caudal pedicle and descends out of the foramen
2. Medial (vertical) border: Traversing nerve root and dural sac (e.g., the L5 nerve root at L4-5) - descends medial to the exiting root to exit at the level below
3. Inferior border (base): Superior endplate of the caudal vertebra (and the superior margin of the caudal pedicle)
4. Floor/anterior: Posterolateral annulus and disc
5. Roof/posterior: Superior articular process and ligamentum flavum (removed during facetectomy)

A useful refinement is the trapezoidal "safe zone" just superior to the pedicle, bounded by the exiting and traversing roots and the superior/inferior pedicle widths - this area is reliably free of nerve roots and is the target for disc access (Hardenbrook 2016).

Kambin's Triangle Dimensions (cadaveric, Hardenbrook 2016):

• Working-triangle surface area: mean approx 1.8 cm² (largest at L5-S1, approx 2.2 cm²)
• Safe-zone surface area: mean approx 1.2 cm² (largest at L5-S1, approx 1.3 cm²)
• Superior to the medial pedicle border, no neural structures were found within approx 1.2 cm at any level; on the lateral pedicle border the exiting root sits closest superiorly (as close as approx 0.3 cm)

Clinical Significance: Kambin's triangle provides a working zone for transforaminal disc access - instruments pass through the corridor to reach the disc without retracting the dural sac or traversing root. Although the bony working triangle is largest at L5-S1, the L5-S1 level remains demanding because the large exiting L5 root, a high iliac crest, and a deep, narrow disc space can limit the obliquity and trajectory available for cage delivery.

CRITICAL LIMITATION: Kambin's triangle is only "safe" if:

1. The facetectomy is complete enough to unroof the foramen and expose both roots (creating space and visualisation for instruments)
2. Disc access stays within the corridor (do NOT extend medially over the traversing root/dural sac)
3. The exiting nerve root is MOBILE (not tethered by scar, osteophyte, or foraminal stenosis)

Nerve Root Anatomy - Exiting vs Traversing

Understanding the DIFFERENCE between exiting and traversing nerve roots is CRITICAL for TLIF safety:

Exiting nerve root:

• Nerve that EXITS at the level of interest (e.g., L4 nerve root exits L4-5 foramen)
• Exits ABOVE the pedicle of the caudal vertebra (L4 nerve exits above L5 pedicle)
• Passes beneath the pars interarticularis and superior articular process, then descends out of the foramen
• Location: forms the superior/oblique border (hypotenuse) of Kambin's triangle; sits close to the superolateral pedicle margin (Hardenbrook 2016)
• MOST VULNERABLE during TLIF - injured during facetectomy/SAP resection, by a too-lateral or too-superior upper pedicle screw, or by aggressive lateral retraction

Traversing nerve root:

• Nerve that TRAVERSES (passes through) the level of interest to exit at the NEXT level (e.g., L5 nerve root traverses L4-5 disc space, exits L5-S1 foramen)
• Descends through the canal/foramen medial to the exiting root, then exits at the next level below
• Location: forms the MEDIAL (vertical) border of Kambin's triangle, with the dural sac, medial to the exiting root
• LESS VULNERABLE during TLIF, but at risk if disc/cage work extends too far medially or if the dural sac is over-retracted

Example at L4-5 level:

• Exiting nerve: L4 nerve root (exits L4-5 foramen, SUPERIOR border of Kambin's triangle, injured during facetectomy or upper pedicle screw)
• Traversing nerve: L5 nerve root (traverses L4-5 disc space, exits L5-S1 foramen, INFERIOR border of Kambin's triangle, relatively safe if staying in triangle)

Pedicle Anatomy - Screw Placement Corridor

The lumbar pedicle is the "corridor" connecting the posterior elements (lamina, facets) to the vertebral body. Pedicle dimensions:

• Width: 8-12mm at L1-L3, 12-16mm at L4-L5 (increases caudally)
• Height: 14-18mm at L1-L3, 16-20mm at L4-L5
• Length (anterior-posterior): 40-50mm
• Angle (transverse plane): 10-15° convergent at L1-L3, 0-5° at L4-L5 (less convergent caudally)

Pedicle Screw Trajectory:

For safe pedicle screw placement, the trajectory is:

• Entry point: Lateral to pars interarticularis, at junction of transverse process and superior facet (the "eye of the Scotty dog" on lateral fluoroscopy)
• Trajectory mediolateral: 10-15° convergent (more medial distally, toward vertebral body midline)
• Trajectory craniocaudal: Parallel to endplates (0-5° caudal angulation)
• Depth: 80-90% of vertebral body AP diameter (40-45mm typical), bicortical preferred for upper lumbar (L1-L3), unicortical acceptable for lower lumbar (L4-L5 where anterior vascular structures at risk)

Pedicle Screw Complications:

• Medial breach: Screw penetrates medial pedicle wall → canal encroachment, nerve root or thecal sac compression (5-10% incidence with freehand technique, less than 2% with navigation)
• Lateral breach: Screw penetrates lateral pedicle wall → exiting nerve root injury in foramen (2-5% incidence)
• Superior breach: Screw placed too superiorly → exiting nerve root injury at superior foramen (1-3% incidence)
• Anterior breach: Screw penetrates anterior vertebral body → vascular injury (aorta, IVC, iliac vessels), very rare less than 0.5% but catastrophic

Indications

TLIF is indicated for lumbar conditions requiring interbody fusion with posterior instrumentation:

1. Degenerative spondylolisthesis (Grade I-II) - MOST COMMON indication
2. Isthmic spondylolisthesis (Grade I-II) with instability
3. Degenerative disc disease with instability or failed conservative management (>6 months PT, injections, medications)
4. Recurrent disc herniation after prior discectomy (unstable segment)
5. Adjacent segment disease after prior fusion
6. Post-laminectomy instability (iatrogenic instability from extensive decompression)

Contraindications:

• High-grade spondylolisthesis (Grade III-IV) - TLIF access difficult, consider ALIF or PLIF
• Severe central stenosis requiring extensive bilateral laminectomy - PLIF or decompression alone
• Osteoporosis with high subsidence risk - consider ALIF (better endplate contact) or supplemental anterior support
• Infection or tumor - requires different approach/techniques

Patient Positioning

• Prone position on Jackson table or Wilson frame (hip flexion 30-45° opens interlaminar space, reduces lumbar lordosis, facilitates access)
• Chest and iliac crest support (avoids abdominal compression - reduces epidural venous pressure, decreases bleeding)
• Arms positioned on arm boards (flexed at shoulder 90°, elbow 90°)
• Face positioned on horseshoe headrest or mirror (avoid eye compression, check eyes every 30-60 minutes during long cases)
• Fluoroscopy positioned for AP and lateral lumbar spine views (confirm level before incision)

Practice Note: General anaesthesia is used; intraoperative neuromonitoring (somatosensory evoked potentials [SSEPs], motor evoked potentials [MEPs], and free-running/triggered electromyography [EMG]) is a common adjunct in many centres for lumbar fusion to monitor nerve-root and cord function and flag a pedicle-screw breach in real time, though its routine use varies between units and remains an adjunct to, not a substitute for, sound technique.

Skin Incision and Posterior Exposure

Step 1: Mark Incision and Confirm Level

Obtain lateral fluoroscopy image - identify target level (count from L5 - most caudal lumbar vertebra with disc space, upward to L4, L3, etc.). Mark skin incision MIDLINE over spinous processes, centered at target level, extending 2 levels above and below (e.g., for L4-5 TLIF, incision from L3 spinous process to L5 spinous process, total 6-8cm length).

Alternative: Paramedian incision (2-3cm lateral to midline) for MIS-TLIF (not described here - this is open technique).

Step 2: Incise Skin and Fascia

Incise skin and subcutaneous tissue MIDLINE down to thoracolumbar fascia. Use electrocautery to incise fascia MIDLINE over spinous processes (bloodless plane), extending full length of incision. Elevate fascia laterally off spinous processes and lamina using electrocautery or Cobb elevator (subperiosteal dissection).

Step 3: Paraspinal Muscle Dissection

Elevate paraspinal muscles (multifidus, longissimus) OFF lamina and facets using electrocautery or Cobb elevator (SUBPERIOSTEAL - stay on bone, reduces bleeding). Dissect laterally to expose:

• Lamina (posterior arch of vertebra)
• Spinous process (midline)
• Facet joints (lateral to lamina)
• Transverse processes (lateral limit of dissection - pedicle screws placed here)

Place self-retaining retractor (e.g., McCullough retractor, Caspar retractor) to hold muscles laterally and maintain exposure. Confirm level with LATERAL fluoroscopy (marker on target level spinous process).

Pedicle Screw Insertion (Performed FIRST, Before Decompression)

Step 4: Pedicle Screw Entry Points

Identify pedicle screw entry points BILATERALLY at target level (L4 and L5 for L4-5 TLIF) and adjacent level if multi-level fusion. Entry point landmarks:

• Mamillo-accessory notch (junction of mammillary process and accessory process on transverse process)
• OR junction of lateral pars interarticularis and superior facet ("eye of Scotty dog" on lateral fluoroscopy)
• Entry point is typically 3-5mm LATERAL to facet joint and 2-3mm INFERIOR to superior endplate of pedicle

Use high-speed burr to decorticate entry point (remove cortical bone, expose cancellous pedicle).

Step 5: Pedicle Probing and Tapping

Insert pedicle probe (Lenke or Magerl probe) into entry point, directed ~10-15° CONVERGENT (medially, toward midline) in transverse plane and PARALLEL to endplates in sagittal plane. Advance probe through pedicle into vertebral body (40-45mm depth typical), palpating walls of pedicle with probe (feel bone on all four sides - superior, inferior, medial, lateral - confirms intra-pedicle trajectory).

CRITICAL: If probe BREACHES pedicle wall (no resistance on one side), REMOVE probe, redirect entry point or trajectory, reprobe. DO NOT advance probe or screw if medial breach (canal encroachment) or lateral breach (exiting nerve root injury).

After successful probing, use pedicle tap (same diameter as intended screw) to create threaded pathway for screw. Confirm trajectory with LATERAL and AP fluoroscopy:

• Lateral view: Probe/tap parallel to endplates, extending into anterior 80-90% of vertebral body
• AP view: Probe/tap 10-15° convergent, within pedicle borders (no medial or lateral breach)

Step 6: Pedicle Screw Insertion

Insert pedicle screws (typically 5.5-6.5mm diameter, 40-50mm length) along probed trajectory. Use fluoroscopy to confirm screw position (AP and lateral views). Perform triggered EMG on each screw:

• Threshold greater than 8-10mA: SAFE (screw in bone, not touching nerve)
• Threshold less than 8mA: CONCERN for nerve proximity (screw may be breaching medial pedicle wall or laterally into foramen), consider screw removal and replacement

Leave screw heads TALL (do NOT fully seat screws) - allows rod connection later without compressing decompression site.

Unilateral Facetectomy and Decompression

Step 7: Choose Side for TLIF

TLIF is performed UNILATERALLY (one side only, typically RIGHT or LEFT). Choose side based on:

• Pathology side: If lateral recess stenosis or foraminal stenosis predominant on one side, choose THAT side for TLIF (combines decompression + fusion)
• Surgeon preference: Most surgeons have a preferred side (right-handed surgeons often prefer RIGHT side for ergonomics)
• Contralateral facet preservation: The NON-TLIF side preserves facet (maintains 40% stability, reduces adjacent segment disease)

For this description, assume RIGHT-SIDED TLIF (access disc from right side).

Step 8: Laminotomy (Partial Laminectomy)

On the RIGHT side, use Kerrison rongeurs to remove the INFERIOR portion of the lamina (cephalad vertebra, e.g., L4 lamina for L4-5 TLIF). Remove lamina medial to facet joint, exposing underlying ligamentum flavum. Extend laminotomy superiorly to expose superior edge of facet joint.

Goal: Create space for facetectomy and access to neural foramen (laminotomy exposes ligamentum flavum and superior facet medially).

Step 9: Complete Unilateral Facetectomy

Perform a COMPLETE unilateral facetectomy on the working side - this is the defining step of TLIF and is what opens the transforaminal corridor. Resect the INFERIOR articular process of the cephalad vertebra first (e.g., the right L4 IAP for a right L4-5 TLIF), then resect the SUPERIOR articular process of the caudal vertebra (the right L5 SAP) down to the level of the pedicle. The resected facet provides excellent local autograft and should be saved and morselised.

Facetectomy Technique:

1. Identify and incise the facet capsule: expose the facet joint surfaces.
2. Remove the IAP: use an osteotome or Kerrison/burr to take the inferior articular process of the cephalad vertebra, exposing the underlying superior articular process of the caudal vertebra.
3. Remove the SAP down to the pedicle: thin/resect the superior articular process until the foramen is unroofed; thin the final bone over the nerve incrementally and switch to a Kerrison rongeur or osteotome (tactile feedback) rather than plunging with a burr. Keep irrigation on (bone dust obscures the root; heat damages nerve).
4. Positively identify both roots: with the foramen unroofed, identify the exiting root in the superior foramen (deep to the SAP) and the traversing root/dural sac medially. The exiting root is a soft, pale structure crossing above the caudal pedicle.
5. Palpate and protect: use a blunt nerve hook/ball-tip probe to confirm the exiting root is mobile and out of the working corridor before disc access.

CRITICAL: An INADEQUATE facetectomy (foramen not unroofed, roots not seen) is a key cause of exiting nerve-root injury - the surgeon then instruments the disc blindly. A complete facetectomy that exposes both roots is the safest path to the disc and yields the local graft.

Step 10: Ligamentum Flavum Removal

After facetectomy, remove ligamentum flavum from interlaminar space using Kerrison rongeurs. Start laterally (at facet) and work medially toward midline. Ligamentum flavum is THICK (3-5mm) and YELLOW (hence "flavum" = yellow).

Goal: Expose epidural space, thecal sac medially, and exiting nerve root laterally (completes decompression of central and lateral recess stenosis).

Discectomy and Endplate Preparation Through Kambin's Triangle

Step 11: Identify Kambin's Triangle

With the facetectomy complete and the ligamentum flavum removed, identify the boundaries of Kambin's triangle:

• Superior/oblique border (hypotenuse): Exiting nerve root (e.g., the RIGHT L4 root for a right L4-5 TLIF) - in the superior foramen, crossing above the L5 pedicle (already exposed during facetectomy)
• Medial (vertical) border: Traversing nerve root and dural sac (e.g., the L5 root) - descending medial to the exiting root, covered by epidural fat
• Inferior border (base): Superior endplate of the caudal vertebra and the superior margin of its pedicle

The disc is accessed through the corridor between these structures, using the nerve-free supra-pedicular safe zone, with the dural sac and traversing root protected medially and the exiting root protected superolaterally.

Step 12: Annulotomy and Discectomy

Using a #15 scalpel blade on a long handle, make an annulotomy (incise annulus fibrosus) over the RIGHT lateral disc space (within Kambin's triangle, between exiting and traversing nerve roots). Typical annulotomy size 10-12mm (vertical incision).

Discectomy Technique:

1. Remove nucleus pulposus: Use pituitary rongeurs and angled curettes to remove soft nucleus centrally (bulk of disc)
2. Remove annulus: Extend discectomy circumferentially, removing annular fibers from anterior, contralateral (left), and posterior disc space. Goal: 360° discectomy (remove ALL disc material down to vertebral endplates).
3. Preserve posterior longitudinal ligament (PLL): Do NOT violate PLL (posterior boundary of disc space, separates disc from thecal sac anteriorly). PLL violation causes CSF leak if dura torn.
4. Contralateral disc access: Use angled curettes and reverse-angle rongeurs to reach LEFT (contralateral) side of disc space through RIGHT-sided annulotomy (work around thecal sac anteriorly - PLL separates instruments from dura).

CRITICAL: Complete discectomy (remove ALL disc material, 360° circumferential) is ESSENTIAL for fusion - residual disc material blocks bone graft incorporation and causes pseudarthrosis.

Step 13: Endplate Preparation

After discectomy, prepare vertebral endplates (superior L5 endplate and inferior L4 endplate) for fusion:

1. Remove cartilaginous endplate: Use curettes or endplate scrapers to remove thin cartilaginous layer (0.5-1mm) from both endplates - exposes bleeding cancellous bone (necessary for fusion)
2. Preserve subchondral bone: Do NOT violate thick subchondral bone (dense bone beneath cartilage) - provides structural support, prevents cage subsidence
3. Create bleeding bone bed: Endplates should be actively bleeding (confirms viable bone for fusion)

Balance: Remove cartilage (non-vascular, blocks fusion) but preserve subchondral bone (structural support). Over-aggressive endplate preparation causes subsidence (cage migrates into soft cancellous bone - 8-15% incidence).

Interbody Cage Insertion and Bone Graft

Step 14: Measure and Size Cage

Measure disc space height and depth using trial spacers or calipers. Select appropriate cage:

• Height: Restore disc height to pre-degenerative state (typically 10-12mm at L4-5, 8-10mm at L5-S1)
• Depth: 25-30mm typical (fits within anterior 60-70% of disc space - avoid oversizing anteriorly, risk of cage migration into retroperitoneum or vascular injury)
• Width: 10-12mm (fits through Kambin's triangle annulotomy)
• Lordosis: 6-10° lordotic angle built into cage (restores lumbar lordosis)

Cage types:

• PEEK cages: Most common, radiolucent (allows fusion assessment), filled with bone graft or BMP
• Titanium cages: Radiopaque (obscures fusion on X-ray), higher subsidence risk
• Expandable cages: Inserted collapsed, expanded in situ (less endplate preparation needed, but higher cost)

Step 15: Pack Cage with Bone Graft

Fill cage central cavity with bone graft:

• Autograft: Local bone (laminectomy bone, facet bone) morselized - GOLD STANDARD (best osteogenic potential)
• Allograft: Freeze-dried or fresh-frozen cancellous chips (if inadequate autograft)
• Bone graft substitute: BMP (bone morphogenetic protein, e.g., Infuse), demineralized bone matrix (DBM), synthetic graft (calcium phosphate, hydroxyapatite)

Compress graft into cage (maximize graft volume). Pack graft around edges of cage as well (additional graft in disc space, outside cage).

Step 16: Insert Cage Under Fluoroscopy

Using cage holder/inserter, advance cage through annulotomy into disc space under continuous LATERAL fluoroscopy (ensures cage positioned centrally in disc space, not posteriorly). Insert cage from RIGHT side, angled slightly LEFT (toward contralateral side) to center cage in disc space.

Fluoroscopy Confirmation:

• Lateral view: Cage at midline of disc space (anteroposterior), parallel to endplates, within anterior 60-70% of vertebral body (NOT too anterior - risk of vascular injury or retroperitoneal migration)
• AP view: Cage centered mediolaterally, symmetric positioning (NOT too far right or left)

CRITICAL: Avoid oversizing cage height (causes subsidence or endplate fracture), under-sizing (inadequate disc height restoration, foraminal stenosis persists), or excessive anterior placement (cage migrates anteriorly into retroperitoneum or injures great vessels - RARE less than 0.5% but catastrophic).

Step 17: Place Additional Bone Graft Posterolaterally

After cage inserted, pack additional bone graft posterolaterally (in gutter between transverse processes, over pedicle screws, along lateral fusion bed). This supplements interbody fusion with posterolateral fusion (360° fusion - interbody PLUS posterolateral).

Rod Placement and Compression

Step 18: Connect Rods to Pedicle Screws

Bend rods (5.5mm diameter cobalt-chromium or titanium rods) to match lumbar lordosis (typically 40-60° lordosis from L1-S1, with most lordosis at L4-5 and L5-S1 levels). Insert rods into screw heads (pass rod through open screw heads from caudal to cephalad). Provisionally tighten set screws (setscrews secure rod to screw head).

Step 19: Apply Compression Across Disc Space

Using rod persuader or compression instrument, apply compression force across disc space (brings vertebral endplates together, compresses bone graft in cage, promotes fusion). Compression is applied by tightening setscrews while maintaining compression force.

Compression Goals:

• Restore disc height (not over-distract)
• Compress graft (but not excessively - graft should be under compression loading, not crushed)
• Maintain lumbar lordosis (rods should match pre-operative lordosis)

Step 20: Final Fluoroscopy and Closure

Obtain AP and lateral fluoroscopy to confirm:

• Pedicle screws: All screws within pedicles, no breaches, appropriate depth
• Cage: Centered in disc space, parallel to endplates, appropriate height
• Rods: Secure to all screws, lordotic contour

If satisfactory, perform FINAL wound irrigation with antibiotic solution (bacitracin 50,000 units in 1L saline), place deep drain (if desired - reduces hematoma), close fascia with #1 absorbable suture (Vicryl), close subcutaneous tissue with 2-0 absorbable, close skin with 3-0 non-absorbable (nylon) or staples.

Post-operative immobilization: LSO brace for 6-12 weeks if single-level TLIF (supports fusion during early healing), NOT required if solid instrumentation and patient has good bone quality.

Post-operative Protocols

Phase 1 (Days 0-2): Immediate Post-op

• ICU/HDU monitoring: Not routinely required (unlike complex multi-level fusions or patients with comorbidities)
• Pain control: Multimodal analgesia (acetaminophen 1g Q6h, NSAIDs cautiously - concern for fusion impairment, opioids PRN via PCA, consider epidural for first 24-48 hours)
• Early mobilization: Out of bed to chair post-op day 1 (early mobilization reduces VTE risk, ileus, pulmonary complications), walking with assistance day 1-2
• Neuromonitoring: Continue EMG/SSEP monitoring for first 2-4 hours post-op (detect delayed neurological deficit from hematoma or retraction injury)
• Drain management: Remove deep drain when output less than 50mL per 8-hour shift (typically 24-48 hours post-op)
• Urinary catheter: Remove day 1 (prolonged catheterization increases UTI risk)
• Discharge: Typically post-op day 3-5 for open TLIF, day 2-3 for MIS-TLIF

Phase 2 (Weeks 0-6): Brace and Activity Modification

• LSO brace: If single-level TLIF - wear brace during upright activities for 6-12 weeks (supports fusion, reduces motion). NOT required if solid instrumentation and multi-level fusion (instrumentation provides adequate stability).
• Activity: NO bending, lifting greater than 10 pounds, twisting for 6-12 weeks (until fusion progressing)
• Walking: Unlimited walking encouraged (promotes healing, cardiovascular fitness, does NOT harm fusion)
• Driving: Resume at 4-6 weeks if no opioids and adequate mobility (twisting to check blind spots may strain fusion site - delay until 6 weeks)
• Return to sedentary work: 6-8 weeks (desk work, no lifting)
• X-rays: AP and lateral lumbar spine at 2 weeks, 6 weeks, 3 months (assess hardware position, disc height, early subsidence)

Phase 3 (Months 3-6): Progressive Activity

• Remove brace: At 3 months if fusion progressing on X-ray (bridging bone across disc space)
• CT scan: At 6 months if fusion questionable on X-ray (CT is gold standard - shows trabecular bone bridging through cage)
• Physical therapy: Core strengthening, lumbar stabilization exercises (once fusion solid - typically 3-6 months)
• Return to manual labor: 6-9 months (based on fusion status and functional recovery)
• Return to high-impact activities: 9-12 months (running, contact sports - only after confirmed solid fusion on CT)

Phase 4 (12+ Months): Long-term Surveillance

• Annual X-rays: Monitor for adjacent segment disease (disc degeneration above or below fusion level)
• Assess function: ODI (Oswestry Disability Index), VAS pain scores (track long-term outcomes)
• Address complications: Hardware failure (screw breakage, rod fracture - rare less than 2% if solid fusion), pseudarthrosis (persistent pain >12 months, no bridging bone on CT - requires revision)

Return to work (general guidance): Typically 6-12 weeks for sedentary work and 6-9 months for manual labour, individualised to fusion progress and functional recovery. Inpatient rehabilitation is occasionally needed for complex multi-level fusions or frail/elderly patients with limited mobility, but is not routine for single-level TLIF.

Complications

Intraoperative Complications

1. Exiting Nerve Root Injury (1-8% - MOST COMMON Neurological Complication)

• Presentation: Intraoperative EMG activity (spontaneous or triggered less than 8mA threshold during facetectomy or pedicle screw placement), patient reports radicular pain in distribution of exiting nerve post-operatively (e.g., L4 nerve injury causes anterior thigh pain and quadriceps weakness)
• Mechanism: Facetectomy/SAP resection (overzealous drilling or rongeur laceration is the commonest mechanism), upper pedicle-screw malposition (too lateral or superior, breaching the foramen), and aggressive lateral retraction stretching the nerve over the pedicle
• Management:
  • Intraoperative detection (EMG fires): STOP, identify cause (facet drilling, screw placement, retraction), address cause (reposition screw, release retraction, stop drilling and use Kerrison rongeurs), confirm nerve intact (visualize nerve, palpate with nerve hook - should be soft, not transected), continue if nerve intact
  • Post-operative deficit (motor or sensory): Obtain URGENT MRI or CT myelogram (rule out hematoma compression - if present, requires emergent re-exploration and evacuation), if imaging shows no compressive lesion (hematoma, cage malposition), likely neuropraxia or stretch injury - manage conservatively
• Prognosis: Neuropraxia (most common) usually recovers over 3-6 months; axonotmesis (axons damaged, nerve in continuity) recovers more slowly and incompletely; neurotmesis (transection) does not recover spontaneously and requires exploration and repair/grafting with generally poor functional outcomes
• Prevention: Complete unilateral facetectomy unroofing the foramen so both roots are seen before disc access, Kerrison/osteotome (not an uncontrolled burr) for the final bone over the nerve, triggered EMG to confirm safe pedicle-screw position, and gentle retraction with frequent release

2. Dural Tear / Durotomy (approx 3-9%)

[Covered comprehensively in SafetyAlert above]

3. Cage Malposition (2-5%)

• Presentation: Post-operative X-ray shows cage too posterior (canal encroachment, nerve root compression), too anterior (risk of vascular injury or retroperitoneal migration), or too lateral (foraminal stenosis, exiting nerve compression)
• Management: If cage causing neural compression (radiculopathy, cauda equina), requires URGENT revision (remove cage, reposition correctly). If asymptomatic malposition, observe.
• Prevention: Continuous fluoroscopy during cage insertion (lateral and AP views), confirm cage position before wound closure

Early Post-operative Complications (less than 6 weeks)

1. Hematoma with Neurological Deficit (2-5%)

• Presentation: New or progressive neurological deficit 6-24 hours post-op (foot drop, cauda equina syndrome), back pain, wound swelling
• Diagnosis: URGENT MRI or CT (shows epidural hematoma compressing thecal sac or nerve roots)
• Management: URGENT re-exploration and evacuation (decompress neural elements, achieve hemostasis, close over drain). Delay >24 hours reduces chance of neurological recovery.
• Prevention: Meticulous hemostasis during closure, deep drain placement (evacuates blood, reduces hematoma formation), monitor neurological status closely first 24 hours (neuro checks every 2-4 hours)

2. Wound Infection (2-5%)

• Superficial infection (1-2%): Erythema, purulent drainage, cellulitis within 2-4 weeks. Management: empirical oral antibiotics covering skin flora (e.g., a first-generation cephalosporin, or clindamycin if penicillin-allergic) per local guidelines, wound care, close monitoring.
• Deep infection (1-3%): Persistent drainage, wound dehiscence, exposed hardware, fever, elevated CRP/ESR. Management: empirical IV antibiotics (broad Gram-positive cover including MRSA, e.g., vancomycin, plus Gram-negative cover, narrowed to culture), surgical debridement (remove necrotic tissue, irrigate, RETAIN hardware if fixation stable - removal causes instability), negative pressure wound therapy (NPWT) where appropriate, and a prolonged antibiotic course (typically several weeks IV then oral) guided by infectious-diseases input.
• Prevention: Pre-operative antibiotics (cefazolin 2g IV within 1 hour of incision), re-dose Q4 hours if surgery >4 hours, meticulous sterile technique, minimize operative time, blood glucose control if diabetic (target less than 180mg/dL perioperatively)

3. DVT/PE (8-12%)

• Risk factors: Posterior lumbar surgery has HIGHER VTE risk than anterior (8-12% vs 2-5%) - prolonged immobility, prone positioning, epidural venous plexus manipulation
• Presentation: Calf pain, leg swelling (DVT), dyspnea, chest pain, hypoxia (PE)
• Management: Venous duplex (DVT), CT pulmonary angiography (PE), therapeutic anticoagulation (enoxaparin 1.5mg/kg SC daily OR apixaban 10mg BD × 7 days then 5mg BD for 3 months)
• Prevention: Mechanical prophylaxis (intermittent pneumatic compression) for all, with chemical prophylaxis (e.g., LMWH) added per institutional protocol once the bleeding/epidural-haematoma risk is acceptable; early mobilisation (out of bed day 1). Note that timing of chemical VTE prophylaxis after spinal surgery is individualised because of epidural haematoma risk, and named-society guidance differs.

Late Complications (greater than 6 weeks)

1. Pseudarthrosis (8-15%)

• Presentation: Persistent back pain >6 months post-op, no improvement with conservative treatment, pain worse with activity
• Diagnosis: CT scan at 12 months (gold standard) shows no bridging bone through cage or posterolateral fusion mass (radiolucency around cage, no trabecular continuity)
• Risk factors: Smoking (a strong, modifiable inhibitor of bone healing), diabetes, chronic NSAID use (may impair fusion - generally avoided in the early postoperative months), inadequate graft volume, and excessive motion (insufficient instrumentation)
• Management: Revision surgery - revision TLIF with larger cage and BMP (bone morphogenetic protein), OR anterior supplementation (ALIF if posterior TLIF failed), OR extension of fusion to adjacent levels if instability adjacent
• Prevention: Smoking cessation (MANDATORY - discuss pre-op, delay elective surgery until smoke-free >4 weeks), avoid NSAIDs >3 months post-op (use acetaminophen for pain), adequate bone graft volume (pack cage and posterolateral gutters completely), brace for 6-12 weeks (reduces motion during healing)

2. Subsidence (8-15%)

• Presentation: Recurrent back pain or radiculopathy 2-6 months post-op (after initial improvement), loss of disc height on X-ray (cage migrates into vertebral body endplate)
• Definition: Cage migration greater than 2mm into endplate (measured on lateral X-ray or CT)
• Risk factors: Osteoporosis (the strongest risk factor), over-aggressive endplate preparation (removing structural subchondral bone), and an oversized cage / over-distraction fracturing the endplate
• Management: Most subsidence is asymptomatic and is observed; symptomatic subsidence may need revision with anterior supplementation (ALIF) or a larger-footprint cage
• Prevention: Screen for osteoporosis pre-operatively (DEXA for at-risk patients) and optimise bone quality before elective surgery (e.g., bisphosphonate or anabolic therapy where indicated); use the largest cage footprint the disc accepts and prepare endplates to remove cartilage while preserving the subchondral bony endplate

3. Adjacent Segment Disease (ASD)

• Presentation: New back pain or radiculopathy 2-5 years after fusion (pain above or below the fusion level)
• Mechanism: Fusion eliminates motion at the fused level and transfers load to adjacent segments, accelerating degeneration. Preserving the contralateral facet and posterior tension band (a feature of TLIF versus bilateral-facetectomy PLIF) is biomechanically attractive, though clinical evidence that this reduces symptomatic ASD is mixed; restoring sagittal alignment/lordosis is at least as important.
• Management: Conservative first (physiotherapy, analgesia, epidural steroid injection); revision surgery (extending the fusion) if conservative measures fail and there is structural adjacent-level pathology
• Prevention: Restore and maintain segmental and global lumbar lordosis at the index fusion, avoid over-distraction, and preserve the posterior tension band where the decompression allows