Posterior Lumbar Interbody Fusion (PLIF)

Indications. PLIF is reserved for symptomatic lumbar pathology where an interbody fusion adds genuine value over decompression or posterolateral fusion alone — that is, when anterior column support, restoration of disc height and foraminal volume, and rigid segmental stabilisation are all required. Absolute indications

• Degenerative disc disease with mechanical low back pain refractory to greater than 6 months of conservative care including physiotherapy and injections
• Recurrent disc herniation with predominant leg pain and imaging evidence of instability or significant disc height loss
• Low-grade isthmic or degenerative spondylolisthesis (Meyerding grade I-II) with instability on flexion-extension radiographs
• Foraminal stenosis requiring indirect decompression via disc height restoration when direct decompression alone is insufficient Relative indications
• Post-discectomy instability or iatrogenic pars fracture
• Lumbar instability after trauma or tumour resection where anterior column reconstruction is needed
• Multilevel degenerative disease where hybrid constructs (PLIF at the index level plus posterolateral fusion) are planned
• Patient preference for a single-stage circumferential fusion avoiding an anterior approach Contraindications.
• Absolute: active spinal infection or discitis/osteomyelitis (requires debridement and staged reconstruction); severe osteoporosis with inability to achieve screw purchase (consider cement augmentation or an alternative approach); high-grade spondylolisthesis (Meyerding III-IV) where reduction and anterior column support may require combined approaches.
• Relative: previous extensive posterior surgery with scarring that would make safe thecal retraction hazardous (consider TLIF or ALIF); smoking or uncontrolled diabetes without willingness to optimise (counsel on elevated pseudarthrosis risk); morbid obesity where exposure and retraction are technically challenging. PLIF versus TLIF versus ALIF. The choice between the three interbody techniques turns on how much neural retraction a given pathology justifies and whether anterior-column lordosis is the priority.

Consent. Discuss dural tear (5-15%), nerve root injury or new radiculopathy (2-5%), cage subsidence or migration (3-8%), pseudarthrosis (4-10%), infection (2-4%), adjacent segment disease (5-10% at 5 years), and the possibility of revision surgery. Setup. Prone on a Jackson spinal table with the hips extended to maintain lumbar lordosis; the abdomen must hang freely to reduce venous pressure (epidural bleeding tracks venous pressure). Arms abducted less than 90 degrees to protect the brachial plexus; head neutral on a foam headrest or Mayfield clamp. General endotracheal anaesthesia with muscle relaxation; total intravenous anaesthesia if neuromonitoring (MEP/SSEP) is used, with an arterial line for prolonged cases and a cell saver available. Obtain true AP and lateral fluoroscopy before incision and confirm the correct level by counting from the sacrum.

The goal is a circumferential arthrodesis from one posterior incision: expose the posterior elements through a midline approach, instrument the segment with pedicle screws, decompress widely and resect both facets to expose the disc, retract the thecal sac and traverse the disc space bilaterally, prepare bleeding endplates and seat two interbody cages, then lock the construct in lordosis. The exposure — the midline approach, the subperiosteal strip to the transverse processes, and the bilateral facetectomy that opens the disc space — is laid out as the first steps below.

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Rehabilitation | Phase | Timing | Mobilisation & activity | Imaging | |-------|--------|-------------------------|---------| | Immediate | Day 0-3 | Sit up day of surgery; walk with assistance on day 1. No brace for single-level rigid fixation. Remove drain at 24-48 hours if output less than 50 mL/12 hours | — | | Early | Week 2-6 | Progressive walking; avoid bending, lifting greater than 5 kg, or twisting. Gentle core activation at 2 weeks; formal physiotherapy from 4-6 weeks | Standing AP/lateral at 6 weeks | | Late | Month 3-12 | Resistance training at 3 months if pain-free; return to sedentary work at 4-6 weeks, manual work at 12 weeks | Fine-cut CT at 6-12 months; flexion-extension films if concern | | Return to sport | Month 4-12 | Low-impact at 4-6 months; contact sport after solid fusion (9-12 months) | Confirm fusion before contact sport | Most patients return to desk work by 4-6 weeks and manual work by 12 weeks. Counsel on adjacent segment disease risk at annual review for two years. Special considerations. Smoking cessation is mandatory — fusion rates drop from greater than 90% to less than 70% in active smokers. Aim for diabetes control with HbA1c less than 7.5% to reduce infection and pseudarthrosis risk. Obtain a pre-operative DEXA in patients greater than 65 years or with risk factors, and consider cement-augmented screws if the T-score is less than -2.5. Revision PLIF carries a higher dural tear risk (up to 20%) from scarring — obtain a preoperative MRI to map the thecal sac and consider navigation or ultrasound for localisation.

Outcomes. Single-level PLIF with modern cages and posterior fixation achieves fusion rates of 90-96% at 2 years in prospective series. Clinical success (greater than 50% pain reduction and functional improvement) occurs in 70-85% of patients with degenerative disc disease. Compared with posterolateral fusion alone, PLIF provides superior disc height restoration and foraminal volume, reducing the need for direct foraminal decompression in selected cases. Why a bilateral approach needs more retraction. The thecal sac at L4-L5 and L5-S1 contains the cauda equina; individual nerve roots exit laterally at each level. The traversing nerve root exits the thecal sac at the axilla and courses laterally and inferiorly in the lateral recess to enter the foramen beneath the superior articular process. The exiting nerve root leaves the foramen at the level of the disc space and is vulnerable during distraction or cage insertion. The dorsal root ganglion lies within the foramen and is sensitive to retraction or compression. PLIF retracts the thecal sac bilaterally to reach the disc, which is why its dural tear rate (5-15%) exceeds TLIF (2-8%). Relevant anatomy for safe screw and cage work.

• Bony: the posterior elements are the spinous process, lamina, pars interarticularis, superior and inferior articular processes, and transverse processes. The lamina is thinnest at its junction with the pars, so an aggressive laminectomy can breach the pars and destabilise the segment. Facet orientation changes from more sagittal at L1-L2 to more coronal at L5-S1, affecting the extent of facetectomy needed.
• Vascular: segmental arteries run along the transverse processes and are at risk during lateral exposure or screw misplacement. Epidural veins form a rich plexus anterior to the thecal sac and can bleed briskly during discectomy. The anterior spinal artery and the artery of Adamkiewicz (usually T9-T12) are at theoretical risk with anterior cage migration but are rarely injured in PLIF.
• Disc and ligament: the posterior longitudinal ligament is thin in the lumbar region and must be divided to reach the posterior annulus; the annulus is thickest posteriorly and thinnest posterolaterally (the site of most herniations). Endplate cartilage is 0.5-1 mm thick centrally and must be removed completely while preserving the subchondral bone and peripheral rim. PLIF versus TLIF — the evidence. A meta-analysis of 12 comparative studies (Zhang, 2014; 841 patients) found no significant difference in fusion rate, complication rate or clinical outcome between PLIF and TLIF at 2 years, though PLIF carried longer operative time and greater blood loss and TLIF a lower dural tear incidence. Choice is therefore dictated by surgeon training and the pathology — bilateral disease favours PLIF. PLIF versus ALIF. ALIF provides superior lordosis restoration and avoids neural retraction but carries vascular and visceral risks (great vessel injury 1-3%, retrograde ejaculation in males 2-5%). PLIF avoids anterior morbidity and allows simultaneous posterior decompression and instrumentation. Combined approaches (ALIF plus posterior fixation) are reserved for high-grade listhesis, severe deformity, or revision with failed posterior fusion.