Spondylolisthesis Reduction and Fusion

Indication. Symptomatic high-grade (Meyerding III to V) isthmic or degenerative spondylolisthesis — mechanical low-back pain with or without L5 radiculopathy or neurogenic claudication — that has an absolute reason to operate, or a low-grade slip that has failed a genuine trial of non-operative care. The isthmic pars defect lies at L5 in 85 to 90 percent of cases; degenerative listhesis is most common at L4-L5 and usually low-grade. Absolute indications

• Progressive slip on serial radiographs greater than 10 percent in 6 months
• Neurologic deficit (L5 radiculopathy or cauda equina) not responding to conservative care
• Severe sagittal imbalance with compensatory lumbar hyperlordosis or knee flexion
• High-grade slip (Meyerding III to V) with intractable mechanical low-back pain Relative indications
• Symptomatic high-grade slip with slip angle greater than 30 degrees even without frank neurologic deficit
• Failed conservative management (greater than 6 months) with activity-limiting pain
• Patient preference for definitive correction of deformity and restoration of sagittal balance Contraindications. Absolute: active spinal infection or tumour; severe untreated osteoporosis (T-score less than minus 3.5) without an augmentation plan; a patient unable to tolerate major surgery or comply with postoperative restrictions. Relative: a low-grade slip (I to II) without neurologic deficit or instability (consider in-situ fusion or decompression alone); prior extensive abdominal surgery (the posterior approach largely avoids this); a smoker unwilling to quit, who carries higher pseudarthrosis risk (consider a staged or BMP-augmented procedure). The one decision that matters — reduce, or fuse in situ? Reduction restores lumbosacral lordosis, improves sagittal balance and unloads the L5-S1 disc, but carries a 5 to 15 percent risk of transient L5 nerve-root injury (2 to 4 percent permanent). In-situ fusion avoids stretch injury but leaves residual kyphosis and may not halt progression in high-grade slips. Reduction is favoured for progressive slip, severe sagittal imbalance, or L5 radiculopathy from foraminal stenosis; in-situ fusion is acceptable when the slip angle is less than 30 degrees, neurology is intact, and balance is acceptable.

Consent specifically for L5 nerve injury (5 to 15 percent transient, 2 to 4 percent permanent foot drop — higher with slips greater than 75 percent and slip angles greater than 45 degrees), dural tear (5 to 8 percent), pseudarthrosis (5 to 12 percent with interbody), hardware failure, adjacent-segment disease (10 to 20 percent at 10 years), infection, and the possible need for staged or revision surgery. Setup. Prone on a Jackson table with the hips extended to increase lumbar lordosis, arms abducted less than 90 degrees, all pressure points padded, and a Foley catheter. Cell-saver and neuromonitoring (somatosensory and triggered EMG of the L5 roots) are mandatory. General endotracheal anaesthesia with total intravenous anaesthesia to allow neuromonitoring, an arterial line for blood-pressure control, preoperative antibiotics (cefazolin, or vancomycin if MRSA risk), and tranexamic acid 1 g at induction and 1 g at closure.

The goal: expose the lumbosacral junction posteriorly, perform a complete Gill decompression so both L5 roots run freely from pedicle to sacral promontory, instrument with pedicle screws, restore the anterior column with an interbody cage, and then — only then — reduce the slip gradually under continuous triggered-EMG protection. The exposure and the Gill decompression are the foundation of a safe reduction; they are laid out in full as the first operative steps below.

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Rehabilitation | Phase | Timing | Precautions / brace | Activity | |-------|--------|---------------------|----------| | Immediate | Day 0 to 3 | Log-roll only; no bending, lifting, twisting | Mobilise with the physiotherapist on day 1 to 2; drain out when output less than 50 mL per 24 h; multimodal analgesia | | Early | Week 1 to 6 | Brace if surgeon preference; no lifting greater than 5 kg | Gradual increase in walking; wound review at 2 weeks; gentle core activation from 4 weeks | | Intermediate | Week 6 to 12 | Transition out of brace | Progressive strengthening and proprioception; return to light work at 8 to 12 weeks if fusing | | Late | Month 3 to 12 | Full activity once fusion confirmed (usually 6 to 9 months) | Sport-specific rehabilitation after 6 months | Rehabilitation milestones. Day 1 to 2 sit-to-stand and short walks; week 6 independent activities of daily living and 30-minute walks; month 3 return to light or office work; month 6 fusion mass usually consolidating, begin impact activities; month 12 full unrestricted activity if the fusion is solid. If any foot drop is present, fit an ankle-foot orthosis and begin physiotherapy. Follow-up imaging. Standing radiographs at 6 weeks, 3 months, 6 months and 12 months, then annually; CT at 6 to 9 months if pseudarthrosis is suspected or to confirm fusion before high-demand activities. Annual radiographic surveillance for 5 years monitors adjacent segments. Complications

Pathoanatomy. The L5-S1 disc and facet joints bear the greatest shear forces in the lumbar spine. In isthmic spondylolisthesis a pars interarticularis defect (L5 in 85 to 90 percent of cases) allows anterior translation of L5 on S1; the loose lamina and hypertrophic callus compress the L5 roots in the foramen. Degenerative spondylolisthesis results from facet arthropathy and disc collapse without a pars defect, is most common at L4-L5, and is usually low-grade. The L5 nerve root exits the L5-S1 foramen and courses over the sacral promontory; in high-grade slips it is already stretched 1.5 to 2 cm longer than normal before any reduction. Meyerding grading and slip angle. Measured on a standing lateral radiograph as the percentage translation of L5 on S1.

The slip angle (lumbosacral angle) — between the superior endplate of L5 and the posterior wall of S1 — greater than 30 degrees predicts progression and favours reduction over in-situ fusion. Structures at risk.

Reduction versus in-situ fusion — the evidence.

Reduction restores lumbosacral lordosis, improves sagittal balance and unloads the L5-S1 disc, but carries a 5 to 15 percent risk of L5 nerve-root injury. In-situ fusion avoids stretch injury but leaves residual kyphosis and may not halt progression in high-grade slips. Modern series with neuromonitoring and wide decompression report permanent L5 palsy rates of 2 to 4 percent — acceptable when the alternative is an untreated high-grade deformity.