Anterior Transperitoneal Approach to L5–S1 (ALIF)

What it exposes. The anterior transperitoneal approach delivers direct midline access to the L5–S1 disc, the sacral promontory and the adjacent vertebral bodies through a midline laparotomy. It gives the most direct trajectory to the lumbosacral junction and allows straightforward placement of a large lordotic interbody cage. Why transperitoneal (and why it is now a niche route). The transperitoneal route is the most direct midline path to L5–S1, especially useful when the iliac crest is high or when previous left retroperitoneal surgery has created dense scarring. It crosses the peritoneal cavity, requires bowel mobilisation, and carries a small but real risk of retrograde ejaculation from superior hypogastric plexus injury. Modern practice has shifted heavily toward the left retroperitoneal approach for most primary ALIF procedures; transperitoneal is reserved for selected L5–S1 cases but remains a core examinable topic. Indications:

• Isolated L5–S1 degenerative disc disease requiring ALIF
• L5–S1 spondylolisthesis (low-grade) with disc degeneration
• Revision ALIF at L5–S1 when the retroperitoneal plane is scarred
• High-riding iliac crest anatomy precluding safe retroperitoneal access
• Selected cases of L5–S1 pseudarthrosis after posterior fusion Contraindications:
• Prior major abdominal surgery with extensive adhesions (relative)
• Active intra-abdominal infection or inflammatory bowel disease
• Morbid obesity with difficult peritoneal access
• Patient refusal of access surgeon involvement
• Need for multilevel fusion (L4–S1 or more) — retroperitoneal or combined is better Alternative approaches:
• Left retroperitoneal approach — preferred for most primary ALIF procedures
• Right retroperitoneal approach — rarely used due to liver and IVC position
• Lateral transpsoas (XLIF/DLIF) — for L2–L5, not L5–S1
• Posterior approaches (PLIF/TLIF) — avoid anterior vascular and plexus risks entirely Position & landmarks. Supine on a radiolucent table with 10–15 degrees of Trendelenburg so the bowel falls cephalad, lumbar lordosis maintained with a small bolster. A general or vascular access surgeon performs the approach. A Foley catheter decompresses the bladder, bilateral sequential compression devices are applied, arms are abducted less than 90 degrees or tucked, and a cell saver with blood products is immediately available. Surface landmarks are the umbilicus (level of L3–L4), the pubic symphysis (inferior limit), the linea alba (midline avascular plane) and the palpable rectus edges. The incision is a vertical midline laparotomy from just below the umbilicus to just above the pubic symphysis (10–15 cm), extended proximally or distally if multilevel exposure or difficult mobilisation is anticipated.

Work down through the abdominal wall in the midline, mobilise the bowel, then open the posterior peritoneum strictly over the sacral promontory, bluntly preserve the superior hypogastric plexus, control the middle sacral vessels, and mobilise the left common iliac vein to reveal the L5–S1 disc.

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Structures at risk, by layer

Intra-operative complications

Post-operative complications

Extensile options. Extend the peritoneal incision proximally along the left side of the aorta to reach L4–L5, but this requires extra mobilisation of the left common iliac vein and L4 segmental vessels and is rarely done through a purely transperitoneal route. Distal extension is limited by the pubic symphysis and sacral curvature — the approach cannot usefully extend below S1. For a 360-degree fusion, the anterior stage is completed first, then the patient is repositioned prone for posterior pedicle screw instrumentation. If the transperitoneal route proves unexpectedly difficult (dense adhesions, obese patient, poor visualisation), convert by closing the peritoneum and developing the left retroperitoneal plane from the same incision. Recovery & monitoring. Full weight bearing is permitted from the day of surgery (anterior column support from the cage), with no heavy lifting or bending for 6–12 weeks. DVT prophylaxis (LMWH or aspirin) is started within 24 hours. The Foley remains until ileus resolves (24–48 hours), with diet advanced as tolerated. Follow-up at 2 weeks (wound check), 6 weeks (radiographs), 3 months (CT if cage position is uncertain) and 6–12 months (confirm fusion). Enquire about sexual function in male patients at 3 and 6 months and document the response. Outcomes. L5–S1 ALIF achieves fusion rates exceeding 90 percent with modern cages and graft substitutes, with clinical success (ODI improvement greater than 15 points) in 80–85 percent of primary cases. Retrograde ejaculation persists long-term in approximately 1–3 percent of males. Adjacent segment degeneration occurs at 5–10 percent per year but is often asymptomatic, and revision rates for pseudarthrosis or hardware issues are 5–10 percent at 5 years. Good prognostic factors are isolated L5–S1 pathology, no prior abdominal surgery, access surgeon involvement, meticulous plexus preservation, a large lordotic cage with good endplate coverage, and a non-smoker with good bone quality.

• L5–S1 ALIF — isolated, or as the anterior stage of a 360-degree fusion with posterior lumbar decompression and fusion (PLDF).
• L5–S1 disc arthroplasty (rare).
• L5–S1 pseudarthrosis revision when the retroperitoneal plane is scarred.
• Selected high-grade spondylolisthesis reduction.
• Biopsy or debridement of an L5–S1 disc space infection.

Guidelines & global practice. Anterior lumbar approaches are performed worldwide, and the core principles — plexus preservation, vascular safety and access surgeon involvement — are consistent across examination systems. AO Spine and NASS guidance emphasise that anterior lumbar surgery should be performed with vascular or general surgical support when the transperitoneal route is chosen; BOA and NICE guidance stress explicit consent discussion of retrograde ejaculation risk in males. Registry data (NJR, AJRR, AOANJRR) show that L5–S1 ALIF is most commonly performed as part of a 360-degree fusion with posterior pedicle screw augmentation. In high-resource centres access surgeons are routine and cell salvage is standard; in resource-limited settings the same approach may be performed by the spine surgeon alone with careful attention to the three protection rules (blunt, midline, no monopolar). The biomechanical goal — a large lordotic cage at L5–S1 with posterior supplementation — is universal. Consent (globally applicable) must cover retrograde ejaculation (1–5 percent in males), vascular injury requiring repair or transfusion, ileus, adhesions, incisional hernia, infection, and the possibility of conversion to a retroperitoneal route or abandonment of the anterior stage.