Anterior Lumbar Interbody Fusion (ALIF)

Indication. Symptomatic degenerative disc disease at L4-L5 or L5-S1 with concordant discogram or MRI changes that has failed six months of conservative treatment; low-grade (Grade I-II) isthmic or degenerative spondylolisthesis with foraminal stenosis needing indirect decompression and lordosis restoration; revision of a failed posterior fusion with pseudarthrosis and anterior column deficiency; or lumbar disc arthroplasty conversion/explantation requiring anterior column reconstruction. Assess the whole patient, not just the disc. Before committing to an anterior approach, exclude or plan for the factors that change the operation or its risk profile:

• Pelvic incidence — a high pelvic incidence patient needs aggressive segmental lordosis restoration (greater than 10 degrees at L5-S1), which is exactly what ALIF delivers well.
• Bone quality — check a DEXA; severe osteoporosis (T-score less than -3.5) without a plan for supplemental posterior fixation and cement augmentation is a contraindication to a stand-alone construct.
• Prior abdominal surgery — extensive left retroperitoneal or lower-abdominal surgery gives a hostile plane; consider XLIF or TLIF instead.
• Male sex — counsel every male patient on the retrograde ejaculation risk at L5-S1 and document preoperative sexual function.
• Grade of listhesis — high-grade (Grade III-IV) spondylolisthesis is usually better served by posterior reduction and fusion. The one decision that matters — is ALIF the right interbody technique? Every interbody option restores disc height and fuses the segment; ALIF is chosen when you need the largest possible cage footprint and maximal lordosis without touching the nerve roots. The alternatives trade those advantages for different risk profiles:

Consent specifically for major vascular injury (1-3 percent), retrograde ejaculation in males (0.5-5 percent), ureteric injury (less than 1 percent), ileus (5-15 percent), wound hernia (2-5 percent), cage subsidence, pseudarthrosis (5-15 percent), and the possible need for posterior supplementation either at the same sitting or staged. Setup. Supine on a radiolucent table with the lumbar spine in slight extension (a bump under the sacrum helps open L5-S1), arms abducted 90 degrees, and a slight left lateral tilt of 10-15 degrees to improve access to the left retroperitoneum. A urinary catheter is placed and preoperative antibiotics (cefazolin plus metronidazole for bowel coverage) are given within 60 minutes of incision. General endotracheal anaesthesia with muscle relaxation, an arterial line and large-bore IV access, and a cell saver on standby for potential vascular injury. An access surgeon is present in most centres for the exposure and vessel mobilisation.

The goal: reach the L4-L5 or L5-S1 disc through a left retroperitoneal exposure, mobilise the great vessels safely, perform a complete discectomy with endplate-preserving preparation, and implant the largest lordotic cage that fits — then decide whether the construct needs posterior supplementation. The exposure and vessel mobilisation are the heart of the operation and the source of its serious complications, so they are laid out as the first steps below.

View larger

Rehabilitation | Phase | Timing | Activity | Brace / imaging | |-------|--------|----------|-----------------| | 1 | Day 0-3 | Out of bed to chair day of surgery; ambulate with assistance from day 1; clear fluids advancing to regular diet; watch for ileus | Drain out when less than 50 mL per 12 h; AP and lateral radiographs before discharge | | 2 | Week 1-6 | Progressive walking; avoid bending, twisting and lifting greater than 5 kg; gentle core activation at 2 weeks, formal physiotherapy at 6 weeks | Optional soft lumbar corset for comfort; sedentary work from 4-6 weeks | | 3 | Month 3-12 | Gradual return to sport and heavy lifting once radiographic fusion is confirmed; manual labour from 3-6 months | CT at 6 months if symptoms persist or before return to heavy labour; annual clinical review for 2 years | Special considerations. For osteoporosis, consider teriparatide or romosozumab peri-operatively and cement-augmented pedicle screws if posterior fixation is used. Smoking cessation is mandatory — 4 weeks pre-operatively and 6 months post-operatively, with a markedly higher pseudarthrosis rate if it continues. For more than two levels or anticipated significant blood loss, plan staged posterior supplementation. Complications

Why the anterior approach works. ALIF gives the largest cage footprint of any lumbar interbody technique, which maximises endplate coverage and the fusion surface area. Because the disc height is restored from the front, foraminal stenosis is decompressed indirectly without any neural retraction, and the anterior position of a lordotic cage restores segmental lordosis effectively — 8-12 degrees at L5-S1, critical for sagittal balance in high pelvic incidence patients. Multiple Level I and II studies report a lower pseudarthrosis rate than posterolateral fusion alone. Disc and endplate geometry. The L4-L5 and L5-S1 discs are trapezoidal in the sagittal plane. The L5-S1 disc carries a steeper lordotic angle (average 10-12 degrees) than L4-L5 (6-8 degrees). The thick anterior longitudinal ligament must be divided to allow distraction, while the posterior longitudinal ligament and posterior annulus are preserved to protect the thecal sac during discectomy. The safe working zone for cage placement is bounded laterally by the psoas muscles and posteriorly by the posterior longitudinal ligament; lateral osteophytes may need removal to seat a large-footprint cage. Great-vessel anatomy. The abdominal aorta bifurcates into the common iliac arteries at approximately L4, though this varies from L3 to L5; the iliac vein confluence usually sits slightly caudal to the arterial bifurcation. The left common iliac vein crosses the L4-L5 disc in 70-80 percent of patients. The entire dissection is performed from the left side, retracting the vessels rightward — the right common iliac vessels are rarely mobilised. At L5-S1, after the bifurcation, the approach runs medial to the left common iliac artery and vein; the left ureter on the psoas fascia and the gonadal vessels are identified and protected but not mobilised with the iliac vessels. Key evidence base. The retroperitoneal route is preferred over transperitoneal for male patients at L5-S1 because it markedly lowers retrograde ejaculation. The vascular injury rate in large series is around 1.7 percent, venous lacerations predominate and are usually repairable, and the risk concentrates at L4-L5 — preoperative mapping and immediate vascular expertise are the safeguards. rhBMP-2 with structural allograft cages improves fusion rates over autograft alone, and careful patient selection with meticulous endplate technique remains the primary determinant of a successful fusion.