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Anterior Lumbar Fusion

Aims

  • Aim to achieve solid union between vertebral bodies by removal of disc & bone graft to disc space
  • Chosen over posterior fusion for higher fusion rate but does not allow decompression or reduction of spondylolisthesis

Indications

  • Disc degeneration with instability
    • e.g. L 4/5 degenerative spondylolisthesis
    • Defined by Knutsson as
      • 5mm
        • anterior translation of 1 vertebrae on another with flexion extension films
      • >11°
        • difference in angular motion of > 11°between adjacent motion segments from T1 – L5
      • >15°
        • difference of angular mvmt between L4 / 5 & L5 / S1
  • As part of scoliosis surgery for fixed curve > 70°
  • L5 / S1 spondylolisthesis
  • Trauma

Contraindications

  • Requirement for posterior decompression

Consent / Preop Planning

  • Good quality XR / CT/ MRI for ? occult spina bifida or syrinx
  • Full neurological examination
  • X-match blood
  • Have II available
  • GA, Abx, IDC, NGT
  • Prep iliac crest

Options

  • Anterior trans peritoneal approach for L5 / S1 or less commonly L 4/5
  • Anterolateral retroperitoneal approach for L 1-4

Position

  • supine

Landmarks

  • symphisis pubis, umbilicus at L3/4 disc, linear alba midline

Incision

Start

  • from 3cm above umbilicus, curved to left around umbilicus down to symphysis

Deep Dissection

  • Incision in rectus sheath, spread recti, pick up & open peritoneum

Dangers

Nerves

  • pre sacral parasympathetics

Vessels

  • aortic bifurcation
  • mid sacral artery

Other

  • ureter

Procedure

  • Anterior trans peritoneal approach for L5 / S1 or less commonly L 4/5

    • 30 degree head down, pack abdominal contents superiorly & identify aortic bifurcation at L4
    • Push bladder distally
    • Infiltrate pre sacral tissue with 10 – 20 ml normal saline to assist dissection & identification of pre sacral parasympathetics
    • Identify disc space at L5 /S1 & check with II
      • Use peanut gauze
    • For L4 / 5
      • incise peritoneum at base of sigmoid colon & mobilise upwards to expose bifurcation of artery & vein & left ureter
      • Identify & ligate 4th & 5th lumbar segmental vessels, tie off 1 cm from aorta, move vessels to right
      • Ligate middle sacral artery
      • Left ureter crosses common iliac vessels at SI joint

    Anterolateral retroperitoneal approach for L 1-4

    • Position patient left side up (usually) in semi lateral position
    • Land marks – 12th rib, symphysis
    • Make oblique flank incision from posterior half of 12th rib to lateral border of rectus about midway between umbilicus & symphysis
    • Fat
    • Divide external oblique muscle in line of incision
    • Divide internal oblique & transversalis in line with wound
    • Move peritoneum & bowel medially
    • Blunt digital dissection of peritoneum off posterior abdominal wall around psoas
    • ureter should go anteriorly with peritoneum
    • genitofemoral nerve pierces psoas
    • sympathetic chain runs between psoas & vertebral bodies
    • Identify & ligate segmental arteries as required. Gently mobilise vessels to reach midline anteriorly. Check level with II
    • Incise ALL in midline, retract medial & laterally, excise disc taking care close to PLL
    • Curette endplates posteriorly down to cancellous bone but maintain cortical endplates anteriorly for strength. Take 3 tricortical grafts from iliac crest. Cut slots in vertebral endplates to accept graft & distract with laminar spreader & insert grafts X 3 ensuring they finish 3-4mm short of PLL.
    • Close ALL as possible & wound in layers

Postop / Rehab

  • Bracing or casting may be required depending on intraoperative stability of graft & reliability of patient
  • Start fluids once bowel sounds return
  • Allow to sit when comfortable, mobilise when able
  • No extension for 6 weeks

Complications / Dangers

Perioperative

General
  • GA & surgical
Local
  • Intra op
    • visceral perforation
    • damage to presacral parasympathetics may cause impotence & retrograde ejaculation in men
    • Ureteric injury
    • Sympathetic chain
    • Catastrophic bleeding from presacral venous plexus, vena cava & tributaries, segmental spinal arteries & median sacral artery
    • Dural tear, nerve root injury, cauda equina

Postoperative

Early
  • wound healing, infection , thrombosis (venous or arterial)
  • bowel obstruction
  • retroperitoneal collection
Late
  • non union
  • recurrence of deformity
  • ↑ stress on other levels
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