Retroperitoneal Anterolateral Approach to the Lumbar Spine

Incision and Superficial Dissection

Incision planning:

Incision location varies by target level:

• L2-L3: More cephalad, parallel to 12th rib
• L3-L4: Midway between costal margin and iliac crest
• L4-L5: Just above iliac crest, oblique
• L5-S1: Along iliac crest or lower abdominal (can use bikini-line in supine)

Standard oblique flank incision (L3-L5):

Length: 8-15cm depending on mini-open versus standard open technique

Incision technique:

1. Skin incision: Begin 2-3cm lateral to rectus sheath, extend obliquely toward flank
2. Subcutaneous tissue: Dissect to identify muscle layers
3. Identify external oblique muscle fibers (run inferiorly and medially)

Layer-by-layer muscle dissection:

Layer 1 - External oblique:

• Split muscle in line with its fibers (inferiorly and medially)
• Use blunt finger dissection or scissors
• Self-retaining retractor placed

Layer 2 - Internal oblique:

• Identify fibers running perpendicular to external oblique
• Split in line with fibers (superiorly and medially)
• Retract to expose transversus abdominis

Layer 3 - Transversus abdominis:

• Fibers run transversely
• Split in line with fibers using blunt dissection
• Expose transversalis fascia (white glistening layer)

Layer 4 - Transversalis fascia:

• CRITICAL layer marking entry to retroperitoneal space
• Incise carefully to avoid entering peritoneum
• Use finger to develop plane between fascia and peritoneum

Entering retroperitoneal space:

This is the KEY step:

1. Open transversalis fascia under direct vision
2. Insert finger and gently sweep anteriorly
3. Peritoneum should peel away anteriorly (smooth, glistening surface)
4. Retroperitoneal fat visible (yellow, lobulated)
5. If bowel visible through peritoneum, correct plane confirmed

The superficial dissection is now complete with entry to retroperitoneal space.

Deep Retroperitoneal Dissection

Developing the retroperitoneal plane:

Finger dissection technique:

1. Insert hand into retroperitoneal space
2. Sweep peritoneum anteriorly and medially with fingers
3. Blunt dissection mobilizes peritoneal sac with bowel away from field
4. Ureter stays ON peritoneal surface (should mobilize with bowel)
5. Feel for psoas muscle posteriorly (firm, muscular)

Identifying key structures:

Psoas muscle:

• First deep structure encountered posteriorly
• Firm, striated muscle
• Genitofemoral nerve visible on muscle surface (small white structure)
• Work MEDIAL to psoas to avoid lumbar plexus

Peritoneal sac:

• Thin, translucent membrane
• Bowel visible through peritoneum
• Ureter on peritoneal surface (white cord-like structure running inferiorly)
• Mobilize anteriorly with gentle retraction

Vascular identification:

Identify vascular structures before spinal exposure:

L2-L3:

• Aorta visible on left side of vertebral body
• Segmental lumbar arteries crossing disc space
• Ligate and divide segmental vessels if needed for exposure

L3-L4:

• Aorta more anterior
• Identify iliolumbar vein (crosses posterior to common iliac vessels)
• Protect iliolumbar vein to prevent catastrophic bleeding

L4-L5 (CRITICAL LEVEL):

• Identify aortic bifurcation (typically at L4 body)
• Left common iliac vein crosses POSTERIOR to right common iliac artery
• Left common iliac vein often adherent to L4-L5 disc
• Gently mobilize vessels to LEFT using vein retractor or sponge stick
• Sharp dissection may be needed to free adherent vein from disc

L5-S1:

• Common iliac vessels diverge laterally
• Middle sacral artery and vein cross disc space (ligate and divide)
• Superior hypogastric plexus visible as fine nerve filaments over disc
• Stay LATERAL to preserve plexus (reduce retrograde ejaculation risk)

Retractor placement:

Use self-retaining retractor system:

• Anterior blade: Retracts peritoneum and bowel anteriorly
• Posterior blade: Gentle retraction on psoas (DO NOT over-retract laterally)
• Superior blade: Retracts vascular structures superiorly
• Inferior blade: Retracts vessels inferiorly

Completed exposure shows:

• Vertebral body visible anteriorly
• Disc space centered in wound
• Vessels safely mobilized to left
• Psoas muscle visible laterally (work medial to muscle)
• No peritoneal perforation (no bowel visible directly)

The retroperitoneal exposure is now complete with full access to anterior column.

Vascular Mobilization and Protection

Principles of safe vascular mobilization:

General technique:

1. Identify vessels before mobilization
2. Use gentle sponge-stick retraction (padded)
3. Avoid rigid retractors directly on vessels
4. Mobilize vessels together (artery and vein as unit)
5. Sharp dissection for adherent vein

Segmental vessel management:

At all levels, segmental lumbar arteries and veins cross disc space:

Ligation technique:

1. Identify segmental vessels crossing disc space
2. Carefully dissect vessels free from surrounding tissue
3. Doubly ligate artery and vein separately
4. Ligate flush with aorta/IVC to avoid postoperative bleeding
5. Divide between ligatures
6. Can use clips instead of suture ligatures

L4-L5 specific technique (highest risk):

This level requires maximum care:

Aortic bifurcation:

• Typically at mid-L4 vertebral body
• Bifurcation creates V-shape with apex at midline
• Left common iliac artery runs obliquely to left
• Right common iliac artery crosses midline to right

Left common iliac vein:

• Runs POSTERIOR to right common iliac artery
• Adherent to posterior artery wall and anterior disc
• THIN-WALLED and vulnerable
• Requires gentle sharp dissection to free from disc

Mobilization sequence for L4-L5:

1. Identify aortic bifurcation and both common iliac arteries
2. Identify left common iliac vein posterior to right common iliac artery
3. Ligate and divide iliolumbar vein (crosses posterior to iliacs)
4. Ligate and divide ascending lumbar vein if present
5. Use vascular forceps to gently elevate right common iliac artery
6. Sharply dissect left common iliac vein from posterior artery wall
7. Mobilize vessels as unit to LEFT
8. Place padded vascular retractor to maintain position
9. Expose L4-L5 disc space

L5-S1 specific technique:

Middle sacral vessels:

• Arise from aortic bifurcation
• Cross L5-S1 disc space in midline
• MUST be ligated and divided for exposure

Technique:

1. Identify middle sacral artery and vein
2. Carefully dissect from presacral fascia
3. Doubly ligate and divide
4. Mobilize common iliac vessels laterally
5. Expose presacral space

Superior hypogastric plexus:

• Visible as fine nerve filaments over L5-S1 disc
• Injury causes retrograde ejaculation
• Preserve by LATERAL dissection approach
• Avoid midline stripping of presacral fascia
• Gentle blunt dissection only

Vessel retraction:

• Use padded retractors (sponge-stick or padded blade)
• GENTLE retraction only
• Release tension every 15-20 minutes
• Warm saline irrigation maintains vessel moisture
• Watch for vessel wall hematoma (sign of injury)

Vascular mobilization is now complete with safe access to disc space.

Discectomy and Endplate Preparation

Once vessels are safely mobilized, proceed with disc space work:

Disc space exposure:

1. Use fluoroscopy to confirm correct level (AP and lateral views)
2. Place marker on disc space
3. Verify with X-ray BEFORE proceeding
4. Count from sacrum upward to confirm level

Anterior longitudinal ligament (ALL):

• Can preserve or divide depending on technique
• If preserving: Make horizontal incision in ALL over disc space, elevate superiorly and inferiorly
• If dividing: Make rectangular window in ALL, save for closure
• Preserve ALL for revision cases (reduces vascular adhesion)

Annulotomy:

1. Incise annulus fibrosus with knife
2. Make rectangular or square window
3. Extend to lateral edges of disc space
4. Use pituitary rongeurs to remove nucleus pulposus

Discectomy technique:

1. Remove nucleus pulposus with pituitary rongeurs
2. Use curettes to remove cartilaginous endplate
3. Preserve bony endplate (subchondral bone)
4. Complete discectomy to posterior annulus
5. Remove osteophytes from anterior vertebral body
6. Create parallel endplates for cage placement

Endplate preparation:

Critical for fusion success:

• Remove ALL cartilaginous endplate (appears shiny, white)
• Expose bleeding subchondral bone
• Create flat, parallel endplates
• Avoid violating endplate (subsidence risk)
• Use shavers or curettes carefully

Posterior annulus:

• Preserve posterior annulus if possible
• Acts as barrier to cage retropulsion
• If deficient, use taller cage or add posterior instrumentation

Interbody cage placement:

Trial sizing:

1. Use trial spacers to determine appropriate cage size
2. Confirm sizing with fluoroscopy
3. Goal: Largest footprint that fits safely
4. Assess lordosis with different cage angles

Cage preparation:

• Pack cage with bone graft (autograft from discectomy, allograft, or BMP)
• Choose lordotic angle appropriate for level (L5-S1: 6-8 degrees)
• Have multiple sizes available

Cage insertion:

1. Insert cage using holder/impactor
2. Advance with gentle taps
3. Use fluoroscopy to confirm position
4. Cage should be flush with anterior cortex or slightly recessed
5. Verify no posterior protrusion on lateral fluoroscopy

Final verification:

• AP and lateral fluoroscopy to confirm cage position
• No posterior migration
• Parallel to endplates
• Appropriate lordosis restored
• Disc height restored

Disc work is now complete with interbody cage in optimal position.

Hemostasis, Closure, and Drain Placement

Hemostasis:

Meticulous hemostasis is CRITICAL to prevent retroperitoneal hematoma:

1. Inspect all vessel ligation sites:

   • Check segmental vessel ligatures secure
   • Look for oozing from vessel walls
   • Inspect middle sacral vessel stumps
   • Ensure no active bleeding

2. Bone bleeding:

   • Apply bone wax to vertebral body edges
   • Thrombin-soaked gelfoam if persistent ooze
   • Bipolar cautery for small bleeding vessels

3. Soft tissue bleeding:

   • Bipolar cautery for muscle edges
   • Warm saline irrigation
   • Check psoas muscle for bleeding (contains vessels)

Anterior longitudinal ligament repair:

If ALL was divided:

• Repair with absorbable suture (2-0 Vicryl)
• Running or interrupted technique
• Reduces postoperative adhesion to vessels
• Helpful for revision surgery

Drain placement:

Controversial, but recommended for:

• Large exposure cases
• Significant vascular mobilization
• Multiple level surgery

Technique:

• 19Fr round drain (Jackson-Pratt or Blake)
• Place in retroperitoneal space
• Exit through separate stab incision lateral to main wound
• Position away from vessels
• Secure to skin

Layer-by-layer closure:

No formal muscle repair needed (muscles split, not divided):

1. Transversalis fascia:

   • Close with running absorbable suture (1 Vicryl)
   • Ensure no dead space

2. Transversus abdominis:

   • Approximate with interrupted sutures if needed
   • Usually reapproximates spontaneously

3. Internal oblique:

   • Simple reapproximation
   • 1 Vicryl interrupted

4. External oblique:

   • Close fascia with running 1 Vicryl
   • Creates strength layer

5. Scarpa's fascia:

   • Close with 2-0 Vicryl to reduce dead space

6. Skin:

   • Subcuticular 3-0 Monocryl
   • Skin glue or steri-strips

Dressing:

• Absorbent gauze over wound
• Adhesive film dressing
• Abdominal binder optional for patient comfort

Drain removal:

• Remove when output less than 30mL per 24 hours
• Typically post-op day 1-3
• Check for chyle (milky fluid indicates lymphatic injury - keep drain until output stops)

The wound is now closed with hemostasis confirmed and drain in place.