High Yield Overview

CAUDA EQUINA DECOMPRESSION

Emergency posterior midline decompression | intermediate

Critical Danger Structures

Dural Sac & Nerve Roots

Location: Central spinal canal, typically 10-15mm diameter at L4-5

Protection: Use Kerrison rongeurs away from dura, place cottonoids between bone and dura, gentle retraction only, foot-plate of rongeur always against bone not dura

Incidental durotomy occurs in 3-17% of cases - repair primarily with 4-0 or 5-0 non-absorbable suture, consider dural sealant and bed rest

Traversing & Exiting Nerve Roots

Location: Lateral recess and neural foramina - L5 root exits below L5 pedicle, S1 crosses sacral ala

Protection: Identify pedicles on lateral fluoroscopy, decompress lateral recesses fully, avoid aggressive retraction especially if nerve adherent to disc, use ball-tip probe to confirm root mobility

Root injury causes permanent dermatomal sensory loss and myotomal weakness

Epidural Venous Plexus

Location: Anterior and lateral epidural space, particularly engorged in acute CES with elevated CSF pressure

Protection: Subperiosteal dissection keeps bleeding paraspinal, bipolar coagulation before dural exposure, maintain abdomen-free positioning to reduce venous pressure, gelfoam and thrombin for persistent ooze

Excessive bleeding obscures anatomy and increases risk of neurological injury

Posterior Longitudinal Ligament & Annulus

Location: Posterior disc space, PLL may be attenuated or ruptured by disc fragment

Protection: Use angled curettes and pituitary rongeurs, always work under direct vision, avoid blind instrumentation anteriorly, check pre-op MRI for vascular anomalies

Anterior perforation risks great vessel injury or retroperitoneal haematoma (rare but catastrophic)

Facet Joints & Pars Interarticularis

Location: Posterolateral - medial 50% of facet must be preserved to maintain stability

Protection: Mark medial pedicle line on fluoroscopy, stop lateral decompression at this landmark, preserve capsule unless stenosis requires facetectomy

Bilateral facetectomy creates iatrogenic instability requiring fusion - approximately 30% increased operative time and morbidity

Mnemonic

SADDLECES Red Flags - SADDLE

Mnemonic

KERRISONLaminectomy Safe Technique - KERRISON

CES Classification

Fraser et al. Classification (Prognostic):

CES-R (Retention): Painless urinary retention, reduced anal tone, worse prognosis
CES-I (Incomplete): Urinary difficulties (frequency, urgency, altered sensation) but no retention, better prognosis if decompressed early
CES-S (Suspected): Bilateral radiculopathy with bladder/bowel symptoms but examination normal

Surgical Indications - Absolute:

Confirmed CES on examination: Saddle anaesthesia, bladder dysfunction, bilateral leg weakness
MRI confirmation of compressive pathology: Disc, tumour, haematoma, abscess
Progressive neurological deficit: Documented deterioration

Surgical Indications - Relative:

CES-S with high clinical suspicion: Patient reports symptoms but examination normal
Isolated severe unilateral radiculopathy: May progress to bilateral

Contraindications - Absolute:

Patient medically unfit for anaesthesia (discuss with anaesthetics - many patients can be optimized rapidly)
Complete cauda equina transection with no recovery potential (rare)

Contraindications - Relative:

Symptom duration greater than 6 months (less likely to benefit but may prevent progression)
Concomitant severe spinal deformity requiring instrumented fusion (may need staged or different approach)

Timing Principles

Critical Evidence:

Within 24 hours: Best outcomes for bladder recovery (Ahn et al., Spine 2000)
24-48 hours: Still significant benefit for motor and sensory recovery
Beyond 48 hours: Diminishing returns but may prevent progression
CES-I to CES-R progression: 70% occur within 24 hours if untreated

Exam Pearl: In viva, emphasize this is a time-dependent neurological emergency analogous to stroke or spinal cord injury - delays worsen prognosis but surgery still indicated even if delayed presentation

Positioning and Preparation

Patient Position: Prone on Wilson frame or Jackson table

Key Points:

Abdomen must be free (reduces epidural venous pressure and bleeding)
Hips flexed to open interspinous spaces
Shoulders abducted less than 90 degrees (avoid brachial plexus stretch)
Face supported on horseshoe or prone view head rest
Pressure point padding (knees, chest, iliac crests)

Surgical Approach: Posterior midline

Instrumentation Required:

Self-retaining retractor (Taylor or McCulloch)
Kerrison rongeurs (various sizes: 2mm, 4mm, 6mm)
Pituitary rongeurs for disc removal
Curettes (straight and angled)
High-speed burr (if thick lamina or osteophytes)
Nerve hooks and ball-tip probes
Bipolar diathermy
Headlight or microscope/loupe magnification

Imaging:

Lateral fluoroscopy mandatory for level confirmation
AP view to check midline positioning

Operative Technique

Step 1: Pre-operative MRI to confirm diagnosis and level

Review MRI immediately before surgery to identify: (1) exact level of maximum compression, (2) extent of decompression required (single vs multi-level), (3) type of pathology (disc, tumour, abscess, haematoma), (4) any anatomical variants (transitional vertebra, spondylolisthesis, vascular anomalies).

Exam Pearl

Technical Tip: Count vertebrae on sagittal MRI from sacrum upwards or C2 downwards to avoid counting errors. Lumbosacral transitional vertebrae (Bertolotti's syndrome) present in 10-15% of population - correlate with pre-op plain radiographs. Mark skin with radiopaque marker at estimated level before positioning.

Dangers at this step

Wrong level surgery (medicolegal catastrophe) - prevented by systematic counting on MRI and fluoroscopic confirmation intra-operatively
Missed additional levels requiring decompression - cranial/caudal disc migration common in CES
Failure to identify abscess or tumour requiring different approach/biopsy/oncology referral

Step 2: General anaesthesia and patient positioning

Induce general anaesthesia, ensure full muscle relaxation for safe intubation and positioning. Position prone on Wilson frame or Jackson table with abdomen free. Confirm adequate padding of all pressure points. Arms positioned alongside body or abducted less than 90 degrees on arm boards.

Exam Pearl

Technical Tip: Check abdomen is hanging free by passing hand underneath patient - this reduces epidural venous pressure by 40-50%, significantly improving surgical field visibility. In obese patients, consider using a Montreal mattress or inflatable cushions. Ensure breasts/genitalia positioned to avoid pressure necrosis during prolonged case.

Dangers at this step

Brachial plexus injury from excessive shoulder abduction or arm hyperextension (permanent nerve palsy)
Eye injury from direct pressure or ischaemia (blindness) - check eyes free and consider protective lubricant
Abdominal compartment syndrome in morbidly obese if abdomen compressed (rare but catastrophic)
Cardiovascular collapse during position change in elderly/hypovolemic patients

Step 3: Prepare and drape operative field

Prepare skin with chlorhexidine or povidone-iodine solution from mid-thoracic spine to sacrum. Drape to expose spinous processes from L3 to sacrum. If radiopaque marker placed pre-positioning, confirm position with fluoroscopy.

Exam Pearl

Technical Tip: Use alcohol-based preparation with care - pooling under patient is fire hazard with diathermy use. Allow adequate drying time (3 minutes for chlorhexidine). In emergency CES, some surgeons omit clipper preparation of hairy backs to save time - no evidence of increased infection if adequate skin prep performed.

Dangers at this step

Diathermy burns from pooled preparation solution (document preparation type used)
Allergic reaction to skin preparation (rare)
Pressure area development if excessive preparation time delays surgery

Step 4: Midline skin incision centered on pathology

Palpate spinous processes of L4, L5, and sacrum. Make midline incision centered on level of pathology confirmed on MRI. For single-level decompression at L4-5, incision 6-8cm; for L5-S1, incision 5-7cm; for multi-level, adjust accordingly. Incise skin and subcutaneous fat to supraspinous ligament using cutting diathermy.

Exam Pearl

Technical Tip: In obese patients, spinous processes may be difficult to palpate - use lateral fluoroscopy to mark skin before incision. Keep incision strictly midline to minimize muscle dissection and bleeding. Use headlight or loupe magnification throughout for precision. Place self-retaining retractor in subcutaneous tissues to improve deep visualization.

Dangers at this step

Off-midline incision causes asymmetric muscle dissection, increased bleeding, difficult deep access
Inadequate skin incision length forces excessive retraction causing wound edge necrosis
Excessive skin incision in thin patients causes cosmetic concerns and denervated skin flaps

Step 5: Subperiosteal dissection to expose laminae

Using Cobb elevator or monopolar diathermy on cutting mode, perform subperiosteal muscle dissection from spinous processes onto laminae bilaterally. Dissect laterally to expose laminae and medial facet joints. Use bipolar coagulation for hemostasis. Place self-retaining Taylor or McCulloch retractor to hold paraspinal muscles laterally.

Exam Pearl

Technical Tip: Keep dissection strictly subperiosteal (elevator against bone at all times) to minimize bleeding from paraspinal muscle belly. Use combination of sharp dissection with cutting diathermy and blunt elevation with periosteal elevator. Expect more bleeding in acute CES due to elevated epidural venous pressure. Control bleeding before proceeding - pools of blood obscure anatomy.

Dangers at this step

Muscle dissection too lateral causes excessive bleeding from paraspinal muscle belly and exposes facet capsule unnecessarily (instability risk)
Inadequate lateral dissection prevents adequate retractor placement, resulting in narrow working corridor
Violation of facet capsule causes post-operative pain and potential instability

Step 6: Fluoroscopic confirmation of level

Place radiopaque marker (artery clip or K-wire) on spinous process or lamina of suspected level. Obtain lateral fluoroscopy image. Confirm correct level by counting vertebrae from sacrum (S1 body is first bony structure below lucent L5-S1 disc). Mark level with marking pen on spinous process.

Exam Pearl

Technical Tip: Always count from sacrum upwards to avoid errors from transitional vertebrae or lumbosacral anomalies. If uncertainty, obtain AP view to confirm midline positioning and count ribs on lateral view (T12 has last rib, L1 has no rib). In obese patients, may need higher-powered fluoroscopy or mini-open approaches to spinous processes for adequate imaging. Never proceed without absolute certainty of correct level.

Dangers at this step

Wrong level decompression (medicolegal nightmare, requires second surgery, poor outcomes) - prevented by systematic counting
Radiation exposure to surgical team (use lead protection, minimize screening time, maximize distance from source)
Transitional vertebrae misidentified (L5 sacralized or S1 lumbarized) - if in doubt, get long lateral radiograph

Step 7: Remove spinous process with rongeur

Using Leksell rongeur or heavy bone cutting rongeur, remove spinous process of affected level(s). Grasp spinous process firmly and remove with controlled fracture or systematic nibbling. Remove interspinous ligament. Expose cranial and caudal laminae.

Exam Pearl

Technical Tip: Removing spinous process first creates working space for subsequent laminectomy and reduces risk of inadvertent dural injury when removing lamina. In elderly osteoporotic patients, spinous process fractures easily with light pressure. Save bone fragments for use as local autograft if fusion considered later. Control bleeding from cancellous bone with bone wax or bipolar coagulation.

Dangers at this step

Excessive force causing uncontrolled fracture extending into lamina or pedicle (destabilization)
Retropulsed spinous process fragment pushing onto dura (neural injury)
Damage to supraspinous ligament complex if preserving spinous process for hemilaminectomy

Step 8: Identify ligamentum flavum

Using Penfield dissector or Woodson elevator, carefully dissect muscle and soft tissue from lateral lamina to identify ligamentum flavum. Ligamentum flavum is yellow, thick (3-5mm), and elastic. It extends from anteroinferior edge of cranial lamina to anterosuperior edge of caudal lamina.

Exam Pearl

Technical Tip: Ligamentum flavum is key anatomical landmark - once identified, you are at boundary of spinal canal. It is typically darker yellow and thicker in stenosis (can be 7-10mm). Use ball-tip probe to gently dissect between ligamentum flavum and underlying dura before resecting - this protective layer prevents dural injury. In revision surgery, ligamentum flavum may be absent or scarred to dura.

Dangers at this step

Misidentifying ligamentum flavum and dissecting too deep causes inadvertent dural tear
Calcified or ossified ligamentum flavum in severe stenosis/OPLL requires burr for removal
In revision surgery, dense scar tissue replaces normal anatomy, increasing dural tear risk from 8% to 20%

Step 9: Laminectomy - remove cranial lamina

Using 2mm or 4mm Kerrison rongeur, remove cranial lamina systematically from caudal to cranial direction. Always place foot-plate of Kerrison against bone (not dura). Work from one lateral edge to midline, then midline to other lateral edge. Remove lamina and ligamentum flavum as single unit or separately depending on anatomy.

Exam Pearl

Technical Tip: Keep Kerrison rongeur foot-plate against bone at all times - this is cardinal safety principle. Work in deliberate, controlled bites (2-3mm per bite), not aggressive larger bites. Use angled Kerrison rongeurs for corners and lateral extent. Irrigate frequently to clear bone dust which obscures visualization. Place cottonoid patties between dura and remaining bone to protect during subsequent bites.

Dangers at this step

Kerrison rongeur foot-plate against dura instead of bone causes dural tear and nerve root injury (20-30% of dural tears occur during laminectomy)
Excessive lateral resection beyond medial pedicle line destabilizes facet joint (requires fusion)
Inadequate resection leaves residual compression and poor neurological outcome

Step 10: Laminectomy - remove caudal lamina

Repeat laminectomy process for caudal lamina using same systematic technique. Remove ligamentum flavum between levels. Ensure complete decompression from cranial edge of cranial lamina to caudal edge of caudal lamina.

Exam Pearl

Technical Tip: For L4-5 decompression, remove inferior L4 lamina and superior L5 lamina. For L5-S1, remove inferior L5 lamina and superior S1 lamina (S1 lamina often thick and more difficult). Ensure adequate cranio-caudal decompression - inadequate vertical decompression is common error in novice surgeons. Dura should be visible pulsating freely throughout decompression zone.

Dangers at this step

Incomplete caudal decompression leaves migrated disc fragment unaddressed (persistent symptoms)
S1 lamina particularly thick, requires patience and sometimes high-speed burr to thin before Kerrison removal
Dural pulsation may be absent in severe CES due to complete block - do not over-retract trying to achieve pulsation

Step 11: Decompress lateral recesses bilaterally

Using Kerrison rongeurs and/or high-speed burr, perform medial facetectomy to decompress lateral recesses. Remove medial 25-30% of facet joint (not more than 50%) to visualize exiting nerve root. Use ball-tip probe to confirm nerve root decompressed and mobile. Repeat on contralateral side.

Exam Pearl

Technical Tip: Lateral recess is bounded by superior facet posterolaterally and vertebral body anteriorly. Use angled Kerrison or burr to undercut facet. Decompress adequately to see exiting nerve root clearly - inadequate lateral decompression is common cause of persistent post-operative leg pain. Use medial pedicle line (identified on lateral fluoroscopy) as lateral limit - do not decompress beyond this or instability results.

Dangers at this step

Excessive facet resection (more than 50% of facet) causes iatrogenic instability requiring fusion
Nerve root injury from aggressive retraction or Kerrison bite on nerve (permanent deficit)
Arterial injury to radicular artery accompanying nerve root (haematoma and nerve ischemia)

Step 12: Identify compressive pathology

With adequate bony decompression complete, inspect epidural space and identify compressive pathology. Most commonly this is large sequestrated disc fragment compressing dural sac and cauda equina. May also find tumour, abscess, or haematoma.

Exam Pearl

Technical Tip: Disc fragment typically sits posterolateral or central, may be intradural in 3-5% of cases. Disc material appears white/grey, firm or soft depending on hydration. Tumour is usually vascular, firm, and distinct from disc. Abscess is purulent, take samples for culture/histology. Haematoma is dark red/brown, often organized. Always send pathological specimens for histology to confirm diagnosis.

Dangers at this step

Mistaking tumour for disc herniation (inadequate decompression, missed oncological diagnosis)
Intradural disc fragment requires durotomy for removal - do not attempt to extract through intact dura
Abscess requires extended antibiotic therapy (6-12 weeks IV), consider infectious disease referral

Step 13: Mobilize dural sac gently

Using nerve hook or Penfield dissector, gently mobilize dural sac away from compressive pathology. Place cottonoid patty between dura and disc fragment. Dura may be adherent to disc, requiring careful dissection to prevent tear.

Exam Pearl

Technical Tip: Use angled nerve hook to dissect plane between dura and disc fragment. Work incrementally, not forcefully. If dura densely adherent (common in large long-standing herniations), leave thin layer of disc on dura and remove bulk of fragment - attempting complete dissection risks dural tear. Some surgeons use microscope magnification for this stage to improve precision.

Dangers at this step

Aggressive retraction of dural sac causes nerve root injury (traction neuropraxia)
Dural tear during mobilization (occurs in 8-15% of cases, increases with revision surgery)
Nerve roots adherent to disc may be injured during dissection

Step 14: Discectomy - remove compressive disc fragment

Using pituitary rongeurs, grasp disc fragment and remove with controlled extraction. Remove all free fragments from spinal canal. Use angled curettes to explore disc space and remove loose material, but avoid aggressive intradiscal curettage (increases recurrence risk and endplate injury).

Exam Pearl

Technical Tip: Disc fragments may be single large sequestrum or multiple smaller fragments. Systematically explore entire canal including behind traversing nerve roots. Use ball-tip probe to check for retained fragments. In CES, disc fragments are often very large (2-4cm) and require piecemeal removal. Do not perform aggressive intradiscal curettage - evidence shows no benefit in reducing recurrence and increases back pain.

Dangers at this step

Retained disc fragment causes persistent compression and poor outcome (re-operation required)
Aggressive anterior instrumentation risks great vessel injury (aorta, IVC) or sympathetic plexus damage
Nerve root injury if fragment adherent to nerve (occurs in 1-3% of cases)
Excessive intradiscal curettage causes endplate injury and discogenic back pain

Step 15: Inspect all nerve roots

Using ball-tip probe or nerve hook, systematically inspect each nerve root to ensure complete decompression. Check L4, L5, S1, S2 roots bilaterally. Roots should be mobile, of normal caliber, and not compressed. Check lateral recesses and neural foramina.

Exam Pearl

Technical Tip: Use ball-tip probe to gently elevate each nerve root and confirm free mobility. Compressed roots appear flattened and pale; decompressed roots are round and pink/grey. In severe CES, roots may be severely compressed and adherent, requiring patience to decompress safely. Ensure dural pulsation restored after decompression - absent pulsation suggests incomplete decompression or CSF block.

Dangers at this step

Missed compression of individual nerve roots causes persistent radiculopathy
Excessive manipulation of nerve roots causes temporary neuropraxia (usually recovers in 6-12 weeks)
Far lateral or extraforaminal pathology requires different exposure (Wiltse approach or transforminal)

Step 16: Explore for cranial/caudal migration

Using angled curettes and ball-tip probe, explore cranially and caudally from disc space to check for migrated fragments. Disc fragments may migrate up or down one level (10-15% of cases), particularly in CES with large herniations.

Exam Pearl

Technical Tip: Correlate intra-operative findings with pre-operative MRI which should show any migration. Cranial migration more common than caudal (fragments follow path of least resistance under PLL). Use angled instruments to reach under facet joints if necessary. If migration extensive (2+ levels), may require extended laminectomy or separate approach. Always achieve complete decompression - incomplete decompression is medicolegal liability.

Dangers at this step

Missed migrated fragment causes persistent compression (re-operation required)
Excessive proximal dissection under facet destabilizes joint (fusion required)
Blind instrumentation cranially or caudally risks dural tear or nerve injury

Step 17: Confirm adequate decompression

Perform systematic check: (1) dural sac pulsating freely, (2) all nerve roots visualized and mobile, (3) lateral recesses decompressed, (4) no residual bone or soft tissue compression. Use ball-tip probe to test decompression.

Exam Pearl

Technical Tip: This is critical step before proceeding to closure. Inadequate decompression is common cause of poor outcome and re-operation. Ask assistant to perform Valsalva maneuver (increase ventilator pressure to 30-40cm H2O for 10 seconds) - dural sac should expand and bulge into decompression space if adequate. If dura does not pulsate or expand, suspect residual compression or CSF block requiring further exploration.

Dangers at this step

Premature closure with inadequate decompression causes poor neurological outcome
Valsalva maneuver may cause dural tear if dura adherent to unrecognized sharp bony edge
Over-decompression causing instability (requires unplanned fusion)

Step 18: Haemostasis

Achieve meticulous haemostasis using bipolar coagulation. Coagulate bleeding bone with bipolar or apply bone wax sparingly. Use gelfoam soaked in thrombin for epidural venous ooze. Irrigate wound thoroughly with warm saline to clear blood clot and identify active bleeding.

Exam Pearl

Technical Tip: Epidural bleeding often stops once dural compression relieved and patient positioned flat at end of case (reduces epidural venous pressure). Use bipolar coagulation at low settings (20-30W) to avoid thermal injury to dura or nerves. Avoid excessive bone wax which can migrate or cause foreign body reaction. Some surgeons use hemostatic agents (Floseal, Surgicel) for persistent ooze.

Dangers at this step

Inadequate haemostasis causes post-operative haematoma requiring evacuation (1-2% incidence)
Excessive bipolar coagulation near nerve roots causes thermal injury (permanent deficit)
Bone wax migration into spinal canal causes compression or foreign body reaction

Step 19: Check for dural tear

Inspect entire dural exposure carefully for any tears. Small tears may be difficult to see but leak CSF. If dural tear identified, repair primarily with 4-0 or 5-0 non-absorbable suture (Prolene or Nurolon). Use dural sealant (DuraSeal, Tisseel) to reinforce repair.

Exam Pearl

Technical Tip: Dural tears occur in 8-15% of cases (higher in revision surgery). Small tears (less than 5mm) can be repaired primarily with interrupted sutures. Larger tears may require patch graft (autologous fascia, synthetic dural substitute). If repair water-tight, no drain required and patient can mobilize normally. If repair under tension or not water-tight, consider 24-48h bed rest and no drain (drain can cause ongoing CSF leak).

Dangers at this step

Missed dural tear causes persistent CSF leak, pseudomeningocele, or headache
Inadequate dural repair causes ongoing leak requiring re-operation (5-10% of dural tears)
Nerve root entrapment in dural repair causes permanent radiculopathy
Meningitis risk if CSF leak communicates with wound (rare, less than 1%)

Step 20: Irrigate wound thoroughly

Irrigate wound with 1-2 liters of warm normal saline using pulsatile lavage or bulb syringe. Remove all bone fragments, disc material, and blood clot. Ensure clear irrigation return.

Exam Pearl

Technical Tip: Thorough irrigation reduces infection risk and removes debris that could cause foreign body reaction or compression. Some surgeons add antibiotics to irrigation (gentamicin 80mg in 1L saline) but evidence for benefit is weak. Ensure all cottonoid patties removed before closure (perform systematic count). Warming irrigation fluid to 37°C prevents hypothermia in prolonged cases.

Dangers at this step

Retained cottonoid patty causes compression or foreign body reaction (medicolegal issue, requires re-operation)
Excessive irrigation pressure risks spreading infection if contamination occurred
Hypothermia from cold irrigation in prolonged cases (coagulopathy risk)

Step 21: Consider drain placement

Decision regarding drain is surgeon preference. Drain reduces haematoma risk but may increase CSF leak if dural tear present. If drain placed, use 14Fr or 16Fr suction drain positioned in epidural space, exit through separate stab incision, secure to skin.

Exam Pearl

Technical Tip: Evidence for drain benefit is equivocal. Arguments for drain: reduces haematoma risk, allows monitoring of post-operative bleeding. Arguments against: increased CSF leak if dural tear, increased infection risk, patient discomfort. Common practice is no drain for single-level discectomy with water-tight dura, drain for multi-level laminectomy or coagulopathic patients. Remove drain when output less than 50ml/24h (typically day 1-2).

Dangers at this step

Drain placed intrathecally instead of epidurally causes CSF leak (ensure drain remains posterior to dura)
Drain causes nerve root injury or compression if placed incorrectly
Drain retained too long increases infection risk (remove by 48 hours maximum)

Step 22: Close fascia

Close fascia (thoracolumbar fascia) with strong absorbable suture (1 Vicryl or PDS) in continuous or interrupted fashion. Ensure water-tight fascial closure to prevent CSF leak if dural tear present. Achieve tension-free closure.

Exam Pearl

Technical Tip: Fascial closure is critical layer for wound integrity and CSF containment. Use continuous suture for speed or interrupted for strength (surgeon preference). Ensure adequate fascial bites (1cm from edge, 1cm apart) to prevent dehiscence. In obese patients or if fascia attenuated, consider figure-of-eight sutures or additional deep dermal layer. Test closure by asking anesthetist to increase ventilator pressure (Valsalva) - fascial closure should be water-tight.

Dangers at this step

Inadequate fascial closure causes wound dehiscence (requires re-operation)
Excessive fascial tension causes ischemia and breakdown (leave skin open if fascia cannot close without tension)
Nerve or vessel entrapment in fascial suture causes post-operative pain

Step 23: Close subcutaneous layer and skin

Close subcutaneous fat with 2-0 or 3-0 absorbable suture (Vicryl) to obliterate dead space and reduce seroma risk. Close skin with 3-0 or 4-0 absorbable subcuticular suture (Monocryl) or staples/clips. Apply waterproof dressing.

Exam Pearl

Technical Tip: Subcutaneous closure reduces dead space and wound tension. Use interrupted or continuous technique depending on preference. Skin closure options include subcuticular absorbable suture (better cosmesis, no removal required), staples/clips (quicker, easier removal), or non-absorbable suture (traditional, requires removal). Ensure skin edges everted (not inverted) for optimal healing. Waterproof dressing allows early shower.

Dangers at this step

Excessive skin tension causes wound edge necrosis (use larger incision or relax tension before closure)
Inadequate subcutaneous closure causes seroma or haematoma collection
Dog-ears at incision ends cause cosmetic concerns (excise or revise closure)

Step 24: Post-operative neurological check

Before leaving operating room, perform and document neurological examination: power in key muscle groups (hip flexion, knee extension, ankle dorsiflexion/plantarflexion), sensation in dermatomes, perianal sensation, bladder function (catheter output and sensation of fullness if catheter removed).

Exam Pearl

Technical Tip: Immediate post-operative neurological examination establishes baseline for recovery monitoring. Document examination clearly in operative note. Some neurological improvement may be evident immediately (return of sensation, improved power), but most recovery occurs over weeks to months. Worsening neurology immediately post-op requires urgent investigation (haematoma, wrong level, nerve injury). Trial of catheter removal within 24-48h to assess bladder recovery.

Dangers at this step

Failure to document baseline neurology obscures subsequent deterioration
Worsening neurology suggests complication (haematoma, recurrent herniation) requiring urgent imaging
Continued urinary retention beyond 48h suggests poor prognosis for bladder recovery (urology referral for ISC teaching)

Complications

Complications of Cauda Equina Decompression

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 45-year-old male presents to ED at 2am with 24 hours of bilateral leg pain and numbness, saddle paraesthesia, and urinary retention requiring catheterization. MRI shows large L4-5 disc herniation with complete canal stenosis. The on-call anaesthetist says theatre not available until 8am list tomorrow. How do you manage this case?"

EXCEPTIONAL ANSWER

This is a neurosurgical emergency requiring urgent decompression. I would immediately escalate to consultant level and hospital management to obtain emergency theatre access. The evidence from Ahn et al. in Spine 2000 demonstrates that decompression within 24 hours gives 80% bladder recovery versus 30% if delayed beyond 48 hours, with our patient already at 24 hours. I would document clearly that this is cauda equina syndrome with retention (CES-R), explaining to anaesthetics and theatre management that this is analogous to spinal cord injury and cannot wait for routine list. If truly no theatre availability, I would consider transfer to nearest neurosurgical unit with theatre capacity, though this delays surgery further and has transfer risks. While awaiting theatre, I would ensure catheter in situ with hourly monitoring, document detailed baseline neurology including perianal sensation and anal tone, consent patient explaining that surgery optimizes recovery but residual deficits likely given 24-hour delay, and ensure patient has IV access and is fasted for emergency surgery. I would also document all delays and escalation attempts for medicolegal protection, as CES is highly litigious. The goal is decompression within 48 hours absolute maximum, ideally within 30 hours given current timeline.

VIVA SCENARIOStandard

EXAMINER

"You are performing emergency cauda equina decompression for L5-S1 disc herniation. During laminectomy with Kerrison rongeur, you notice clear fluid leaking and realize you have created a dural tear approximately 8mm in length. The neural tissue is visible through the tear. How do you manage this intra-operatively?"

EXCEPTIONAL ANSWER

I would first remain calm and acknowledge the complication, informing the anaesthetist and theatre team. I would ensure adequate exposure by extending the decompression slightly if needed to visualize the full extent of the tear. I would irrigate gently to clear blood and improve visualization, then place cottonoid patties to protect the neural elements and control CSF flow temporarily. Using microscope or loupe magnification, I would identify both ends of the tear to plan repair. For this 8mm tear, I would perform primary repair using 4-0 or 5-0 non-absorbable suture (Prolene or Nurolon) with interrupted sutures placed approximately 2-3mm apart, ensuring bites include adequate dural tissue (2-3mm from edge) but avoiding neural injury. I would use tenting sutures if needed to elevate dura away from nerve roots during repair. After completing the water-tight primary repair, I would reinforce with dural sealant (DuraSeal or Tisseel). I would perform Valsalva test (increasing ventilator pressure to 30-40cm H2O) to confirm repair is water-tight. I would not place a drain as this encourages ongoing CSF leak. During closure, I would ensure meticulous water-tight fascial closure with 1-Vicryl continuous suture. Post-operatively, I would consider 24-48 hours bed rest (controversial, some evidence suggests early mobilization is safe), maintain patient well-hydrated, and monitor for CSF leak signs (wound leak, persistent headache). I would document the dural tear, repair technique, and plan in operative notes, and inform patient post-operatively as part of transparent complication disclosure.

VIVA SCENARIOStandard

EXAMINER

"You are referred a 62-year-old male with cauda equina syndrome secondary to L4-5 disc herniation. He has had gradual onset of bilateral leg weakness and saddle numbness over 1 week, with urinary retention for 48 hours. MRI shows large central disc herniation. He is on rivaroxaban 20mg daily for atrial fibrillation (last dose this morning). How do you proceed?"

EXCEPTIONAL ANSWER

This case requires balancing the urgency of neurological decompression against the bleeding risk from ongoing anticoagulation. I would first confirm the patient has genuine CES with bilateral lower limb neurological deficit, saddle anaesthesia, and urinary retention documented on examination. I would then assess the timing: symptoms progressive over 1 week with retention for 48 hours means we are at critical 48-hour threshold where delay further reduces recovery potential. Regarding the rivaroxaban, I would check renal function (rivaroxaban cleared renally, half-life affected by renal impairment) and calculate time since last dose. Rivaroxaban has peak effect at 2-4 hours and half-life of 5-9 hours in normal renal function, so if last dose this morning (assume 8am) and now afternoon (assume 2pm), we are 6 hours post-dose with declining but still significant anti-coagulant effect. I would discuss with haematology regarding reversal options: rivaroxaban can be reversed with andexanet alfa (specific reversal agent) or prothrombin complex concentrate (PCC) though evidence limited. However, reversal agents themselves carry thromboembolic risk in AF patient. My approach would be: (1) Involve haematology and cardiology in decision-making, (2) Delay surgery 12-18 hours if possible to allow rivaroxaban to decline naturally (two half-lives), operating early tomorrow morning, (3) If neurological deterioration during observation period or already significant delay, consider proceeding with surgery using meticulous haemostatic technique, accepting increased bleeding risk as preferable to neurological devastation, (4) Consider reversal with andexanet alfa if surgery cannot be delayed, (5) Ensure meticulous surgical haemostasis, consider drain placement, low threshold for return to theatre if post-op haematoma. I would document shared decision-making with patient regarding risks of delaying versus proceeding with anticoagulation, and multidisciplinary input from haematology and cardiology.