Lumbar Disc Arthroplasty (Total Disc Replacement)

SB Charité III (DePuy Spine)

Design: Three-component mobile-bearing device with unconstrained ultra-high molecular weight polyethylene (UHMWPE) core between two cobalt-chromium-molybdenum (CoCrMo) endplates.

Biomechanics:

• Unconstrained motion allows translation and rotation
• Low constraint may reduce stress on bone-implant interface
• Self-centering core design intended to maintain center of rotation
• Potential for core dislocation with improper positioning

Clinical Use:

• First FDA-approved device (2004)
• FDA IDE trial showed non-inferiority to circumferential fusion
• Strict midline placement required to prevent core subluxation
• Sagittal alignment restoration more challenging than fixed-bearing designs

Outcomes:

• 73.7% success rate at 2 years in FDA trial
• Motion preservation: average 7.8° at 5 years
• Heterotopic ossification rate: 35-65% (may limit motion)

The mobile-bearing design philosophy emphasizes reduced constraint to minimize implant-bone stress, but requires precise surgical technique for optimal outcomes.

ProDisc-L (Synthes/DePuy Synthes)

Design: Two-component semi-constrained device with fixed UHMWPE inlay in inferior cobalt-chromium endplate, articulating with superior convex endplate. Center of rotation anatomically positioned posterior to midline.

Biomechanics:

• Ball-and-socket articulation with posterior center of rotation
• Constrained design limits translation, may increase interface stress
• Keel fixation (inferior component) for rotational stability
• Better lordosis restoration than mobile-bearing designs

Clinical Use:

• FDA approved 2006 based on IDE trial vs circumferential fusion
• Easier surgical technique than mobile-bearing (less positioning critical)
• Better sagittal balance achievement with lordotic endplate angles
• Lower reoperation rate than fusion in 5-year follow-up

Outcomes:

• Non-inferior to fusion at 2 and 5 years
• Motion preservation: average 9.2° at 5 years
• Lower adjacent level degeneration rate than fusion (10% vs 28% at 5 years)

The fixed-bearing design prioritizes reproducible biomechanics and ease of surgical implantation, with excellent long-term clinical results.

Maverick (Medtronic)

Design: Two-component metal-on-metal (MOM) articulation with CoCrMo alloy surfaces, avoiding polyethylene entirely.

Theoretical Advantages:

• No polyethylene wear debris (potential for reduced inflammatory response)
• Thinner profile allows use in more collapsed disc spaces
• Greater wear resistance than metal-on-poly designs

Concerns:

• Metallosis from cobalt and chromium ion release
• Systemic metal levels elevated in some patients
• Long-term safety unknown beyond 5-10 years
• FDA approval limited (humanitarian device exemption only)

Clinical Status:

• Not FDA approved for general use in US
• European experience shows good short-term results
• Declining use due to metallosis concerns following hip MOM issues

Most modern TDR designs have moved away from metal-on-metal articulations due to safety concerns, favoring metal-on-polyethylene bearings.

Imaging Analysis

Standing lateral radiograph:

• Measure disc height at target level (at least 4-5mm required)
• Assess sagittal alignment (lordosis, pelvic parameters)
• Identify transitional anatomy (sacralization, lumbarization)
• Measure implant size needed (AP and lateral dimensions)

MRI review:

• Confirm disc degeneration (Pfirrmann grade)
• Rule out facet arthropathy (greater than Grade 2 excludes patient)
• Identify high-intensity zone (HIZ) if present
• Rule out stenosis (central, lateral, foraminal)
• Assess adjacent level disease

CT scan (if needed):

• Better evaluate facet joints
• Assess endplate integrity
• Identify vascular calcification
• Rule out posterior element pathology

Flexion-extension radiographs:

• Rule out instability (greater than 3mm translation or greater than 10° angulation)
• Assess motion at target level (if already fused spontaneously, TDR not indicated)

Implant Sizing

Most systems use trial implants with fluoroscopic verification:

• Anteroposterior size: Typically 38-50mm (avoid anterior cortex overhang)
• Mediolateral size: Typically 30-42mm (stay within lateral borders)
• Height: Match native disc height or restore slightly (avoid over-distraction)
• Lordotic angle: ProDisc-L offers 6° or 11° options for sagittal balance

Patient Positioning

• Supine on radiolucent table
• Slight Trendelenburg (15-20°) to move bowel contents cephalad
• Arms tucked or positioned on arm boards (not extended over head)
• Hip flexion minimal to reduce tension on femoral vessels
• C-arm positioning: Test lateral view before draping (true lateral critical)

Preoperative planning ensures appropriate patient selection, correct implant sizing, and anticipation of anatomical challenges during the anterior approach.

Skin Incision

L5-S1 approach:

• Vertical midline infraumbilical incision (6-8cm) OR
• Transverse Pfannenstiel incision 2cm above pubic symphysis (cosmetic)
• Incision extends through skin, subcutaneous fat, anterior rectus sheath

L4-5 approach:

• Vertical midline incision extended more cephalad (8-10cm)
• Higher positioning requires longer incision for vessel mobilization

Retroperitoneal Dissection

Left retroperitoneal approach (standard):

1. Incise linea alba in midline (avascular plane)
2. Retract rectus muscles laterally
3. Identify peritoneum as glistening white membrane
4. Develop retroperitoneal space by blunt dissection
5. Mobilize peritoneum medially to expose psoas muscle laterally
6. Identify ureter running over psoas (protect and retract medially with peritoneum)

Key anatomic landmarks:

• Psoas muscle (lateral boundary)
• Peritoneum (medial boundary)
• Vertebral bodies (posterior)

Vascular Mobilization

At L5-S1:

• Palpate sacral promontory to identify L5-S1 disc space
• Identify aortic bifurcation (usually at L4-5 level)
• Identify middle sacral artery/vein running over L5-S1 disc
• Ligate middle sacral vessels with clips or ties
• Access disc space between bifurcation (iliac vessels retracted laterally)

At L4-5:

• More challenging due to iliac vein location
• Left common iliac vein crosses anterior to L4-5 disc (must be mobilized)
• Mobilize vein cranially with gentle dissection
• Control lumbar segmental vessels if present
• Higher risk of vascular injury than L5-S1 approach

Sympathetic Plexus Preservation

Hypogastric plexus location:

• Runs over L5-S1 disc space anteriorly
• Controls ejaculation in males (sympathetic)
• Must be protected and retracted laterally with vessel mobilization

Technique:

• Identify filmy tissue anterior to disc (plexus within)
• Retract laterally with vessels (usually right side safer)
• Avoid cautery directly on plexus
• Gentle retraction (excessive stretch causes neuropraxia)

Retrograde ejaculation risk: 1-5% at L5-S1 (higher with inexperienced surgeons or excessive dissection).

Discectomy

1. Confirm level with fluoroscopy (count up from sacrum)
2. Incise annulus with cruciate incision or rectangular window
3. Remove nucleus with pituitary rongeurs and curettes
4. Complete discectomy to posterior annulus (avoid posterior longitudinal ligament violation)
5. Preserve peripheral annulus (contains implant, prevents migration)

Endplate Preparation:

• Remove cartilaginous endplate with curettes (expose bleeding bone)
• Preserve bony endplate integrity (avoid violation into vertebral body)
• Flat endplate preparation essential for implant seating
• Avoid over-distraction during retractor placement

Implant Positioning

Critical positioning principles:

• Center implant mediolaterally (equal overhang both sides)
• Midline sagittal positioning (slightly posterior acceptable for ProDisc-L)
• No anterior overhang (vascular erosion risk)
• No posterior placement (spinal canal risk)

Charité-specific:

• Strict midline positioning required for mobile core
• Symmetric endplate preparation to allow core centering
• Posterior position risks core dislocation posteriorly

ProDisc-L-specific:

• Slightly posterior positioning acceptable (mimics native center of rotation)
• Keel alignment with midline for rotational control
• Lordotic angle selection (6° vs 11°) based on sagittal alignment needs

Trialing and Final Implant

1. Insert trial implant (same size as planned final implant)
2. Check fluoroscopic positioning (AP and lateral views)
3. Assess fit (no rocking, no overhang, no endplate violation)
4. Remove trial and inspect endplates
5. Insert final implant (typically impacted with gentle mallet)
6. Confirm final position with fluoroscopy (AP and lateral)

Intraoperative imaging checklist:

• Implant centered mediolaterally (AP view)
• No anterior or posterior overhang (lateral view)
• Parallel to endplates (lateral view)
• Appropriate height restoration (lateral view)
• No subsidence (lateral view)

The disc preparation and implant placement are the most technique-sensitive steps, requiring meticulous attention to positioning and endplate preparation.

Hemostasis and Inspection

1. Remove retractors carefully (inspect vessels for injury)
2. Achieve meticulous hemostasis (check all dissected planes)
3. Inspect vessels for intimal tears or hematoma
4. Check hypogastric plexus area (ensure no stretch injury or bleeding)

Layer-by-Layer Closure

1. Peritoneum: Usually not closed (self-seals)
2. Rectus sheath: Close anterior sheath with running absorbable suture (0 or 1 Vicryl)
3. Subcutaneous layer: Close with absorbable suture (2-0 or 3-0 Vicryl)
4. Skin: Subcuticular closure (4-0 Monocryl) or staples

No drain typically placed (retroperitoneal approach, minimal dead space).

Postoperative Imaging

• Lateral and AP radiographs in recovery room
• Confirm implant position unchanged
• Rule out immediate subsidence or migration
• Assess sagittal alignment

Postoperative care focuses on early mobilization, as the anterior approach causes less soft tissue trauma than posterior approaches.

Intraoperative Complications

Vascular Injury (1-3%):

• Most feared complication during anterior approach
• Iliac vessels at highest risk (vein greater than artery)
• Left common iliac vein particularly vulnerable at L4-5
• Management: Immediate vascular surgery consultation, direct repair, possible blood transfusion
• Prevention: Gentle retraction, good lighting, vascular surgeon availability

Visceral Injury:

• Bowel perforation: Rare if peritoneum intact (recognize and repair primarily)
• Ureter injury: Retract with peritoneum, identify and protect
• Bladder injury: Rare (more common with low transverse incisions)

Neurological Injury:

• Nerve root injury: Rare (posterior approach risk, not anterior)
• Sympathetic plexus injury: 1-5% at L5-S1 (retrograde ejaculation in males)

Implant Malposition:

• Recognized intraoperatively with fluoroscopy
• Requires removal and repositioning if significant
• Easier with trial implants (check before final)

Early Postoperative Complications (Less Than 6 Weeks)

Retrograde Ejaculation:

• Incidence: 1-5% at L5-S1, less than 1% at L4-5
• Mechanism: Hypogastric plexus stretch or thermal injury
• Presentation: Inability to ejaculate (orgasm intact, dry ejaculation)
• Management: Usually permanent (counsel preoperatively), urology referral for fertility issues
• Prevention: Protect plexus during retraction, avoid cautery near plexus, gentle handling

Wound Complications:

• Infection: 1-2% (prophylactic antibiotics standard)
• Hematoma: Rare (retroperitoneal approach less dead space)
• Dehiscence: Rare with proper fascial closure

Ileus:

• Incidence: 5-10% (bowel manipulation during retraction)
• Management: Conservative (NPO, NG tube if needed)
• Usually resolves within 3-5 days

Subsidence:

• Early subsidence (first 6 weeks) suggests osteoporosis or endplate violation
• Imaging: Serial radiographs to monitor (greater than 3mm concerning)
• Management: Usually observational if asymptomatic; fusion if progressive/symptomatic

Late Complications (Greater Than 6 Weeks)

Heterotopic Ossification (HO):

• Incidence: 5-60% depending on grading system (clinically significant HO: 5-15%)
• Mechanism: Ectopic bone formation in paraspinal soft tissues (not in disc space)
• Classification: McAfee (Grade 0-4), Brooker (Grade 1-4)
• Impact: May limit motion if severe (Grade 3-4), usually asymptomatic in Grade 1-2
• Prevention: NSAIDs postoperatively (indomethacin 75mg daily for 6 weeks), low-dose radiation (controversial)
• Management: Observation if asymptomatic; excision rarely indicated

Facet Degeneration:

• Progression of facet arthropathy despite motion preservation
• Suggests poor patient selection (unrecognized facet disease preoperatively)
• May require fusion if symptomatic

Implant Wear and Loosening:

• Polyethylene wear: Long-term concern (greater than 10 years)
• Osteolysis: Rare but reported with wear debris
• Subsidence: Progressive endplate failure (osteoporosis risk factor)
• Migration: Very rare with modern designs (keel and teeth fixation)

Core Dislocation (Charité-specific):

• Mobile core subluxation or dislocation (1-3%)
• Related to malposition at surgery (non-midline placement)
• May cause recurrent pain or clicking sensation
• Diagnosis: Lateral radiographs (core position assessment)

Adjacent Segment Disease:

• Despite theoretical benefit, ASD still occurs after TDR (lower rate than fusion in some studies)
• Radiographic ASD: 10-20% at 5 years
• Symptomatic ASD requiring surgery: 2-4% per year (similar to fusion)

Persistent/Recurrent Pain:

• Incidence: 10-30% (similar to fusion)
• Causes: Facetogenic pain (missed at selection), persistent discogenic pain, psychosocial factors
• Workup: Rule out implant-related issues (subsidence, malposition, HO)
• Management: Conservative care; fusion if TDR clearly failed

Revision Surgery

Indications:

• Implant malposition causing symptoms
• Progressive subsidence with instability
• Infection
• Intractable pain despite appropriate patient selection

Revision Options:

1. Anterior revision TDR: Remove and replace implant (technically demanding)
2. Anterior implant removal + fusion: Convert to ALIF with cage and screws
3. Circumferential fusion: Add posterior instrumentation (most common)

Revision Challenges:

• Severe scar tissue from previous anterior approach
• Vascular adhesions to vertebral bodies
• Implant fixation (keels, teeth) makes removal difficult
• Higher complication rate than primary surgery (5-10% major complications)

Success Rate:

• Revision to fusion: 60-80% pain relief
• Revision TDR: Limited data (less predictable outcomes)