What are the reasons for movement of a corpectomy (surgical removal of a vertebra) cage in the post-operative period following cervical spine surgery from an anterior approach?

Reasons for Movement of Corpectomy Cage in Post-Operative Period Following Cervical Spine Surgery from Anterior Approach

The most common reasons for movement of a corpectomy cage after anterior cervical spine surgery include subsidence, hardware failure, pseudarthrosis (nonunion), and retrolisthesis, with subsidence being the most frequently encountered complication. 1, 2

Primary Causes of Cage Movement

1. Subsidence

• Subsidence (sinking of the cage into adjacent vertebral bodies) is the most common specific complication causing cage movement, occurring in approximately 7-10% of cases 1, 2
• More commonly observed with titanium mesh cages (average 1.91 mm) compared to carbon fiber reinforced polymer cages (average 0.5 mm) 2
• Most cases of subsidence are asymptomatic and can be managed conservatively 1
• Significant subsidence (>3 mm) is more likely to cause symptoms requiring intervention 2

2. Hardware Failure

• Occurs in approximately 10% of anterior cervical corpectomy and fusion (ACCF) cases 1
• Includes screw loosening, plate dislodgement, or cage fracture 1
• More common in multi-level corpectomies (two or more levels) compared to single-level procedures 3
• Can lead to kyphotic deformity requiring revision surgery 3

3. Pseudarthrosis (Nonunion)

• Failure of solid fusion between the corpectomy cage and adjacent vertebral bodies 4
• Documented based on motion between involved spinous processes observed on flexion-extension radiographs 4
• Symptomatic pseudarthrosis occurs in approximately 10.9% of cases 4
• Can lead to persistent pain, neurological symptoms, and eventual hardware failure 4

4. Retrolisthesis

• Posterior displacement of a vertebra relative to the vertebra below it 5
• Can occur even after "successful" fusion procedures 5
• May present with new onset of neck pain and headaches months after surgery 5
• Often requires posterior stabilization to address the instability 5

Risk Factors for Cage Movement

1. Surgical Technique Factors

• Inadequate end plate preparation leading to poor bone-cage interface 1
• Improper sizing of the corpectomy cage 2
• Incorrect screw placement (reported in approximately 3% of cases) 1
• Insufficient plate fixation or stabilization 4

2. Patient-Related Factors

• Poor bone quality (osteoporosis) 1
• Pre-existing cervical kyphosis 3
• Multi-level corpectomy (two or more levels) 3
• Severe myelopathy before surgery (Nurick grades 4-5) 1

3. Biomechanical Factors

• Excessive motion at the operated segments 4
• Inadequate anterior column support 4
• Uneven load distribution across the construct 2
• Absence of posterior stabilization in multi-level cases 5

Monitoring and Management

1. Routine Imaging Follow-up

• Radiographic evaluation at 4-12 weeks post-surgery can detect early cage movement 3
• Asymptomatic abnormalities are more common in multi-level corpectomies 3
• Single-level ACCF rarely requires intervention based on routine imaging findings alone 3
• CT scans provide better assessment of fusion status and hardware position than plain radiographs 3

2. Management Options

• Conservative management for asymptomatic minor subsidence 1
• Revision surgery with posterior stabilization for symptomatic retrolisthesis 5
• Anterior revision with plate stabilization for pseudarthrosis (83.3% good/excellent outcomes) 4
• Posterior approach revision for hardware failure (94% fusion rate compared to 45% with anterior revision) 4

3. Prevention Strategies

• Appropriate cage selection based on vertebral body dimensions 2
• Proper end plate preparation 1
• Consideration of posterior augmentation for multi-level corpectomies 1
• Use of locking plates to enhance stability 1

Clinical Pearls and Pitfalls

• Maintain high index of suspicion for cage movement in patients with persistent or new symptoms even after apparently successful surgery 5
• Subsidence alone does not necessarily correlate with poor clinical outcomes unless significant (>3 mm) 2
• Multi-level corpectomies (three or more levels) have significantly higher complication rates and should be approached with caution 1
• Patients with pre-existing cervical kyphosis are at higher risk for construct failure and may benefit from combined anterior-posterior approaches 3, 5