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Variables affecting pedicle screw plate fixation of an unstable L3-L4 defect
K L Markolf1, R B Delamarter, I Fyodorov
1Biomechanics Research Section, Department of Orthopaedic Surgery, University of California at Los Angeles, USA.
Clinical Orthopaedics and Related Research
|June 1, 1996
Summary
Steffee plates stabilize spinal defects, with longer plates reducing torsional rotation at the defect site. Locking plates did not affect spinal stability, while spanning an adjacent disc reduced motion at that level.
Area of Science:
- Spinal biomechanics
- Orthopedic surgery
- Spinal instrumentation
Background:
- Spinal instability due to disc defects requires surgical stabilization.
- Pedicle screw-based plating systems are commonly used for spinal fusion.
- Understanding the biomechanical effects of different plating configurations is crucial for optimizing surgical outcomes.
Purpose of the Study:
- To evaluate the biomechanical stability of different bilateral Steffee plate configurations in a cadaveric spine model with a L3-L4 disc defect.
- To assess the impact of plate length and screw number on intervertebral rotations.
- To determine the effect of locking versus unlocked plate configurations on spinal motion.
Main Methods:
- Fresh frozen human cadaveric spinal specimens (T8-S1) were used.
- Pure flexion-extension bending and axial torque loads were applied.
- Intervertebral rotations were measured at L3-L4, L2-L3, and L1-L2 discs.
- A standardized L3-L4 disc defect was created.
- Two bilateral Steffee plate configurations were tested: a 2-screw construct and a 3-screw construct spanning the defect and adjacent disc.
- Plates were tested in unlocked and locked states.
Main Results:
- Locking the plates did not alter intervertebral rotations at any level.
- A longer plate (3-screw) significantly reduced torsional rotation at the defect site by approximately 50% compared to a shorter plate (2-screw).
- Flexion rotation increased slightly at the L2-L3 level with the 2-screw plate, but was reduced with the 3-screw plate spanning this level.
- No significant changes in motion were observed at the L1-L2 level.
Conclusions:
- Bilateral Steffee plating can provide stability to spinal defects.
- A longer plate construct with more screws offers improved torsional stability at the defect site.
- Plate locking does not enhance biomechanical stability in this model.
- Spanning an adjacent uninjured disc with a longer construct can help control motion at that level.