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Cadaveric morphometric analysis for atlantal lateral mass screw placement.
Michael Y Wang1, Srinath Samudrala
1Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, 90033, USA. myw@usc.edu
Neurosurgery
|May 26, 2004
Summary
Atlantal lateral mass screws offer a viable alternative for C1/C2 fixation. Despite anatomical variations, the large size of the C1 lateral mass allows for forgiving screw placement with proper technique.
Area of Science:
- Neurosurgery
- Orthopedic Surgery
- Anatomy
Background:
- Atlantal lateral mass screws are an increasingly popular alternative to C1/C2 transarticular screws.
- This technique can potentially avoid occipital extension of fusions.
- Challenges exist due to critical local anatomy and unfamiliarity with C1 screw placement.
Purpose of the Study:
- To conduct a morphometric analysis of the C1 lateral mass.
- To determine critical measurements for screw placement using the Harms and Melcher technique.
Main Methods:
- Morphometric analysis of 74 cadaveric spines.
- Measurement of screw entry points, trajectories, and lengths.
- Evaluation of screw placement feasibility for 3.5-mm lateral mass screws.
Main Results:
- Mean screw entry dimensions: 3.9 mm height, 7.3 mm width.
- Mean medialized screw trajectory: 33 degrees (range, 25-45 degrees).
- Mean maximal screw length for bicortical purchase: 22.5 mm; mean minimum depth: 14.4 mm.
- Posterior arch overhang averaged 11.4 mm.
- All specimens accommodated bilateral 3.5-mm screws with preparation.
Conclusions:
- C1 morphology exhibits significant variations.
- The atlantal lateral mass size generally allows for forgiving screw placement.
- Preoperative CT scans and intraoperative fluoroscopy are valuable tools.
- Careful preparation of the screw entry site is crucial.