Factors affecting lateral mass screw placement at C-7

Area of Science:

• Spine surgery
• Orthopedic instrumentation
• Anatomical studies

Background:

• The C-7 lateral mass presents unique anatomical challenges for spinal instrumentation.
• Existing lateral mass screw placement techniques do not fully accommodate C-7's specific morphology.

Purpose of the Study:

• To evaluate the relationship between C-7 lateral mass morphological measures and the success of screw placement.
• To compare the efficacy of Magerl, Roy-Camille, and a modified Roy-Camille technique for C-7 lateral mass screw fixation.

Main Methods:

• Virtual screw placement using CT scans in 50 patients (25 male, 25 female).
• Analysis of 12 morphological measures of the C-7 lateral mass.
• Assessment of complications including foraminal and articular process violations.

Main Results:

• A combined measure of T-1 facet intrusion and C-7 lateral mass length was the only significant predictor for screw placement success with the Roy-Camille technique.
• Screw placement was successful in 28 patients (Magerl), 24 patients (Roy-Camille), and 46 patients (modified technique).
• Four patients had no successful screw placement with any method.

Conclusions:

• A specific anatomical ratio, combining C-7 lateral mass length and T-1 facet intrusion, influences screw placement.
• A modified Roy-Camille technique, using a higher starting point, may reduce C-7 screw placement complications by avoiding the T-1 facet.