Optimal screw placement for base plate fixation in reverse total shoulder arthroplasty

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Anatomy

Background:

• Scapular anatomy is crucial for secure glenoid base plate fixation in reverse shoulder arthroplasty (RSA).
• Optimal screw placement requires detailed understanding of scapular cortical thickness variations.
• Current characterization of scapular bone thickness is insufficient for guiding screw selection in RSA.

Purpose of the Study:

• To comprehensively map scapular cortical thickness.
• To determine optimal screw trajectories and lengths for glenoid base plate fixation in RSA.
• To identify safe and effective screw placement regions within the scapula.

Main Methods:

• High-resolution CT scans of 12 cadaveric scapulae were performed.
• 3D reconstructions and detailed wall thickness analyses were conducted.
• Virtual screw placements were simulated using two distinct scenarios (intraosseous vs. thickest cortex).

Main Results:

• Specific optimal screw lengths and angles were determined for superior, inferior, and posterior screws across both simulated scenarios.
• Anterior screw placement was consistent, averaging 29 mm in length.
• Thicker cortical bone was found in the suprascapular notch, scapular spine base, and inferior pillar.

Conclusions:

• Key areas of thicker scapular cortex were identified.
• These thicker regions are accessible for screw fixation in RSA, with minor exceptions.
• Findings provide valuable anatomical data for improving screw fixation in reverse shoulder arthroplasty.