Optimal baseplate rotational alignment for locking-screw fixation in reverse total shoulder arthroplasty: a...

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Medical Imaging

Background:

• Baseplate loosening is a significant concern in reverse total shoulder arthroplasty (RTSA).
• Optimizing fixation by placing screws into dense scapular bone pillars is crucial.
• 3D computer-aided design (CAD) aids in analyzing implant positioning.

Purpose of the Study:

• To determine the optimal rotational alignment of RTSA baseplates.
• To maximize peripheral locking-screw purchase within the scapular bone pillars.
• To investigate screw fixation in the three distinct scapular pillars.

Main Methods:

• Reconstruction of 73 arthritic scapulae from CT images.
• Importing scapular models and RTSA baseplate designs into 3D CAD software.
• Rotating the baseplate to optimize screw purchase in individual and combined scapular pillars.

Main Results:

• Optimal individual screw placements: coracoid pillar at 6°, inferior pillar at 198°, and scapular spine pillar at 295°.
• Significant difficulty (78%) in achieving optimal screw purchase in the scapular spine pillar.
• Excellent purchase achieved in the coracoid (100%) and inferior (99%) pillars.
• Maximal combined fixation achieved at 11° internal rotation.

Conclusions:

• An approximate 11° internal rotation is ideal for maximal baseplate fixation in RTSA.
• Achieving optimal screw purchase in the scapular spine pillar presents a significant challenge.
• These findings can inform surgical planning for improved RTSA outcomes.