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Humeral head size predicts baseplate lateralization in reverse shoulder arthroplasty: a comparative computer model
Stefan Bauer1,2, William G Blakeney2,3, Arnaud Meylan1,4
1Chirurgie de l'épaule et du coude, Service d'Orthopédie et de Traumatologie, Ensemble Hospitalier de la Côte, Morges, Switzerland.
JSES International
|March 11, 2024
Summary
This study found that a less distalized 135° reverse shoulder arthroplasty (RSA) with specific glenoid configurations significantly improves range of motion (ROM) in female patients. Humeral head size (HS) strongly correlates with baseplate lateralization (BL) for planning optimal RSA outcomes.
Area of Science:
- Orthopedic Surgery
- Biomechanical Engineering
- Medical Imaging Analysis
Background:
- Determining optimal component positioning in reverse shoulder arthroplasty (RSA) is crucial for functional outcomes.
- Key parameters like baseplate lateralization (BL), glenosphere size (GS), and glenosphere overhang (GOH) require precise understanding.
- This study investigates these factors in relation to patient anatomy and gender for 145° and 135° neck shaft angles (NSA).
Purpose of the Study:
- To evaluate the correlation between patient anthropometrics (body height, humeral head size) and gender with optimal glenoid configurations in RSA.
- To compare range of motion (ROM) and implant positioning between 145° and 135° NSA designs.
- To identify configurations that maintain anatomic lateralization (aLAT) and optimize muscle length.
Main Methods:
- A computer modeling study analyzed 22 computed tomographies (11 male/female).
- Various glenoid configurations (20 types) were combined with 145° and 135° NSA stems.
- Abduction-adduction, flexion-extension, rotation, total ROM (TROM), and total notching relevant (TNR) ROM were computed.
Main Results:
- The best 145° models utilized eccentric glenospheres with mean BL of 3.5 mm and GOH of 8.8 mm.
- The 135° models featured concentric glenospheres with mean BL of 3.8 mm and GOH of 6.9 mm.
- Humeral head size (HS) showed the strongest positive correlation with BL (0.65/0.79). A 135° NSA significantly increased TROM and TNR ROM in females, despite reduced abduction.
Conclusions:
- Humeral head size (HS) is a practical predictor for baseplate lateralization (BL) in RSA planning.
- A less distalized 135° NSA design, even with reduced glenosphere overhang (GOH), enhances TROM and specific ROM components (extension, external rotation, adduction) in smaller female patients.
- This 135° RSA configuration optimizes muscle length and may improve subscapularis repair outcomes.
