Stemless reverse humeral component neck-shaft angle has an influence on initial fixation.

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Implant design

Background:

• Stemless anatomic humeral components are a viable alternative to stemmed implants in patients with good bone quality.
• Limited research exists on factors influencing primary fixation of stemless reverse humeral implants.
• This study investigates the impact of neck-shaft angle on stemless reverse humeral implant stability.

Purpose of the Study:

• To assess the effect of surgical neck-shaft angle on the primary time-zero fixation of stemless reverse humeral implants.
• To determine the optimal neck-shaft angle for maximizing implant stability.

Main Methods:

• Finite element analysis of eight CT-derived humeral models.
• Simulated implantation of a generic stemless humeral implant at neck-shaft angles of 130°, 135°, 140°, 145°, and 150°.
• Analysis of four simulated daily living loading scenarios to measure bone-implant micromotion.

Main Results:

• The greatest implant-bone distraction occurred at the 130° neck-shaft angle.
• Increasing the neck-shaft angle significantly reduced micromotion (P=.0001).
• Each 5° increase in neck-shaft angle resulted in an average 17% reduction in bone-implant distraction.

Conclusions:

• Neck-shaft angle is a critical, modifiable factor for stemless reverse humeral component stability.
• Varus neck-shaft angles (e.g., 130°) increase bone-implant distraction.
• Humeral head osteotomies at higher neck-shaft angles may improve stemless implant stability.