Variable Prosthetic Neck-Shaft Angle in Total Shoulder Arthroplasty

Joseph P. Iannotti, MD, PhD

The normal anatomy of the proximal part of the humerus is highly variable with respect to head size, humeral offsets, version, and neck-shaft angle. When a surgeon uses a canal-filling press-fit humeral stem, his or her ability to place the prosthetic humeral head in a position that replicates the natural anatomy is dictated by the prosthetic head size and the offsets between the stem and the humerus. Many prosthetic designs have been developed to provide adaptability to accommodate both variations in normal humeral anatomy and the changes that occur as a result of pathologic conditions. The ability to vary the orientation of the humeral head with respect to the stem is embodied by prosthetic designs that (1) have modularity between the head and stem, (2) have a centered and eccentric taper between the head and stem, and (3) offer the capacity to vary the neck-shaft angle and version between the head and stem. These design features distinguish modern-day prostheses from the older monobloc prostheses. It is believed that these modern design features allow the prosthesis to be adapted to variations in normal anatomy with use of a more uniform surgical technique or to be adapted to deviations in anatomy as a result of pathologic conditions. When there is less adaptability of the prosthetic system, the surgical procedure can be modified to improve the ability of the system to achieve an anatomic reconstruction. It is clear that a fixed-angle prosthesis with an anatomically sized humeral head cannot be implanted properly when there is an excessive varus or valgus neck-shaft angle and the osteotomy is performed along the native anatomic neck. This JBJS/VJO video supplement demonstrates the advantages of an adjustable-head prosthesis as compared with a fixed-head prosthetic device for a wide range of neck-shaft angles. It also demonstrates the surgical techniques required to adapt the anatomy and optimize the result when only a fixed neck-shaft angle device is available.

Material Covered

• Modern vs. Monobloc designs
• Advantages of Variable Prosthetic Neck-Shaft Angle
• Avoiding Complications
• Surgical Pearls

Specifications

• Total Run Time: 32:54 minutes
• Catalog Number: 7070
• VJO Publication Date: December, 2009