Biomechanical evaluation of the effect of varying humeral implant length in total elbow replacement: a finite element analysis.

BACKGROUND

Total elbow arthroplasty (TEA) is increasingly used for expanding indications but complications like aseptic loosening and periprosthetic fractures persist. Our objective is to examine the biomechanical behavior of the total elbow implant in response to varying implant lengths by investigating the stresses and the stress shielding effect in the bone-implant assembly using finite element (FE) modeling.

METHODS

A fourth-generation synthetic humerus sawbone and its corresponding digital model were used in this study. Total elbow implants are laser scanned to obtain the 3D implant models. FE models of 2-mm cemented bone-prosthesis assemblies of different implant lengths were generated. While fixing the mid-humerus, a compressive load of 400 N was applied at the distal humerus at varying flexion angles of 60°, 90°, and 150° to represent activities of daily living. A validated intact model was used to compare the experimental and computational strains. The von Mises stress, a scalar quantity that represents the state of stress the object is in, was then evaluated and compared in all intact and implanted models.

RESULTS

Longer humeral implants demonstrated larger areas of reduced peak stress, despite similar maximum cortical stress locations and magnitude. Cortical bone stress was observed to be lower along the implant insertion length. Maximum implant stress was also consistently higher in the 8-in implant for all loading conditions. Significant stress shielding was observed in all implants, with maximum %Δ stress consistently falling within the 15%-20% region of humerus length from the distal end.

DISCUSSION: Longer implants displayed larger stress-shielding areas, emphasizing the potential for shorter prostheses to preserve more bone stock and limit stress shielding.