EFFECT OF IMPLANT POSITION ON ULNOHUMERAL LOAD TRANSFER IN TOTAL ELBOW ARTHROPLASTY

Abstract

This study investigated the effect of the articulation position on joint load transfer in total elbow arthroplasty. To quantify loading, an adjustable humeral component, instrumented with a load cell, was developed to measure ulnohumeral loads in-vitro. Computer guidance was implemented to accurately place the linked articulation into eight cadaveric elbows. Axial compression and bending about the flexion axis produced the greatest loads during simulated active elbow flexion. An anteriorly malpositioned flexion-extension axis resulted in increased joint loads during flexion. Translational positional errors were more influential than rotational position on articular loading.

To quantify the relationship between total elbow arthroplasty position and elbow joint loading.

Eight cadaveric upper extremities were tested using a motion-controlled testing device, which simulated muscle activity. Computer guidance was employed to accurately position a linked implant consisting of a custom-designed adjustable humeral component and commercial ulnar component. The testing apparatus was instrumented with a six-degree-of-freedom load cell to measure axial and bending loads. Seven implant positions were tested including anterior-posterior translation (−5.0, −2.5, 0.0, 2.5, 5.0 mm) and internal-external rotation (−5, 0, 5°) during supinated and pronated flexion.

The resultant joint force decreased for all prosthetic hinge positions as elbow flexion increased (p< 0.001). Anterior hinge positions produced greater ulnohumeral loads (p< 0.001) and moments (p< 0.001) than posterior hinge positions during simulated elbow flexion. The greatest bending moment occurred about the flexion axis which reached maximum magnitudes during mid-flexion. Implant hinge malrotation did not have a significant effect on axial (p=0.07) or bending (p=0.6) forces experienced at the joint. The distance between the flexion (hinge) axis and the muscular line-of-action of flexors is reduced with anterior hinge placement, likely increasing the force necessary to produce flexion.

An anteriorly malpositioned flexion-extension axis resulted in an increase in joint loading during flexion and should be avoided during elbow arthroplasty.

This is the first reported study to measure the effect of elbow prosthesis positioning on joint loading. The knowledge gained about joint loads should improve future prosthetic designs and treatment options.

Funding: Canadian Institute for Health Research.

Please contact author for graphs and/or diagrams.