Forces across the middle of the intact clavicle during shoulder motion

The optimal management of displaced middle third clavicle fractures is currently under investigation. Advances in fracture fixation technology have expanded the indications for operative fracture management. Data are currently unavailable regarding the normal forces and moments that occur in the middle clavicle with motion of the glenohumeral joint. This study tested our null hypothesis that active range of motion in internal rotation, external rotation, and abduction would produce a similar magnitude of force across the middle clavicle.

Clavicle forces were measured in 6 whole fresh frozen cadavers using a 6 degree-of-freedom load cell mounted to the middle third of the clavicle. The rotator cuff tendons were isolated, divided, and connected to a system of weights. The forces across the clavicle in 3 orthogonal directions were quantified during simulated active abduction, internal rotation, and external rotation.

There were statistically greater axial compressive force and torque in the clavicle during humeral abduction compared with internal or external rotation. During external rotation, there were statistically greater tensile forces compared with abduction or internal rotation. There were no statistical differences in the superior-inferior or anterior-posterior forces with the 3 motions studied.

Overall, active abduction caused the greatest increase in middle clavicle forces and torque. Abduction resulted in the most significant axial compressive force, whereas active external rotation caused the greatest tensile force across the intact middle clavicle.

To our knowledge, these findings represent the first results describing the forces across the intact clavicle during glenohumeral motion. These data can be used to aid clinicians in treating these fractures, guide the design of future biomechanical studies, and develop rehabilitation protocols.