The Effect of Elbow Flexion On Valgus Carrying Angle

This study aimed to examine the effect of flexion on valgus carrying angle in the human elbow using a dynamic elbow testing apparatus.

Active elbow motion was simulated in seven cadaveric upper extremities. Six electromechanical actuators simulated muscle action, while 6 degrees-of-freedom joint motion was measured with an optical tracking system to quantify the kinematics of the ulna with respect to the humerus as the elbow was flexed at the side position. Repeatability of the testing apparatus was assessed in a single elbow over five flexion-extension cycles. The varus angle change of each elbow was compared at different flexion angles with the arm at 0° of humerothoracic abduction or dependent arm position.

The testing apparatus achieved excellent kinematic repeatability (intraclass correlation coefficient, >0.95) throughout flexion and extension. All elbows decreased their valgus carrying angle during flexion from 0° to 90° when the arm was maintained at 0° of humerothoracic abduction. Elbows underwent significant total varus angle change from full extension of 3.9° ± 3.4° (P = .007), 7.3° ± 5.2° (P = .01), and 8.9° ± 7.1° (P = .02) at 60°, 90°, and 120° of flexion, respectively. No significant varus angle change was observed between 0° and 30° of flexion (P = .66), 60° and 120° of flexion (P = .06), and 90° and 120° of flexion (P = .19).

The dynamic elbow testing apparatus characterized a decrease of valgus carrying angle during elbow flexion and found that most varus angle changes occurred between 30° and 90° of flexion. All specimens underwent varus angle change until at least 90° of flexion.

Our model establishes the anatomic decrease in valgus angle by flexion angle in vitro and can serve as a baseline for testing motion profiles of arthroplasty designs and ligamentous reconstruction in the dependent arm position. Future investigations should focus on characterizing motion profile change as the arm is abducted away from the body.