Biomechanical impact of elbow motion in elbow stiffness

Abstract

Background: A mechanical block in the elbow due to osteophytes in the olecranon fossa is a common clinical symptom for elbow stiffness.

Purpose/hypothesis: This study aims to understand the biomechanical characteristics or changes in the stiff elbow in the resting (or neutral) and swing position of the arm using a cadaveric model. The hypotheses included the following: (1) a difference exists in the articular contact pressure of the elbow by comparing the non-stiff and stiff models in in vivo studies; (2) the degree of stiffness would affect the increase of the joint loading of the elbow.

Study design: Controlled laboratory study, cadaveric study.

Methods: Eight fresh-frozen specimens from individuals of both sexes were included in the biomechanical study. The specimen was mounted on a custom-designed jig system with gravity-assisted muscle contracture to mimic the elbow in a standing position. The elbow was tested in two conditions (the resting and passive swing). Contact pressure was recorded for three seconds in the resting position, which was the neutral position of the humerus. By dropping the forearm from 90° of the elbow flexion, the passive swing was performed. The specimens were tested sequentially in three stages of stiffness (stage 0, no stiffness; stage 1, 30° of extension limitation; and stage 2, 60° of extension limitation). After data collection was completed in stage 0, a stiff model was sequentially created for each stage. The stiff model of the elbow was created by blocking the olecranon by inserting a 2.0 K-wire into the olecranon fossa horizontally with the intercondylar axis.

Results: The mean contact pressures were 279 ± 23, 302 ± 6, and 349 ± 23 kPa in stages 0, 1, and 2, respectively. The increases in the mean contact pressure in stages 2 versus 0 were significant (P < 0.0001). The mean contact pressures were 297 ± 19, 310 ± 14, and 326 ± 13 kPa in stages 0, 1, and 2, respectively. The peak contact pressures were 420 ± 54, 448 ± 84, and 500 ± 67 kPa in stages 0, 1, and 2, respectively. The increases in mean contact pressure in stage 2 versus 0 were significant (P = 0.039). The increases in peak contact pressure in stages 0 versus 2 were significant (P = 0.007).

Conclusions: The elbow bears the load created by gravity and muscle contracture in the resting and swing motion. Moreover, extension limitation of stiff elbow increases the load bearing in the resting position and swing motion. Careful surgical management should be considered for meticulous clearance of bony spur around olecranon fossa to resolve the extension limitation of the elbow.

Keywords: Arm swing; Biomechanics; Contact pressure; Elbow motion; Stiff elbow.