Abstract
The role of anconeus in elbow stability has been a long-standing debate. Anatomical and electromyographic studies have suggested a potential role as a stabilizer. However, to our knowledge, no clinical or biomechanical studies have investigated its role in improving the stability of a lateral collateral ligament (LCL) deficient elbow.
Seven cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. An LCL injured model was created by sectioning of the common extensor origin, and the LCL. The anconeus tendon and its aponeurosis were sutured in a Krackow fashion and tensioned to 10N and 20N through a transosseous tunnel at its origin. Varus-valgus angles and ulnohumeral rotations were recorded using an electromagnetic tracking system during simulated active elbow flexion with the forearm pronated and supinated. During active motion, the injured model resulted in a significant increase in varus angulation (5.3°±2.9°, P=.0001 pronation, 3.5°±3.4°, P=.001 supination) and external rotation (ER) (8.6°±5.8°, P=.001 pronation, 7.1°±6.1°, P=.003 supination) of the ulnohumeral articulation compared to the control state (varus angle −2.8°±3.4° pronation, −3.3°±3.2° supination, ER angle 2.1°±5.6° pronation, 1.6°±5.8° supination).
Tensioning of the anconeus significantly decreased the varus angulation (−1.2°±4.5°, P=.006 for 10N in pronation, −3.9°±4°, P=.0001 for 20N in pronation, −4.3°±4°, P=.0001 for 10N in supination, −5.3°±4.2°, P=.0001 for 20N in supination) and ER angle (2.6°±4.5°, P=.008 for 10N in pronation, 0.3°±5°, P=.0001 for 20N in pronation, 0.1°±5.3°, P=.0001 for 10N in supination, −0.8°±5.3°, P=.0001 for 20N in supination) of the injured elbow. Comparing anconeus tensioning to the control state, there was no significant difference in varus-valgus angulation except with anconeus tensioning to 20N with the forearm in supination which resulted in less varus angulation (P=1 for 10N in pronation, P=.267 for 20N in pronation, P=.604 for 10N in supination, P=.030 for 20N in supination). Although there were statistically significant differences in ulnohumeral rotation between anconeus tensioning and the control state (except with anconeus tensioning to 10N with the forearm in pronation which was not significantly different), anconeus tensioning resulted in decreased external rotation angle compared to the control state (P=1 for 10N in pronation, P=.020 for 20N in pronation, P=.033 for 10N in supination, P=.001 for 20N in supination).
In the highly unstable varus elbow orientation, anconeus tensioning restores the in vitro stability of an LCL deficient elbow during simulated active motion with the forearm in both pronation and supination. Interestingly, there was a significant difference in varus-valgus angulation between 20N anconeus tensioning with the forearm supinated and the control state, with less varus angulation for the anconeus tensioning which suggests that loads less than 20N is sufficient to restore varus stability during active motion with the forearm supinated. Similarly, the significant difference observed in ulnohumeral rotation between anconeus tensioning and the control state suggests that lesser degrees of anconeus tensioning would be sufficient to restore the posterolateral instability of an LCL deficient elbow. These results may have several clinical implications such as a potential role for anconeus strengthening in managing symptomatic lateral elbow instability.
