Biomechanical significance of the collateral ligaments in transolecranon fracture-dislocations.

Background: It is widely accepted that transolecranon fracture-dislocations are not associated with collateral ligament disruption. The aim of the present study was to investigate the significance of the collateral ligaments in transolecranon fractures.
Methods: Twenty cadaveric elbows with a mean age of 46.3 years were used. All soft tissue was dissected to the level of the capsule, leaving the anterior band of the medial collateral ligament (MCL) and lateral collateral ligament (LCL) intact. A standardized, oblique osteotomy starting from the distal margin of the cartilage bare area of the ulna was made. The elbows were loaded with an inferiorly directed force of 5 and 10 N in the intact, MCL cut, LCL cut, and both ligaments cut states. All measurements were recorded on lateral calibrated radiographs.
Results: The mean inferior translation with intact ligaments (n = 20) when the humerus was loaded with 5 and 10 N was 1.52 mm (95% confidence interval [CI], 1.02-2.02) and 2.23 mm (95% CI, 1.61-2.85), respectively. When the LCL was cut first (n = 10), the inferior translation with 5 and 10 N load was 4.11 mm (95% CI, 0.95-7.26) and 4.82 mm (95% CI, 1.91-7.72), respectively. When the MCL was cut first (n = 10), the inferior translation when loaded with 5 and 10 N was 3.94 mm (95% CI, 0.796-7.08) and 5.68 mm (95% CI, 3.03-8.33), respectively. The inferior translation when loaded with 5 and 10 N and both ligaments cut was 15.65 mm (95% CI, 12.59-18.79) and 17.50 mm (95% CI, 14.86-20.13), respectively. There was a statistical difference between the intact and MCL cut first at 10 N and when both ligaments were cut at 5 and 10 N.
Conclusions: The findings suggest that collateral ligament disruption is a prerequisite for a transolecranon fracture-dislocation. An inferior translation of more than 3 mm suggests that at least one of the collateral ligaments is disrupted, and more than 7.5 mm indicates that both collateral ligaments are disrupted.
(Copyright © 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)