Biomechanical evaluation of the modified lasso technique.

Background: The Terrible Triad of the elbow is a constellation of elbow dislocation, radial head fracture and coronoid process fracture. A common type of coronoid fracture documented with this triad is type II Regan-Morrey coronoid fractures. The preferred fixation method for this fracture type is the lasso technique, medial-lateral tunnel orientation being the traditional approach. Considering elbow anatomy, we saw an opportunity to potentially improve fixation by altering the suture lasso tunnel orientation to a proximal-distal orientation.

Hypothesis: Two tunnels in the proximal-distal direction would result in greater biomechanical stability as compared to the traditional lasso technique.

Material and methods: A type 2 Regan-Morrey fracture was created in 12 fresh frozen cadaveric elbows at 50% of the coronoid height using an oscillating saw. The humero-ulnar joint was placed in 0 degrees flexion then loaded at a rate of 10mm/min to failure.

Results: The control technique (medio-lateral tunnels) showed failure load of 150±81N that was not significantly different (p=0.825) than the 134±116N measured for the modified technique (distal-proximal tunnels). The portion of the load-displacement curve used to calculate stiffness was linear (R^2=0.94±0.04) with determination coefficients that did not differ between the two groups (p=0.351). For stiffness, we measured 17±13N/mm and 14±12N/mm respectively for control and modified techniques that did not result in a significant difference (p=0.674).

Conclusion: In this attempt to improve the shortcomings of the lasso technique, we found that changing from medio-lateral to proximal-distal drilling directions did not result in an appreciable biomechanical benefit.

Level of evidence: Basic science study; Biomechanics.