Biomechanical comparison of the docking technique with and without humeral bioabsorbable interference screw fixation.

BACKGROUND: Surgical reconstruction of the ulnar collateral ligament has evolved since Frank Jobe's original description. The "docking technique" is a popular modification that allows for securing the graft within a single humeral tunnel. More recently, interference screw fixation has been introduced as a means of improving the ultimate strength, stiffness, and kinematics of these constructs.

PURPOSE: This study was conducted to compare the biomechanical performance of the docking technique with and without interference screw fixation in the humerus.

STUDY DESIGN: Controlled laboratory study.

METHODS: Nine matched pairs of human cadaveric elbows (age 49.9 +/- 8.0 years) were reconstructed with a tendon graft using the docking technique (group 1) or the docking technique with the addition of a 4.75-mm bioabsorbable humeral interference screw (group 2). Before the reconstruction, joint laxity was measured on each specimen with the ulnar collateral ligament intact and then after transection of the ligament. Laxity measurements were repeated after the reconstruction. Failure testing was then performed at 70 degrees of elbow flexion. The specimens were preloaded with a 1-N.m moment and then loaded to failure at a displacement rate of 14 mm/s to approximate 50% strain per second.

RESULTS: Within group 1, the elbow laxity of the reconstructed state was significantly greater than the intact state at all tested flexion angles (P < .021). Within group 2, no statistically significant difference existed in elbow laxity between the intact state and the reconstructed state. When comparing laxities between groups, group 1 tended to be more lax at all tested flexion angles but was only significantly greater at 105 degrees of flexion. The most common mode of failure for both groups involved the sutures pulling out of the tendon. No significant difference was found for ultimate moment of failure between the 2 groups. However, the moment associated with 3 mm of gap formation for group 2 (12.8 +/- 4.2 N x m) was statistically greater than that of group 1 (7.5 +/- 1.2 N x m) (P = .001). The stiffness of group 2 (14.7 +/- 6.4 N/mm) was significantly greater than group 1 (9.9 +/- 3.1 N/mm) (P = .044).

CONCLUSION: The biomechanical performance of the docking technique with and without a humeral interference screw is similar.

CLINICAL RELEVANCE: The stiffness of the construct, along with the difference in moment that allows a 3-mm gap formation, suggests that the addition of a humeral interference screw is potentially beneficial. Further research in a healing model will help clarify this benefit.