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° 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° 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·m) was statistically greater than that of group 1 (7.5 ± 1.2 N·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.
Background
Ulnar collateral ligament reconstruction of the elbow using a variety of techniques has been successful in enabling overhead athletes with ulnar collateral ligament insufficiency to return to competition. Most current postoperative rehabilitation programs begin with a period of motion restriction, including limiting elbow extension, that is followed by a transition from elbow strengthening to an interval throwing program, to competition. Motion restrictions early in the postoperative period may increase the risk for contractures. There is limited information to support current motion restrictions.
Purpose
(1) To determine strain on the reconstructed ulnar collateral ligament during a rehabilitation protocol that includes passive range of motion, isometric muscle contraction, and varus and valgus torques. (2) To develop guidelines for a safe initial rehabilitation protocol.
Study Design
Controlled laboratory study.
Methods
Eight cadaveric elbows underwent ulnar collateral ligament reconstruction with the docking technique using a gracilis tendon graft. Differential variable reluctance transducers on the anterior and posterior bands of the reconstructed anterior bundle of the ulnar collateral ligament were used to measure strain, while an optical motion tracking system monitored elbow motion. Strain was measured in the following 3 settings: passive range of motion, 22.2 N isometric flexion and extension contractions, and 3.34 N·m varus and valgus torques with the arm at 90° of flexion.
Results
Range of motion from maximum extension to 50° of flexion produced 3% or less strain in both bands of the reconstructed ligament. Forearm rotation did not significantly affect strain in the anterior or posterior bands (P = .336 and P = .357). Strain at 90° approached 7% in the posterior band (upper 95% confidence interval). Isometric muscle contractions had no measurable effect on strain. Varus torques decreased and valgus torques increased strain significantly (P < .05).
Conclusion
In the immediate postoperative period, full extension is safe, while flexion beyond 50° may place deleterious strain on the reconstruction. Isometric flexion and extension exercises do not increase ligament strain but may be unsafe at 90° of flexion, while valgus exercises (internal rotation at the shoulder) can increase strain in the reconstructed ligament.
Clinical Relevance
The results have implications for the development of appropriate rehabilitation protocols after ulnar collateral ligament reconstructive surgery.
