Abstract
Objectives:
The standard of care for treating anterior shoulder instability caused by a labral detachment is the Bankart repair. In the case of a deficient labrum with significant antero-inferior glenoid bone loss, the latarjet technique can be used instead. However, when the labrum is deficient and the bone loss is minimal, labral reconstruction has been recently proposed as an alternative. A new technique called Anterior Labral Circumferential Onlay Technique (ALCOT) was developed, which reconstructs the labrum using the long head of the biceps tendon. The purpose of this study was to biomechanically evaluate the efficacy of the ALCOT to stabilize the shoulder joint against anterior dislocation in the setting of a deficient labrum with no glenoid bone loss.
Methods:
Ten fresh-frozen cadaveric shoulders were tested in 5 consecutive states using a 6-degrees-of-freedom robotic arm: (1) Native, (2) Capsular Repair, (3) Labral Tear (4) ALCOT (5) Latarjet. The capsule repair state used as a control because the joint capsule needed to be opened and repaired to perform the other states. This state ensured that any differences were due to the surgical procedure being tested, and not because of any iatrogenic damage to the capsule. The Labral Tear was performed by detaching the labrum from the glenoid between 3-6 o’clock and removing it from the joint. For the ALCOT, the biceps tendon was shortened at the distal portion and pulled into the joint. Three knotless all suture anchors were placed at 3, 4:30 and 6 o’clock position on the glenoid rim, and the biceps tendon was secured to the suture anchors using mattress stitches. For the latarjet, a coracoid autograft was cut 25 mm from the tip, keeping the conjoint tendons intact, and secured to the glenoid using two screws. In the native state, each specimen underwent an initial test to determine the appropriate amount of anterior and inferior displacement for future tests. In this test, a 50N compressive load was maintained while an 80N force was applied in the sagittal plane at a 45° angle between the anterior and inferior axes. The corresponding anterior and inferior displacements were recorded. Then, in each state including native, a dislocation test was performed. In this test, a 50N compressive load was maintained while the joint was driven in position control to the previously recorded positions on the anterior and inferior axes. The amount of force needed to displace the shoulder and the lateral displacement of the humeral head were recorded throughout the motion. Higher lateral translation was considered more stable, because it corresponded to a larger obstacle to overcome during the dislocation. To account for variation in the amount of compressive load during the test, antero-inferior dislocation load was normalized by compressive load to create a force ratio. This metric accounts for the fact that the amount of force required to dislocate depends on the amount of stabilizing compressive load provided by the robot in vitro, and by muscle tension in vivo.
Results:
No significant differences were found between the native and capsular repair states. Compared to native, the labral tear significantly decreased the lateral translation of the humeral head during dislocation from 6.5mm to 5.4mm (p<0.001) and decreased the force ratio from 1.8 to 1.1 (p=0.002), corresponding to a decrease from 90N to 55N at 50N of compressive load. The ALCOT restored these values to 6.4 mm and 1.4, respectively, showing no significant difference from native. The latarjet restored the force ratio to 1.3 (not significant from native) but failed to restore lateral translation with a value of 5.6 mm (p=0.003 from Native, not significantly different from the labral tear). The force ratio is shown on figure 1 and the lateral translation is shown on figure 2.
Conclusions:
The ALCOT is a novel technique for labral reconstruction that can be considered as a treatment option for anterior instability in the setting of a deficient labrum. Compared to the latarjet technique, the ALCOT involves less morbidity and represents a more anatomic glenoid surface by replacing the labrum without changing the bony morphology. In this study, the ALCOT also showed superior stabilization by restoring native force ratio and lateral humerus translation. Further research is necessary to clinically validate this technique, and possibly to expand indications to small degrees of glenoid bone loss.
