The 6-O'clock Anchor Increases Labral Repair Strength in a Biomechanical Shoulder Instability Model

The Long Head of the Biceps Has a Stabilizing Effect on the Glenohumeral Joint in Simulated Infraspinatus or Subscapularis but Not Supraspinatus Rotator Cuff Deficiency: A Biomechanical Study

PURPOSE

To investigate the stabilizing role of the long head of the biceps (LHB) for different simulated rotator cuff (RC) tears.

METHODS

Human cadaveric specimens (n = 8) were fixed in a robotic-based experimental setup with a static loading of the RC, deltoid, and the LHB. RC tears were simulated by unloading of the corresponding muscles. A throwing motion and an anterior load-and-shift test were simulated under different RC conditions by unloading the supraspinatus (SS), subscapularis (SSc), infraspinatus (IS), and combinations (SS + SSc, SS + IS, SS + SSc + IS). The LHB was tested in 3 conditions: unloaded, loaded, and tenotomy. Translation of the humeral head and anterior forces depending on loading of the RC and the LHB was captured.

RESULTS

Loading of LHB produced no significant changes in anterior force or glenohumeral translation for the intact RC or a simulated SS tear. However, if SSc or IS were unloaded, LHB loading resulted in a significant increase of anterior force ranging from 3.9 N (P = .013, SSc unloaded) to 5.2 N (P = .001, simulated massive tear) and glenohumeral translation ranging from 2.4 mm (P = .0078, SSc unloaded) to 7.4 mm (P = .0078, simulated massive tear) compared to the unloaded LHB. Tenotomy of the LHB led to a significant increase in glenohumeral translation compared to the unloaded LHB in case of combined SS + SSc (2.6 mm, P = .0391) and simulated massive tears of all SS + SSc + IS (4.6 mm, P = .0078). Highest translation was observed in simulated massive tears between loaded LHB and tenotomy (8.1 mm, P = .0078).

CONCLUSIONS

Once SSc or IS is simulated to be torn, the LHB has a stabilizing effect for the glenohumeral joint and counteracts humeral translation. With a fully loaded RC, LHB loading has no influence.

CLINICAL RELEVANCE

With an intact RC, the condition of the LHB showed no biomechanical effect on the joint stability. Therefore, from a biomechanical point of view, the LHB could be removed from the joint when the RC is intact or reconstructable. However, since there was a positive effect even of the unloaded LHB in this study when SSc or IS is deficient, techniques with preservation of the supraglenoid LHB origin may be of benefit in such cases.

[Clinical application of Fastpass Scorpion suture passer for arthroscopic Bankart repair]

Objective

To explore the effectiveness and advantages of using Fastpass Scorpion suture passer to stitch the inferior capsulolabral complex in arthroscopic Bankart repair compared with traditional arthroscopic suture shuttle.

Methods

The clinical data of 41 patients with Bankart lesion, who met the selection criteria and were admitted between August 2019 and October 2021, was retrospectively analyzed. Under arthroscopy, the inferior capsulolabral complex was stitched with Fastpass Scorpion suture passer in 27 patients (FS group) and with arthroscopic suture shuttle in 14 patients (ASS group). There was no significant difference between the two groups ( P>0.05) in gender, age, injured side, frequency of shoulder dislocation, time from first dislocation to operation, and preoperative Rowe score of shoulder. Taking successful suture and pull-tightening as the criteria for completion of repair, the number of patients that were repaired at 5∶00 to 6∶00 (<6:00) and 6∶00 to 7∶00 positions of the glenoid in the two groups was compared. The operation time, and the difference of Rowe shoulder score betwee pre- and post-operation, the occurrence of shoulder joint dislocation, the results of apprehension test, and the constituent ratio of recovery to the pre-injury movement level between the two groups at 1 year after operation.

Results

Both groups completed the repair at 5∶00 to 6∶00 (<6∶00), and the constituent ratio of patients completed at 6∶00 to 7∶00 was significantly greater in the FS group than in the ASS group ( P<0.05). The operation time was significantly shorter in the FS group than in the ASS group ( P<0.05). All incisions in the two groups healed by first intention. All patients were followed up 12-36 months (mean, 19.1 months). No anchor displacement or neurovascular injury occurred during follow-up. Rowe score of shoulder in the two groups significantly improved at 1 year after operation than preoperative scores ( P<0.05), and there was no significant difference in the difference of Rowe shoulder score between pre- and post-operation between the two groups ( P>0.05). At 1 year after operation, no re-dislocation occurred, and there was no significant difference in the apprehension test and the constituent ratio of recovery to the pre-injury movement level between the two groups ( P>0.05).

Conclusion

Compared with the arthroscopic suture shuttle, using Fastpass Scorpion suture passer to stitch the inferior capsulolabral complex in arthroscopic Bankart repair is more convenient, saves operation time, and has good effectiveness.

In Vitro Simulation of Shoulder Motion Driven by Three-Dimensional Scapular and Humeral Kinematics

In vitro simulation of three-dimensional (3D) shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein, we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: (1) robotically simulate seven healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in six cadavers, (2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics, and (3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5 deg were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3 deg mean absolute error (MAE) was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over five repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform for future laboratory studies to investigate shoulder biomechanics and consider the impacts of variable input kinematics from populations of interest, as they can significantly impact study outputs and resultant conclusions.

Anterior Shoulder Instability Part I-Diagnosis, Nonoperative Management, and Bankart Repair-An International Consensus Statement

PURPOSE

The purpose of this study was to establish consensus statements via a modified Delphi process on the diagnosis, nonoperative management, and Bankart repair for anterior shoulder instability.

METHODS

A consensus process on the treatment using a modified Delphi technique was conducted, with 65 shoulder surgeons from 14 countries across 5 continents participating. Experts were assigned to one of 9 working groups defined by specific subtopics of interest within anterior shoulder instability.

RESULTS

The independent factors identified in the 2 statements that reached unanimous agreement in diagnosis and nonoperative management were age, gender, mechanism of injury, number of instability events, whether reduction was required, occupation, sport/position/level played, collision sport, glenoid or humeral bone-loss, and hyperlaxity. Of the 3 total statements reaching unanimous agreement in Bankart repair, additional factors included overhead sport participation, prior shoulder surgery, patient expectations, and ability to comply with postoperative rehabilitation. Additionally, there was unanimous agreement that complications are rare following Bankart repair and that recurrence rates can be diminished by a well-defined rehabilitation protocol, inferior anchor placement (5-8 mm apart), multiple small-anchor fixation points, treatment of concomitant pathologies, careful capsulolabral debridement/reattachment, and appropriate indications/assessment of risk factors.

CONCLUSION

Overall, 77% of statements reached unanimous or strong consensus. The statements that reached unanimous consensus were the aspects of patient history that should be evaluated in those with acute instability, the prognostic factors for nonoperative management, and Bankart repair. Furthermore, there was unanimous consensus on the steps to minimize complications for Bankart repair, and the placement of anchors 5-8 mm apart. Finally, there was no consensus on the optimal position for shoulder immobilization.

LEVEL OF EVIDENCE

Level V, expert opinion.

Mapping of the Inferior Glenohumeral Ligament for Suture Pullout Strength: A Biomechanical Analysis

Background

Suture pullout during rehabilitation may result in loss of tension in the inferior glenohumeral ligament (IGHL) and contribute to recurrent instability after capsular plication, performed with or without labral repair. To date, the suture pullout strength in the IGHL is not well-documented. This may contribute to recurrent instability.

Purpose/Hypothesis

A cadaveric biomechanical study was designed to investigate the suture pullout strength of sutures in the IGHL. We hypothesized that there would be no significant variability of suture pullout strength between specimens and zones. Additionally, we sought to determine the impact of early mobilization on sutures in the IGHL at time zero. We hypothesized that capsular plication sutures would fail under low load.

Study Design

Descriptive laboratory study.

Methods

Seven fresh-frozen cadaveric shoulders were dissected to isolate the IGHL complex, which was then divided into 18 zones. Sutures in these zones were attached to a linear actuator, and the resistance to suture pullout was recorded. A suture pullout strength map of the IGHL was constructed. These loads were used to calculate the load applied at the hand that would initiate suture pullout in the IGHL.

Results

Mean suture pullout strength for all specimens was 61.6 ± 26.1 N. The maximum load found to cause suture pullout through tissue was found to be low, regardless of zone of the IGHL. Calculations suggest that an external rotation force applied to the hand of only 9.6 N may be sufficient to tear capsular sutures at time zero.

Conclusion

This study did not provide clear evidence of desirable locations for fixation in the IGHL. However, given the low magnitude of failure loads, the results suggest the timetable for initiation of range-of-motion exercises should be reconsidered to prevent suture pullout through the IGHL.

Clinical Relevance

From this biomechanical study, the magnitude of force required to cause suture pullout through the IGHL is met or surpassed by normal postoperative early range-of-motion protocols.

Editorial Commentary: More Is Better? The 6-O'clock Anchor in Instability Surgery

Placing an anchor at the 6-o'clock position on the glenoid when performing an arthroscopic Bankart repair has been suggested by multiple authors as a potential key step in improving the outcomes of arthroscopic repair. Placement of a 6-o'clock anchor increases the peak resistance force to displacement over a traditional 3-anchor repair. Determining what technique issues are relevant remains problematic, and the ultimate preferred technique remains elusive.