Summary

A cadaveric imaging analysis of arthroscopic anterior shoulder stabilization anchor placement in the lateral decubitus and beach chair positions.

Abstract

Introduction

Glenohumeral instability is a common pathology. Despite advancements in surgical techniques, recurrent instability remains problematic, with rates reported from 10-30%. While numerous risk factors have been identified to predict recurrence, patient positioning has become of recent interest as positioning may influence anchor placement. Arthroscopic repair can be performed in the beach chair (BC) or lateral decubitus (LD) positions. Limited research exists evaluating these two positioning techniques, particularly from an anchor position and trajectory perspective.

Purpose

To perform a cadaveric imaging analysis of arthroscopic anterior shoulder stabilization in the lateral decubitus and beach chair positions.

Methods

Nine matched pairs of cadaveric shoulders (18 total shoulders) were used. Specimens underwent arthroscopic anterior inferior labral repair using 3 suture anchors placed in the 3:30, 4:30, and 5:30 positions. Repairs were performed by two expert surgeons each trained in a respective technique. Specimens then underwent CT scan analysis to evaluate anchor positions and trajectories. Target anchor location was determined using a 3D CT model of the glenoid, using ImageJ software, with the clock-face onlayed onto the glenoid. We set the 3 o’clock position at 0° for our reference, with the 3:30, 4:30 and 5:30 anchor positions set at -15°, -45°, and -75° respectively. One-tailed t-tests were used to compare anchor position deviation with target ideals.

Results

Inferior anchor (5:30) placement was found to be more accurate in the LD specimens while superior anchor (3:30) placement was found to be more accurate in the BC specimens. Specifically, the LD group did not demonstrate statistically significant deviation from the target ideal (-75°) for the 5:30 anchor. The true deviance for LD group from the 5:30 target angle is between -78.6° and -58.5° (p = 0.178). While the BC group did not demonstrate statistically significant deviation for the target ideal (-15°) for the 3:30 anchor. The true deviance from target angle is between -37.9° and 1.79° (p = 0.732). Both groups demonstrated adequate anchor trajectories.

Discussion

Controversy remains regarding optimal positioning for arthroscopic anterior shoulder stabilization. This cadaveric analysis demonstrates that the LD position may predict more accurate inferior anchor placement, which is widely felt to be the most important anchor in instability repair. However, all anchors remain of importance, and the accuracy of the BC position for the superior anchor suggests further insight and technical modification may be needed.

Conclusion

Both positioning techniques remain safe and efficacious. The LD position may offer improved inferior anchor placement. Further studies are needed to delineate advantages and disadvantages of one positioning technique relative to the other.