Summary

The effects of chondral and bony defects, bone block reconstructions, and concavity of the glenoid on glenohumeral stability were investigated using human cadaveric specimen in a robotic test setup.

Abstract

Purpose

Surgical treatment of shoulder instability with glenoid bone loss is currently based on a critical threshold of the defect size. However, recent simulation-based studies indicate that glenoid concavity is a crucial factor in glenohumeral stability. Although cartilage and labrum contribute to concavity depth, the biomechanical impact of a chondral defect, as present in a GLAD lesion, and its effect on clinical outcomes is controversial. Likewise, the replication of concavity to restore glenohumeral stability remains unaddressed in bone block reconstructions such as the Latarjet procedure. Nevertheless, this surgical procedure shows high success rates for large bony glenoid defects. The effects of chondral and bony defects, bone block reconstructions, and concavity of the glenoid on glenohumeral stability appear to be biomechanically under-researched. Therefore, these relationships were analyzed in three consecutive biomechanical studies on human cadaveric specimens.

Methods

The Stability Ratio (SR), a widely used biomechanical parameter for glenohumeral stability, was determined by anterior glenohumeral dislocations and detection of occurring forces in a robot-based experimental setup. Morphometric properties and stepwise created glenoid defects were captured using a 3D measuring arm. The influence of concavity and bony defect size on SR was investigated on 17 glenoids using linear models. The effect of a chondral lesion was recorded on 10 additional glenoids. Furthermore, the restoration of stability by bone block reconstruction was investigated with 14 glenoids. Here, the effect of mediolateral placement was examined using a 3D-printed model of the bone block. For group comparisons, repeated measures ANOVA with post hoc tests for multiple testing were used.

Results

The SR is significantly dependent on glenoid concavity, whereas the bony defect size has a low explanatory value. The linear model yielded a high correlation (R² = 0.98) and a low error (MSE = 4.22 %). The loss of stability due to bony defects is significantly dependent on initial concavity. The SR is also significantly affected by a chondral lesion (p = 0.002), decreasing the SR from 28.31 % to 23.6 %. A 20 % bony defect related to the glenoid width caused a further reduction to 20.39 % (p = 0.004). Bone block reconstruction significantly increased SR to 35.45 % (p<0.001). Lateral displacement of the bone block by 1 mm achieved a mean SR of 40.75 % (p<0.001). In contrast, no significant gain in SR was observed with a medial shift of the block by 1 mm (SR = 21.54 %, p = 0.75).

Conclusion

Assessment of glenoid concavity provides a more precise estimate of glenohumeral stability than the defect size alone. The significant effect of a chondral defect on stability indicates a high importance of chondral integrity, which should be addressed in surgical treatment. Moreover, restoration of glenohumeral stability is significantly dependent on the positioning of the bone block in Latarjet reconstructions. These findings reinforce the conjectures of recent studies regarding the importance of concavity and challenge the irrelevance of the GLAD lesion to shoulder instability. In addition, new aspects regarding the placement of bone block reconstruction were obtained.