Purpose

With increasing recognition of posterior shoulder instability, there is greater need for an accurate posterior portal to perform labral repair and allograft reconstruction. Therefore, we sought to present a novel technique for a patient-specific imaging-guided working portal to compare to standard approaches.

Methods

We retrospectively analyzed arthroscopic labral repairs with preoperative advanced imaging at a single institution between 2010-2020. We randomly selected 30 each of isolated anterior or posterior labral repairs. MRI measurements included posterior acromial height and acromial tilt. A novel imaging-guided posterior portal was measured along the glenoid equator with distances to the coracoid and posterolateral acromion measured. Then, unguided portal positions of 2 and 4cm from the posterolateral acromion were made and the distances and angles between the guided/unguided positions were measured. ANOVA analysis and linear regression models were used to evaluate differences.

Results

Sixty shoulders were included for analysis (30 anterior, 30 posterior). Instability patterns differed by acromial tilt (p=0.037). The guided portal distance to the acromion differed between instability types (p<0.001).

The 4cm unguided portal deviated less from the guided portal intersection with the glenoid in both instability patterns (p<0.0001) but did not differ between groups (p=0.990). However, the 4cm unguided portal angle deviated more compared to the guided portal in both instability patterns (p<0.0001).

Using the unguided 2 and 4cm portals aiming towards the coracoid, there was more than 5mm deviation from the guided portal at the glenoid and would require replacement of the portal 89.8% (86.2% anterior, 93.0% posterior) and 45.5% (37% anterior, 53.6% posterior) of the time, respectively.

Conclusion

Variation exists between instability patterns for accurate posterior working portal placement for arthroscopic shoulder labral repair. Traditional landmarks may be inadequate as currently utilized.