Type E2 glenoid bone loss orientation and management with augmented implants.

BACKGROUND

The purpose of this study was 2-fold: (1) to quantify type E2 bone loss orientation and its association with rotator cuff fatty infiltration and (2) to examine reverse baseplate designs used to manage type E2 glenoids.

METHODS

Computed tomography scans of 40 patients with type E2 glenoids were examined for pathoanatomic features and erosion orientation. The rotator cuff fatty infiltration grade was compared with the erosion orientation angle. To compare reconstructive options in light of the pathoanatomic findings, virtual implantation of 4 glenoid baseplate designs (standard, half wedge, full wedge, and patient-matched) was conducted to determine the volume of bone removal for seating and impingement-free range of motion.

RESULTS

The mean type E2 erosion orientation angle was 47° ± 17° from the 0° superoinferior glenoid axis, resulting in the average erosion being located in the posterosuperior quadrant directed toward the 10:30 clock-face position. The type E2 neoglenoid, on average, involved 67% of the total glenoid surface (total surface area, 946 ± 209 mm; neoglenoid surface area, 636 ± 247 mm). The patient-matched baseplate design resulted in significantly (P ≤ .01) less bone removal (200 ± 297 mm) for implantation, followed by the full-wedge design (1228 ± 753 mm), half-wedge design (1763 ± 969 mm), and standard (non-augmented) design (4009 ± 1210 mm). We noted a marked difference in erosion orientation toward a more superior direction as the subscapularis fatty infiltration grade increased from grade 3 to grade 4 (P < .001).

CONCLUSION

The average type E2 erosion orientation was directed toward the 10:30 clock-face position in the posterosuperior glenoid quadrant. This orientation resulted in the patient-matched glenoid augmentation requiring the least amount of bone removal for seating, followed by the full-wedge, half-wedge, and standard designs. Implant selection also substantially affected computationally derived range of motion in external rotation, flexion, extension, and adduction.