Total shoulder arthroplasty does not correct the orientation of the eroded glenoid

Abstract

Background and purpose: Alignment of the glenoid component with the scapula during total shoulder arthroplasty (TSA) is challenging due to glenoid erosion and lack of both bone stock and guiding landmarks. We determined the extent to which the implant position is governed by the preoperative erosion of the glenoid. Also, we investigated whether excessive erosion of the glenoid is associated with perforation of the glenoid vault.

Methods: We used preoperative and postoperative CT scans of 29 TSAs to assess version, inclination, rotation, and offset of the glenoid relative to the scapula plane. The position of the implant keel within the glenoid vault was classified into three types: centrally positioned, component touching vault cortex, and perforation of the cortex.

Results: Preoperative glenoid erosion was statistically significantly linked to the postoperative placement of the implant regarding all position parameters. Retroversion of the eroded glenoid was on average 10° (SD10) and retroversion of the implant after surgery was 7° (SD11). The implant keel was centered within the vault in 7 of 29 patients and the glenoid vault was perforated in 5 patients. Anterior cortex perforation was most frequent and was associated with severe preoperative posterior erosion, causing implant retroversion.

Interpretation: The position of the glenoid component reflected the preoperative erosion and "correction" was not a characteristic of the reconstructive surgery. Severe erosion appears to be linked to vault perforation. If malalignment and perforation are associated with loosening, our results suggest reorientation of the implant relative to the eroded surface.

Figure 1.

On the left part of the figure is shown the appearance of the staple marker in the Neer II prosthesis on two different views of a reconstructed scapula (a). The middle part of the figure shows the reference points outlining marker and scapula (b). On the right part of the figure is shown the reconstructed glenoid and the straight line shape of the metallic marker of the Ulys Ceraver prosthesis with reference points indicated on the marker as well as on the subchondral bone of the glenoid rim (c). StS: staple-shaped marker in the Neer II prosthesis; SLS: straight line marker in the Ulys prosthesis; LBL: lateral border line of the scapula; SFL: supraspinous fossa line; OEP: rim of the subchondral bone of the rim.

Figure 2.

Glenoid and scapula reference points imported into 3D- Reshaper software. Glenoid-related descriptors are marked in red and scapula blade descriptors are marked in blue. On the left is shown the postoperative glenoid implant staple shape marker relative to the scapula plane (SbP). On the right is shown the preoperative eroded glenoid outer edge relative to the scapula plane. GP: glenoid plane; AG: glenoid supero-inferior axis; CG: central point of the glenoid; pCG: orthogonal projection of the central point of the glenoid on the scapula blade plane; Psj: intersecting line between scapula blade plane and glenoid plane.

Figure 3.

The four position parameters (version, inclination, rotation, and antero-posterior offset distance) are illustrated graphically. Calculated glenoid orientation is shown in red and scapula blade orientation is shown in blue.

Figure 4.

Axial CT views passing through the middle of the glenoid of 3 implants. On the left is shown the implant keel centrally positioned into the glenoid vault (a). In the middle is shown contact between the glenoid keel and the anterior glenoid wall (b). On the right is shown the glenoid keel perforating the anterior glenoid wall (c).

Figure 5.

Preoperative axial view of the posteriorly eroded glenoid (left) and postoperative axial view of the same specimen with an implant (right). The orientation of the glenoid vault is indicated by the dotted line. The orientation of the eroded glenoid is indicated by the black line on the left part of the figure. The orientation of the glenoid implant is indicated by the white line on the right part part of the figure. The white arrow indicates anterior perforation of the glenoid vault due to the retroverted orientation of the implant in this preoperatively eroded glenoid.