Glenoid deformity in shoulder arthritis presents significant challenges for surgeons performing total shoulder arthroplasty (TSA). The etiology of glenoid deformity can be acquired or, less commonly, congenital in nature. Acquired glenoid deformity is commonly present in arthritic shoulders in the form of glenoid wear or glenoid erosion. Other less common causes of acquired glenoid deformity include shoulder trauma (glenoid fracture), infection, or prior shoulder surgery (Latarjet or Bristow procedure). In this chapter, we will focus on treatment of glenoid deformity in the setting of primary reverse total shoulder arthroplasty (RTSA). The treatment of glenoid bone loss in revision RTSA is covered in Chapter 43
The location of glenoid wear in glenohumeral arthritis is dictated by the underlying pathology. Posterior glenoid wear is commonly encountered in primary glenohumeral arthritis; superior glenoid wear is encountered in the setting of rotator cuff tear arthropathy; anterior glenoid wear is encountered in association with anterior instability, and concentric glenoid wear is encountered in inflammatory arthritis. However, these specific patterns are not exclusive to the aforementioned individual pathologies, and combination patterns (posterior-superior) of glenoid wear are often present.
Pathologic glenoid wear, if not corrected during RTSA, can result in implant malposition, which has the potential to affect stability, function, and implant longevity. Excessive superior tilt of the glenosphere predisposes to dislocation, subacromial impingement, scapular notching, and excessive shear forces resulting in baseplate loosening and failure. Excessive medialization of the glenoid component can lead to decreased rotator cuff muscle tension, inferior-medial impingement with scapular notching, and polyethylene wear; abnormal version of the glenosphere can lead to decreased internal or external rotation.1
There is considerable variation in the physiologic version and inclination of the native, nonarthritic glenoid. Therefore, correction of the morphometric glenoid anatomy to neutral in TSA may not necessarily be patient specific in every case. The end point of correction of glenoid wear during shoulder arthroplasty is unclear at this time. Placing the glenoid component within 10° of Freidman axis for correction of posterior glenoid wear and within 10° of neutral tilt is considered acceptable in RTSA although further research with long-term data is required to confirm that these end points for correction of glenoid wear are truly acceptable. RTSA is a constrained arthroplasty design, and consequently, the acceptable limits for correction of glenoid wear and glenoid component placement are less stringent compared to anatomic total shoulder arthroplasty (ATSA).
There are several recognized techniques that can be used to correct glenoid wear during RTSA. These techniques include eccentric glenoid reaming, glenoid bone grafting, use of augmented baseplates, and combinations of these aforementioned techniques. However, the indications and end point of deformity correction varies among surgeons. In this chapter, we will present our strategy for the evaluation and treatment of glenoid wear when performing RTSA.
We routinely use a preoperative computer-planning tool for RTSA. Different preoperative planning software programs that utilize manufacturer-specific implant simulation are commercially available in the United States (TABLE 25.1)
. These preoperative planning tools are typically based on 3D CT imaging of the glenohumeral joint and require thin cuts, which are typically 0.6 mm or less with slice increments of 0.6 mm or less of the entire scapula. The raw CT images are transferred to a computer application, which generates a 3D image of the glenoid and is uploaded into the preoperative planning software for planning. The planning software provides automated measurements of glenoid version and inclination using the scapular plane method, and if the surgeon disagrees with the measurements, there is an option to obtain manual measurements.
We preoperatively plan all of our shoulder arthroplasties with planning software irrespective of our decision to use computer navigation, PSI guides, or standard instrumentation. The software allows us to determine
the extent of glenoid wear in a 3D plane, size the implants, and choose the final position of the implant with respect to the glenoid axis. The preoperative planning software, by default, places the selected glenoid implant neutral to Freidman axis. The inclination and version of the selected glenoid implant is then changed to match the patient’s anatomy using computer controls on a 3D and 2D CT image interface. The preoperative planning software provides real-time feedback during manipulation of the glenoid component with respect to changes in the version and inclination. During simulation of the surgical plan, we evaluate for critical findings like peg perforation of the glenoid (in ATSA) or wall/vault perforation by the central peg or post (ATSA and RTSA) and adjust the implant position and/or implant size accordingly. The extent of reaming and implant stability is determined virtually using the assessment of backside contact of the implant with the glenoid. The size of the augmented components and their position on the glenoid can be determined preoperatively, and the degree of correction achieved can be visualized in real time. The preoperative plan, once finalized by the surgeon, is transferred to the computer station to be used intraoperatively if computer navigation is being utilized.
FIGURE 25.1 Walch classification of glenoid deformity. (Redrawn with permission from Bercik, Michael J, et al. A modification to the Walch classification of the glenoid in primary glenohumeral osteoarthritis using three-dimensional imaging. J Shoulder Elbow Surg. 2016;25(10):1601-1606.)
CLASSIFICATION OF GLENOID WEAR
Classification of glenoid wear patterns in arthritis is presented in detail in Chapters 5
. We use the modified Walch classification for documenting glenoid wear in the axial plane (FIGURE 25.1)
, and we classify superior glenoid wear using the classification by Favard et al (FIGURE 25.2)
More recently, we have found the use of classification systems to be less helpful as a result of the development of preoperative planning software, which provides the opportunity to both assess the degree of deformity and determine the necessary correction. However, classifying glenoid wear is important for understanding the impact of glenoid wear on outcomes of reconstructive techniques and for education and research purposes.