Addressing Glenoid Deformity in Reverse Total Shoulder Arthroplasty

Michael A. Boin, MD

Mandeep Singh Virk, MD

INTRODUCTION

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.¹,²,³,⁴,⁵,⁶

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.

HOW DO I TREAT GLENOID DEFORMITY IN RTSA?

Imaging Studies

All patients undergoing RTSA obtain standard radiographs that include true anterior-posterior (AP; Grashey), axillary, and outlet (scapular Y) views. Superior glenoid wear and posterior or anterior glenoid wear patterns can be visualized on true AP and axillary views, respectively. We routinely obtain computed tomography (CT) with three-dimensional (3D) reconstruction on patients undergoing shoulder arthroplasty. This allows for accurate classification of glenoid wear patterns and is used for preoperative planning for guided shoulder arthroplasty (computer-assisted navigation [CAN] or with patient-specific instrumentation [PSI] guides). Three-dimensional computed tomography (3D CT) has been shown to be superior to two-dimensional computed tomography (2D CT) when critically evaluating the degree and location of glenoid deformity.⁷ As 3D CT is not affected by the scapular position in the CT scanner, it can reliably and accurately determine glenoid anatomy.

TABLE 25.1 Computer Navigation System and Patient-Specific Instrumentation Guides With Three-Dimensional Computer Planning Software Commonly Used in the United States

Proprietary Name	Company	Guidance Technology	Features
Blueprint	Wright Medical/Tornier	PSI (single use)	3D planning software with templating for glenoid and humerus in ATSA and RTSA available 3D bone model of glenoid provided PSI guide arms (4) rests on the glenoid edge
ExactechGPS	Exactech	Computer-assisted navigation surgery	3D planning software + Glenoid navigation for ATSA and RTSA Intraoperative modification of plan permissible Templating for augments available
Match Point System	DJO Surgical	PSI (single use)	3D planning software with templating for glenoid for ATSA and RTSA available 3D bone model of glenoid provided PSI guide arm rests on the coracoid
Signature Personalized Patient Care Glenoid System	Zimmer-Biomet	PSI (single use)	3D planning software with templating for glenoid for ATSA and RTSA available 3D bone model of glenoid provided Pin placement guide for glenoid for ATSA and RTSA present in a single PSI guide PSI guide rests directly on the glenoid face and anterior glenoid rim
TrueSight	Stryker	PSI (singe use)	3D planning software with templating for glenoid for RTSA available 3D bone model of glenoid provided PSI guide arm rests on the coracoid and can be pinned with a K-wire
TruMatch	DePuy Synthes	PSI (singe use)	3D planning software with templating for glenoid for ATSA and RTSA available 3D bone model of glenoid provided PSI guide arm rests on the coracoid and can be pinned with a K-wire
Virtual Implant Positioning (VIP) system	Arthrex	PSI (reusable)	3D planning software with templating for glenoid for ATSA and RTSA available 3D bone model of glenoid provided Reusable glenoid targeter with arms (4) resting on the glenoid face and anterior glenoid rim
Zimmer PSI Shoulder System	Zimmer	PSI (single use)	3D planning software with templating for glenoid for RTSA available 3D bone model of glenoid provided PSI guide rests directly on the glenoid face and anterior glenoid rim; separate guides are available for glenoid pin placement, depth of reaming, screw placement, and implant positioning on the glenoid
3D, three dimensional; ATSA, anatomic total shoulder arthroplasty; K-wire, Kirschner wire; PSI, patient-specific instrumentation; RTSA, reverse total shoulder arthroplasty.

PREOPERATIVE PLANNING

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 and 6. 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).⁸,⁹,¹⁰,¹¹ 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.

TREATMENT OPTIONS

Eccentric Reaming

Eccentric or “high side” reaming refers to reaming of the nondeformed/less deformed part of the glenoid (paleoglenoid and intermediate glenoid) to meet the level of the worn glenoid (neoglenoid). It is usually performed for mild degrees of glenoid wear which require less than 10° to 15° of correction in coronal or axial plane with removal of a limited amount of bone.⁵,¹²,¹³,¹⁴ Eccentric reaming is technically easy to perform and is preferred for correction of mild glenoid deformity. However, use of eccentric reaming to completely correct severe asymmetric glenoid wear can result in considerable iatrogenic bone loss, especially of the subchondral bone, which is critical to long-term stability of fixation of the glenoid component⁵,¹²,¹⁵ (FIGURE 25.3). Eccentric reaming for severe glenoid wear also results in excessive joint-line medialization, which results in loss of rotator cuff tension/function and predisposes to impingement and instability.⁴ Furthermore, excessive reaming and medialization results in downsizing of the glenoid face and loss of glenoid neck predisposing to scapular notching and baseplate overhang at the anterior or posterior margin.

Glenoid Bone Grafting

Glenoid bone grafting is an option in severe glenoid erosion where accepting the deformity or eccentric reaming alone is not a reasonable approach. The major benefit of glenoid bone grafting is the ability to restore bone stock. Another benefit is the ability to customize each graft to fit the unique bone-loss pattern in each specific patient. Glenoid bone grafting is better tolerated in RTSA than in ATSA because the graft fixation is more secure in RTSA. The graft is secured using the baseplate post and/or screws, which can also provide compression across the bone graft as well as secure fixation.¹¹,¹⁶,¹⁷,¹⁸,¹⁹

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