52.1 Goals of Procedure

Reverse shoulder arthroplasty (RSA) can provide excellent function to patients with a spectrum of glenohumeral pathology. Implant selection and positioning, however, remains a potential challenge of this nonanatomic prosthesis, especially in cases of significant glenoid bone loss. Patient-specific preoperative planning using 3D CT can allow for selection of optimal implant size and position in these cases of severe deformity, including allowing the surgeon to decide whether bone graft is needed. The use of patient-specific instrumentation (PSI) provides the surgeon with tools to transfer information from the preoperative planning software to the surgical site. The focus of this chapter will be on the techniques for utilization of patient-specific surgical planning software and instrumentation for surgical treatment using RSA in cases of severe glenoid bone loss.

52.2 Advantages

The glenosphere and baseplate may be defined by their superoinferior (SI), anteroposterior (AP), and mediolateral (ML) positions, or by their orientation relative to the glenoid and scapular planes (inclination, version, and rotation). The position and orientation of the glenosphere directly influence glenohumeral range of motion, stability, implant impingement, and scapular notching. Ideal glenosphere placement is in a location that maximizes impingement-free range of motion and stability while avoiding notching. Multiple studies have shown lateral offset and inferior placement of the glenosphere results in increased range of motion and reduced scapular notching, ^{1 – 5} while neutral or slight inferior tilt of the glenosphere limits the risk of decreased postoperative range of motion. ^{4 , 6 – 9} Despite our understanding of appropriate implant position, execution of correct glenosphere placement still remains a challenge. Verborgt et al showed standard instrumentation without advanced imaging resulted in an error range of 16 degrees for glenosphere inclination and 12 degrees for glenosphere version. ⁹ This finding supports the value of 3D templating to determine the optimal location of the implant. Virtual 3D implant templating has been shown to improve the accuracy of guide pin position and orientation when using standard instrumentation or PSI when compared to 2D imaging and use of standard instrumentation, both in a preclinical sawbones study and in a prospective clinical trial. ^{10 , 11} In the preclinical sawbones study, PSI provided additional accuracy for guide pin placement when used in combination with 3D preoperative planning, while in the clinical trial, PSI tools were not of further benefit in guide pin accuracy compared to 3D preoperative planning alone. ^{10 , 11}

52.3 Indications

The use of RSA has expanded since its inception. Indications for RSA include rotator cuff-tear arthropathy (CTA) with or without glenoid bone loss, ¹² massive irreparable rotator cuff tear, primary osteoarthritis (OA) with rotator cuff tear, primary OA with an intact rotator cuff but with severe glenoid bone loss, posttraumatic arthritis with glenoid bone loss with or without malunion, failed hemiarthroplasty with glenoid bone loss and/or rotator cuff deficiency, and failed total shoulder arthroplasty (TSA) with bone loss and/or rotator cuff deficiency. The use of RSA for primary OA with severe glenoid bone loss or deformity has increased in the recent years, due to the worse clinical outcomes that have been reported in this setting with anatomic TSA using a standard nonaugmented glenoid component. ¹³ Walch et al originally reported on glenoid bone loss in OA and defined three fundamental types of glenoid morphology patterns, type A, B, and C glenoids, ¹⁴ with worse clinical outcomes reported in B2 glenoids when using an anatomic TSA with a nonaugmented glenoid component. More recent studies of primary OA using 3D CT reconstructions have defined additional patterns of glenoid pathoanatomy that have modified the original Walch classification ^{15 , 16} and further differentiated more severe forms of glenoid bone loss and deformity that may not perform well with an anatomic TSA. Glenoid bone loss remains a significant challenge in all cases of shoulder arthroplasty and is not isolated to primary OA. Severe superior glenoid bone loss can occur in CTA, and large contained or uncontained defects are often present in revision TSA. Despite the presence of glenoid bone loss in these different clinical settings, RSA offers the potential for stable fixation into the glenoid because of the locking screw construct of the glenoid baseplate that can incorporate a bone graft into the glenoid construct. Patient-specific tools can increase the ability to place the glenoid component in optimal position to maximize patient function and implant fixation, and to determine the optimal location for bone graft placement, if needed.

52.4 Contraindication

There are several relative and absolute contraindications to RSA, which include severe deltoid deficiency or dysfunction that cannot be reconstructed, axillary nerve injury with severe loss of deltoid function, severe near total loss of glenoid bone that prevents placement of a stable glenoid baseplate even with bone grafting, active infection, neurological conditions such as syringomyelia, Charcot’s arthropathy, and patients with medical comorbidities that prevent surgical treatment. 3D preoperative planning tools can be particularly helpful to determine if the amount of glenoid bone loss is severe enough to not allow for stable fixation of the glenoid baseplate or if the risk of baseplate failure will be high due to inadequate glenoid bone stock.

52.5 Preoperative Planning/Positioning

52.5.2 Imaging and Patient-Specific Presurgical Planning

Standard 2D CT scans can be helpful to assess glenoid pathology, including glenoid retroversion and bone loss, but are limited by the ability to acquire imaging planes perpendicular to the plane of the scapula resulting in inaccurate measurements of glenoid version and inclination. However, 3D CT imaging and implant templating provide superior accuracy over 2D CT imaging for quantifying glenoid bone loss and guiding surgical decision-making. ^{17 , 18} 3D planning with a CT scan should include the entire scapula with 1 mm or thinner slices imported within a software application that allows for both 3D and reconstructed 2D imaging in planes orthogonal to the plane of the scapula. Modern 3D surgical planning applications also include methods to define glenoid bone loss, glenoid version, and inclination, and allow placement and manipulation of a desired implant system. The plane of the scapula can be defined by the inferior angle of the scapula, the center of the glenoid, and the scapula trigonum, which is defined as the confluence of the scapular body and spine at the medial border. The plane of the glenoid is defined by three points on the glenoid surface that generally represent the surface of the glenoid on coronal and axial 2D imaging ( Fig. 52.1a).

The glenoid vault model has been used as a research tool to define the premorbid anatomy from the pathologic state. Although the authors have used this tool for surgical planning, this tool is not commercially available in any Food and Drug Administration (FDA) approved software. The vault model is the 3D shape of the normal glenoid vault ^{10 , 19} and can be used with 3D planning to estimate native glenoid version, inclination, and joint line position in the setting of glenoid bone loss. ^{19 – 22} When the vault model is positioned correctly, its anterior and medial portion will closely follow the preserved 3D internal architecture of the patient’s anterior glenoid ( Fig. 52.1b). In pathologic shoulders, the lateral surface of the vault model represents the premorbid glenoid version, inclination, and joint line ( Fig. 52.1c, d). By this method, the bone loss associated with the patient’s pathology can be defined. The senior authors have used the vault model for surgical planning in the selection of implant type and its placement for both anatomic and reverse TSA, as well as to define the size and location of bone graft needed. After placement of the glenoid vault model and the desired implant, simulated bone reaming is defined as well as the location and orientation of the glenoid guide pin ( Fig. 52.1e). The location of the guide pin in relation to the glenoid bone landmarks can then be replicated at the time of surgery using standard or patient-specific instrumentation ( Fig. 52.1f). ^{23 , 24} Bone loss can be accurately visualized ( Fig. 52.1g, h) and may be addressed by bone grafting the glenoid or selecting an implant system with a lateralized glenosphere design. Patients with a pathologic or a short native scapular neck may be another indication to bone graft the glenoid or select an implant system with a lateralized glenosphere design to avoid bony impingement and scapular notching. Paisley et al suggested lateralizing the glenosphere in patients with a scapular neck length less than 9 mm measured on a true anteroposterior radiograph. ²⁴

Once the desired implant and its location are chosen with the 3D preoperative templating, the implant can be placed intraoperatively using PSI tools or standard instrumentation used in a patient-specific way based on the 3D preoperative plan.

Related posts:

45 Posterior Glenoid Wear in Total Shoulder Replacement: Eccentric Reaming 46 Posterior Glenoid Wear in Anatomic Total Shoulder Replacement: Augmented Polyethylene Glenoid Component 48 Convertible Components in Shoulder Arthroplasty 58 Stem Removal: Humeral Osteotomy 43 Stemless Anatomic Shoulder Replacement 57 Surgical Technique for Converting a Failed Total Shoulder Arthroplasty to Reverse Shoulder Arthroplasty

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