Glenohumeral Arthritis: Total Shoulder Arthroplasty With Augmented Glenoid

Joseph P. Iannotti

Eric T. Ricchetti

INTRODUCTION

The presence of acquired posterior glenoid bone loss in advanced glenohumeral osteoarthritis (OA) results in increased retroversion described as a biconcave (B2) or monocave (B3) glenoid.¹^, ² ^and ³ This presents a particularly difficult problem when treating glenohumeral OA with anatomic total shoulder arthroplasty (TSA). Treatment goals of advanced glenohumeral OA with asymmetric bone loss using anatomic TSA include (1) correction of glenoid bony deformity to restore the patient’s premorbid version, inclination, and location of the joint line; (2) balancing of the soft tissues; and (3) long-term centering of the humeral head. This chapter describes the use of the augmented glenoid component and its ability to restore native glenohumeral anatomy (version, inclination, and joint line) in anatomic TSA for these types of acquired deformities (B2 and B3). This chapter does not address surgical management of A1, A2, B1, C, or D glenoid deformity (Figure 48-1).

FIGURE 48-1 Walch classification includes the A and B glenoid pathology in osteoarthritis.

The A2 glenoid has central glenoid concentric wear and the glenoid version and inclination remains similar to the premorbid glenoid. B1 glenoid has significant humeral head (HH) posterior translation without significant posterior glenoid bone loss. B2 glenoid pathology has HH translation and asymmetric posterior glenoid erosion resulting in a biconcave glenoid. The biconcave glenoid is characterized by a remaining paleoglenoid of variable AP length, typically 30% or more of the premorbid AP length of the glenoid. The paleoglenoid in the B2 glenoid represents a good representation of the premorbid location of the joint line, version, and inclination when excluding the osteophyte. The B3 glenoid is a progression of the B2 glenoid. There is more central glenoid bone loss resulting in more medialization of the join line, variable recentering of the HH, and progressive loss of the paleoglenoid. In the classic B3 morphology the glenoid is single concavity (monocave) retroverted glenoid pathoanatomy.

INDICATIONS

The correction of pathologic version and posterior glenoid bone loss in anatomic TSA has been shown to improve outcomes by balancing forces across the shoulder joint and recreating an anatomic alignment of the humeral head and glenoid. This concept and practice results in converting an unbalanced preoperative B2 or B3 glenohumeral articulation to an A1 postoperative reconstructed glenohumeral prosthetic joint. Correction of glenoid bone loss resulting in increased glenoid retroversion has been proposed using a variety of augmented polyethylene glenoid designs. These designs vary in their shape and degree of augmentation (Figure 48-2).

FIGURE 48-2 Representative examples of augmented glenoid components of anatomic TSA (noninclusive).

Enovis standard and symmetric, half- and full-wedge augmented glenoid components, DePuy Stepped augmented component.

Biomechanical, computational, and now clinical data have demonstrated the benefits of the use of augmented polyethylene glenoid components when addressing significant posterior glenoid wear and deformity. These studies have shown improved clinical function and outcome scores with low rates of radiolucency and complications and the ability to restore native glenoid anatomy (version, joint line, and humeral head centering).⁴^, ⁵^, ⁶^, ⁷^, ⁸^, ⁹^, ¹⁰^, ¹¹^, ¹²^, ¹³^, ¹⁴^, ¹⁵^, ¹⁶^, ¹⁷^, ¹⁸^, ¹⁹^, ²⁰^, ²¹^, ²² ^and ²³

The primary indication for an augmented glenoid component is glenohumeral OA with an intact rotator cuff and posterior glenoid bone loss not correctable to within 5 degrees of the patient’s premorbid version and inclination, and to within 3 millimeters of premorbid joint line, with a standard component. Premorbid version and inclination vary between individuals; therefore, there is not a single version or inclination for all patients. Reconstructive goals should be individualized based upon use of three-dimensional (3D) imaging that can define premorbid bony anatomy. Use of a standard glenoid to treat asymmetric glenoid bone loss where these criteria cannot be met has shown a high revision rate (16%) of failure at an average of 77 months’ (14-180 months) follow-up.²⁴

Determining the indications for use of an augmented glenoid component is through the use of preoperative 3D planning software using a thin-cut computed tomography (CT) scan (1 cm or less slice thickness). The software should define the patient-specific premorbid bony glenoid anatomy to define which component and its location best achieves restoration of premorbid anatomy.

Alternatives to use of an augmented glenoid component for acquired moderate to severe posterior glenoid bone loss (moderate to severe B2 or B3 glenoid), including reaming the high side in cases to match the native version or to an arbitrary “normal” version, can cause significant joint line medialization with increased risk of peg perforation, loss of the stronger cortical bone, and decreased tensioning of the soft tissues. Alternatively, reaming the glenoid in its pathologic plane or partial correction of pathologic version will result in excessive retroversion of the glenoid component with further medialization of the joint line, which can lead to persistent or recurrent posterior subluxation of the humeral head resulting in increased rates of osteolysis and potential component loosening. This result has been defined when the component is placed in >15° of retroversion.²⁵^, ²⁶^, ²⁷^, ²⁸^, ²⁹^, ³⁰^, ³¹^, ³² ^and ³³ In contrast, use of bone graft with a standard glenoid component may result in correction of version and maintenance of joint line. However, this procedure is technically more difficult than use of an augmented component, is imprecise in correcting version and creating the premorbid joint line, and requires stability and incorporation of the bone graft to obtain long-term stability of the polyethylene component. A few level IV clinical studies have demonstrated good clinical success, but a high incidence of radiolucency and complications associated with graft preparation, fixation, and incorporation have been reported.³⁴^, ³⁵^, ³⁶ ^and ³⁷

CONTRAINDICATIONS

Contraindications to use of an augmented anatomic glenoid component include rotator cuff deficiency and very severe bone loss generally requiring more than 20° of correction to achieve patient-specific version, which typically results in the inability to achieve the aforementioned goals, including the ability to restore the premorbid joint line. This degree of bone loss is most commonly seen with a severe B3 glenoid. In cases of advanced bone loss or pathology when criteria cannot be met, reverse TSA with or without bone grafting or use of an augmented baseplate may be a more reliable option for implant stability and longevity.

PREOPERATIVE PLANNING: EVALUATION OF THE GLENOID PATHOLOGY

The Walch classification defines the shape of the acquired glenoid bone loss and the position of the humeral head (Figure 48-1). The classification does not rely on severity of the bone loss. Severity of glenoid bone loss is best measured quantitatively in 3D using a method that compares the pathology with the premorbid bony anatomy. Recent software technology has used statistical shape modeling techniques to estimate premorbid anatomy from the pathological anatomy.³⁸^, ³⁹ ^and ⁴⁰ Others have validated the use of the glenoid vault model as a reference defining the location of the premorbid joint line, the premorbid version, and premorbid inclination (Figure 48-3).⁴¹^, ⁴²^, ⁴³^, ⁴⁴ ^and ⁴⁵ Without defining the premorbid anatomy, patient-specific reconstructive goals for use of an augmented component are difficult to achieve. The surgeon can select an average version and inclination as reported in anatomic studies to be approximately −6.0 degrees of retroversion and +5.0 degrees of superior inclination.⁴²^,⁴³ When a classic B2 glenoid morphology is present and the paleoglenoid is approximately 50% of the native glenoid anteroposterior (AP) diameter, the paleoglenoid is also an adequate guide to define patient-specific version, inclination, and joint line position.

FIGURE 48-3 Case example of a patient with osteoarthritis with a classic B2 glenoid shown on CT imaging with three orthogonal 2D views taken perpendicular within the plane of the scapula. The pathologic retroversion is −30° (green line in relation to the white line), and inclination was 3.8° of superior tilt. The humeral head is translated posteriorly and is articulating with the neoglenoid. The vault model (orange in all panels) is used in the software to define the premorbid anatomy. In this method a 3D virtual model of the normal glenoid vault is virtually implanted into the pathologic 3D images of the scapula by aligning (red dotted lines) with the anterior surface of the vault model to the (A, C and D) anterior wall of the glenoid bone in the lower third of the glenoid. The curvature of the vault model is aligned on the coronal images (B and E) at the spinoglenoid notch. This determines the medial placement of the vault model. Rotational placement is defined by the curvature of the vault model to the curvature of the anterior glenoid near is distal end (C). This method assumes that in osteoarthritis the anterior wall is unaffected by the progressive glenoid bone pathology. It also excludes the use of this method with glenoid dysplasia. The premorbid location of the joint line, version, and inclination are defined by the orange vault model demonstrated the glenoid to be −6° of retroversion and 3° of inclination, which is closely aligned with the paleoglenoid. The total version correction of 24° and no correction needed of inclination.

Regardless of the method used, defining the premorbid anatomy for an individual patient allows the surgeon to preoperatively select the ideal implant and its placement to most closely reconstruct the patient’s premorbid version, inclination, and medial lateral location of the joint line.

In a similar way, reconstruction of the size, location, and version of the humeral head restores the normal humeral bony anatomy and the premorbid center of humeral rotation. The perfect sphere or circle fit concept⁴⁶^, ⁴⁷ ^and ⁴⁸ can be used to define anatomic sizing of the prosthetic humeral head relative to the anatomy for that patient (Figure 48-4). It is difficult to use an anatomic humeral head reconstruction and achieve a balance shoulder without correction of the glenoid bony anatomy. Alternatives to an anatomic humeral head reconstruction (larger head, eccentric head placement, changes in humeral version) are often used to compensate for not achieving the anatomic glenoid reconstruction.

FIGURE 48-4 A, AP radiograph of patient with osteoarthritis without significant bone deformity. The white circle represents the radius of curvature of the humeral head, and the anatomic neck (dotted blue line) represents the size of the humeral head articular surface, which represents the osteotomy location and the ideal size and location of the prosthetic humeral head. It should be noted that the center of rotation (COR) is 1 to 3 mm from the humeral osteotomy surface. The humerus does not have a significant lateral offset from either the center of the humeral canal or the COR. The joint line is defined by the location of the glenoid surface and can be defined as the perpendicular distance (thin red line) from the base of the coracoid (vertical black line). The lateral glenohumeral offset (native or prosthetic) is defined as the combined distance of the joint line and the size and location of the humeral head. The lateral glenohumeral offset (LGHO) defines the tension of the soft tissues (capsule, cuff, and deltoid). The soft tissue tension greatly influences passive and active range of motion and strength and stability. In anatomic TSA the LGHO is influenced by location of the joint line, component version, and inclination as well as the size and location of the prosthetic humeral head. The anatomic location of the humeral head is defined by three nonarticular landmarks defined by the three red circles. The landmarks are the medial insertion site of the supraspinatus, the lateral flare of the greater tuberosity, and the junction of the proximal medial calcar and the medial articular surface of the humeral head. The circle that fits these three landmarks defines the location and radius of curvature of the articular surface. These landmarks define the anatomic sizing and location of the prosthetic humeral head. B, Intraoperative and postoperative radiographs showing the nonarticular landmarks in the operating room to assess the location and size of the prosthetic humeral head trial. The postoperative radiographs demonstrate the same relationships for the humeral prosthetic. With balancing of the soft tissues-associated capsular releases, healing, and rehabilitation of the intact rotator cuff, it is expected that the clinical outcome will result in a stable shoulder with excellent mobility and acceptable longevity of the implant.

Use of an Augmented Anatomic Glenoid Component for an Anatomic Reconstruction

When planning an anatomic TSA, the recommendation for asymmetric glenoid bone loss is use of an asymmetric augmented glenoid component. The recommended goals are to restore to within 5° of the patient-specific premorbid glenoid version and to restore the premorbid joint line, with minimal
reaming of the anterior glenoid to preserve the remaining denser subcortical bone and to obtain full back side contact of the implant on bone (Figure 48-5). Matching the glenoid bony defect with an implant shape allows these goals to be more easily achieved.

FIGURE 48-5 A, Same patient as in Figure 48-2 with the surgical planning to manage the posterior bone loss. B, The implant is a 7-mm half wedge. This implant results in matching the shape of the pathology and removes the least amount of bone thereby minimizing reaming and preserving the better cortical bone to support the implant. This results in the center peg being centered near the tip of the vault model and the anterior glenoid wall. This surface of the implant closely follows the surface of the vault model thereby replicating the version, inclination, and location of the joint line of the premorbid joint line. C, The 7-mm full wedge is used. It replicates the same correction of joint line version and inclination. It does not replicate the shape of the defect as well as the half wedge resulting in more bone removal centrally and slight increases in medialization of the center peg indicated by the blue arrows.

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