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    Options for Dealing with Posterior Glenoid Bone Loss in Anatomic TSA

    The authors review multiple strategies available to reduce the negative effects of glenohumeral retroversion and/or posterior subluxation in total shoulder arthroplasty, including eccentric reaming, bone grafting, and augmented glenoid components.

    Authors

    Michael Priddy, MD; Brad S. Schoch, MD; Thomas W. Wright, MD; and Joseph J. King, MD

    Introduction

    Total shoulder arthroplasty (TSA) has been shown to provide lasting pain relief and good long-term implant survival in many patients. Using first-generation total shoulder implants, Torchia et al [1,2] demonstrated a 93% survival rate at 10 years and an 87% survival rate at 15 years. Similarly, 83% of patients had significant pain relief after TSA.

    However, certain patient populations may not do as well with a standard anatomic TSA. Iannotti et al [3] showed that patients with preoperative posterior subluxation had lower ASES scores, more pain, and less external rotation than patients without subluxation. Glenoid version affects not only posterior subluxation and posterior loading, [4] but also glenoid component loosening. [5] Fifteen degrees of retroversion has been shown to decrease contact area, increase contact pressure, and decrease inferior and posterior glenohumeral forces in TSA. [6]

    Multiple strategies can be used to reduce the negative effects of glenohumeral retroversion and/or posterior subluxation in TSA. For example, eccentric reaming, bone grafting, and augmented glenoid components are intended to allow placement of an anatomic total shoulder implant in patients with significant glenoid wear. In more severe cases of glenoid wear, the surgeon can consider 2-stage TSA with glenoid bone grafting, [7] the “ream and run” procedure, [8] or the use of a reverse total shoulder arthroplasty with a glenoid baseplate, [9] depending on the clinical picture and degree of bone loss.

    This article describes eccentric reaming, bone grafting, and augmented glenoid components in patients with glenoid bone loss who are undergoing primary anatomic TSA. Our article on managing glenoid bone loss in reverse TSA patients can be found here.

    Eccentric Glenoid Reaming

    Eccentric reaming consists of attempting to ream down the “high-side” of the glenoid to change the glenoid version to a more anatomic version (Figure 1). This improves the version of the glenoid without requiring any additional techniques, and it is recommended by many authors for the correction of small defects (generally less than 15°). More extensive eccentric reaming can lead to:

    • Increased risk of peripheral peg perforation [10]
    • Medialization of the center of rotation [11]
    • Shortening of the rotator cuff muscle-tendon units [12]
    • Loss of subchondral bone, which may cause component migration [13]

    Iannotti et al [14] also showed that correction of large deformities by eccentric reaming is difficult even in the hands of experienced surgeons: 3 of 7 cadaveric specimens with more than 10° of retroversion continued to have more than 10° of retroversion after eccentric reaming.

    Figure 1. Schematic showing a Walsh B2 glenoid and the difference with off-axis reaming and eccentric reaming.

    Technique: Eccentric Reaming

    • The glenoid is prepared by removing the labrum and any remaining articular cartilage.
    • A guidewire is placed down the centerline of the scapula, feeling the wire barely protrude through at Matsen’s point to ensure adequate placement. A second guidewire can be used to gauge the length of the wire in the vault and confirm adequate depth.
    • Reaming is then performed using cannulated reamers along this axis. We prefer no more than 5° of residual glenoid retroversion after reaming.
    • The anterior aspect of the glenoid is lightly reamed, taking care to avoid complete loss of the subchondral bone under the glenoid component.
    • The glenoid component holes can be drilled once the glenoid is properly shaped to accept an implant.

    Glenoid Autograft Bone Grafting

    Neer and Morrison [15] described results of autograft glenoid bone grafting in 19 patients undergoing TSA. At more than 2 years of follow-up, they reported no loosening, with 16 patients having excellent results, 1 having a satisfactory result, and 2 having unsatisfactory results. [15]

    Since then, the literature has reported mixed results for bone grafting in primary TSA. Hill et al [16] described 17 patients with an average of 70 months of follow-up. Only 3 patients had excellent results, 6 had satisfactory results, and 8 had unsatisfactory results (3 had graft complications including non-union, dissolution, and shifting). Hill et all had used Neer’s technique, [15] incorporating humeral head in 15 patients and autograft iliac crest in 2 patients. [16]

    Klika et al [17] described a significant loosening rate – 10 of 25 shoulder – at an average of 7.6 years of follow-up, with 2 patients undergoing revision for aseptic loosening. They had used autograft humeral head grafting to fill the glenoid defect. [17] Walch et al [18] recommended against using bone graft to treat patients with a biconcave glenoid. They used a structural posterior bone graft from the humeral head when they could not ream the anterior glenoid to a retroversion of less than 10° while maintaining a vault length of at least 17 mm. Of the 7 patients who underwent bone grafting, 2 had satisfactory results, 2 experienced graft collapse and component migration, and 3 returned with a posterior dislocation. [18]

    Nicholson et al [19] reported the results of 34 patients with a minimum 2-year follow-up (mean 4.0 years) after autograft humeral head grafting during primary TSA. They found improvement in retroversion from -28° ± 4° preoperatively to -4° ± 2° postoperatively and decreased posterior subluxation. They did not revise any patients for graft collapse or component migration.

    They had used a patented, commercially available drill guide and cannulated reaming system (Zimmer Biomet; Warsaw, Indiana) to place a pin down the center of the vault. The glenoid face was then reamed gently to create a curved surface. The resected humeral head was matched to the glenoid defect by measuring the length and width of the glenoid defect. The cortical surfaces were placed flush to minimize dead space. Prior to fixation, both articulating cortical surfaces were lightly “scarified” with a burr. The head segment was then fixed with a Kirschner wire, followed by 2 3.5-mm screws placed perpendicular to the graft surface and into the native glenoid. The screw heads were tightened below the cancellous surface to avoid screw head prominence. [19]

    Technique: Autograft Bone Grafting

    • After the humeral head is resected, the area that articulated with the glenoid defect is identified and selected. The graft is cut about 1-cm thick to allow it to more than fill the defect.
    • Humeral head autograft is then placed on the glenoid and secured with 2 Kirschner wires. A central guidewire is placed in the standard fashion in the glenoid.
    • The glenoid is then reamed until it is flat. Care is taken to leave the bone graft in position.
    • Once the reaming is finished, the bone graft is affixed to the glenoid with 2 cortical screws.
    • The implant is then inserted in standard fashion. Care is taken with the position of the screws so that a pegged glenoid can be used. If this is not possible, a keeled or in-line pegged component can be inserted instead.

    Glenoid Component Augmentation

    Glenoid augmentation has been performed to allow a non-biologic material to restore more normal glenoid positioning and muscle function. Rice et al [20] found that the use of an older augmented glenoid design demonstrated poor satisfaction in 13 patients. Cil et al [21] later reported on 38 patients from the same institution who were treated for bone loss with 3 non-standard glenoid components. They found 10-year survival rates of 73% for angled keel glenoids, 69% for extra-thick glenoids, and 31% for posterior-augmented metal-backed glenoids, leading them to recommend against the use of these implants. [21]

    Since then, new implants have become available, including full-wedge (Exactech; Gainesville, Florida), hemi-wedge (Wright Medical Group; Memphis, Tennessee), and step-cut (Depuy Synthes; Raynham, Massachusetts) designs (Figure 2). Biomechanical studies have reported on theoretical advantages of each. The full-wedge design theoretically removes less bone [22, 23] and generates lower stresses at the glenoid interface [22] compared with the step-cut design. However, the lift-off resistance during cyclic loading has been reported to be better with step-cut designs. [24] There are no biomechanical studies comparing the hemi-wedge design with either of the other 2 designs.

       

    Figure 2. Full-wedge 8° augmented glenoid (left), hemi-wedge augmented glenoid (center), and step-cut augmented glenoid (right).

    Favorito et al [25] reported on 22 patients who underwent glenoid augmentation with a step-cut design at a mean follow-up of 36 months. They had a 9.1% complication rate: 2 patients with postoperative instability that required further surgery. Similarly, Stephens et al [26] reported on 22 patients with a minimum 2-year follow-up, finding some radiolucent lines around the glenoid components but no clinical failures. Short-term results are not yet published for either of the 2 commercially available wedge designs.

    Technique: Augmented Glenoid (Full-Wedge Component)

    • Retroversion of the glenoid is determined preoperatively via CT imaging using the technique reported by Friedman et al. [2]
    • The 8° glenoid wedge is planned. Off-axis reaming is also planned if necessary to correct the glenoid version, including the addition of the augment to within 5 of neutral version (see Figure 1, above).
    • Intraoperatively, the posterior augmented guide is placed on the glenoid in the standard position. The guide has 2 holes: 1 for the reaming axis and 1 for the central guidewire placement.
    • The reaming axis pin is placed first and is placed with increased anteversion if more eccentric reaming is necessary (Figure 3).
    • Reaming is then performed on the reaming axis pin, with the goal of minimal bone removal. With the computer navigation system used by the authors (ExactechGPS, Guided Personalized Surgery), reaming on the reaming axis can also be done without the pin.
    • The guide is then placed on the reaming axis pin. It should lay flat against the glenoid at this point, without rocking.
    • The central axis pin is then placed and the reaming axis pin is removed. The central hole is drilled, followed by the peripheral pegs.
    • The component is placed in the standard fashion. As always, soft tissue balancing is checked. The rotator interval is partially tightened to limit posterior translation in cases with more than 50% translation of the humeral head posteriorly.
    • Final radiographs of the full-wedge design show increased space where the posterior augmented polyethylene is thicker (Figure 4).

    Figure 3. Guide showing the difference between the center-line pin and the 8° off-axis pin for reaming.

     

     

    Figure 4. Preoperative Grashey (top left) and axillary lateral (top right) radiographs showing significant glenoid wear in a Walch B2 pattern. Postoperative Grashey (bottom left) and axillary lateral (bottom right) radiographs showing a posterior augmented cemented glenoid component (all-polyethylene cemented). This is currently available in an augmented caged glenoid.

    The hemi-wedge design implant has an offset reamer that is used to ream down the posterior glenoid to the desired angle (Figure 5). This allows for adequate backside contact of the glenoid component on the native glenoid.

    Figure 5. Offset reamer used for the hemi-wedge design. Note the second hole drilled anteriorly in the glenoid, which is needed to stabilize the reamer and to allow for reaming of the posterior half of the glenoid.

    Glenoid Bone Grafting and Potential Delayed Glenoid Component Reimplantation

    Bone grafting of the glenoid with placement of a hemiarthroplasty can be performed in patients with glenoid bone stock that is insufficient for either an acute bone graft procedure with glenoid implantation or glenoid augmentation. This is not a technique we routinely use or recommend in primary TSA patients; it is more commonly used in revision shoulder procedures.

    Technique: 2-Stage Glenoid Bone Grafting and Reimplantation

    • A standard deltopectoral approach to the proximal humerus is performed.
    • The humeral head is resected in the standard fashion and kept as a potential source for bone graft.
    • The glenoid is exposed and the type of defect is classified.
    • Impaction grafting is recommended for cavitary defects, which can be filled with corticocancellous autograft, humeral or femoral head allograft, iliac crest autograft, or a combination of these grafts.
    • Iliac crest autograft and humeral/ femoral head allograft are preferred for rebuilding the glenoid in larger, uncontained defects. These should be affixed with at least 2 screws placed out of the way of future glenoid pegs and slightly buried, if possible.
    • Humeral hemiarthroplasty is then performed.
    • After at least 6 months and radiographic evidence of bony incorporation of the graft, revision to TSA can be attempted (screws can be removed if possible).
    • CT scan should be considered to confirm graft healing to the native glenoid prior to revision with glenoid component placement.

    Author Recommendations

    We routinely perform glenoid reaming alone in patients with minimal glenoid defects. The goal is to place an implant with less than 5° to 8° of retroversion with minimal reaming. Due to concerns for subsidence, we do not want to ream to the point at which we have reamed away the subchondral bone, leaving us with only cancellous bone at the implant interface.

    We do not routinely perform either autograft bone grafting of the humeral head as a single-stage or a 2-stage procedure. Although this is an option, the reported high failure rate has led us to use other techniques. In patient with a deformity, we will use an 8° posterior augment and reaming to decrease the retroversion of the glenoid. We aim for less than 10° of residual retroversion of the glenoid component, frequently using intraoperative navigation to help achieve this goal. Once again, we do not ream to the point at which we have reamed away the subchondral bone.

    We recommend performing a reverse TSA if there is too much residual deformity to correct the retroversion to less than 10° with reaming and augmentation, or if there is near complete posterior subluxation of the native shoulder.

    Conclusion

    Many methods are available to deal with glenoid bone loss and excessive retroversion in patients undergoing primary anatomic TSA. No technique is currently without limitations. Eccentric reaming is limited to smaller defects. While bone grafting and augmentation can be used to address these defects, long-term data in many studies of bone grafting are concerning, and data have not yet been published for augmented devices.

    Author Information

    Michael Priddy, MD; Brad S. Schoch, MD; Thomas W. Wright, MD; and Joseph J. King, MD, are from the Department of Orthopaedics and Rehabilitation at the University of Florida in Gainesville.

    Disclosures

    Dr. Priddy and Dr. King have no disclosures relevant to this article. Dr. Wright has disclosed that he receives royalties from and is a consultant for Exactech. Dr. Schoch has disclosed that he is a paid speaker for DJO Surgical.

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