DOI: 10.1148/rg.271065076
RadioGraphics 2007;27:223-235
© RSNA, 2007
Radiologic Assessment of Reverse Shoulder Arthroplasty1
Catherine C. Roberts, MD,
Anders L. Ekelund, MD,
Kevin J. Renfree, MD,
Patrick T. Liu, MD and
Felix S. Chew, MD
1 From the Departments of Radiology (C.C.R., P.T.L.) and Orthopedics (K.J.R.), Mayo Clinic College of Medicine, 13400 E Shea Blvd, Scottsdale, AZ, 85259; the Department of Orthopedics, Capio St Goran Hospital, Stockholm, Sweden (A.L.E.); and the Department of Radiology, University of Washington, Seattle, Wash (F.S.C.). Recipient of a Cum Laude award for an education exhibit at the 2005 RSNA Annual Meeting. Received April 24, 2006; revision requested May 30 and received June 26; accepted June 28. A.L.E. is a consultant with DePuy; all remaining authors have no financial relationships to disclose.
Address correspondence to C.C.R. (e-mail: roberts.catherine{at}mayo.edu).
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Abstract
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The reverse shoulder prosthesis was approved for clinical use in the United States in March 2004. This new prosthesis reverses the normal ball-and-socket relationship of the shoulder joint. As a result of replacement of the glenoid component with a ball and of the humeral head with a socket, the center of rotation is moved distally and medially, allowing more control of shoulder motion by the deltoid muscle. This improved geometric configuration allows shoulder reconstruction in patients who have irreparable rotator cuff damage with secondary arthropathy, pain, and "pseudoparalysis" (ie, inability to lift the arm above the horizontal). Patients experience a significant improvement in range of motion and markedly decreased pain after undergoing reverse shoulder arthroplasty; however, the procedure is associated with a relatively high rate of complications, including dislocation, infection, loosening, malpositioning of the glenoid component or fixation screws, disassembly of the humeral component, periprosthetic fracture, and inferior glenoid impingement leading to scapular erosion. Therefore, it is important that the radiologist be familiar with the normal and abnormal imaging appearances of this new prosthesis.
© RSNA, 2007
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:- Discuss the mechanics of a reverse shoulder prosthesis and the indications for its use.
- Describe the normal radiologic appearance of this new prosthesis.
- Recognize complications related to failure of this prosthesis.
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Introduction
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In the mid-1980s, a new design for a shoulder prosthesis was envisioned by Professor Paul Grammont (1), and the prosthesis was released for use in Europe in the early 1990s. Professor Grammont published his initial experience with his newly redesigned Delta shoulder prosthesis in 1993 in an article coauthored by E. Baulot (2). This new prosthesis, also called the reverse shoulder prosthesis or Grammont prosthesis, was developed to help patients with irreparable rotator cuff tears. The prosthesis reverses normal shoulder anatomy (Fig 1, left) by replacing the humeral head with a cup and the scapular glenoid fossa with a ball. Previously, all shoulder arthroplasties reproduced the normal anatomy (Fig 1, right). This new reversed design allows more control of shoulder motion by the deltoid muscle in rotator cuff–deficient patients. In this article, we review the different types of reverse shoulder prostheses currently available for use in the United States in terms of their components and biomechanical features. In addition, we discuss the indications for the use of this new prosthesis as well as the preoperative evaluation of affected patients and the surgical techniques used for reverse shoulder arthroplasty. We also discuss and illustrate the normal radiologic appearance of a reverse shoulder prosthesis, the typical clinical course of patients who undergo reverse shoulder arthroplasty, and some potential complications of this procedure.
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Figure 1. Drawings illustrate normal reverse shoulder arthroplasty (left) and standard total shoulder arthroplasty (right). (Reprinted with permission from the Mayo Foundation for Education and Research, Rochester, Minn.)
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Prosthesis Types and Components
At present, three reverse shoulder prosthesis designs have been approved by the U.S. Food and Drug Administration (FDA) for use in the United States: the Delta CTA Reverse Shoulder System (DePuy Orthopaedics, Warsaw, Ind) (Fig 2); the Reverse Shoulder Prosthesis (Encore Medical, Austin, Tex) (Fig 3); and the Aequalis Reversed Shoulder Prosthesis (Tornier, Stafford, Tex) (Fig 4). The DePuy and Encore prostheses were approved by the FDA for clinical use in the United States in March 2004 and the Tornier prosthesis in May 2004.
Reverse shoulder arthroplasty makes use of a semiconstrained prosthesis consisting of a humeral component, lateralized polyethylene insert, glenosphere, and metaglene (Fig 5). The humeral component consists of a stem and a cup-shaped proximal portion. All humeral components available in the United States are cemented in place, whereas uncemented humeral components are available in Europe. The polyethylene inserts are radiolucent and vary in thickness. The glenosphere and metaglene convert the glenoid into a ball configuration. The metaglene consists of a base plate that is secured by screws to the native glenoid. The glenosphere is the rounded portion of the prosthesis that is attached to the metaglene (base plate) by a central screw. The glenoid component is uncemented, although a variety of substances, including graft material, may be used to reinforce deficient glenoid bone.
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Figure 5. Photograph shows the components of the Delta CTA Reverse Shoulder System, which includes a humeral component (H), lateralized polyethylene cup (P), glenosphere (G), and metaglene (M). (Reprinted with permission from DePuy Orthopaedics.)
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Biomechanical Features
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The reversed ball-and-socket configuration moves the center of rotation of the shoulder joint distal and medial compared with the anatomic center of rotation. This configuration improves the leverage of the three components of the deltoid muscle, allowing them to exert more control over humeral motion. The deltoid muscle can thus compensate for deficient rotator cuff musculature and provide an increased range of motion of the shoulder (3). The reason previous attempts at reverse prostheses failed in the 1970s was that the more lateral center of rotation would lever out of the more frail scapula.
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Indications for Use
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The reverse shoulder prosthesis is indicated for use in any patient with a nonfunctioning rotator cuff, pain, secondary arthropathy, and "pseudoparalysis" (inability to lift the arm above the horizontal). This clinical presentation is most commonly due to a chronic rotator cuff tear. Other causes of an irreparably damaged or nonfunctional rotator cuff include the natural progression of some rotator cuff tears as well as trauma (4,5), rheumatoid arthritis (6,7), tumor (8,9), osteonecrosis (10), and previous infection. Affected patients cannot undergo standard total shoulder arthroplasty because, without the stabilizing effect of the rotator cuff, rapid loosening of the glenoid component can occur. A typical preoperative radiograph is shown in Figure 6, demonstrating marked superior subluxation of the humeral head with secondary erosion of the acromion from a chronic full-thickness rotator cuff tear. Use of the reverse shoulder prosthesis is not indicated in patients with functional range of motion because they will usually have a good outcome with routine hemiarthroplasty. Pain relief is always the primary goal of surgery.
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Figure 6. Preoperative anteroposterior radiograph demonstrates sequelae of a chronic full-thickness rotator cuff tear, including superior subluxation of the humeral head and secondary erosion of the acromion.
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Preoperative Evaluation
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Patients typically present with shoulder pain and an inability to lift the arm (pseudoparalysis) (Fig 7). Preoperative imaging evaluation includes radiography and computed tomography (CT). A standard preoperative three-view radiographic series of the shoulder is essential and should include a true anteroposterior view. This view is most important for assessment of the shape of the axillary border (pillar) of the scapula. If the axillary scapular border is squared off (Fig 8a) as opposed to having a normal sloped appearance (Fig 8b), the metaglene (base plate) must be placed higher on the glenoid if a DePuy or Encore prosthesis is used. Otherwise, the metaglene should normally be placed as low as possible on the glenoid surface to reduce impingement between the humeral component and scapula ("notching"). The screw angles for the superior and inferior screws on the DePuy and Encore metaglene components are fixed; consequently, if the base plate were placed in a centered location in a patient with a squared-off scapular neck, the inferior transfixing screw would protrude outside the scapula. This problem is avoided in the Tornier prosthesis, which has variable-angle locking screws. A squared-off axillary scapular border can be advantageous in that, assuming the screw fixation problems can be overcome, there is less chance of scapular erosion by the medial aspect of the humeral component.
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Figure 8a. (a) Anteroposterior radiograph shows a squared-off axillary scapular border (arrows). A metaglene with fixed screw angles must be placed higher than normal on the glenoid to avoid having the inferior screw extend outside the bone. (b) Anteroposterior radiograph obtained in a different patient shows the gently curving axillary border of a normal scapula (arrowheads).
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Figure 8b. (a) Anteroposterior radiograph shows a squared-off axillary scapular border (arrows). A metaglene with fixed screw angles must be placed higher than normal on the glenoid to avoid having the inferior screw extend outside the bone. (b) Anteroposterior radiograph obtained in a different patient shows the gently curving axillary border of a normal scapula (arrowheads).
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CT should be used to assess glenoid bone stock. Although this assessment is somewhat subjective, there must be enough glenoid bone to ensure adequate purchase of the screws anchoring the metaglene. Ideally, the glenoid bone stock should be at least 2 cm in depth centrally, between the articular surface and the region where the glenoid narrows at the scapular neck (Figs 9, 10).
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Figure 10. CT scan obtained in a different patient shows marked erosion of the glenoid (arrow), which excluded the patient from being a candidate for reverse shoulder arthroplasty. However, as bone grafting techniques continue to improve, more patients with significant glenoid erosion will become eligible for this procedure.
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If a patient has undergone magnetic resonance imaging of the shoulder for evaluation of the rotator cuff, the study should be reviewed and the appearance of the teres minor tendon and muscle commented upon. Patients with a functioning teres minor have better active external rotation postoperatively than do patients with a nonfunctioning teres minor (11). This improved function is possible only if the teres minor insertion on the greater tuberosity is preserved. In most patients with primary placement of a reverse shoulder prosthesis, the humeral head is resected to the level of the anatomic neck, thereby preserving the teres minor insertion. In a revision procedure—for example, after failed conventional shoulder arthroplasty—bone resection may extend to the surgical neck of the humerus, thus not allowing preservation of the teres minor insertion.
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Surgical Technique
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Placement of a reverse shoulder prosthesis requires the use of new surgical techniques and can be technically challenging. Key elements of reverse shoulder arthroplasty include removal of the superomedial humeral head, smoothing of the glenoid surface, placement and anchoring of the metaglene, placement of the cemented humeral component, and attachment of the glenosphere.
The most technically challenging portion of the operation is the placement and anchoring of the metaglene to the glenoid. The metaglene is uncemented, and stable fixation is essential for the long-term success of the prosthesis (12). Placement can be double checked in the operating room using a C-arm to ensure that the metaglene component is flush with the native glenoid. The humeral component is cemented using standard technique. Reverse shoulder prostheses can easily dislocate in the immediate postoperative period, especially if the patient was anesthetized with an interscalene block and has been transferred from bed to bed by being lifted in a sheet. This lifting process can place the shoulder in internal rotation and extension, which should be avoided. If the elbow is padded to lie anterior to the body so that the patient can see it, it will not dislocate. An anteroposterior radiograph should be obtained immediately after surgery to ensure that the prosthesis did not become dislocated while the patient was being moved.
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Normal Radiographic Appearance and Interpretation Search Pattern
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Anteroposterior, axillary, and scapular Y-view radiographs of a normal Delta shoulder prosthesis are shown in Figures 11–13. The mildly posterior position of the humeral component with respect to the glenosphere seen in Figure 12 is a common finding but is not clinically significant.
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Figure 13. Anteroposterior radiographs show a normal reverse shoulder prosthesis. The mildly posterior position of the humeral component (H) with respect to the glenosphere (G) is a common but clinically insignificant finding on the axillary view. These two components should align as shown on the scapular Y view. The coracoid process (C) projects anteriorly on the axillary view.
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Several regions of the prosthesis should be carefully examined on radiographs (Table). The metaglene should be placed flush with the native glenoid, and any defects should be grafted. The superior, anterior, and posterior screws are usually bicortical, whereas the inferior screw should lie entirely within the scapular bone if possible. The ball-shaped glenoid component should align within the cup of the humeral component, but the amount of space between them is variable, since the radiolucent polyethylene inserts have a relatively wide range of thicknesses to optimize stability. Any regions of radiolucency at the prosthesis-bone or cement-bone interface should be compared with immediate postoperative views for change and assessed with radiographs obtained in two right-angle planes. The prosthesis components, anchoring screws, and supporting bones should all be intact. The inferior border of the glenoid should be examined specifically for erosion, and heterotopic ossification in the surrounding soft tissues should be commented upon.
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Clinical Course
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Patients typically experience a dramatic improvement in shoulder range of motion and a marked decrease in shoulder pain (13–15). In patients who were unable to lift the affected arm preoperatively, the shoulder can be restored to a near normal range of motion (Fig 14). In our first 2 years of experience placing these devices, patients have been almost universally very pleased, even when complications occurred.
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Figure 14a. Postoperative photographs obtained in the same patient as in Figure 7 show full range of motion by abduction with internal rotation (a) and extension (b). The patient was unable to raise her arm prior to undergoing surgery.
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Figure 14b. Postoperative photographs obtained in the same patient as in Figure 7 show full range of motion by abduction with internal rotation (a) and extension (b). The patient was unable to raise her arm prior to undergoing surgery.
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Complications
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The most common clinically significant complication of reverse shoulder arthroplasty is an anterior dislocation. In our first year of experience placing these prostheses, nearly 20% of patients experienced an anterior dislocation, often with no identifiable trauma (16). There were no posterior shoulder dislocations. Prosthesis positioning is best assessed on radiographs, which include an anteroposterior view and either an axillary or a scapular Y view. An anteroposterior view of an anteriorly dislocated reverse shoulder prosthesis demonstrates an abnormally high location of the humeral component relative to the glenoid. An axillary view will demonstrate the anterior dislocation of the humeral component (Fig 15). It is important to note that, although an anteriorly dislocated native shoulder tends to lie below the coracoid process on an anteroposterior view, the reverse humeral component dislocates in the anterior-superior direction because of rotator cuff deficiency and pull of the deltoid muscle, which allow this anterior-superior "escape."
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Figure 15a. Anteroposterior (a) and axillary (b) radiographs show an anteriorly dislocated reverse shoulder prosthesis. On the anteroposterior view, the humeral component lies higher than an anteriorly dislocated native humerus would lie; the axillary view shows anterior dislocation of the humeral component.
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Figure 15b. Anteroposterior (a) and axillary (b) radiographs show an anteriorly dislocated reverse shoulder prosthesis. On the anteroposterior view, the humeral component lies higher than an anteriorly dislocated native humerus would lie; the axillary view shows anterior dislocation of the humeral component.
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The most common clinically evident but radiographically occult complication in the immediate postoperative period has been reported to be a hematoma, which was seen in up to 21% of patients in one series (17). Less common complications include prosthesis loosening (Fig 16) or infection (Fig 17); the latter should be suspected when irregular regions of radiolucency and bone resorption develop around the prosthesis. The prosthesis can increase biomechanical stress, leading to periprosthetic fracture (Fig 18). If the metaglene becomes loose, it can migrate in the joint (Fig 19). Intraoperative complications include malpositioning of the metaglene (Fig 20) or fixation screws (Fig 21). Disassembly of the humeral component (Fig 22) and glenosphere-metaglene component were complications of early versions of the reverse shoulder prosthesis used in Europe (18). Prosthesis redesign has virtually eliminated these complications.
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Figure 16. Anteroposterior radiograph obtained in an asymptomatic patient at 1-year follow-up shows early loosening of the humeral component of the prosthesis. Irregular regions of radiolucency have developed at the cement-bone interface (arrows) of the proximal humerus.
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Figure 17. Anteroposterior radiograph shows bone resorption (arrows) along the proximal aspect of the humeral component due to a Staphylococcus epidermidis infection. Inferior scapular notching (arrowheads) is also present.
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Figure 19. Anteroposterior radiograph shows metaglene loosening and migration. The posterior aspect of the metaglene (black arrows) should lie parallel to the native glenoid (white arrows), which, in this case, has been eroded from contact with the medial aspect of the humeral component.
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Figure 22a. Anteroposterior radiographs show partial (a) and complete (b) disassembly of the humeral component (arrows). Metaphyseal unscrewing will typically be accompanied by humeral loosening and polyethylene wear.
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Figure 22b. Anteroposterior radiographs show partial (a) and complete (b) disassembly of the humeral component (arrows). Metaphyseal unscrewing will typically be accompanied by humeral loosening and polyethylene wear.
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In the late postoperative period, scapular erosion, osteophyte formation, and heterotopic ossification may also be seen. Scapular erosion (Fig 23) occurs due to repetitive contact of the medial border of the humeral component with the inferior border of the scapula and is relatively common (15,19).
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Figure 23a. Serial anteroposterior radiographs show erosion of the humeral component into the inferior scapula (white arrow) and, over time, damage to the metaglene fixation screw (black arrow in b).
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Figure 23b. Serial anteroposterior radiographs show erosion of the humeral component into the inferior scapula (white arrow) and, over time, damage to the metaglene fixation screw (black arrow in b).
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The erosion tends to stabilize around 1 year after surgery (17). Scapular erosion should not be confused with inferiorly directed osteophytes (Fig 24), which can form in the first year and are seen to mature over time. Heterotopic bone can form around the shoulder and is most often seen in the region of the deltoid muscle (Fig 25). An acromial stress fracture may be clinically diagnosed due to point tenderness over the acromion, but this entity can be difficult to detect on radiographs unless periosteal reaction is present or the fracture displaces.
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Figure 25. Anteroposterior radiograph obtained in an asymptomatic patient at routine 1-year follow-up shows heterotopic bone (arrowheads) that has developed in the deltoid muscle. Either an additional focus of heterotopic bone or an osteophyte is present along the inferior scapula (arrow).
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Conclusions
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The altered geometric configuration created with reverse shoulder arthroplasty allows reconstruction of rotator cuff–deficient shoulders. Patients experience a significant improvement in range of motion and markedly decreased pain. However, the reverse shoulder prosthesis has a relatively high complication rate; thus, it is important that the radiologist be familiar with the normal and abnormal imaging appearances of this device.
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Acknowledgments
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We would like to thank Tom R. Norris, MD, San Francisco, California, and Robert H. Cofield, MD, Department of Orthopedics, Mayo Clinic, Rochester, Minnesota, for contributing images and sharing their personal experience.
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Footnotes
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Abbreviations: FDA = Food and Drug Administration
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References
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- De Wilde L, Mombert M, Van Petegem P, Verdonk R. Revision of shoulder replacement with a reversed shoulder prosthesis (Delta III): report of five cases. Acta Orthop Belg 2001;67(4):348–353.[Medline]
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- Sirveaux F, Favard L, Oudet D, Huquet D, Walch G, Mole D. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff: results of a multicentre study of 80 shoulders. J Bone Joint Surg Br 2004;86(3):388–395.
- Roberts CC, Hattrup SJ, Renfree KJ. The delta reverse shoulder arthroplasty: reinventing the wheel [abstr]. Skeletal Radiol 2005;34(10):687–688.
- Werner CM, Steinmann PA, Gilbart M, Gerber C. Treatment of painful pseudoparesis due to irreparable rotator cuff dysfunction with the Delta III reverse-ball-and-socket total shoulder prosthesis. J Bone Joint Surg Am 2005;87(7):1476–1486.[Abstract/Free Full Text]
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Abstract
LEARNING OBJECTIVES
