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      Acromial Fractures in Reverse Shoulder Arthroplasty: A Clinical and Radiographic Analysis

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          Abstract

          Background

          The purpose of this study is to assess the incidence of acromial stress fractures in a population of reverse shoulder arthroplasties (RSA) and determine potential risk factors for fracture.

          Patients and Methods

          Between August 2004 and December 2013, 1082 primary RSA were performed at a single institution. Twelve (1.11%) patients were diagnosed with a postoperative acromial stress fracture. This group was case-matched to a control group of 48 shoulders. Clinical and radiographic risk factors for fracture were assessed.

          Results

          Compared to controls, fractures were less satisfied with their outcome despite equivalent American Shoulder and Elbow Surgeons scores, pain scores, and range of motion. Osteoporosis was significantly associated with acromial fractures ( P = .027). A smaller lateral offset of the greater tuberosity, greater arm lengthening, and a thinner acromion were more common in the fracture group ( P = .026, P = .004, and P = .008, respectively).

          Conclusions

          In summary, postoperative acromial stress fractures appear to be incidental lesions with little influence on the outcome after RSA. The combination of a thin acromion and superior migration of the humeral head increase the risk of acromial fracture. Lateralized designs that do not excessively verticalize the deltoid line of pull on the acromion may decrease the risk of postoperative acromial fractures.

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          Most cited references26

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          Grammont reverse prosthesis: design, rationale, and biomechanics.

          Combined destruction of the rotator cuff and the glenohumeral joint may lead to a painful and pseudo-paralyzed shoulder. In this situation a nonconstrained shoulder prosthesis yields a limited functional result or may even be contraindicated. Previous constrained prostheses (ball-and-socket or reverse ball-and-socket designs) have failed because their center of rotation remained lateral to the scapula, which limited motion and produced excessive torque on the glenoid component, leading to early loosening. The reverse prosthesis designed by Paul Grammont, unlike any previous reverse ball-and-socket design, has introduced 2 major innovations that have led to its success: (1) a large glenoid hemisphere with no neck and (2) a small humeral cup almost horizontally oriented with a nonanatomic inclination of 155 degrees, covering less than half of the glenosphere. This design medializes and stabilizes the center of rotation, minimizes torque on the glenoid component, and helps in recruiting more fibers of the anterior and posterior deltoid to act as abductors. Furthermore, the humerus is lowered relative to the acromion, restoring and even increasing deltoid tension. The Grammont reverse prosthesis imposes a new biomechanical environment for the deltoid muscle to act, thus allowing it to compensate for the deficient rotator cuff muscles. The clinical experience does live up to the biomechanical concept: the reverse prosthesis restores active elevation above 90 degrees in patients with a cuff-deficient shoulder. However, external rotation often remains limited, particularly in patients with an absent or fat-infiltrated teres minor. Internal rotation is also rarely restored after a reverse prosthesis. Failure to restore sufficient tension in the deltoid may result in prosthetic instability. The design does appear to protect against early loosening of the glenoid component, but impingement of the humeral cup on the scapular neck can lead to scapular notching and polyethylene wear. This is a cause for concern, especially as the notch is often more extensive than can be explained by impingement alone. Bony lysis of the scapula may also be related to a polyethylene granuloma. Further follow-up is required to ensure that loosening does not become a problem in the long term, and it has been recommended to limit its use to elderly patients, arguably those aged over 70 years. Despite these concerns, the reverse prosthesis, based on the biomechanical Grammont concept, offers a true surgical option in several situations where only limited possibilities were previously available: cuff tear arthrosis, persistent shoulder pseudo-paralysis due to a massive and irreparable cuff tear, severe fracture sequelae, prosthetic revision in a cuff-deficient shoulder, and tumor surgery. Finally, surgeons must be aware that results are less predictable and complication/revision rates are higher in revision surgery.
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            Neer Award 2005: The Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture sequelae, and revision arthroplasty.

            This clinical study was performed to analyze the midterm results and potential complications of the reverse prosthesis in different diagnosis. Forty-five consecutive patients with Grammont prosthesis were evaluated clinically and radiographically with a mean follow-up of 40 months (range, 24-72 months). The indication was a massive and irreparable cuff tear associated with arthrosis (CTA) in 21 cases, fracture sequelae (FS) with arthritis in 5 cases, and failure of a revision arthroplasty (revision) in 19 cases. Fourteen complications occurred in 11 patients. 3 dislocations, 3 deep infections (all 3 in the revision group), 1 case of aseptic humeral loosening, 2 periprosthetic humeral fractures, 1 intraoperative glenoid fracture, 1 wound hematoma, 2 late acromial fractures, and 1 axillary nerve palsy. Of the patients, 10 (22%) required further surgery: 4 reoperations, 4 prosthesis revisions, and 2 prosthesis removals. Complications were higher in revision than in CTA (47% vs. 5%). All 3 groups showed a significant increase in active elevation (from 55 degrees preoperatively to 121 degrees postoperatively) and Constant score (from 17 to 58 points) but no significant change in active external rotation (from 7 degrees to 11 degrees ) or internal rotation (S1 preoperatively and postoperatively). Of the patients, 78% were satisfied or very satisfied with the result and 67% had no or slight pain. However, the postoperative Constant score, adjusted Constant score, and American Shoulder and Elbow Surgeons shoulder score were all significantly higher in the CTA group with as compared with the revision group (P = .01, .004, and .002, respectively). Scapular notching was seen in 24 cases (68%). No glenoid loosening was observed at current follow-up, even when the notch extended beyond the inferior screw (28% of cases). Atrophy of severe fatty infiltration of the teres minor was associated with lower external rotation (15 degrees vs 0 degrees , P = .02) and lower functional results (Constant score of 46 points vs 66 points, P < .007). The Grammont reverse prosthesis can improve function and restore active elevation in patients with incongruent cuff-deficient shoulders; active rotation is usually unchanged. Results are less predictable and complication and revision rates are higher in patients undergoing revision surgery as compared with those in patients with CTA. Results of the reverse prosthesis depend on the diagnosis and on the remaining cuff muscles, specifically the teres minor. Surgeons should be vigilant with regard to low-grade infection in revision surgery.
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              Roentgenographic findings in massive rotator cuff tears. A long-term observation.

              It is difficult to determine the size and localization of rotator cuff tears preoperatively. But with the special arthrographic technique, a diagnosis with about 80% accuracy was possible in 65 surgically confirmed rotator cuff tears. With this technique, 22 massive cuff tears were found in conservatively treated patients. In these patients, the plain roentgenograms obtained at the initial examination were also analyzed. The roentgenographic findings included narrowing of the acromiohumeral interval and degenerative changes of the humeral head, the tuberosities, the acromion, the acromioclavicular joint, and the glenohumeral joint. Based on these data, five roentgenographic grades of massive cuff tears were identified. Of seven patients with massive tears, which had been treated conservatively and followed for more than eight years, the roentgenographic grades advanced in five. One shoulder progressed to cuff-tear arthropathy. Based on these observations, it is proposed that the following pathogenetic mechanisms are responsible for the progressive roentgenographic changes: (1) arm elevation in activities of daily living, (2) rupture of the long head of biceps tendon, (3) the abnormal fulcrum of the humeral head against the acromion and the coracoacromial ligament, and (4) the weakness of external rotation. A massive cuff tear will progress to cuff-tear arthropathy, with each step of progression accompanied by characteristic roentgenographic changes.
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                Author and article information

                Journal
                Journal of Shoulder and Elbow Arthroplasty
                Journal of Shoulder and Elbow Arthroplasty
                SAGE Publications
                2471-5492
                2471-5492
                January 2018
                May 25 2018
                January 2018
                : 2
                : 247154921877762
                Affiliations
                [1 ]Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota
                [2 ]Department of Biomechanics, Mayo Clinic, Rochester, Minnesota
                Article
                10.1177/2471549218777628
                e37d82d6-4b3a-4290-9915-9c7427f564fe
                © 2018

                http://journals.sagepub.com/page/policies/text-and-data-mining-license

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