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Case Report

Shoulder & Elbow

Arthroscopically-Guided, Cannulated, Headless Compression Screw Fixation of the Symptomatic Os Acromiale

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Author Affiliation | Disclosures

Authors’ Disclosure Statement: The authors report no actual or potential conflict of interest in relation to this article.

Dr. Walton is an Assistant Professor, Department of Orthopaedics and Physical Medicine, Medical University of South Carolina, and the Ralph H. Johnson VA Medical Center, Charleston, South Carolina. Dr. Holmes is a Fellow, University of Texas, Houston, Texas. Dr. Woolf is an Associate Professor and Chief of Sports Medicine, Department of Orthopaedics and Physical Medicine, Medical University of South Carolina, Charleston, South Carolina.

Address correspondence to: Shane K. Woolf, MD, Department of Orthopaedics and Physical Medicine, Medical University of South Carolina, CSB 708, 171 Ashley Avenue, Charleston, SC 29425 (tel, 843-792-3180; email, woolfsk@musc.edu).

Am J Orthop. 2018;47(9). Copyright Frontline Medical Communications Inc. 2018. All rights reserved.

Abstract

Os acromiale is a failure of fusion between 1 or more ossification centers of the scapula and the acromion process. Pain can be caused by motion and impingement of the unfused segment. Several methods for the management of os acromiale have been described. Internal fixation is the most common surgical technique, followed by excision and acromioplasty. We present a novel technique for treatment of symptomatic os acromiale using arthroscopically-guided headless compression screws. This is a viable technique in the management of symptomatic os acromiale due to preservation of the periosteal blood supply and less concern for symptomatic hardware.




Take-Home Points

  • Os acromiale is a failure of acromial ossification centers to fuse, and occurs in 8% of the population.
  • Symptomatic os acromiale can be treated with repair, or sometimes excision or acromioplasty.
  • Repair preserves the anterior deltoid origin and can result in less pain than excision of the fragment.
  • Repair of larger fragments can be completed with cannulated screws to reliably achieve union.
  • The arthroscope-assisted repair technique described in this article preserves vascularity and can reduce the risk of hardware-related complaints.

Os acromiale results from a failure of fusion between 1 or more ossification centers and the acromion process.1 The acromion consists of 4 different ossification centers, which appear by 14 years of age and fuse by age 25 years. The 4 ossification centers are the basi-acromion, meta-acromion, mesoacromion, and pre-acromion (Figure 1). Formation of an os acromiale occurs most often due to failure of fusion between the meta-acromion and mesoacromion. Os acromiale appears to occur in approximately 8% of the population, according to cadaveric studies.2 This anatomic variant occurs more commonly in African-Americans than Caucasians, and shows a preponderance for males over females.3

Plain radiographs are usually adequate for diagnosis. Axillary views are most sensitive for detection, which can be difficult to see on anteroposterior radiographs.4 In os acromiale, the unfused segment is connected to the acromioclavicular joint and the coracoid, which can lead to motion of the segment and impingement of the rotator cuff.2-4 Patients frequently experience localized tenderness and symptomatic pain with signs and symptoms of impingement. Rotator cuff tears may occur secondary to chronic impingement.5

Various forms of repair have been described. A recent meta-analysis showed that internal fixation (60%) was the most common surgical technique reported, followed by excision (27%) and acromioplasty (13%).6 Rotator cuff repair is a common concurrent surgical procedure.7-11 The available literature favors internal fixation through an open technique with or without bone grafting.5,7,8,12-15 Various forms of fixation have been presented in the literature, including Kirschner wire fixation, cannulated screw fixation alone, cannulated screw fixation with FiberWire Suture (Arthrex), and cannulated screw fixation with a stainless steel wire tension band technique. Based on the results of the meta-analysis, surgical fixation with cannulated screws has been shown to lead to a significantly greater rate of radiographic healing (23/24 patients) compared to Kirschner wire fixation (31/49 patients).6 Further, radiographic healing is significantly associated with improved clinical outcomes.12 Removal of symptomatic internal fixation hardware is significantly more common after Kirschner wire fixation cases (88%; 43/49) compared to cannulated screw fixation cases (38%; 9/24). However, hardware issues may also be encountered with screw fixation, with 1 case series reporting a 25% rate of hardware complication.16 The patient provided written informed consent for print and electronic publication of this case report.

Case Report

The patient is a 19-year-old right-hand-dominant woman who injured her right shoulder while diving into the bleachers during a volleyball game 4 years prior to presentation. She suffered a direct blow to her shoulder and immediately became symptomatic. She underwent a long period of nonoperative management, which included physical therapy, strengthening, nonsteroidal anti-inflammatory drug (NSAID) therapy, and narcotic pain medications. Her primary complaints upon presentation were pain with lifting, as well as mechanical symptoms. On examination, the patient had moderate tenderness directly over the acromion. She also had evidence of mild impingement symptoms. Plain radiographs revealed a mesoacromial-type os acromiale clearly seen on the axillary lateral film (Figure 2). She underwent magnetic resonance imaging, which suggested rotator cuff tendinosis and evidence of edema at the os acromiale site. She underwent a diagnostic injection directly into the site of maximal tenderness at the os, which provided complete transient relief of her pain. Despite the transient pain relief, the patient continued to be symptomatic after the local anesthetic effect wore off. Surgical options were then discussed with the patient.

Surgical Technique

A standard diagnostic shoulder arthroscopy was performed using anterior, posterior and direct lateral portals. The rotator cuff was evaluated, and no evidence of a tear was found. The undersurface of the acromion was exposed, and the os acromiale was identified arthroscopically (Figure 3). This was found to be unstable under direct digital pressure.

We then elected to repair the unstable fibrous os acromiale (Figures 4A-4D). The fibrous nonunion was first debrided to bleeding bone with a 4.0-mm round burr aligned with the os using the direct lateral portal (Smith & Nephew Endoscopy). Through the anterior portal, two AcutrakTM guide wires (Acumed) were placed under arthroscopic visualization from the anterior margin of the acromion, across the os site, and into the posterior acromion. A 1-cm counter incision was made at the level of the posterior acromion to allow confirmation of the guide wire position and to permit placement of a large, pointed reduction clamp, used to reduce the mesoacromial fragment to the stable portion of the acromion. The calibrated, cannulated drill bit was passed over each guide wire to a depth of 34 mm, according to standard technique, and viewed arthroscopically from the subacromial space. Two 34-mm AcutrakTM cannulated headless compression screws (Acumed) were then placed across the defect. Direct arthroscopic visualization confirmed reduction and complete intraosseous placement of the screws (Figure 5). Screw position was also assessed with image intensification. Fluoroscopic views showed the repair to be stable when the shoulder was taken through range of motion. The os site was never exposed directly through an incision. The surgery was performed on an outpatient basis.

Postoperative Course

The patient was maintained in a sling and small abduction pillow (Ultrasling IIITM, DonJoy). She was kept non-weight-bearing but was permitted unrestricted motion through the elbow, wrist, and hand for the first 6 weeks. She was permitted supine passive external rotation of the shoulder to 30° and forward flexion to 45° for the first 2 weeks, and 90° through 6 weeks. At her initial postoperative visit 2 weeks later, she noted minimal pain in the shoulder, much improved from her preoperative pain. She was no longer taking any pain medicine, including NSAIDs. Radiographs showed no change in fixation.

At her second visit (6 weeks), she was completely pain free. Clinical examination showed no tenderness at the acromion, healed incisions, and pain-free passive ROM. Radiographs demonstrated early evidence of consolidation and no sign of fixation failure (Figures 6-8). Her Single Assessment Numeric Evaluation (SANE) score was 85%, and her Simple Shoulder Test (SST) score was 3/12. She was permitted to discontinue the sling, to begin using the arm actively at the side, and progress with unloaded use above shoulder height over the next 6 weeks.

She was seen in follow-up at 4 months, where she was found to have no pain but had not yet returned to sports. At her 6-month follow-up, she showed continued improvement with no limitation of activity. At 1-year follow-up, her SANE score improved from 85% at 6 weeks postoperatively to 100%, and her SST improved from 3/12 at 6 weeks to 12/12. She demonstrated full function of her shoulder with no evidence of hardware loosening. At that time, her os acromiale had completely fused radiographically.

Discussion

A variety of methods for the management of os acromiale have been described in the literature. Internal fixation is reported as the most common surgical technique, followed by excision and acromioplasty.6 Surgical fixation with cannulated screws is effective at achieving radiographic union.5,9,12,13,15

Excision is also an option in cases where there is a symptomatic pre-acromion with a relatively small fragment. In the case of a larger fragment, techniques that preserve the vascularity of the os acromiale appear more likely to be successful than excision.17 While excision can be performed arthroscopically to preserve the blood supply, a recent report showed that 35% of patients still had residual pain.18 Another study suggests that protecting the vascular supply with an arthroscopic technique would be a better option to promote healing to union.19

Given that removal of symptomatic internal fixation hardware is significantly more common after Kirschner wire fixation (88%; 43/49) than after cannulated screw fixation (38%; 9/24),6 and given that significant hardware complications can arise from screw tips,16 we chose headless, cannulated Acutrak compression screws for arthroscopic-assisted fixation. Performing the operation arthroscopically minimized soft-tissue violation, allowing us to directly visualize the reduction and also allowing confirmation that the screws were not at risk for impingement of the rotator cuff. The tapered nature of the Acutrak screws allowed for excellent compression at the reduction site without a prominent screw head.

Conclusion

Arthroscopic management of the symptomatic os acromiale has been documented in the literature. Cannulated screw fixation has shown to lead to a higher rate of radiographic union than Kirschner wire fixation. Arthroscopically guided placement of headless, cannulated compression screw fixation may be a viable repair alternative in the management of the symptomatic os acromiale with less concern for symptomatic hardware.6,20-27

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References

References

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14. Satterlee CC. Successful osteosynthesis of an unstable mesoacromion in 6 shoulders: a new technique. J Shoulder Elbow Surg. 1999;8(2):125-129. doi:10.1016/S1058-2746(99)90004-6.

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20. Kummer FJ, Van Gelderen J, Meislin RJ. Two-screw, arthroscopic fixation of os acromiale compared to a similar, open procedure incorporating a tension band: a laboratory study. Shoulder Elbow. 2011;3(2):85-87. doi:10.1111/j.1758-5740.2011.00115.x.

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