The Reverse Shoulder Arthroplasty: Interim Analysis and Future Directions

Darren S. Drosdowech M.D., FRCSC
Assistant Professor, Orthopaedic Surgery
Hand and Upper Limb Centre
University of Western Ontario
London, ON

Introduction
Paul Grammont is credited with today's current design of a modern reversed total shoulder arthroplasty. Previous constrained shoulder designs have universally failed usually due to the high degree of glenohumeral constraint, inadequate glenoid fixation and a lateralized centre-of-rotation. Grammont's eventual modifications addressed the need for a semi-constrained design, improved glenoid fixation and a medialized centre-of-rotation1.

The need for such a design has been justified primarily by the less than optimal results seen over time with hemiarthroplasty for patients with rotator cuff tear arthropathy2,3,4. However, many other pathological states, which result in a severe deficiency of glenohumeral soft tissue constraint and/or proximal humeral bone, lend themselves favourably to this design in an attempt to maintain shoulder function. In the past, such conditions may have only been addressed by less functionally reliable options such as arthrodesis or resection arthroplasty.

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Figure 1a & b - Preoperative AP scapular and axillary views. Classic rotator cuff tear arthropathy with anterosuperior humeral head migration, acromiohumeral narrowing/ wear and well - preserved glenoid bone stock. CT confirmation of the latter is recommended.

Literature Review, Indications and Complications
The primary indication for a reverse shoulder prosthesis is the painful pseudoparalysis of forward elevation in a patient who lacks a mechanical fixed centre-of-rotation of the shoulder joint. There are relatively few documented large prospective clinical series to guide surgeons as to the ideal indications for a reverse shoulder arthroplasty. Werner et al5 reported on 58 patients of whom 41 received a revision prosthesis. The relative Constant scores improved from 29% to 64% and active forward elevation improved from 42 to 100. The authors noted a 50% complication rate requiring re-operation to correct the problem in 33% of cases.

Boileau6 reviewed his series of 45 patients and showed similar improvements in both patient outcome scores and range of motion. Most importantly, he observed that fewer complications were seen when the prosthesis was used primarily for rotator cuff tear arthropathy compared to other complex or revision indications (5% vs. 47%).

To date, 60 reverse shoulders have been performed at our institution since Health Canada clearance was granted in March 2003. Although the details of a full prospective clinical review of our results are pending, it is clear that an initial review of the local results parallel those mentioned above. The prosthesis has been an ideal option for primary indications such as rotator cuff tear arthropathy, however; other indications such as post-traumatic reconstruction or use as a revision prosthesis have a notably higher complication rate requiring re-operation in a number of instances. The most common complications have been instability, infection and lateral scapular erosion. Instability is a complex issue and is addressed with appropriate humeral component version to minimize periglenoid impingement, ideal height restoration (resting tissue tension) and possibly increasing the diameter of the bearing surfaces. There is a marginally higher rate of infection compared to traditional shoulder arthroplasty but this has been noted amongst more complex, revision cases. The significance of lateral scapular erosion is currently poorly understood but has rarely resulted in frank loosening of the glenoid component. It is felt to be a combination of mechanical impingement of the humeral polyethylene cup against the inferior glenoid neck/lateral scapular body and osteolysis due to particulate wear debris7. Mechanical solutions currently include more inferior placement of the glenoid base plate8, avoiding retentive cups whenever possible and surgically decompressing the inferior scapula at the time of implant insertion.

Technical Issues
The deltopectoral approach is preferred in order to minimize surgical trauma to the axillary nerve and allow an extensile approach to the humerus should that be deemed necessary. Intraoperative glenoid fracture can be avoided by careful glenoid exposure and reaming - especially in patients with poor bone quality. Routine exposure of the axillary nerve in order to safely identify the inferior glenoid neck-lateral scapular body junction allows accurate placement of the inferior locking screw in order to achieve ideal glenoid fixation.

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Figure 2a & b - Immediate postoperative AP scapular and axillary views. Inferomedialized centre-of-rotation with Delta III prosthesis. Note low placement of metaglene allowing overlap of glenosphere relative to inferior glenoid neck. This will reduce inferior humeral-scapular impingement and help to minimize lateral scapular erosion.

A full review of surgical technique and technical pearls and are beyond the scope of this article. It should be understood however, that surgeons undertaking this procedure should be committed to becoming familiar with one system which can provide consistent and reproducible results in their hands. Even in a tertiary care subspecialty shoulder practice, technique-related complications occur with a higher frequency than with conventional total shoulder arthroplasty and their management can be equally challenging.

Future Directions
The current market for reverse shoulder arthroplasty is growing and the number of different implant systems available to the surgeon to choose from is ever expanding. While much of the current literature reflects our experience with the Delta III/Tornier designs, subtle modifications such as variable angle locking screws and a vertical-plane offset glenoshphere are forthcoming advances that will hopefully result in lower implant-related complication rates. Platform, or "all-in-one" style modular shoulder arthroplasty systems have been introduced (ex. Zimmer Anatomic) to allow the surgeon to change the bearing surfaces (ex. hemiarthroplasty to reverse) without the need for revision of a well-fixed humeral stem. Rigorous prospective clinical follow-up of all our patients is ongoing and will help us to tailor both clinical indications and the necessary mechanical advances needed to improve outcomes.

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Figure 3 - Clinical follow up 6 months postoperative. Operated right shoulder demonstrating approximately 110 of active forward elevation compared to 30 noted preoperatively.

High cost has limited or outright prevented the use of these prostheses that will increasingly challenge hospital budgets as use increases in the future. Despite the current wait-time initative focus on hip and knee arthroplasty, it is imperative that attention be given to other equally effective and essential orthopaedic implants including, but not limited to, the shoulder.

Conclusions
Reverse shoulder arthroplasty will add to the surgeon's potential treatment options in patients with a variety of shoulder conditions which all share the need for a fixed centre-of-rotation to improve the painful pseudoparalysis of shoulder elevation. Rotator cuff tear arthropathy has responded most favourably to this type of prosthesis with the fewest perioperative complications. Indications for less common and more complex shoulder problems are promising, given the lack of adequate alternative management options, but lead to higher incidence of complications of which both the surgeon and patient need to be aware. Ongoing prospective clinical analysis as well as future implant/procedural related modifications are necessary to further refine this implant's role.

References

1. Grammont P.M., Baulot. Delta shoulder prosthesis for rotator cuff rupture. Orthopaedics Jan 1993; Vol 16(1): 33-36.

2. Sanchez-Sotelo J., Cofield R.H., Rowland C.M. Shoulder hemiarthroplasty for glenohumeral arthritis associated with severe rotator cuff deficiency. JBJSA Dec 2001;83-A(12):1814-22.

3. Field L.D., Dines D.M., Zabinski S.J., Warren R.F. Hemiarthroplasty of the shoulder for rotator cuff arthropathy. JSES Jan/Feb 1997;Vol 6(1): 18-23.

4. Zuckerman J.D., Scott A.J., Gallagher M.A. Hemiarthroplasty for cuff tear arthropathy. JSES May/June 2000;Vol 9(3):169-72.

5. Werner C.M.L., Steinmann P.A., 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. JBJSA Jul 2005; Vol 87-A (7):1476-86.

6. Boileau P., Watkinson D., Hatzidakis A.M., Hovorka I. Neer Award 2005: The Grammont reverse shoulder prosthesis: Results in cuff tear arthritis, fracture sequelae, and revision arthroplasty. JSES Sept/Oct 2006; Vol 15(5):527-40.

7. Nyffeler R.W., Werner C.M.L., Simmen B.R., Gerber C. Analysis of a retrieved Delta III total shoulder prosthesis. JBJSB Nov 2004; Vol 86-B (8):1187-91.

8. Nyffeler R.W., Werner C.M.L, Gerber C. Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis. JSES Sept/Oct 2005; Vol 14(5):524-28.

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