We read with much interest the article entitled ‘Metal-backed glenoid implant with polyethylene insert is not a viable long-term therapeutic option.’ This article is a retrospective study of 165 total shoulder arthroplasties (TSAs) with a metal-backed implant performed for osteoarthritis between 1994 and 1999. At a mean follow-up of 8.5 years (range, two-16 years), this study shows a 37 per cent rate of failure for this specific implant. Indeed, as the authors point out, the complication rate in this series is very high. They conclude from their series that the whole concept of a metal-backed glenoid implant with polyethylene insert is not a viable long-term therapeutic option and does not facilitate revision cases. To support their statements, the authors add a review of the literature in their paper. Although references to articles against metal-backed glenoid implants are complete and often relate to older designs, [5,13] numerous references that support the use of metal-backed implants are lacking. [4,7,8,11,12,14]
In addition, they do not provide any criticisms regarding the design of the glenoid implant that was used in their series. Indeed, it has been shown in the literature that a convex-backed glenoid achieves better fixation than a flat-backed implant,  and the use of an expansion screw has been proven to be unable to achieve strong initial fixation.  Improved survivorships have been described by modifying the original glenoid design. [4,11,14] This suggests that the design of the glenoid is key to the survival of the implant and may explain the variation in the reported survivorship of different metal-backed glenoid implants.
In the present study, wear of the polyethylene insert was observed in 51 per cent of the shoulders with a rate of revision of 37 per cent and a survival rate of 46 per cent at 10 years. These findings are not in agreement with our own experience or with what has been reported in recent publications concerning uncemented metal-backed implants like the SMR (Lima LTO, Udine, Italy) and the BioModular TSR (Biomet,Warsaw, IN, USA), which have been found to have a survival rate of 100 per cent at 6.3 years  and 93 per cent at 10 years,  respectively, or the Arrow (FH Orthopedics, Mulhouse, France), which has been found to have a revision rate of 5.59 per cent at 38 months.  A possible explanation for the high rate of complications observed in this series could be related to the number of biconcave or dysplastic glenoids (B2 or C), which reached 50 per cent. These patients are known to be at risk of recurrent postoperative subluxation, which may lead to glenoid failures.
In their series, the authors were able to perform revision without replacing the implants in only two cases. The ease of revision from TSA to reverse shoulder arthroplasty with convertible platform systems has been recognized by several authors, [15,16] including Clitherow et al  from the joint registry of New Zealand, Castagna et al  with the SMR implant, and Kany et al  with the Arrow implant. In this paper we reported on 16 cases of revisions from TSA with a metal-backed glenoid to reverse shoulder arthroplasty. In 12 of these cases, the revisions were performed without having to remove the glenoid baseplate or humeral stem. This retention rate is much higher than in the paper of Boileau. Therefore, as opposed to what has been described in this article, the concept of a fully convertible universal platform is useful in our experience, allowing easy revisions by only changing the inserts (on both the humeral and glenoid sides). Because the bone on both the glenoid and humeral sides remained untouched during the revision procedures, these were performed in less than an hour with limited blood loss, quicker recovery and a functional result that can be expected to be similar to that of a primary case. [13,14] On the other hand, the revision of a loose cemented glenoid is often associated with severe glenoid bone loss, making the implantation of a new glenoid implant challenging with an often-limited functional result. 
We therefore disagree with the statement of the article and find it unjustified to reject the concept of a metal-backed glenoid implant with polyethylene insert based on the failure of one specific implant design.
Denis Katz, Jean Kany and Philippe Valenti receive royalties for shoulder prosthesis design from FH Orthopedics. Jean-David Werthel, his immediate family and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
Denis Katz, MD, Clinique du Ter, Douar Gwen, Ploemeur, France
Jean-David Werthel, MD, Institut de la Main, Clinique Jouvenet, Paris, France
Jean Kany, MD, Clinique de l’Union, Saint-Jean, France
Philippe Valenti, MD, Institut de la Main, Clinique Jouvenet, Paris, France
- Anglin C, Wyss UP, Nyffeler RW, Gerber C. Loosening performance of cemented glenoid prosthesis design pairs. Clin Biomech (Bristol,Avon) 2001;16:144-50.
- Boileau P, and others. Cemented polyethylene versus uncemented metal-backed glenoid components in total shoulder arthroplasty: a prospective, double-blind, randomized study. J Shoulder Elbow Surg 2002;11:351-9. http://dx.doi.org/10.1067/mse.2002.125807
- Castagna A, and others. Conversion of shoulder arthroplasty to reverse implants: clinical and radiological results using a modular system. Int Orthop 2013;37:1297-305. http://dx.doi.org/10.1007/s00264-013-1907-4
- Castagna A, and others. Mid-term results of a metal-backed glenoid component in total shoulder replacement. J Bone Joint Surg Br 2010;92:1410-5. http://dx.doi.org/10.1302/0301-620x.92b10.23578
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- Cheung EV, Sperling JW, Cofield RH. Revision shoulder arthroplasty for glenoid component loosening. J Shoulder Elbow Surg 2008;17:371-5. http://dx.doi.org/10.1016/j.jse.2007.09.003
- Colling RC, Stirrat AN, Clement ND, Duckworth AD. An uncemented metal-backed glenoid component in total shoulder arthroplasty for osteoarthritis: factors affecting survival and outcome. J Orthop Sci 2013;18:22-8. http://dx.doi.org/10.1007/s00776-012-0308-7
- Clement ND, Mathur K, Colling R, Stirrat AN. The metal-backed glenoid component in rheumatoid disease: eight- to 14-year follow-up. J Shoulder Elbow Surg 2010;19:749-56. http://dx.doi.org/10.1016/j.jse.2009.11.005
- Clitherow HD, Frampton CM, Astley TM. Effect of glenoid cementation on total shoulder arthroplasty for degenerative arthritis of the shoulder: a review of the New Zealand National Joint Registry. J Shoulder Elbow Surg 2014;23:775-81. http://dx.doi.org/10.1016/j.jse.2013.08.022
- Kany J, and others. A convertible shoulder system: is it useful in total shoulder arthroplasty revisions? Int Orthop 2015;39:299-304. http://dx.doi.org/10.1007/s00264-014-2563-z
- Katz D, and others. New design of a cementless glenoid component in unconstrained shoulder arthroplasty: a prospective medium-term analysis of 143 cases. Eur J Orthop Surg Traumatol 2013;23:27-34. http://dx.doi.org/10.1007/s00590-012-1109-6
- Katz DC, Sauzières P, Valenti P, Kany J. The case for the metal-backed glenoid design in total anatomical shoulder arthroplasty. Eur J Orthop Surg Traumatol 2011;22:9-16. http://dx.doi.org/10.1007/s00590-011-0796-8
- Martin SD, Zurakowski D, Thornhill TS. Uncemented glenoid component in total shoulder arthroplasty. Survivorship and outcomes. J Bone Joint Surg Am 2005;87:1284-92. http://dx.doi.org/10.2106/jbjs.c.00947
- Rosenberg N, and others. Improvements in survival of the uncemented Nottingham Total Shoulder prosthesis: a prospective comparative study. BMC Musculoskelet Disord 2007;8:76. http://dx.doi.org/10.1186/1471-2474-8-76
- Weber-Spickschen TS, Alfke D, Agneskirchner JD. The use of a modular system to convert an anatomical total shoulder arthroplasty to a reverse shoulder arthroplasty: clinical and radiological results. Bone Joint J 2015;97-B:1662-7. http://dx.doi.org/10.1302/0301-620x.97b12.35176
- Werner BC, Dines JS, Dines DM. Platform systems in shoulder arthroplasty. Curr Rev Musculoskelet Med 2016;9:49-53. http://dx.doi.org/10.1007/s12178-016-9317-z
Reference: This letter was submitted to Journal of Shoulder and Elbow Surgery, December 2016, volume 25, Issue 12, Pages e394-e395 DOI: http://dx.doi.org/10.1016/j.jse.2016.05.021
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