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Comparison of clinical outcomes of reverse shoulder arthroplasty with glenospheres of different designs, diameters and materials

 Reverse total shoulder arthroplasty (RSA) is a relatively recent concept that has proven to provide an effective surgical method in the management of disabling shoulders where no other satisfactory option is available to restore function and limit pain1,2,3,4. The early functional outcome of reverse shoulder prosthesis has been encouraging in short and midterm follow-up1. Nevertheless, the procedure is not without its complications, and many authors advocate caution and advise this prosthesis to be used on carefully selected patients2.The relatively high complication rate when compared with anatomic shoulder replacement also remains a concern.
Scapular notching leads to glenoid erosion because the poly-humeral component is closer to the glenoid component as a consequence of the medialization of the centre of rotation, this causes an abutment of the polyethylene liner against the inferior (anterior/posterior) rim of the glenoid cavity and against the scapular neck, especially at extreme angles of motion. The release of polyethylene debris due to polyethylene liner deformation, (and failure breakage), causes osteolysis. Glenoid erosion is thus a clear result of scapular notching.
The SMR Reverse shoulder system minimises, as far as possible, the main limitations of reverse shoulder prosthesis, and includes alternative designs with eccentric and larger diameter glenospheres in addition to standard ones. This particular design allows the glenosphere to extend in a lower position in  respect to the inferior rim of the glenoid, thus limiting impingement of the humeral insert and the inversion of materials (metal liner and cross-linked UHMWPE glenosphere) reduces PE debris although impingement between liner and bone persists. 
The eccentric design was found to improve range of motion by allowing a higher degree of adduction. Larger diameter glenospheres were found to improve range of motion by increasing adduction and abduction. Compared to the 36 mm concentric (standard) glenosphere, the 36 mm eccentric glenosphere improved adduction by 14.5 degrees, the 44 mm concentric glenosphere improved adduction by 11.6 degrees, the 44 mm eccentric glenosphere improved adduction by 17.7 degrees.
The multicentre retrospective study performed in 5 European shoulder units (Orthopaedie Am Rosenberg, Heiden (Switzerland), Istituto Humanitas, Milano (Italy), Istituti Ortopedici Cremona (Italy), Sportsclinic, Hannover (Germany), Ars Medica Clinic, Gravesano (Switzerland) was designed to compare range of motion, pain level, incidence of scapular notching, implant stability and outcome of 3 types of reverse shoulder arthroplasty.  Between 2003 and 2008, 133 patients were divided in 3 groups: 36 mm standard CoCrMo glenosphere (A), 36 mm eccentric CoCrMo glenosphere (B) and 44 mm X-UHMWPE glenosphere (C)5. The average follow up was 38.3± 17.4 months. In the results, the average CS significantly increased from preoperative assessment to all postoperative time-points for all 3 groups. Group C had a higher and more stable ROM increase and had significantly lower scapular notching than Group B and Group A at all time points. So in conclusion, we found significantly higher scores, better outcomes and a lower rate of complications with the use of 44 mm X-UHMWPE and 36 mm eccentric CoCrMo glenospheres than with the 36 mm standard CoCrMo one due to the decrease inferior notching and to the inversion of the materials. This means increased ROM and faster functional recovery even in worse initial preoperative conditions. 

A. Bischof, MD1, A. Castagna, MD2, P. Budassi, MD3, J. D. Agneskirchner, MD4, C. Domenghini, MD5
M. Borroni, MD2, S. Frattini, MD3, S. Zoni, MD5, H. R. Bloch, MD5 

1 Orthopaedie Am Rosenberg, Heiden (Switzerland) 
2 Istituto Humanitas, Milano (Italy) 
3 Istituti Ortopedici Cremona (Italy) 
4 Sportsclinic, Hannover (Germany) 
5 Ars Medica Clinic, Gravesano (Switzerland) 

 

References 
  1. 1. Neer CS, Craig EV, Fukuda H. Cuff-tear arthropathy. J Bone Joint Surg Am. 1983 Dec;65(9):1232-44. 
  2. Matsen FA, Boileau P, Walch G, Gerber C, Bicknell RT. The reverse total shoulder arhroplasty. J Bone Joint Surg Am 2007;89A:660-7. 
  3. Nicholson GP. Current concepts in reverse shoulder replacement. Curr Opin Orthop 2006;17:306-9. 
  4. Rockwood CA. The reverse total shoulder prosthesis. The new kid on the block. J Bone Joint Surg Am 2007;89A:233-5. 
  5. Castagna A et al; under submission 2011
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