Acta Orthopædica Belgica, Vol. 75 - 2 - 2009 No benefits or funds were received in support of this study The purpose of this retrospective study was to assess the effect of the reduced medialisation of the Arrow R reverse shoulder prosthesis on short-term clinical and radiological results. The clinical and radiological results of 47 Delta III R reverse prostheses and 49 Arrow R reverse prostheses were retrospectively compared at a minimum of twelve months follow-up. There was a significant increase (p < 1.10 -4 ) in range of motion from the preoperative range in the two groups except for internal rotation in the Delta III group (p = 0.1). Radiological analysis on antero- posterior view in neutral position showed greater lateralisation (p < 0.001) with the Arrow prosthesis. Scapular notching was noted in 32 patients with a Delta III prosthesis, and in no instance with an Arrow prosthesis. Complication rates were 14.9% for the Delta group and 10.2% for the Arrow group. The design features of the Arrow prosthesis – reduced medialisation of the center of rotation with lateralisa- tion of the humerus – were found to be associated with slight improvement in range of motion and absence of scapular notching. Keywords : reverse shoulder arthroplasty ; scapular notching. INTRODUCTION Reverse shoulder arthrosplaty can yield satisfac- tory results in patients with pseudoparalysis of the shoulder due to glenohumeral osteoarthritis associ- ated with an irreparable rotator cuff tear (5,25,26, 28,30). Medialising and lowering the center of rota- tion improves the lever arm of the deltoid, particu- larly when the rotator cuff is deficient. This design of reverse prostheses decreases shearing forces at the glenoid component bone interface, and results in improved survival rate of the glenoid component compared with other constrained and semicon- strained designs (5,26,28,30). However medialisation of the center of rotation and of the humerus stem encourages impingement of the humeral polyethyl- ene insert on the scapular neck, resulting in inferior scapular notching. The high rates of scapular notch- ing reported (28,30) adversely affect the mid-term clinical outcome (27) and represent a potential risk of glenoid loosening on the long term (9). As reported by Nyfeller et al (23) mechanical failure of the baseplate has been associated with polyethylene wear, chronic inflammation of the Acta Orthop. Belg., 2009, 75, 158-166 Reverse shoulder arthroplasty : Does reduced medialisation improve radiological and clinical results ? Ibrahim KALOUCHE, Nuno SEVIVAS, Abhijeet WAHEGAONKER, Philippe SAUZIERES, Denis KATZ, Philippe V ALENTI From the Institut de la Main, Paris, and Ter Clinic, Ploemeur, France ORIGINAL STUDY ■ Ibrahim Kalouche, MD, Fellow. ■ Nuno Sevivas, MD, Fellow. ■ Abhijeet Wahegaonker, MD, Fellow. ■ Philippe Sauzières, MD, Orthopaedic surgeon. ■ Philippe Valenti, MD, Orthopaedic surgeon. Institut de la Main, 6 Square Jouvenet, 75016 Paris, France. ■ Denis Katz, MD, Orthopaedic surgeon. Ter Clinic, 56270 Ploemeur, France. Correspondence : Philippe Valenti, M.D., Institut de la main, 6 Square Jouvenet, 75016 Paris, France. E-mail : philippe.valenti@wanadoo.fr © 2009, Acta Orthopædica Belgica.