Loosening performance of cemented glenoid prosthesis design pairs C. Anglin a,b, * , U.P. Wyss a,b , R.W. Nyeler c , C. Gerber c a Sulzer Orthopedics Ltd., P.O. Box 65, 8404 Winterthur, Switzerland b Queen's University, Kingston, Canada c Department of Orthopaedics, University of Zurich, Balgrist, Zurich, Switzerland Received 31 May 2000; accepted 27 September 2000 Abstract Objective. The purpose of this pilot study n 3) was to compare the loosening performance of glenoid prosthesis design pairs where only one design variable diered. Design. Glenoids were subjected to dynamic edge loading in a biaxial test setup. Background. Glenoid component loosening is the primary concern in total shoulder arthroplasty. Methods. After the humeral head was cycled 100,000 times to the superior and inferior edges of the glenoid, the tensile edge displacements were measured under superior and inferior o-center loading. Results and conclusions. Based on this study, a rough-backed design had dramatically better loosening performance than a smooth-backed; curved-backed was superior to ¯at-backed; a less-constrained articular surface was better than a more-constrained articular surface; pegs outperformed a keel; threaded pegs were marginally preferable to cylindrical pegs; and an all-polyethylene design rocked slightly less than a metal-mesh-backed design. Relevance A comparison of the laboratory loosening behavior of glenoid prostheses may lead to improved designs, subsequently leading to a reduction in the incidence of clinical loosening. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Shoulder arthroplasty; Glenoid; Loosening; Dynamic testing 1. Introduction Loosening of the glenoid component is clearly the primary concern in total shoulder arthroplasty [1±3]. Although the causes of loosening are multi-factorial, glenoid design plays an important role; this was most dramatically demonstrated by the high loosening rates of fully-constrained prostheses [1,2]. Many dierent glenoid designs are available, having dierent articulation radii, ¯ange shapes, ®xation fea- tures, and materials. Little evidence exists favoring one design over another. Although the gold standard would be a randomized prospective clinical trial of comparable pairs, this has not been done to our knowledge. Another possibility, as done in this study, is to compare the loosening performance using a physical test under con- trolled conditions. The purpose of this study was to identify the pre- ferred design characteristics of a glenoid prosthesis with respect to reducing the likelihood of loosening. 2. Methods The major cause of glenoid loosening is considered to be o-center loading, called the ``rocking-horse'' phe- nomenon [4]. A laboratory test was developed to com- pare the loosening performance of glenoid prostheses based on the tensile displacement of o-center-loaded prostheses after dynamic rocking of the prosthesis [5]. This test method was recently accepted as an industry standard by the American Society for Testing and Ma- terials ASTM) [6]. The test's concept is to load the superior and infe- rior rims of the glenoid cyclically Fig. 1). The cyclic loading was achieved using a bi-axial apparatus: the humeral head was compressed horizontally into the glenoid at a constant load, 750 5 N, by a 50 mm Clinical Biomechanics 16 2001) 144±150 www.elsevier.com/locate/clinbiomech * Corresponding author. Address: 2865 Revelstoke Court, Van- couver, BC, Canada V6T 1N8. E-mail address: carolynanderic@telus.net C. Anglin). 0268-0033/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0268-003300)00078-4