Does keel size, the use of screws, and the use of bone cement affect fixation of a metal glenoid implant? Ryan T. Bicknell, MSc, MD, a Allan S. L. Liew, MD, FRCSC, a Matthew R. Danter, BSc(Hon), b Stuart D. Patterson, MBChB, FRCSC, a,b Graham J. W. King, MD, FRCSC, a,b,c,d David G. Chess, MD, FRCSC, a,b,c,d and James A. Johnson, PhD a,b,c,d London, Ontario, Canada The objective of this study was to determine the effect of screws and keel size on the fixation of an all-metal glenoid component. A prototype stainless-steel glenoid component was designed and implanted in 10 cadav- eric scapulae. A testing apparatus capable of produc- ing a loading vector at various angles, magnitudes, and directions was used. The independent variables included six directions and three angles of joint load, and five fixation modalities—three different-sized cross- keels (small, medium, and large), screws, and bone cement. Implant micromotion relative to bone was measured by four displacement transducers at the su- perior, inferior, anterior, and posterior sites. The com- ponents displayed a consistent response to loading of ipsilateral compression and contralateral distraction. Use of progressively larger keels did not significantly improve implant stability. Stability decreased as the angle of load application increased (P  .05). Screw and cement fixation resulted in the most stable fixation (P  .05). (J Shoulder Elbow Surg 2003;12:268-75.) L oosening of the glenoid component remains a fac- tor limiting the long-term success of total shoulder arthroplasty. 19,22,51,56,57 Various designs have at- tempted to achieve fixation to bone through the use of anchoring systems on the undersurface of the glenoid component. In vitro studies have been conducted to assess the strength of fixation and the stability or micromotion of various implant designs relative to bone. 2,8,9,17,34,46 Theoretical finite element studies have also analyzed the state of stress in the implant-bone struc- ture. 16,32,33,45,46,52 However, these studies have not conclusively defined the optimal method(s) to maxi- mize the stability between the glenoid component and bone. The objective of this study was to determine the effect of various fixation modalities on the relative motion between the glenoid component and bone. Two design features were included in order to in- crease the possibility of achieving optimal stability of the implant to bone. First, an all-metal glenoid implant prototype was developed. The use of an all-metal prosthetic component presents the advantage of a thinner implant in comparison to currently used poly- ethylene implants. Thicker components currently in use may produce overstuffing of the joint and in- creased lateral offset of the humeral head. This affects the moment arms of muscles attached to the humerus, altering the associated articular joint contact pres- sure. 21 Moreover, a thinner component will reduce the eccentricity of the joint reaction force, reducing the tilting moment at the implant-bone interface. Sec- ond, in addition to the standard keel in the coronal plane, another keel placed orthogonally in the trans- verse plane was included. This provided the potential to counteract superiorly and inferiorly directed joint forces. Our specific aims were to determine the effect of cross-keel size, supplemental screw fixation, and ce- menting on the stability of uncemented all-metal gle- noid components. We hypothesized that increasing keel size, as well as supplemental screw fixation, would improve implant stability as quantified by the magnitude of micromotion between implant and bone. MATERIALS AND METHODS Implant design With the use of data obtained from a previous anthro- pometric investigation of the glenoid, 6 a prototype all- metal, stainless-steel glenoid component with three cross- keel sizes (small, medium, and large) was developed for use in this study (Figure 1). The articular surface of the component was based on the Neer II component (3M, Orthopaedic Products Division, St Paul, Minn). 18,27 This From the Departments of Surgery, a Mechanical and Materials Engineering, c and Medical Biophysics, d University of Western Ontario; and Hand and Upper Limb Centre, St Joseph’s Health Centre b . Reprint requests: James A. Johnson, PhD, Hand and Upper Limb Centre, St Joseph’s Health Centre, 268 Grosvenor St, London, ON, Canada, N6A 4L6 (E-mail: jajohnso@uwo.ca). Copyright © 2003 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2003/$35.00 + 0 doi:1067/msc.2003.27 268