Three-dimensional finite element analysis of glenoid replacement prostheses: A comparison of keeled and pegged anchorage systems

Glenoid component loosening is the dominant cause of failure in total shoul der arthroplasty. It is presumed that loosening in the glenoid is caused by high stresses in the cement layer. Several anchorage systems have been des igned with the aim of reducing the loosening rate, the two major categories being ''keeled'' fixation and ''pegged'' fixation. However, no three-dimen sional finite element analysis has been performed to quantify the stresses in the cement or to compare the different glenoid prosthesis anchorage syst ems The objective of this study was to determine the stresses in the cement layer and surrounding bone for glenoid replacement components. A three-dim ensional model of the scapula was generated using CT data for geometry and material property definition. Keeled and pegged designs were inserted into the glenoid, surrounded by a 1-mm layer of bone cement. A 90 deg arm abduct ion load with a full muscle and joint load was applied following van der He lm (1994). Deformations of the prosthesis, stresses in the cement, and stre sses in the bone were calculated Stresses were also calculated for a simula ted case of rheumatoid arthritis (RA) in which bone properties were modifie d to reflect that condition. A maximum principal stress-based failure model was used to predict what quantity of the cement is at risk of failure at t he levels of stress computed. The prediction is that 94 percent (pegged pro sthesis) and 68 percent (keeled prosthesis) of the cement has a greater tha n 95 percent probability of survival in normal bone. In RA bone, however, t he situation is reversed where 86 percent (pegged prosthesis) and 99 percen t (keeled prosthesis) of the cement has a greater than 95 percent probabili ty of survival. Bone stresses are shown to be not much affected by the pros thesis design, except at the tip of the central peg or keel. It is conclude d that a "pegged" anchorage system is superior normal bone, whereas a "keel ed" anchorage system is superior for RA bone. [S0148-0731(00)01804-5].