IN-VIVO EFFECT OF PRESSURIZATION OF POLYMETHYL METHACRYLATE BONE-CEMENT - BIOMECHANICAL AND HISTOLOGIC ANALYSIS

Sixteen goats underwent total hip arthroplasty, half with pressurized and half with unpressurized bone-cement. The animals underwent hemiart hroplasty of the contralateral hip immediately prior to sacrifice 6 we eks later. Samples were tested for interface strength and evaluated hi stologically. Pressurization of polymethyl methylacrylate improves the strength of the bone-cement interface in vivo, as well as in vitro. T here is a regional variation in the strength of the bone-cement interf ace both in vivo and in vitro. The regional variation in the in vivo m odel is at least in part due to a biologic effect. Membranes forming a t the bone-cement interface are usually fibrous and incomplete, allowi ng direct cement-to-bone contact. Membranes appear to be involved in t he remodeling of bone. Polymethyl methacrylate causes significant necr osis of the cortex, with ensuing resorption of the cortical bone. Ther e is a small, statistically insignificant trend toward increased resor ption and decreased bone formation with pressurized cement. The amount of necrosis appears to be similar with pressurized and nonpressurized cement. Bone remodels to fill defects in the cement mantle.