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 hemiarthroplasty of the contralateral hip immediately prior to sacrifice 6 weeks later. Samples were tested for interface strength and evaluated histologically. Pressurization of polymethyl methylacrylate improves the strength of the bone-cement interface in vivo, as well as in vitro. There is a regional variation in the strength of the bone-cement interface both in vivo and in vitro. The regional variation in the in vivo model is at least in part due to a biologic effect. Membranes forming at the bone-cement interface are usually fibrous and incomplete, allowing direct cement-to-bone contact. Membranes appear to be involved in the remodeling of bone. Polymethyl methacrylate causes significant necrosis of the cortex, with ensuing resorption of the cortical bone. There is a small, statistically insignificant trend toward increased resorption 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.