Today's News

Saturday, February 15, 1997

Study casts doubt that failure of joint prostheses due to pores in cement

An experiment reported Friday in scientific paper 295 casts doubt on previously stated hypotheses which attribute failure of fixation of cemented total joint arthroplasties to fractures from pores within the cement mantle.

The data generated for the study implies that implant shape and the localized forces generated in areas of thin cement mantles appear to have a greater role in the initiation and propagation of cement mantle fractures in cemented hip replacements, said E. Brooke Roberts, MD, Baylor College of Medicine, Houston, Texas.

"Many theories have been developed to explain the etiology of aseptic loosening of cemented femoral prostheses, based on upon mechanisms involving mechanical failure of metal, cement, bone or biological failure secondary to resorption or necrosis of bone," Dr. Brooke said. "While this process is often multifunctional, mechanical failure of the cement mantle and its interfaces appears central to the pathomechanics of failure in many cases.

"Of all of these factors, it has been proposed that voids introduced into the cement during mixing play a significant role in the mechanical failure of the cement mantle under repetitive loading conditions. Various studies have lead to the suggestion that measures which reduce the porosity of the cement mantle may extend the duration of fixation of the components in cemented total joint arthroplasty."

In the specimens studied by Roberts and his colleagues, voids were identified within the cement mantles, but played a relatively minor role in the initiation of fractures. Eleven cadaveric femora with cemented total hip arthroplasties were examined. The femoral components were extracted from three specimens and their cement mantles were examined prior to each being cut into 6 millimeter sections. Coronal sections were made of two specimens to allow examination of the entire cement mantle. The remaining specimens were sectioned transversely with their implants in situ. The sections obtained in the experiment were inspected by stereomicroscopy.

"Incomplete mantle fractures, defined as fractures which did not propagate through the entirety of the cement mantle were observed in 28 of 150 sections (19 percent)," Dr. Robert said. "All fractures appeared to propagate towards the cement/bone interface. Complete mantle fractures, defined as those which propagated through the entire thickness of the cement mantle, were observed in 23 sections (15 percent). Sections from four of the specimens contained 29 pores larger than 1 millimeter in diameter. These pores were randomly distributed throughout the cement mantle of the affected specimens. None of the these voids were associated with either a complete or incomplete fracture of the cement corners of the prosthesis or in areas in which the prosthesis was enveloped by a cement mantle less than 2 millimeters in thickness."

Co-authors of the study, all of Baylor College of Medicine, are Nimish R. Kadakia, MD; Philip C. Noble, PhD; Trent A. Carlyle, MD; and High S. Tullos, MD.