Effects of preheating of hip prostheses on the stem-cement interface.
BACKGROUND
Debonding of the cement from metal implants has been implicated in the loosening of cemented total hip prostheses. Strengthening of the stem-cement interface has been suggested as a way to prevent loosening of the component. Previously, it was reported that preheating the stem to 44 degrees C reduced the porosity of the cement at the stem-cement interface. The purpose of this study was to determine the effect of stem preheating on the characteristics of the stem-cement interface.


METHODS
The effects of stem preheating, at temperatures of 37 degrees C, 44 degrees C, and 50 degrees C, on the stem-cement interface were studied in a test model and a preparation that closely simulated the clinical situation. Static interface strength was determined initially and after the stems had been kept in isotonic saline solution at 37 degrees C for two weeks. Fatigue lifetimes were measured, and the nature and extent of porosity at the interface were quantified.


RESULTS
Stem preheating had significant effects on the stem-cement interface. Stems preheated to 37 degrees C had greater interface shear strength than stems at room temperature both initially (53% greater strength) and after simulated aging (155% greater strength). Fatigue lifetimes were also improved, and there was a >99% decrease in interface porosity. The setting time of the cement decreased 12%, and the maximum temperature at the cement-bone interface increased 6 degrees C. Similar effects were found after preheating to 44 degrees C and 50 degrees C.


CONCLUSIONS
Stem preheating had significant effects on the stem-cement interface, with significant improvements in the shear strength and cement porosity of the interface. Also, polymerization temperatures at the cement-bone interface increased. The possible biological effects of these increased interface temperatures at the cement-bone interface require further study.
Iesaka
Kazuho
K
Department of Orthopaedic Surgery, Musculoskeletal Research Center, New York University-Hospital for Joint Diseases, New York, NY 10003, USA. kazuho@biomech.org
Jaffe
William L
WL
Kummer
Frederick J
FJ
D019644:Arthroplasty, Replacement, Hip / Q000379:methods; D001843:Bone Cements; D002484:Cementation / Q000379:methods*; D006622:Hip Prosthesis; D006358:Hot Temperature; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D016062:Porosity; D013499:Surface Properties
D001843:Bone Cements