To evaluate the effect of hydroxyapatite coating, two same shape cementless stems were compared in this randomized control trial study. Between May 2003 and February 2010, 88 patients had a primary cementless total hip arthroplasty with two different types of cementless stems. Forty-three patients had Proarc stems (P group) (Kyocera Medical, Osaka, Japan), and Forty-five patients had Proarc HA stems (HA group) (Kyocera Medical, Osaka, Japan) which was coated with thin (20 micrometer) hydroxyapatite on Proarc rough porous coating. Gender distribution, average age at surgery, average weight and average follow-up period were same in the two groups. The average follow-up period was 8.5 years (range, 5 to 13 years). The average age at the time of surgery was 63 years. Porous acetabular shells and highly crosslinked polyethylene liners made by Kyocera Medical corporation were implanted into all hips. Stems were implanted with a modified Hardinge surgical approach without trochanteric osteotomy. Harris Hip Score was used for clinical evaluation. Post-op radiographs of these patients were evaluated. Fisher's exact probability test was used for statistical analysis. P values of less than 0.05 were considered to be significant.Introduction
Methods
The material properties of gamma irradiated Ultra High Molecular Weight (UHMW) polyethylene are known to degrade during exposure to air. Though gamma inert-sterilization has been developed to decrease free radicals, the rate of degeneration of UHMW polyethylene in vivo has not well known. This study aimed to compare the properties of gamma inert-irradiated highly-cross-linked UHMW polyethylene samples after exposure to air and the properties of gamma inert-irradiated highly-crosslinked UHMW polyethylene samples after exposure to liquid. UHMW polyethylene samples were machined from heat-compressed sheet made of medical grade GUR 1050 (Ticona, Kelsterbach, Germany). Samples were rectangular, where the dimensions were 50mm in length, 5 mm in width and 2 mm in thickness. Samples were divided into four groups of 0, 60, 100 and 200 kGy irradiation in N2 gas. These samples were then exposed to air or Ringer’s solution for half a year. Dynamic vis-coelastic measurements and, Fourier Transform Infrared Spectrometry (FTIR) and Electron Spin Resonance (ESR) analyses were performed on samples immediately after inert-irradiation, after half-year-exposure to 25°C air (Air-exposure) and after half-year-exposure to 37°C Ringer’s solution (Liquid-exposure). Dynamic viscoelastic measurements were conducted over a temperature range of −150 to 350°C using a Dynamic Mechanical Spectrometer (Seiko Instruments, Osaka, Japan). FTIR analysis was conducted using a Perkin-Elmer Spectra BX (Norwalk, CT) with 100-μm thick slices. ESR analysis was also conducted using a JES-TE200 (Nippon-Denshi, Akishima, Japan). Although the dynamic viscoelastic performance of 0 kGy irradiated storage sample was not different from that of original sample, the loss tangent value (tanδ, E”/E’) of 60, 100 and 200 kGy irradiated storage samples was different from that of original samples (Fig. 1). The difference of Liquid-exposure was larger than that of Air-exposure. Although a FTIR peak at 1718 cm-1 wave numbers was not observed in 0 kGy irradiated storage sample, obvious peak was observed in 100 and 200 kGy irradiated storage samples (Fig. 2). The peak of Liquid-exposure was larger than that of Air-exposure. The ESR analysis showed free radicals in storage samples. The dynamic viscoelastic performance of 60, 100, 200 kGy irradiated storage sample was different from that of original sample, whereas the performance of 0 kGy irradiated storage sample was not different from that of original sample. The difference of Liquid-exposure was larger than that of Air-exposure. The storage modulus value of 60, 100, 200 kGy irradiated Liquid-exposure decreased and the reason for this was thought to be chain scission by oxidation for half-year exposure to Ringer’s solution. Obvious FTIR peak at 1718 cm-1 wave numbers was observed in 100 and 200 kGy irradiated storage samples. The peak of Liquid-exposure was larger than that of Air-exposure. This indicated that the oxidation of Liquid-exposure quickly progressed during half-year storage and the reason for this was thought to be chain scission by high liquid temperature. The results of the present study suggested that the properties of gamma irradiated UHMW polyethylene quickly degraded in vivo.
