Laser-engineered net shaping (LENS) of coated surfaces can overcome the limitations of conventional coating technologies. We compared the The Objectives
Methods
Since 1984, we began to use Interface Bioactive Bone Cement (IBBC) technique by interposing osteoconductive and not resorbable crystalline HA granules of 0.3 to 0.6 mm in diameter between bone and bone cement at cementation during surgery. We expected super long term longevity of bone/bone cement bonding in IBBC technique. Specimens were retrieved at the revision THA from the eight patients. They were operated for hip due to OA and RA. Revision THAs were done 4, 6, 8, 10, 13, 14, 18, 19 and 21 years after primary THA due to separation of polyethylene cup with metal-back from the bone cement, late infection and ceramic cup breakage. The specimens were obtained in bloc to keep the bone cement-HA granules-bone interfaces intact. Non-decalcified specimens were cut perpendicular to the interface and were stained by Toluidine blue. They were investigated by an optical microscopy. Cancellous bone entered into the space of HA granules from the cancellous bone base and cortical bone entered into the space of HA granules from the cortical bone base. When several layers of HA granules were smeared densely on the bone, bone ingrowth into the spaces of HA granules was obvious and thick bone layer with HA granules directly contacted to the bone cement. When HA granules were smeared sparsely even if several layer of HA granules were smeared, bone ingrowth into the spaces of HA granules was not dense. Even if one layer of HA granules was smeared sparsely, bone formation was seen around the HA. Through out 4 to 21 years bone ingrowth into the spaces of HA granules was the same at the interface of bone/bone cement. However, at the area existing no HA granule, bone formation at the interface of bone/bone cement decreased after the onset of osteoporosis due to aging. When HA granules were smeared in several layers and densely, thick bone layer with HA granules directly contacted to the bone cement even after 21 years after surgery and after onset of osteoporosis due to aging. As previously reported, the appearance rate of radiolucent line on the radiograph was extremely low even 21 years after surgery. Form these clinical results long term longevity over 30 to 40 years could be expected.
One of important issues of concern in total hip arthroplasty (THA) is osteolysis due to wear debris of ultra-high molecular weight polyethylene (PE), and it often leads to aseptic loosening. Reduction of PE wear debris is essential to prevent osteolysis, and different bearing interfaces as well as improvement of the bearing material itself have been attempted. Alumina ceramics as the bearing material for THA was introduced in Europe and Japan in the 1970s in aim to reduce the PE wear debris. The clinical results have proved the superiority of ceramic on PE couples to metal on PE couples in wear resistance. PE materials cross-liked by irradiation have also demonstrated a significant low wear by in vitro studies. Several types of highly cross-linked polyethylene (CLPE), with the irradiation dose of 50 to 105 kGy, have been developed and extensively used since 1998. In this study, the in vivo wear and oxidation of CLPE acetabular cup combined with ceramic femoral head were evaluated using retrieved cups. Eight retrieved CLPE acetabular cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) with clinical use for 3–80 months (mean 34 months) were examined. All cups were used against alumina or zirconia ceramic femoral heads. The linear wear of the retrieved CLPE cups was measured using a three-dimensional coordinate measurement machine. The worn surfaces of retrieved CLPE cups were observed by a scanning electron microscope (SEM). Oxidative degradation of the retrieved CLPE cups was expressed in terms of an oxidation index which was calculated from microscopic Fourier transformed infrared spectroscopy analysis, according to ASTM F2102. The linear wear rate of retrieved CLPE cups was in 0.006–0.08 mm/year range, which was similar to the results reported by the previous radiographic study. In the worn surface of the CLPE cup retrieved after clinical use shorter than 39 months, machine marks were observed. In contrast, those retrieved after clinical use of 70 and 80 months were smooth. Oxidation indices of retrieved CLPE cups were: 0.12–0.37 in worn surface and 0.13–0.34 in unworn surface, respectively. There was no difference in the oxidation indices between the worn surface and unworn surface. The retrieved CLPE acetabular cups in this study showed low and stable wear rates. The results showed a notable reduction in wear of the CLPE cups compared to that of conventional PE cups in the previous studies. And also, the oxidation indices of the retrieved CLPE cups were the same level as conventional PE cups. These findings from this retrieval study showed that there is neither progressive wear in the clinical use for 3–80 months, material failures due to wear, delamination nor cracks. The lower wear rate and smooth surface of the CLPE acetabular cup suggest the possibility of reduced wear debris from those cups articulated against the ceramic femoral head. We expect that the CLPE acetabular cup has favorable wear properties in long-term clinical use.
Different studies have shown that gamma-irradiated polyethylene generally results in degradation by oxidation. On the other hand, we clinically used ultra-high molecular weight polyethylene sterilized by gamma-irradiation of 1,000kGy dose in the air (100Mrad cross-link polyethylene) for total hip prostheses from 1970 to 1978, and excellent clinical results extending for 30 years were shown. In the present study, the wear characteristics were evaluated by hip simulator on 100Mrad cross-link polyethylene cups which were available after shelf-aging for extremely long term (about 30 years). The results are compared with those ofthe explanted cup after 30 years of clinical use as well as the cups aged by acceleration in order to review the influence of aging environments and themechanism of degradation. The 100Mrad polyethylene cups were manufactured by Mizuho Medical Instruments in the 1970s and they have been in stock on the shelf in air-containing package or without being packed for 30 years. These cups were tested with alumina heads (36mm in diameter) by the AMTI hip-joint simulator. The 100Mrad polyethylene cup aged for 30 years without a package showed considerable initial wear. In case of the same cup aged in an air-containing package, however, a significant reduction of wear was observed even with the presence of the oxidized surface layer. This observation agreed with the low wear of explanted 100Mrad polyethylene after 30 years of clinical use. These results suggest that wear properties of this gamma-irradiated polyethylene are significantly affected by the environmental conditions it was kept for long period of time.
