One of serious issues in total hip arthroplasty (THA) is the osteolysis which results in aseptic loosening caused by the wear particles from a polyethylene (PE) acetabular cup. In addition, oxidation degradation of PE cup resulting in the fracture or the severe wear caused by the reduction of mechanical properties in vivo is also the issue. The oxidation degradation is considered to be induced by residual free radicals generated by gamma-ray irradiation for cross-linking to reduce wear or for sterilization. In this study, (1) wear property, (2) oxidation degradation of retrieved PE and highly cross-linked PE (CLPE) cups against alumina ceramic femoral heads, and (3) the correlation between those properties were evaluated.

The radiographic wear of six conventional PE cups with the mean follow-up of 19.1–23.3 years and 60 CLPE cups with the mean follow-up of 3.1–9.1 years were measured by a non-radiostereometric analysis method (Vectorworks^® 10.5 software package). As a retrieval analysis, 26 retrieved acetabular cups were evaluated; 16 cups were ethylene oxide gas-sterilized conventional PE cups with clinical use for 16.0–24.9 years and 10 cups were gamma-ray-sterilized CLPE cups with clinical use for 0.9–6.7 years. The linear and the volumetric wear were measured using a three-dimensional (3D) coordinate measurement machine. The shapes of unworn and worn surfaces with 15- and 30-point intervals, respectively, were measured. Oxidation degradation of the surface, sub-surface and inner for both worn and unworn parts of the retrieved cups was measured using a Fourier-transform infrared (FT-IR) spectroscopy. Oxidation indices were calculated using the peak at 1740 cm⁻¹ and 1370 cm⁻¹ according to ASTM F2012.

In the radiographic analysis, the linear wear rate of CLPE cups was significantly lower than that of conventional PE cups [Fig. 1]. In the retrieval analysis, the linear wear rate of CLPE cups (mean: 0.07 mm/year) showed a 51% reduction (p = 0.002) compared to conventional PE cups (mean: 0.14 mm/year) [Fig. 2]. The retrieval and the radiographic analysis for both conventional PE and CLPE cups showed similar results (p = 0.7 and 0.1, respectively). Maximum oxidation indices for CLPE cups were similar to those of conventional PE cups regardless of the difference of clinical duration [Fig. 3]. This result is different from in vivo wear, which increases as the clinical duration. For both conventional PE and CLPE cups, the oxidation indices of subsurface were higher than those for surface. The worn parts showed higher oxidation indices than those for unworn parts. From the results, even when the free radicals were so few or absent, the oxidation degradation would be induced in vivo.

In conclusion, the wear resistance for CLPE cups was greater than that for conventional PE cups from both radiographic and retrieval analyses. The in vivo oxidation degradation might not be caused by only residual free radicals. It was found that oxidation degradation of PE cups when used with alumina ceramic femoral heads is not correlated to their wear properties.

In total hip arthroplasty (THA), aseptic loosening induced by polyethylene (PE) wear debris is the most important cause that limits the longevity of implants. Abrasive wear generated through the mechanism such that micrometer-roughened regions and small asperities on the metallic femoral heads surface locally plow through the PE cup surface. Abrasive wear results in the PE material being removed from the track traced by the asperity during the motion of the metallic femoral heads surface. For the purpose of reducing wear, alumina ceramics was introduced in Europe and Japan in 1970s. The clinical results of ceramic-on-PE bearings regarding the wear resistance have been superior to that of the metal-on-PE bearings. Compared with Co–Cr–Mo alloys, alumina ceramics is advantageous for precision machining because of its higher hardness, enable to form spherical and smooth surface. The fracture resistance of the alumina ceramics itself is related to grain size; the grain size reduction leads to the improvement of its resistance. In this study, we evaluated the roundness and the roughness of retrieved two distinct alumina ceramics having different grain size, and Co–Cr–Mo alloy heads.

Fourteen retrieved alumina ceramic femoral heads; ten heads with a diameter of 28 mm made of small grain size alumina (SG-alumina; mean grain size is 3.4 μm) with clinical use for 16–28 years and four heads with a diameter of 26 mm made of extra-small grain size alumina (XSG-alumina; mean grain size is 1.3 μm) with clinical use for 14–19 years, were examined. Six retrieved Co–Cr–Mo alloy femoral heads with a diameter of from 22 to 32 mm with average clinical use for 12–28 years were examined.

SG-alumina and XSG-alumina heads showed significantly lower roundness compared with Co–Cr–Mo alloy heads, due to higher precision machining [Fig. 1]. The surface roughness for the contact area of the heads increased in order of XSG-alumina, SG-alumina and Co–Cr–Mo alloy. The surface roughness of the non-contact area for all kinds of heads was lower than that for the contact area [Fig. 2]. Surface profiles of the SG-alumina and XSG-alumina showed the reentrant surface while Co–Cr–Mo alloy heads showed the protrusion surface. The roundness and roughness of the Co–Cr–Mo alloy or ceramic surface and the presence or absence of hard third-body particles correlate to the amount of abrasive PE wear. When the third-body was entrapped during the clinical use, a reentrant surface might be formed on the ceramic while protrusion surface formed on the Co–Cr–Mo alloy. The differences in clinical results may be due in part to the influence of third-body particles. The ceramic becomes more resistant than Co–Cr–Mo alloy against the scratching by the entrapped abrasive contaminants because of its harder surface. From the good clinical results of more than 20 years using SG-alumina, the greater long term clinical results using XSG-alumina will be expected.

Different types of highly cross-linked polyethylene (HXLPE) have been introduced widely in acetabular cups in hip prostheses to reduce the incidence of wear debris-induced osteolysis. Also, we reported that HXLPE cups with 28-mm alumina ceramic femoral head exhibited lower wear than conventional PE cups. Recently, the combination of HXLPE cup and larger diameter femoral head is used widely to prevent dislocation. In this study, we examined the wear of HXLPE with 32-mm alumina ceramic femoral head and compared it with the wear of HXLPE with 28-mm alumina ceramic femoral head.

The in vivo wear of 60 HXLPE cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) with 28-mm alumina ceramic femoral head with clinical use for 3.1–9.1 years (mean 7.4 years) and eight HXLPE cups with 32-mm alumina ceramic femoral head used for 2.3–3.2 years (mean 2.8 years) were examined by radiographic analysis.

The early wear rate for the first year of HXLPE cups with 28-mm and 32-mm alumina ceramic femoral head were 0.24±0.10 mm/year and 0.29±0.12 mm/year respectively. There was no significant difference in both femoral head groups (p>0.05). The steady wear rate after 1 year were 0.001±0.03 mm/year and −0.03±0.10 mm/year respectively. There was no significant difference either in both femoral head groups (p>0.05).

These findings from this radiographic analysis suggest that the early wear rate in the first 1 year probably represents the creep deformation in bedding-in stage; and the steady wear rate after 1 year probably represents mainly the wear than of the creep deformation. By the radiographic analysis, HXLPE cups in both femoral head groups exhibited low steady wear rate.

In conclusion, we expect that the combination of HXLPE cup and 32-mm diameter alumina ceramic femoral head has favorable wear properties with possibility of prevention of dislocation in long-term clinical use.

INTRODICTION

Since 1985, not resorbable crystalline osteoconductive hydroxyapatite (HA) granules were interposed on the interface between bone and bone cement at the cementation (Interface Bioactive Bone Cement: IBBC) of total hip arthoplasty (THA) to prevent generation of connective tissue and osteolysis for the longevity of cemented THA. To prevent the patients from infection, we are planning to use b-tricalcium phosphate (Beta-TCP) impregnated with antibiotics along with HA granules. However, there have been no reports on the loading and release of antibiotics from fine granules of Beta-TCP. Here, we have investigated the loading of antibiotics on Beta-TCP and their release in vivo.

INTRODUCTION

We have conducted interface bioactive bone cement method (IBBC) in total hip arthoplasty (THA) to prevent generation of connective tissue and osteolysis for the longevity of cemented THA since 1985, in which non-resorbable crystalline osteoconductive hydroxyapatite (HA) granules were interposed on the interface between bone and bone cement. To prevent the patients from infection, we use HA granules impregnated with antibiotics. However, there have been no reports on the loading and release of antibiotics from fine granules of HA. Here, we have investigated the loading of antibiotics on HA and their release in vitro.

In total hip arthroplasty (THA), one of concerned issues is osteolysis due to wear debris of ultra-high molecular weight polyethylene (PE) which often leads to aseptic loosening. Reduction of PE wear debris is essential to prevent osteolysis, and different bearing combination as well as improvement of the bearing material itself have been attempted. Hence alumina ceramics was introduced for THA, aiming to reduce PE wear debris. Ceramic on PE couple showed good results in clinical wear compared with metal on PE couples. Highly cross-linked PE (HXLPE) with gamma-ray or electron-beam irradiation followed by thermal treatment has also demonstrated a remarkably low wear in the previous in vitro studies. In in vivo studies, the wear of HXLPE acetabular cups against alumina ceramic femoral head was evaluated to compare with that of conventional PE cups against alumina ceramic femoral head.

The in vivo wear of 61 HXLPE cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) against alumina ceramic femoral head of 28 mm in diameter with clinical use for 2.1–7.1 years (mean 5.6 years) and eight conventional PE cups against an alumina ceramic femoral head of 28 mm in diameter used for 18.7–23.3 years (mean 20.4 years) were examined by radiographic analysis with Vector Works 10.5. The in vivo wear of eight retrieved HXLPE cups with clinical use for 0.9–6.7 years (mean 2.9 years) and 14 retrieved conventional PE cups used for 16.0–28.0 years (mean 22.0 years) were examined by using a three-dimensional coordinate measuring machine. The worn surfaces of retrieved HXLPE and conventional PE cups were observed by a scanning electron microscope.

In the radiographic study, penetration rate of alumina head into HXLPE and conventional PE for the first 1 year were 0.24 mm/year and 0.34 mm/year respectively. One year later, the HXLPE showed significant lower penetration rate of 0.001 mm/year than the conventional PE penetration rate of 0.12 mm/year (p< 0.01). By the retrieval analysis, the mean penetration of retrieved HXLPE and conventional PE cups were 0.11 and 2.97 mm, and they were similar to the results by radiographic analysis. In the worn surface of the retrieved HXLPE cups used for around 1 year, machine marks were observed. In contrast, the worn surface of the retrieved HXLPE cups used for more than five years were smooth, and furthermore, in high magnification observation they had wear morphology different from conventional PE. These findings from this retrieval study suggest the penetration in the first 1 year detected by radiographic measurement was probably caused by creep deformation in bedding-in stage; and 1 year after, the penetration was probably caused mainly by wear.

By the radiographic analysis, HXLPE cups against alumina ceramic femoral head has a 99 % lower wear rate compared with conventional PE cups. Also, retrieved HXLPE cups against alumina ceramic femoral head exhibited lower wear compared with conventional PE cups. In conclusion, we expect that the HXLPE cup used with alumina ceramic femoral head has favorable wear properties in long-term clinical use.

A consensus on total hip arthroplasty (THA) concluded that the major remaining issues of concern included the long-term fixation of the joint replacement, osteolysis due to poluethylene (PE) wear debris which often leads to aseptic loosening. Alumina ceramics had been extensively used in medicine, and we started using the alumina ceramic for THA bearing surface in hopes to reduce the PE debris. It was because alumina ceramics is advantageous for precision machining compared with metal materials, and its hardness is higher than that of metal materials. Also, to augment cement–bone bonding, we interposed hydroxyl apatite (HA) granules at the cement–bone interface, so called “Interface Bioactive Bone Cement (IBBC) technique”. HA granules (2–3 g) were smeared on the bone surface of the acetabulum and femur just before cementing. In this study, we evaluated 19–22 years clinical results of THA with alumina ceramic head combined with PE cup fixated IBBC technique.

Total 285 joints (212 patients) were implanted by one senior surgeon from January 1986 to December 1988, and 265 joints (192 patients) were traceable. Alumina ceramic femoral head of 28 mm in diameter and acetabular cup of the conventional PE sterilized with ethylene oxide gas were used in all patients. The PE cup and stem were fixed with IBBC technique in all cases. The presence of radiolucent line, loosening and osteolysis were observed using radiograph of the traceable cases. The locations of radiolucent lines were identified according to the zones described by DeLee and Charnley for acetabular cups and the zones described by Gruen et al. for femoral stems. The in vivo wear of 21 PE acetabular cups for 19.0–21.9 years (mean 20.3 years) was measured from the latest radiographs using computer assistant technique with Vector Works 10.5 software.

Features of the clinical radiograph images of the IBBC case were classified as follows: the radiolucent line represented “gap” between the HA layer and the cement; the loosening represented “opening” between the HA layer and the cement. For the quantitative analysis, we divided the surrounding bones of the THA into several zones as done in the previous studies. The “gap” appeared in zone 4 in three joints (1.4 %), in zone 3 in two joints (0.9 %) of acetabular cup. In femoral side, in zone 1 in four joints (1.8 %) in zone 7 in one joint (0.4 %). The “opening” appeared in three acetabular cup (1.4 %). Since no opening was appeared in zone 3 or zone 4, however, no re-operation was needed. Images of osteolysis were seen one in zone 1 (0.5 %), and one in zone 2 (0.5 %) in acetabular side and two in zone 1 (0.9 %) of the femur. The mean linear wear rate of PE acetabular cups was 0.13 mm/year.

The fixation to the bone by the IBBC technique has been maintained for long term. We think that the result was brought by the biological integration between bone and HA granules. In conclusion, this study has shown satisfactory results of the cemented THA with ceramic head combined with PE cup for 19–22 years.

Aseptic loosening induced by wear debris of polyethylene (PE) is the most common cause of long-term total hip arthroplasty failure. In the previous studies, we reported that the protruding contour and surface morphology of metallic femoral head brought an increase of PE wear. Alumina ceramics is advantageous (neutral shape and smooth surface) for precision machining compared with metal materials, because hardness of ceramics is higher than that of metal materials. In this study, we measured the roundness and the roughness of retrieved alumina ceramic and metallic heads, aiming to evaluate the change of surface morphology of those heads in vivo.

Fourteen retrieved alumina ceramic femoral heads (Kyocera Corp., currently Japan Medical Materials Corp.) were examined: ten femoral heads were made of small grain-size alumina ceramic (SG-alumina; mean grain size is 3.4 um) with a diameter of 28 mm, with clinical use for 16–28 years (mean 22 years) and four femoral head was made of extra-small-grain size alumina ceramic (XSG-alumina; mean grain size is 1.3 um) with a diameter of 26 mm, with clinical use for 14–19 years (mean 16 years). Six retrieved metallic femoral heads with average clinical use for 12–28 years (mean 18 years) were examined: a diameter of from 22 to 32 mm (e.g. Zimmer Inc., Stryker Corp.) The roundness of the retrieved femoral heads was measured by a contour tracer. The surface roughness in the contact area and the non-contact area of the retrieved femoral heads was measured by a surface roughness tester.

Out-of-roundness of SG-alumina and XSG-alumina heads was 0.15 um and 0.19 um, respectively. In contrast, that of metal heads was 2.43 um, and the profiles were in wide distortion compared with both alumina heads. The surface roughness was 0.012 um in the contact area, and 0.009 um in the non-contact area of retrieved SG-alumina heads. The surface roughness in the contact area, 0.007 um, of XSG-alumina was slightly higher than that in the non-contact area, 0.003 um, and the both area of XSG-alumina represent lower value than SG-alumina, with all alumina heads having a reentrant surface profile. In contrast, the surface roughness of metallic heads was in a range of 0.003–0.053 um and several heads showed the protrusion surface profile.

In this retrieval study, the roundness and the roughness of both alumina ceramic femoral heads after long-term clinical use were low and stable compared with metallic heads. And also, the surface roughness increased in the order of XSG-alumina < SG-alumina < metallic head. The alumina ceramic femoral head showed the reentrant surface whereas the metallic head showed the protruding surface. When third-body wear occurs during the clinical use, generally reentrant form may occur on the ceramic surface whereas protrusion form may occur on the metallic surface. We have good clinical results more than 20 years using the SG-alumina, and clinical results for a long term will be expected with XSG-alumina of improved microstructure.

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.

Introduction: Recently, highly cross-linked polyethylene has been highlighted in THAs, which is thought to reduce wear. However, little is known about an accurate nature of cross-linked polyethylene particles and long term wear in vivo. One of the authors implanted all polyethylene cups irradiated by 100 Mrad in 1970’s. Recently, we performed two revisions with this cup. In the present study, we extracted polyethylene particles and analyzed them.

Methods: Case1 was revised for a stem fracture and ace-tabular loosening at 25 years postoperatively and case2 for acetabular loosening at 27 years postoperatively. There was no osteolysis on X rays. We extracted polyethylene particles using a tiussue digestion and iamge analysis using computed iamge analyzer developed by Cambell.

Results: Equivalent circle diameter (ECD) was 0.73mm, roundness was 0.69, aspect ratio (AR) was 1.4 and number of particles was 6.0x108/g wet tissue in case1. ECD was 0.57mm, roundness was 0.62, AR was 1.54 and number of particles was 5.8x108/g in case2. SEM showed that granule or globular shapes were abundant and fibril shapes were rare.

Discussion and conclusion: Cross-linked polyethylene particles were less, a little smaller and much rounder in compared with our previous result of conventional polyethylene particles in peri-implant tissue after more than 25 years postoperatively in vivo.

Introduction: In 1970’s, Oonishi et al found out that the polyethylene cross-linked by gamma-ray irradiation (dose=100Mrad) had high wear performance, and then clinically used it as the material for acetabular sockets. He has reported excellent outcomes. In this study, we measured the wear three-dimensionally, and the oxidation by microscopic Fourier transform infrared spectrophotometry in retrieved high-dose cross-linked polyethylene [100Mrad PE] sockets implanted over 25 years.

Materials and methods: We revised two 100Mrad PE sockets (SOM type manufactured by Mizuho medical (JAPAN)), due to aseptic loosening, which had been implanted for 27 years approximately. The liner and volumetric wear were measured as previously reported [1]. Measuring points for oxidation index were (1) near surface point in unworn area, (2) near surface point in worn area, and (3) inner area which left any surface by > =2.5mm.

Results and discussion: The liner wears were 0.06mm and 0.29mm respectively. The volumetric wears were 25.8mm3 and 91.8mm3. The liner-wear rate of them were 0.002mm/year and 0.010 mm/year. The oxide index of each socket was 0.75, 0.62, 0.25 and 1.73, 0.67, 0.28, in order of the unworn area, the worn area and the inner area. Many researchers have reported that the annual liner-wear rate of UHMWPE sockets is from 0.1 to 0.2mm/year. We showed extremely less wear rate of the 100 Mrad PE sockets in comparison with UHMWPE sockets. Oxidation index in the worn area was approximately the same as that of UHMWPE sockets, which were determined in our previous study [2]. These results showed that 100Mrad PE sockets had maintained the high performance to the wear for long-term clinical use.

Introduction: The excellent character of cross-linked polyethylene on wear has been reported from basic researches. However, few clinical results were seen about irradiated polyethylene sockets. This presentation reports a long-term clinical result of irradiated polyethylene sockets.

Material and method: Two 100M-rad gamma irradiated polyethylene sockets were retrieved, each 25 and 27 years after implantation. Socket joint surface were scanned by 3-D scanner and analyzed. On the other hand, ten patients had total hip replacements with 6.5M-rad irradiated polyethylene sockets. Anterior-posterior and lateral radiograph were taken and the movement of the head to the socket was analyzed by 3-D wear measurement software GAWDI. The results were compared to conventional polyethylene sockets of matched patients.

Results: Wear of the 100M-rad sockets were 0.23mm/ 25yrs and 0.46mm/27yrs respectively. The direction of wear was observed over the whole surface. Wear of the conventional polyethylene socket retrieved 15yrs after implantation were 2.54mm/15yes and 1.76mm/12yrs. The wear were toward weight bearing directions.

The average movement of heads in 6.5M-rad irradiated polyethylene sockets was 0.22mm one year post operation and its direction was toward backside of patients’ body. The average movement of conventional polyethylene sockets was 0.24mm one year post operation and its direction was just the same as irradiated polyethylene sockets.

Discussion: The difference of long term results between 100M-rad irradiated polyethylene and conventional one was obvious. A definite wear path way was observed on conventional polyethylene sockets. However, it was ambiguous on 100M-rad irradiated polyethylene because it was small or it did not exist. No remarkable difference was observed in short term after operation between 6.5M-rad irradiated and conventional sockets. The present analysis suggests that a high dose irradiated polyethylene socket may benefit a good long-term clinical result.

According to the knee simulator test results in 1970s, the total decrease in thickness of UHMWPE tibial tray in combination with ceramic femoral component [F-Comp] was less than one tenth as that of the combination with metal [1]. These advantages led to development of total knee prosthesis [TKP] with alumina ceramics. In this study, we report the wear surface observation, the clinical wear and the oxidation of the retrieved TKP used clinically for 23 years, comparing with a metal TKP.

The retrieved TKP was implanted in 1979, and retrieved on January 9th in 2002. This TKP consisted of an alumina ceramic F-Comp and a UHMWPE tray combined with a alumina ceramic tibial component. Observations of the surface of alumina F-Comp and UHMWPE tray were carried out using SEM. Shape of UHMWPE tray was determined three-dimensionally. Comparing the result with original shape based on the product’s plan, liner wear and volumetric wear were calculated. Oxidation index was determined by Fourier transform infrared spectrophotometry.

Alumina F-Comp did not have any scratch on the surface by seeing with naked eye. UHMWPE tray had deformation and scratches obviously. The liner wear rate was 37 micrometer/year and volumetric wear rate was 18.8 mm3/year. The oxidation indexes were 0.6 in the unworn area, 1.2 in the worn area and 0.2 in the inner area.

SEM observations of the F-Comp demonstrated no scratch or pit. In contrast, many scratches were clearly observed on the UHMWPE tray. However, higher magnification observations did not demonstrate severe wear, which was shown on the wear analysis of a metallic F-Comp. Oxidation degradation is a problem to solve. However, the low wear rate and mild wear pattern demonstrate that ceramic F-Comp reduced UHMWPE wear.

Improved cement technique by interposing less than two layers of hydroxyapatite (HA) granules between bone and bone cement at the cementing (Interface Bio-active Bone Cement : IBBC) have been performed in total knee arthroplasty (TKA) since 1987.

We performed IBBC technique in 153 knees (130 patients) in TKA from 1987 to 1993. One hundred and forty knees (120 patients) could be followed up clinically and radiologically. Follow up rate was 91.5%. A mean follow-up period was 9.5 years (6 to 13 years) after surgery. As a control, clinical results of TKA with conventional cementing (Non-IBBC) which were operated in 44 knees (44 patients) in 1986 were used.

In IBBC cases, radiolucent lines on the tibial components were seen 7.1%, 2.9%, 1.4%, 3.6%, 0%, 0% and 0% at Zone ‡T to ‡Z of the anteroposterior view, while in Non-IBBC cases, 40.9%, 13.6%, 9.1%, 27.3%, 11.4%, 4.5% and 13.6% at Zone ‡T to ‡Z, respectively. In IBBC cases peri-prosthetic osteolysis of the tibial components were seen in three knees (2.1%), while 29.5% in Non-IBBC cases. Aseptic loosening of the tibial component was only one case (0.7%) in IBBC cases, while 9.1% in Non-IBBC cases.

In IBBC, bone cement bound to HA mechanically immediately after surgery and HA granules bound to the bone physicochemically after bone ingrowth into the spaces around the HA granules. In Non-IBBC, spaces will appear between bone and bone cement due to osteoporosis and/or atrophy after long years. However, in IBBC, bone and bone cement will contact by interposing HA forever due to osteoconductive effect of HA.

In conclusion, the IBBC has significantly reduced the incidence of radiolucent lines and periprosthetic osteolysis in TKAs. IBBC is a method combining the advantage of cementless HA coating and bone cement.

We have used Interface Bioactive Bone Cement (IBBC) in all cases of total joint arthroplasties since 1987. The method is improved cement technique by interposing less than two layers of hydroxyapatite (HA) granules between bone and the polymethylmethacrylate (PMMA) bone cement. We report one patient who underwent revision surgery after total knee arthroplasty (TKA) using IBBC.

The patient is a woman aged 70 years at the time of revision surgery. Right TKA was performed with the diagnosis of rheumatoid arthritis. An alumina ceramic total knee prosthesis was inserted using IBBC. Pain and walking ability were once improved after the primary TKA. However, the gait disturbance recurred after the patient fell on the ground. Radiographic findings showed severe genu varum, but neither radiolucent lines around the components nor migration of the components were seen. This was revised with semiconstrained prosthesis for the purpose of improving lateral instability at 31 months after the primary TKA.

Avulsion of fibular attachment of collateral ligament was seen at the time of the revision surgery. As PMMA cement was strongly adhered to the bone, it was removed together with cancellous bone. Histologically, HA granules bound to the bone directly after bone ingrowth into the spaces around the HA granules. This is the reason we have described IBBC as a method having the both advantages of cementless HA coating and PMMA bone cement.

After the revision surgery, the walking ability was improved.

In conclusion, this case showed excellent characteristics of IBBC.

The objective of this study was to compare the wear mode of 100 Mrad PE cups run in a hip simulator to retrieved 100 Mrad PE cups, and to evaluate the efficacy of the PE wear model.

15 In-vitro PE cups: 3 each 0,2.5.50,100 and 150 Mrad (9 channel hip simulator, 6.2 million cycle duration, physiological load profile by Paul, 2000N maximum load at 1Hz using 30% bovine serum). 5 Retrieved PE cups: three SOM cups (Mizuho Medical Instrument Co., COP alloy 28 mm head)-0 Mrad after 8 years of clinical use, two 100 Mrad cups after 15 years of clinical use, two T28 PE 2.5 Mrad cups (Zimmer): 18 years and 13 years of clinical use. The cups were examined using a SEM (Philip XL30 FEG) for wear scar locations and PE wear-topography.

Original machine marks were observed in the weight-bearing areas of the highly cross-linked in-vitro PE. No machine marks were observed for the 0 and 2.5 Mrad in-vitro cups and none were seen in any of the retrieved cups. The formation of more nodules and fibrils in the 0Mrad cups compared to the extensivley cross-linked cups (in-vitro and retrieved) was striking. The frequency of occurrence and length of the fibrils and nodules was dependent on the dose of gamma irradiation. More ripples were formed in the 2.5 Mrad and higher cups compared to the non-irradiated cups (in-vitro and retrieved). The in-vitro cups formed more ripples than the retrieved cups. In general, the SEM features for in-vitro Mrad cups appeared similar to those of the retrieved Mrad cups.

The in-vitro Mrad cups accurately reflected the conditions of the artificial joint in living body. Therefore, comparisons of retrieved PE cups with simulator PE cups appeared to be a very powerful research tool.

(2) SEM observation demonstrated far less wear damage in the extensively cross-linked cups than in the non-extensively cross-linked PE. Thus the extensive cross-linked PE cups appeared to be a significant improvement over conventional PE cups in terms of wear resistance.