Three-dimensional architecture of the acetabular labrum in the human hip joint.

The acetabular labrum is frequently damaged with advancing age. As collagen fibers are the main sources of strength, knowledge of their ultrastructure is important to determine the cause of age-induced changes. We aimed to investigate the ultrastructure of collagen fibers constituting the acetabular labrum using scanning electron microscopy (SEM). Acetabular labrum samples obtained during total hip arthroplasty were studied. The samples were specially prepared to observe the steric construction of collagen fibrils constituting the acetabular labrum under light microscopy followed by SEM. The acetabular labrum was mostly composed of cartilage tissue, consisting of chondrocytes and collagen type II, with a layer of collagen type I. In adults, chondrocytes with a rich cytoplasm were surrounded by a dense network of fine type II collagen fibrils, and small bundles of type I collagen fibrils were interposed in the cartilage layer. In elderly individuals, the chondrocytes atrophied and both type I and II collagen fibrils were sparse. We suggest that cartilage has three to five layers, consisting of type I and type II collagen fibrils with a solid cartilage substrate. In elderly individuals, the density of chondrocytes decreases and the cellular shape and architecture of collagen fibrils also changes.

Ultrastructure and three-dimensional architecture of the anterior cruciate ligament in the knee joints of young and old monkeys.

We examined the ultrastructure of the anterior cruciate ligament and assessed age-related changes by comparing the ligaments of young and old monkeys. Ultrathin sections of the anterior cruciate ligament were observed by transmission electron microscopy. The three-dimensional architecture of collagen fibers in the ligament was examined by scanning electron microscopy after tissue specimens were treated with 2 N NaOH to digest the extracellular matrix. At the surface layer of the cruciate ligament in young monkeys, fusiform-shaped fibroblasts actively produced collagen fibrils. The ligament consisted of parallel bundles of dense collagen fibrils of approximately 200 nm in diameter. Collagen fibrils appeared to run linearly. Ligament fibrocytes in the deep layer had a stellate form. Ligament fibrocytes decreased in number and showed marked atrophy in old age. Collagen fibrils had a looser configuration in older monkeys. Despite atrophy of fibroblasts in the deep layer of the anterior cruciate ligament, the area with atrophic fibroblasts in the ligament expands with age, which can likely cause deterioration of and a reduction in collagen fibers. This information can be applied in studies on the cause of the low repair ability of and aging-related changes in the anterior cruciate ligament in humans.

The mechanical effects of cup inclination and anteversion angle on the bearing surface.

BACKGROUND: Regarding the cup setting in total hip arthroplasty, range of motion and prevention of dislocation are important. From past reports, the wear of the bearing surface may affect long-term results. This study evaluated the stress applied to the bearing surface by the combined use of the three-dimensional rigid spring model and the finite-element analysis. METHODS: For contact pressure distribution of the bearing surface, interference analysis was performed using a three-dimensional rigid body spring model. Furthermore, stress was applied to the inner surface of the cup installed in the bone so that the same stress distribution obtained from the interference analysis was achieved. The finite-element analysis was then performed at each condition, which changed the inclination and anteversion angles of the cup to examine the relationship of maximum equivalent stress. RESULTS AND DISCUSSION: The maximum equivalent stresses on the bearing surface under the condition with fixation of an anteversion angle of 0° were 0.78, 0.85, and 1.15 MPa at inclination angles of 25°, 40°, and 55°, respectively. The stress value at 55° was approximately 1.5 times greater than that at 25°. The maximum equivalent stresses on the bearing surface under the condition with fixation of an inclination angle of 40° were 0.85, 0.9, and 1.02 MPa at anteversion angles of 0°, 15°, and 30°, respectively. The stress value at 30° was approximately 1.2 times greater than that at 0°. This study suggests that large inclination and anteversion angles may enhance the stress on the bearing surface and affect long-term results.

Isolated acetabular revision with femoral stem retention after bipolar hip arthroplasty.

INTRODUCTION: In bipolar hemiarthroplasty, migration of the outer cup component into the acetabular cup, with evidence of severe osteolysis in the acetabulum, commonly occurs without loosening of the femoral component. The merits of retaining the stable femoral component in these cases have been debated. Our study aimed to determine whether revision of the acetabular component in isolation could be successfully performed. MATERIALS AND METHODS: The data of 54 patients (61 hips), 44 women, and 10 men, aged 67.7 (range 47-86) years at the time of the index revision, were analyzed. The average time from primary operation to revision surgery was 14.9 (range 1.0-27.0) years, with an average follow-up time after revision of 5.2 (range, 1.0-18.7) years. Indications for acetabular revision included migration of the outer cup component (N = 55), disassembly of the bipolar cup (N = 4), and recurrent dislocation (N = 2). Fixation of the femoral stem was cementless in 49 hips and cemented in 12. Bone grafting for osteolysis of the proximal femur around the stem was performed in six hips. An acetabular reinforcement ring with a cemented cup was used in 31 hips, with cementless cup fixation in 29 hips, and cemented cup in one case. RESULTS: On average, the Harris hip score improved from 57.0 ± 21.6 to 87.4 ± 6.40 points after revision. Two cases of femoral periprosthetic fracture were treated with osteosynthesis 3 year post-revision. There was no evidence of loosening of the femoral stem or subsidence, with a non-progressive radiolucent line <2 mm identified in one case. There was no incidence of dislocation or deep infection, and all components were judged to be stable at the final follow-up. CONCLUSION: Isolated acetabular revision can be reliably performed in cases of failed bipolar hemiarthroplasty with a well-fixed femoral component.

Cement Anchors With Screw Holes For Liner Cementation Into Cementless Acetabular Metal Shells.

This mechanical study was conducted with the shellcement interface in order to construct an acetabular metal shell, and to fix a polyethylene liner with bone cement. Six types of models were tested, with all cementations performed under similar conditions. The "lever out" test was conducted 3 times for each group in order to measure the dissociation strength. The average dissociation strength values were 11.5 N• m for those without screw holes; 33.6, 34.7, and 78.7 N• m for those with single holes at 1, 3, and 6 mm depth, respectively; and 41.3 and 101.1 N• m for 2 different configurations with 3 holes at 3 mm depth. The strength of adhesion increased with the use of a cement anchor, and with an increasing length and number of anchors. The application of a cement anchor with a screw hole is clinically useful for increasing the mechanical strength of the shellcement interface.

Influence of cup-center-edge angle on micro-motion at the interface between the cup and host bone in cementless total hip arthroplasty: three-dimensional finite element analysis.

We verified the index cup position required for bulk bone grafting instead of morcellized grafting immediately after cementless total hip arthroplasty. Three-dimensional finite element analysis was used to evaluate changes in the volume of the slippage of the cup-host bone interface as micro-motion of the cup at the acetabular bone defect site depending on the cup-center-edge (CE) angle. The conditions of bulk bone grafts were similar to those of cortical bone. Slippage increased with decreasing cup-CE angle. A bulk bone graft tightly fixed to the host bone prevented considerably larger slippage between the cup and host bone. A smaller cup-CE angle increased the impact of the bulk bone graft on slippage. When the cup-CE angle was 0° or -10°, the criterion for slippage in favorable initial fixation in all conditions was <40 µm. Even if transplanted bulk bone is used, unless good fixation is obtained between the host bone, and the cup and bone graft, it is impossible to obtain reliable fixation of the cup with a cup-CE angle <-10° and slippage exceeding 40 µm. Bulk bone grafting tightly fixed to the host bone improves initial the cup-host bone fixation, especially when the cup-CE angle is small, such as <-10°. In clinical practice, negative factors are implicated in the initial fixation of various cups, and sufficient fixation between the host bone and cup or bulk bone graft using a screw is effective when the cup-CE angle is extremely small.

Mechanical evaluation of hip cement spacer reinforcement with stainless steel Kirschner wires, titanium and carbon rods, and stainless steel mesh.

INTRODUCTION: In two-stage treatments for infections after total hip arthroplasty, antibiotic-loaded cement spacers help treat the infection by antibiotic elution and prevent contraction. However, such spacers are weak and may fracture while awaiting replacement, impairing functionality. We evaluated whether a Kirschner wire (K-wire) mounted into the spacer reinforced its strength along with the effects of the reinforcing material, position, and intensity. METHODS: Spacers without reinforcing materials constituted the control group. As reinforcing materials, stainless steel K-wires (diameters 3 and 6 mm), titanium alloy and carbon fibers (diameter 3.175 mm), and stainless steel meshes (inner and outer diameters, 6 and 9 mm, respectively) were inserted into the spacer mold before filling with cement. The spacers complied with ISO 7206-4; a compressive load was applied using a testing machine with a velocity of 25.4 mm/min, and the maximum load was recorded. We used 1-3 K-wires positioned on the medial side, lateral side, neck only, and stem only and tested 3 specimens for each condition. RESULTS: The control group withstood the highest load. Stainless steel was the strongest material; 3-mm K-wires in the neck and lateral side withstood a higher load. The computed tomography (CT) imaging revealed a cavity between the K-wires and cement. When K-wires were inserted along the whole length, despite cement fractures, continuity was maintained because of the reinforcing materials. CONCLUSION: It is difficult to improve the reinforcing strength of spacers using K-wires; however, K-wires prevented dislocation of cement spacer fragments, which can help prevent contraction and facilitate spacer removal during replacement.

Initial stability of cementless acetabular cups: press-fit and screw fixation interaction--an in vitro biomechanical study.

BACKGROUND: Press-fit and screw fixation are important technical factors to achieve initial stability of a cementless acetabular cup for good clinical results of total hip arthroplasty. However, how these factors affect one another in initial cup fixation remains unclear. Therefore, this study aimed to evaluate the mutual influence between press-fit and screw fixation on initial cup stability. METHODS: Foam bone was subjected to exact hemispherical-shape machining to diameters of 48, 48.5 and 49 mm. A compressive force was applied to ensure seating of a 48-mm-diameter acetabular cup in the foam bone prior to testing. Screws were inserted in six different conditions and tightened in a radial direction at the same torque strength. Then, the socket was rotated with a twist-testing machine, and the torque value at the start of axial rotation between the socket and the foam bone was measured under each screw condition. RESULTS: The torque values for the 48-mm-diameter reaming were >20 N m higher than those for the 48.5- and 49-mm-diameter reaming in each screw condition, indicating that press-fit fixation is stronger than screw fixation. Meanwhile, torque values for the 48.5- and 49-mm-diameter reaming tended to increase with increasing the number of screws. CONCLUSIONS: According to our experiment, press-fit fixation of a cementless acetabular cup achieved rigid stability. Although the supplemental screws increased stability of the implant under good press-fit conditions, they showed little impact on whole-cup stability. In the case of insufficient press-fit fixation, cup stability depends on screw stability and increasing the number of additional screws increases cup stability.

Contact between the acetabulum and dome of a Kerboull-type plate influences the stress on the plate and screw.

We used a three-dimensional finite element method to investigate the conditions behind the Kerboull-type (KT) dome. The KT plate dome was divided into five areas, and 14 models were created to examine different conditions of dome contact with the acetabulum. The maximum stress on the KT plate and screws was estimated for each model. Furthermore, to investigate the impact of the contact area with the acetabulum on the KT plate, a multiple regression analysis was conducted using the analysis results. The dome-acetabulum contact area affected the maximum equivalent stress on the KT plate; good contact with two specific areas of the vertical and horizontal beams (Areas 3 and 5) reduced the maximum equivalent stress. The maximum equivalent stress on the hook increased when the hardness of the bone representing the acetabulum varied. Thus, we confirmed the technical importance of providing a plate with a broad area of appropriate support from the bone and cement in the posterior portion of the dome and also proved the importance of supporting the area of the plate in the direction of the load at the center of the cross-plate and near the hook.

Influence of the volume of bone defect, bone grafting methods, and hook fixation on stress on the Kerboull-type plate and screw in total hip arthroplasty: three-dimensional finite element analysis.

For total hip arthroplasty or revision surgery using acetabular reinforcement cross-plates, choosing between bulk and morselized bone grafts for filling acetabular defects is challenging. We used finite element model (FEM) analysis to clarify various stresses on the cross-plate based on bone defect size, bone graft type, and presence or absence of hook fixation to the bone. We constructed 12-pattern FEMs and calculated the maximum stress generated on the Kerboull-type (KT) plate and screw. Bone defects were classified into four patterns according to the volume. Regarding the bone graft type, bulk bone grafts were considered as cortical bone, and morselized bone grafts were considered to consist of cancellous bone. Models were compared based on whether hook fixation was used and whether a gap was present behind the plate. The upper surface of the host bone was fixed, and a 1,000-N load was imposed on the horizontal axis at 71°. Larger bone defects increased the stress on the KT plate and screws. This stress increased when no bone was grafted; it was lower when bulk cortical bone grafts were used for filling than when morselized cancellous bone grafts were used. For cortical bone grafts, the increased stress on the KT plate and screws was lowered with hook removal. Attaching the hook to the bone and filling the gap behind the KT plate with an adequate bone graft reduced the stress on the KT plate and screws, particularly for large bone defects filled by bulk bone grafting.

Effects of mechanical properties of muscle and tendon on performance in long distance runners.

The purpose of this study was to investigate the mechanical properties of muscle and tendon in long distance runners and their relations to running performance. Fifteen long distance runners (LDR) and 21 untrained subjects (CON) participated in this study. Muscle strength and activation level of knee extensors and plantar flexors were measured. Tendon elongation was determined using ultrasonography, while subjects performed ramp isometric knee extension and plantar flexion up to the voluntary maximum. Relative MVC (to body mass) of LDR was significantly lower than that of CON for knee extensors, but not for plantar flexors. No significant difference in the neural activation levels was found between LDR and CON for both sites. Maximal tendon elongation of LDR was significantly lower than that of CON for knee extensors, but not for plantar flexors. Furthermore, faster running time in a 5,000 m race (best official record of LDR) was associated with lower tendon stiffness for both sites. In conclusion, the tendon of long distance runners is less extensible than those of untrained subjects for knee extensors, but not for plantar flexors. For both sites, however, the lower tendon stiffness may be in favor of the running performance in long distance runners.

A longitudinal assessment of running economy and tendon properties in long-distance runners.

The aim of this study was to investigate longitudinal changes in tendon properties and running economy of long-distance runners (LDRs) in the preparatory periods of track season (TS) and road season (RS). Eleven well-trained LDRs and 6 untrained subjects participated in the present study. In each period, muscle strength, neural activation level, and tendon elongation for both knee extensors and plantar flexors, jump performances, and oxygen consumption during submaximal running velocities were measured. No significant differences observed in any measured variables between the 2 seasons for untrained subjects. For LDRs, the total running distance during 1 month preceding RS (832 +/- 95 km) was significantly longer than that during 1 month preceding TS (718 +/- 80 km). No significant differences in the muscle strength, neural activation level, and jump performances were found between TS and RS. The stiffness of tendon structures in RS was significantly lower than those in TS for both knee extensors (-14.4%, p = 0.023) and plantar flexors (-16.6%, p = 0.040). At 3 running velocities, the oxygen consumptions in RS were significantly lower than those in TS. These results suggested that the lower oxygen consumption during submaximal running velocities observed in the preparatory period of RS may be attributable to the more compliant tendon structures but not in the neuromuscular characteristics.

Long-term clinical results of bipolar hemiarthroplasty for osteoarthritis and rheumatoid arthritis of the hip: A retrospective study.

We aimed to clarify the possibility of using bipolar hip arthroplasty (BHA) for degenerative diseases by examining long-term results postoperatively in 336 hips. Patients' average age was 61.0 years (range, 34-88 years), and the average follow-up period was 12.5 years (range, 5.0-27.3 years). The 5-year, 10-year, and 20-year Kaplan Meier survival rates (end point: revision) were 92.1%, 81.8%, and 20.1% in the osteoarthritis group and 96.4%, 90.1%, and 24.6% in the rheumatoid arthritis group, respectively. Since the survival rate for more than 10 years decreases rapidly, the use of BHA for treating degenerative diseases should be restricted.

Comparison of cementless and cemented cups in revision total hip arthroplasty using a computed tomography-based navigation system.

BACKGROUND: Studies comparing cementless and cemented cups are lacking, especially for revision total hip arthroplasty (THA). The aim of this study was to investigate and compare the differences in implant accuracy between two fixation methods in revision THA. METHODS: We conducted a retrospective study of 85 hips in 70 patients who underwent revision THA using a computed tomography (CT)-based navigation system. Among these, 53 hips underwent cementless THA and 32 hips underwent cemented THA. We measured cup inclination and anteversion using the Kyocera two-dimensional-template with X-ray (Japan-Kyocera, Shiga, Japan) and stem anteversion with CT. We calculated the combined anteversion [cup anteversion+0.7×stem anteversion]. RESULTS: There were no significant differences between the two groups with respect to definitive cup inclination and anteversion. The mean deviations in the inclination and anteversion angle were 40.3 ±â€¯4.3 and 19.6 ±â€¯6.2° in the cementless group and 40.5 ±â€¯3.3 and 17.1 ±â€¯5.1° in the cemented group. There were 11 outliers with respect to the Lewinnek safe zone in the cementless group and two in the cemented group (P = 0.072). Although there was no statistically significant difference, the number of safe zone outliers in the cemented group was less than that in the cementless group. CONCLUSION: We conclude that when using a navigation system for revision THA, high precision can be obtained for the cup placement angle with or without cement. However, it seems that a major error in the installation angle of the cup is less likely to occur when using a cemented cup than when using a cementless cup in revision THA with a navigation system.

Effects of ball head diameter and stem neck shape in range of motion after total hip arthroplasty: A simulation study.

Simulations using three-dimensional computer-aided design were performed with the various conditions to research the movement distance of the ball head and total range of motion until impingement and dislocation (ROM(t)) which involved in joint stability. Although a large ball head increases the entire ROM(t) and oscillation angle, it decreases stability transitioning from impingement to dislocation. Conversely, though large neck diameter increases the simulated stability from impingement to dislocation, it reduces the ROM(t) and oscillation angle. ROM(t) decreases with change in neck shape and is greatly affected by the presence of osteophytes, even if the head-neck ratio remains the same.

Radiographic evaluation of linear wear of bipolar hemiarthroplasty devices in vivo.

BACKGROUND: The indications for bipolar hemiarthroplasty (BHA) have been narrowing as those for total hip arthroplasty (THA) have been expanding in cases of femoral neck fracture and initial stages of osteonecrosis of femoral head (ONFH). It is difficult to measure wear in vivo after BHA because the equipment used has a dual bearing system with an inner head inside a metal outer cup. The present study aimed to (1) use a roentgenograph to measure linear wear in vivo after BHA with different acetabular conditions around the bipolar cup, and (2) compare the linear wear of polyethylene between integral bipolar cup (IBC) and Centrax prostheses. METHODS: From among patients who had undergone BHA in our department after 1996, we analyzed 48 joints with osteoarthritis (OA) and without acetabular cartilage, as well as 25 joints with ONFH of stage 3 or less, in which the acetabular cartilage remains. Two types of bipolar cup prostheses were used: the IBC, which was gamma-sterilized in air using 2-Mrad irradiation, and the Centrax, which was gamma-sterilized in nitrogen using 3-Mrad irradiation. To image the inner head in vivo, we used high-pressure X-ray photography; we measured linear wear of the polyethylene with software using Martell Method 1. RESULTS: Comparing mean annual linear wear between the OA and ONFH groups, using IBC prostheses in both groups, there was a significant difference (0.213 mm vs. 0.096 mm, respectively; P = 0.0177). There was a significant difference between the Centrax and IBC prostheses in OA patients in terms of linear wear (0.04 mm vs. 0.213 mm; P = 0.0181). CONCLUSION: The linear wear of polyethylene in BHA implants can be affected by the material used to manufacture the bipolar cup. Such implants should only be used for appropriate indications.

Efficacy of Computed Tomography-Based Navigation for Cup Placement in Revision Total Hip Arthroplasty.

BACKGROUND: Navigation systems are an effective tool to improve the installation accuracy of the cup in primary total hip arthroplasty. This study aimed to evaluate the efficacy of a computed tomography-based navigation system in achieving optimal installation accuracy of implants in revision total hip arthroplasty and to clarify the usefulness of the navigation system. METHODS: We conducted a retrospective study of 23 hips in 23 patients who underwent revision total hip arthroplasty using a computed tomography-based navigation system; the control group comprised 33 hips in 33 patients who underwent revision total hip arthroplasty without a navigation system. RESULTS: The average cup position with the navigation system was 40.0° ± 3.7° in radiographic abduction angle, 18.8° ± 4.8° in radiographic anteversion, and 41.2° ± 8.9° in combined anteversion; without the navigation system, the average cup position was 38.7° ± 6.1°, 19.0° ± 9.1°, and 33.6° ± 20.5°, respectively. The achievement rate of cup positioning within the Lewinnek safe zone was not significantly different between the navigation group (82.6%) and control group (63.6%). In contrast, the achievement rate of cup positioning within the Widmer combined anteversion guidelines was significantly greater in the navigation group (78.3%) than in the control group (48.0%, p = 0.029). Furthermore, outlier cases in the navigation group had a smaller variance of deviation from the optimal cup position than those in the control group did. CONCLUSIONS: The results show that the use of navigation for revision total hip arthroplasty improved cup positioning and reduced the range of outliers. Improvement of cup placement accuracy influenced the installation of the stem and also improved the achievement rate of combined anteversion. Thus, a computed tomography-based navigation system is very useful for surgeons when placing the cup within the target angle in revision total hip arthroplasty.

Influence of hip center position, anterior inferior iliac spine morphology, and ball head diameter on range of motion in total hip arthroplasty.

BACKGROUND: Acetabular component orientation, such as high placement and femoral head diameter influence joint stability in total hip arthroplasty (THA), wherein anterior inferior iliac spine (AIIS) shape could cause femoro-acetabular impingement. Little is known regarding the combined influence of these parameters, particularly in the context of developmental dysplasia of the hip. Therefore we conducted a computer simulation study based on computed tomography (CT) data to determine whether: (1) AIIS shape, (2) high placement of acetabular cups, and (3) ball head diameter influence the range of motion (ROM) after THA. HYPOTHESIS: The decrease in ROM depends on AIIS shape and the ROM decreases even if the femoral head diameter is increased when high placement of acetabular cups. PATIENTS AND METHODS: CT data from 14 hips of 14 patients were evaluated. Hips were categorized by Hetsroni classification type I (n=6), type II (n=6), and type III (n=2) depending on AIIS shape. ROM was evaluated using CT-based software. Cups were placed at and 5 and 10mm above the normal hip position. The femoral heads used were 28 (standard simulation), 32, and 36mm in diameter. ROM at impingement was measured under flexion (Flex), internal rotation (IR) at 90° flexion (IR at 90Flex), IR at 45° flexion with a 20° adduction (IR at 45Flex20Add), and external rotation at 10° extension (ER at 10Ext). RESULTS: The mean ROM standard simulation for Flex, IR at 90Flex, IR at 45Flex20Add and ER at 10Ext were: 119.8±5.4°, 31.0±11.3°, 70.0±11.9°, and 33.0±9.7° for type I; 118.5±5.5°, 31.5±2.9°, 71.3±2.2°, and 33.3±3.3° for type II; and 105.5±13.4°, 21.0±15.6°, 61.0±11.3°, and 34.5±2.1° for type III, respectively. There were no significant differences in the ROMs of each type (Flex, p=0.252; IR at 90Flex, p=0.461; IR at 45Flex20Add, p=0.261; and ER at 10Ext, p=0.655). For the high placement of acetabular cups, ROM increase was restricted despite the femoral head diameter increase. DISCUSSION: Larger femoral head diameters increased ROM, with a lower increase in type III because of bony impingement. ROM decreased with higher cup placement. Expansion effects were minimal, even with larger ball head diameters, and were further decreased in types II and III. Attention should be paid to AIIS shape because bony impingements occur early with higher acetabular cup placement. LEVEL OF EVIDENCE: VI Simulation study.

A new and simple intraoperative method for correction of leg-length discrepancy in total hip arthroplasty.

Total hip arthroplasty (THA) can eliminate pain caused by hip joint destruction and correct leg-length discrepancies (LLD). We present a short and simple intraoperative method for LLD correction in THA. We performed 55 primary THAs using this technique. The measurement error was 1.86 ±â€¯1.4 mm, which was within 3 mm in 49 of 55 cases (89%) and within 5 mm in 54 of 55 cases (98%). This method is simple and does not require specialized devices, making it versatile to be used anywhere. No new skin incisions or extra costs are required, which will likely make it attractive to surgeons.

Efficacy of vitamin E for mechanical damage and oxidation of polyethylene rim by stem neck impingement.

BACKGROUND: The aim of this study is to determine the influence of crosslinking and addition of 0.3 wt% vitamin E in a polyethylene rim on its mechanical damage and oxidation caused by impingement. METHODS: Six ultrahigh-molecular weight polyethylene samples were studied (control; crosslinked; vitamin-E containing; crosslinked and vitamin-E containing; aged control; and aged crosslinked and vitamin-E containing). Crosslinking was attained by irradiation with a 300 kGy electron beam; vitamin E incorporation was at 0.3 wt%; and aging was performed through forced oxidation for 14 days. Resistance to impingement was evaluated by stereoscopic observations, three-dimensional measurements, and oxidation measurements by Fourier transform infrared spectroscopy. FINDINGS: Rim breakage (delamination and fracture) due to impingement was observed only for the aged control specimen. In contrast, crosslinked specimens containing vitamin E showed no failure of the rim after aging. The addition of vitamin E to polyethylene suppressed its oxidation and reduced the oxidation caused by crosslinking or impingement. The impingement resistance of the control sample deteriorated upon oxidation, whereas that of vitamin E-containing crosslinked polyethylene remained high due to the antioxidant property of vitamin E. INTERPRETATION: Vitamin E-containing polyethylene showed a reduced risk of wear/breakage of polyethylene rims by impingement.