Introduction

Large wear rate reductions have been shown for crosslinked PE in simulators and short- to mid-term clinical wear studies. However, concerns persist about long-term in-vivo oxidation (especially with annealed PE), late accelerating wear and the possibly higher osteolytic potential of crosslinked PE particle debris. This is the first long-term study comparing conventional to crosslinked PE investigating whether the wear reduction is maintained in the long-term and if reduced osteolysis becomes evident.

While squeaking ceramic bearings in total hip arthroplasty are increasingly reported in the literature, the etiology remains unclear. Cup inclination and anteversion have been correlated with the phenomenon but even amongst well positioned cups bearing noise is observed. Most studies do not distinguish between different types of noise or incidence rate and do only investigate actively complaining patients. This study analysed the incidence of ceramic bearing noise in a single type of hip implant and investigates correlations with patient, implant and surgery parameters.

In a consecutive series of 145 ceramic-on-ceramic primary hips (Stryker ABG-II, 28mm head) in 132 patients (m/f=72/60, avg. age=54yrs) and an average follow-up of 3.0 (1–7) years, noisy bearings were identified by a patient questionnaires stating the type of noise (squeaking, clicking, scratching, combinations), time of initial incidence, incidence rate (permanent, often, sometimes, rare) and type of movement. Patient demographics (age, gender, height, weight, BMI, side of surgery, leg length difference), implant parameters (cup and stem size, neck length) and surgery parameters (cup and stem position, leg length correction) were recorded and compared between the noisy and silent groups (t-test, Fisher Exact test).

Twenty-eight noisy hips (19.3%) were identified with 14 patients reporting squeaking, 16 clicking and 5 scratching including 7 with a combination of noises. Quasi permanent noises were reported for 7 hips (2 often) but in 17 cases the noise appeared only sometimes (2 rare). The average time of first incidence was 1.74 years port-op with 7 hips reporting noise directly after operation and 15 after 2 years or more. Silent and noisy hips were statistically not different regarding age, gender, follow-up time, side of operation, height, weight, BMI, cup and stem size, leg length difference or stem position. Significant differences were identified with the noise group having a steeper cup inclination (49.9° vs 46.9°, p< 0.05) and less frequent shorter (−2.7mm) necks (0 vs 22%, p< 0.01) but more frequent longer (+4mm) necks (50% vs 37%, p< 0.05). Leg length correction was performed less frequent (31 vs 55%, p< 0.01). In the noise group 5 (17%) and in the silent group only 1 (0.9%) cup revisions was performed (p< 0.01).

The incidence of noisy ceramic bearings was higher than usually reported (< 5%) as not only actively complaining subjects but all patients were interviewed. Cup position was confirmed to be a contributing factor but patient weight, height or BMI did not play a role. However, the use of long necks, the absence of short necks and less frequently performed leg length corrections significantly contributed to producing bearing noise. Biomechanical restoration, preoperative planning and soft tissue tension seem to be important factors in bearing noise etiology.

Introduction: Simulator wear studies of crosslinked polyethylene (PE) show promising results but long-term clinical investigations addressing concerns about in-vivo aging, PE deterioration, late wear and osteolysis are scarce. This study reports the longest published follow-up comparing conventional to crosslinked PE.

Methods: Crosslinked PE (Stryker Duration: 3MRad gamma irradiation in N2, post-irradiation annealed) was compared to conventional PE (3MRad gamma irradiation in air) in a MTS hip simulator and a prospective randomized clinical study involving 48 THA patients (Stryker ABG-II stem and cup, 28mm ball diameter) with a mean follow-up of 8 (7–9) years. Patients were followed-up annually using the HHS, radiographs and wear measurements applying a digital Livermore method.

Results: Forty patients (23 conventional, 17 Duration) were left for analysis (five premature deaths, 3 loss to follow-up). Both groups were statistically non-different (p> 0.1) regarding age (63.9 years), gender, BMI, stem size, cup size, cup inclination and liner thickness leaving the insert material as the only variable. Pre-op HHS (39.7) and post-op HHS (93.7) were also not different.

At 8-years the wear rate was significantly (p< 0.01) lower for Duration [0.088 ± 0.03 mm/yr (0.02–0.14)] than conventional PE [0.142 ± 0.07 mm/yr (0.05–0.31)]. This reduction (−38%) compared well to the simulator (−45%) and did not change over time (−33% at 5-years). Radiolucencies and signs of osteolysis were also less in the Duration group (n.s.).

Discussion: In-vivo wear reduction by crosslinked PE is similar as predicted by the simulator and does not seem to deteriorate over time. Concerns over higher levels of residual free radicals after annealing instead of remelting do not seem justified. The lower wear correlated with reduced radiographic signs of osteolysis which may result in superior survival at longer follow-up.

Introduction: Wear of the polyethylene (PE) acetabular component is widely regarded as the primary factor limiting the longevity of total hip arthroplasties (THA). To compare wear patterns of different polyethylene inserts computer assisted measurement techniques for in vivo polyethylene wear were developed. This study was performed to investigate which software out of four programs is most precise and easy to use in daily clinical practice.

Materials and Methods: 24 anteroposterior digital radiographs of patients with a THA (Stryker ABG-II with N2Vac and Duration PE inserts in metal backed cups) with an average of 8.0 years follow-up were measured twice by a blinded single observer for linear wear (head penetration) in a single image analysis. Four computer assisted wear measurement methods were compared, the commercially available Martell Hip Analysis suite 7.14 and Rogan Hyperview, a not yet available Rogan beta-version called View Pro-X and Roman v1.70, freely available software to download from the internet. While both Rogan software can read the DICOM format from the hospital image server, images had to be converted for Martell (greyscale TIFF only) and Roman (any format).

The annual wear rates were compared and intra-observer variability was calculated as the difference between both measurements (precision). The average time it takes to measure one image (without format conversions) was documented and practicality of daily clinical use was evaluated.

Results: The annual wear rates measured were (mean +/− SD): Martell=0.09+/−0.21,, Hyperview=0.14 +/−0.10, Pro-X=0.12+/−0.07 Roman=0.12 +/−0.06. Martell was the only method measured negative wear (7/24 cases).

The precision was (mean +/− SD): Martell = 1.74+/−1.53, Hyperview = 0.36 +/−0.92, Pro-X = 0.10+/−0.11 Roman = 0.08 +/−0.08.

The average measuring time per image was: Martell = 94s, Hyperview = 94s, Pro-X = 92s Roman = 158s.

Discussion: The Roman method is the most precise and easiest to use in daily practice, but takes the longest time to measure. The Rogan View Pro-X software is nearly as precise and easy to use but not on the market yet. It is an improvement over the Hyperview which looses precision by using a elliptical interpolation necessary for non-metal backed cups instead of circular interpolation which is more precise for metal backed cups. The Mar-tell method produced the intolerable low precision and in some cases “negative wear”. Only on large patient groups it may produce realistic average wear rates. We found out that the Martell edge detection method, originally developed for scanned analogue x-rays, functions inferiorly with digital images, the coming hospital standard. Image processing (smoothening) of the digital x-rays did increase accuracy and precision. We recommend the Roman software, a digital version of the Livermore method, for precision, ease of use and cost.

Introduction: In uncemented total hip arthroplasty (THA) stem sizing and stem insertion affect the fit and fill of the prosthesis in the medullary canal. This study investigates how tightness of the stem fit influences bone remodelling and if there is a correlation between radiological and clinical Results: Methods: In a retrospective study a consecutive series of 64 patients following uncemented THA with a proximally coated anatomic stem (ABG-II, Stryker) was followed-up for 5 years using the Merle d’Aubigne (MdA) clinical score. Radiographic analysis of bone remodelling features per Gruen zone (R1 to R7) was performed on AP and lateral x-rays at 5 years. Femoral fit was measured at three levels (proximal, mid-stem, distal) on the direct postop x-ray using the femoral fit ratio (f) of Kim and Kim (tight femoral fit: f≥0.8, non-tight: f< 0.8). The medullary canals were categorised according to Noble (normal, stove pipe, champagne flute). Bone remodelling was compared to literature values of the ABG-I stem and correlated to clinical findings.

Results: The MdA improved from 9.6 pre-op to 17.1 at 5 years with no difference between tight and non-tight implants. Lateral thigh pain (LTP) occurred in 10/64 cases (3 requiring medication). Patients with LTP had significantly lower proximal (0.75 vs 0.80) and distal fit & fill (0.72 vs 0.79. LTP was equally frequent with a normal or varus position.

Proximal bone resorption occurred in 27% (R1) or 34% (R7) which is lower than the values reported for the ABG-I stem (R1: 48%, R7: 45%). Bone resorption was significantly higher with tight than non-tight mid-stem fit (69% vs 27%, p=0.04). The same trend was true for tight distal fit (56% vs 37%).

Cancellous densifications were frequent at mid-stem level (R2: 83%, R6:88%) but much less distally (R3: 44%, R5:25%). No influence of fit & fill was measured.

Cortical densifications were noted in 16% (ABG-I 15%) overall with a higher proportion measured for tight distal fit (25%) than loose distal fit (6%, p=0.07). A similar observation was made for cortical thickening (11% overall, tight:non-tight=16%:6%). Pedestal formation (17% overall) was more likely with a non-tight proximal fit (23% vs 12%) and mid-stem fit (20% vs 8%)

A proximal tight fit was achieved more frequently with normal (55%) and stovepipe femora (50%) than champagne flute femora which had the highest proportion of tight distal fit (85%).

Discussion: At 5 years femoral implant fit influenced bone remodelling reactions which are in agreement with the design philosophy of proximally press-fitting anatomic stems. However, implant fit could not be correlated to clinical outcome yet. This may require a longer follow-up.

As LTP occurred with non-tight fit it seems that elastic mismatch is not the main cause.

Less proximal bone resorption and less distal densifications confirm the design changes from ABG-I to ABG-II.

Introduction: Investigating the correlations between bone ongrowth and HA resorption on coated implants is important to understand the contribution of resorbable coatings on implant fixation and periprosthetic bone remodelling. It is only possible histomorphometrically and this study measured bone apposition and residual HA on hip stems of one single design.

Methods: Post-mortem retrievals of 13 ABG-I (Stryker) hip stems from 13 patients (10f, 3m, age: 58–86yrs, uneventful THA, death unrelated to hip diseases). The time from implantation (stem in-vivo) ranged between 3.3 to 11.2yrs.

Three cross sections were cut from the metaphyseal femur and surrounding bone proximal to Gruen zones 2 and 6 (regions with HA coating). The three sections were A (proximal), B (mid-part) and C (distal). Sections were prepared using the Donath technique and then paragon stained for quantitative histomorphometry using an Axioskop microscope (Carl Zeiss, Germany) with image analysing (SAMBA, France).

For each segment the total implant perimeter, percentage of implant perimeter covered by bone and the total percentage of residual HA coating were measured. Bone implant contact was defined as direct ongrowth of bone to the coating or the titanium surface.

Results: HA resorption increased significantly with the time in-vivo as measured by the residual HA (e.g. < 6yrs: Avg.=36.7%, > 6yrs: Avg.=10.1%, p=0.02). This correlation was true for all sections A, B and C (p=0.02–0.03). Beyond 8yrs HA was almost gone.

Bone ongrowth ranged between 18%–56% and was independent of the time in-vivo. Bone ongrowth was most strongly correlated to patient age with younger patients having significantly higher bone ongrowth (p=0.001). Bone ongrowth was correlated with HA-resorption only in the most proximal zone A (p=0.001) with lower ongrowth associated with lower levels of residual HA. However, HA resorption was not significantly correlated with patient age.

HA resorption was significantly higher most proximally with less residual HA (13.0%) than mid-stem (22.6%, p=0.05) and distal (28.1%, p=0.05). Metaphyseal stem level and bone ongrowth were not significantly correlated in this manner.

Discussion: HA resorption increased with implantation time and was nearly completed at 8yrs. As bone ongrowth was independent of time in-vivo and independent of HA resorption on the mid-part and distal coated stem sections there is evidence that long term implant fixation is not diminished while the HA coating is being resorbed.

Bone ongrowth but not HA resorption was strongly correlated to patient age indicating that the bone remodelling process is more affected by individual bone health than it can be stimulated by HA coating.

HA resorption increased significantly from the distal to mid-stem and the most proximal coating level in the same way as stress shielding and thus osteoclastic stimulation goes up.

Introduction. Periprosthetic femoral fractures (PPF) have become more common as the population at risk, patients with joint arthroplasty, has increased. The choice of treatment depends on the location of the fracture relative to the implant, the residual fixation of the implant and patient factors such as deficient bone stock or osteopenia. The Vancouver classification categorises types of PPF and identifies strategies for its management. However, the Vancouver classification is mainly based and focused on cemented implants. Recently a modified algorithm for the management of PPF based on the Vancouver classification has been published. We analysed PPF with a single type of uncemented hip stem and compared our treatment to the most recent management algorithm.

Methods. From a consecutive series of 619 uncemented proximal hydroxyapatatite coated ABG-I prostheses, 14 patients (2.3%) sustained a PPF after an adequate trauma. The mean time between the index operation and the fracture was 6.9 years(range: 2.0 to 13.7 years). The mean age of the patients at the time of fracture was 79 years (range 59–87). The fracture patterns and state of stem fixation were analysed.

Results. In 5 patients the fracture was limited to the proximal Gruen zones 1 and 7 with the stem still firmly fixed (type A). Fracture treatment was conservative but in one patient the greater trochanter had to be reat-tached. Six B1,two B2 fractures and one B3 fracture were seen. Compared to the Vancouver classification we observed a different pattern in the type B fractures. No fractures at the tip of the stem were seen as common and characteristic in cemented implants. Three B1 fractures were operated due to fracture displacement and three were treated conservately. THe B2 and B3 fractures were managed with long uncemented revision stems because of a disrupted bone-prosthesis interface. Type C fractures were not seen. All fractures healed well.

Conclusion. The ABG-I shows a bone remodelling pattern consisting of mid stem bone condensation and proximal bone resorption, which leads to a high bone density gradient. This gradient acts as a stress riser and thus can be a preferred location for the initiation of a fracture. This pattern is distinctly different from the fracture types observed for cemented implants. . As a result the ABG-I stem was modified to the ABG-II design permitting more proximal and less mid-stem load transfer, smoothening the bone density gradient.

This study confirms that the Vancouver classification and the modified algorithm for the management of PPF are a simple,reproducible classification system also for the uncemented treatment modality. Conservative treatment is a valid option in case of a stable implant, while in case of a loose implant surgical intervention is mandatory.

Introduction: After total hip arthroplasty (THA) the periprosthetic bone is loaded in an unphysiological manner (stress shielding), a major cause for periprosthetic bone resorption and aseptic loosening. Design, material and surface properties of the implant influence the stress shielding effect. This study investigates whether the design changes from the successful ABG-I to the ABG-II stem can be verified in perioprosthetic bone remodelling using Dual-Energy X-ray Absorptiometry (DEXA).

Methods: 51 THA patients (22f, 29m, avg. age: 60.8 years) were randomised to either ABG-I or ABG-II. DEXA measurements were performed preoperatively and 10 days (baseline), 3 weeks, 3, 6, 12 and 24 months postoperatively using standard Gruen zone analysis. At the same time clinical Merle d’Aubigne (MdA) scores were measured. Changes in bone mineral density (BMD) were expressed as percentage changes from the baseline for each of the Gruen zones (R).

Results: The average MdA score (25 ABG-I, 26 ABG-II) increased from 10.3 preoperatively to 17.3 at 24 months postoperative. The improvement was higher for ABG-II (7.5) than ABG-I (6.5) but not significant (p=0.15). During the first three postoperative months the average BMD of all zones combined dropped steeply for both the ABG-I (−5.5%) and ABG-II (−4.5%, n.s.). Beyond 3 months, the overall BMD change (zones combined) continued to develop without significant difference between both implant designs (plateau and slight recovery) but the individual zones showed distinct differences. The average BMD loss in the proximal Gruen zones was much lower for ABG-II (R1: −7.9%, R7: −3.7%) than for ABG-I (R1: −9.3%, R7: −11.9%) while distally the situation was reversed with better bone preservation for the ABG-I (R3: −2.9%, R4: −1.5%, R5: −1.7%) than for the ABG-II (R3: −6.0%, R4: −2.8%, R5: −4.6%). In the mid-stem region a transitional area was identified with better bone preservation for ABG-II in Gruen zone 6 (+2.7% vs −1.4%) and for ABG-I in Gruen zone 2 (-4.9% vs 7.9%). However, the p-values (two-sided t-test) ranged from 0.05–0.35 at statistically non-significant levels.

Discussion: The steep initial bone loss for both stem designs and all Gruen zones combined indicates that during this early postoperative phase surgical trauma and reduced loading dominate the bone remodelling process and not the type of implant. The different development of proximal and distal BMD for ABG-I and II in the period thereafter demonstrates the long-term effect of implant design verifies the design improvements (less proximal stress shielding). A parallel study identified the dominant influence of preoperative BMD on BMD loss. This explains our high standard deviation and the lack of statistical significance. The study is now expanded with patients matched for preoperative BMD.

Introduction Periprosthetic bone loss is a major cause of concern in patients undergoing total hip arthroplasty (THA). In this study we monitored the periprosthetic bone loss around two different types of femoral implant to evaluate their design and investigate the relationship with the preoperative bone mineral density (BMD).

Materials and Methods Sixty patients (35 female, 25 male, mean age 63 (range, 46–75) years) undergoing THA were randomised to either the ABG or Mallory Head femoral stem. Preoperative DEXA scans were acquired of the posteroanterior (PA) and lateral lumbar spine, the contra-lateral hip and the non-dominant forearm. Postoperative DEXA scans were performed at 10 days (treated as baseline), six weeks, and 3, 6, 12, 24 and 36 months after THA.

Results A total of 50 patients (24 ABG, 26 MH) completed the study. Three months after THA there was a statistically significant BMD decrease in every Gruen zone that varied between 5.6% and 13.8% for the ABG pros-thesis and between 3.8% and 8.7% for the MH prosthesis. Subsequently, in most zones BMD reached a plateau or showed a small recovery. However, BMD continued to fall in Gruen zones 1 and 7 in ABG patients and Gruen zone 1 in MH patients. Bone loss was less in every Gruen zone in MH patients compared with ABG with the largest difference (10%, P = 0.018) in Gruen zone 7. After adjustment for multiple comparisons the relationship between peri-prosthetic bone loss and preoperative BMD was highly statistically significant for spine, hip and radius BMD.

Discussion The present study showed that statistically significant bone loss occurred with both stems during the first three months following implantation, and confirmed that prosthesis design influences peri-prosthetic bone loss. Although the greater bone loss in patients with lower spine, hip or forearm BMD may not adversely affect the outcome for patients in the short and mid-term, preservation of femoral bone stock may be important in the longer term because a low femoral BMD can adversely affect the results of a subsequent revision. Greater femoral bone stock may be particularly advantageous in younger patients in whom a future revision is more likely.

Introduction: The Stryker ABG-I Total Hip Arthroplasty system with a Hydroxyapatite coated stem and cup has shown very promising short and mid-term clin-cial results at 2, 5 and 8 years. However, large discrepancies in component survival of the stem and cup have recently been published and require more data and further investigation about the potential causes.

Methods: All peer reviewed publications on the survival of the ABG-I hip prosthesis (9) were analysed regarding clinical results, polyethylene (PE) wear, osteolysis and survival. Own results from the first 250 consecutive ABG-I hips with a long-term follow-up of 10–15 years were added and compared.

Results: In the literature excellent survival rates of the ABG-I stem against osteolysis and aseptic loosening were reported with values ranging between 98%–100% after 5–10 years. In our own series stem survival against aseptic loosening was 100% at 10 years. No radiographic evidence of distal linear lysis was found around any stem. This was confirmed also in a histological investigation.

For the ABG-I cup the literature review gave survival rates between 59%–97% after 8–10 years. In our own study cup survival was 97.4% at 10 years. Looking at PE-wear, the literature gave average wear rates ranging from 0.24 to 0.32mm/year, values clearly above the wear rate boundary of 0.10–0.15mm/year usually considered as critical. In our own study augmented PE-wear (> 0.15mm/year) was noted in 23.6% of all implants. The majority (77%) of these implants were from patients younger than 70 years although this group only represented 57% of the total. The revision rates at 10 years reflect a similar trend with values much higher for patients below 70 years (2.8%) than above(4.9%).

Conclusions: Stem survival in our series was high, comparable to other published series and above the golden standard (cemented Charnley). However, the ABG-I cup showed lower survival rates, elevated PE-wear and augmented osteolysis around the holes. The comparatively high cup survival of our study is partly due to the high proportion of older patients. In the younger patient group PE-wear and revision rates were elevated. PE-wear is multifactorial and depends mainly on use. Some studies speculate it might be accelerated by low PE quality, crosslinking, liner fit or thickness. We found osteolysis not mainly at the rim but mostly around the 12 holes of the metal backed cup pointing at a possible pathway for wear particle migration into the reamed acetabulum as reported for other holed designs (Harris-Galante, Universal, Duraloc). As high wear and cyst formation did not always correlate it seems as if the pumping effect between flexing cup and acetabulum varies with component size, anatomy and bone quality influencing fluid flow, particle migration and osteolytic stimulus. A non-hole cup could alleviate this potential problem.

Introduction: In total knee arthroplasty (TKA) it remains a topic if cementless designs offer long-term stability equivalent to cemented procedures and if the components should be coated with calciumphosphate to enhance fixation. This study compares the three-dimensional migration patters of cemented and uncoated and periapatite (PA) coated tibial trays during a 2-year clinical follow-up study using roentgen stereophotogram-metric analysis (RSA) measurements as a predictor of long-term implant loosening (Ryds definition).

Methods: A double blind randomized prospective study was performed on 101 osteoarhtritic patients receiving 115 Duracon TKA. The tibial tray was either cemented (25), uncoated and uncemented (46) or PA-coated and uncemented (44). The groups were matched for sex, age, BMI and pre-op Insall score. Patients were evaluated at 1 week, 3, 6, 12 and 24 months post-operatively using standard radiographs and Insall scores. At each evaluation RSA measurements determined the translational (medial-lateral (ML), caudal-cranial (CC), anterior-posterior(AP)) and rotational (anterior tilt, external and valgus rotation) displacements of the tibial tray.

Results: Insall scores were not statistically different between the groups. Average component displacement was low for the cemented components in all directions. For the uncemented trays migration was highest in the CC direction (subsidence) and steep during the first 6 weeks. At two years the uncoated trays showed significantly more subsidence (−0.5 0.63 mm, range: −2.1 to 0.5 mm) than the cemented components (0.1 0.17 m, range: −0.2 to 0.4 mm, p< 0.05) and the PA-coated group (−0.1 0.60 mm, range: −2.8 to 0.3 mm, p< 0.05). Average subsidence of the cemented and PA-coated implants was nearly the same but variability was higher for the coated trays (p=0.01). Displacements in all other directions were not significantly different between the groups. Using Ryds definition, a total of 10 tibial trays from the cemented group (40%), 29 trays from the uncoated group (63%) and 11 trays from the PA-coated group (26%) were identified to be at risk for long-term loosening. In seven cases (all cemented) component tilt was critical.

Conclusion: At 2 years no clinical differences were found between cemented, uncoated and PA-coated tibial trays. However, RSA measurements showed significantly different migration patterns and predictions for long-term implant stability. Steep initial subsidence before stabilisation seems an inherent characteristics of uncemented fixation. In contrast, the cement layer below cemented trays can lead to AP tilt. Uncoated uncemented components migrate significantly indicating a high risk of late loosening. PA-coating reduces tray migration and the risk of long-term failure to levels equivalent to cemented fixation.

Introduction: In total hip arthroplasty (THA) polyethylene (PE) wear debris is major cause of osteolysis and aseptic implant loosening. Wear particle volumes must be reduced to increase implant survival. Various ways of crosslinking the molecular chains of PE have been proposed to increase the wear resistance of the bearing material but prospective long-term follow-up studies are scarce.

Materials & Methods A crosslinked PE acetabular insert was developed by gamma irradiating in a nitrogen atmosphere at a dose of 3MRad and subsequent annealing at 50° C for 144 hours to promote further crosslinking (“Duration” process). The Duration PE was compared to a conventionally prepared PE insert (irradiated at 3 MRad in air, no annealing) in a series of small punch tests, a hip wear simulator study and in-vivo as part of a randomized double-blind clinical study at three medical centers the PE-insert being the only variable. A total of 127 patients with 133 inserts (67 conventional, 66 Duration) were followed up between three and five years post-operatively. Wear was measured yearly by using a computer-based image analysis system. Radiographic appearance of potentially wear related phenomena such as osteolysis or loosening was assessed by an independent reviewer.

Results: Higher load at break during the small punch test confirmed the elevated crosslinking levels of Duration PE against the conventional PE. In the joint simulator Duration PE showed significantly lower volumetric wear rates (Mean SD: 21.7 2.3 mm3/10E6 cycles) than conventional PE (39.7 1.5 mm3/10E6 cycles, p< 0.05). A corresponding and significant level of wear reduction for the Duration PE was identified in-vivo (Duration: 43.7 33.6 mm3/year, conventional: 60.4 42.7 mm3/year, p=0.04). Radiographic analysis at the last follow-up gave evidence of femoral osteolytic lesions in five hips with conventional PE inserts and only one hip with a Duration insert.

Conclusions: Acetabular inserts made of crosslinked PE using the Duration process can significantly reduce in-vivo wear rates and the occurrence of potentially wear related osteolytic effects in the long-term follow-up of THA patients. The reduced clinical wear rates corresponded well with the results from the wear simulator measurements. This suggests that a PE with further increased crosslinking which shows even lower wear rates in simulator studies will lead to even lower wear and associated osteolysis in long-term clinical application.

In a preliminary experiment the paired radii and femora of dogs were tested for bone mineral mass and mechanical properties including the load at break, the ultimate bending strength and the modulus of elasticity; symmetry was observed for most of the parameters determined. The influence of the elasticity of materials used for the internal splintage of bone and its relationship to bone remodeling were then investigated for stainless steel and plastic plates applied to the femora of dogs. A significant decrease in bone mineral mass per centimetre length of bone and in mechanical properties was demonstrated for the femora plated with steel, and microradiography showed that this was due to massive endosteal resorption. A model for determining the influence of protection from stress in bone is presented.