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.

We have compared four computer-assisted methods to measure penetration of the femoral head into the acetabular component in total hip replacement. These were the Martell Hip Analysis suite 7.14, Rogan HyperOrtho, Rogan View Pro-X and Roman v1.70. The images used for the investigation comprised 24 anteroposterior digital radiographs and 24 conventional acetate radiographs which were scanned to provide digital images. These radiographs were acquired from 24 patients with an uncemented total hip replacement with a follow-up of approximately eight years (mean 8.1; 6.3 to 9.1). Each image was measured twice by two blinded observers. The mean annual rates of penetration of the femoral head measured in the eight-year single image analysis were: Martell, 0.24 (SD 0.19); HyperOrtho, 0.12 (SD 0.08); View Pro-X, 0.12 (SD 0.06); Roman, 0.12 (SD 0.07). In paired analysis of the six-month and eight-year radiographs: Martell, 0.35 (SD 0.22); HyperOrtho, 0.15 (SD 0.13); View Pro-X, 0.11 (SD 0.06); Roman, 0.11 (SD 0.07). The intra- and inter-observer variability for the paired analysis was best for View Pro-X and Roman software, with intraclass correlations of 0.97, 0.87 and 0.96, 0.87, respectively, and worst for HyperOrtho and Martell, with intraclass correlations of 0.46, 0.13 and 0.33, 0.39, respectively.

The Roman method proved the most precise and the most easy to use in clinical practice and the software is available free of charge. The Martell method showed the lowest precision, indicating a problem with its edge detection algorithm on digital images.

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: 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 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.

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.