Ion release in ceramic bearings for total hip replacement: Results from an in vitro and an in vivo study.

INTRODUCTION: Literature on the potential release of trace elements following implantation of Zirconia-platelet toughened alumina (ZPTA) ceramic components is scant. The present study therefore analysed the in vitro and in vivo potential release of ions from ZPTA bearings. MATERIAL AND METHODS: An in vitro and in vivo study was conducted. The in vitro study compared leaching in bovine serum from two groups: ZPTA ceramic heads and Co-28Cr-6Mo alloy heads, both 28-mm diameter. A third group without implant served as reference group. An in vivo clinical study compared trace elements in the whole blood of patients with 36-mm diameter ZPTA ceramic-on-ceramic articulation after three and 12 months. A cohort of subjects without any prosthesis was used as control group. The release of ions was determined by high resolution-inductively coupled plasma-mass spectrometry. RESULTS: In the in vitro experiment, significant differences (p ≤ 0.01) in trace element release for chromium, cobalt and molybdenum were found, with increased levels of ion release in the Co-28Cr-6Mo metal group. The very low detection limit for yttrium allowed detection of a small yttrium release from the ZPTA heads, which was not confirmed by the in vivo study. No significant difference between the groups was found for strontium, aluminium, and zirconium. In the in vivo study, no relevant differences in ion levels between the reference group without any implant and the study group were found at the three and 12-month follow-up. CONCLUSION: This study supports that ZPTA ceramic articulation components are safe in terms of ion release, and may be an excellent alternative to bearings based on Co-28Cr-6Mo alloys.

Blood cytokine pattern and clinical outcome in knee arthroplasty patients: comparative analysis 5 years after standard versus "hypoallergenic" surface coated prosthesis implantation.

Background and purpose - Metal sensitivity might provoke complications after arthroplasty. Correspondingly, coated "hypoallergenic" implants are of interest but long-term follow-up data are missing. Thus, we assessed immunological and clinical parameters in such patients. Patients and methods - 5 years' follow-up data were obtained from 3 centers, which used either a standard total knee replacement (TKR) or the identical implant with multilayer surface zirconium nitride based coating. Of the 196 patients (mean age 68 years (44-84), 110 females) 97 had arthroplasty with a coated surface, and 99 were treated by a standard TKR of the same type. Investigations were Knee Society Score (KSS), Knee injury and Osteoarthritis Outcome Score (KOOS), radiographic analysis, and cytokine measurement in peripheral blood. Pro- and anti-inflammatory cytokines were evaluated by cytometric beads assay and RT-PCR. Results - Survival rate (Kaplan-Meier) was 98% for coated and 97% for uncoated implants after 5 years. Mechanical axis and KSS pain score (42 vs. 41 (0-50)) were comparable. Most serum cytokine levels were comparable, but mean interleukin-8 and interleukin-10 levels were higher in the group with an uncoated implant. IL-8: 37 (SD 7.5) pg/mL vs. 1.1 (SD 4.3) (p < 0.001); IL-10: 3.6 (SD 2.5) vs. 0.3 (SD 1.8) pg/mL (p < 0.001). Interpretation - There was similar clinical outcome 5 years after standard and surface-coated TKR. In peripheral blood there was an increased pro-inflammatory status, i.e., significant elevation of IL-8 and the anti-inflammatory IL-10, after standard uncoated prosthesis. Any long-term effects of these cytokine changes are unknown.

Biomechanics of a calcar loading and a shortened tapered femoral stem: Comparative in-vitro testing of primary stability and strain distribution.

PURPOSE: The most common femoral short stems available on the market can, in principle, be divided with regard to their anchoring concepts into a calcar loading and a shortened tapered design. The purpose of this study was to compare the primary stability and stress-shielding of two short stems, which correspond to these two different anchoring concepts. METHODS: Using seven paired fresh frozen human cadaver femurs, primary axial and rotational stabilities under dynamic load (100-1600 N) were evaluated by miniature displacement transducers after 100,000 load cycles. Changes in cortical strains were measured before and after implantation of both stem types to detect implant-specific load transmission and possible stress-shielding effects. RESULTS: Reversible and irreversible micromotions under dynamic load displayed no significant differences between the two implants. Implantation of either stem types resulted in a reduction of cortical strains in the proximal femur, which was less pronounced for the calcar loading implant. CONCLUSIONS: Both short stems displayed comparable micromotions far below the critical threshold above which osseointegration may disturbed. Neither short stem could avoid proximal stress-shielding. This effect was less pronounced for the calcar loading short stem, which corresponds to a more physiological load transmission.

Anterior pelvic plane registration accuracy and cup position measurement using ultrasound- and pointer-based navigation in primary total hip arthroplasty.

BACKGROUND: Incorrect cup positioning in primary total hip arthroplasty is known as a risk factor for early implant failure. The use of navigation systems leads to more accurate cup positioning. OBJECTIVE: The aim of this study was to compare the registration accuracy of the anterior pelvic plane and the measurement accuracy of the definite cup position for a pointer computer-assisted orthopaedic navigation system (P-CAOS) and an ultrasound-based navigation tool (US-CAOS) in an intra-individual study design. METHODS: Anterior pelvic plane registration was performed in 44 patients receiving a primary total hip arthroplasty with P-CAOS and US-CAOS. The cup implantation was performed using US-CAOS. Intraoperatively, the cup position was assessed using P-CAOS and US-CAOS. The postoperative cup position was determined via CT scan. Inclination and anteversion errors were calculated using intraoperative values and CT data. All operations were performed by a single, high-volume surgeon using a minimally invasive anterolateral approach. RESULTS: The mean inclination error was 0.9∘ in the US-CAOS group and -1.1∘ in the P-CAOS group. This was not statistically significant. The mean anteversion error was significantly reduced (p< 0.001) in the US-CAOS group (1.4∘) compared to the P-CAOS group (-8.0∘). Significantly more cups (23 of 44; 52%) in the P-CAOS group were outliers regarding to the defined anteversion error range of 15∘± 10∘. Outliers in the US-CAOS group amounted to two (of 44; 5%) (p< 0.001). The number of outliers regarding the inclination error range of 40∘± 10∘, did not differ significantly between the P-CAOS (2; 5%) and US-CAOS (1; 2%) group. CONCLUSION: We were able to show a systematic anterior pelvic plane registration error in this intraindividual study design. US-CAOS based APP landmark registration showed to be significantly more precise compared to P-CAOS registration. The anteversion error of the cup using US-CAOS showed to be significantly reduced compared to the P-CAOS method.

Ultrasound vs pointer palpation based method in THA navigation: a comparative study.

Intraoperative registration of the anterior pelvic plane is necessary for navigation during total hip arthroplasty (THA). Ultrasound referencing of bony landmarks was implemented in a THA navigation system (OrthoPilot, B. Braun Aesculap; Tuttlingen, Germany) as an alternative to pointer palpation. This study compared the accuracy of manual pointer palpation with ultrasound registration for determining anterior pelvic plane registration in a consecutive series of 37 cases. Findings showed postoperative radiographic anteversion was lower than ultrasound and pointer navigated anteversion. Because ultrasound registers the bony landmarks of the anterior pelvic plane with a high degree of accuracy, we conclude radiographs 2 weeks post-operatively are not suited to evaluate anteversion, because they still display a pelvic tilt due to a pre-operative flexion contraction.

OrthoPilot total hip arthroplasty workflow and surgery.

To analyze the workflow and navigation principles of the OrthoPilot total hip arthroplasty (THA) Version 2.0 (B. Braun-Aesculap, Tuttlingen, Germany), a consecutive series of 60 patients was used to compare the navigated intraoperative data and postoperative measurements of stem and cup position. Within the safe zone, 96.3% of 54 acetabular cups were positioned. The rotational accuracy of femoral instruments was 65 degrees in 41 THAs. The femoral offset was medialized by 6.05 mm in 76% and lateralized by 2.1 mm in 14%. The data for leg length and range of motion from 60 THAs and the navigated data were similar. Thus, the first clinical validation of the workflow of the OrthoPilot THA Version 2.0 is encouraging.

Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case-control study of 235 cases compared with 235 conventionally implanted prostheses.

The aim of the study was to assess the consistency of the non-image-based navigation system OrthoPilot, Aesculap, Tuttlingen, Germany, in total knee arthroplasty (TKA) implantation in 5 European centers. Two hundred thirty-five TKAs implanted with this navigation system were matched (according to severity of the preoperative coronal deformation and body mass index) to a historical control group of 235 TKAs implanted with a conventional technique. Consistency of implantation was studied on a 3-month postoperative radiological control with coronal long-leg and sagittal standard x-rays. The use of the OrthoPilot navigation system allowed a statistically significant improvement in the consistent placement of both tibial and femoral components. In accordance with current literature, survival of the navigated implanted prostheses is expected to be longer.

OrthoPilot cup navigation--how to optimise cup positioning?

UNLABELLED: The kinematic cup navigation procedure is a surgically simple technique for improving the precision of cup placement. Without CT scans, a reduction of cup malpositions is possible. The rate of desired cup inclination and anteversion angles is markedly increased as shown by the first results of 147 navigated cups. While the inclination is reached precisely with a tendency to a slightly larger angle than desired, the postoperative anteversion angle shows a somewhat bigger variation than the intraoperatively navigated angle with a tendency to less anteversion. This might be due to a lack of information about the real pelvis position during X-ray control. CLINICAL RELEVANCE: dislocations of the prostheses might be reduced significantly. The kinematic cup navigation with the use of the OrthoPilot is an additional and useful tool for the surgeon. The procedure is simple, quick, and cost effective, does not cause specific complications, and does not require additional CT or MRI scans. Further improvement can be expected by additional hip stem navigation techniques in the near future.