Head Penetration Research Articles

Results of Primary Total Hip Arthroplasty Using 36 mm Femoral Heads on 1st Generation Highly Cross Linked Polyethylene in Patients 50 Years and Less with Minimum Five Year Follow-up.

PurposeWe evaluated the clinical and radiographic midterm results of primary total hip arthroplasty (THA) using a 36 mm diameter femoral head on 1st generation highly cross-linked polyethylene (HXLPE) in patients 50 years and less with minimum five year follow-up.Materials and MethodsWe retrospectively reviewed 31 patients (41 hips) aged 50 years and less underwent primary THA with a 36 mm diameter femoral head on HXLPE between 2004 and 2010. Clinical follow-ups included specific measurements like modified Harris hip scores (HHS) and Merle d'Aubigne and Postel score. For radiologic evaluations, together with position of acetabular cup at six weeks later of postoperation, we separately calculated the penentrations of femoral head into polyethylene liners during postoperation and one year later check-ups, and during one year later check-ups and final check-ups.ResultsThere were no major complications except for one case of dislocation. Average modified HHS at final follow-up was 88 (81-98), and Merle d'Aubigne and Postel scores were more than 15. Mean acetabular cup inclination and anteversion were 45.81°(36.33°-54.91°) and 13.26°(6.72°-27.71°), respectively. Average femoral head penetration of steady-state wear rate determined using radiographs taken at one-year postoperatively and at latest follow-up was 0.042±0.001 mm/year.ConclusionBased on minimum 5 years clinical results, we think 36 mm metal head coupling with HXLPE as the good alternate articulation surface when planning THA for patients aged 50 years and less.

Do temperature variations at the bearing surface during gait affect polyethylene wear in Charnley low-friction arthroplasty of the hip? Simulator study comparing UHMWPE and highly cross-linked polyethylene

IntroductionThere are significant individual variations in the polyethylene (PE) wear of Charnley total hip arthroplasty (THA) in published studies. This could be in part related to variations in hip joint kinematics with abnormal heating at the metal/PE interface. The objectives of our hip simulator experiment were: (1) to measure PE wear as a function of hip kinematics and temperature variations at the interface; (2) to compare ultra-high molecular weight polyethylene (UHMWPE) to latest generation highly cross-linked PE (XLPE). HypothesisOur hypothesis was that PE wear is correlated with temperature increases at the interface and thereby hip joint kinematics. Material and methodsA simulator study was performed with four UHMWPE cups (Initiale™, Amplitude, Valence, France) and two XLPE cups (X3, Stryker, Kalamazoo, Michigan, USA) subjected to 5 million cycles each. The temperature at the femoral head/cup interface was measured every 500 cycles and implant dimensions were measured every 1 million cycles. ResultsThe average temperature was 42°C for 1Hz and 50°C for 1.5Hz, no matter the type of PE tested. There was a large difference between UHMWPE and XLPE in their roughness, but no temperature variations or wear effects. Femoral head penetration after the first 1 million cycles was 0.18mm for the XLPE and 0.075mm UHMWPE on average. Between 1 and 5 million cycles, the penetration was less than 0.1mm per million cycles, with XLPE being similar to UHMPWE. DiscussionOur study found a significant temperature increase at the bearing interface as a function of frequency. But there was no correlation between temperature variations and PE degradation. However, shear stresses were under-estimated because our simulator could not reproduce abduction and adduction movements. Our hypothesis was not confirmed because PE deformation was not correlated to temperature variations. XLPE was not better than UHMWPE in the particular conditions of this study. Simulator studies are limited because of the lack of standards on cycling and the simulator bath. Level of evidenceIII–prospective case-control study in vitro.

Quantification of clearance and creep in acetabular wear measurements.

This study aimed to measure femoral head penetration before occurrence of real wear, and to quantify the portions attributable respectively to clearance and plastic deformations in various acetabular designs. We analyzed CT scans from 15 patients at 'day five' after total hip arthroplasty (THA). All patients received Exafit(®) femoral stems and 28 mm heads: 5 patients had cemented Durasul(®) all-PE cups, 5 patients had un-cemented Allofit(®) metal-backed cups, and 5 patients had un-cemented Stafit(®) dual-mobility cups. We also analyzed CT scans of samples of the three head-cup combinations to compare in vivo and in vitro measurements. The mean femoral head penetration measured on 'day five' was lower for all-PE cups (0.196 mm) than for metal-backed cups (0.551 mm) and dual-mobility cups (0.634 mm). The present study indicates that isolated measurements of femoral head penetration include 0.15-0.46 mm of radial clearance and 0.05-0.27 mm of creep, and confirms that the majority of so-called bedding-in observed in the first post-operative months is not entirely due to wear.

Radiostereometric analysis using clinical radiographic views: Validation measuring total hip replacement wear.

Radiostereometric analysis (RSA) is a stereo X-ray technique used in clinical research studies to evaluate micro-motion and wear of orthopaedic implants within bone. While highly accurate and precise, its adoption has been limited due to technical requirements such as the need for implanted marker beads and radiograph view angles determined by a calibration cage. We propose a new technique that separates the calibration procedure from the patient examination, enabling clinical radiograph views to be used for RSA measurements. The concept of a reference plate was adapted to establish the link between calibration procedure and patient examination procedure for cassette radiography, which may not be necessary for digital radiography. A hip wear phantom was used to validate this technique by comparing the error and repeatability of the novel procedure with that of conventional RSA. Femoral head penetration was measured versus the acetabular cup (head/cup) and marker beads in the acetabular liner (head/liner). Conventional RSA had lower inferior-superior average error (p = 0.03 for head/cup) while the modified RSA had lower anterior-posterior average error (p = 0.01). Average error was greater but not significantly so for the medial-lateral (p = 0.06) and 3D (p = 0.97) measurements. The head/liner method had lower average errors (p < 0.0001) for both procedures, but did not affect repeatability, which was similar between techniques. The novel procedure's average error and repeatability was therefore, similar to conventional RSA. This new technique could be applied to any joint with two clinical radiograph view angles pending further validation in subjects. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1521-1528, 2016.

The effect of friction and impact angle on the spermatozoa–oocyte local contact dynamics

Although a large proportion of biomolecules involved in spermatozoa–oocyte interaction has been discovered so far, many details of fertilization mechanism remain unknown. Both biochemical and biomechanical components exist in the fertilization process. Mammalian sperm evolved a ZP (zona pelucida) thrust reduction penetration strategy probably in response to the ZP resilient elasticity.Using a biomechanical approach and FEM analysis, local contact stress, ZP deformations during impact and attempt of sperm head penetration relative to different sperm impact angles (SIA) were studied. The sperm–oocyte contact was defined as non-linear frictional contact. A transient structural analysis at 37°C revealed that, from the mechanical standpoint there are SIA that are more favorable for possible ZP penetration due to larger equivalent stress of ZP. An “slip-stick” resembling effect was identified for almost all examined SIA. The sperm head–ZP contact area increases as SIA decreases. Favorable ZP-stress state for sperm penetration regarding SIA are discussed.

Five-Year Experience of Vitamin E–Diffused Highly Cross-Linked Polyethylene Wear in Total Hip Arthroplasty Assessed by Radiostereometric Analysis

BackgroundVitamin E–diffused highly cross-linked polyethylene (VEPE) was developed to reduce oxidation without compromising mechanical strength. The purpose of this study was to evaluate VEPE in vivo using radiostereometric analysis (RSA) and patient-reported outcome measures (PROMs). MethodsFifty-one hips were enrolled. Each patient received a VEPE liner, a porous titanium shell, and an uncemented stem with a 32-mm cobalt–chrome femoral head. Tantalum beads were inserted into the VEPE to measure femoral head penetration using RSA. RSA radiographs and PROMs were obtained preoperatively immediately after surgery, 6 months, 1, 2, 3, and 5 years after surgery. ResultsForty-seven hips returned at 3 years, and 42 hip at 5 years. The mean ± standard error of the mean proximal head penetration into the polyethylene was 0.06 ± 0.01 at 5 years. The amount of head penetration did not change significantly with increasing time in vivo. The mean ± standard error of the mean Harris Hip Score was 58 ± 2 preoperatively, which improved significantly to 93 ± 2 at 5 years (P < .001). ConclusionThe head penetration into VEPE liners was low compared with non-VEPE at 5 years. After settling of the liners in the early period, no significant head penetration occurred from 2- to 5-year follow-up. All PROMs improved significantly from preoperative to postoperative and remained very favorable at 5 years. This study documents the longest-term evaluation of in vivo wear performance of VEPE.

3-year follow-up of a long-term registry-based multicentre study on vitamin E diffused polyethylene in total hip replacement.

Preclinical studies of vitamin E diffused highly cross-linked polyethylene (E-XLPE) has shown enhanced mechanical properties with less wear. The purpose of our study was to document the early clinical outcome of E-XLPE to ensure, for the safety of patients, that there are no unforeseen early adverse events from using this new biomaterial. The enrolled patients (n = 977) have received either a porous titanium coated or porous plasma sprayed acetabular shell with either a E-XLPE liner or a medium cross-linked (AXL) liner. At each follow-up 5 patient-reported outcome measures (PROMs) were completed: Harris Hip Score, Case Mix Indicator, UCLA Activity Score, SF-36, and EQ-5D. Radiographs were measured for cup and stem position, as well as femoral head penetration into the liner (wear). Postoperative complications and revisions were collected. At 3 years follow-up, there were 13 revisions due to: 4 periprosthetic fractures; 1 sepsis; 6 instabilities; and 2 implant mismatches at surgery. Wear of the hip implant, calculated by software analysis of pelvis x-rays, from the postoperative interval to 3 years showed a liner penetration rate of 0.027 mm/year for AXL and 0.005 mm/year for E-XLPE with no significant difference between the 2 (p = 0.24). Improvement was seen in all PROMs from the preoperative interval to 3 years after surgery (p&lt;0.0001). Early follow-up of the E-XLPE and AXL liners show low penetration. PROMs indicate improvement after total hip arthroplasty in functionality and quality of life across the centers. We have not observed any early in vivo adverse effects from diffusing the liners with vitamin E. ClinicalTrials.gov Identifier: NCT00545285.

The rates of wear of X3 highly cross-linked polyethylene at five years when coupled with a 36 mm diameter ceramic femoral head in young patients.

Polyethylene wear debris can cause osteolysis and the failure of total hip arthroplasty. We present the five-year wear rates of a highly cross-linked polyethylene (X3) bearing surface when used in conjunction with a 36 mm ceramic femoral head. This was a prospective study of a cohort of 100 THAs in 93 patients. Pain and activity scores were measured pre- and post-operatively. Femoral head penetration was measured at two months, one year, two years and at five years using validated edge-detecting software (PolyWare Auto). At a mean of 5.08 years (3.93 to 6.01), 85 hips in 78 patients were available for study. The mean age of these patients was 59.08 years (42 to 73, the mean age of males (n = 34) was 59.15 years, and females (n = 44) was 59.02 years). All patients had significant improvement in their functional scores (p < 0.001). The steady state two-dimensional linear wear rate was 0.109 mm/year. The steady state volumetric wear rate was 29.61 mm(3)/year. No significant correlation was found between rate of wear and age (p = 0.34), acetabular component size (p = 0.12) or clinical score (p = 0.74). Our study shows low steady state wear rates at five years in X3 highly cross-linked polyethylene in conjunction with a 36 mm ceramic femoral head. The linear wear rate was almost identical to the osteolysis threshold of 0.1 mm/year recommended in the literature.

Oxinium modular femoral heads do not reduce polyethylene wear in cemented total hip arthroplasty at five years: a randomised trial of 120 hips using radiostereometric analysis.

We report the five-year outcome of a randomised controlled trial which used radiostereometric analysis (RSA) to assess the influence of surface oxidised zirconium (OxZr, Oxinium) on polyethylene wear in vivo. A total of 120 patients, 85 women and 35 men with a mean age of 70 years (59 to 80) who were scheduled for primary cemented total hip arthroplasty were randomly allocated to four study groups. Patients were blinded to their group assignment and received either a conventional polyethylene (CPE) or a highly cross-linked (HXL) acetabular component of identical design. On the femoral side patients received a 28 mm head made of either cobalt-chromium (CoCr) or OxZr. The proximal head penetration (wear) was measured with repeated RSA examinations over five years. Clinical outcome was measured using the Harris hip score. There was no difference in polyethylene wear between the two head materials when used with either of the two types of acetabular component (p = 0.3 to 0.6). When comparing the two types of polyethylene there was a significant difference in favour of HXLPE, regardless of the head material used (p < 0.001). In conclusion, we found no advantage of OxZr over CoCr in terms of polyethylene wear after five years of follow-up. Our findings do not support laboratory results which have shown a reduced rate of wear with OxZr. They do however add to the evidence on the better resistance to wear of HXLPE over CPE.

PWSCC Assessment by Using Extended Finite Element Method

The head penetration nozzle of control rod driving mechanism (CRDM) is known to be susceptible to primary water stress corrosion cracking (PWSCC) due to the welding-induced residual stress. Especially, the J-groove dissimilar metal weld regions have received many attentions in the previous studies. However, even though several advanced techniques such as weight function and finite element alternating methods have been introduced to predict the occurrence of PWSCC, there are still difficulties in respect of applicability and efficiency. In this study, the extended finite element method (XFEM), which allows convenient crack element modeling by enriching degree of freedom (DOF) with special displacement function, was employed to evaluate structural integrity of the CRDM head penetration nozzle. The resulting stress intensity factors of surface cracks were verified for the reliability of proposed method through the comparison with those suggested in the American Society of Mechanical Engineering (ASME) code. The detailed results from the FE analyses are fully discussed in the manuscript.

Precision of radiostereometric analysis (RSA) of acetabular cup stability and polyethylene wear improved by adding tantalum beads to the liner

Background and purpose — In traditional radiostereometric analysis (RSA), 1 segment defines both the acetabular shell and the polyethylene liner. However, inserting beads into the polyethylene liner permits employment of the shell and liner as 2 separate segments, enabling distinct analysis of the precision of 3 measurement methods in determining femoral head penetration and shell migration.Patients and methods — The UmRSA program was used to analyze the double examinations of 51 hips to determine if there was a difference in using the shell-only segment, the liner-only segment, or the shell + liner segment to measure wear and acetabular cup stability. The standard deviation multiplied by the critical value (from a t distribution) established the precision of each method.Results — Due to the imprecision of the automated edge detection, the shell-only method was least desirable. The shell + liner and liner-only methods had a precision of 0.115 mm and 0.086 mm, respectively, when measuring head penetration. For shell migration, the shell + liner had a precision of 0.108 mm, which was better than the precision of the shell-only method. In both the penetration and migration analyses, the shell + liner condition number was statistically significantly lower and the bead count was significantly higher than for the other methods.Interpretation — Insertion of beads in the polyethylene improves the precision of femoral head penetration and shell migration measurements. A greater dispersion and number of beads when combining the liner with the shell generated more reliable results in both analyses, by engaging a larger portion of the radiograph.

Do new materials improve acetabular fixation and reduce wear? Commentary on an article by David C. Ayers, MD, et al.: "radiostereometric analysis study of tantalum compared with titanium acetabular cups and highly cross-linked compared with conventional liners in young patients undergoing total hip replacement".

Commentary The bearing articulation remains the nemesis of total hip arthroplasty. Obtaining and maintaining component stability and minimizing wear of the articulation represent the two most important factors for the longevity of any hip replacement. This article by Ayers et al. evaluates the stability of two different types of cementless fixation, a titanium fiber mesh compared with ultra-porous tantalum. The authors further investigate wear of an ultra-high molecular weight conventional polyethylene liner compared with a highly cross-linked polyethylene liner. This article represents a sequel to a previously published two-year follow-up evaluation of noncemented total hip arthroplasty acetabular migration and polyethylene wear as determined by radiostereometric analysis (RSA)1. A total of forty-six young, active individuals undergoing primary total hip arthroplasty were randomized into four cohorts: ultra-high molecular weight conventional polyethylene liner and titanium cup, highly cross-linked polyethylene liner and titanium cup, ultra-high molecular weight conventional polyethylene liner and tantalum cup, and highly cross-linked polyethylene liner and tantalum cup. There were no clinical or non-RSA radiographic differences among the groups. RSA demonstrated significantly less femoral head penetration, a surrogate for polyethylene wear, in the highly cross-linked polyethylene liners compared with ultra-high molecular weight conventional polyethylene liners by an order of magnitude. There was no significant difference in proximal migration between the titanium and tantalum acetabular components through five years of follow-up. The type of polyethylene liner or acetabular component had no effect on patient activity, pain, and well-being, which were maximized by six months following surgical intervention. The strength of this article is that it is a prospective, randomized, blinded study utilizing a very sophisticated technology, namely RSA, to obtain precise measurements of component micromotion relative to the bone that is otherwise undetectable by routine radiographs and to measure femoral head penetration2. The radiodense tantalum cups obscure the identification of the center of the femoral head with use of edge detection. Therefore, Ayers et al. developed a novel method known as the “fictive femoral head” to assess wear. This method is based on the identification of two radiopaque tantalum markers attached to the stem proximally and a priori knowledge of the femoral head and stem configuration of the inserted total hip replacement. From a series of radiographs, a stem configuration library was created, which provided geometrical information used to place a fictive femoral head center in three-dimensional space. This fictive femoral head center will be used by the RSA software. Although others have reported a substantial decrease in the wear of highly cross-linked polyethylene3, this article clearly shows the superiority of highly cross-linked polyethylene over conventional polyethylene, with a tenfold reduction in wear. Wear rates from one to five years were 0.04 mm/yr for ultra-high molecular weight conventional polyethylene liners and 0.004 mm/yr for highly cross-linked polyethylene liners. With respect to fixation, Ayers et al. demonstrated excellent fixation of both titanium mesh and tantalum acetabular components, as has been previously documented4. At the five-year follow-up, the median migration (and standard error) was 0.05 ± 0.20 mm proximally for titanium mesh cups and 0.21 ± 0.05 mm for tantalum cups. No implants were shown to be loose on radiographs. There was no evidence of osteolysis and no revisions were performed through five years of follow-up. The take-home points from this article are as follows. With use of femoral head penetration according to precise RSA measurements as a surrogate for wear, highly cross-linked polyethylene demonstrates ten times lower wear than ultra-high molecular weight conventional polyethylene at up to five years of follow-up3. Titanium mesh and tantalum (Trabecular Metal; Zimmer) materials provide excellent cementless fixation for acetabular components with little evidence of clinically relevant migration as measured by sophisticated RSA technology at up to five years of follow-up4. These results cannot and should not be extrapolated to other types of porous and ultra-porous cementless fixation.

Three Year RSA Evaluation of Vitamin E Diffused Highly Cross-linked Polyethylene Liners and Cup Stability

Vitamin E diffusion into highly cross-linked polyethylene (E-XLPE) is a method for enhancing oxidative stability of acetabular liners. The purpose of this study was to evaluate in vivo penetration of E-XLPE using radiostereometric analysis (RSA). Eighty-four hips were recruited into a prospective 10-year RSA. This is the first evaluation of the multicenter cohort after 3-years. All patients received E-XLPE liners (E1, Biomet) and porous-titanium coated cups (Regenerex, Biomet). There was no difference (P=0.450) in median femoral head penetration into the E-XLPE liners at 3-years comparing cobalt-chrome heads (−0.028mm; inter-quartile range (IQR) — 0.065 to 0.047) with ceramic heads (−0.043mm, IQR — 0.143to0.042). The 3-year follow-up indicates minimal E-XLPE liner penetration regardless of head material and minimal early cup movement.

CORR Insights ®: Metal-on-conventional total hip arthroplasty bearing surfaces have a higher risk of revision than metal-on-highly crosslinked polyethylene: results from a US registry.

H ighly crosslinked polyethylene (XLPE) has essentially supplanted conventional polyethylene for use in total hip arthroplasty (THA) during the past decade. There now exists good evidence to demonstrate a clear reduction in femoral head penetration (and presumably polyethylene wear) and periprosthetic osteolysis associated with the use XLPE compared to conventional polyethylene in THA [2, 3]. While the annual reports of Australian Orthopaedic Association National Joint Replacement Registry continue to show the clinical benefits of XLPE (demonstrating a reduction in revision rates) [1], other investigators have not demonstrated a clear reduction in revision rates with the use of XLPE at mid-term followup [4]. The current study by Paxton and colleagues attempts to demonstrate the clinical benefits resulting from the use of XLPE compared to conventional polyethylene through the analysis of a large US-based patient database. Their findings demonstrate that, for two specific implant designs, the revision rate was significantly decreased for XLPE compared to the use of conventional polyethylene. Therefore, this work essentially confirms the experience reported by the Australian Orthopaedic Association National Joint Replacement Registry during the past decade. While important work, this study is limited by the observational nature of the study, inherent to all registry or database analysis, and only provides information about two specific hip designs (both of which having been replaced by more recent designs by their respective manufacturers). Furthermore, analysis of this type does not provide any radiological, functional or patient-derived outcomes This CORR Insights is a commentary on the article ‘‘Metal-on-conventional Total Hip Arthroplasty Bearing Surfaces Have a Higher Risk of Revision Than Metal-on-highly Crosslinked Polyethylene: Results From a US Registry’’ by Paxton and colleagues available at: DOI: 10.1007/s11999-014-4105-9 The author certifies that he, or any member of his immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/ licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR or the Association of Bone and Joint Surgeons. This CORR Insights comment refers to the article available at DOI: 10.1007/s11999-0144105-9

CORR Insights®: Retrieval analysis of sequentially annealed highly crosslinked polyethylene used in total hip arthroplasty.

I n vivo oxidation of highly crosslinked polyethylene (HXLPE) components, particularly among annealed polyethylenes, resulted in the development of the so-called ‘‘secondgeneration HXLPEs’’ (defined as HXLPEs that incorporate manufacturing modifications to improve minor deficiencies with unclear consequences). Among those, sequentially annealed polyethylenes were designed to decrease the detected in vivo oxidation that could adversely affect the durability of these components in vivo. Radiostereometric analysis of THAs using sequentially annealed secondgeneration HXLPE liners suggested that head penetration and threedimensional wear remained low at 5 years [1]. However, recent retrieval studies [2, 3] stressed the persistence of oxidation in the HXLPE in the face of remelting, annealing, or sequential annealing. While in vivo oxidation was higher in the tibial retrievals than in the acetabular liners, the debate regarding this topic continues. The location and mechanical effects of residual oxidation that develops in vivo may influence the risk of component failure, in particular in THAs.

Migration of the penetrated rib head following deformity correction surgery without rib head excision in dystrophic scoliosis secondary to type 1 Neurofibromatosis.

Dystrophic scoliosis secondary to Neurofibromatosis type 1 (NF1) may predispose to rib penetration into the spinal canal. No clear consensus was established regarding whether or not to resect the compressing rib head during correction maneuvers. The purpose of this study was to present imaging quantification of the migration of intraspinal-dislocated rib head in order to assess the extraction degree of dislocated rib heads and the associated influencing factors. Imaging data of NF1 scoliotic patients with intraspinal rib head dislocation from March 1998 to April 2014 were retrospectively reviewed. The location and migration of the rib head were evaluated in a spinal canal-based coordinate system to calculate their pre- and postoperative vector coordinates. Differences in multiple parameters representative of rib head position were compared by paired sample t test. We also explored whether correction of vertebral rotation and translation could contribute to the extraction of intra-canal rib head by linear regression analysis. The incidence of apical convex rib head penetration into the canal was 15.9 % (23/145). Only 14.8 % of the dislocated rib heads invaded into the concave half-circle of the spinal canal, which was reduced to 3.7 % postoperatively. The directions of rib head migration were mostly toward the anterior convex quadrant of the spinal canal (70.4 %). Paired sample t tests revealed significant reduction in intraspinal rib length (9.2 ± 3.6 vs. 5.2 ± 3.6 mm, p < 0.001) and improvement in distance between the rib head tip and the most concave spot of the spinal canal (DRCSSC) (14.2 ± 2.6 vs. 18.1 ± 3.3 mm, p < 0.001). Change of rib-vertebrae angle (RVA) was demonstrated to be positively correlated with reduction in intraspinal rib length (β = 0.534, p = 0.004), while Change of RVA (β = -0.460, p = 0.008) and vertebral translation (VT) (β = -0.381, p = 0.024) was negatively correlated with change of DRCSSC. Spontaneous migration of the dislocated rib head following posterior correction surgery resulted in shorter intraspinal rib length and larger uninvaded area. More correction of vertebral translation and rib-vertebrae angle could increase the degree of extraction from the spinal canal immediately after the surgery.

ICONE23-1712 SENSITIVITY ANALYSIS OF THE BWR PASSIVE DEPRESSURIZATION SYSTEM UNDER SEVERE ACCIDENT CONDITIONS

Reactor vessel depressurization is an important measure before an accident sequence progresses to the point of vessel bottom head penetration failure under high-pressure condition. The passive depressurization systems can depressurize the reactor coolant system to prevent or to mitigate the effects of direct containment heating instead of the safety/relief valves (SRV) if SRV is inoperable or it is stuck in the closed position. The sensitivity analysis performed with SAMPSON code in this study demonstrated that the passive depressurization system with an optimized leakage area and failure condition is more efficient in managing a severe accident.

Results of Primary Total Hip Arthroplasty with 36-mm Femoral Heads on Highly Cross-linked Polyethylene-Minimum Seven-years Follow-up.

PurposeWe evaluate the clinical and radiographic midterm results of primary total hip arthroplasty (THA) using a 36 mm diameter femoral head on highly cross-linked polyethylene (minimum 7-year follow-up).Materials and MethodsWe retrospectively reviewed 73 patients (74 hips) that underwent primary THA with a 36 mm diameter femoral head on highly cross-linked polyethylene between July 2004 and February 2007. Clinical follow-ups included specific measurements like modified Harris hip scores (HHS) and Merle d'Aubigne and Postel score. For radiologic evaluations, together with position of acetabular cup at 6 weeks later of post-operation, we separately calculated the penentrations of femoral heads into polyethylene liners during post-operation and one year later check-ups, and during one year later check-ups and final check-ups.ResultsThere were no complications except for one case of dislocation. Average modified HHS at final follow-up was 88±7.5 (range, 81-96), and Merle d'Aubigne and Postel scores were more than 15 (range, 15-18). Mean acetabular cup inclination and anteversion were 50.1°(range, 35°-58°) and 23.6°(range, 5°-38°), respectively. Average femoral head penetration during the first postoperative year was 0.071±0.034 mm/year, and steady-state wear rate determined using radiographs taken at one-year postoperatively and at latest follow-up was 0.051±0.022 mm/year. Average femoral head penetration during entire follow-ups was 0.058±0.013 mm/year.ConclusionPrimary THA with a large diameter femoral head on highly cross-linked polyethylene was found to produce the results comparable to previous in vitro laboratory hip simulation studies. And we also find out good scores in terms of patient's functionality.

Minimum five-year wear rate of metal-on-highly cross-linked polyethylene in primary total hip arthroplasty.

Highly cross-linked polyethylenes (PE) have been developed with encouraging results in terms of wear. Another body of the literature has indicated potential catastrophic failures related to reduced fatigue properties and oxidation. Each PE available on the market has its own processing characteristics. The aim of this retrospective study was to evaluate the minimum five-year wear properties of an original highly cross-linked PE in a consecutive series of primary THAs. Between August 2005 and December 2007, 80 patients with a mean age of 62.7 years were included. All patients had a 28-mm CoCr femoral head articulating with a highly cross-linked insert (Highcross®, Medacta SA) that was 100 Mrads gamma radiated, remelted at 150 °C, and ethylene oxide sterilized. The primary criterion for evaluation was the femoral head penetration, as measured by Hip Analysis Suite software. The steady state wear was also calculated. Functional results were evaluated according to the WOMAC score. Complete data were available for analysis in 67 patients at a mean follow-up of 5.5 years. The mean femoral head penetration was 0.128 ± 0.62 mm and the steady state wear was-0.025 ± 0.22 mm/year. The WOMAC score significantly decreased from 16.5 ± 5.93 pre-operatively to 4.12 ± 5.5 at the latest follow-up (p <0.001). The minimal five-year results of this retrospective study indicate that this particular highly cross-linked and remelted polyethylene had a low wear rate. Longer-term results are needed to warrant that these mid-term data will generate less osteolysis and resultant aseptic loosening.

Total hip replacement using a highly crosslinked polyethylene liner in Asians with small acetabulum.

To evaluate the medium-term outcomes of total hip replacement (THR) using a thin highly cross-linked polyethylene (HXLPE) liner in an Asian population. Medical records of 20 men and 44 women aged 26 to 80 (mean, 59) years who underwent 80 THRs using a thin HXLPE liner by a single surgeon were reviewed. Indications for THR included dysplasia (n = 26), avascular necrosis (n=26), osteoarthritis (n = 22), rheumatoid arthritis (n = 4), and ankylosing spondylitis (n = 2). The surgical technique, implant used, and rehabilitation protocol were standardised. Radiographs were evaluated for cup migration and peri-implant radiolucency. Femoral head penetration was assessed at day 1 and last follow-up using the Kang modification of the Dorr and Wan method and the PowerPoint method. After a mean follow-up of 7.5 (range, 5.0-11.9) years, no patient had undergone acetabular revision. Two hips were revised for the femoral stem. Femoral head penetration did not correlate with sex, age at surgery, hip pathology, acetabular inclination angle, cup size, or liner thickness. The maximum femoral head penetration was 0.09 mm/year, which was below the osteolysis threshold of 0.1 mm/year. The mean ± standard deviation femoral head penetration was 0.29 ± 0.12 mm (or 0.04 ± 0.02 mm/year) by the PowerPoint method and 0.17 ± 0.22 mm (or 0.02 ± 0.03 mm/year) by the Kang modification of the Dorr and Wan method. Femoral head penetration correlated with the number of years of follow-up (p = 0.012). The use of a thin HXLPE liner in primary THR for patients with small acetabulum achieved good outcomes after a mean of 7.5 years.