Femoral Cup Research Articles

Radiostereometric analysis and clinical outcomes of a novel reverse total hip system at two years.

Instability is a common cause of failure after total hip arthroplasty. A novel reverse total hip has been developed, with a femoral cup and acetabular ball, creating enhanced mechanical stability. The purpose of this study was to assess the implant fixation using radiostereometric analysis (RSA), and the clinical safety and efficacy of this novel design. Patients with end-stage osteoarthritis were enrolled in a prospective cohort at a single centre. The cohort consisted of 11 females and 11 males with mean age of 70.6 years (SD 3.5) and BMI of 31.0 kg/m2 (SD 5.7). Implant fixation was evaluated using RSA as well as Western Ontario and McMaster Universities Osteoarthritis Index, Harris Hip Score, Oxford Hip Score, Hip disability and Osteoarthritis Outcome Score, 38-item Short Form survey, and EuroQol five-dimension health questionnaire scores at two-year follow-up. At least one acetabular screw was used in all cases. RSA markers were inserted into the innominate bone and proximal femur with imaging at six weeks (baseline) and six, 12, and 24 months. Independent-samples t-tests were used to compare to published thresholds. Mean acetabular subsidence from baseline to 24 months was 0.087 mm (SD 0.152), below the critical threshold of 0.2 mm (p = 0.005). Mean femoral subsidence from baseline to 24 months was -0.002 mm (SD 0.194), below the published reference of 0.5 mm (p < 0.001). There was significant improvement in patient-reported outcome measures at 24 months with good to excellent results. RSA analysis demonstrates excellent fixation with a predicted low risk of revision at ten years of this novel reverse total hip system. Clinical outcomes were consistent with safe and effective hip replacement prostheses.

Величина шеечно-диафизарного угла ножки эндопротеза тазобедренного сустава как биомеханическая предпосылка развития асептической нестабильности вертлужного компонента (экспериментальное исследование)

Introduction Causes of aseptic loosening of THA components and improvement of the implants remain the subject of scientific discussions. The objective was to perform comparative analysis of the results of biomechanical modeling of cementless total hip arthroplasty using implants with different stem neck-shaft angles as a prerequisite of aseptic loosening of the acetabular component. Material and methods A biomechanical model of the pelvis and an implant with different stem neck-shaft angles was constructed based on computed tomography findings. Stresses and strains that the patient typically experienced under full weight-bearing on the operated lower limb were explored. Results The use of a stem neck-shaft angle of 125° provided the most favorable localization of the contact patch at the border of the acetabular component – the pelvic bone and lower values of equivalent stresses and contact pressure in comparison with more "valgus" femoral components (135° and 145°). Discussion The data obtained were fully consistent with the results of biomechanical studies by L. Quagliarella et al. (2006) who reported the substantial significance of the neck-shaft angle for on the parameters of contact pressure, since wear and debris-associated osteolysis decrease with a decreased neck-shaft angle. The use of stem neckshaft angles equal to 125° can be indicated for young patients with good bone quality and equal lower limb length. Unstable femoral cup can be caused by eccentric position of the contact spot at the border of the bone and the acetabular component and distribution of contact pressure and equivalent stresses inside the spot that are typical for artificial joints with stem neck-shaft angle of 145°. Conclusion The findings suggested that the value of stem neck-shaft angle was likely be considered a prerequisite for aseptic loosening of the acetabular component.

Surface Finish of Total Hip Arthroplasty Implants: Are We Evaluating and Manufacturing Them Appropriately?

Abstract A recent change in the ISO 7206-2, Implants for Surgery – Partial and Total Hip Joint Prostheses – Part 2: Articulating Surfaces Made of Metallic, Ceramic and Plastics Materials, with regard to hip joint prostheses, altered the recommended cutoff for measuring the roughness of the articulating surfaces of the femoral head and acetabular cup but did not encompass two key sites: the bore head and the trunnion. The aim of this study was to evaluate whether the standardized parameters and sites established in ISO 7206-2 are appropriate for evaluating the quality of the surface finish of total hip arthroplasty implants. Three kits containing the polymeric acetabular components, metallic heads, and stems from 5 manufacturers were used for testing. Contact profilometry was performed on the internal acetabular cup, external head, head bore, and trunnion surfaces. Additionally, the external head surface was evaluated with an interferometer to increase the accuracy. The evaluation of the external surface of the femoral head with a profilometer seems to be inadequate, because of a limitation of the contact method associated with highly polished surfaces. The average roughness (Ra) values obtained with an interferometer were lower than those measured with the profilometer and revealed significant differences between the manufacturers. The use of an 0.80-mm cutoff is more appropriate for the Ra range normally found for acetabular cups, enhancing the power to detect acetabular cups with inadequate roughness. The absence of a standard for the surface finish of the stem-head interface generates heterogeneity between manufacturers and between samples produced by a single manufacturer, revealing a lack of quality control.

Assessment of an Orthopaedic Templating Software Package for Uncemented Total Hip Arthroplasty

AbstractThe aim of this study was to assess a large, single-surgeon dataset of uncemented total hip arthroplasties that had been templated using software. This assessment compared preoperative templated predictions with what was implanted with regard to (1) femoral prosthesis size and (2) acetabular cup size. The operation notes for two types of uncemented total hip arthroplasty performed by a single surgeon between January 9, 2008, and March 21, 2019, were assessed. The data were refined so that only those that were fully templated on a correctly calibrated pelvic radiograph were included. This provided a total of 153 cases. The predicted software template was compared with actual implanted component sizes. With regard to the femoral stems, the templating software was exactly correct in 45.75% of cases and was accurate to within one size in 87.59% of cases. With regard to the acetabular component, the templating software was exactly correct in 52.94% of cases and was accurate to within one size (2 mm) in 86.94% of cases. Templating software offers an accurate prediction of the size of uncemented femoral and acetabular components. In addition, the benefits of templating include cognitive rehearsal, insight into potentially challenging aspects of surgery, and highlighting intraoperative issues where there is a large intraoperative deviation from what is templated. This study demonstrates the congruence and reproducibility of templating software when compared with other smaller studies performed in the literature.

Prosthetic Impingement in Total Hip Arthroplasty—The Trigger for Adverse Wear

Development of total hip arthroplasty (THA) now spans more than 5 decades encompassing combinations of metal-on-metal (MOM), ceramic-on-metal (COM), metal-on-plastic (MOP), ceramic-on-plastic (COM), and ceramic-on-ceramic (COC). In every arena of extensive technical development, there exists a data set that when viewed in isolation seemed of little import, but when assembled in-toto may produce a generational shift in perception. Our review focused on two such THA events. Firstly, COC retrieval studies (1999-2001) noted habitual wear patterns on heads and peripheral wear stripes, along with femoral-neck impingement, and ceramic surfaces stained gray by metal debris. These COC data indicated THA risks included, 1) cup edge-loading (E/L) on heads producing “stripe wear”, 2) component impingement releasing metal particles resulting in 3) tissues contaminated by metal debris. A corresponding MOM impingement-debris mechanism was only perceived by Howie (2005) in a McKee-Farrar retrieval study. Our anticipation at LLUMC was that MOM retrievals would provide superior wear details to those seen on COC retrievals. We noted stripe wear in the polar zone of CoCr heads and basal stripes in the non-wear areas. The basal-polar stripe combinations were found in all MOM retrievals. Basal-polar stripe combinations followed cup-rim profiles in our LLUMC simulations of prosthetic impingement. LPUH videos demonstrated the formation of stripe wear in functional-standing and functional-sitting postures for both impingement and subluxation episodes using THA and RA designs. The stripes on CoCr heads revealed the large scratches we now term “microgrooves”. Microgroove width varied from 40 - 400 um with 100 um being typical. The longitudinal striations in microgrooves, the raised jagged lips, scratches with shallow entry and exit termini, were all indicative of a classic 3rd-body wear mechanism. The THA impingement simulations denoted four sites of edge-loading, i.e. neck-E/L, inferior cup-E/L, superior cup-E/l and head-E/L, and ingress of Ti64 particles as a contaminating-roughness effect. Individual MOM cases referred to LLUMC demonstrated dramatic evidence of neck notching. At one end of the debris spectrum, a Ti64-notch model predicting a 6 mm3 annual wear-rate represented the release of 5700 particles of 126 um-size (approximating daily release of 16 particles). At the other end of the spectrum, if metal particles were crushed between MOM surfaces to the equivalent nanometer size found in tissues, our notch model represented approximately 22-trillion Ti64 particles annually deposited in tissues. The anatomical THA models represented in LPUH videos demonstrated that even 1-degree of head subluxation from a rigid cup created a cup “lift-off” scenario (CLO) that would open a gap of 250 - 400 microns between femoral head and cup. This would void all lubrication potential and focus the total hip-joint force along the beveled cup rim, i.e. stripe wear. It is therefore interesting that MOM impingement/debris predictions by Howie et al. have not been confirmed until now or discussed in contemporary literature. Therefore, this review of 50 years of THA data demonstrated that hip impingement was always the trigger for adverse wear and that metal-backed cups represent the potential for release of metal debris at extremes of functional standing and sitting postures.

Assessment of an Orthopaedic Templating Software Package for Cemented Total Hip Arthroplasty

AbstractThe main aim of this article was to assess a large, multisurgeon dataset of cemented total hip arthroplasties that had been templated using software. This assessment compared preoperative templated predictions with what was implanted with regard to (1) femoral prosthesis size, (2) offset, and (3) acetabular cup size. A database of total hip arthroplasties performed by four surgeons between the dates November 7, 2014 and October 31, 2017 was interrogated. The data was refined so that only primary cemented collarless polished tapered stem hip arthroplasties, fully templated on a correctly calibrated pelvic radiograph, were included. This provided 354 cases. The predicted software template was compared with actual implanted component sizes. With regard to the femoral stem, the software was exactly correct in 70.9% and accurate to within one size in 96.89% of cases. With regard to the femoral offset, the software was exactly correct in 87.01% and accurate to within one size in 99.72% of cases. With regard to the acetabular cup size, the software was exactly correct in 61.3% and accurate to within +/− 2 mm in 87.29% of cases. Templating software offers an accurate prediction of the femoral prosthesis size and offset, as well as acetabular cup size. Preoperative insight into likely component sizes and offset provides the operating surgeon with many benefits; templating the pelvic radiograph is a method of cognitive rehearsal, provides insight into potentially challenging aspects of the upcoming surgery, may highlight intraoperative issues where there is a large intraoperative deviation from what is templated, and enables efficient stock keeping for the healthcare institution.

Femoral neck fracture in acetabular protrusions secondary to rheumatoid arthritis: a case report and literature review

The present study shows the case of a patient with acetabular protrusions secondary to rheumatoid arthritis pro-gressing to femoral neck fracture. The patient, a 64 years female, had a history of rheumatoid arthritis for 38 years. The left hip pain and abnormal sound occurred when hip flexion for picking up. She was diagnosed with rheumatoid arthritis secondary to acetabular pelvic retraction and left femoral neck fracture by medical history, physical examination and imaging. Total hip arthroplasty was performed after preoperative examination. Hip dislocation, femoral head removal, acetabular reconstruction, cup fixation, and bone mass assessment are technical challenges during surgery. Based on literature review, this case is belonging to secondary acetabular pelvic retraction, which may be related to acetabular softening caused by rheumatoid arthritis. When the stress from the femoral head exceeds the endurance of the softened acetabulum, the acetabulum protrudes into the pelvis and gradually wraps around the femoral head. Based on the pathological characteristics, it is speculated that the cause of femoral neck fracture is the direct hit of the femoral neck-acetabular rim during hip flexion. In this case, spiral cup prosthesis was used to achieve both the initial stability of the prosthesis and saving bone mass around the acetabulum. The patient was followed up for 3 months with satisfactory position of prosthesis and joint function.

Joint replacement surgery in Ghana (West Africa)\u2014an observational study

IntroductionWith the continued and effective transfer of orthopaedic knowledge and skills across continents, the incidence of hip and knee replacement surgery has increased in the developing world. More patients are having these procedures done locally rather than having to travel over to the more developed western countries at great financial costs for those who cannot really afford it. We report the data collected by an orthopaedic charity MOTEC LIFE UK which has been offering hip and knee arthroplasty procedures to patients who require them. The time period of the procedures was February 2013–October 2017.MethodsThe data was collated prospectively and this included age, sex, indication for procedure, and side of procedure (including if bilateral). The information on hip implants used were also collected—implant type (cemented or uncemented), type of bearing surface, size of acetabular cup, liner, femoral head size, and stem size and including if screws were used to augment the fixation of the femoral cup. For the knee implants used, information on the type of implant (semi-constrained, cruciate retaining, or Stanmore hinge knee prosthesis), femoral and tibia stem size, insert type (fixed bearing or mobile bearing), and size; patella button size (whether patella replacement or circumcision) were collected. The surgical approach used in both knee and hip arthroplasty cases was noted.ResultsIt is seen from the data collected that a total of 113 hip arthroplasty procedures from 109 patients were carried out and for total knee replacements, 82 knee arthroplasty procedures from 76 patients were carried out. The above procedures were carried out in two separate hospitals. Degenerative osteoarthritis still remains the main indication for hip and knee arthroplasty surgery in our study and this is similar to other joint registries around the world. It was noted that the incidence of avascular necrosis as an indication hip surgery was higher than that seen in registries for developed countries. The mean age for the hip and knee replacement patient in our data was much lower than that what is obtained in the developed world. Furthermore, it was observed that there was increased use of semi-constrained knee prosthesis due to the severe osteoarthritic deformities noted in the patients seen when compared to rate of use of similar implants in the developed world.ConclusionThis observational study could serve as a springboard for establishment of arthroplasty registries for countries in the sub-region as a whole.

Study of Sensor Deflection in Hip Simulator : Numerical and Experimental Method

A lot of Hip Joint Simulator have been made nowadays, most of them use different structure and method. This research reports a pin-on-ring tribometer design that is used to became hip joint simulator based on the movement of the salat (salat gait). Modified femoral head and acetabular cup holder are performed, to design a reciprocating motion for simulation of artificial hip movement. An interesting finding from this study is a new linked-bar mechanism that leads to the ability to move femoral head against the acetabular cup and measure wear volume of an THR patients during normal salat gait. The designed motion angle is 121.5° in the flexion direction and 15.5° in the direction of abduction. Linked bar for sensor dial indicator have enough adjustment, but there is still a movement that is not rigid upon running hip joint process simulator. This research concentrates on the bar is already linked in accordance or not when compared with the data in the simulate on a computer. Estimation error and deviations that occur between numerical and experimental is going forward to improve hip joint simulator Undip to be more precise and relevant research to use THR Undip.

Total Hip Arthroplasty in Overweight Patients: Do Obesity and BMI Affect Implant Positioning, Outcomes, and Complications?

AbstractObesity is one of the most problematic issues for health organizations worldwide because of its relationship with several chronic diseases. It is also demonstrated to increase early onset of hip arthritis, consequently leading to early failure of implants of total hip arthroplasty (THA). The aim of the study was to assess the influence of obesity on the positioning of prosthetic components and potential complications. A total of 312 patients underwent THA from 2006 to 2015 at our institute. All procedures were performed by a single surgeon (M.F.S.). As indicated by the World Health Organization (WHO), our population was stratified on the basis of body mass index (BMI): Four underweight, 112 nonobese, 131 overweight, 51 grade-1 obese, 10 grade-2 obese, and 4 grade-3 obese patients were included. No superobese patients were reported. The population was assessed clinically (implant survival, surgery time, blood loss, and complications) as well as radiologically (femoral offset, cup abduction and anteversion, and periacetabular osteolysis). Higher cup inclination (48.70 vs. 45.94 degrees), surgical time (86 vs. 80 min), and total blood losses (1,026 vs. 761 mL) were reported in overweight/obese patients (p &lt; 0.01). Statistical analysis documented a significant relationship between obesity and cup inclination, surgical time, intraoperative and total blood losses, as well as BMI and age at surgery (p &lt; 0.05). The overall correct positioning of prosthetic components is not significantly related to obesity. Although maintained in the “safe zone,” cup abduction, blood loss, and operative time tend to significantly increase with BMI.

STAND FOR TRIBOLOGICAL TESTING OF HIP ENDOPROSTHESES

The paper presents a new construction of hip-joint simulator. The SBT-01.2 simulator is designed for conducting tribological testing of hip endoprostheses based on ISO 14242-1, which specifies the requirements for the range of motion and load characteristics of the friction pair (femoral head vs. acetabular cup) during one test cycle. The construction of the simulator is based on the anatomical structure of the human hip joint. The prosthesis acetabulum is mounted in the upper part of the mounting head while maintaining the inclination angle relative to the axis of the socket to the direction of the loading force. The head of the prosthesis is mounted on a pin embedded in the bottom, movable base. After placing a special sleeve on the lower base, liquid lubricant is applied on the head-cup tribological system. The employed software enables continuous control, online visualization, and data recording. During testing, parameters such as lubricant temperature, instantaneous loading force, friction torque, and the number of cycles are recorded.

Backflow from a Metallosis-Induced Intrapelvic Mass into a Revision Hip Arthroplasty: A Case Report.

Recently, there has been an increase in the number of cases reported concerning formation of a soft-tissue mass around hip joints associated with total hip arthroplasty, mostly caused by metal debris from metal-on-metal articulations1-5. This metal-induced mass has also been noted in so-called adverse reactions to metal debris6 and histologically in aseptic lymphocyte-dominated vasculitis-associated lesions (ALVALs)7,8. Additionally, similar mass formations have been reported in metal-on-polyethylene (MOP) total hip arthroplasties9-15. Polyethylene debris induces granulomatous reactions9,10; however, tissue reactions caused by metal debris due to corrosion at the head-neck taper junction recently have been reported in MOP total hip arthroplasties13,16. In addition, severe polyethylene abrasions can produce metal debris due to breakage of the liner17,18, which then can cause tissue reactions to the metal debris14,15. These masses, associated with various types of total hip arthroplasty, sometimes develop in the pelvis, as summarized by both Hananouchi et al.19 and Leigh et al.9. A majority of these intrapelvic masses are asymptomatic, and resection may not always be necessary because such masses can decrease in size once the source of wear is eliminated9,20. We report the case of a patient who developed a large asymptomatic intrapelvic mass containing black metallic debris due to an abrasion between the femoral head and metal cup, which was caused by breakage of the polyethylene liner in a MOP total hip arthroplasty that had been performed nineteen years earlier. It is notable that the mass not only was one of the largest reported asymptomatic intrapelvic masses associated with total hip arthroplasty, but it also caused persistent backflow of metallic fluid from the mass to …

Radiological validation of a fluoroscopic guided technique for femoral implant positioning during hip resurfacing

The positioning of the femoral cup in hip resurfacing is essential for the survival of the implant. We described a technique in 2005 to position the femoral cup guided by fluoroscopy independent of the approach performed. The main objectives were to study the positioning of the femoral components of the implant and the accuracy of the technique. Between 2003 and 2011 we conducted a prospective study of 160 consecutive hip resurfacings all operated with this fluoroscopic-guided technique. Three independent observers performed a radiographic analysis at the pre-operative planning stage and on postoperative radiographs using OsiriX software. The statistical analysis was based on comparison of two groups by Student's t test. The entire implant was positioned in valgus, with an average of 7.816° valgus (p <0.001). All implants were positioned in neutral or anteverted with a mean of 1.98° (p <0.001). The risk of malpositioning on the antero-posterior plane was less than 1.41° with p <0.019. The risk of profile positioning error was lower than 0.80° with p <0.047. This study validates a technique of femoral implant positioning for resurfacing. It is simple, precise and independent of the approach performed.

Are component positioning and prosthesis size associated with hip resurfacing failure?

BackgroundRecent studies suggest that there is a learning curve for metal-on-metal hip resurfacing. The purpose of this study was to assess whether implant positioning changed with surgeon experience and whether positioning and component sizing were associated with implant longevity.MethodsWe evaluated the first 361 consecutive hip resurfacings performed by a single surgeon, which had a mean follow-up of 59 months (range, 28 to 87 months). Pre and post-operative radiographs were assessed to determine the inclination of the acetabular component, as well as the sagittal and coronal femoral stem-neck angles. Changes in the precision of component placement were determined by assessing changes in the standard deviation of each measurement using variance ratio and linear regression analysis. Additionally, the cup and stem-shaft angles as well as component sizes were compared between the 31 hips that failed over the follow-up period and the surviving components to assess for any differences that might have been associated with an increased risk for failure.ResultsSurgeon experience was correlated with improved precision of the antero-posterior and lateral positioning of the femoral component. However, femoral and acetabular radiographic implant positioning angles were not different between the surviving hips and failures. The failures had smaller mean femoral component diameters as compared to the non-failure group (44 versus 47 millimeters).ConclusionsThese results suggest that there may be differences in implant positioning in early versus late learning curve procedures, but that in the absence of recognized risk factors such as intra-operative notching of the femoral neck and cup inclination in excess of 50 degrees, component positioning does not appear to be associated with failure. Nevertheless, surgeons should exercise caution in operating patients with small femoral necks, especially when they are early in the learning curve.

Friction and tribocorrosion of 316L stainless steel against UHMWPE or alumina in saline solution

Friction, wear and tribocorrosion properties of 316L stainless steel were studied when sliding against ultra high molecular weight polyethylene (UHMWPE) or against alumina. 316L stainless steel and UHMWPE are widely used as femoral head and acetabular cup in hip prostheses. In this paper, tribological properties of this couple of biomaterials have been studied. The experiments were conducted in saline solution between metallic balls of various roughness values and UHMWPE samples using a ball on disc reciprocating tribometer and a hip joint simulator built in the authors' laboratory. The results clearly show that friction and wear of the polymer depend strongly on the roughness of the steel balls. These results are discussed and compared to previous experimental data. Tribocorrosion of 316L stainless steel was also studied when sliding in saline solution against an alumina ball. The effect of the normal load and the electrochemical applied potential on friction and wear of the metal have been discussed in terms of passivating film stability and repassivation kinetics.

Revisionschirurgie des Oberflächenersatzes

Early results of contemporary hip resurfacing are encouraging and consequently an increasing number of this procedure has been performed worldwide. A theoretical advantage of hip resurfacing is that failed components can be revised safely and successfully revised to a conventional total hip arthroplasty. As the number of systematically analyzed failures is still limited, however, current data from the literature cannot substantially support this assumption. Our personal results indicate that the conversion of a failed femoral cup (i.e., due to neck fracture or aseptic loosening) to a conventional stem is a relatively simple and safe procedure. If and how potential wear of a firmly integrated acetabular component might have any impact on this type of revision, warrants further investigations. The conversion of acetabular components is influenced by the quality of the remaining pelvic bone stock and can therefore be compared to conventional revision surgery. However, as most providers of hip resurfacings systems only offer one-piece acetabular shells, the possibility of an isolated modular insert exchange is rare. In conclusion, the argument of easy revision surgery after hip resurfacing should be used with care.

Doppelschalen-Hüfttotalendoprothesen nach Freeman

From July 1976 up to the end of 1979 forty-three Double Cup hip replacements of the Freeman type were implanted in thirty-seven patients at the Department of Orthopaedic Surgery, Balgrist, of the University of Zurich. Now, four to seven years after implantation, 15% of early complications have developed and only 25% of all the hips are free of pain. Radiographically, every second femoral cup shows migration of about 2 mm. pro year at an average. Clinical and radiographical investigations, as well as biomechanical experiments and calculations show the possible reasons for the unsatisfactory results. Subsequently, we are now very cautious when considering the indications for the implantation of Double Cups.

Knochen- und Grenzschichtveränderungen nach Implantation von Double-Cup-Arthroplastiken

21 femoral heads of 20 patients with double cup arthroplasty were examined after an implantation period of 1 to 5 years, in one case after 18 years. In 8 cases the hipe socket and in 10 cases the femoral cup became loose. Therefore an operative removal was necessary. 2 patients showed extensive periarticular ossifications. In connection with the metal cup the resected femoral heads were cut in slices of 1 cm. thickness. After taking an X-ray they were embedded without decalcification in methylmetacrylate. The sections were stained with different methods (Goldner, v. Kossa modification). In the group with fixed cup a local osteoporosis is dominating. The fibrous tissue membrane between cement and bone tissue is varying in thickness. It is thicker at the periphery of the cup. In the group with loosened cups large irreparable bone necrosis with included histiocytic granulomas, could be observed. The clinical problems are discussed in accordance to the long term prognosis on the basis of the morphological results.

A Method of Calculation for Contact Pressure between Femoral Head and Cup of Artificial Hip Joint

A method of calculation for contact pressure between a hard femoral head and soft plastic cup of a hip joint was studied. Providing that the contact pressure is proportional to the radial deformation of the cup, an equation of equilibrium in terms of a nondimensional parameter was derived. Once the magnitude of the parameter is determined by solving the equation, the contact pressure distribution is easily obtained. An effect of the radial clearance between a femoral head and cup on contact pressure was evaluated using the equation. Furthermore, the effect of Young's modulus and thickness of a plastic cup on contact pressure were also evaluated. According to the results, contact pressure increased with an increment of clearance and Young's modulus. The contact pressure increased with a decrement of thickness of the plastic cup. The analytical solution was compared with the finite element method (FEM) analysis and the agreement was confirmed. An equation of frictional torque was also derived

Short Term Results of Cementless Total Hip Arthroplasty With a Tapered Femoral Component

Purpose: This study investigated the results of cementless total hip arthroplasty using a circumferentially porous coated tapered femoral stem and a porous coated acetabular cup after a follow-up of more than 2 years. Materials and Methods: 70 hips in 65 patients were followed up for more than 2 years after surgery who underwent total hip arthroplasty with a Versys Fiber Metal Taper femoral stem (Zimmer, Warsaw, IN) and Trilogy acetabular cup (Zimmer, Warsaw, IN). Results: The mean Harris hip score increased to 96.2 points. There was no osteolysis in the acetabulum. There was no distal osteolysis in the femur but there was osteolysis observed in Gruen zone I in 1 hip (1.4%). Endosteal bone formation was observed in 67 hips (95.7%) mostly in Gruen zones II and VI. There was no subsidence of the stem. The survival with an acetabular and femoral revision for aseptic loosening was 100% respectively. Conclusion: Cementless total hip arthroplasty using a circumferentially porous coated tapered femoral stem and a porous coated acetabular cup showed excellent results after a follow-up of more than 2 years, inducing good bone ingrowth, as well as no migration of the cup and no osteolysis around the distal femur and acetabulum. However, a long term follow up is necessary.