Polyethylene Cup Research Articles

A dynamic model of polyethylene damage in dry total hip arthroplasties: wear and creep

The creep and wear of ultra-high-weight polyethylene hip prostheses under physiological conditions are studied in the present research work. A fully integrated contact-coupled dynamic model based upon multibody dynamics methodology is developed, allowing the evaluation of not only sliding distance, but also contact mechanics as well as cross-shear effects and both average pressure and in-service duration associated with the creep phenomenon. In vivo forces and motions of hip joint are used as input for the dynamic simulation, which result in more realistic contact point trajectory and contact pressure, and consequently wear and creep, compared to simplified inputs. The analysis also takes into account inertia forces due to hip motion, tribological properties of bearing bodies, and energy loss owing to contact-impact events. The principal molecular orientation (PMO) of the polyethylene cup is determined through an iterative algorithm and dynamic outcomes. Archard’s wear law is also integrated into the multibody dynamics model for wear prediction in hip implants. Creep, besides wear, is attributed to polyethylene damage, which is investigated by implementing a creep model extracted from experimental data. The model is validated using clinical data and numerical results available from previously published studies. It is shown that creep plays a significant role in hip damage along with wear, both of which can be influenced by hip parameters, e.g., hip and clearance sizes. Moreover, the creep mechanism according to creep experiment is discussed, and contributing factors to the wear phenomenon are analyzed throughout this study.

Mechanical loading characteristics of total hip prosthetics subjected to dynamic loading cycles.

The selection of best material pair in the hip prosthetics design for improved performance and life relies on the estimation of hip joint contact stresses and contact pressure distribution during various dynamic loading cycles: Climbing Upstairs, Climbing downstairs and Knee bending. The maximum Von Mises stress, contact pressure and deformation are considered factors in selecting the material pair in this current study. This is done by analysis of a three-dimensional finite element model of the acetabular component during the different dynamics cycles using ANSYS®. The different material combination of bearing couples considered for this analysis are metal in contact with plastic, metal on metal, metal on ceramic, ceramic on plastic, ceramic on metal and ceramic on ceramic. The numerical results were validated by comparing them with the FEA results of Hai-Bo Jiang et al. for the existing material combinations and a high correlation of 92% was observed. We found that the Alumina femoral head paired with ultra-high molecular weight polyethylene (UHMWPE) cup reduces the maximum Von Mises stress and maximum contact pressure developed at the interface amongst other material pairs.

RESEARCH ON FRICTION WEAR OF HIP JOINT ENDOPROSTHESES OF POLYETHYLENE-METAL MATERIAL COMBINATION ON HIP JOINT SIMULATOR

The article presents the results of friction wear tests of hip joint endoprostheses. The study comprised tests of endoprostheses, commercially available on the European market, used in total hip arthroplasty. The friction pair was formed by an actual cupacetabular cup made of ultra-high molecular weight polyethylene (PE-UHMW) along with a head having a diameter of 28 mm made of stainless steel FeCrNiMnMoNbN. The friction and wear tests were performed using an SBT 01.2 hip joint simulator of the authors’ own design, which was constructed taking into account the ISO 14242-1 standard. Bovine serum was used as the lubricant. The tests of each friction pair were made up to 5·106cycles of motion. During the tests, simulator operation was interrupted every 5·105 cycles to replace the lubricating liquid, and mass control was performed every 1·106 cycles. Prior to testing, the polyethylene cup was soaked in the lubricant to minimize liquid absorption during the test. Proper preparation of the cup and testing by taking into account a control group weight measurement allowed an accurate determination of the mass loss of the polyethylene cup.

Finite Element Simulations of Hard-On-Soft Hip Joint Prosthesis Accounting for Dynamic Loads Calculated from a Musculoskeletal Model during Walking.

The hip joint replacement is one of the most successful orthopedic surgical procedures although it involves challenges to overcome. The patient group undergoing total hip arthroplasty now includes younger and more active patients who require a broad range of motion and a longer service lifetime for the replacement joint. It is well known that wear tests have a long duration and they are very expensive, thus studying the effects of geometry, loading, or alignment perturbations may be performed by Finite Element Analysis. The aim of the study was to evaluate total deformation and stress intensity on ultra-high molecular weight polyethylene liner coupled with hard material head during one step. Moving toward in-silico wear assessment of implants, in the presented simulations we used a musculoskeletal multibody model of a human body giving the loading and relative kinematic of the investigated tribo-system during the gait. The analysis compared two frictional conditions -dry and wet and two geometrical cases- with and without radial clearance. The loads and rotations followed the variability of the gait cycle as well as stress/strain acting in the UHWMPE cup. The obtained results allowed collection of the complete stress/strain description of the polyethylene cup during the gait and calculation of the maximum contact pressure on the lateral edge of the insert. The tensional state resulted in being more influenced by the geometrical conditions in terms of radial clearance than by the variation of the friction coefficients due to lubrication phenomena.

Bone preserving techniques for explanting the well-fixed cemented acetabular component

BackgroundRemoval of a well-fixed, cemented acetabular component at the time of revision hip surgery can be complex. It is essential to remove the implant and cement mantle in a timely fashion while preserving bone stock and osseous integrity. The biomechanical properties of polymethylmethacrylate cement and polyethylene can be utilised to aid with the removal of well cemented implants which are often harder than the surrounding bone. While removal of loose components may be relatively straightforward, the challenge for the revision arthroplasty surgeon often involves the removal of well-fixed implants. Here, we present three established techniques for the removal of a well-fixed cemented acetabular component and one novel modification we have described before. MethodWe collate and review four techniques for removing well-fixed cemented acetabular implants that utilise the different biomechanical properties of bone cement and polyethylene. These techniques are illustrated with a photographic series utilising saw bones. A step-by-step approach to our new technique is shown in photographs, both in the clinical setting and with a “Sawbone”. This is accompanied by a clinical video that details the surgical technique in its entirety. ResultsThese techniques utilise different biomechanical principles to extract the acetabular component. Each technique has advantages and disadvantages. Our new technique is a simplification of a previously published extraction manoeuvre that utilises tensile force between cement and the implant to remove the polyethylene cup. This is a safe and reproducible technique in patients with a well-fixed cemented acetabular implant. ConclusionUnderstanding the biomechanical properties of polymethylmethacrylate bone cement and polyethylene can aid in the safe removal of a well-fixed cemented acetabular component in revision hip surgery. The optimal technique for removal of a cemented acetabular component varies depending on a number of patient and implant factors. This summary of the available techniques will be of interest to revision arthroplasty surgeons.

Creep and Wear in Vitamin E-Infused Highly Cross-Linked Polyethylene Cups for Total Hip Arthroplasty: A Prospective Randomized Controlled Trial.

Aseptic loosening, the most common indication for revision surgery in total hip arthroplasty, can result from osteolysis caused by polyethylene (PE) wear particles. PE wear is increased by age-related oxidation of PE and free radicals emerging during irradiation cross-linking. Diffusion of vitamin E into PE stabilizes free radicals to maintain the biomechanical properties of PE. The purpose of this study was to determine whether vitamin E-infused highly cross-linked PE cups could reduce wear rates. We performed a prospective randomized controlled trial, in which 62 patients were allocated to 2 groups: a study group that received a vitamin E-infused highly cross-linked PE (HXLPE/VitE) cup and a control group that received an ultra-high molecular weight PE (UHMWPE) cup. Using radiostereometric analysis, we measured the penetration of the femoral head into the cup 7 days after surgery (baseline) and then again at 6 months and at 1, 2, and 3 years later. Baseline variables did not differ significantly between the groups. At 1, 2, and 3 years after surgery, the HXLPE/VitE cup showed significantly less cumulative penetration (creep and wear) than the UHMWPE cup (p = 0.004, p < 0.0001, and p < 0.0001, respectively). The cumulative penetration after 3 years was 0.200 mm for the HXLPE/VitE cup versus 0.317 mm for the UHMWPE cup (p < 0.0001). From 1 to 3 years after surgery, after creep had stabilized and further penetration was mainly due to wear, the mean penetration increased only 0.04 mm in the HXLPE/VitE cup and 0.116 mm in the UHMWPE cup. Our results confirm that wear rates over the first 3 years following surgery were lower in HXLPE/VitE cups than in UHMWPE cups. This suggests that HXLPE/VitE cups may prevent osteolysis, implant loosening, and eventually revision surgery. Long-term follow-up data continue to be collected to confirm these findings. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Mechanical tests, wear simulation and wear particle analysis of carbon-based nanomultilayer coatings on Ti6Al4V alloys as hip prostheses.

Carbon-based nanomultilayer coatings were deposited on medical-grade Ti6Al4V alloy using a magnetron sputtering technique under a graded bias voltage. The mechanical properties of the nanomultilayer coatings were investigated by nanoindentation, Rockwell and scratch tests as well as a ball-on-disk tribometer. The biological properties related to the immunological response of the coatings were investigated by wear simulation and wear particles analysis. Wear simulation was done according to ISO 14242, wear particles were analysed according to ISO 17853, and then compared with CoCr femoral heads. The results revealed that the carbon-based nanomultilayer coatings showed a multilayer structure, with a hardness of ∼20 GPa, an elastic modulus of ∼175 GPa, an adhesion higher than 80 N, and a low average coefficient of friction of 0.1. The average gravimetric wear rate of the polyethylene cups between the coated and CoCr groups had no statistical difference (P = 0.098). The average equivalent circle diameter of particles produced in the coated group was larger than that in CoCr (P = 0.001), but the proportion of submicron particles and globular/circular particles was not significantly different between the two groups (P > 0.05). Results showed lower Co/Cr ion contamination in the coated group. Hence, the carbon-based nanomultilayer coating on Ti6Al4V has good mechanical and tribological properties, releases fewer harmful metal ions and would not cause a more intense immunological host response than a CoCr prosthesis. The newly designed a-C nanomultilayer coatings are expected to prolong the longevity of artificial hip joints.

Midterm survival analysis of a cemented dual-mobility cup combined with bone impaction grafting in 102 revision hip arthroplasties.

Revision hip arthroplasty is associated with higher dislocation rates than primary hip arthroplasty. A dual-mobility cup (DMC) can reduce this risk. Another problem is destruction of the acetabulum, induced by aseptic loosening of the prosthesis. Bone impaction grafting (BIG) can be used to reconstruct these defects, but is usually performed with cemented all polyethylene cups. The purpose of this study is to evaluate midterm cup survival and dislocation rate for the combination of BIG and DMC. Between 2007 and 2013, 96 patients received 102 DMCs combined with BIG of the acetabulum during revision surgery. These data were first compared with a control group, consisting of 59 cases from the same hospital receiving a cemented all polyethylene cup combined with BIG. In addition, the control group was expanded with 41 cases operated on in 2007 in 'an orthopaedic centre of excellence', resulting in a 'combined control group' of 100 patients. Log-rank tests and chi-square tests were used to compare survival and dislocation rates, respectively. Cumulative survival of the DMC was 95.8% (range 3 months-7 years). This was comparable to the survival in the control groups (96.5% and 94.7%). The dislocation rate of 2.9% (3/102) in the dual-mobility group was lower (p = 0.02) compared to the dislocation rate of 11.8% (7/59) in the control group, but not (p = 0.12) compared to 8% in the combined control group (8/100). This study shows that combining a DMC with BIG does not compromise outcome in terms of midterm survival of the cup.

Finite element analysis of elastohydrodynamic lubrication in an artificial hip joint under squeeze film motion using fluid–structure interaction method

Classical approach for elastohydrodynamic lubrication problems contains solution of Reynolds and elasticity equations simultaneously, where elasticity equation was derived based on semi-infinite solid assumption. Fluid–structure interaction method which uses finite element formulation is another alternative approach for elastohydrodynamic lubrication problems. Present study contains two sections: first finite element method was used to evaluate accuracy of semi-infinite assumption for deformation in an artificial joint cup for a verity of material and geometrical properties. Then fluid–structure interaction method was used to simulate an artificial hip joint lubrication under squeeze film motion and efficiency and accuracy of this method was speculated by comparing the results to a previously done work. In the first section, deformation of a cup under Hertzian contact was calculated by finite element software ADINA. Various combinations of cup thickness, material properties, and dimensions of contact ellipse were modeled and results compared to the answer of semi-infinite assumption and column method for the same problem. Then a ball-in socket configuration for an artificial hip joint was modeled by an ultra-high-molecular-weight polyethylene cup and a Stainless Steel ball in the same software. Fluid film pressure and thickness were extracted from the results and compared to a previous study. Results for deformation of cup show that semi-infinite assumption and column method do not lead to acceptable accuracy for geometrical conditions of artificial hip joint. For fluid–structure interaction analysis of squeeze film motion, at first time steps, pressure distribution shows differences with the previous work, but at last time steps, fluid film pressure matches the previous study. For all time steps, film thickness of fluid–structure interaction method is higher than what was reported by previous work. The main reason is that no mesh independency check was performed for previous work, while for this study mesh independency of answers was analyzed by creating two other models.

Retrieval and radiographic analysis of the Contour antiprotrusio cage.

Acetabular reconstruction in the setting of severe bone loss or pelvic discontinuity remains a challenging problem. Multiple methods of treatment have been described including antiprotrusio cages (APCs). The objective of this study is to combine biomechanical analysis of retrieved APCs with radiographic and clinical data to determine which factors influence or predict APC failure. 41 APCs were identified. Sequential radiographs were examined for cage and polyethylene cup abduction angles, change in centre of rotation, screw placement, progression of cage failure, and failure mechanism. Cages were manually examined for gross macroscopic findings, breakage, and the location of breakage. High-resolution microscopy was used for further analysis. 24 cages were included in the analysis. Mean age of patients was 64.5 years (range 43-85 years); average length of implantation was 42.5 months (range 3-108 months). Average cage abduction angles were 56°; abduction for the cemented polyethylene cup was 44°. 14 of 24 cages were broken; 10 were intact. Of the broken cages, 10/14 broke through a screw hole in the ischial flange or just superior to the ischial flange. In the intact group, 6/10 failed due to pullout of the ischial screws. All cages had superior and lateralised centres of rotation. The majority of cages failed due to breakage or pullout at the ischial flange. Pelvic discontinuity was a large risk factor for a broken cage. Future design and technique modifications may result in superior outcomes in these complex acetabular reconstructions.

Does using a polyethylene RM press-fit cup modify the preparation of the acetabulum and acetabular offset in primary hip arthroplasty?

IntroductionWhen performing total hip arthroplasty (THA), it is important to maintain the femoral and acetabular offsets to ensure good joint stability and to restore the function of the hip abductor muscles. In our practice, we mainly use a lateralized stem and hollow out the acetabulum to the quadrilateral plate to accommodate a press-fit polyethylene cup. However, the repercussions of this preparation method, which is driven by the cup's design, are not known. We carried out a retrospective study to assess: (1) the changes in the femoral and acetabular offset; (2) the height of the center of rotation; and (3) the repercussions on wear. HypothesisWe hypothesized there would be no significant differences between the preoperative and postoperative femoral and acetabular offsets. Patients and methodsWe reviewed 88 primary THA cases performed with the RM Pressfit™ cup that had a minimum of 5 years’ follow-up. A lateralized self-locking Muller-type cemented femoral stem was used in 92.0% of cases and a standard stem in 8.0%. Measurements were done on plain radiographs with MHP™ and Mesurim Pro™ software. The average follow-up was 6.5 years (5–8). ResultsOn average, the acetabular offset was reduced by 2.75mm±5.9 mm (range: –17.5 to +10.6 mm) (P<0.001) and the femoral offset was increased by 0.01mm±5.5 mm (range: –17.8 to +11.0 mm) (P=0.99). In terms of total offset, medialization of 2.74mm±7 mm (range: –17.7 to +18.2mm) was found (P=0.001). The acetabular center of rotation was on average 4.77mm±5.1 mm higher (P<0.001). The mean annual wear at the more recent follow-up (min.: 5 years) was 0.068mm (range: 0.01 to 0.25mm) per year. The wear was not impacted by having more than 5mm change in offset. DiscussionMeasurements of acetabular offset revealed statistically significant medialization due to the type of implant used and the surgical technique. The anatomical technique consists of positioning the cup in subchondral bone without contacting the quadrilateral plate. This preserves bone stock, which may be useful later on if the cup is revised, particularly in younger patients. Conversely, the femoral offset did not change significantly, despite the use of lateralized stems in 92.0% of cases. We measured an annual wear rate of 0.068mm per year, which is lower than in other published studies, possibly because our patient population was older. Level of evidenceIV, retrospective study.

The impact of surface and geometry on coefficient of friction of artificial hip joints

Coefficient of friction (COF) tests were conducted on 28-mm and 36-mm-diameter hip joint prostheses for four different material combinations, with or without the presence of Ultra High Molecular Weight Polyethylene (UHMWPE) particles using a novel pendulum hip simulator. The effects of three micro dimpled arrays on femoral head against a polyethylene and a metallic cup were also investigated. Clearance played a vital role in the COF of ceramic on polyethylene and ceramic on ceramic artificial hip joints. Micro dimpled metallic femoral heads yielded higher COF against a polyethylene cup; however, with metal on metal prostheses the dimpled arrays significantly reduced the COF. In situ images revealed evidence that the dimple arrays enhanced film formation, which was the main mechanism that contributed to reduced friction.

The effect of humeral polyethylene insert constraint on reverse shoulder arthroplasty biomechanics.

There is little information on the effects of altering reverse shoulder arthroplasty (RSA) polyethylene constraint on joint load, load angle and deltoid force. The present biomechanical study aimed to investigate the effects of changing RSA polyethylene constraint on joint load, load angle, deltoid force and range of motion. A custom RSA implant capable of measuring forces across the joint with varying polyethylene constraint was tested in six cadaveric shoulders. Standard-, low- and high-constraint (retentive) polyethylene liners were tested, and joint kinematics, loads and muscle forces were recorded. When polyethylene constraint was altered, joint load and load angle during active abduction were not affected significantly (p > 0.19). Additionally, the force required by the deltoid for active abduction was not affected significantly by cup constraint (p = 0.144). Interestingly, active abduction range of motion was also not affected significantly by changes in cup constraint (p > 0.45). Altering polyethylene cup constraint in RSA to enhance stability does not significantly alter resultant joint loads and deltoid forces. Surprisingly, terminal abduction range of motion was also not significantly different with varying cup constraint, indicating that terminal impingement may be tuberosity related rather than polyethylene.

Cementing a polyethylene cup into a well fixed acetabular metal-on-metal resurfacing component? An experimental investigation.

Adverse reactions to metal debris often indicate revision surgery in metal-on-metal (MoM) hip arthroplasty and an exchange of the MoM bearing into either a metal on polyethylene or a ceramic-on-polyethylene articulation. At the moment the removal of the entire implant system is the most reasonable method. In order to avoid bone loss caused by the removal of a well-fixed acetabular component, the purpose of this study was to measure the stability of a cemented polyethylene (PE) cup in an acetabular hip resurfacing component and to examine if such a method could be suitable for clinical use. PE cups were cemented into 2 different hip resurfacing components and biomechanical tests were applied to measure failure torques under lever out and rotational load. In all cases failure of the interface between the resurfacing components and the cement layer occurred at a very low load (0.14 Nm-61.50 Nm). The early failure occurred due to lacking interdigitation of cement and the polished metal surface. Thus we warn against cementing a PE cup into acetabular hip resurfacing components for clinical use.

Over-the-Top Cementing Technique in Cup-Cage Reconstructions

Cup-cage constructs have been used for acetabular reconstruction in the setting of severe defects as well as pelvic discontinuity. This construct consists of a porous tantalum shell augmented with screws with an ilio-ischial cage that is placed over it. The superior flange of the cage is then affixed into the ilium with screws while the inferior flange is impacted into the ischial bone. A polyethylene cup is then cemented into the cage to complete the construct. The over-the-top cementing technique extends the extruded cement mantle from the polyethylene cup impaction over the superior flange creating a buttress construct to prevent screw back-out. In the setting of these complex cases this buttress effect can possibly improve the strength of the cup-cage construct.

THE EFFECT OF ASPHERICITY OF ACETABULAR BEARING SURFACE ON CONTACT MECHANICS OF UHMWPE TOTAL HIP IMPLANTS BY FINITE ELEMENT ANALYSIS

Asphericity and out-of-roundness are generally used to evaluate the manufacturing quality of ultra-high molecular weight polyethylene (UHMWPE) cup inner surfaces, which can potentially affect initial clinical wear and contribute to osteolysis of total hip arthroplasty. This study measured the location and magnitude of asphericity and the out-of-roundness value for four UHMWPE cups in a single set, and then investigated the effects of the asphericity on the contact mechanics of UHMWPE cups. A co-ordinate measuring machine (CMM) was used for the surface measurement and finite element analysis (FEA) was adopted for contact mechanics study. The results demonstrated that the asphericity varied between cups with the maximum value as 0.088[Formula: see text][Formula: see text][Formula: see text]0.004[Formula: see text]mm. Although such a value met the ISO specification, large difference of volume appeared for the asphericity above 0.060[Formula: see text]mm. Actual surface profile accounting for the asphericity was found to affect the value of contact pressure and contact area by around 12%. The inferior asphericity resulted in a nonsmoothly distributed contact pressure, which had a negative effect on the contact mechanics of UHMWPE cups and the edge loading was predicted to occur for the sample with a large asphericity. In conclusion, the asphericity of UHMWPE cup could affect the contact mechanics of the articular bearings and may subsequently contribute to initial wear during bedding-in phase.

Clinical Outcomes of Ceramicized Ball Heads in Total Hip Replacement Bearings: A Literature Review

Metallic ball heads for total hip replacement (THR) bearings with ceramicized surfaces were introduced in orthopedics during the second half of the 1980s, with the aim of decreasing the wear of polyethylene cups. An analysis was made of the literature regarding outcomes for metallic ball heads with ceramicized surfaces now in clinical use (TiN, TiNbN, ZrN, monoclinic ZrO2), as well as carbon coatings (pyrolytic carbon, diamond-like carbon) and silicon nitride as coatings in ball heads for THR bearings. Notwithstanding the diffusion of ceramicized ball heads in THRs, there are few reports about their clinical outcomes in hip arthroplasty. In addition, several clinical studies and some registry data are putting under scrutiny the clinical advantages of ceramicized ball heads over cobalt chrome (CoCr) alloy and ceramic ball heads. The wear of THR bearings with ceramicized ball heads looks like it depends more on the behavior of the polyethylene cups than on the treatment of the ball head surface. The risk of coating damage and of its consequences has to be taken into account in selecting this type of bearing.

Titanium wire mesh and impact bone allograft in treating acetabular bone defects in revision total hip arthroplasty

Objective To investigate the method and efficacy in treating acetabular bone defects by the use of titanium wire mesh and impact bone allograft in revision total hip arthroplasty. Methods Twenty-two patients (22 hips) with acetabular bone defects in revision total hip arthroplasty were treated with wire mesh and impact bone allograft from January 2008 to December 2013. There were 7 males and 15 females in the present study. The average age of the patients at the surgery was 64.8 (37-78) years. According to Paprosky classification, there were 9 cases of type IIA, 4 cases of IIB, 7 cases of IIC and 2 cases of IIIB. Twenty cases with aseptic loosen and 2 with periprosthetic infection were underwent revision surgery. Deep frozen cancellous bone allograft was sterilized and morselized to particles with the size of 7 to 10 mm. After removal of loosed acetabular component, the bone grafts were impacted into the acetabular defects area to restore the bone quantity. Titanium wire mesh with appropriate diameter was chosen to fix on impacted bone graft and fixed acetabulum with screws. Polyethylene cup was cemented in the mesh wire with proper position. Harris hip score system was used to evaluate the hip joint function. The AP pelvis X-ray was taken at 1 week, 3 months, 12 months and annually thereafter postoperatively to evaluate the rotation center, fusion of the bone graft and loosening of cup. Results All patients were followed up with the average period 5.1 years (3-7 years). The average Harris hip score before revision was 43.75±13.45, while the score was 85.33±7.84 at last follow-up (t=7.930, P=0.000). The average height of hip rotation center of surgical side was 3.49±0.77 cm before surgery, while its height at last follow-up was 2.22±0.22 cm (t=4.390, P=0.005). The distance between hip rotation center and the base of acetabulum was 3.54±0.45 cm before surgery, while its value was 3.52± 0.76 cm at last follow-up. All the bone grafts came to infusion with the average time 12 months (9-15 months). There was no case with cup migration more than 4 mm or rotation greater than 5° at last follow-up. One patient had the symptom of sciatic nerve injury. No case was with infection or dislocation. Conclusion In the treatment of acetabular bone defects, wire mesh and impact bone allograft with cemented cup in revision total hip arthroplasty can reconstruct hip rotation center and the acetabular bone quantity effectively. Satisfied early-midterm curative effects could be acquired by using this method. Key words: Arthroplasty, replacement, hip; Reoperation; Acetabulum; Bone transplantation; Transplantation, homologous; Surgical mesh

Favorable Early Results of Impaction Bone Grafting With Reinforcement Mesh for the Treatment of Paprosky 3B Acetabular Defects

BackgroundWe present the early institutional experience with the use of impaction bone grafting, mesh augmentation, and cement fixation of an all-polyethylene cup for the treatment of Paprosky 3B acetabular defects during revision total hip arthroplasty. MethodsBetween 2005 and 2014, 21 patients (9 men, 12 women) with Paprosky 3B acetabular defects who underwent revision total hip arthroplasty using this technique were reviewed clinically and radiographically. Average age and body mass index were 72.4 (range, 48-91) years and 24.5 (range, 18.9-31) kg/m2, respectively. All patients underwent revision for aseptic loosening. Surgical technique included the use of a peripheral mesh to contain the defect, followed by impaction of morselized fresh-frozen bone graft and cement fixation of a polyethylene cup. ResultsComplications occurred in 6 patients (29%) including limp (2), sciatic nerve palsy that resolved (1), limb length discrepancy (1), and greater trochanteric fracture (1). After an average follow-up of 47 months (range, 13-128 months), the average Hospital for Special Surgery hip score was 35.5 (range, 20-40). Radiographic assessment revealed cephalad cup migration of 2.29 mm (range, 0-20 mm) and medial migration of 1.57 mm (range, 0-6 mm). One patient has radiographic loosening and no symptoms 120 months postoperatively. No patient returned to the operating room for a related reason or is scheduled to undergo acetabular re-revision surgery. ConclusionImpaction bone grafting is a reliable technique for the treatment of Paprosky 3B acetabular defects. It restores bone stock like no other available for addressing these defects. Longer follow-up is required to assess potential deterioration of fixation.

Un essai pilote comparant le comportement à l’arrachement des cupules metal-back vissantes et cimentées en polyéthylène : étude cadavérique cas témoin

BackgroundThe removal of well-fixed acetabular components following total hip arthroplasty (THA) is a difficult operation and could be accompanied by the loss of acetabular bone stock. The optimal method for fixation is still under debate. The aim of this pilot study was to compare the tear-out resistance and failure behavior between osseo-integrated and non-integrated screw cups. Furthermore, we examined examined whether there are differences in the properties mentioned between screw sockets and cemented polyethylene cups. HypothesisTear-out resistance and related mechanical work required for the tear-out of osseo-integrated screw sockets are higher than in non-integrated screw sockets. Patients and methodsTen human coxal bones from six cadavers with osseo-integrated screw sockets (n=4), non-integrated (implanted postmortem, n=3) screw sockets and cemented polyethylene cups (n=3) were used for tear-out testing. The parameters axial failure load and mechanical work for tear-out were introduced as measures for determining the stability of acetabular components following THA. ResultsThe osseo-integrated screw sockets yielded slightly higher tear-out resistance (1.61 ± 0.26kN) and related mechanical work compared to the non-integrated screw sockets (1.23 ± 0.39kN, P=0.4). The cemented polyethylene cups yielded the lowest tear-out resistance with a failure load of 1.18±0.24kN. Compared to the screw cups implanted while alive, they also differ on a non-significant level (P=0.1). Osseous failure patterns differed especially for the screw sockets compared to the cemented polyethylene cups. DiscussionOsseo-integration did not greatly influence the tear-out stability in cementless screw sockets following axial loading. Furthermore, the strength of the bone–implant interface of cementless screw sockets appears to be similar to cemented polyethylene cups. However, given the high failure load, high mechanical load and because of the related bone failure patterns, removal should not be performed by means of tear-out but rather by osteotomes or other curved cutting devices to preserve the acetabular bone stock. Level of evidenceLevel III, case-control-study.