Aims

This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads.

We investigated the revision rates of primary total hip replacement (THR) reported in the National Joint Registry (NJR) by types of bearing surfaces used. We analysed THR procedures across all orthopaedic units in England and Wales. Our analyses estimated all-cause and cause-specific revision rates. We identified primary THRs with heads and monobloc cups or modular acetabular component THRs with head and shell/liner combinations. We used flexible parametric survival models to estimate adjusted hazard ratios (HR). A total of 1,026,481 primary THRs performed between 2003–2019 are included in the primary analysis (Monobloc: n=378,979 and Modular: n=647,502) with 20,869 (2%) of these primary THRs subsequently undergoing a revision episode (Monobloc: n=7,381 and Modular: n=13,488). Compared to implants with a cobalt chrome head and highly crosslinked polyethylene (HCLPE) cup, the all-cause risk of revision for monobloc acetabular implant was higher for patients with cobalt chrome or stainless steel head and non-HCLPE cup. The risk of revision was lower for patients with a delta ceramic head and HCLPE cup implant, at any post-operative period. Compared to patients with a cobalt chrome head and HCLPE liner primary THR, the all-cause risk of revision for modular acetabular implant varied non-constantly. THRs with a delta ceramic or oxidised zirconium head and HCLPE liner had a lower risk of revision throughout the entire post-operative period. The all-cause and indication-specific risk of prosthesis revision, at different time points following the initial implantation, is lower for implants with a delta ceramic or oxidised zirconium head and a HCLPE liner/cup than commonly used alternatives such as cobalt chrome heads and HCLPE liner/cup

Hip bearing surfaces materials are typically broadly reported in national registry (metal-on-polyethylene, ceramic-on-ceramic etc). We investigated the revision rates of primary total hip replacement (THR) reported in the National Joint Registry (NJR) by detailed types of bearing surfaces used. We analysed THR procedures across all orthopaedic units in England and Wales. Our analyses estimated all-cause and cause-specific revision rates. We identified primary THRs with heads and monobloc cups or modular acetabular component THRs with detailed head and shell/liner bearing material combinations. We used flexible parametric survival models to estimate adjusted hazard ratios (HR). A total of 1,026,481 primary THRs performed between 2003–2019 were included in the primary analysis (Monobloc cups: n=378,979 and Modular cups: n=647,502) with 20,869 (2%) of these primary THRs subsequently undergoing a revision episode (Monobloc: n=7,381 and Modular: n=13,488). Compared to implants with a cobalt chrome head and highly crosslinked polyethylene (HCLPE) cup, the overall risk of revision for monobloc acetabular implant was higher for patients with cobalt chrome or stainless steel head and non-HCLPE cup. The risk of revision was lower for patients with a delta ceramic head and HCLPE cup implant, at any post-operative period. Compared to patients with a cobalt chrome head and HCLPE liner primary THR, the overall risk of revision for modular acetabular implant varied non-constantly. THRs with a delta ceramic or oxidised zirconium head and HCLPE liner had a lower risk of revision throughout the entire post-operative period. The overall and indication-specific risk of prosthesis revision, at different time points following the initial implantation, is reduced for implants with a delta ceramic or oxidised zirconium head and a HCLPE liner/cup in reference to THRs with a cobalt chrome head and HCLPE liner/cup

Introduction This study was performed to evaluate the wear rates of Zirconia ceramic heads manufactured prior to the introduction of hot isostatic pressing, on a modular cementless polyethylene cup, and to compare this with the wear rate of a cobalt chrome head coupled with the same cup. Methods Radiological analysis of 281 primary uncemented ABG total hip arthroplasties performed between 1991 and 1994 was carried out. Patients were divided into three groups: 203 patients with 28 mm zirconia head/polyethylene bearings, 47 patients with 32 mm zirconia ceramic head/polyethylene bearings, 31 patients with 28 mm cobalt chrome head/polyethylene bearings. Wear analysis was performed using the Martel software after digitising radiographs on a flatbed scanner. Initial radiographs were at a minimum of one year to exclude bedding in, and follow-up radiographs a minimum of two years later. Mean follow-up was 6.5 years. Results The mean linear wear rate of the groups following age and gender matching: for 28 mm Zirconia heads 0.22 mm/yr, for 32 mm Zirconia heads 0.20 mm/yr and for 28 mm metal heads 0.14 mm/yr (p< 0.05). The patients with Zirconia heads had higher rates of osteolysis and revision than those with cobalt chrome heads. Conclusions The reason for this increased wear rate of Zirconia on polyethylene may well be the transformation of the tetragonal stable phase of the Zirconia to the monolithic unstable phase on the surface of the material. This transformation at grain boundaries on the surface results in ceramic grain “pull-out” by the sliding action of the head against the polyethylene cup. This phenomenon may well occur as a result of the Zirconia processing; the ceramic studied was produced prior to hot isostatic pressing, which produces an inherently more stable ceramic i.e. a higher percentage of the tetragonal phase. In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source

Adverse reaction to metal debris (ARMD) is well recognised as a complication of large head metal on metal total hip replacement (THR) leading to pain, bone and tissue loss and the need for revision surgery. An emerging problem of trunnionosis in metal on polyethylene total hip replacements leading to ARMD has been reported in a few cases. Increased metal ion levels have been reported in THR's with a titanium stem and a cobalt chrome head such as the Accolade-Trident THR (Stryker). We present 3 cases of ARMD with Accloade-Trident THR's with 36mm cobalt chrome head and a polyethylene liner. Metal ion levels were elevated in all three patients (cobalt 10.3 – 161nmol/l). Intraoperative tissue samples were negative for infection and inflammatory markers were normal. Abnormal fluid collections were seen in all three cases and bone loss was severe in one patient leading to a proximal femoral replacement. Histology demonstrated either a non-specific inflammatory reaction in a case which presented early or a granulomatous reaction in a more advanced case suggesting a local foreign body reaction. All patients had improved symptoms post-operatively. 1 patient who had staged bilateral Accolade-Trident THR's required revision of both THR's. ARMD in metal on polyethylene THR's with a titanium stem represents a potential emerging problem. Further studies are required to assess whether these occurrences are rare or represent the tip of an iceberg

Introduction: Increased wear is associated with aseptic loosening and late dislocations. Hard on hard bearings may reduce wear but still have topics of concern such as free metal ions in metal on metal bearings and the risk for fracture in ceramic articulations. Ceramic heads against conventional polyethylene is also used with the intention to reduce wear. But this effect has not been conclusively documented in the literature and is still discussed. 87 patients were operated consecutively by the same surgeon with the same surgical technique. All patients received a cemented all poly cup sterilized with irradiation in inert atmosphere and a cemented stem. Head size was 28 mm in all patients. 40 patients received cobalt-chrome heads and 47 patients aluminiumoxid heads. The patients were followed with RSA for 10 years and analysed for wear. Results: Mean (SEM) wear for the group with cobalt chrome heads was 0.93 mm (0.13) and for the group with aluminiumoxide was 0.43 mm (0.08) (p = 0.001). Discussion: We found significantly less wear with aluminumoxide heads compared to cobalt-chrome heads. The wear results in the cobalt-chrome group correlate well to wear values in the literature for conventional polyethylene. Although the polyethylene in this study is partly cross-linked (3Mrad) it is not clear whether these results can be extrapolated directly to the use of highly cross-linked PE. If longer follow-ups confirm the mechanical stability of highly cross-linked PE, ceramic heads might contribute additionally to the reduction of wear. In conclusion we found significantly reduced wear for aluminumoxide heads compared to cobalt chrome heads which could be beneficial for young and active patients

Aims: To investigate whether the use of mini-spigots result in enhanced wear and corrosion of tapers compared to standard spigots and the influence of the surface finish on this. Methods: The heads were cobalt chrome and the stems titanium alloy. Firstly wear and corrosion of standard spigots were compared with mini-spigots and secondly, these mini-spigots with another mini-spigot with a smoother surface finish. The samples were immersed in aerated Ringers solution (37°C) and loaded for 10 million cycles. Then samples were sectioned and the surface parameters measured and interfaces investigated using scanning electron microscopy. Static corrosion tests were used under loaded and non-loaded conditions and pitting tests for non-loaded samples. Results: Pre-experimentation the surfaces of the female tapers were similar for all heads. At the end of the first test the surface parameters on the female tapers had become significantly greater (p=0.034) for the mini-spigots compared with standard spigots and an abrupt change noted on the surface profile of the female taper where it contacted the male taper, indicating that the cobalt chrome head had corroded. Scanning electron microscopy showed that the coarser profile in the corroded region of the cobalt chrome head was similar to the profile on the titanium stem taper. Pitting corrosion was evident in the grooves on the cobalt chrome. The smooth mini-spigots were less affected. Conclusions: In cobalt chrome- titanium alloy combinations where the surface finish on the taper is coarse, corrosion is increased on a mini spigot compared with standard spigot. Surface finish is crucial and corrosion of the mini spigot is reduced if the surface finish is smooth

Introduction: Highly cross-linked polyethylene acetabular cups and Oxinium femoral heads were developed to reduce wear debris induced osteolysis. Laboratory tests have shown less wear with these new materials. This RSA-study was performed to compare these new materials in vivo with conventional bearing materials used in total hip arthroplasty. Methods:150 patients were randomized to 5 groups. The patients received either a cemented Charnley mono-block stainless steel femoral stem with a 22.2 mm head or a cemented Spectron EF femoral stem with a 28 mm head. The Charnley stem articulated with a cemented Charnley Ogee acetabular cup. The Spectron EF stem was used with either cemented Reflection All-Poly EtO-sterilized ultra-high molecular weight polyethylene (UHMWPE) acetabular cups or cemented Reflection highly cross-linked polyethylene (XLPE) acetabular cups, combined with either Cobalt Chrome or Oxinium 28 mm femoral heads. Patients were followed up with repeated radiostereometric analysis (RSA) for two years to assess the rate of penetration of the femoral head into the cup (MTPM). Results: At 2 years follow-up the mean MTPM (95 % CI) for Charnley Ogee (n=25) was 0.20 mm (0.11–0.29). For the Spectron EF femoral stem used with Reflection All-Poly UHMWPE acetabular cups the mean MTPM (CI) at 2 years was 0.40 mm (0.23–0.57) when combined with Cobalt Chrome femoral head (n=23) and 0.50 mm (0.29–0.71) when combined with Oxinium femoral head (n=16). When using the Spectron EF femoral stem with Reflection XLPE combined with Cobalt Chrome (n=27) or Oxinium (n=24) femoral head the mean MTPM (CI) at 2 years was 0.19 mm (0.10–0.28) and 0.18 mm (0.07–0.29), respectively. There were no differences in penetration between the Charnley/Ogee, XLPE/CoCr and XLPE/Oxinium groups (student t-test, p=0.5–0.8). There was no statistically significant difference between the two Reflection All-Poly UHMWPE groups (p=0.09). The groups with Reflection All-Poly cups had a statistically significant higher penetration than the three groups mentioned above (p< 0.001). Discussion: The use of Reflection XLPE cups instead of Reflection All-Poly cups reduced femoral head penetration at 2 years. We used the Charnley Ogee cup as a reference due to a long clinical record. This cup was superior to Reflection All-Poly, but not Reflection XLPE, regarding femoral head penetration. Because the femoral head of Charnley Ogee is smaller than the Oxinium/Cobalt Chrome head it might be more clinical relevant to measure volumetric wear. The groups with Oxinium heads did not have less wear than the groups with Cobalt Chrome heads after 2 years follow-up. Further follow-up is needed to evaluate the benefits, if any, of Oxinium femoral heads in the clinical setting

Introduction/Aims. The Exeter Stem can be used with metal femoral head that are made of either cobalt chrome, or stainless steel. The aim of this study was to compare the rates of revision of these two metal femoral head types when used with this femoral component. Method. Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) Data from September 1999 until December 2015 for all primary THRs using an Exeter or an Exeter v40 stem with the diagnosis of osteoarthritis were analysed. Only bearing couples that used a metal head with polyethylene were included. The cumulative percent revision (CPR) calculated using Kaplan-Meier estimates were compared for the two metal head types. CPR were further analysed by age, polyethylene type and head size. Reasons for revision and types of revision were assessed. Results. There were 51666 THR that used Exeter or Exeter v40 stems of which 12554 had femoral heads made of cobalt chrome and 39112 had heads made of stainless steel. There was no difference in the rate of revision overall when head types were compared. There was also no difference in CPR between the two head types with age. Hips that used cobalt chrome heads had a higher CPR than stainless steel heads when these were used against non-crosslinked polyethylene. When heads with a diameter of 32mm or greater were compared, those made of cobalt chrome had a higher rate of revision than stainless steel HR 1.38 (1.15, 1.66) P<0.001). Conclusion. There was no difference comparing cobalt chrome or stainless-steel heads, except where non-crosslinked polyethylene was used, or where the heads size was 32mm or greater. In these comparisons, heads made from cobalt chrome had a higher rate of revision

Introduction. Manifestation of high interface stresses coupled with micromotion at the interface can render the taper lock joint in a modular hip replacement prosthesis at risk for failure. Bending can lead to crevice formation between the trunnion and the head and can potentially expose the interface to the biological fluids, generating interface corrosion. Additionally, development of high stresses can cause the material to yield, ultimately leading to irreversible damage to the implant. The objective of this study is to elucidate the mechanical response of taper junction in different material combination assemblies, under the maximum loads applied during everyday activities. Methods. Computer simulations were executed using a verified FE model. A stable hexahedral mesh (33648 elements) was generated for the trunnion (taper size: 12/14mm) and a tetrahedral mesh (51182 elements) for the head (CoCr, size: 32mm). An assembly load of 4000N was applied along the trunnion axis followed by the application of a load of 230–4300N at 25° and 10° angle to the trunnion axis in the frontal and sagittal planes. A linear static solution was set up using Siemens NX Nastran. Two material combinations were tested - cobalt-chrome head with a titanium alloy trunnion and cobalt chrome head with a cobalt-chrome trunnion. Results. Table1 compares the results obtained from the simulation to those observed in experimental simulations performed under similar loading conditions in our lab. Larger vertical interface displacement was observed in the CoCr-CoCr assembly during toggle-inducing loads. The trunnion bending inside the femoral head was higher in the Ti-CoCr assembly (0.056) compared to the CoCr-CoCr assembly (0.027) with the overall bending of the Ti-CoCr assembly also observed to be much higher (Fig.1). Negligible difference between the stress measured in the femoral head and taper was observed (Fig.2). Discussion. Bending could potentially lead to the development of higher stresses especially under multiple cycles of loading. Fatigue and plastic deformation could result in irreparable damage to the interface leading to implant failure. Additionally, bending causes a separation of the interfaces at the trunnion-head junction, leading to crevice formation, triggering corrosion by exposure to the surrounding physiological environment. Thus, it is crucial that we understand the mechanics of the trunnion-head junction especially under conditions of functional loading

Introduction. Wear and corrosion between head and stem tapers of modular hip implants have recently been related to clinical failures, possibly due to high friction moments in poorly lubricated joints [1–2]. In-vivo measurements have revealed reversing joint friction moments in the hip during a gait cycle [3], which may foster relative motion between the modular components. Blood, soft tissue or bone debris at the taper interface during assembly can lead to decreased stability or increased stress concentrations due to non-uniform loading [4]. The purpose of this study is to investigate the influence of taper contamination and the assembly force on the seating characteristic of the head on the stem incorporating realistic reversing joint friction moments. Methods. Cobalt chrome heads (M-SPEC, 36mm, +1.5mm; n=5) were assembled on titanium femoral stems (Corail 12/14, both components Depuy Synthes; n=5) by quasistatic axial push-on forces (F=0.5kN, 1kN, 2kN). Heads were modified by milling a flat plane, to which the joint load was applied alternately to point A and point B for 20 cycles to provide reversing moments (heel-strike FA=1971N, MA=5.4Nm; toe-off FB=807N, MB=4.6Nm; Fig. 1). All 6 degrees of freedom of relative displacement between head and stem were determined in the unloaded state and after each loading cycle. A coordinate measurement machine (accuracy ±2µm) was used to determine the components positions. Pull-off forces were measured after the last loading cycle. Each taper was tested in pristine condition and then contaminated with a bone chip (1.7±0.2mg). Results. Contaminated tapers exhibited significantly larger seating than clean samples for all assembly forces (p<0.001, Fig. 2). Higher assembly forces led to decreased translation and rotation (p<0.001). Pull-off forces remained constant (F=890±99N) and independent of assembly force (p=0.303), or contamination condition (p=0.192). No further seating of the head on the stem taper was seen for the 20th load cycle. Discussion. This study shows that contamination, even in very small quantities, can increase initial translation and rotation, which could initiate corrosion. This can be countered, to some extent by applying sufficiently high assembly forces. It is noted that no further seating was measurable by the 20th loading cycle for any assembly condition but this does not rule out increased cyclic motion, particularly in contaminated interfaces [5]. The final pull-off forces were independent of the magnitude of the assembly force but might rather be related to the maximum joint load, suggesting that the assembly force should be at least as great as the maximum joint load. To view tables/figures, please contact authors directly

Introduction. The National Joint Registry has recently identified failure of large head metal on metal hip replacements. This failure is associated with the high torque at the interface of standard modular taper junction leading to fretting and corrosion. A number of manufacturers produce mini spigots, which in theory, provide a greater range of motion as the neck head junction is reduced. However, the relative torque to interface ratio at this junction is also increased. In this study we investigated hypothesis that the use of small spigots (minispigots) will increase wear and corrosion on modular tapers. Methods. Wear and corrosion of spigots were compared in-vitro when loaded with a force representative of the resultant force passing through the hip. The heads (female tapers) were made of cobalt-chrome-molybdenum (CoCrMo) and the stems (male tapers) of titanium alloy (Ti). Commercially available tapers and heads were used. The surface parameters & profiles were measured before & after testing. Electrochemical static and dynamic corrosion (pitting) tests were performed on minispigots under loaded and non-loaded conditions. Results. Post-testing the surface parameters Ra, Ry & Rz on the head taper associated with the minispigots had become greater compared with standard spigots. In all instances the profile of the titanium male tapers was unchanged. SEM showed the corroded region of the head was similar to the profile on the Ti male taper, with evidence of pitting in the cobalt chrome. In the CoCrMo/ Ti combinations, wear and corrosion were increased in minispigots compared with standard spigots. On minispigots the rough surface finishes were affected more severely than those with a smoother surface. Static corrosion tests showed evidence of fretting in the rough but not the smooth minispigots. Pitting scans showed a greater hysteresis with the rough surface finishes on the minispogot indicating potentially greater corrosion in the former. Conclusion. The relative size of the taper in comparison to the head combined with the surface finish was crucial. As the relative torque to interface ratio at this junction increased corrosion of the cobalt chrome head increases and is further enhanced if the surface finish on the tapers is rough

Introduction and Aims: This is a prospective randomised trial comparing the ABG uncemented total hip replacement with the Charnley in 243 patients less than 65 years of age. A standardised protocol and anterolateral approach was used. Method: The ABG I cup was used in combination with a polyethylene liner. All stems were templated and a 28mm cobalt chrome head was used. Early mobilisation with partial weightbearing for six weeks was allowed. In the Charnley group, Elite polyethylene cups were used in conjunction with 22mm monoblock stems. All hips were inserted with pressurised CMW cement. Patients were followed up annually. Standardised radiographs were taken at each visit and the Harris hip score and Merle d’Aubigné outcome measures recorded. There were 222 hips available for follow-up, 96 ABG hips and 126 Charnley hips (17 died and 10 were lost to follow-up), with the mean age at surgery and mean length of follow-up comparable. Most hips were replaced due to osteoarthritis. There was no significant difference in the mean Harris hip or Merle d’Aubigné scores at one year and at latest follow-up. Results: Radiographic results demonstrated accelerated polyethylene wear in the ABG hips with mean polyethylene wear at seven years being 2.1mm compared with 0.9mm for Charnley hips. Wear associated lysis around the ABG cup was the major reason for failure, with a total of eight cups (8.3%) undergoing revision. Conclusion: There was no evidence of subsidence of the stem or osteolysis around the stem despite the polyethylene wear. Conversely, in the Charnley group the stem was the major reason for failure with 12 stems (9.5%) being revised for aseptic loosening. The Kaplan Meier Survivorship at 10 years was 66.6% ± 19.1% for the ABG and ± 82% for the Charnley group. This was not significant

Introduction: Dislocation rates with THA vary from 3% to 15%. One specialist centre reported a 6.4% early dislocation rate with a 28mm ceramic on polyethylene THA in young patients (mean age 56 years) in a single surgeon series. Although young patients have the advantage of better soft tissues, their greater mobility demands increase dislocation risk. Dislocation rates in large headed metal-on-metal resurfacings are extremely low. However, many patients are unsuitable for resurfacing and need a replacement. In such cases, it is attractive to transfer the large-headed metal-metal bearing advantage to replacement arthroplasty in order to reduce wear and dislocation rates. Does large diameter metal-metal total hip replacement really reduce the early dislocation rate?. Methods: 206 consecutive primary metal-metal THRs (189 patients) were included. The device consists of an uncemented cup, a matching modular cobalt chrome head (head diameter ranged 38 – 58mm) fixed on a stem through a 12/14 cone. Cemented stems were used in 107 procedures and 99 were proximal-porous uncemented stems. Age at operation ranged from 37 to 83 years. Thirty patients were 55 years or under, eighty one were 56 – 65 years and ninety five were over 65 years. There were 122 females and 67 males. Posterior approach was used in all. Results: There were no dislocations in these 206 consecutive procedures. Discussion: Metal-metal hips have lower dislocation rates than hips containing polyethylene (0.9% against 6.4% in a matched series). This is attributed to the suction-fit effect of metal-metal bearings. Large diameter bearings have the additional benefit of having to translate a greater jump distance before a dislocation. This dual advantage leading to extremely low dislocation rates was first noted in metal-metal resurfacings. In large headed metal-metal THRs, the head-neck ratio is even more favourable and these devices appear to eliminate early dislocation as a major complication

This is a retrospective assessment of the performance of a consecutive series of the titanium uncemented Gemini femoral component. The Gemini uncemented stem (De Puy) is a modular titanium femoral stem with a cobalt chrome head. It has proximal porous coating allowing stable fixation by bony in-growth and a smooth distal stem allowing mechanical fixation. Using a direct lateral approach, 152 consecutive patients underwent a total hip replacement using the Gemini uncemented femoral component and an unce-mented cup. Patients were regularly assessed clinically (Harris hip score) and radiologically (Engh’s criteria for fixation of the prosthesis). Kaplan Meier survivorship analysis was used to assess survival. 16 patients were lost to follow-up and 30 were dead with the THR in situ, leaving 106 hips for final analysis, at a mean follow-up of 106 months. The mean age of the group was 60 years (range 25–83) and OA was the commonest diagnosis. The mean Harris hip score improved from 34 to 92(range 83–100). 7 stems have been revised, four of which for aseptic loosening and a further two are radiologically loose. Mean time to revision was 41 months (range 14–76). By Engh’s criteria, 90% of the hips had stable bony fixation; only 4% of the patients complained of thigh pain at final follow-up. Kaplan Meier survivorship analysis with aseptic loosening as endpoint indicated a survival of 93% at 8 years. A mid-term result with the Gemini uncemented stems at a mean follow-up of approximately 9 years was excellent. This is in sharp contrast to the cemented stem of similar design, even though the uncemented version was used in younger and more active group of patients. Titanium alloy is biocompatible allowing for excellent bony in growth, making it an ideal alloy in the manufacture of uncemented stems. Having a modulus of elasticity close to that of bone explains the low incidence of thigh pain

A multitude of different bearing combinations exist to recreate the artificial hip joint. To date, there is no particular ‘gold-standard’ total hip arthroplasty (THA) couple since none is faultless. Strategies to improve performance are aimed either at modifying the shape and design of components or their material properties. Wear particle generation is now well recognised as a cause of aseptic loosening which consistently features amongst the most common indication for revision THA and thus minimising wear lies at the cornerstone of developing bearing couples. However, history has shown the use of supposed newer and improved materials have not been without occasional catastrophic failure. Hard-on-hard bearings are theoretically more resistant to wear but component fracture and squeaking has been witnessed with ceramic-on-ceramic articulations whilst metal-on-metal articulations have been plagued by reports of pseudotumor and ALVAL formation. This has all led to resurgence in the hard-on-soft couple. More recently, corrosion at taper junctions has been identified as a significant factor in hip arthroplasty failure. Femoral head materials, surface changes or coatings may therefore have an increasing role to play. In 2005, a multi-center, prospective, assessor and patient-blinded, randomised control trial was initiated. This was designed as a three armed study with either cobalt-chrome or oxidized zirconium femoral heads articulating against highly cross-linked polyethylene (XLPE) liners and oxidized zirconium articulating against ultra-high molecular weight polyethylene (UHMWPE). Early reports that XLPE was significantly superior to UHMWPE when coupled with cobalt-chrome meant no patient involved in the study was approved to receive a couple of cobalt-chrome and UHMWPE since it was deemed to be a high wear group. We hypothesised that oxidized zirconium femoral heads would produce less linear wear than cobalt- chrome femoral heads at mid-term evaluation, whilst maintain similar outcomes when recording WOMAC, SF-36 and pain scores, and complication rates. All three groups were statistically comparable preoperatively and at five years when measuring normalised WOMAC, SF-36 and pain scale scores; all groups showed a statistically significant improvement in scores from baseline compared to at five years (p<0.001). There was no significant difference in mean femoral head penetration when either oxidized zirconium or cobalt-chrome where articulated with XLPE (p=0.1533) but a significant difference in mean femoral head penetration was observed between the group that had used UHMWPE and both the other groups which had used XLPE (p<0.001). There were no hips in which either acetabular or femoral osteolysis was observed. We have demonstrated that oxidized zirconium femoral heads are safe with low rates of wear when coupled with XLPE. However at five year follow-up, it appears that the choice of material of the acetabular bearing is more important than the choice of femoral head bearing. Further follow-up is needed in order to see if femoral head choice leads to a difference in outcome beyond 5 years as laboratory data suggests. Moreover the potential reduction of corrosion with ceramic or oxidized zirconium heads may yet also prove to be significant. It is likely that current and future data will lead us away from the use cobalt chrome heads towards alternatives that are less likely to be associated with corrosion or wear and osteolysis

Introduction and Aims: Polyethylene wear and associated osteolysis is a major factor limiting arthroplasty longevity. The Duration process has the theoretical advantage of reducing wear. Our aim was to evaluate the wear rate of standard and Duration polyethylene using either metal or zirconia ceramic heads in the Anatomique Benoist Girard II hip system. Method: Of 510 patients, 258 had appropriate radiographs for wear measurement. There were five bearing-couple groups. Group 1, 73 patients: metal (cobalt chrome) head on standard polyethylene; group 2, 73 patients: metal head on Duration polyethylene; group 3, 21 patients: (HIPed) zirconia ceramic head on standard polyethylene; group 4, 63 patients: HIPed zirconia head on Duration polyethylene; and group 5, 28 patients: non-HIPed zirconia head on standard polyethylene. All patients had 28mm heads. Sequential radiographs – at least one year after surgery and at least two years apart thereafter – were digitally scanned and images were analysed using computer software. Results: Group 1: metal on standard polyethylene (n=73) – mean linear wear rate of 0.138 mm/yr (range 0.023–0.462 mm/yr). Group 2: metal on Duration polyethylene (n=73) – mean linear wear rate of 0.106 mm/yr (range 0.067–0.405 mm/yr). Group 3: HIPed zirconia heads on standard polyethylene (n=21) – mean linear wear rate of 0.124 mm/yr (range 0.037–0.225 mm/yr). Group 4: HIPed zirconia heads on Duration polyethylene (n=63) – mean linear wear rate of 0.120 mm/yr (range 0.001–0.427 mm/yr). Group 5: non-HIPed zirconia heads on standard polyethylene (n=28) – mean linear wear rate of 0.119 mm/yr (range 0.044–0.0330 mm/yr). Comparison of linear wear rates of standard (group 1) and Duration polyethylene (group 2) bearings with metal heads revealed a difference of statistical significance (p=0.0083), with lower annual wear rates with Duration polyethylene. Further comparison between these two groups revealed a male preponderance in the Duration group (p=0.000001). There was also a statistically significant difference in body weight between these groups, with the Duration group being heavier by a mean of 5.1 kilograms (p=0.05). There was no significant difference in wear rates between standard and Duration polyethylene bearings with HIPed zirconia heads. There was no statistically significant difference in age in our patient groups. Conclusion: Duration polyethylene has lower linear wear rates when coupled with a cobalt chrome head. This is despite a male preponderance and higher body weight. Wear rates between standard and Duration polyethylene bearings coupled with zirconia heads were not statistically different

The concept of stainless steel dual mobility cups in total hip arthroplasty has demonstrated very low long-term instability rates and a 98% survival rate after 12 years. We systematically implanted titanium alloy acetabular cups during a one year period. The purpose of our retrospective study was to report the 18-year clinical outcome data in a homogeneous and continuous series of 103 primary total hip replacements after implantation of a cementless titanium cup. All patients were implanted with NOVAE Ti (SERF) cups made of titanium alloy combined with a retentive polyethylene liner and a 22.2 mm cobalt chrome prosthetic head. Mean patient age at the time of surgery was 53 years. All patients were clinically and radiographically evaluated. The overall 18-year actuarial cup survival rate with a 95% confidence interval was 87.4%. At last follow-up, there was no evidence of implant instability whereas acetabular aseptic loosening was reported in one case and high wear of the retentive liner in 9. The results of this investigation confirmed the long-term stability of dual-mobility implants. The main limitation of this system was early wear of the polyethylene liner in contact with the titanium metal back and reaction with third body along with loss of liner retentivity. In our study, titanium demonstrated favourable osteointegration properties but poor tribologic characteristics, therefore suggesting its interest at the bone-cup interface only

Introduction. Geometric variations of the hip joint can give rise to abnormal joint loading causing increased stress on the articular cartilage, which may ultimately lead to degenerative joint disease. In-vitro simulations of total hip replacements (THRs) have been widely reported in the literature, however, investigations exploring the tribology of two contacting cartilage surfaces, and cartilage against metal surfaces using complete hip joint models are less well reported. The aim of this study was to develop an in-vitro simulation system for investigating and comparing the tribology of complete natural hip joints and hemiarthroplasties with THR tribology. The simulation system was used to assess natural porcine hip joints and porcine hemiarthroplasty hip joints. Mean friction factor was used as the primary outcome measure to make between-group comparisons, and comparisons with previously published tribological studies. Method. In-vitro simulations were conducted on harvested porcine tissue. A method was developed enabling natural acetabula to be orientated with varying angles of version and inclination, and natural femoral heads to be potted centrally with different orientations in all three planes. Acetabula were potted with 45° of inclination and in the complete joint studies, natural femoral heads were anatomically matched and aligned (n=5). Hemiarthroplasty studies (n=5) were conducted using cobalt chrome (CoCr) heads mounted on a spigot (Figure 1), size-matched to the natural head. Natural tissue was fixed using PMMA (polymethyl methacrylate) bone cement. A pendulum friction simulator (Simulator Solutions, UK), with a dynamic loading regime of 25–800N, ± 15° flexion-extension (FE) at 1 Hertz was used. The lubricant was a 25% (v/v) bovine serum. Axial loading and motion was applied through the femoral head and frictional torque was measured using a piezoelectric transducer, from which the friction factor was calculated. Results. The correct anatomical orientation and positioning was achieved enabling in-vitro simulation testing to be conducted on hemiarthroplasty and complete hip joint samples for two-hours. Mean friction increased rapidly followed by a continued gradual increase to ≈0.03 ± 0.00 in the complete joints, with the hemiarthroplasty group plateauing at ≈0.05 ± 0.01 (Figure 2). Mean friction factor was significantly lower (t-test; p < 0.05) in the complete natural joint group. Discussion. An in-vitro simulation system for the natural hip joint with controlled orientation of the femur and acetabulum was successfully developed and used to measure friction in complete porcine hip joints and porcine hip hemiarthroplasties. A non-linear increase in friction indicative of biphasic lubrication was observed in both groups with slower exudation of fluid from the complete joints compared to the hemiarthroplasties, inferring a quicker move towards solid-phase lubrication. Higher friction in the hemiarthroplasties, which was similar to that measured in-vitro in metal-on-polyethylene THRs, was most likely due to variable clearances between the non-conforming spherical metal head and aspherical acetabulum, causing poorer congruity and distribution of the load. This could in time lead to abrasive wear and cartilage degradation. This methodology could have an important role when investigating associations between hip geometric variations, interventions for hip disease/pathology, and risk factors for cartilage degeneration

Aims

Vitamin E-infused highly crosslinked polyethylene (VEPE) has been introduced into total hip arthroplasty (THA) with the aim of further improving the wear characteristics of moderately and highly crosslinked polyethylenes (ModXLPE and HXLPE). There are few studies analyzing the outcomes of vitamin E-infused components in cemented arthroplasty, though early acetabular component migration has been reported. The aim of this study was to measure five-year polyethylene wear and acetabular component stability of a cemented VEPE acetabular component compared with a ModXLPE cemented acetabular component.