Introduction

Failure of metal on metal (MOM) total hip arthroplasty (THA) and resurfacing arthroplasty (HRA) due to development of adverse local tissue reaction (ALTRs) is a significant problem. The prevalence of ALTRs in asymptomatic MOM arthroplasty patients is highly variable. The purpose of this prospective, longitudinal study was to: 1) determine MRI ALTR prevalence in patients with HRA; 2) determine if patients with HRA have a greater rate of MRI ALTRs compared to control patients with ceramic on poly (COP) THA; and 3) evaluate changes in patient reported outcomes between these implant designs.

Introduction

The Birmingham Hip Resurfacing (Smith & Nephew London, UK) is the most popular hip resurfacing (HR) in the UK. However, it is now subject to two Medical Device Alerts (MDA) from the Medicines and Healthcare products Regulatory Agency (MHRA).

Patients from a randomised trial on resurfacing hip arthroplasty (RHA) (n = 36, 19 males; median age 57 years, 24 to 65) comparing a conventional 28 mm metal-on-metal total hip arthroplasty (MoM THA) (n = 28, 17 males; median age 59 years, 37 to 65) and a matched control group of asymptomatic patients with a 32 mm ceramic-on-polyethylene (CoP) THA (n = 33, 18 males; median age 63 years, 38 to 71) were cross-sectionally screened with metal artefact reducing sequence-MRI (MARS-MRI) for pseudotumour formation at a median of 55 months (23 to 72) post-operatively. MRIs were scored by consensus according to three different classification systems for pseudotumour formation.

Clinical scores were available for all patients and metal ion levels for MoM bearing patients.

Periprosthetic lesions with a median volume of 16 mL (1.5 to 35.9) were diagnosed in six patients in the RHA group (17%), one in the MoM THA group (4%) and six in the CoP group (18%). The classification systems revealed no clear differences between the groups. Solid lesions (n = 3) were exclusively encountered in the RHA group. Two patients in the RHA group and one in the MoM THA group underwent a revision for pseudotumour formation. There was no statistically significant relationship between clinical scoring, metal ion levels and periprosthetic lesions in any of the groups.

Periprosthetic fluid collections are seen on MARS-MRI after conventional CoP THA and RHA and may reflect a soft-tissue collection or effusion.

Currently available MRI classification systems seem to score these collections as pseudotumours, causing an-overestimatation of the incidence of pseudotumours.

Cite this article: Bone Joint J 2015;97-B:1175–82.

Introduction

Metal on metal articulations produce chromium (Cr) and cobalt (Co) debris, particularly when the articulations are worn in. High levels in the peripheral blood are indicative of excess wear and may cause adverse effects. The present RCT investigates metal ion levels and the relationship of Co, Cr ions and lymphocyte counts during the running-in period.

This study examined whether TiNbN surface characteristics can reduce corrosion and wear of Chrome Cobalt Molybdenum Metal-on Metal bearings. Two series of patients had plasma concentrations of chromium and cobalt at intervals following surgery. The First Series comprised a retrospective analysis of 52 consecutive cases (49 patients, 73–96 months following operation; age at surgery: 33–78) who had undergone an ACCIS (Implantcast, Germany) Modular Large Head hip replacement. The Second Series comprised a prospective, consecutive series of 125 cases (109 patients, 1–61 months following operation; age at surgery: 24–75) who had undergone an ACCIS Resurfacing Hip Replacement in whom pre-operative samples and periodic post-operative metal ion analysis was obtained. Cup inclination and anteversion angles, patient outcome and Harris hip scores at last follow-up were also recorded. The first series revealed medians for [Cr] of 1.2 (range <0.5–2.4) ug/l and [Co] of 3.3 (range <0.15–8.18) ug/l. Four patients were not available for measurement. The second series gave one year [Cr] of 0.8 (range <0.5–1.6) ug/l and [Co] of 0.2 (range <0.15–0.9) ug/l and at two years [Cr] of 0.2 (range <0.5–1.5) ug/l and [Co] of 0.8 (range <0.15–1.0) ug/l. There was no correlation with cup inclination (38° to 62°) or anteversion (0° to 32°) in either group. Mean Harris Hip Scores were 80.9 and 92.3 respectively. Low median levels of metal ions were found in the First Series (despite differing stem type usage). The low median ion levels were more consistent in the Resurfacing patients of the Second Series. The Titanium Niobium Nitride Ceramic Surface Engineering Metal-on-Metal bearing implants appear to protect against raised plasma [Cr] and [Co] both over time and with outlying cup positions. The Harris Hip Scores suggest a good patient outcome for the hip replacements in both series. Further study by a randomised controlled prospective analysis is suggested

It is accepted that resurfacing hip replacement preserves the bone mineral density (BMD) of the femur better than total hip replacement (THR). However, no studies have investigated any possible difference on the acetabular side.

Between April 2007 and March 2009, 39 patients were randomised into two groups to receive either a resurfacing or a THR and were followed for two years. One patient’s resurfacing subsequently failed, leaving 19 patients in each group.

Resurfaced replacements maintained proximal femoral BMD and, compared with THR, had an increased bone mineral density in Gruen zones 2, 3, 6, and particularly zone 7, with a gain of 7.5% (95% confidence interval (CI) 2.6 to 12.5) compared with a loss of 14.6% (95% CI 7.6 to 21.6). Resurfacing replacements maintained the BMD of the medial femoral neck and increased that in the lateral zones between 12.8% (95% CI 4.3 to 21.4) and 25.9% (95% CI 7.1 to 44.6).

On the acetabular side, BMD was similar in every zone at each point in time. The mean BMD of all acetabular regions in the resurfaced group was reduced to 96.2% (95% CI 93.7 to 98.6) and for the total hip replacement group to 97.6% (95% CI 93.7 to 101.5) (p = 0.4863). A mean total loss of 3.7% (95% CI 1.0 to 6.5) and 4.9% (95% CI 0.8 to 9.0) of BMD was found above the acetabular component in W1 and 10.2% (95% CI 0.9 to 19.4) and 9.1% (95% CI 3.8 to 14.4) medial to the implant in W2 for resurfaced replacements and THRs respectively. Resurfacing resulted in a mean loss of BMD of 6.7% (95% CI 0.7 to 12.7) in W3 but the BMD inferior to the acetabular component was maintained in both groups.

These results suggest that the ability of a resurfacing hip replacement to preserve BMD only applies to the femoral side.

Introduction

Current standard cups of metal on metal resurfacing hip arthroplasty (RHA) have no dome holes and it is very difficult for surgeons to confirm full seating of these cups. This sometimes results in gap formation between the cup and acetabular floor. Although the incidence of initial gaps using modular press-fit cups with dome screw holes has been reported to range from 20 to 35%, few studies have reported the incidence of gap formation with monoblock metal cups and its clinical consequences in RHA. The purpose of this study was to investigate retrospectively the incidence of initial gap formation and whether the initial gap influences the clinical results in RHA.

Background

Correct positioning of the femoral component in resurfacing hip arthroplasty (RHA) is an important factor in successful long-term outcomes. The purpose of computer-assisted navigation (CAS) in resurfacing is to insert the femoral neck guide wire with greater accuracy and to help size the femoral component, thus reducing the risk of notching at the head and neck junction. Several recent studies reported satisfactory precision and accuracy of CAS. However, there is little evidence that CAS is useful in the presence of anatomical deformities of the proximal femur, which is frequently observed in young patients with secondary degenerative joint disease.

Background: Resurfacing hip arthroplasty has re-emerged as an option in total hip arthroplasty and by 2008 these prostheses constituted 7.8% of the total number of primary hip replacements in Australia. In the Scandinavian countries the use of resurfacing prostheses is substantially less, reported from 0.6–2.8% in the different national arthroplasty registries. The resurfacing implant preserves proximal bone stock and is expected to retain a physiological load transfer in the proximal femur. Mid-term results for the resurfacing implants are promising, but periprosthetic neck fractures remains the most frequent complication. Finite element analyses have suggested increased strains in the femoral neck area after resurfacing arthroplasty. This has not yet been proved in a cadaver model. Purpose: This study compared the strain pattern of the femoral neck and the proximal femur in cadaver femurs before and after insertion of a resurfacing femoral component. Material and method: When load transfers trough the hip joint to the femur, the bone undergoes a deformation, which can be measured by strain gauges. In this study, ten strain gauge rosettes were distributed on the femoral neck and proximal femur of thirteen human cadaver femurs. The femurs were loaded in a hip simulator for single leg stance and stair climbing. Cortical strains were measured on the femoral neck and proximal femur before and after implantation of a resurfacing femoral component (DePuy ASRTM). Results: After resurfacing the mean tensile strain increased by 15 % (CI: 6 – 24%, p=0.003) on the lateral femoral neck, and mean compressive strain increased by 11 % (CI: 5 – 17%, p=0.002) on the medial femoral neck during single leg stance simulation. On the anterior side of the femoral neck the strain increased up to 16%, however this difference was not found statistically significant. On the proximal femur the deformation pattern remained similar to the strains measured on the unoperated femurs. Discussion: Both patient related factors such as female gender, obesity and high age, and surgical factors such as notching, lack of seating and varus-orientation of the implant have been associated with increased risk of neck fracture after resurfacing arthroplasty. We asked ourselves if there could be a biomechanical factor contributing to the risk of periprosthetic fracture. The small increase of strains in the neck area would probably not alone be sufficient to cause a neck fracture. Acting together with patient-specific and surgical factors it may however contribute to the risk of early periprosthetic fracture

Resurfacing hip arthroplasty is a successful option for the treatment of the young and active patient with hip arthritis. However, it is complicated by femoral neck fracture and avascular necrosis, which result from devascularisation during surgery. Devascularisation maybe caused by thermal necrosis. Thermal necrosis of bone has been shown to occur in temperatures of 47°C and above. We investigated the temperatures generated during femoral head preparation to see if the temperatures reached were great enough to induce osteonecrosis. Method: Eight patients with osteoarthritis underwent standard resurfacing hip arthroplasty through the posterior approach. From the first over-drilling of the femoral heads until the prosthesis was cemented in place the temperatures generated at the bone surface were recorded using an infra-red thermal imaging camera. Images were captured every 4 seconds as the operation was performed with no interference to the surgeon. Results: The maximum temperatures generated occurred during sleeve reaming at 88.4°C. Seven patients had a temperature recorded greater than 47°C. Removing the femoral caput with an oscillating saw had the highest mean temperature 62.2°C, followed by sleeve reaming (mean 48.7°C). Female patients had the lowest temperature rises and patients receiving the larger femoral prosthesis the greatest temperatures at the bone surface. Conclusions: Heat generated during femoral head preparation exceeded 47°C in all but one case. Osteonecrosis secondary to thermal insult is likely to occur during femoral head preparation. Strategies need to be devised to decrease the temperatures generated during femoral head preparation

Introduction: Peri-prosthetic fractures following hip resurfacing arthroplasty are difficult fractures to treat. The surgeon is faced with the task of either attempting to fix the fracture if feasible or revise the resurfacing implant to a conventional total hip replacement.

Method & Results: Here we report of a novel way of fixing a peri-prosthetic fracture following resurfacing hip arthroplasty using Polyaxial locking plate fixation. A 53 year old man sustained a intertrochanteric fracture below his resurfacing metal on metal hip prosthesis following a fall. He had his hip resurfaced 3 years back for osteoarthritis in another hospital. He underwent surgery to fix the fracture using a polyaxial locking plate with no post-operative complications. He was mobilised non-weight bearing for the initial six weeks and weight bearing as tolerated thereafter. He went on to union and was moblising without any problems in three months time. His follow-up x-rays at 8 months showed fracture healed with no evidence of prosthesis problems.

Discussion: There are various methods of treating a periprosthetic fracture of a well fixed resurfaced hip implant. The two types of management are open reduction and internal fixation and revision to a stemmed hip implant. These fractures can be fixed with cannulated hip screws, blade plate device or plating with screws avoiding the stem of the resurfacing prosthesis. We used the polyaxial locking plate device with good result thereby avoiding the need for revision surgery with its attendant risks. Using this implant is a useful alternative for these fracture patterns.

Aim: The purpose of the study was to compare the position of the femoral guide wire for during hip resurfacing, computer navigation and an alignment device.

Materials and Methods: 26 cadaver specimens divided in 3 randomly selected groups and 25 patients were used to evaluate the position of the femoral guide wire in resurfacing hip arthroplasty. In two groups of cadavers the Computer Navigation was used to register and template the position of the implant. The position of the guide wire was compared to the one achieved using the alignment device. In the third group of cadaver specimens only the alignment device was used to implant the guide wire. Version was determined from the transversely cut sections of the cadaver specimens. Pre operative and post operative radiographs were used for analysis. In the patient group after registration and templating the guide wire was passed using the alignment device.

Results: There was no notching of the superior femoral neck in either of the groups. The mean and standard deviation of the anatomic neck-shaft angles was 124.91? ? 14.25?. The wire-shaft angle in the Navigation group was 131.46? ? 5.27? and in the alignment device group 134.08? ? 3.80?. In the navigation group the wire was in 0.85? ? 2.15? of retroversion as compared to 1.38? ? 4.19? of anteversion in Jig group. The position of the wires at the narrowest cross section of the femoral neck is shown in figure. The wire shaft angle as per navigation was 134.44(±5.55) as compared to 134.74 (±5.11).

Conclusion: The alignment device consistently positioned the wire more valgus and anteverted than Computer aided navigation. In all cases, the wire position was well within acceptable limits. Computer aided navigation does not seem to offer distinct advantages in resurfacing hip replacements.

Aim: We studied the payments received by our hospital for 109 elective lower limb arthroplasty cases to see if this was fair and consistent under Payment by Results. Methods: A cohort of patients who had Total Hip Replacement (THR), Total Knee Replacement (TKR), Resurfacing Hip Arthroplasty and Unicompartmental Knee Replacements were taken from the departmental database. Their diagnostic codes, operation details and comorbidities were established and compared with the payment the trust received using the Dr Foster database. This was confirmed with their hospital notes and the finance department. Results: Twenty THRs and twenty TKRs were paid the standard tariff with one exception. Fifteen Hip Resurfacing arthroplasties showed variable payment from £4690 to £6673 per case. Most interesting were the Unicompartmental Knee Replacements. Despite having almost the same operative and diagnostic codes 46 out of 54 cases were significantly underpaid. During one financial year the trust lost more than £70,000 from this operation alone. This does not meet the Department of Health’s stated aim of being fair and consistent. Out of 109 cases reviewed 51 could have been coded differently and 47 of these were “underpaid”. Conclusion: In an NHS increasingly driven by financial pressures it is vital that surgeons understand how Payment by Results works. There are significant financial gains to be made by those trusts who pay attention to the small print

Introduction: Resurfacing hip arthroplasty is a successful option for the treatment of the young and active patient with hip arthritis. However, it is complicated by femoral neck fracture and avascular necrosis, which may result from devascularisation during surgery. Devascularisation maybe caused by thermal necrosis. Thermal necrosis of bone has been shown to occur in temperatures of 47°C and above. We investigated the temperatures generated during femoral head preparation to see if the temperatures reached were great enough to induce osteonecrosis. Method: Eight patients with osteoarthritis underwent standard resurfacing hip arthroplasty through the posterior approach. From the first over-drilling of the femoral heads until the prosthesis was cemented in place the temperatures generated at the bone surface were recorded using an infra-red thermal imaging camera. Images were captured every 4 seconds as the operation was performed with no interference to the surgeon. Results: The maximum temperatures generated occurred during sleeve reaming at 88.4°C. Seven patients had a temperature recorded greater than 47°C. Removing the femoral caput with an oscillating saw had the highest mean temperature 62.2°C, followed by sleeve reaming (mean 48.7°C). Female patients had the lowest temperature rises and patients receiving the larger femoral prosthesis the greatest temperatures at the bone surface. Conclusions: Heat generated during femoral head preparation exceeded 47°C in all but one case. Osteonecrosis secondary to thermal insult is likely to occur during femoral head preparation. Strategies need to be devised to decrease the temperatures generated during femoral head preparation

Implant malposition is one of the most common causes of failure in resurfacing arthroplasty of the hip (RAH). Recent advances in computer technology have made available navigation systems for RAH and other orthopaedic procedures. The purpose of our study was:

to develop a method to assess the accuracy of an image-free RAH navigation system;

We used the Ci-CAS RAH navigation system (DePuy - BrainLab). To facilitate measurements, an artificial leg (phantom) was constructed from machined aluminium with simulated hip and knee joints. The hip and knee articulating surfaces were synthetic bone material (Sawbones – Pacific Laboratories). An additional joint located at the trochanteric region allowed deformation in varus/valgus and ante/retroversion of the head/neck segment. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual anatomy and leg alignment. This technique was verified using repeated measurement with variable co-ordinates, giving accuracy to within 0.05 of a degree.

Simulated procedures were performed with both normal and abnormal anatomy of the proximal femur. At specific points in the procedure, information was compared between the FaroARM digital measurements and the Ci-CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within 0.5 degrees was demonstrated. In the setting of abnormal alignment (varus/valgus and ante/retroversion) of the proximal femur, accuracy to within 2 degrees was demonstrated.

To our knowledge, this is the first study to assess accuracy of a RAH navigation system. The study demonstrates a satisfactory level of accuracy for the Ci-CAS in both normal and abnormal anatomical settings. Currently, no international standard or methodology exists against which these results can be compared. In the near future, introduction of new navigation technologies will make crucial the development of international standards for pre-clinical validation of computer-assisted navigation systems. The present study is a first attempt to address this issue.

Introduction: Prevalence of femoral neck fracture in resurfacing hip arthroplasty continues to question if failure is technique-related or due to the inherent bone quality. This study aimed to correlate cement penetration profile during resurfacing hip with inherent bone density. The hypothesis is that osteoporotic bone is unable to support the prosthesis leading to fatigue failure. Methods: Fifteen patients scheduled for total hip replacement (THR) were recruited to undergo resurfacing arthroplasty prior to THR. Each patient was implanted with a resurfacing femoral component (BHR, Smith & Nephew, Memphis, TN). Antibiotic simplex cement was inserted one minute after mixing at 18°C to fill 10% of the femoral component volume. The femoral head-implant section was removed and kept in buffered formalin. The patients then proceeded with standard THR. The femoral head-cement-prosthesis section was separated using electrical discharge (ED) machining technique and CT-scanned. The depth and volume of cement penetration were measured from the CT scans and correlated with femoral neck bone densities. Results: Cement penetration was compared for three groups of bone density: normal, osteopenic, osteoporotic. Average cement thickness were found to be 0.36 ± 0.16mm (proximal), 0.28 ± 0.11 mm (centre) and 0.12 ± 0.05 mm. During hip resurfacing, cement is forced into the porous structure, e.g. the trabeculae and airspaces when the femoral component is fixed onto the head of the femur. In normal bone, the trabeculae is dense and air spaces occupy a small volume of the bone. Greater cement penetration was expected in osteopenic and osteoporotic bones. However, no significant difference was found between cement thickness and volume against inherent patient bone density (p> 0.05). High viscosity of the cement may have prevented more cement to penetrate the bone. While the exterior cortex of the femoral head is strengthened by a cement layer, the interior structure of the femoral neck is still susceptible to fracture at high loads. In addition, increased bone necrosis due to the exothermic reaction during cement fixation may predispose patients to fracture. Discussion: Resurfacing hip replacement is a viable technique if the fracture risk can be reduced by gaining the best possible cement penetration. This would provide continuous cement stiffness with the bone

Introduction: Hip resurfacing arthroplasty is increasing in popularity, particularly in young and active patients. One unique advantage is retention of upper femoral bone stock with the hypothesis of easy revision should the resurfacing fail. The pupose of this study was to document the complexity or otherwise of our early experience with failed hip resurfacing.

Methods: We retrospectively reviewed all the patients who had revision surgery for failed hip resurfacing arthroplasty at our institution.

Results: Eleven patients with mean age of 52.8 years underwent revision of resurfacing at a mean time of 21.2 months following primary surgery. Revision was performed for deep infection in 4, cup loosening in 4 and 1 patient each for femoral neck fracture, avascular necrosis, and femoral loosening. For the 4 patients with cup loosening, the acetabular component was revised in 3 using a dysplasia Birmingham cup while 1 patient had both components revised. Of the 4 patients with deep infection, 3 had both components revised as one-stage revision with cemented components and 1 patient had a pseudarthosis. For the 3 cases with femoral loosening, neck fracture or avascular necrosis only the femoral component was revised using a cemented stem. Bone grafting was performed in 1 patient who had revision for loosening of acetabular cup with protrusio.

Conclusion: Acetabular failure appears to be equally common as femoral failure in resurfacing arthroplasty. Revision of both aseptic and septic failure appears to be relatively straightforward with primary implants used in all cases.

Aim: To test the accuracy of implant positioning in using computer navigation in Resurfacing hip arthroplasty. Materials and methods: Brain Lab was used to register 13 cadavers. The component position was fine tuned to a desirable valgus angle. Wire was passed using navigation. The femoral heads were sectioned after insertion of the prosthesis. The measurements from the screen-shots and the transverse sections were analysed using AutoCad®. Results: The Brain lab Registered the femoral heads to 124.91° ± 14.25° (Range 97° −148° ) CCD. The actual neck shaft angles were 126.11° ± 5.33°. The implants were placed in an angulation’s of 131.46° ± 5.27 ° (Range 116° −137° ) and a version of −0.85° ± 2.1° this gave a valgus of 5.91° ± 13.66°. The position of the wire in the isthmus of the neck was −0.52 mm ± 0.69 mm inferior to the centre and 1.7mm ± 1.9 mm posterior to the centre on the transverse sections (n=6). The components were in 8.69° ± 4.95° (n= 6) valgus to the native neck shaft angle. In only 1 hip the femoral head implanted was of the same size as suggested by navigation, in all the rest of the hips the femoral component was of a larger size. This was because it was felt that implanting a smaller size would cause notching of the superolateral neck. Conclusion: There is a learning curve involved for registering the femoral heads using computer navigation systems, however the navigation gives the surgeon a distinct advantage of being able to choose the point of entry, implant the prosthesis in as valgus position as possible in relation to the femoral head, translate the implant anteriorly and place the peg in the centre of the femoral neck in both the planes. The computer-aided navigation can optimise the component positioning and thereby provide excellent results

Aim: To test the accuracy of implant positioning in using computer navigation in Resurfacing hip arthroplasty. Materials and methods: Brain Lab was used to register 13 cadavers. The component position was fine tuned to a desirable valgus angle. Wire was passed using navigation. The femoral heads were sectioned after insertion of the prosthesis. The measurements from the screenshots and the transverse sections were analysed using AutoCad. Results: The Brain lab Registered the femoral heads to 124.91° ± 14.25° (Range 97°–148° ) CCD. The actual neck shaft angles were 126.11° ± 5.33°. The implants were placed in an angulation’s of 131.46° ± 5.27 ° (Range 116° –137° ) and a version of –0.85° ± 2.1° this gave a valgus of 5.91° ± 13.66°. The position of the wire in the isthmus of the neck was –0.52 mm ± 0.69 mm inferior to the centre and 1.7mm ± 1.9 mm posterior to the centre on the transverse sections (n=6). The components were in 8.69° ± 4.95° (n= 6) valgus to the native neck shaft angle. In only 1 hip the femoral head implanted was of the same size as suggested by navigation, in all the rest of the hips the femoral component was of a larger size. This was because it was felt that implanting a smaller size would cause notching of the supero-lateral neck. Conclusion: There is a learning curve involved for registering the femoral heads using computer navigation systems, however the navigation gives the surgeon a distinct advantage of being able to choose the point of entry, implant the prosthesis in as valgus position as possible in relation to the femoral head, translate the implant anteriorly and place the peg in the centre of the femoral neck in both the planes. The computer-aided navigation can optimise the component positioning and thereby provide excellent results

The authors report their preliminary experience with a minimum of one year follow –up of hydroxyapatite coating as the means of fixation of the femoral head in hip resurfacing.

Between Dec 2003 and Dec 2004, of the 23 cases performed by the senior author,22 were available for follow up,15 were women (68.2%) and 7 were men (31.8). The femoral and acetabular components of the uncemented version of the CORMET 2000(Corin,Cire ncester,UK) were used. The surgical approach was the Hardinge approach in all cases. Patients were assessed pre-operatively for pain and function,using the Harris Hip Score. Post operatively they were assessed in clinic with x rays at 6 weeks,6 months and annually thereafter. X rays were evaluated for pre and post op neck shaft angle,giving an indication of varus or valgus placement of the head prosthesis. The lateral view was assessed to reveal anterior or posterior tilting of the prosthesis. Neck thinning was evaluated by measuring the ratio of the metal cup and bony neck diameters at the cup neck junction, recorded post op and at one year.

None of the femoral implants were placed in varus. Only one case had inferior notching, which had remodelled at one year. In the lateral view none of the cups showed a displacement of more than ten degrees in the AP direction. There were no stem lucencies or signs of femoral implant migration in any of the cases. None of our cases showed neck thinning (change in ratio greater than 10%). Uncemented femoral implant in a metal on metal resurfacing hip replacement appears to perform well and shows no catastrophic problems at the short term one year follow up. Longer follow up studies are necessary