The effects of the method of fixation and interface conditions on the biomechanics of the femoral component of the Birmingham hip resurfacing arthroplasty were examined using a highly detailed three-dimensional computer model of the hip. Stresses and strains in the proximal femur were compared for the natural femur and for the femur resurfaced with the Birmingham hip resurfacing. A comparison of cemented versus uncemented fixation showed no advantage of either with regard to bone loading. When the Birmingham hip resurfacing femoral component was fixed to bone, proximal femoral stresses and strains were non-physiological. Bone resorption was predicted in the inferomedial and superolateral bone within the Birmingham hip resurfacing shell. Resorption was limited to the superolateral region when the stem was not fixed. The increased bone strain observed adjacent to the distal stem should stimulate an increase in bone density at that location. The remodelling of bone seen during revision of failed Birmingham hip resurfacing implants appears to be consistent with the predictions of our finite element analysis

The aim of our study was to investigate whether placing of the femoral component of a hip resurfacing in valgus protected against spontaneous fracture of the femoral neck. We performed a hip resurfacing in 20 pairs of embalmed femora. The femoral component was implanted at the natural neck-shaft angle in the left femur and with a 10° valgus angle on the right. The bone mineral density of each femur was measured and CT was performed. Each femur was evaluated in a materials testing machine using increasing cyclical loads. In specimens with good bone quality, the 10° valgus placement of the femoral component had a protective effect against fractures of the femoral neck. An adverse effect was detected in osteoporotic specimens. When resurfacing the hip a valgus position of the femoral component should be achieved in order to prevent fracture of the femoral neck. Patient selection remains absolutely imperative. In borderline cases, measurement of bone mineral density may be indicated

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10° and 20°) and relative valgus (10° and 20°), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20° of valgus resulted in a significant increase in load to failure. Placing the component in 10° of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10° of varus were significantly weaker than the neutrally-aligned specimens.

The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of ≥ 142°. However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study.

Bone surface strains were measured in cadaver femora during loading prior to and after resurfacing of the hip and total hip replacement using an uncemented, tapered femoral component. In vitro loading simulated the single-leg stance phase during walking. Strains were measured on the medial and the lateral sides of the proximal aspect and the mid-diaphysis of the femur. Bone surface strains following femoral resurfacing were similar to those in the native femur, except for proximal shear strains, which were significantly less than those in the native femur. Proximomedial strains following total hip replacement were significantly less than those in the native and the resurfaced femur.

These results are consistent with previous clinical evidence of bone loss after total hip replacement, and provide support for claims of bone preservation after resurfacing arthroplasty of the hip.

Hip resurfacing arthroplasty (HRA) became a popular procedure in the early 90s because of the improved wear characteristic, preserving nature of the procedure and the optimal stability and range of motion. Concerns raised since 2004 when metal ions were seen in blood and urine of patients with a MoM implant. Design of the prosthesis, acetabular component malpositioning, contact-patch-to-rim distance (CPR) and a reduced joint size all seem to play a role in elevated metal ion concentrations. Little is known about the influence of physical activity (PA) on metal ion concentrations. Implant wear is thought to be a function of use and thus of patient activity levels. Wear of polyethylene acetabular bearings was positively correlated with patient's activity in previous studies. It is hypothesized that daily habitual physical activity of patients with a unilateral resurfacing prosthesis, measured by an activity monitor, is associated with habitual physical activity. A prospective, explorative study was conducted. Only patients with a unilateral hip resurfacing prosthesis and a follow-up of 10 ± 1 years were included. Metal ion concentrations were determined using ICP-MS. Habitual physical activity of subjects was measured in daily living using an acceleration-based activity monitor. Outcome consisted of quantitative and qualitative activity parameters. In total, 16 patients were included. 12 males (75%) and 4 females (25%) with a median age at surgery of 55.5 ± 9.7 years [43.0 – 67.9] and median follow-up of 9.9 ± 1.0 years [9.1 – 10.9]. The median cobalt and chromium ion concentrations were 25 ± 13 and 38 ± 28 nmol/L. A significant relationship, when adjusting for age at surgery, BMI, cup size and cup inclination, between sit-stand transfers (p = .034) and high intensity peaks (p = .001) with cobalt ion concentrations were found (linear regression analysis). This study showed that a high number of sit-stand transfers and a high number of high intensity peaks is significantly correlated with high metal ion concentrations, but results should be interpreted with care. For patients it seems save to engage in activities with low intensity peaks like walking or cycling without triggering critical wear or metal ions being able to achieve important general health benefits and quality of life, although the quality (high intensity peaks) of physical activity and behaviour of patients (sit-stand-transfers) seem to influence metal ion concentrations

Abstract. Objectives. Although hip replacement and resurfacing procedures both aim to restore mobility, improve joint function, and relieve pain, it is unclear how each differ in terms of gait mechanics and if they are affected by varying walking speeds. We compared limb symmetry and ground reaction force (GRF) profiles between bilateral total hip arthroplasty patients (THA), bilateral hip resurfacing arthroplasty patients (HRA), and healthy control participants (CON) during level-treadmill walking at different speeds. Methods. Bilateral THA and bilateral HRA patients (nTHA = 15; nHRA = 15; postoperative 12–18 months), and age-, mass-, and height-matched CON participants (nCON = 20) underwent gait analysis on an instrumented treadmill. Walking trials started at 4 km/h and increased in 0.5 km/h increments until top walking speed (TWS) was achieved. Gait symmetry index (SI = 0% for symmetry) was assessed between limbs during weight-acceptance, mid-stance and push-off phases of gait; and vertical GRFs were captured for the normalised stance phase using statistical parametric mapping (SPM; CI = 95%). Results. THA had a significantly lower TWS (6.51 ± 0.06 km/h) compared to HRA (7.09 ± 0.07 km/h, p = 0.01) and CON (7.15 km/h ± 0.06, p = 0.02). There were no SI differences between groups nor between walking speeds (SI < 5%). There were no GRF differences between groups at slower walking speeds (4.0–5.0 km/h). However, at 5.5 and 6 km/h, THA had lower GRF at the push-off phase (0.88 ± 0.09 N/BW), compared to HRA (1.06 ± 0.08 N/BW, p = 0.01) and CON (1.04 ± 0.02 N/BW, p = 0.01). Conclusions. The main finding was that HRA patients demonstrated restored gait function and similar walking profiles to CON participants at any speed. With a diverging gait profile, walking speeds over 5.5 km/h provided a functional challenge for THA patients

Introduction. The treatment of osteonecrosis of the femoral head (ONFH) in young and active patients remains a challenge. The purpose of this study was to determine and compare the clinical and radiographic results of the two different hip resurfacing systems; hemi-resurfacing and metal-on-metal total hip resurfacing in patients with ONFH. Methods. This study was a retrospective review of 20 patients with 30 hips who had ONFH and underwent hemi-resurfacing or total hip resurfacing between November 2002 and February 2006. We mainly performed hemi-resurfacing for early stage ONFH, and total hip resurfacing for advanced stages. Fifteen hips in 11 patients had a hemi-resurfacing component (Conserve, Wright Medical Co) with a mean age at operation of 50 years and an average follow-up of 5.5 years. Fifteen hips in 10 patients had a metal-on-metal total hip resurfacing component (Birmingham hip resurfacing, Smith & Nephew Co.) with a mean age at operation of 40 years and an average follow-up years. Results. The average postoperative Japanese Orthopaedic Association (JOA) hip scores were 86 points in hemi-resurfacing and 96 points in total hip resurfacing. The difference of pain score was a main factor to explain the difference of total JOA hip score in the two groups. Both implants were radiographically stable, but radiolucent lines around the metaphyseal stem were more frequent in total hip resurfacing. In hemi-resurfacing patients, ten of 15 hips had groin pain or groin discomfort and three hips were revised to total hip arthroplasties (THA) because of femoral neck fracture, acetabular protrusio, and osteoarthritic changes, respectively. In total hip resurfacing patients, there were no revisions and no groin pain observed. Conclusion. In the prosthetic treatment of young active patients with ONFH, it is theoretically desirable to choose an implant with a conservative design in anticipation of the future revision surgery. Hemi-resurfacing hip arthroplasty is the most conservative implant for the treatment of ONFH. However, the results of hemi-resurfacing in this study have been disappointing due to high revision rates and insufficient pain relief despite of the good implant stability. However, the pain relief and implant survivorship after total hip resurfacing were superior to the results of hemi-resurfacing, although the usages of the total hip resurfacing were for more advanced cases. These results suggest that total hip resurfacing was a more valuable treatment option for active patients with ONFH than hemi-resurfacing

Financial and human cost effectiveness is an increasing evident outcome measure of surgical innovation. Considering the human element, the aim is to restore the individual to their “normal” state by sparing anatomy without compromising implant performance. Gait lab studies have shown differences between different implants at top walking speed, but none to our knowledge have analysed differing total hip replacement patients through the entire range of gait speed and incline to show differences. The purpose of this gait study was to 1) determine if a new short stem femoral implant would return patients back to normal 2) compare its performance to established hip resurfacing and long stem total hip replacement (THR) implants. 110 subjects were tested on an instrumented treadmill (Kistler Gaitway, Amherst, NY), 4 groups (short-stem THR, long-stem THR, hip resurfacing and healthy controls) of 28, 29, 27, and 26 respectively. The new short femoral stem patients (Furlong Evolution, JRI) were taken from the ongoing Evolution Hip trial that have been tested on the treadmill with minimum 12months postop. The long stem total hip replacements and hip resurfacing groups were identified from out 800 patient gait database. They were only chosen if they were 12 months postop and had no other joint disease or medical comorbidities which would affect gait performance. All subjects were tested through their entire range of gait speeds and incline after having a 5 minute habituation period. Speed intervals were at 0.5kms increments until maximum walking speed achieved and inclines at 4kms for 5, 10, 15%. At all incremental intervals of speed, the vertical component of the ground reaction forces, center of pressure and temporal measurements were collected for both limbs with a sampling frequency of 100Hz. Body weight scaling was applied to correct for mass differences and a symmetry index to compare the implanted hip to the contralateral normal hip. All variables for each subject group were compared to each other using an analysis of variance (ANOVA) with Tukey post hoc test with significance set at α=0.05. The four experimental groups were reasonably matched for demographics and the implant groups for PROMs. Hip resurfacing had a clear top walking speed advantage, but when assessing the symmetry index on all speeds and incline, all groups were not significantly different. Push-off and step length was statistically less favourable for the short/long THR group (p=0.005–0.05) depending on speed/incline. The primary aim of this study was determine if implant design affected gait symmetry and performance. Interestingly, irrespective of implant design, symmetry with regards to weight acceptance, impulse, push-off and step length was returned to normal when comparing to healthy controls. However individual implant performance on the flat and incline, showed inferior (p<0.05) push-off force and step length in the short stem and long stem THR groups when compared to controls. Age and gender may have played a part for the short stem group. It appears that the early gait outcomes for the short stem device are promising. Assessment at the 3 year mark should be conclusive

Hip resurfacing procedures have gained increasing popularity for younger, higher demand patients with degenerative hip pathologies. However, with concerns regarding revision rates and possible adverse metal hypersensitivity reactions with metal-on-metal articulations, some authors have questioned the hypothesised superiority of hip resurfacing over total hip arthroplasty. The purpose of this meta-analysis was to compare the clinical and radiological outcomes and complication rates of these two procedures. A systematic review was undertaken of all published and unpublished research up to January 2010. The primary search was of the databases Medline, CINAHL, AMED and EMBASE, searched via Ovid using MeSH terms and Boolian operators ‘hip’ AND ‘replacement’ OR ‘arthroplasty’ AND ‘resurfacing’. A secondary search of unpublished literature was conducted using the databases SIGLE, the National Technical Information Service, the National Research Register (UK), the British Library's Integrated Catalogue and Current Controlled Trials databases using the same search terms as the primary search. All included studies were critically appraised with the CASP appraisal tool. In total, 46 studies were identified from 1124 citations. These included 3799 hip resurfacings and 3282 total hip arthroplasties. On meta-analysis, functional outcomes for subjects following hip resurfacing were better than or the same as subjects with a total hip arthroplasty, with significantly higher WOMAC score (Mean Difference (MD)=−2.41; 95% Confidence Interval (CI): −3.88, −0.94; p=0.001), and significantly better Harris Hip Score (range of motion component) (MD=−0.05; 95% CI: (−0.07, −0.03; p<0.0001) and overall Harris Hip Score (MD=2.51; 95% CI: 1.24, 3.77; p=0.0001) in the hip resurfacing compared to total hip arthroplasty cohorts. However, there were significantly greater incidences of heterotopic ossification (Risk Ratio (RR)=1.62; 95% CI: 1.23, 2.14; p=0.006), aseptic loosening (RR=3.07; 95% CI:1.11, 8.50;p=0.03) and revision surgery (RR=1.72; 95% CI: 1.20, 2.45; p=0.003) with hip resurfacing compared to total hip arthroplasty. The evidence-base presented with a number of methodological inadequacies such as the limited use of power calculations and poor or absent blinding of both patients and assessors, potentially giving rise to assessor bias. In respect to these factors, the current evidence-base, whilst substantial in its size, may be questioned in respect to its quality in determining superiority of hip resurfacing over total hip arthroplasty

Patients undergoing hip resurfacing arthroplasty (HRA) is typically reserved for highly active patients. Patient Reported Outcome Measures (PROMs) such as the Oxford Hip Score (OHS) are reported to have ceiling effects, which may limit physicians' ability to measure health gain in these patients. The Metabolic Equivalent of Task (MET) index is a validated compendium assigning energy expenditure to a wide range of activities; for example, a slow walk expends 2.9 kcal/kg/hour, golf expends 4.0 kcal/kg/hour, while moderate lacrosse typically expends 8.1 kcal/kg/hour. We hypothesized that for patients with high OHS (47–48) after HRA, the MET index could better discriminate between high-performing individuals. We evaluated 97 consecutive HRA patients performed by a single surgeon. They prospectively completed an online Oxford Hip Score. They also listed three activities which they had performed independently in the preceding 2 weeks with a Likert-scale slider denoting intensity of effort. Matched data-sets were obtained from 51 patients, from which 23 had OHS of 47–48 at 6-months. Their activity with the highest MET index was selected for analysis. The 23 patients' OHS improved from 29.3 ± 7.0 preoperatively to 47.6 ± 0.5 after 6-months, while their MET indices improved from 8.5 ± 3.7 to 12.9 ± 3.5 kcal/kg/hr. The activities performed by these high-performance individuals ranged from the lowest, pilates (8.05 kcal/kg/hour), to highest, running at 22km/hr (23 kcal/kg/hour). 45% of patients undergoing HRA in this cohort had OHS of 47 and 48 at 6-months after surgery. Unlike the OHS, the MET index described variation in physical activity in these high-performance individuals, and did so on an objective measurable scale

The renewed interest in the clinically proven low wear of the metal-on-metal bearing combined with the capacity of inserting a thin walled cementless acetabular component has fostered the reintroduction of hip resurfacing. As in other forms of conservative hip surgery, i.e. pelvic osteotomies and impingement surgery, patient selection will help minimize complications and the need for early reoperation. Patient Selection and Hip Resurfacing. Although hip resurfacing was initially plagued with high failure rates, the introduction of metal on metal bearings as well as hybrid fixation has shown excellent survivorships of 97 to 99% at 4 to 5 years follow-up. However, it is important to critically look at the initial published results. In all of these series there was some form of patient selection. For example, in the Daniel and associates publications, only patients with osteoarthritis with an age less than 55 were included with 79% of patients being male. Treacy and associates stated that: “the operation was offered to men under the age of 65 years and women under the age of 60 years, with normal bone stock judged by plain radiographs and an expectation that they would return to an active lifestyle, including some sports”. However in the materials and methods, although the mean age is 52 years, the range is from 17 to 76 years including some patients with rheumatoid arthritis as well as osteonecrosis. Obviously, some form of patient selection is needed; but how one integrates them is where the Surface Arthroplasty Risk Index (SARI) is useful. With a maximum score of 6, points are assigned accordingly: femoral head cyst >1cm: 2 points; patient weight <82kg: 2 points; previous hip surgery: 1 point; UCLA Activity level >6: 1 point. A SARI score >3 represented a 4 fold increase risk in early failure or adverse radiological changes and with a survivorship of 89% at four years. The SARI index also proved to be relevant in assessing the outcome of the all cemented McMinn resurfacing implant (Corin¯, Circentester, England) at a mean follow-up of 8.7 years. Hips which had failed or with evidence of radiographic failure on the femoral side had a significantly higher SARI score than the remaining hips, 3.9 versus 1.9. Finally, one must consider the underlying diagnosis when evaluating a patient for hip resurfacing. In cases of dysplasia, acetabular deficiencies combined with the inability of inserting screws through the acetabular component may make initial implant stability unpredictable. This deformity in combination with a significant leg length discrepancy or valgus femoral neck could compromise the functional results of surface arthroplasty, and in those situations a stem type total hip replacement may provide a superior functional outcome. In respect to other diagnoses (osteonecrosis, inflammatory arthritis), initial analyses have not demonstrated any particular diagnostic group at greater risk of earlier failure. The only reservation we have is in patients with compromised renal function since metal ions generated from the metal-on-metal bearing are excreted through the urine and the lack of clearance of these ions may lead to excessive levels in the blood. Surgical Technique. Because resurfacing has not been within the training curriculum of orthopaedic surgeons for the last 2 decades, there will most likely be a learning curve in the integration of this implant within clinical practice. This data was confirmed for hip resurfacing when looking at the Canadian Academic Experience where in the first 50 cases of five arthroplasty surgeons only a 3.2% failure rate was noted of which 1.6% were due to neck fracture. Femoral neck fracture can occur because of significant varus positioning as well as osteonecrosis of the femoral head due to either disruption of the blood supply or over cement penetration. Finally, abnormal wear patterns leading to severe soft tissue reactions are being increasingly recognized and are related to either impingement or vertically placed acetabular components. Although impingement has long been recognized after total hip arthroplasty to limit range of motion and in extreme cases to hip instability, the risk after hip resurfacing may be greater since the femoral head-neck unit is preserved. Beaulé and associates have reported that 56% of hips treated by hip resurfacing have an abnormal offset ratio pre-operatively, with the two main diagnostic groups presenting deficient head-neck offset being osteonecrosis and osteoarthritis both of which have been associated with femoroacetabular impingement in the pre arthritic state. Conclusion. Although patients with a high activity level are likely to put their hip arthroplasties at risk for earlier failure, limiting a patient's activity because of fear of revision with a stem type hip arthroplasty has been shown to negatively impact the quality of life at long term follow-up. Thus hip resurfacing arthroplasty plays a significant role in the treatment of hip arthritis by permitting a return to full activities or what the patient perceives as his/her full capacities to do so, permitting them to enjoy a better quality of life without fearing a major hip revision

Introduction of new implants has been widely debated lately, mainly in response to the problems surrounding hip resurfacing and one company recalling its product. Medicines and Healthcare products Regulatory Agency (MHRA) also issued advice about the management and monitoring of patients implanted with metal-on-metal articulations. In response to MHRA advice all the patients who underwent hip resurfacing in our hospital were assessed by two consultants according to MHRA guidelines. Here we present the findings from our District General Hospital. Between November 2006 and March 2009 we performed 42 hip resurfacings in 39 patients. Nearly all the procedures were performed by a single surgeon (39 out of 42). There were 27 males (28 hips) and 12 females (14 hips). Mean age of the patients at the time of surgery was 55.6 years (age range 40–67 years). Patients were followed up for a mean of 49 months (range 33–66 months). 27 patients (28 hips) were asymptomatic at the time of last follow up. Serum cobalt and chromium ion levels were measured in 21 patients (24 hips). Both the ion levels were within the recommended levels in 20 patients and over the recommended limit in 2 patients (one with bilateral hip resurfacing). MRI was diagnostic in 2 out of 5 patients. 5 patients (7 hips) were revised (one hip for neck resorption, 4 hips in 3 patients with lesions on MRI, 1 patient with bilateral hips for elevated serum ion levels). Considering the revision rate (7 hips out of 42 hips, 16%), we do believe that the review of the hip resurfacings in spite of the controversies surrounding the diagnostic criteria is necessary. This group of patients need to have continued surveillance, preferably by a select group of surgeons

Background. Hip resurfacing has resurged in the last decade due to a renewed interest in metal on metal bearing. One of the proposed advantages is ease of revision of the femoral component. Short term functional results after femoral revision are similar to those after conventional total hip replacement. Survival and function after revision of the acetabular component only or of both components have not been reported. We aimed to assess hip function and implant survival after revision of the acetabular component for failed Birmingham hip resurfacing (BHR). Methods. The Oswestry Outcome Centre collected data prospectively on 5000 patients who underwent hip resurfacing between 1997 and 2002. Of these, 182 hips were revised: 42% had revision of the femoral component only, 8% revision of the acetabular component only, and 50% revision of both components. This study analyzed patients who had revision of the acetabular component, either in isolation or in combination with the femoral component. Results. In the isolated acetabular revision group the median Harris Hip Score was 74 at a mean of 4.5 years post-revision. In the both components revision group the median Harris hip score was 85 at a mean of 4 years. There was no significant difference in function between the groups. Kaplan-Meier survivor ship analysis after revision showed an average survival of 91% at 10 years. There was a significant difference between survival of isolated acetabular revision (75%) and both component revision (96%). Conclusions. Revision total hip replacement subsequent to failure of hip resurfacing has good outcome and good midterm survival. Isolated acetabular revision and revision of both components had similar function but survival was significantly worse in the isolated acetabular revision group

We report the survival, functional and radiological outcome of a series of Birmingham hip resurfacing procedures performed by a single surgeon at a district general hospital. The aim of this study was to retrospectively report the medium term outcome and survival of our patients. There were 45 hip resurfacings performed in 38 patients between 2004 and 2010. Patients were followed for a mean duration of four years. Mean age of 52.6 years (range 26 to 65). Although no patients were lost to follow up, four did not complete the oxford hip scoring assessment. The median Oxford hip score was 16.25 points (range 12–39 points, standard deviation 5.9) at 48 months follow up (range 11.5–84.2 months). The mean acetabular inclination was 46.9 (range 40.9–59.9) in the 45 hip resurfacings post operatively. There was one patient with varus subsidence of the prosthesis and one patient with persistent hip pain post operatively under investigation currently. There was no definite radiological evidence of loosening or of narrowing of the femoral neck. No cases were revised and no cases developed any other complications. These medium-term results from a district general hospital are comparable to the other studies performed. Few independent studies have reported the outcome of resurfacing arthroplasty of the hip in a district general hospital. Further evaluation and follow up of these patients is required to address the concerns raised by other centers related to fracture and metal debris

Hip resurfacing has generally been used in younger patients with early osteoarthritis of the hip. There has been considerable recent interest in this over the past few years. We conducted a prospective randomised trial comparing 2 hip resurfacing implants, Durom and ASR looking at radiological and clinical outcomes. Forty-nine patients (78% male) with hip osteoarthritis which met the criteria for hip resurfacing were randomised to receive either a Durom or ASR resurfacing implant. These patients have so far been followed up for a minimum of one year. The groups were comparable in age (p=0.124) and gender (p=0.675). The average age in the ASR group was 54.04 years and in the Durom group it was 51.25. Radiological views were scrutinised immediately post op and at final follow up so far to look at cup inclination, stem-shaft angle, and acetabular osseointegration. Clinical outcomes were compared using the Oxford hip scores, WOMAC scores and SF12 scores. At minimum follow up of 1 year the mean post operative Oxford hip score was not significantly different between the Durom (45.32, SD 3.93) and ASR (43.44, SD 8.44). The mean post operative WOMAC score was also not significantly different between the Durom (52.56, SD 6.06) and ASR (49.63, SD 2.23). There was no difference between the groups with regards to signs of osseointegration from radiological assessment (p=0.368). There were 3 periprosthetic femoral neck fractures (5.7%) and one revision for pain. We conclude from this trial that there is no difference in the clinical or radiological findings between the Durom and ASR implants

Patients report similar or better pain and function before revision hip arthroplasty than before primary arthroplasty but poorer outcomes after revision surgery. The trajectory of post-operative recovery during the first 12 months and any differences by type of surgery have received little attention. We explored the trajectories of change in pain and function after revision hip arthroplasty to 12-months post-operatively and compared them with those observed after primary hip arthroplasty. We conducted a single-centre UK cohort study of patients undergoing primary (n = 80) or revision (n = 43) hip arthroplasty. WOMAC pain and function scores and 20-metres walking time were collected pre-operatively, at 3 and 12-months post-operatively. Multilevel regression models were used to chart and compare the trajectories of post-operative change (0–3 months and 3–12 months) between the types of surgery. Patients undergoing primary arthroplasty had a total hip replacement (n=74) or hip resurfacing (n=6). Osteoarthritis was the indication for surgery in 92% of primary cases. Patients undergoing revision arthroplasty had revision of a total hip arthroplasty (n=37), hemiarthroplasty (n=2) or hip resurfacing (n=4). The most common indication for revision arthroplasty was aseptic loosening (n=29); the remaining indications were pain (n=4), aseptic lymphocyte-dominated vasculitis-associated lesion (n=4) or other reasons (n=6). Primary (87%) and revision arthroplasties (98%) were mostly commonly performed via a posterior surgical approach. The improvements in pain and function following revision arthroplasty occurred within the first 3-months following operation (WOMAC-pain, p<0.0001; WOMAC-function, p<0.0001; timed 20-metres walk, p<0.0001) with no evidence of further change beyond this initial period (p>0.05). While the pattern of recovery after revision arthroplasty was similar to that observed after primary arthroplasty, improvements in the first 3-months were smaller after revision compared to primary arthroplasty (p<0.0001). Patients listed for revision surgery reported lower pre-operative pain levels (p=0.03) but similar post-operative levels (p=0.268) compared to those undergoing primary surgery. At 12-months post-operation patients who underwent a revision arthroplasty had not reached the same level of function achieved by those who underwent primary arthroplasty (WOMAC-function p=0.015; Time walk p=0.004). Patients undergoing revision hip arthroplasty should be informed that the majority of their improvement will occur in the first 3-months following surgery and that the expected improvement will be less marked than that experienced following primary surgery. More research is now required to 1.) identify whether specific in-patient and post-discharge rehabilitation tailored towards patients undergoing revision arthroplasty would improve or achieve equivalent outcomes to primary surgery and 2.) whether patients who are achieving limited improvements at 3-months post-operative would benefit from more intensive rehabilitation. This will become all the more important with the increasing volume of revision surgery and the high expectations of patients who aspire to a disease-free and active life

Positioning of the hip resurfacing is crucial for its long term survival and is critical in young patients for some reasons; manly increase the wear in the components and change the load distribution. THR have increased in the last years, mainly in young patients between 45 to 59 years old. The resurfacing solution is indicated for young patients with good bone quality. A long term solution is required for these patients to prevent hip revision. The resurfacing prosthesis Birmingham Hip Resurfacing (BHR) was analyzed in the present study by in vitro experimental studies. This gives indications for surgeons when placing the acetabular cup. One synthetic left model of composite femur (Sawbones®, model 3403), which replicates the cadaveric femur, and four composite pelvic bones (Sawbones®, model 3405), were used to fix the commercial models of Hip resurfacing (Birmingham model). The resurfacing size was chosen according to the head size of femurs with 48 mm head diameter and a cup with 58 mm. They were introduced by an experimented surgeon with instrumental of prosthesis. The cup is a press fit system and the hip component was cemented using bone cement Simplex, Stryker Corp. The acetabular cup was analyzed in 4 orientations; in anteverion with 15º and 20°; and in inclination 40 and 45°. Combinations of these were also considered. The experimental set-up was applied according to a system previously established by Ramos et al. (2013) in the anatomic position. The femur rotates distally and the Pelvic moves vertically as model changes, such that the same boundary conditions are satisfied. This system allows compensating motions of the acetabular cup orientation. A vertical load of 1700 N was applied on all cases, which have resulted in joint reaction force of 2.4 kN. The femur and iliac bone was instrumented with rosettes. 5 repetitions at each position were conducted. When the femur was instrumented with three rosettes in medial, anterior and posterior aspect, the maximum strain magnitude was observed in the medial aspect of femur with a minimum principal strain of −2070µε for 45° inclination and 20° of anterversion. The pubic region was found most critical region after instrumenting the Iliac bone with four rosettes, with a minimum principal strain around −2500µε (rosette 1), for the 45° inclination and 20° of anterversion. We have observed the great influence of the inclination on the strain distribution, changing its magnitude from compression to traction in different bone regions. The minimum principal strain is more critical in medial aspect of the femur and the influence of strain is about 7% when orientation and inclination change. The maximum influence was observed in the anterior aspect, where the anteversion presents a significant influence. The results show the interaction between inclination and anterversion in all aspects, being observed lower values in lower angles. The orientation of the acetabular cup significantly influences the strain distribution on the iliac surface. Besides, as anterversion increases, more strains are induced, mainly in the region of iliac body (rosette 3)

A cadaver study using six pairs of lower limbs was conducted to investigate the accuracy of computer navigation and standard instrumentation for the placement of the Birmingham Hip Resurfacing femoral component. The aim was to place all the femoral components with a stem-shaft angle of 135°. The mean stem-shaft angle obtained in the standard instrumentation group was 127.7° (120° to 132°), compared with 133.3° (131° to 139°) in the computer navigation group (p = 0.03). The scatter obtained with computer-assisted navigation was approximately half that found using the conventional jig. Computer navigation was more accurate and more consistent in its placement of the femoral component than standard instrumentation. We suggest that image-free computer-assisted navigation may have an application in aligning the femoral component during hip resurfacing

The aim of this study was to report the procedure survival and patient-reported outcomes in a consecutive series of patients <50yrs at the time of hip arthroplasty with a metal-on-metal hip resurfacing system who have progressed to a minimum of 10yrs follow-up. Patients presenting for treatment of degenerative conditions of the hip electing to undergo hip resurfacing were included in a clinical registry (N=226 patients; 238 procedures). Procedure survival was confirmed by crosschecking to the Australian Orthopaedic Association National Joint Replacement Registry and comparing to all procedures by other surgeons nationwide. Kaplan-meier survival curves with 95% confidence intervals were constructed, while patient-reported outcome measures were compared with t-tests and postoperative scores assessed with anchor analysis to age and gender-matched normative data. At mean follow up of 12 years, six cases were revised with a cumulative survival rate of 96.8% (95%CI 94.2–99.4) at 15 years. Majority of revisions were early (<3yrs) and occurred in females (N=4). Patient-reported general health, disease state, hip function and activity level maintained large improvements beyond 10 years post-implantation and were equal to or exceeded age and gender-matched normative data. Metal-on-metal hip resurfacing in males and females aged <50 years at time of surgery demonstrated a high rate of cumulative survival beyond 10 years follow up. The results demonstrate excellent outcomes in this age group

Finite element analysis was used to examine the initial stability after hip resurfacing and the effect of the procedure on the contact mechanics at the articulating surfaces. Models were created with the components positioned anatomically and loaded physiologically through major muscle forces. Total micromovement of less than 10 μm was predicted for the press-fit acetabular components models, much below the 50 μm limit required to encourage osseointegration. Relatively high compressive acetabular and contact stresses were observed in these models. The press-fit procedure showed a moderate influence on the contact mechanics at the bearing surfaces, but produced marked deformation of the acetabular components. No edge contact was predicted for the acetabular components studied. It is concluded that the frictional compressive stresses generated by the 1 mm to 2 mm interference-fit acetabular components, together with the minimal micromovement, would provide adequate stability for the implant, at least in the immediate post-operative situation