Objectives. Modern metal-on-metal (MoM) hip resurfacing arthroplasty (HRA), while achieving good results with well-orientated, well-designed components in ideal patients, is contraindicated in women, men with head size under 50 mm, or metal hypersensitivity. These patients currently have no access to the benefits of HRA. Highly crosslinked polyethylene (XLPE) has demonstrated clinical success in total hip arthroplasty (THA) and, when used in HRA, potentially reduces metal ion-related sequelae. We report the early performance of HRA using a direct-to-bone cementless mono-bloc XLPE component coupled with a cobalt-chrome femoral head, in the patient group for whom HRA is currently contraindicated. Methods. This is a cross-sectional, observational assessment of 88 consecutive metal-on-XLPE HRAs performed in 84 patients between 2015 and 2018 in three centres (three surgeons, including the designer surgeon). Mean follow-up is 1.6 years (0.7 to 3.9). Mean age at operation was 56 years (. sd. 11; 21 to 82), and 73% of implantations were in female patients. All patients were individually counselled, and a detailed informed consent was obtained prior to operation. Primary resurfacing was carried out in 85 hips, and three cases involved revision of previous MoM HRA. Clinical, radiological, and Oxford Hip Score (OHS) assessments were studied, along with implant survival. Results. There was no loss to follow-up and no actual or impending revision or reoperation. Median OHS increased from 24 (interquartile range (IQR) 20 to 28) preoperatively to 48 (IQR 46 to 48) at the latest follow-up (48 being the best possible score). Radiographs showed one patient had a head-neck junction lucency. No other radiolucency, osteolysis, component migration, or femoral neck thinning was noted. Conclusion. The results in this small consecutive cohort suggest that metal-on-monobloc-XLPE HRA is successful in the short term and merits further investigation as a conservative alternative to the current accepted standard of stemmed THA. However, we would stress that survival data with longer-term follow-up are needed prior to widespread adoption. Cite this article: R. B. C. Treacy, J. P. Holland, J. Daniel, H. Ziaee, D. J. W. McMinn. Preliminary report of clinical experience with metal-on-highly-crosslinked-polyethylene hip resurfacing. Bone Joint Res 2019;8:443–450. DOI: 10.1302/2046-3758.810.BJR-2019-0060.R1

Objectives. To study the vascularity and bone metabolism of the femoral head/neck following hip resurfacing arthroplasty, and to use these results to compare the posterior and the trochanteric-flip approaches. Methods. In our previous work, we reported changes to intra-operative blood flow during hip resurfacing arthroplasty comparing two surgical approaches. In this study, we report the vascularity and the metabolic bone function in the proximal femur in these same patients at one year after the surgery. Vascularity and bone function was assessed using scintigraphic techniques. Of the 13 patients who agreed to take part, eight had their arthroplasty through a posterior approach and five through a trochanteric-flip approach. Results. One year after surgery, we found no difference in the vascularity (vascular phase) and metabolic bone function (delayed phase) at the junction of the femoral head/neck between the two groups of patients. Higher radiopharmaceutical uptake was found in the region of the greater trochanter in the trochanteric-flip group, related to the healing osteotomy. Conclusions. Our findings using scintigraphic techniques suggest that the greater intra-operative reduction in blood flow to the junction of the femoral head/neck, which is seen with the posterior approach compared with trochanteric flip, does not result in any difference in vascularity or metabolic bone function one year after surgery

Aims. The aims of the study were to report for a cohort aged younger than 40 years: 1) indications for HRA; 2) patient-reported outcomes in terms of the modified Harris Hip Score (HHS); 3) dislocation rate; and 4) revision rate. Methods. This retrospective analysis identified 267 hips from 224 patients who underwent an hip resurfacing arthroplasty (HRA) from a single fellowship-trained surgeon using the direct lateral approach between 2007 and 2019. Inclusion criteria was minimum two-year follow-up, and age younger than 40 years. Patients were followed using a prospectively maintained institutional database. Results. A total of 217 hips (81%) were included for follow-up analysis at a mean of 3.8 years. Of the 23 females who underwent HRA, none were revised, and the median head size was 46 mm (compared to 50 mm for males). The most common indication for HRA was femoroacetabular impingement syndrome (n = 133), and avascular necrosis ( (n = 53). Mean postoperative HHS was 100 at two and five years. No dislocations occurred. A total of four hips (1.8%) required reoperation for resection of heterotopic ossification, removal of components for infection, and subsidence with loosening. The overall revision rate was 0.9%. Conclusion. For younger patients with higher functional expectations and increased lifetime risk for revision, HRA is an excellent bone preserving intervention carrying low complication rates, revision rates, and excellent patient outcomes without lifetime restrictions allowing these patients to return to activity and sport. Thus, in younger male patients with end-stage hip disease and higher demands, referral to a high-volume HRA surgeon should be considered. Cite this article: Bone Jt Open 2023;4(6):408–415

Metal-on-metal (MoM) hip resurfacing was developed in the 1990s by surgeons in Birmingham, UK, as a surgical solution to the problem of osteoarthritis in younger, more active patients. Early results were promising and the procedure gained in popularity. However, adverse reports of soft-tissue reaction and failure started to appear from 2008 onwards. Surgeons may be asked to write medico-legal reports on the surgical aspects of an individual case for claimant lawyers or in defence for the NHSLA or indemnity insurers. The purpose of this article is to cover some of the aspects of the operation that may be considered in such medico-legal reports

Background. High functional aspirations and an active ageing population equate to a growing number of patients awaiting hip arthroplasty demanding superior biomechanical function. The purpose of this study was to compare the biomechanics of top walking speed between two commonly used hip arthroplasty procedures to determine if a performance advantage existed. Methods. A retrospective comparative study was performed using sixty-seven subjects, twenty-two subjects in both hip resurfacing and total hip arthroplasty groups along with twenty-three healthy controls. All arthroplasty subjects were recruited based on high psychometric scoring and had been performed through a posterior approach, and had been discharged from follow-up. On an instrumented treadmill each subject was measured by a researcher blinded to which procedure that patient had undergone. After a six minute acclimatization period, the speed was increased incrementally until top walking performance had been attained. At all increments, ground reaction forces and temporospatial measurements were collected. Results. The two arthroplasty groups were well matched demographically, with no significant differences with regards to age, sex, height, BMI and pre-operative radiological severity. Treadmill temporospatial analysis demonstrated significant differences between the two groups. The hip resurfacing group were able to walk statistically faster (p=0.023) with an increased step length(p=0.041). The top walking speed mean of 2.06m/sec by the resurfacing almost matched the healthy controls. Assessing ground reaction forces and symmetry also demonstrated hip resurfacing was superior (Graph 1). [Graph 1: Mean Gait Biomechanics at Top Speed]. Conclusion. This study is the first to focus on high end performance following hip arthroplasty, encouraging patients to achieve as high a speed as they comfortably could. The total hip arthroplasty group walked nine percent faster than the previously published top speed of 1.73m/sec, however the resurfacings still walked ten percent faster, matching the normal controls for speed and step length

Metal on Metal hip resurfacing (MoM HR) can be an effective operation for the young arthritic hip population. However, errors in cup orientation have been associated with increased wear, circulating blood metal ions, and soft tissue abnormalities that can lead to premature failure of the bearing surface and subsequent revision surgery. While image free computer guidance has been shown to increase surgical accuracy in total hip arthroplasty, the role of image based technology in MoM HR is unclear. In this study, we compared the accuracy of cup orientation in MoM HR performed by either freehand technique or CT based navigation. Seventy five patients (81 hips) underwent either freehand (n=42) or navigation (n=39) surgery, both requiring a three dimensional (3D) CT surgical plan. Surgery was conducted by hip specialists blind to the method of cup implantation until the operation. Deviation in inclination and version from the planned orientation, as well as, number of cups within a 10° safe zone and 5° optimal zone of the target position was calculated using post operative 3D CT analysis. Error in inclination was significantly reduced with navigation compared to freehand technique (4° vs 6°, p=0.02). We could not detect a difference between the two groups for version error (5° vs 7°, p=0.06). There was a significantly greater number of hips within a 10° (87% vs 67%, p=0.04) and 5° (50% vs 20%, p=0.06) safe zone when navigated. Image based navigation can substantially improve accuracy in cup orientation. The results of our freehand group appear better than historic controls, suggesting the use of a 3D plan may help to reduce technical error and improve the learning curve in this technically demanding procedure. We advocate the use of image based navigation in MoM hip resurfacing arthroplasty

Aims

In metal-on-metal (MoM) hip arthroplasties and resurfacings, mechanically induced corrosion can lead to elevated serum metal ions, a local inflammatory response, and formation of pseudotumours, ultimately requiring revision. The size and diametral clearance of anatomical (ADM) and modular (MDM) dual-mobility polyethylene bearings match those of Birmingham hip MoM components. If the acetabular component is satisfactorily positioned, well integrated into the bone, and has no surface damage, this presents the opportunity for revision with exchange of the metal head for ADM/MDM polyethylene bearings without removal of the acetabular component.

Background. We have previously described the relationship between wear rates of MOM components and soft tissue necrosis. In this study we investigated the link between wear rates, metal ion concentrations and osteolysis. Methods. All unilateral patients who underwent revision of hip resurfacings at our centre were included. Retrieved components were analysed using a coordinate measuring machine to determine total volumetric material loss and rates of wear. Given the accuracy of the wear calculations (which we have previously published), wear rates were considered “abnormal” if ≥3mm. 3. /yr. ROC curves were constructed to determine a Co concentration which would be clinically useful to detect abnormal wear. During revision, the presence/absence of osteolysis was documented. Results. There were 65 patients in total (mean time to revision was 41 months (2 to 98). 60 patients had suffered ARMD. 2 hips were revised for infection, 1 for osteolysis and 1 due to a loose cup and 1 for unexplained pain. A blood cobalt concentration >5µg/l was found to be 100%(62.2–100) specific and 94.4%(84.2–98.6) sensitive for the detection of abnormal wear. All patients with wear rates greater than 12mm. 3. /yr (n=21) were found to have osteolysis (the minimum total loss of material in this group of patients was 16mm3). ROC analysis showed that a blood cobalt ≥44.6µg/l was 97.2% specific for the detection of this rate of wear. 3 of the 21 patients with these rates of wear were asymptomatic. They decided on revision after discussion with the surgeon. Two were revised following acute femoral collapse but were completely pain free prior to these events. Conclusion. These data suggest that a blood cobalt concentration of 5µg/l can reliably identify an abnormally wearing resurfacing prosthesis. Elevated metal ion concentrations are associated with osteolysis, even in the absence of symptoms

Introduction. Metal on metal hip resurfacing arthroplasty (MoM HR) has the highest revision rates according to the UK National Joint Registry. Revisions for lesions associated with soft tissue necrosis (pseudotumors) have been associated with poor outcomes. There is a relative paucity of information on early revision of painful HR prostheses. We present the results of a series of patients who underwent early revision of painful MoM HR procedures. Methods. This prospective study involved a consecutive series of patients undergoing revision of HR to THA. The diagnoses leading to revision are discussed. Clinical and radiological assessments were performed pre operatively as well as 6 weeks, 12 months postoperatively and yearly thereafter. Pre and post operative Harris Hip Score, Oxford Hip Score and WOMAC scores were calculated. Patient satisfaction was assessed using a visual analogue scale. Results. Revisions were performed for recurrent pain and effusion, infection and proximal femoral fractures. Both components were revised in 20 cases. There were 12 male and 13 female patients with average time to revision of 34.4 and 26.4 months respectively. The mean follow up period was 12.7 months (3 to 31). All patients reported relief of pain and excellent satisfaction scores (9/10 compared to 2/10 pre-operatively). Two patients experienced stiffness up to three months post operatively. Pre operative Oxford, Harris and WOMAC hip scores were 39.1, 36.4 and 52.2 respectively. Mean post operative scores at last follow up were 17.4, 89.8 and 6.1 respectively (p< 0.0001 for each score). All patients except those with femoral neck fractures had at least a small effusion. Conclusion. These results show that conversion of painful hip resurfacing prostheses to total hip arthroplasty is associated with improved function, pain relief and high levels of patient satisfaction

Objectives. The aims of this piece of work were to: 1) record the background concentrations of blood chromium (Cr) and cobalt (Co) concentrations in a large group of subjects; 2) to compare blood/serum Cr and Co concentrations with retrieved metal-on-metal (MoM) hip resurfacings; 3) to examine the distribution of Co and Cr in the serum and whole blood of patients with MoM hip arthroplasties; and 4) to further understand the partitioning of metal ions between the serum and whole blood fractions. Methods. A total of 3042 blood samples donated to the local transfusion centre were analysed to record Co and Cr concentrations. Also, 91 hip resurfacing devices from patients who had given pre-revision blood/serum samples for metal ion analysis underwent volumetric wear assessment using a coordinate measuring machine. Linear regression analysis was carried out and receiver operating characteristic curves were constructed to assess the reliability of metal ions to identify abnormally wearing implants. The relationship between serum and whole blood concentrations of Cr and Co in 1048 patients was analysed using Bland-Altman charts. This relationship was further investigated in an in vitro study during which human blood was spiked with trivalent and hexavalent Cr, the serum then separated and the fractions analysed. Results. Only one patient in the transfusion group was found to have a blood Co > 2 µg/l. Blood/Serum Cr and Co concentrations were reliable indicators of abnormal wear. Blood Co appeared to be the most useful clinical test, with a concentration of 4.5 µg/l showing sensitivity and specificity for the detection of abnormal wear of 94% and 95%, respectively. Generated metal ions tended to fill the serum compartment preferentially in vivo and this was replicated in the in vitro study when blood was spiked with trivalent Cr and bivalent Co. Conclusions. Blood/serum metal ion concentrations are reliable indicators of abnormal wear processes. Important differences exist however between elements and the blood fraction under study. Future guidelines must take these differences into account

Objectives. Metal-on-metal (MoM) hip resurfacing was introduced into clinical practice because it was perceived to be a better alternative to conventional total hip replacement for young and active patients. However, an increasing number of reports of complications have arisen focusing on design and orientation of the components, the generation of metallic wear particles and serum levels of metallic ions. The procedure introduced a combination of two elements: large-dimension components and hard abrasive particles of metal wear. The objective of our study was to investigate the theory that microseparation of the articular surfaces draws in a high volume of bursal fluid and its contents into the articulation, and at relocation under load would generate high pressures of fluid ejection, resulting in an abrasive water jet. Methods. This theoretical concept using MoM resurfacing components (head diameter 55 mm) was modelled mathematically and confirmed experimentally using a material-testing machine that pushed the head into the cup at a rate of 1000 mm/min until fully engaged. Results. The mathematical model showed the pattern but not the force of fluid ejection, the highest pressures were expected when the separation of the components was only a fraction of one millimetre. The experimental work confirmed the results; with the mean peak ejection pressure of 43 763 N/m. 2. equivalent to 306 mmHg or 5 psi. Conclusions. The mechanical effect of the high-pressure abrasive water jet is the likely cause of the spectrum of complications reported with metal-on-metal resurfacing. Investigating serum levels of metallic elements may not be the best method for assessing the local mechanical effects of the abrasive water jet

Aims

We investigated whether blood metal ion levels could effectively identify patients with bilateral Birmingham Hip Resurfacing (BHR) implants who have adverse reactions to metal debris (ARMD).

Objectives

We aimed to determine the effect of surgical approach on the histology of the femoral head following resurfacing of the hip.

Aims. Hip resurfacing remains a potentially valuable surgical procedure for appropriately-selected patients with optimised implant choices. However, concern regarding high early failure rates continues to undermine confidence in use. A large contributor to failure is adverse local tissue reactions around metal-on-metal (MoM) bearing surfaces. Such phenomena have been well-explored around MoM total hip arthroplasties, but comparable data in equivalent hip resurfacing procedures is lacking. In order to define genetic predisposition, we performed a case-control study investigating the role of human leucocyte antigen (HLA) genotype in the development of pseudotumours around MoM hip resurfacings. Methods. A matched case-control study was performed using the prospectively-collected database at the host institution. In all, 16 MoM hip resurfacing 'cases' were identified as having symptomatic periprosthetic pseudotumours on preoperative metal artefact reduction sequence (MARS) MRI, and were subsequently histologically confirmed as high-grade aseptic lymphocyte-dominated vasculitis-associated lesions (ALVALs) at revision surgery. ‘Controls’ were matched by implant type in the absence of evidence of pseudotumour. Blood samples from all cases and controls were collected prospectively for high resolution genetic a nalysis targeting 11 separate HLA loci. Statistical significance was set at 0.10 a priori to determine the association between HLA genotype and pseudotumour formation, given the small sample size. Results. Using a previously-reported ALVAL classification, the majority of pseudotumour-positive caseswere found to have intermediate-grade group 2 (n = 10; 63%) or group 3 (n = 4; 25%) histological findings. Two further patients (13%) had high-grade group 4 lesions. HLA-DQB1*05:03:01 (p = 0.0676) and HLA-DRB1*14:54:01 (p = 0.0676) alleles were significantly associated with a higher risk of pseudotumour formation, while HLA-DQA1*03:01:01 (p = 0.0240), HLA-DRB1*04:04:01 (p = 0.0453), HLA-C*01:02:01 (p = 0.0453), and HLA-B*27:05:02 (p = 0.0855) were noted to confer risk reduction. Conclusion. These findings confirm the association between specific HLA genotypes and the risk of pseudotumour development around MoM hip resurfacings. Specifically, the two ‘at risk’ alleles (DQB1*05:03:01 and DRB1*14:54:01) may hold clinical value in preoperative screening and prospective surgical decision-making. Cite this article: Bone Jt Open 2023;4(3):182–187

Objectives

Pseudotumours (abnormal peri-prosthetic soft-tissue reactions) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated metal ion levels, suggesting that excessive wear may occur due to edge-loading of these MoM implants. This study aimed to quantify in vivo edge-loading in MoMHRA patients with and without pseudotumours during functional activities.

Hip resurfacing may be a useful surgical procedure when patient selection is correct and only implants with superior performance are used. In order to establish a body of evidence in relation to hip resurfacing, pseudotumour formation and its genetic predisposition, we performed a case-control study investigating the role of HLA genotype in the development of pseudotumour around MoM hip resurfacings. All metal-on-metal (MoM) hip resurfacings performed in the history of the institution were assessed. A total of 392 hip resurfacings were performed by 12 surgeons between February 1st 2005 and October 31st 2007. In all cases, pseudotumour was confirmed in the preoperative setting on Metal Artefact Reduction Sequencing (MARS) MRI. Controls were matched by implant (ASR or BHR) and absence of pseudotumour was confirmed on MRI. Blood samples from all cases and controls underwent genetic analysis using Next Generation Sequencing (NGS) assessing for the following alleles of 11 HLA loci (A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPB1, DPA1). Statistical significance was determined using a Fisher's exact test or Chi-Squared test given the small sample size to quantify the clinical association between HLA genotype and the need for revision surgery due to pseudotumour. Both groups were matched for implant type (55% ASR, 45% BHR in both the case and control groups). According to the ALVAL histological classification described by Kurmis et al., the majority of cases (63%, n=10) were found to have group 2 histological findings. Four cases (25%) had group 3 histological findings and 2 (12%) patients had group 4 findings. Of the 11 HLA loci analysed, 2 were significantly associated with a higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) and 4 were noted to be protective against pseudotumour formation (DQA1*03:01:01, DRB1*04:04:01, C*01:02:01, B*27:05:02). These findings further develop the knowledge base around specific HLA genotypes and their role in the development of pseudotumour formation in MoM hip resurfacing. Specifically, the two alleles at higher risk of pseudotumour formation (DQB1*05:03:01 and DRB1*14:54:01) in MoM hip resurfacing should be noted, particularly as patient-specific genotype-dependent surgical treatments continue to develop in the future

A ceramic-on-ceramic hip resurfacing implant (cHRA) was developed and introduced in an MHRA-approved clinical investigation to provide a non metallic alternative hip resurfacing product. This study aimed to examine function and physical activity levels of patients with a cHRA implant using subjective and objective measures both before and 12 months following surgery in comparison with age and gender matched healthy controls. Eighty-two unilateral cHRA patients consented to this study as part of a larger prospective, non-randomised, clinical investigation. In addition to their patient reported outcome measures (PROMs), self- reported measures of physical activity levels and gait analysis were undertaken both pre- operatively (1.5 weeks) and post operatively (52 weeks). This data was then compared to data from a group of 43 age gender and BMI matched group of healthy controls. Kinetics and kinematics were recorded using an instrumented treadmill and 3D Motion Capture. Statistical parametric mapping was used for analysis. cHRA improved the median Harris Hip Score from 63 to 100, Oxford Hip score from 27 to 48 and the MET from 5.7 to 10.3. cHRA improved top walking speed (5.75km vs 7.27km/hr), achieved a more symmetrical ground reaction force profile, (Symmetry Index value: 10.6% vs 0.9%) and increased hip range of motion (ROM) (31.7° vs 45.9°). Postoperative data was not statistically distinguishable from the healthy controls in any domain. This gait study sought to document the function of a novel ceramic hip resurfacing, using those features of gait commonly used to describe the shortcomings of hip arthroplasty. These features were captured before and 12 months following surgery. Preoperatively the gait patterns were typical for OA patients, while at 1 year postoperatively, this selected group of patients had gait patterns that were hard to distinguish from healthy controls despite an extended posterior approach. Applications for regulatory approval have been submitted

Competitive dancers represent a unique patient population in the setting of hip arthroplasty given the high degree of hip strength and mobility required by their profession. We sought to determine the clinical outcomes and ability to return to competitive dance after total hip arthroplasty (THA) or hip resurfacing arthroplasty (HRA) among competitive dancers. Active competitive dancers who underwent primary THA or HRA at a single institution with minimum one-year follow-up were included in the study. Primary outcomes included (1) the rate of return to competitive dance, (2) three PROMs (modified Harris Hip Score [mHHS], Hip Disability and Osteoarthritis Outcome Score for Joint Replacement [HOOS-JR], and Lower Extremity Activity Scale [LEAS]), and (3) post-operative complications. Forty-nine hips in 39 patients (mean age 56±13 years; 80% female) were included. Mean follow-up was 4.9±5.1 years. Thirty-seven THAs and 12 HRAs were performed. Ninety-six percent of patients returned to competitive dance activities post-operatively. With respect to PROMs, there were statistically significant improvements in mHHS, HOOS-JR, and LEAS from baseline to ≥ 1 year post-operatively. There were complications in 9/49 (18%) hips post-operatively, five (10%) of which required revision surgery. Active competitive dancers experienced significant improvements in functional outcome scores after THA or HRA, with a rate of return to competitive dance of 96%

Aims. This study investigates the use of the metabolic equivalent of task (MET) score in a young hip arthroplasty population, and its ability to capture additional benefit beyond the ceiling effect of conventional patient-reported outcome measures. Methods. From our electronic database of 751 hip arthroplasty procedures, 221 patients were included. Patients were excluded if they had revision surgery, an alternative hip procedure, or incomplete data either preoperatively or at one-year follow-up. Included patients had a mean age of 59.4 years (SD 11.3) and 54.3% were male, incorporating 117 primary total hip and 104 hip resurfacing arthroplasty operations. Oxford Hip Score (OHS), EuroQol five-dimension questionnaire (EQ-5D), and the MET were recorded preoperatively and at one-year follow-up. The distribution was examined reporting the presence of ceiling and floor effects. Validity was assessed correlating the MET with the other scores using Spearman’s rank correlation coefficient and determining responsiveness. A subgroup of 93 patients scoring 48/48 on the OHS were analyzed by age, sex, BMI, and preoperative MET using the other metrics to determine if differences could be established despite scoring identically on the OHS. Results. Postoperatively the OHS and EQ-5D demonstrate considerable negatively skewed distributions with ceiling effects of 41.6% and 53.8%, respectively. The MET was normally distributed postoperatively with no relevant ceiling effect. Weak-to-moderate significant correlations were found between the MET and the other two metrics. In the 48/48 subgroup, no differences were found comparing groups with the EQ-5D, however significantly higher mean MET scores were demonstrated for patients aged < 60 years (12.7 (SD 4.7) vs 10.6 (SD 2.4), p = 0.008), male patients (12.5 (SD 4.5) vs 10.8 (SD 2.8), p = 0.024), and those with preoperative MET scores > 6 (12.6 (SD 4.2) vs 11.0 (SD 3.3), p = 0.040). Conclusion. The MET is normally distributed in patients following hip arthroplasty, recording levels of activity which are undetectable using the OHS. Cite this article: Bone Joint Res 2022;11(5):317–326

Background. Proper positioning of the acetabular component is critical for prevention of dislocation and excessive wear for total hip arthroplasty (THA) and hip resurfacing. Consideration of preoperative pelvic tilt (PT) may aid in acetabular component placement. The purpose of this study was to investigate how PT changes after hip resurfacing, via pre and post-operative radiographic analysis of anterior pelvic plane (APP), and whether radiographic analysis of the APP is a reproducible method for evaluating PT in resurfaced hips. Methods. A consecutive group of 228 patients from a single surgeon who had hip resurfacing were evaluated. We obtained x-rays from an institutional database for these patients who had their surgeries between January 1. st. , 2014 to December 31. st. , 2016. Pelvic tilt (PT) was measured by two observers before and after resurfacing utilizing a standardized radiographic technique. Correlation coefficients were calculated for PT measurements between observers, and pre- and post-surgery. Results. Mean preoperative PT was 0.7° (SD ± 6.6°) and 0.4° (SD ± 6.1°). Mean post-operative PT was −1.2° (SD ± 6.2°) and −1.2° (SD ± 6.0°). Correlations between pre and post-operative PT were R=.829 (p<.001) and R = .837 (p<.001). 80.6% to 82.5% of patients had variation <5°, 15.8% to 17.8% had variation between 5–10°, and 1.6 to1.8% had a variation >10°. Intraclass correlation coefficients between observers were R = .987 (95% CI, .963–.981; p<.001) preoperatively, and R=.985 (95 CI, .963–.981; p<.001) postoperatively. (See Fig 1). Conclusion. After hip resurfacing arthroplasty, the mean difference between preoperative and postoperative PT was less than 1°. These results suggest that near-native PT is maintained with consistency after hip resurfacing, a finding that is variable following THA. Since variations in PT affect functional acetabular position, these results support the use of pelvic tilt measurement in pre-operative planning for hip arthroplasty with a high degree of inter-observer reliability. For any figures or tables, please contact the authors directly