Acetabular component positioning is commonly referenced with the pelvis in the supine position in direct anterior approach THA. Changes in pelvic tilt (PT) from the pre-operative supine to the post-operative standing positions have not been well investigated and may have relevance to optimal acetabular component targeting for reduced risk of impingement and instability. The aims of this study were therefore to determine the change in PT that occurs from pre-operative supine to post-operative standing, and whether any factors are associated with significant changes in tilt ≥13° in posterior direction. 13° in a posterior direction was chosen as that amount of posterior rotation creates an increase in functional anteversion of the acetabular component of 10°. 1097 THA patients with pre-operative supine CT and standing lateral radiographic imaging and 1 year post-operative standing lateral radiographs (interquartile range 12–13 months) were reviewed. Pre-operative supine PT was measured from CT as the angle between the anterior pelvic plane (APP) and the horizontal plane of the CT device. Standing PT was measured on standing lateral x-rays as the angle between the APP and the vertical line. Patients with ≥13° change from supine pre-op to standing post-op (corresponding to a 10° change in cup anteversion) were grouped and compared to those with a <13° change using unpaired student's t-tests. Mean pre-operative supine PT (3.8±6.0°) was significantly different from mean post-operative standing PT (−3.5±7.1°, p<0.001), ie mean change of −7.3±4.6°. 10.4% (114/1097) of patients had posterior PT changes ≥13° supine pre-op to standing post-op. A significant number of patients, ie 1 in 10, undergo a clinically significant change in PT and functional anteversion from supine pre-op to standing post-op. Surgeons should be aware of these changes when planning component placement in THA.
Evaluation of patient specific spinopelvic mobility requires the detection of bony landmarks in lateral functional radiographs. Current manual landmarking methods are inefficient, and subjective. This study proposes a deep learning model to automate landmark detection and derivation of spinopelvic measurements (SPM). A deep learning model was developed using an international multicenter imaging database of 26,109 landmarked preoperative, and postoperative, lateral functional radiographs (HREC: Bellberry: 2020-08-764-A-2). Three functional positions were analysed: 1) standing, 2) contralateral step-up and 3) flexed seated. Landmarks were manually captured and independently verified by qualified engineers during pre-operative planning with additional assistance of 3D computed tomography derived landmarks. Pelvic tilt (PT), sacral slope (SS), and lumbar lordotic angle (LLA) were derived from the predicted landmark coordinates. Interobserver variability was explored in a pilot study, consisting of 9 qualified engineers, annotating three functional images, while blinded to additional 3D information. The dataset was subdivided into 70:20:10 for training, validation, and testing. The model produced a mean absolute error (MAE), for PT, SS, and LLA of 1.7°±3.1°, 3.4°±3.8°, 4.9°±4.5°, respectively. PT MAE values were dependent on functional position: standing 1.2°±1.3°, step 1.7°±4.0°, and seated 2.4°±3.3°, p< 0.001. The mean model prediction time was 0.7 seconds per image. The interobserver 95% confidence interval (CI) for engineer measured PT, SS and LLA (1.9°, 1.9°, 3.1°, respectively) was comparable to the MAE values generated by the model. The model MAE reported comparable performance to the gold standard when blinded to additional 3D information. LLA prediction produced the lowest SPM accuracy potentially due to error propagation from the SS and L1 landmarks. Reduced PT accuracy in step and seated functional positions may be attributed to an increased occlusion of the pubic-symphysis landmark. Our model shows excellent performance when compared against the current gold standard manual annotation process.
The study of spinopelvic anatomy and movement has received great interest as these characteristics influence the biomechanical behavior (and outcome) following hip arthroplasty. However, to-date there is little knowledge of what “normal” is and how this varies with age. This study aims to determine how dynamic spino-pelvic characteristics change with age, with well-functioning hips and assess how these changes are influenced by the presence of hip arthritis. This is an IRB-approved, cross-sectional, cohort study; 100 volunteers (asymptomatic hips, Oxford-Hip-sore>45) [age:53 ± 17 (24-87) years-old; 51% female; BMI: 28 ± 5] and 200 patients with end-stage hip arthritis [age:56 ± 19 (16-89) years-old; 55% female; BMI:28 ± 5] were studied. All participants underwent lateral spino-pelvic radiographs in the standing and deep-seated positions to determine maximum hip and spine flexion. Parameters measured included lumbar-lordosis (LL), pelvic incidence, pelvic-tilt (PT), pelvic-femoral angles (PFA). Lumbar flexion (ΔLL), hip flexion (ΔPFA) and pelvic movement (ΔPT) were calculated. The prevalence of spinopelvic imbalance (PI–LL>10?) was determined. There were no differences in any of the spino-pelvic characteristics or movements between sexes. With advancing age, standing LL reduced and standing PT increased (no differences between groups). With advancing age, both hip (4%/decade) and lumbar (8%/decade) flexion reduced (p<0.001) (no difference between groups). ΔLL did not correlate with ΔPFA (rho=0.1). Hip arthritis was associated with a significantly reduced hip flexion (82 ±;22? vs. 90 ± 17?; p=0.003) and pelvic movements (1 ± 16? vs. 8 ± 16?; p=0.002) at all ages and increased prevalence of spinopelvic imbalance (OR:2.6; 95%CI: 1.2-5.7). With aging, the lumbar spine loses its lumbar lordosis and flexion to a greater extent that then the hip and resultantly, the hip's relative contribution to the overall sagittal movement increases. With hip arthritis, the reduced hip flexion and the necessary compensatory increased pelvic movement is a likely contributor to the development of hip-spine syndrome and of spino-pelvic imbalance.
A stiff spine leads to increased demand on the hip, creating an increased risk of total hip arthroplasty (THA) dislocation. Several authors propose that a change in sacral slope of ≤10° between the standing and relaxed-seated positions (ΔSSstanding→relaxed-seated) identifies a patient with a stiff lumbar spine and have suggested use of dual-mobility bearings for such patients. However, such assessment may not adequately test the lumbar spine to draw such conclusions. The aim of this study was to assess how accurately ΔSSstanding→relaxed-seated can identify patients with a stiff spine. This is a prospective, multi-centre, consecutive cohort series. Two-hundred and twenty-four patients, pre-THA, had standing, relaxed-seated and flexed-seated lateral radiographs. Sacral slope and lumbar lordosis were measured on each functional X-ray. ΔSSstanding→relaxed-seated seated was determined by the change in sacral slope between the standing and relaxed-seated positions. Lumbar flexion (LF) was defined as the difference in lumbar lordotic angle between standing and flexed-seated. LF≤20° was considered a stiff spine. The predictive value of ΔSSstanding→relaxed-seated for characterising a stiff spine was assessed. A weak correlation between ΔSSstanding→relaxed-seated and LF was identified (r2= 0.15). Fifty-four patients (24%) had ΔSSstanding→relaxed-seated ≤10° and 16 patients (7%) had a stiff spine. Of the 54 patients with ΔSSstanding→relaxed-seated ≤10°, 9 had a stiff spine. The positive predictive value of ΔSSstanding→relaxed-seated ≤10° for identifying a stiff spine was 17%. ΔSSstanding→relaxed-seated ≤10° was not correlated with a stiff spine in this cohort. Utilising this simplified approach could lead to a six-fold overprediction of patients with a stiff lumbar spine. This, in turn, could lead to an overprediction of patients with abnormal spinopelvic mobility, unnecessary use of dual mobility bearings and incorrect targets for component alignment. Referring to patients ΔSSstanding→relaxed-seated ≤10° as being stiff can be misleading; we thus recommend use of the flexed-seated position to effectively assess pre-operative spinopelvic mobility.
Adverse spinopelvic mobility (SPM) has been shown to increase risk of dislocation of primary total hip arthroplasty (THA). In patients undergoing THA, prevalence of adverse SPM has been shown to be as high as 41%. Stiff lumbar spine, large posterior standing pelvic tilt and severe sagittal spinal deformity have been identified as risk factors for increased hip instability. Dislocation rates for dual mobility articulations have been reported to be 0% to 1.1%. The aim of this study was to determine the early survivorship from the Australian National Joint Replacement Registry (AOANJRR) of patients with adverse SPM who received a dual mobility articulation. A multicentre study was performed using data from 229 patients undergoing primary THA, enrolled consecutively. All the patients who had one or more adverse spine or pelvic mobility parameters had a dual mobility articulation inserted at the time of their surgery. Average age was 76 (22 to 93) years and 63% were female. At a mean of 2.1 (1 – 3.3) years post-op, the AOANJRR was analysed for follow-up. Reasons for revision and types of revision were identified. The AOANJRR reported two revisions. One due to infection and the second due to femoral component loosening. No revisions for dislocation were reported. One patient died with the prosthesis in situ. Kaplan Meier survival was 99.3% (CI 98.3% − 100%) at 2 years. DM bearings reduce the risk of dislocation of primary THA in patients with adverse spine and pelvic mobility.
Excessive standing posterior pelvic tilt (PT), lumbar spine stiffness, low pelvic Incidence (PI), and severe sagittal spinal deformity (SSD) have been linked to increased dislocation rates. We aimed to compare the prevalence of these 4 parameters in unstable and stable primary Total Hip Arthroplasty (THA) patients. In this retrospective cohort study, 40 patients with instability following primary THA for osteoarthritis were referred for functional analysis. All patients received lateral X-rays in standing and flexed seated positions to assess functional pelvic tilt and lumbar lordosis (LL). Computed tomography scans were used to measure pelvic incidence and acetabular cup orientation. Literature thresholds for “at risk” spinopelvic parameters were standing pelvic tilt ≤ −10°, lumbar flexion (LLstand – LLseated) ≤ 20°, PI ≤ 41°, and sagittal spinal deformity (PI – LLstand mismatch) ≥ 10°. The prevalence of each risk factor in the dislocation cohort was calculated and compared to a previously published cohort of 4042 stable THA patients.Introduction
Methods
The prevalence of the various patterns of spinopelvic abnormalities that increase the risk for prosthetic impingement is unknown. While prior surgery or lumbar fusion are recognized as a risk factors for postoperative dislocation, many patients presenting for THA do not have obvious radiographic abnormalities. The purpose of this study is to determine the prevalence of large posterior pelvic tilt (PPT) when standing, stiff lumbar-spine (SLL) and spino-pelvic sagittal imbalance (SSI) in patients undergoing primary THA. A consecutive series of 1592 patients (56% female) over 2 years underwent functional analysis of spinopelvic mobility using CT, standing, and flexed seated lateral radiographs as part of pre-operative THA planning. The average age was 65 (20–93). We investigated the prevalence of these 3 validated spinopelvic parameters known to increase the risk for impingent and correlated them to the patient's age and gender using Chi squared analysis. Finally, the risk of flexion and extension impingement was modeled for each patient at a default supine cup orientation (DSCO) of 40°/20° (±5°).Introduction
Methods
Apparently well-orientated total hip replacements (THR) can still fail due to functional component malalignment. Previously defined “safe zones” are not appropriate for all patients as they do not consider an individual's spinopelvic mobility. The Optimized Positioning System, OPSTM (Corin, UK), comprises preoperative planning based on a patient-specific dynamic analysis, and patient-specific instrumentation for delivery of the target component alignment. The aim of this study was to determine the early revision rate from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) for THRs implanted using OPSTM. Between January 4th 2016 and December 20st 2017, a consecutive series of 841 OPSTMcementless total hip replacements were implanted using a Trinity acetabular cup (Corin, UK) with either a TriFit TS stem (98%) or a non-collared MetaFix stem (2%). 502 (59%) procedures were performed through a posterior approach, and 355 (41%) using the direct superior approach. Mean age was 64 (range; 27 to 92) and 51% were female. At a mean follow-up of 15 months (range; 3 to 27), the complete list of 857 patients was sent to the AOANJRR for analysis.Introduction & aims
Method
It is well accepted that larger heads provide more stability in total hip arthroplasty. This is due to an increase in jump height providing increased resistance to subluxation. However, other implant parameters also contribute to the bearing's stability. Specifically, the liner's rim design and the centre of rotation relative to the liner's face. Both these features contribute to define the Cup Articular Arc Angle (CAAA). The CAAA describes the degree of dysplasia of the acetabular liner, and plays an important role in defining the jump height. The aim of this study was to determine the difference in jump height between bearing materials with a commonly used acetabular implant system. From 3D models of the Trinity acetabular implant system (Corin, UK), the CAAA was measured in CAD software (SolidWorks, Dassault Systems, France) for the ceramic, poly and modular dual mobility (DM) liners, for cup sizes 46mm to 64mm. The most commonly used bearing size was used in the analysis of each cup size. For the ceramic and poly liners, a 36mm bearing was used for cups 50mm and above. For the 46mm and 48mm cups, a 32mm bearing was used. The DM liners were modelled with the largest head size possible. Using a published equation, the jump height was calculated for each of the three bearing materials and each cup size. Cup inclination and anteversion were kept constant.Introduction
Methods
In total hip arthroplasty, correct sizing is critical for fixation and longevity of cementless components. Previously, three-dimensional CT templating has been shown to be more accurate than using 2D radiographs. The accuracy of the Optimized Positioning System (OPSTM) planning software has not been reported. The aim of this study was to measure the accuracy of the OPS planning software in predicting the implanted acetabular cup and femoral stem size when used with the direct anterior approach. Between October 2018 and March 2019, 95 patients received a bone preserving cementless MiniHip stem (Corin, UK). Sixty-three of these patients also received a cementless Trinity cup (Corin, UK). All patients were sent for OPSTM pre-operative planning, a patient-specific dynamic modelling software used to determine the optimal acetabular and femoral component size and positions. Average age was 57 (28 to 78) and 44% were female. All cases were performed using the direct anterior approach. The sizes of implants used were retrospectively compared to the planned OPSTM sizes.Introduction
Method
Femoral component loosening is one of the most common failure modes in cementless total hip arthroplasty (THA). Patient age, weight, gender, osteopenia, stem design and Dorr-C bone have all been proposed as risk factors for poor fixation and subsequent stem subsidence and poor outcome. With the increased popularity of CT-based assistive technologies in THA, (Stryker MAKO and Corin OPSTM), we sought to develop a technique to predicted femoral stem fixation using pre-operative CT. Fourteen patients requiring THA were randomly selected from a previous study investigating component alignment. Mean age was 64 (53 to 76), and 57% were female. All patients received pre-operative CT for 3D dynamic templating (OPSTM), and a TriFit stem and Trinity cup (Corin, UK) implanted through a posterior approach. Post-operatively, patients received an immediate CT and AP x-ray prior to leaving the hospital, and a 1-year follow-up x-ray. On both the immediate post-op x-ray and 1-year follow-up x-ray, the known cup diameter was used to scale the image. On both images, the distance between the most superior point of the greater trochanter and the shoulder of the stem was measured. The difference was recorded as stem subsidence. Subsidence greater than 4mm was deemed clinically relevant. The post-operative CT was used to determine the precise three-dimensional placement of the stem immediately after surgery by registering the known 3D implant geometry to the CT. For each patient, the achieved stem position from post-op CT was then virtually implanted back into the pre-operative OPSTM planning software. The software provides a colour map of the bone density at the stem/bone interface using the Hounsfield Units (HU) of each pixel of the CT [Fig. 1]. Blue represents low density bone transitioning through to green and then red (most dense).Introduction
Methods
The functional pelvic tilt when standing and sitting forward of 7402 cases on the OPS, Optimized Ortho, Australia Data Base were reviewed. All patients had undergone lateral radiographs when standing simulating extension of the hip, and sitting forward when the hip is near full flexion. Pelvic tilt was measured as the angle of the Anterior Pelvic Plane to the vertical Sagittal Plane, rotation anteriorly being given a positive value. Pelvises that had rotated more than 13 degrees anteriorly (+ve) when sitting forward or posteriorly (-ve) when standing were considered to place the hip at increased risk of dislocation or edge loading when flexed or extending respectively. This degree of rotation has the effect of changing the acetabular version by approximately100. Most safe zones that have been described have given a range of anteversion of 200 as safe. A change of 100 would potentially place the acetabular orientation outside this range. Further, clinical studies have supported this concept. All lateral radiographs were reviewed to confirm that 281 had undergone instrumented spinal fusion at some level between T12 and S1. There was a large variability in the number and the levels arthrodesed. The range of pelvic mobility in the non-arthrodesed group in extension was −370 to 310 (mean −0.90, Standard deviation 7.49) and in flexed position was −700 to 490 (mean −1.90, Standard deviation 14.01). For the group with any fusion the range of pelvic tilt in extension was −310 to 220 (mean −40, Standard deviation 8.21) and flexed −320 to 460 (mean 4.40, Standard deviation 13.79). Of the 7121 cases without instrumented fusion, 15.5% were considered to be at risk when in flexion and 6.1% when extended. The risk for those with any fusion was approximately doubled in both flexion and extension. Further, those with extensive arthrodesis from T12 to S1 had a range of pelvic tilts similar to the non-fused group, although they had a significantly higher percentage of cases in the ‘at risk’ zones. The proportion of the cases in the ‘at risk’ zones decreased progressively as the arthrodesed levels moved from L5/S1 to the upper lumbar spine, and with decreasing number of levels fused. Spinal fusion is not just one group as there are many combinations of different levels fused. Patients with instrumented spinal fusions do have a proportionately high risk of failure of their THR than the majority of cases with no instrumentation, though the risk varies significantly with the number of levels and actual levels arthrodesed. Further approximately 21% of cases with no spinal fusion have functional pelvic movements that would potentially place them ‘at risk’ of edge loading or dislocation. For any figures or tables, please contact authors directly.Conclusion
Instability continues to be the number one reason for revision in primary total hip arthroplasty (THA). Commonly, impingement precedes dislocation, inducing a levering out the prosthetic head from the liner. Impingement can be prosthetic, bony or soft tissue, depending on component positioning and anatomy. The aim of this virtual study was to investigate whether bony or prosthetic impingement occurred first in well positioned THAs, with the hip placed in deep flexion and hyperextension. Twenty-three patients requiring THA were planned for a TriFit/Trinity ceramic-on-poly cementless construct using the OPSTM dynamic planning software (Corin, UK). The cups were sized to best fit the anatomy, medialised to sit on the acetabular fossa and orientated at 45° inclination and 25° anteversion when standing. Femoral components and head lengths were then positioned to reproduce the native anteversion and match the contralateral leg length and offset. The planned constructs were flexed and internally rotated until anterior impingement occurred in deep flexion [Fig. 1]. The type (bony or prosthetic), and location, of impingement was then recorded. Similarly, the hips were extended and externally rotated until posterior impingement occurred, and the type and location of impingement recorded [Fig. 2]. Patients with minimal pre-operative osteophyte were selected as a best-case scenario for bony impingement.Introduction
Methods
The direct anterior approach (DAA) for total hip arthroplasty continues to gain popularity. Consequently, more procedures are being performed with the patient supine. The approach often utilizes a special leg positioner to assist with femoral exposure. Although the supine position may seem to allow for a more reproducible pelvic position at the time of cup implantation, there is limited evidence as to the effects on pelvic tilt with such leg positioners. Furthermore, the DAA has led to increased popularity of specific softwares, ie. Radlink or JointPoint, that facilitate the intra-op analysis of component position from fluoroscopy images. The aim of this study was to assess the difference in cup orientation measurements between intra-op fluoroscopy and post-op CT. A consecutive series of 48 DAA THAs were performed by a single surgeon in June/July 2018. All patients received OPSTM pre-operative planning (Corin, UK), and the cases were performed with the patient supine on the operating table with the PURIST leg positioning system (IOT, Texas, USA). To account for variation in pelvic tilt on the table, a fluoroscopy image of the hemi-pelvis was taken prior to cup impaction, and the c-arm rotated to match the shape of the obturator foramen on the supine AP Xray. The final cup was then imaged using fluoroscopy, and the radiographic cup orientation measured manually using Radlink GPS software (Radlink, California, USA). Post-operatively, each patient received a low dose CT scan to measure the radiographic cup orientation in reference to the supine coronal plane.Introduction
Methods
It is not always clear why some patients experience recurrent dislocation following total hip arthroplasty (THA). In order to plan appropriate revision surgery for such patients, however, it is important to understand the specific biomechanical basis for the dislocation. We have developed a novel method to analyse the biomechanical profile of the THA, specifically to identify edge loading and prosthetic impingement, taking into account spinopelvic mobility. In this study we compare the results of this analysis in THA patients with and without recurrent dislocation. Post-operative CT scans and lateral standing and seated radiographs of 40 THA patients were performed, 20 of whom had experienced postoperative dislocation. The changes in pelvic and femoral positions on the lateral radiographs were measured between the standing and seated positions, and a 3D digital model was then generated to simulate the movement of the hip when rising from a chair for each patient. The path of the joint reaction force (JRF) across the acetabular bearing surface and the motion of the femoral neck relative to the acetabular margin were then calculated for this “sit-to-stand” movement, in order to identify where there was risk of edge loading or prosthetic impingement.Background
Methods
Appropriate femoral stem anteversion is an important factor in maintaining stability and maximizing the performance of the bearing after total hip replacement (THR). The anteversion of the native femoral neck has been shown to have a significant effect on the final anteversion of the stem, particularly with a uncemented femoral component. The aim of this study was to quantify the variation in native femoral neck anteversion in a population of patients requiring total hip replacement. Pre-operatively, 1215 patients received CT scans as part of their routine planning for THR. Within the 3D planning, each patient's native femoral neck anteversion, measured in relation to the posterior condyles of the knee, was determined. Patients were separated into eight groups based upon gender and age. Males and females were divided by those under 55 years of age, those aged 55 to 64, 65 to 74 and those 75 or older.Introduction
Methods
It is important to consider sagittal pelvic rotation when introducing
the acetabular component at total hip arthroplasty (THA). The purpose
of this study was to identify patients who are at risk of unfavourable
pelvic mobility, which could result in poor outcomes after THA. A consecutive series of 4042 patients undergoing THA had lateral
functional radiographs and a low-dose CT scan to measure supine
pelvic tilt, pelvic incidence, standing pelvic tilt, flexed-seated
pelvic tilt, standing lumbar lordotic angle, flexed-seated lumbar
lordotic angle, and lumbar flexion. Changes in pelvic tilt from
supine-to-standing positions and supine-to-flexed-seated positions
were determined. A change in pelvic tilt of 13° between positions was
deemed unfavourable as it alters functional anteversion by 10° and
effectively places the acetabular component outside the safe zone
of orientation.Aims
Patients and Methods
The pelvis moves in the sagittal plane during functional activity. These movements can have a detrimental effect on functional cup orientation. The authors previously reported that 17% of total hip replacement (THR) patients have excessive pelvic rotation preoperatively. This increased pelvic rotation could be a risk factor for instability and edge-loading in both flexion and/or extension. The aim of this study was to investigate how gender, age and lumbar spine stiffness affects the number of patients at risk of excessive sagittal pelvic rotation. Pre-operatively, 3428 patients had their pelvic tilt (PT) and lumbar lordotic angle (LLA) measured in three positions; supine, standing and flexed-seated, as part of routine planning for THR. The pelvic rotation from supine-to-standing and from supine-to-seated was determined from the difference in pelvic tilt measurements between positions. Lumbar flexion was determined as the difference between LLA standing and LLA when flexed-seated. Patients were stratified into groups based upon age, gender and lumbar flexion. The percentage of patients in each group with excessive pelvic rotation, defined by rotation ≥13° in a detrimental direction, was determined.Introduction
Method
The Intellijoint HIP system is a mini-optical navigation system designed to intraoperatively assist with cup orientation, leg length and offset in total hip replacement (THR). As with any imageless navigation system, acquiring the pelvic reference frame intraoperatively requires assumptions. The system does however have the ability to define the native acetabular orientation intra-operatively by registering 3-points along the bony rim. In conjunction with a pre-operative CT scan, the authors hypothesised that this native acetabular plane could be used as an intraoperative reference to achieve a planned patient-specific cup orientation. Thirty-eight THR patients received preoperative OPSTM dynamic planning (Optimized Ortho, Sydney). On the pre-operative 3D model of each patient's acetabulum, a 3-point plane was defined by selecting recognisable features on the bony rim. The difference in inclination and anteversion angles between this native 3-point reference plane and the desired optimal orientation was pre-operatively calculated, and reported to the surgeon as “adjustment angles”. Intraoperatively, the surgeon tried to register the same 3-points on the bony rim. Knowing the intraoperative native acetabular orientation, the surgeon applied the pre-calculated adjustment angles to achieve the planned patient specific cup orientation. All patients received a post-operative CT scan at one-week and the deviation between planned and achieved cup orientation was measured. Additionally, the cup orientation that would have been achieved if the standard Intellijoint pelvic acquisition was performed was retrospectively determined.Introduction
Method
Appropriate prosthetic alignment is an important factor in maintaining stability and maximising the performance of the bearing after total hip replacement (THR). With a cementless component, the anteversion of the native femur has been shown to influence the anteversion of the prosthetic stem. However, the extent to which anteversion of a cementless stem can be adjusted from the native anteversion has seldom been reported. The aim of this study was to investigate the difference between native and stem anteversion with two different cementless stem designs. 116 patients had 3-dimensional templating as part of their routine planning for THR (Optimized Ortho, Sydney). 96 patients from 3 surgeons (AS, JB, SM) received a blade stem (TriFit TS, Corin, UK) through a posterior approach. 18 patients received a fully HA-coated stem (MetaFix, Corin, UK) through a posterior approach by a single surgeon (WB). The anteversion of the native femoral neck was measured from a 3D reconstruction of the proximal femur. All patients received a post-operative CT scan which was superimposed onto the pre-op CT scan. The difference between native and achieved stem anteversion was then measured. As surgeons had differing philosophies around target stem anteversion, the differences amongst surgeons were also investigated.Introduction
Method
