INTRODUCTION. Poor acetabular cup orientation in total hip arthroplasty (THA) can cause dislocation and impingement, and lead to osteolysis (Little et al., 2009) and inflammatory soft tissue reactions (Haan et al., 2008). While the intrinsic accuracy of cup positioning in navigation is reported as low as 1° (Parratte et al., 2009), a large anterior pelvic tilt may lead to an offset of the same magnitude in the final cup anteversion (Wolf et al., 2005). The objectives of this study are to demonstrate feasibility of a new, non-invasive radiographic tool for accurate preoperative determination of a patient's specific pelvis angle, and intraoperative and postoperative assessment of the acetabular cup orientation with respect to boney landmarks. METHODS. The methodology stitches multiple radiographic views around the pelvis using a multi-planar radiography setup (Amiri et al., 2011) and reconstructs the reference boney landmarks and the acetabular cup in three dimensions using previously developed algorithms and software (Amiri et al., 2012). To validate the methodology, a Sawbone model of the pelvis and femur was implanted with a standard cementless metal-on-polyethylene THA, and was tracked and digitized by an Optotrak motion tracking system. Five radiographic views were acquired at the pubic tubercle (PT) and anterior-superior iliac spine (ASIS) levels (Views 1 to 5 in Fig 1). Imaging and analysis were repeated 10 times. Custom software (Joint 3D) was used to reconstruct the right and left PT and ASIS by fitting spheres to the corresponding pairs of images (Fig 1). The three-dimensional pose of the acetabular cup was reconstructed in the software by solving a back-projection equation of the elliptical shadow of the cup opening. Accuracies were measured as mean differences from the digitized references. A sample of the reconstructed graphical output for the anterior pelvic plane (APP) and the cup, in comparison to the digitized reference, is shown in Fig 2. Repeatability was estimated as standard deviation of the measures for the reconstructed locations of the boney landmarks and the APP (known as a standard reference plane for cup placement). RESULTS. Accuracy for the pelvis pose angles was <1.6°, with SD <0.8° (Fig 3). Pelvic tilt was the most accurate with accuracy of 0.1° and SD=0.4°. For the acetabular cup, accuracy was 2.5° or better, with SD <0.2°. Accuracies in the cup operative anteversion and inclination were 2.4° and 0.6°, with SD=0.4° and 0.9°, respectively. DISCUSSION. The measured accuracies were within an acceptable range, according to previous studies that recommended a 5° cut-off error for acetabular anteversion. The method shows accuracy and radiation dose advantages over current radiographic, fluoroscopic and computed tomography methods. These results suggest that the proposed method is feasible for assessing cup placement with reference to the functional and anatomical references. CONCLUSION. Use of this technique could improve acetabular cup placement and reduce the incidence of instability, wear and loosening, by providing tools to incorporate the individual's pelvic pose in preoperative planning of the surgery, and by serving as an accurate and reliable tool for intraoperative and postoperative assessment of the acetabular cup position

Introduction. Appropriate acetabular cup orientation is an important factor in reducing instability and maximising the performance of the bearing after Total Hip Arthroplasty (THA). However, postoperative analyses of two large cohorts in the US have shown that more than half of cups are malorientated. In addition, there is no consensus as to what inclination and anteversion angles should be targeted, with contemporary literature suggesting that the orientation should be customised for each individual patient. The aim of this study was to measure the accuracy of a novel patient specific instrumentation system in a consecutive series of 22 acetabular cups, each with a customised orientation. Methodology. Twenty-two consecutive total hip replacement patients were sent for Trinity Optimized Positioning System (OPS) acetabular planning (Optimized Ortho, Sydney). The Trinity OPS planning is a preoperative, dynamic analysis of each patient performing a deep flexion and full extension activity. The software calculates the dynamic force at the hip to be replaced and plots the bearing contact patch as it traces across the articulating surface. The software modelled multiple cup orientations and the alignment which best centralised the load was chosen by the surgeon from the preoperative reports. Once the target orientations had been determined, a unique patient specific guide was 3D printed and used intra-operatively with a laser guided system to achieve the planned alignment, Fig 1. All patients received a post-operative CT scan at 3 months and the radiographic cup inclination and anteversion was measured. The study was ethically approved by The Avenue Hospital Human Research Ethics Committee, Trial Number 176. Results. The mean planned radiographic inclination, reference to the Anterior Pelvic Plane (APP), was 42.8° (range 36.2° – 50.1°). The mean planned radiographic anteversion, reference to the APP, was 28.3° (range 19.4° – 37.0°). Only 23% of the planned orientations fell within Lewinnek's “safe zone”, taking into consideration that that this safe zone is not comparable to the coronal plane of radiographs. However, all 22 cups were planned within a range of 40° ± 10° of inclination and 25° ± 10° of anteversion, when referenced to the coronal plane when supine. The mean inclination difference between the planned and achieved orientations was −1.3° (range −7.6° – 9.2°). The mean anteversion difference was 1.2° (range −5.3° – 7.0°). The mean absolute difference was 4.2° for inclination (range 0.4° – 9.2°) and 3.6° for anteversion (range 0.6° – 7.0°). All 22 cups were within ±10° of their intended target orientation, Fig 2. All 22 cups were within the range of 40° ± 10° of inclination and 25° ± 10° of anteversion, when reference to the coronal plane when supine, Fig 3. Conclusions. These are the early results of a new technology for planning and delivering a customised acetabular cup orientation. We expect further improvements in accuracy with current developments. However, the results suggest that Trinity OPS is a simple way to achieve a patient-specific cup orientation, with accuracy comparable to imageless navigation

Optimal alignment of the acetabular cup component is crucial for good outcome of total hip arthroplasty [THA]. Increased accuracy of implant positioning may improve clinical outcome. To achieve this, patient specific instrumentation was developed. A patient-specific guide manufactured by 3D printing was designed to aid in positioning of the cup component with a pre-operatively defined anteversion and inclination angle. The guide fits perfectly on the acetabular rim. An alignment K-wire in a pre-operatively planned orientation is used as visual reference during cup implantation. Accuracy of the device was tested on 6 cadaveric specimens. During the experiment, cadavers were positioned for a THA procedure using a posterolateral approach. A normal-sized incision was made and approach used as in the conventional surgical procedure. The PSI was subsequently fitted onto the acetabular rim and secured into its unique position due to its patient specific design. The metallic pin was placed in a drill hole of the PSI. Post-operative CT image data of each acetabulum with the placed pin were transferred to Mimics and the 3D model was registered to the pre-operative one. The anteversion and inclination of the placed pin was calculated and compared to the pre-operatively planned orientation. The absolute difference in degrees was evaluated. A secondary test was carried out to assess the error during impaction while observing the alignment K-wire as a visual reference. In a laboratory setting, error during impaction with a visual reference of the K-wire was measured. Deviation from planning showed to be on average 1.04° for anteversion and 2.19° for inclination. By visually aligning the impactor with this alignment K-wire, the surgeon may achieve cup placement as pre-operatively planned. The effect of the visual alignment itself was also evaluated in a separate test-rig showing minimal deviations in the same range. The alignment validation test resulted in an average deviation of 1.2° for inclination and 1.4° for anteversion between the metallic alignment K-wire used as visual reference and the metallic K-wire impacted by the test subjects. The inter-user variability was 0.9° and 0.8° for anteversion and inclination respectively. The intra-user variability was 1.6° and 1.0° for anteversion and inclination respectively. Tests per test subject were conducted in a consecutive manner. We investigated the accuracy of two factors affecting accuracy in the cup insertion with PSI, i.e. accuracies of the errors of bony fitting and cup impaction. Since the accuracy of the major contributing factors to the overall accuracy of PSI for cup insertion with linear visual reference of a metallic K-wire was within the acceptable range of 2 to 3 degrees, we state that the PSI we have designed assists to achieve the preoperatively planned orientation of the cup and as such leads to the reduction of outliers in cup orientation. This acetabular cup orientation guide can transfer the pre-operative plan to the operating room

Achieving optimal acetabular cup orientation in Total Hip Replacement (THR) remains one of the most difficult challenges in THR surgery (AAOR 2013) but very little has been added to useful understanding since Lewinnek published recommendations in 1978. This is largely due to difficulties of analysis in functional positions. The pelvis is not a static reference but rotates especially in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic rotation have a substantial effect on the functional orientation of the acetabulum, not appreciated on standard radiographs [Fig1]. Studies of groups of individuals have found the mean pelvic rotation in the sagittal plane is small but large individual variations commonly occur. Posterior rotation, with sitting, increases the functional arc of the hip and is protective of a THR in regards to both edge loading and risk of dislocation. Conversely Anterior rotation, with sitting, is potentially hazardous. We developed a protocol using three functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair). Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane (defined by the line joining both anterior superior iliac spines and the pubic symphysis). In the supine position pelvic tilt was defined as the angle between a horizontal reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography. Proprietary software (Optimized Ortho, Sydney) based on Rigid Body Dynamics then modelled the patients’ dynamics through their functional range producing a patient-specific simulation which also calculates the magnitude and direction of the dynamic force at the hip and traces the contact area between prosthetic head/liner onto a polar plot of the articulating surface, Fig 2. Given prosthesis specific information edge-loading can then be predicted based on the measured distance of the contact patch to the edge of the acetabular liner. Delivery of desired orientation at surgery is facilitated by use of a solid 3D printed model of the acetabulum along with a patient specific guide which fits the model and the intra-operative acetabulum (with cartilage but not osteophytes removed) - an incorporated laser pointer then marks a reference point for the reamer and cup inserter to replicate the chosen orientation. Results and conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Spinal pathology is a potent “driver” of pelvic sagittal rotation, usually unrecognised on standard radiographs. Pre-operative patient assessment can identify potential orientation problems and even suitability for hard on hard bearings. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles. Post-operatively this technique can identify patient and implant factors likely to be causing edge loading leading to early failure in metal on metal bearings or squeaking in ceramic on ceramic bearings

Iliopsoas tendonitis after total hip arthroplasty (THA) can be a considerable cause of pain and patient dissatisfaction. The optimal cup position to avoid iliopsoas tendonitis has not been clearly established. Implant designs have also been developed with an anterior recess to avoid iliopsoas impingement. The purpose of this cadaveric study was to determine the effect of cup position and implant design on iliopsoas impingement.

Bilateral THA was performed on three fresh frozen cadavers using oversized (jumbo) offset head center revision acetabular cups with an anterior recess (60, 62 and 66 mm diameter) and tapered wedge primary stems through a posterior approach. A 2mm diameter flexible stainless steel cable was inserted into the psoas tendon sheath between the muscle and the surrounding membrane to identify the location of the psoas muscle radiographically. CT scans of each cadaver were imported in an imaging software. The acetabular shells, cables as well as pelvis were segmented to create separate solid models of each. The offset head center shell was virtually replaced with an equivalent diameter hemispherical shell by overlaying the outer shell surfaces of both designs and keeping the faces of shells parallel. The shortest distance between each shell and cable was measured. To determine the influence of cup inclination and anteversion on psoas impingement, we virtually varied the inclination (30°/40°/50°) and anteversion (10°/20°/30°) angles for both shell designs.

The CT analysis revealed that the original orientation (inclination/anteversion) of the shells implanted in 3 cadavers were as follows: Left1: 44.7°/23.3°, Right1: 41.7°/33.8°, Left2: 40/17, Right2: 31.7/23.5, Left3: 33/2908, Right3: 46.7/6.3. For the offset center shells, the shell to cable distance in all the above cases were positive indicating that there was clearance between the shells and psoas. For the hemispherical shells, in 3 out of 6 cases, the distance was negative indicating impingement of psoas. With the virtual implantation of both shell designs at orientations 40°/10°, 40°/20°, 40°/30° we found that greater anteversion helped decrease psoas impingement in both shell designs. When we analyzed the influence of inclination angle on psoas impingement by comparing wire distances for three orientations (30°/20°, 40°/20°, 50°/20°), we found that the effect was less pronounced. Further analysis comparing the offset head center shell to the conventional hemispherical shell revealed that the offset design was favored (greater clearance between the shell and the wire) in 17 out of 18 cases when the effect of anteversion was considered and in 15 out of 18 cases when the effect of inclinations was considered.

Our results indicate that psoas impingement is related to both cup position and implant geometry. For an oversized jumbo cup, psoas impingement is reduced by greater anteversion while cup inclination has little effect. An offset head center cup with an anterior recess was effective in reducing psoas impingement in comparison to a conventional hemispherical geometry. In conclusion, adequate anteversion is important to avoid psoas impingement with jumbo acetabular shells and an implant with an anterior recess may further mitigate the risk of psoas impingement.

In order to avoid complications of hip arthroplasty such as dislocation, impingement and eccentric liner wear accurate acetabular orientation is essential. The three-dimensional assessment of acetabular cup orientation using two-dimensional plain radiographs is inaccurate. The aim of this study was to develop a CT-based protocol to accurately measure postoperative acetabular cup inclination and anteversion establishing which bony reference points facilitate the most accurate estimation of these variables. An all-polyethylene acetabular liner was implanted into a cadaveric acetabulum. A conventional pelvic CT scan was performed and reformatted images created in both functional and anterior pelvic planes. CT images were transferred to a Freedom-Plus Graphics software package enabling an identical, virtual, three dimensional model of the cadaveric pelvis to be created. Using a computer interface this model could be ‘palpated’, bony landmarks accurately identified and definitive acetabular cup orientation established. Using original CT scans, acetabular cup inclination and anteversion were measured on five occasions by eight radiographers using differing predetermined bony landmarks as reference points. The intra- and inter-observer variation in measurement of acetabular cup orientation using varying bony reference points was assessed in comparison to the previously elucidated definitive cup position. Statistical analysis using appropriate ANOVA models was performed in order to assess the significance of the results obtained. Virtually derived definitive acetabular cup orientation was measured showing cup inclination and anteversion as 41.0 and 22.5 degrees respectively. Mean CT-based measurement of cup inclination and anteversion by eight radiographers were 43.1 and 20.8 degrees respectively. No statistically significant difference was found in intra- and inter-observer recorded results. No statistically significant differences were found when using different bony landmarks for the measurement of inclination and anteversion (p= 0.255 and 0.324 respectively). CT assessment of acetabular component inclination and anteversion is accurate, reliable and reproducible when measured using differing bony landmarks as reference points. We recommend measuring acetabular inclination and anteversion from the inferior acetabular wall/teardrop and posterior ischium respectively. The Perth CT hip protocol is easily reproducible in the clinical setting both in the routine assessment of hip arthroplasty patients and as research tool. In our unit its initial application will be to validate commercially available hip navigation systems

The goal of this study was to validate accuracy and reproducibility of a new 2D/3D reconstruction-based program called “HipRecon” for determining cup orientation after THA. “HipRecon” uses a statistical shape model based 2D/3D deformable registration technique that can reconstruct a patient-specific 3D model from a single standard AP pelvic X-ray radiograph. Required inputs include a digital radiograph, the pixel size, and the film-to-source distance. No specific calibration of the X-ray, or a CAD (computer-assisted design) model of the implant, or a CT-scan of the patient is required. Cup orientation is then calculated with respect to the anterior pelvic plane that is derived from the reconstructed 3D-model. The validation study was conducted on datasets of 29 patients (31 hips). Among them, there were 15 males and 14 females. Each dataset has one post-operative X-ray radiograph and one post-operative CT-scan. The post-operative CT scan for each patient was used to establish the ground truth for the cup orientation. Radiographs with deep centering (7 radiographs), or of pelvises with fractures (2 radiographs), or with both (1 radiograph), or of non-hemispherely shaped cup (1 radiograph) were assessed separately from the radiographs without above mentioned phenomena (18 radiographs) to estimate a potential influence on the 2D/3D reconstruction accuracy. To make the description easier, we denote those radiographs with above mentioned phenomena as non-normal cases and those without as normal cases. The cup anteversions and inclinations that were calculated by “HipRecon” were compared to the associated ground truth. To validate the reproducibility and the reliability, one observer conducted twice measurements for each dataset using “HipRecon”. The mean accuracy for the normal cases was 0.4° ± 1.8° (−2.6° to 3.3°) for inclination and 0.6° ± 1.5° (−2.0° to 3.9°) for anteversion, and the mean accuracy for the non-normal cases was 2.3° ± 2.4° (−2.1° to 6.3°) for inclination and 0.1° ± 2.8° (−4.6° to 5.1°) for anteversion. Comparing the measurement from the normal radiographs to those from the non-normal radiographs using the Mann-Whitney U-test, we found a significant difference in measuring cup inclination (p = 0.01) but not in measuring cup anteversion (p = 0.3). Bland-Altman analysis of those measurements from the normal cases indicated that no systematical error was detected for “HipRecon,” as the mean of the measurement pairs were spread evenly and randomly for both inclination and anteversion. “HipRecon” showed a very good reproducibility for both parameters with an intraclass correlation coefficient (ICC) for inclination of 0.98 (95% Confidence Limits (CL): 0.96–0.99) and for anteversion of 0.96 (95% CL: 0.91–0.98). Accurate assessment of the acetabular cup orientation is important for evaluation of outcome after THA, but the inability to measure acetabular cup orientation accurately limits one's ability to determine optimal cup orientations, to assess new treatment methods of improving acetabular cup orientation in surgery, and to correlate the acetabular cup orientation to osteolysis, wear, and instability. In this study, we showed that “HipRecon” was an accurate, consistent, and reproducible technique to measure cup orientation from post-operative X-ray radiographs. Furthermore, our experimental results indicated that the best results were achieved with the radiographs of non-fractured pelvises that included the anterior superior iliac spines and the cranial part of the non-fractured pelvis. Thus, it is recommended that these landmarks should be included in the radiograph whenever the 2D/3D reconstruction-based method will be used

Introduction. Acetabular cup orientation has been shown to be a factor in edge-loading of a ceramic-on-ceramic THR bearing. Currently all recommended guidelines for cup orientation are defined from static measurements with the patient positioned supine. The objectives of this study are to investigate functional cup orientation and the incidence of edge-loading in ceramic hips using commercially available, dynamic musculoskeletal modelling software that simulates each patient performing activities associated with edge-loading. Methodology. Eighteen patients with reproducible squeaking in their ceramic-on-ceramic total hip arthroplasties were recruited from a previous study investigating the incidence of noise in large-diameter ceramic bearings. All 18 patients had a Delta Motion acetabular component, with head sizes ranging from 40 – 48mm. All had a reproducible squeak during a deep flexion activity. A control group of thirty-six patients with Delta Motion bearings who had never experienced a squeak were recruited from the silent cohort of the same original study. They were matched to the squeaking group for implant type, acetabular cup orientation, ligament laxity, maximum hip flexion and BMI. All 54 patients were modelled performing two functional activities using the Optimized Ortho Postoperative Kinematics Simulation software. The software uses standard medical imaging to produce a patient-specific rigid body dynamics analysis of the subject performing a sit-to-stand task and a step-up with the contralateral leg, Fig 1. The software calculates the dynamic force at the replaced hip throughout the two activities and plots the bearing contact patch, using a Hertzian contact algorithm, as it traces across the articulating surface, Fig 2. As all the squeaking hips did so during deep flexion, the minimum posterior Contact Patch to Rim Distance (CPRD) can then be determined by calculating the smallest distance between the edge of the contact patch and the true rim of the ceramic liner, Fig 2. A negative posterior CPRD indicates posterior edge-loading. Results. The mean CPRD was significantly less in the squeaking group than the control group, −2.5mm and 2.9mm respectively, (p < 0.001), Fig 3. The mean pelvic tilt in the flexed seated position was 12.6° (range −13.5° to 30.3°) for the squeaking group and 5.1° (−9.8° to 26.4°) for the control group. Consequently, the mean functional cup anteversion at seat-off was significantly less in the squeaking group than the control group, 8.1° (−10.5° to 36.0°) and 21.1° (−1.9° to 38.4°) respectively (p < 0.001), Fig 3. There were 67% (12) of patients in the squeaking group that showed posterior edge-loading in the simulation compared to only 28% (10) in the control group that exhibited posterior edge-loading in the simulation. Conclusions. Acetabular cup orientation during activities associated with edge-loading are likely very different from those measured when supine. Patients with large anterior pelvic tilts during deep flexion activities might be more susceptible to posterior edge-loading and squeaking in ceramic-on-ceramic bearings, as a consequence of a significant decrease in cup anteversion. If these patients can be identified preoperatively, cup orientation and bearing choice could be customised accordingly to accommodate these individual motion patterns

Background. Acetabular cup malpositioning during total hip arthroplasty (THA) is known to lead to impingement, instability, wear-induced osteolysis, and increased rates of revision surgery. The purpose of this study was to independently evaluate the accuracy of acetabular cup orientation using a novel mechanical navigation device. Methods. Postoperative acetabular cup orientation was reviewed in 47 primary THAs using the HipSextant mechanical navigation device. Angles were measured with a validated two-dimensional/three-dimensional matching application. An outlier was defined as +/− 10 degrees outside of the preoperative plan for inclination and anteversion. Results. Of the 47 THAs, 47 (100%) met our inclination target, 46 (98%) met our anteversion target, and 46 (98%) simultaneously met both targets. There were no outliers for inclination and one outlier (−12.7°) for anteversion (Figure 1). The absolute errors for both inclination and anteversion were significantly less than 10° (p<0.001). There were no intraoperative complications related to the use of this mechanical navigation system. Conclusions. The HipSextant reliably navigates acetabular cup inclination and anteversion according to a preoperative plan that is individualized for each patient. This should decrease the risk of postoperative complications related to acetabular component malposition during THA. Further research is warranted to assess the clinical impact of reducing outliers using this device

Component placement and the individual's functional posture play key roles in mechanical complications and hip dysfunction after total hip arthroplasty (THA). The challenge is how to measure these. X-rays lack accuracy and CT scans increase radiation dose. A newer imaging modality, EOSTM, acquires low-dose, simultaneous, perpendicular anteroposterior and lateral views while providing a global view of the patient in a functional standing or sitting position, leading to a 3D reconstruction for parameter calculation. The purpose of the present study was to develop an approach using the EOS system to compare patients with good versus poor results after THA and to report our preliminary experiences using this technique. A total of 35 patients were studied: 17 with good results after THA (G-THA), 18 with poor results (P-THA). The patients were operated on or referred for follow-up to a single expert surgeon, between 2001 and 2011, with a minimum follow-up of at least two years. Acetabular cup orientation differed significantly between groups. Acetabular version relative to the coronal plane was lower in P-THA (32°±12°) compared to G-THA (40°±9°) (p=0.02). There was a strong trend towards acetabular cup inclination relative to the APP being higher in P-THA (45°±9°, compared to 39°±7°; p=0.07). Proportions of P-THA vs. G-THA patients with cup orientation values higher or lower than 1 SD from the overall mean differed significantly and substantially between groups. All revision cases had a least four values outside 1 SD, including acetabular cup orientation, sagittal pelvic tilt, sacral slope, femoral offset and neck-shaft angle. This is the first study to our knowledge to provide acetabular, pelvic and femoral parameters for these two groups and the first to provide evidence that a collection of high/low parameters may together contribute to a poor result. The results show the importance of acetabular component placement, in both inclination and version and the importance of looking at individuals, not just groups, to identify potential causes for pain and functional issues. With the EOS system, a large cohort of individuals can be studied in the functional position relatively quickly and at low dose. This could lead to patient-specific guidelines for THA planning and execution

Introduction. Accurate and reproducible cup positioning is one the most important technical factors that affects outcomes of total hip arthroplasty (THA). Although Lewinnek's safe zone is the most accepted range for anteversion and abduction angles socket orientation, the effect of fixed lumbosacral spine on pelvic tilt and obliquity is not yet established. Questions:. What is the change in anteversion and abduction angle from standing to sitting in a consecutive cohort of patients undergoing THA?. What is the effect of fixed and flexible spinal deformities on acetabular cup orientation after THA?. Material and Methods. Between July 2011 and October 2011, 68 consecutive unilateral THAs were implanted in 68 patients with a mean age of 71 ± 6 years old. Radiographic evaluation included standing anteroposterior (AP) and lateral pelvic radiographs, and sitting lateral pelvic radiograph, measuring lumbosacral angle (LSA), sacral angle (SA), and sagittal pelvic tilt angle (SPTA). Computer generated 3D pelvis models were used to analyze the correlation between different pelvic tilts and acetabular cup orientation in abduction and anteversion. Results. The mean standing STPA was 3.7º of anterior tilt (range: −9º of anterior tilt to 25º of posterior tilt). The mean SPTA in sitting was −17.7º of posterior tilt (range: −38º of posterior tilt to 7º of anterior tilt). In a fixed spinal deformity (54%) the SPTA was significantly smaller compared to the flexible pelvis group (10º versus 30.9º, p=0.0001). Flexible pelvises (46%) had a posterior tilt from standing to sitting resulting in increased anteversion. Overall, mean change in LSA and SA from standing to sitting was 22.5º and 20.2º, respectively. The mean post-operative functional anteversion and abduction angles were 19.2º and 42.1º, respectively. In the virtual 3D pelvic models, when the abduction angle was between 40 and 45 degrees, anteversion changed of 0.75 degrees for 1 degree of change of pelvic tilt. Discussion. There is a significant change in pelvic tilt from standing to sitting, especially in patients with flexible spines, where the functional anteversion increases with sitting. Patients with a fixed pelvis have significantly less change in sagittal tilt and therefore less change in anteversion from standing to sitting position. Care should be taken to adjust cup positioning in fixed spinal deformity

Introduction. 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. Methods. 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 (LL. stand. – LL. seated. ) ≤ 20°, PI ≤ 41°, and sagittal spinal deformity (PI – LL. stand. 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. Results. Median supine cup inclination for the dislocating cohort was 43° (range, 26°- 58°). Median cup anteversion was 23° (range, 7° − 40°) for the dislocating cohort. 65% of the dislocating patients had socket positions within the Lewinnek safe zone (Figure 1). Standing PT (-10° v −1°), lumbar flexion (20° v 45°), and PI-LL mismatch (12° v −1°) were all significantly different (p < 0.001) in the dislocating group compared to the stable THA population (Figure 2). There was no difference in PI between the dislocating group and the stable THA population (58° v 56° respectively, p = 0.33), with the numbers available. 80% of the dislocating patients had one or more of the 3 statistically significant risk factors, compared to only 24% of the stable THA population. Conclusion. Excessive standing posterior pelvic tilt, low lumbar flexion and a severe SSD are highly prevalent in unstable THAs. Pre-op screening for these parameters may reduce the prevalence of dislocation. For any figures or tables, please contact the authors directly

Introduction & aims. 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, OPS. TM. (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 OPS. TM. . Method. Between January 4. th. 2016 and December 20. st. 2017, a consecutive series of 841 OPS. TM. cementless 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. Results. There were 5 revisions: . a periprosthetic femoral fracture at 1-month post-op in a 70F. a ceramic head fracture at 12-months post-op in a 59M. a femoral stem loosening at 7-months post-op in a 58M. a femoral stem loosening at 16-months post-op in a 64M. an anterior dislocation in a 53M, that was revised 9 days after the primary procedure. CT analysis, prior to revision surgery, revealed acetabular cup orientation of 46°/31° (inclination/anteversion) and femoral stem anteversion of 38°. Conclusions. These preliminary findings suggest the OPS. TM. dynamic planning and delivery system provides good early results, with a low rate of revision for dislocation. Limitations of the study will be discussed

Introduction. Most of studies on Total Hip Arthroplasty (THA) are focused on acetabular cup orientation. Even though the literature suggests that femoral anteversion and combined anteversion have a clinical impact on THA stability, there are not many reports on these parameters. Combined anteversion can be considered morphologically as the addition of anatomical acetabular and femoral anteversions (Anatomical Combined Anatomical Anteversion ACA). It is also possible to evaluate the Combined Functional Anteversion (CFA) generated by the relative functional position of femoral and acetabular implants while standing. This preliminary study is focused on the comparison of the anatomical and functional data in asymptomatic THA patients. Material and methods. 50 asymptomatic unilateral THA patients (21 short stems and 29 standard stems) have been enrolled. All patients underwent an EOS low dose evaluation in standing position. SterEOS software was used for the 3D measurements of cup and femur orientation. Cup anatomical anteversion (CAA) was computed as the cup anteversion in axial plane perpendicular to the Anterior Pelvic Plane. Femoral anatomical anteversion (FAA) was computed as the angle between the femoral neck axis and the posterior femoral condyles in a plane perpendicular to femoral mechanical axis. Functional anteversions for the cup (CFA) and femur (FFA) were measured in the horizontal axial patient plane in standing position. Both anatomical and functional cumulative anteversions were calculated as a sum. All 3D measures were evaluated and compared for the repeatability and reproducibility. Statistical analysis used Mann-Whitney U-test considering the non-normal distribution of data and the short number of patients (<30 for each group). Results. Functional cumulative anteversion was significantly higher than anatomical cumulative anteversion for all groups (p<0.05). No significant difference could be noted between the cases according to the use of short or standard stems. Conclusion. This study shows the difference of functional implant orientation as compared to the anatomical measurements. This preliminary study has limitations. First the limited sample of patients. Then this series only includes asymptomatic subjects. Nevertheless, this work focused on the feasibility of the measurements shows the potential interest of a functional analysis of cumulated anteversion. Standing position influences the relative position of THA implants according to the frontal and sagittal orientation of the pelvis. The relevance of these functional measurements in instability cases must be demonstrated, especially in patients with anterior subluxation in standing position which is potentially associated with pelvic adaptative extension. Further studies are needed for the feasibility of measurements on EOS images in sitting position and their analysis in case of instability. For any figures or tables, please contact authors directly

Introduction. Accurate acetabular cup orientation could lead to successful surgical results in total hip arthroplasty (THA). We introduce a novel CT-based three-dimensional (3D) planning system, HipCOMPASS (Fig.1) and TARGET (Fig.2), which enable to design suitable alignment not only cup also surgical devices calculatingly, according to each pelvic inclination. Patients and Methods. We performed THA in 45 hips in 43 patients (female 37 and 6 men) between April 2014 and October 2015. Average age were 68 years old. THA operation was based on each parameter of the cup and device, providing a preoperative planning by ZedView system. HipCOMPASS and TARGET is linked with ZedView software, which is simultaneously calibrated adjustable parameters on this devices. Cup alignment was assessed by ZedView as well. Results. The differences of component alignment from the preoperative planning were shown in Tables. Conclusion. HipCOMPASS and TARGET might be more accurate than conventional method and more accessible system than navigation system in THA

Introduction. Accurate acetabular cup orientation could lead to successful surgical results in total hip arthroplasty (THA). We introduce a novel CT-based three-dimensional (3D) planning system, HipCOMPASS (Fg.1) and TARGET (Fig.2), which enable to design suitable alignment not only cup also surgical devices calculatingly, according to each pelvic inclination. Patients and methods. We performed THA in 13 patients (10 female and 3 men) between September 2014 and April 2014. Average age were 67 years old. THA operation was based on each parameter of the cup and device, providing a preoperative planning by ZedView system. HipCOMPASS and TARGET is linked with ZedView software, which is simultaneously calibrated adjustable parameters on this devices. Cup alignment was assessed by ZedView as well. Result. The differences of component alignment from the preoperative planning were shown in table. Conclusion. HipCOMPASS and TARGET might be more accurate than conventional method and more accessible system than navigation system in THA

Acetabular cup placement in total hip replacement surgery is often difficult to assess, especially in the lateral position and using the posterior approach. On table control X-Rays are not always accessible, especially in the government sector. Conventional techniques and computer assisted surgery (CAS), are currently the two most popular methods for proper placement of the acetabular cup in Lewinnek's safe zone of orientation (anteversion 15°–10° and lateral inclination 40°±10°). We developed a simple way to get accurate cup placement using Smartphone technology. Methods:. A spirit level application was downloaded to the Smartphone. The acetabulum inclination was measured on the pre-operative X-Rays. The phone is placed in a sterile bag and then used intra-operatively, to measure and set our acetabular cup orientation to our pre-operative measurements. The inclination level was measured before and after final placement of the acetabular cup. This was compared to the acetabular cup inclination in our post-operative X-Rays. Results:. In our series of 50 cup placements we found high accuracy. The results show less than 5° deviation between our pre-, intra- and post-operative measurements. Conclusions:. Smartphone technology proves to be good alternative to conventional methods and CAS, to improve Acetabular Cup placement in Total Hip Arthroplasty

INTRODUCTION. Femoral stem impingement can damage an acetabular liner, create polyethylene wear, and potentially lead to dislocation. To avoid component-to-component impingement, many surgeons aim to align acetabular cups based on the “Safe Zone” proposed by Lewinnek. However, a recent study indicates that the historical target values for cup inclination and anteversion defined by Lewinnek et al. may be useful but should not be considered a safe zone. The purpose of this study was to determine the effect of altering femoral head size on hip range-of-motion (ROM) to impingement. METHODS. Ten healthy subjects were instrumented and asked to perform six motions commonly associated with hip dislocation, including picking up an object, squatting, and low-chair rising. Femur-to-pelvis relative motions were recorded throughout for flexion/extension, abduction/adduction, and internal/external rotation. A previously reported custom, validated hip ROM three-dimensional simulator was utilized. The user imports implant models, and sets parameters for pelvic tilt, stem version, and specific motions as defined by the subjects. Acetabular cup orientations for abduction and anteversion combinations were chosen. The software was then used to compute minimum clearances or impingement between the components for any hip position. Graphs for acetabular cup abduction vs. anteversion were generated using a tapered wedge stem with a 132º neck angle, a stem version of 15°, and a pelvic tilt of 0°. The only variable changed was femoral head size. Head sizes reviewed were 32mm, 36mm, and a Dual-Mobility liner with an effective head size of 42mm. All femoral head sizes can be used with a 50mm acetabular cup. RESULTS. We found that the “Safe Zone” varies considerably depending on the size of the femoral head used for all subjects. A typical plot illustrating the ROM to impingement is presented in Figures 1a-1c. The area to the left of each curve represents an impingement zone for that motion, and to the right, a non-impingement zone. In all cases the non-impingement area is smaller than the Lewinnek safe zone. Motions like picking up an object and squatting had the greatest influence on impingement. CONCLUSIONS. The true acetabular target for impingement-avoidance motion is much smaller than previously believed and identifies the need to take into account the size of the femoral head to be used. This may explain why approximately 70% of dislocations have been reported to be found even when cups were placed within the Lewinnek safe zone. Certain activities, such as picking up an object and squatting reduce the size of the safe zone. This study supports the need for better patient planning and intraoperative execution for placement of the acetabular component

Introduction. There is increasing interest in the functional positions the pelvis assumes with activities of daily living and its effect on acetabular cup orientation. A number of systems are commercially available to assess these movements, and attempt to position the acetabular component of a total hip replacement in a patient specific safe zone. However, these functional positions are assessed pre operatively when the patient still has the arthritis which may affect the range of movement of the hips, and thus affect the functional position of the pelvis. Obviously the planned acetabular position must take into account any changes in the functional movement of the pelvis as a result of the surgery. Ishida et al showed that a pelvis with more than a 10° anterior tilt when standing can be expected to correct towards neutral by 12 months post-surgery. However many of Ishida's cases were dysplastic. Hip arthritis in the Caucasian population is far less likely due to dysplasia and this may affect these pelvic tilt changes post-operatively. Methods. 120 patients who underwent total hip replacement by two surgeons through a posterior approach had had their acetabular planning based on functional imaging according to the Optimized Ortho Protocol (Optimized Ortho, Sydney Australia). They were re-assessed at 12 months post-surgery to determine the changes in their functional pelvic tilts. The Optimized Ortho protocol includes lateral radiographs with the patient standing, sitting forward about to lift off a seat, stepping up with the contralateral leg and a limited supine CT. The functional views are designed to display common functional activities. Results. There was minimal change in pelvic position post-operatively when supine. Patients with a significant anterior tilt when standing tended to revert to a more neutral position. Moreover, patients with a significant posterior tilt also tended to correct towards neutral when standing. The seated forward positions changed from pre to post surgery. Those patients who has a large seated posterior pelvic rotation, corrected significantly towards neutral post operation. Conclusions. These predicted standing changes are similar to those seen by Ishida and are important for planning patient specific positioning of acetabular components. There are no previous reports on the changes in forward sitting position. Confounding contra-lateral issues need to be taken into account when planning these predicted changes

INTRODUCTION. Acetabular cup malpositioning has been implicated in instability and wear-related complications after total hip arthroplasty. Although computer navigation and robotic assistance have been shown to improve the precision of implant placement, most surgeons use mechanical and visual guides to place acetabular components. Authors have shown that, when using a bean bag positioner, mechanical guides are misleading as they are unable to account for the variability in pelvic orientation during positioning and surgery. However, more rigid patient positioning devices may allow for more accurate free hand cup placement. To our knowledge, no study has assessed the ability of rigid devices to afford surgeons with ideal pelvic positioning throughout surgery. The purpose of this study is to utilize robotic-arm assisted computer navigation to assess the reliability of pelvic position in total hip arthroplasty performed on patients positioned with rigid positioning devices. METHODS. 100 hips (94 patients) prospectively underwent total hip Makoplasty in the lateral decubitus position from the posterior approach; 77 stabilized by universal lateral positioner, and 23 by peg board. After dislocation but prior to reaming, one fellowship trained arthroplasty surgeon manually placed the robotic arm parallel to both the longitudinal axis of the patient and the horizontal surface of the operating table, which, if the pelvis were oriented perfectly, would represent 0 degrees of anteversion and 0 degrees of inclination. The CT-templated computer software then generated true values of this perceived zero degrees of anteversion and inclination based on the position of the robot arm registered to a preoperative pelvic CT. Therefore, variations in pelvic positioning are represented by these robotic navigation generated values. To assure the accuracy of robotic measurements, cup anteversion and inclination at times of impaction were recorded and compared to those calculated via the trigonometric ellipse method of Lewinnek on standardized 3 months postoperative X-rays. RESULTS. Mean alteration in anteversion and inclination values were 1.7 degrees (absolute value 5.3 degrees, range −20 – 20 degrees) and 1.6 degrees (absolute value 2.6 degrees, range −8 – 10 degrees) respectively. 22% of anteversion values were altered by >10 degrees; 41% by > 5 degrees. There was no difference between positioners (p=0.36) and regression analysis revealed that anteversion differences were correlated with BMI (p=0.02). Robotic navigation acetabular cup anteversion (mean 21.8 degrees) was not different from postoperative X-ray anteversion (mean 21.9 degrees)(p=0.50), nor was robotic navigation acetabular cup inclination (mean 40.6 degrees) different from postoperative X-ray inclination (mean 40.5 degrees)(p=0.34). DISCUSSION AND CONCLUSION. Rigid pelvic positioning devices present 5 to 20 degrees of variability in acetabular cup orientation, particularly with regards to anteversion. Compounding this with 20 degree safe zones and prior author demonstrations that human error is prone to 10 degrees of anteversion inaccuracy in a fixed pelvis model, there is a clear need to pay particular attention to anatomic landmarks or computer assisted techniques to assure accurate acetabular cup positioning. Patient positioning by itself should not be trusted