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

Dislocation is one of the most common complications in total hip arthroplasty (THA) and is primarily driven by bony or prosthetic impingement. The aim of this study was two-fold. First, to develop a simulation that incorporates the functional position of the femur and pelvis and instantaneously determines range of motion (ROM) limits. Second, to assess the number of patients for whom their functional bony alignment escalates impingement risk. 468 patients underwent a preoperative THA planning protocol that included functional x-rays and a lower limb CT scan. The CT scan was segmented and landmarked, and the x-rays were measured for pelvic tilt, femoral rotation, and preoperative leg length discrepancy (LLD). All patients received 3D templating with the same implant combination (Depuy; Corail/Pinnacle). Implants were positioned according to standardised criteria. Each patient was simulated in a novel ROM simulation that instantaneously calculates bony and prosthetic impingement limits in functional movements. Simulated motions included flexion and standing-external rotation (ER). Each patient's ROM was simulated with their bones oriented in both functional and neutral positions. 13% patients suffered a ROM impingement for functional but not neutral extension-ER. As a result, 48% patients who failed the functional-ER simulation would not be detected without consideration of the functional bony alignment. 16% patients suffered a ROM impingement for functional but not neutral flexion. As a result, 65% patients who failed the flexion simulation would not be detected without consideration of the functional bony alignment. We have developed a ROM simulation for use with preoperative planning for THA surgery that can solve bony and prosthetic impingement limits instantaneously. The advantage of our ROM simulation over previous simulations is instantaneous impingement detection, not requiring implant geometries to be analysed prior to use, and addressing the functional position of both the femur and pelvis

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

Postoperative dislocation following total hip arthroplasty (THA) remains a significant concern with a reported incidence of 1% to 10%. The risk of dislocation is multifactorial and includes both surgeon-related (i.e. implant position, component size, surgical approach) and patient-related factors (i.e. gender, age, preoperative diagnosis, neurologic disorders). While the majority of prior investigations have focused on the importance of acetabular component positioning, recent studies have shown that approximately 60% of “dislocators” following primary THA have an acceptably aligned acetabular component. Therefore, the importance of the relationship between the spine and pelvis, and its impact on functional component position has gained increased attention. Kanawade and Dorr et al. have shown patients can be categorised into having a stiff, normal, or hypermobile pelvis based on their change in pelvic tilt when moving from the standing to seated position. The degree of change in functional position of both the acetabular and femoral components is impacted by the degree of pelvic motion each patient possesses. In the “normal” pelvis, as a patient moves from the standing to seated position the pelvis typically tilts posteriorly, thus increasing the functional anteversion of the acetabular component. However, patients with lumbar degeneration or spine pathology often have a decrease in posterior pelvic tilt in the seated position, thus potentially increasing their risk of dislocation. Bedard et al. noted an 8.3% dislocation risk in patients with a spinopelvic fusion after THA vs. 2.9% in those without. There is the potential that preoperative, dynamic imaging can be used to predict the ideal component position for each individual patient undergoing THA. However, this assumes that a patient's preoperative pelvic motion will be the same following implantation of a total hip prosthesis, and that a patient's pelvic motion will remain consistent over time postoperatively. A recent study has shown that the impact of THA on pelvic motion can be highly variable, thus potentially limiting the utility of preoperative dynamic imaging in predicting a patient's ideal component position. Future investigations must focus on preoperative factors that can be used to predict postoperative pelvic motion and how pelvic motion changes over time following implantation of a total hip arthroplasty

Total hip replacement is among the most successful interventions in medicine and has been termed “The Operation of the Century”. Most major problems have been solved including femoral fixation, acetabular fixation, and wear. With a success rate of over 95% at 10 years in both hip and knee arthroplasty in a number of studies, the question remains as to whether the current status quo is optimal or acceptable. The literature, however, reports are from centers that represent optimised results and registry data, including the Medicare database, indicates that substantial short-term problems persist. The major issue is the variability in the performance of the procedure. The inability to consistently position components, particularly the acetabular component, results in major problems including instability and limb length discrepancy. A report by Malchau, et al. reveals that even among the best surgeons, optimal acetabular component positioning is only achieved 50% of the time. The penalty for missing the target is increased incidence of instability, increased wear rate, and diminished function due to restricted motion. Complications are related to position and a major potential explanation is the impact of patient position. Traditional imaging presents a two-dimensional rather than three-dimensional view of the patient and the patient is in a supine, non-functional position at the time that imaging is performed. Adverse events attributed to malposition, however, occur in functional positions and there is evidence that the orientation of the pelvis changes from the supine position at which imaging is performed. This topic has been studied extensively on three continents and the consensus is that the pelvis shifts on the order of 30–40 degrees from the supine to standing and sitting and furthermore, the acetabular component position changes proportionally with the rotation of the pelvis that occurs. How do we incorporate this information into imaging arthroplasty patients? This would require imaging the entire body, acquiring AP and lateral images simultaneously so that 3D imaging can be performed, performing imaging in a functional position (standing or sitting) and optimally at a lower radiation dose since these patients have repeated images and therefore a cumulative radiation dose over their lifetime. This technology was FDA approved for use in the hip and knee in 2011 and pilot studies have been performed at Washington University School of Medicine in St. Louis to validate the number of the hip and knee arthroplasty applications. In conclusion, weightbearing and rotation have substantial impact on the standard measurements obtained before and after hip and knee arthroplasty. These differences in measurements between supine, sitting, and standing as well as correction for rotation may explain the lack of a stronger correlation between component position and a variety of complications that are observed such as variability in wear rates as well as instability. In knee arthroplasty, the change in mechanical axis that occurs from restoring all of patients to a neutral mechanical axis may explain some of the persistent pain and dissatisfaction that has been recently been reported at a relatively high percentage of knee arthroplasty patients. Because of the numerous potential clinical implications of three-dimensional weightbearing imaging, it is likely that the future of arthroplasty imaging will focus on functional three-dimensional imaging of the patient

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. Deciding the acetabular cup inclination and anteversion is an important step in total hip arthroplasty. Despite numerous studies focusing on enhancement of precise positioning into anatomical safe zone, problem remains regarding which is the “optimal anteversion” and what is the proper anatomical reference during the surgery. Objectives. The purpose of this study is to evaluate pelvic tilt angle measured in standing lateral view of pelvis in patients with hip osteoarthritis, and to find out the correlations between pelvic tilt angle (on Lewinnek anterior pelvic plane) and optimal anteversion position in total hip arthroplasty surgery. Results. The average pelvic tilt angle is 8.79 degree with standard deviation 8.25 degree. There have no statistically significant difference between the pelvic tilt angles of male and female patients, or patients received total hip arthroplasty and patients did not received surgery. The pelvic tilt angle significantly greater in patients older than 60 years old compared with patients younger than 60 years old (12 degree Vs 4 degree, p<0.005). Conclusions. There are large variations in the pelvic AP tilting between individuals, and the posterior tilting of pelvis increased with aging. Our findings suggested that instead of body axis measured when patient is in decubitus position on the table, cup positioning during total hip arthroplasty should be based on the functional position when patients is in upright position. The difference between functional position and bony axis might increase with age; hence increase the risk of over anteversion in cup positioning. This might lead to impingement between cup and femur prosthesis and cause early failure or dislocation. While positioning the patient using lateral position, surgeons should pay attention to anterior pelvic plane and pelvic tilt angle (taking from lateral standing position) for estimation of anteversion of cup

Malorientation of the acetabular cup in Total Hip replacement (THR) may contribute to premature failure of the joint through instability (impingement, subluxation or dislocation), runaway wear in metal-metal bearings when the edge of the contact patch encroaches on the edge of the bearing surface, squeaking of ceramic-ceramic bearings and excess wear of polyethylene bearing surfaces leading to osteolysis. However as component malorientation often only occurs in functional positions it has been difficult to demonstrate and often is unremarkable on standard (usually supine) pelvic radiographs. The effects of spinal pathology as well as hip pathology can cause large rotations of the pelvis in the sagittal plane, again usually not recognized on standard pelvic views. While Posterior pelvic 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. 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. Given prosthesis specific information edge-loading can then be predicted based on the measured distance of the edge of the contact patch to the edge of the acetabular bearing. 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 can be an insidious “driver” of pelvic rotation, in some cases causing sagittal plane spinal imbalance or changes in orientation of previously well oriented acetabular components. Squeaking of ceramic on ceramic bearings appears to be multi factorial, usually involving some damage to the bearing but also usually occurring in the presence of anterior or posterior edge loading. Often these components will appear well oriented on standard views [Fig 1]. Runaway wear in hip resurfacing or large head metal-metal THR may be caused by poor component design or manufacture or component malorientation. Again we have seen multiple cases where no such malorientation can be seen on standard pelvic radiographs but functional studies demonstrate edge loading which is likely to be the cause of failure [Fig 2]. Clinical examples of all of these will be shown

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

Introduction. Literature describes pelvic rotation on lateral X rays from standing to sitting position. EOS full body lateral images provide additional information about the global posture. The projection of the vertical line from C7 (C7 VL) is used to evaluate the spine balance. C7 VL can also measure pelvic sagittal translation (PST) by its horizontal distance to the hip center (HC). This study evaluates the impact of a THA implantation on pelvic rotation and sagittal translation. Materials and Method. Lumbo-pelvic parameters of 120 patients have been retrospectively assessed pre and post- operatively on both standing and sitting acquisitions (primary unilateral THA without complication). PST is zero when C7VL goes through the center of the femoral heads and positive when C7VL is posterior to the hips' center (negative if anterior). Three subgroups were defined according to pelvic incidence (PI): low PI <45°, 45°<normal PI<65° or high PI>65°. Results. Pre-operatively PST standing was −0.9 cm (SD 4.5; [−15.1 to 7.2]) and PST sitting was 1.3cm (SD 3.3; [−7.7 to 11.8]). The overall mean change from standing to sitting was 2.2 cm ([−7.2 to 17.4]) (p<0.05). Post-operatively PST standing was 0.2 cm (SD 4.7; [−17 to 8.1]) and PST sitting was 1.4cm (SD 3.5; [−7.3 to 10.4]). The overall mean change from standing to sitting was 1.2 cm ([−14.2 to 22.4]) (p<0.05). In low PI group pre and post-operatively, PST increased significantly from standing to sitting (p<0.05; with HC going anterior to C7VL). When comparing pre and post operative changes, standing PST significantly increased (p=0.001). Pre to postoperative PST variation (sitting-standing) decreased significantly (p=0,01). In normal PI group pre-operatively, PST increased from standing to sitting (p=0.004). When comparing pre and postoperative changes, PST increased (p=0.006). Pre to postoperative PST variation (sitting-standing) decreased significantly (p=0,04). In high PI group pre and post operatively, PST increased from standing to sitting (p=0.034) while there are no significant changes from pre to post-operative status in standing and in sitting. Discussion. Anteroposterior pelvic tilt is not the only adaptation strategy for postural changes from standing to sitting positions. Anteroposterior pelvic translation (quantified by PST) is an important adaptation mechanism for postural changes. Comparison of pre and post-operative values of PST points out the importance of pelvic translation for low and standard PI patients after THA. The anteroposterior translation appears to change significantly in different functional positions pre and post operatively. This is an important variable to consider when assessing the patients' posture change or investigating the causes of the hip dislocation after total hip arthroplasty or spinal fusion. Conclusion. Pelvic translation must be considered as a significant mechanism of adaptation after THA. Further studies are needed to study the impact on subluxation or dislocation

Sagittal pelvic tilt (PT) has been shown to effect the functional position of acetabular components in patients with total hip replacements (THR). This change in functional component position may have clinical implications including increased likelihood of wear or dislocation. Surgeons can use computer-assisted navigation intraoperatively to account for a patient's pelvic tilt and to adjust the position of the acetabular component. However, the accuracy of this technique has been questioned due to the concern that PT may change after THR. The purpose of this study was to measure the change in PT after THR, and to determine if preoperative clinical and radiographic parameters can predict PT changes after THR. 138 consecutive patients who underwent unilateral THR by one surgeon received standing bi-planar lumbar spine and lower extremity radiographs preoperatively and six weeks postoperatively. Patients with prior contralateral THR, conversion THR and instrumented lumbosacral fusions were excluded. PT and pelvic incidence (PI) were measured preoperatively for each patient, and PT was measured on the postoperative imaging. A negative value for PT indicated posterior pelvic tilt. Patient demographics were collected from the chart. Average age was 56.8±10.9 years, average BMI was 28.3±6.0 kg/m2, and 67 patients (48.6%) were female. Mean preoperative pelvic tilt was 0.6°±7.3° (range: −19.0° to 17.9°). We found greater than 10° of sagittal PT in 23 out of 138 (16.6%) patients in this sample. Mean post-operative pelvic tilt was 0.3°±7.4° (range: −18.4° to 15.0°). Mean change in pelvic tilt was −0.3°±3.6° (range: −9.6° to 13.5°). PT changed by less than 5° in 119 of 138 patients (86.2%). The mean difference in pre-operative and post-operative PT is not statistically significant (p = 0.395). Pre-operative PT was strongly correlated with post-operative PT (r2 = 0.88, p = 0.0001) (Figure 1). There was not a statistically significant relationship between PI and change in PT (r2 = −0.16, p = 0.06). In conclusion, based on the variability in pelvic tilt in this study population and the relatively small change in pelvic tilt following THA tilt-adjustment of the acetabular component position based on standing pre-operative imaging is likely to be of benefit in the majority of patients undergoing navigated THA. However, we have been unable to predict the relatively rare occurrence of a large change in pelvic tilt, which would confound tilt-adjusted component position

Introduction. Femoral stem anteversion after total hip arthroplasty (THA) has always been assessed using CT scan in supine position. In this study, we evaluated the anteversion of the femoral prosthesis neck in functional standing position using EOS® technology with repeatability and reproducibility of the measurements. The data obtained were compared with conventional anatomic measurements. Materials and Methods. We measured the anteversion of the femoral prosthesis neck in 45 consecutive patients who had THA performed in nine hospitals. All measurements were obtained using the EOS® imaging system with patients in comfortable standing position. The orientation of the final vector representing the femoral neck was measured on 3-dimensional reconstructions. The anatomic femoral anteversion was calculated as in a transverse plane relative to the scanner and to the plane of the reconstructed bicondylar femoral segment (femoral prosthesis neck against the femoral condyles). Functional femoral anteversion (FFA) was measured in the horizontal plane relative to the frontal plane of the patient through the center of two femoral heads. FFA embodies true anteversion of the femoral prosthesis neck relative to the pelvis, representing the combined lower extremity anteversion. Results. The average anatomic anteversion was 8.7° (−42.2 to 32.8; SD 15.2). The average functional anteversion was −0.2° (−32.7 to 30.2; SD 14.3). The paired Student t test showed a significant difference between these values (p = 0.036). Discussion. In a significant number of cases, the anatomic orientation of the prosthesis in relation to the posterior bicondylar plane does not correlate with the functional orientation of the frontal plane of the standing patient. Other factors such as tibial, femoral and acetabular anatomic features determine the overall posture of the lower limb and the functional anteversion of the femoral neck prosthesis, highlighting adaptations related to hip-knee relations. EOS® technology can assess patients in functional positions of standing, sitting, squatting or bending forward at the cost of very low exposure to irradiation. These data may be useful in future studies of the orientation of the acetabulum that explore both qualitatively and quantitatively the combined functional anatomy of hip joint and, more precisely, the phenomena of instability and subluxation

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

Introduction. The pelvis is not a static structure. It rotates in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic tilt have a substantial effect on the functional orientation of the acetabulum. The aim of this study was to quantify the changes in sagittal pelvic position between three functional postures. Methodology. Pre-operatively, 1,517 total hip replacement patients had their pelvic tilt measured in 3 functional positions – standing, supine and flexed seated (point when patients initiate rising from a seated position). 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. Results. The mean supine pelvic tilt was 4.2°, with a range of −20.5° to 24.5°. The mean standing pelvic tilt was −1.3°, with a range of −30.2° to 27.9°. Mean pelvic tilt in the flexed seated position was 0.6°, with a range of −42.0° to 41.3°. The mean absolute change from supine to stand, and supine to flexed seated was 6.0° (SD = 3.8°) and 10.7° (SD = 8.1°) respectively. 6% of patients rotated posteriorly by more than 13° from supine to stand, consequently putting them at risk of excessive functional anteversion in extension. 11% of patients rotated anteriorly by more than 13° from supine to seated, consequently retroverting their cup and putting them at risk in flexion. Therefore, 17% of patients had sagittal pelvic rotations that could lead to functional cup malorientation even with a supposedly ideal orientation of 40°/20°. Factoring in an intraoperative delivery error of ± 5° extends this risk to 51% of patients. Conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. 17% of patients had sagittal pelvic rotations that could lead to functional cup malorientation in functional flexion or extension, even with an apparently perfectly-orientated component. This number extended to 51% when an intra-operative delivery error of ± 5° was considered. Planning and measurement of cup placement in the supine position can lead to large discrepancies in orientation during more functionally relevant postures. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles

Anatomic studies have demonstrated that bipolar glenoid and humeral bone loss have a cumulative impact on shoulder instability, and that these defects may engage in functional positions depending on their size, location, and orientation, potentially resulting in failure of stabilisation procedures. Determining which lesions pose a risk for engagement remains a challenge, with Itoi's 3DCT based glenoid track method and arthroscopic assessment being the accepted approaches at this time. The purpose of this study was to investigate the interaction of humeral and glenoid bone defects on shoulder engagement in a cadaveric model. Two alternative approaches to predicting engagement were evaluated; 1) CT scanning the shoulder in abduction and external rotation 2) measurement of Bankart lesion width and a novel parameter, the intact anterior articular angle (IAAA), on conventional 2D multi-plane reformats. Hill-Sachs and Bony Bankart defects of varying size were created in 12 cadaveric upper limbs, producing 45 bipolar defect combinations. The shoulders were assessed for engagement using cone beam CT in various positions of function, from 30 to 90 degrees of both abduction and external rotation. The humeral and glenoid defects were characterised by measurement of their size, location, and orientation. The abduction external rotation scan and 2D IAAA approaches were compared to the glenoid track method for predicting engagement. Engagement was predicted by Itoi's glenoid track method in 24 of 45 specimens (53%). The abduction external rotation CT scan performed at 60 degrees of glenohumeral abduction (corresponding to 90 degrees of abduction relative to the trunk) and 90 degrees of external rotation predicted engagement accurately in 43 of 45 specimens (96%), with sensitivity and specificity of 92% and 100% respectively. A logistic model based on Bankart width and IAAA provided a prediction accuracy of 89% with sensitivity and specificity of 91% and 87%. Inter-rater agreement was excellent (Kappa = 1) for classification of engagement on the abduction external rotation CT, and good (intraclass correlation = 0.73) for measurement of IAAA. Bipolar lesions at risk for engagement can be identified using an abduction external rotation CT scan at 60 degrees of glenohumeral abduction and 90 degrees of external rotation, or by performing 2D measurements of Bankart width and IAAA on conventional CT multi-plane reformats. This information will be useful for peri-operative decision making around surgical techniques for shoulder stabilisation in the setting of bipolar bone defects

Introduction. The pelvis is not a static structure. It rotates in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic tilt have a substantial effect on the functional orientation of the acetabulum. The aim of this study was to quantify the changes in sagittal pelvic position between three functional postures. Methodology. Pre-operatively, 90 total hip replacement patients had their pelvic tilt measured in 3 functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair), Fig 1. 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, Fig 2. Results. The mean standing pelvic tilt was −2.1° ± 7.4°, with a range of −15.2° – 15.3°. Mean supine pelvic tilt was 4.1° ± 5.5°, with a range of −9.7° – 17.9°. Mean pelvic tilt in the flexed seated position was −1.8° ± 14.1°, with a range of −31.8° – 29.1°, Fig 3. The mean absolute change from supine to stand, and stand to flexed seated was 6.9° ± 4.1° and 11.9° ± 7.9° respectively. 86.6% of patients had a more anteriorly tilted pelvis when supine than standing. 52.2% of patients had a more anteriorly tilted pelvis when seated than standing. Conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Planning and measurement of cup placement in the supine position can lead to large discrepancies in orientation during more functionally relevant postures. As a result of the functional changes in pelvic position, cup orientations during dislocation and edge-loading events are likely to be significantly different to that measured from standard CT and radiographs. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles

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. The posterior condylar axis of the distal femur is the common reference used to describe femoral anteversion. In the context of Total Hip Arthroplasty (THA), this reference can be used to define the native femoral anteversion, as well as the anteversion of the stem. However, these measurements are fixed to a femoral reference. The authors propose that the functional position of the proximal femur must be considered, as well as the functional relationship between stem and cup (combined anteversion) when considering the clinical implications of stem anteversion. This study investigates the post-operative differences between anatomically-referenced and functionally-referenced stem and combined anteversion in the supine and standing positions. Method. 18 patients undergoing pre-operative analysis with the Trinity OPS® planning (Optimized Ortho, Sydney Australia, a division of Corin, UK) were recruited for post-operative assessment. Anatomic and functional stem anteversion in both the supine and standing positions were determined. The anatomic anteversion was measured from CT and referenced to the posterior condyles. The supine functional anteversion was measured from CT and referenced to the coronal plane. The standing functional anteversion was measured to the coronal plane when standing by performing a 3D/2D registration of the implants to a weight-bearing AP X-ray. Further, functional acetabular anteversion was captured to determine combined functional anteversion in the supine and standing positions. Results. The average anatomical stem anteversion was 9.9° (6.7° to 13.0°). In all cases, the anatomical stem anteversion was different than the measured functional stem anteversion in both the supine and standing positions. The functional femoral anteversion decreased from supine to stand by an average of 7.1° (4.9°−9.2°), suggesting more internal rotation of the femurs when weight-bearing. In all patients, the pelvis rotated posteriorly in the sagittal plane from supine to standing, increasing the functional acetabular anteversion by a mean of 5.1°. Conclusions. Anatomic stem anteversion differs significantly from functional stem anteversion in both the supine and standing positions, as a consequence of the patient specific differences in internal/external rotation of the femur in the functional postures. In the same way that the Anterior Pelvic Plane is now widely recognized as an inappropriate reference for cup orientation due to variation in sagittal pelvic tilt, referencing the femoral stem anteversion to the native anatomy (distal femur) maybe also be misleading and not provide a suitable description of the functional anteversion of the stem. This has implications for determining optimal combined alignment in THA

Introduction. Total Knee Replacement (TKR) alignment measured intra-operatively with Navigation has been shown to differ from that observed in long leg radiographs (Deep 2011). Potential explanations for this discrepancy may be the effect of weight bearing or the dynamic contributions of soft tissue loads. Method. A validated, 3D, dynamic patient specific musculoskeletal model was used to analyse 85 post-operative CT scans using a common implant design. Differences in coronal and axial plane tibio-femoral alignment in three separate scenarios were measured:. Unloaded as measured in a post-op CT. Unloaded, with femoral and tibial components set aligned to each other. Weight bearing with the extensor mechanism engaged. Scenario number two illustrates the tibio-femoral alignment when the femoral component sits congruently on the tibia with no soft tissue acting whereas scenario three is progression of scenario number two with weight applied and all ligaments are active. Two tailed paired students t-test were used to determine significant differences in the means of absolute difference of axial and coronal alignments. Results. The mean coronal alignment were 1.7° ± 2.1° varus (range, −3.0° to 7.0°), 0.8° ± 2.0° varus (range, −3.7° to 4.8°), 0.4° ± 2.0° varus (range, −3.9° to 5.1°) for unloaded, unloaded with implants set aligned and weight bearing scenarios respectively. The mean of absolute difference in coronal alignment between the unloaded and weight bearing scenario was 1.8° ± 1.5° (range 0.0° to 5.9°). The mean axial alignment were 6.8° ± 5.5° external rotation (ER) (range, 20.0° ER to 11.0° internal rotation (IR)), 5.2° ± 6.1° ER (range, 24.8° ER to 12.6° IR), 7.1° ± 5.5° ER (range, 20.7° ER to 6.8° IR) for unloaded, unloaded with implants set to congruency and weight bearing scenarios respectively. The mean of absolute difference in axial alignment between the unloaded and weight bearing scenario was 2.8° ± 2.0° (range 0.1° to 8.8°). Statistically significant absolute differences in coronal and axial alignments were found. Conclusions. ‘Correct’ alignment has long been considered and important predictor of longevity and function following TKR surgery (Sikorski 2008). However, recent reports have challenged these long held beliefs. One possible reason is that these alignments are measured in static condition, not in a functional position where soft tissue is active. This study showed that knee joint alignment changes significantly between unloaded and loaded scenarios. This suggest that static, unloaded measurements do not represent functional alignment. Thus, tibio-femoral alignment measured from unloaded condition may not describe a ‘correct’ alignment for a particular patient. Further work should focus on dynamic and functional descriptions of component and/or limb alignment

Despite of the high success of TKA, 20% of recipients remain dissatisfied with their surgery. There is an increasing discordance in the literature on what is an optimal goal for component alignment. Furthermore, the unique patient specific anatomical characteristics will also play a role. The dynamic characteristic of a TKR is a product of the complex interaction between a patient's individual anatomical characteristics and the specific alignment of the components in that patient knee joint. These interactions can be better understood with computational models. Our objective was to characterise ligament characteristics by measuring knee joint laxity with functional radiograph and with the aid of a computational model and an optimisation study to estimate the subject specific free length of the ligaments. Pre-operative CT and functional radiographs, varus and valgus stressed X-rays assessing the collateral ligaments, were captured for 10 patients. CT scan was segmented and 3D–2D pose estimation was performed against the radiographs. Patient specific tibio-femoral joint computational model was created. The model was virtually positioned to the functional radiograph positions to simulate the boundary conditions when the knee is stressed. The model was simulated to achieve static equilibrium. Optimisation was done on ligament free length and a scaling coefficient, flexion factor, to consider the ligaments wrapping behaviour. Our findings show the generic values for reference strain differ significantly from reference strains calculated from the optimised ligament parameters, up to 35% as percentage strain. There was also a wide variation in the reference strain values between subjects and ligaments, with a range of 37% strain between subjects. Additionally, the knee laxity recorded clinically shows a large variation between patients and it appears to be divorced from coronal alignment measured in CT. This suggests the ligaments characteristics vary widely between subjects and non-functional imaging is insufficient to determine its characteristics. These large variations necessitate a subject-specific approach when creating knee computational models and functional radiographs may be a viable method to characterise patient specific ligaments