Introduction:. The lateral radiographs are useful in evaluation of the acetabular cup anteversion. However, this method was affected by variations in pelvic position and radiographic technique. In this study, we employed the ischial axis (IA) as an anatomical landmark on the lateral radiographs, and we investigated a relationship between IA and the anterior pelvic plane (APP) using three-dimensional computed tomography (3D-CT). Using these findings, we report a new method for accurate measurement of the acetabular cup anteversion on plain lateral radiographs using IA as an anatomical reference. Materials and Methods:. At first, preoperative3D-CT images were obtained in 109 patients who underwent total hip arthroplasty. The diagnosis was osteoarthritis in all patients. The angle between the IA (defined by a line connecting the anterior edge of the greater sciatic notch and the lesser sciatic notch) and APP (defined by the bilateral anterosuperior iliac spine and the symphysis) was measured on 3D-CT (Fig. 1). Secondly, postoperative lateral radiographs were obtained at 2 weeks, 4 weeks, 12 weeks, 24 weeks, and 52 weeks after surgery in 15 patients. The angle between a line tangential to the opening of the cup and a line perpendicular to APP was measured (Fig. 2). Three methods of acetebular cup position assessment were compared: 1) the present method, 2) Woo and Morrey method, and 3) software (2D template, Kyocera) method. Results:. The mean angle between IA and APP was 18.0 ± 3.5°. The mean acetabular cup anteversion measured using present method was 21.3°, Woo and Morrey method was 26.6°, and software method was 21.2°. The mean SDs of present method was 0.64°, Woo and Morrey method was 1.17°, and software method was 0.46°. Conclusions:. APP, considered as vertical in weight bearing, has a relatively consistent relationship between IA. The findings of this study provide a more consistent measurement of acetabular cup by reducing variation due to pelvic position

INTRODUCTION. Component impingement in total hip arthroplasty (THA) can cause implant damage or dislocation. Dual mobility (DM) implants are thought to reduce dislocation risk, but impingement on metal acetabular bearings may cause femoral component notching. We studied the prevalence of (and risk factors for) femoral notching with DM across two institutions. METHODS. We identified 37 patients with minimum 1-year radiographic follow-up after primary (19), revision (16), or conversion (2) THA with 3 distinct DM devices between 2012 and 2017. Indications for DM included osteonecrosis, femoral neck fracture, concomitant spinal or neurologic pathology, revision or conversion surgery, and history of prosthetic hip dislocation. Most recent radiographs were reviewed and assessed for notching. Acetabular anteversion and abduction were calculated as per Widmer (2004). Records were reviewed for dislocations and reoperations. RESULTS. 2/37 of cases demonstrated femoral component notching, best seen on Dunn views (available in 7/37 cases). Notching was associated with increased mean acetabular anteversion (32.5° with notch, 19.6° without; p=.03). 2/5 patients with anteversion greater than 30° had notching, while no patients with less anteversion had notching (p=.01). Recurrent posterior instability was the indication for 6 revision THAs studied. Both cases of notching were in this group. Although not statistically associated with implant design, notching occurred in 2/18 MDM, 0/10 ADM and 0/9 G7 constructs. Dislocation occurred in 0/18 MDM, 0/10 ADM and 2/9 G7 constructs (p=.04), resulting in one revision to a constrained liner. We observed no significant differences in rate of notching or dislocation with respect to age, cup or head size, or component abduction. DISCUSSION AND CONCLUSION. Femoral notching was identified in 5% of DM cases, equal to the rate of dislocation. Dunn views are not routine after THA, so the incidence may be underestimated. Increasing acetabular anteversion to minimize posterior dislocation is a risk factor. Dislocation and notching incidence may vary between DM components based on design features. Further study is warranted to determine clinical significance. For any figures or tables, please contact authors directly

Introduction. Pelvic flexion and extension in different body positions can affect acetabular orientation after total hip arthroplasty, and this may predispose patients to dislocation. The purpose of this study was to evaluate functional acetabular component position in total hip replacement patients during standing and sitting. We hypothesize that patients with degenerative lumbar disease will have less pelvic extension from standing to sitting, compared to patients with a normal lumbar spine or single level spine disease. Methods. A prospective cohort of 20 patients with primary unilateral THR underwent spine-to-ankle standing and sitting lateral radiographs that included the lumbar spine and pelvis using EOS imaging. Patients were an average age of 58 ± 12 years and 6 patients were female. Patients had (1) normal lumbar spines or single level degeneration, (2) multilevel degenerative disc disease or (3) scoliosis. We measured acetabular anteversion (cup relative to the horizontal), sacral slope angle (superior endplate of S1 relative to the horizontal), and lumbar lordosis angles (superior endplates of L1 and S1). We calculated the absolute difference in acetabular anteversion and the absolute difference in lumbar lordosis during standing and sitting (Figure 1). Results. Nine patients had normal lumbar spines or scoliosis, and 11 patients had multilevel disc disease. The median change in cup anteversion for normal and scoliosis patients was 29° degrees (range 11° to 41°) compared to 21° degrees (range 1° to 34°) for multilevel disc disease patients (p=0.03). There was a positive correlation between the change in cup anteversion and the change in lumbar lordosis (p=0.01; Figure 2). From standing to sitting, cup anteversion always increased and lumbar lordosis always decreased. Conclusions. The change in cup anteversion from standing to sitting was variable in patients with normal, degenerative, and scoliosis lumbar spines. Patients with degenerative disc disease have less pelvic extension, and thus less acetabular anteversion in the sitting position compared to normal spines. This may increase their risk of posterior dislocation

Introduction. Implant position plays a major role in the mechanical stability of a total hip replacement. The standard modality for assessing hip component position postoperatively is a 2D anteroposterior radiograph, due to low radiation dose and low cost. Recently, the EOS® X-Ray Imaging Acquisition System has been developed as a new low-dose radiation system for measuring hip component position. EOS imaging can calculate 3D patient information from simultaneous frontal and lateral 2D radiographs of a standing patient without stitching or vertical distortion, and has been shown to be more reliable than conventional radiographs for measuring hip angles[1]. The purpose of this prospective study was to compare EOS imaging to computer tomography (CT) scans, which are the gold standard, to assess the reproducibility of hip angles. Materials and Methods. Twenty patients undergoing unilateral THA consented to this IRB-approved analysis of post-operative THA cup alignment. Standing EOS imaging and supine CT scans were taken of the same patients 6 weeks post-operatively. Postoperative cup alignment and femoral anteversion were measured from EOS radiographs using sterEOS® software. CT images of the pelvis and femur were segmented using MIMICS software (Materialise, Leuven, Belgium), and component position was measured using Geomagic Studio (Morrisville, NC, USA) and PTC Creo Parametric (Needham, MA). The Anterior Pelvic Plane (APP), which is defined by the two anterior superior iliac spines and the pubic symphysis, was used as an anatomic reference for acetabular inclination and anteversion. The most posterior part of the femoral condyles was used as an anatomic reference for femoral anteversion. Two blinded observers measured hip angles using sterEOS® software. Reproducibility was analysed by the Bland-Altman method, and interobserver reliability was calculated using the Cronbach's alpha (∝) coefficient of reliability. Results. The Bland-Altman analysis of test-retest reliability indicated that the 95% limits of agreement between the EOS and CT measurements ranged from −3° to 4° for acetabular inclination, from −5° to 5° for acetabular anteversion, and from −7° to 2° for femoral anteversion. The average difference between EOS measurements and CT measurements was 2° ± 2° for acetabular inclination, 3°± 2° degrees for acetabular anteversion and 4° ± 4° femoral anteversion. Interobserver agreement was good for acetabular inclination (Cronbach's α = 0.55), acetabular anteversion (Cronbach's α = 0.76) and femoral components (Cronbach's α = 0.98) using EOS imaging. Conclusions. EOS imaging can accurately and reliably measure hip component position, while exposing patients to a much lower dose of radiation than a CT scan

Background. Supine positioning during direct anterior approach total hip arthroplasty (DAA THA) facilitates use of fluoroscopy, which has been shown to improve acetabular component positioning on plane radiograph. This study aims to compare 2- dimensional intraoperative radiographic measurements of acetabular component position with RadLink to postoperative 3- dimensional SterEOS measurements. Methods. Intraoperative fluoroscopy and RadLink (El Segundo, CA) were used to measure acetabular cup position intraoperatively in 48 patients undergoing DAA THA. Cup position was measured on 6-week postoperative standing EOS images using 3D SterEOS software and compared to RadLink findings using Student's t-test. Safe-zone outliers were identified. We evaluated for measurement difference of > +/− 5 degrees. Results. RadLink acetabular cup abduction measurement (mean 43.0°) was not significantly different than 3D SterEOS in the anatomic plane (mean 42.6°, p = 0.50) or in the functional plane (mean 42.7°, p = 0.61) (Fig. 1–2). RadLink acetabular cup anteversion measurement (mean 17.9°) was significantly different than 3D SterEOS in both the anatomic plane (mean 20.6°, p = 0.022) and the functional plane (mean 21.2°, p = 0.002) (Fig. 3–4). RadLink identified two cups outside of the safe-zone. However, SterEOS identified 12 (anatomic plane) and 10 (functional plane) outside of the safe-zone (Fig. 5–7). In the functional plane, 58% of anteversion and 92% of abduction RadLink measurements were within +/− 5° of 3D SterEOS. Conclusion. Intraoperative fluoroscopic RadLink acetabular anteversion measurements are significantly different than 3D SterEOS measurements, while abduction measurements are similar. Significantly more acetabular cups are placed outside of the safe- zone when evaluated with 3D SterEOS versus RadLink

The problem associated with ceramic on ceramic total hip replacement (THR) is audible noise. Squeaking is the most frequently documented sound. The incidence of squeaking has been reported to wide range from 0.7 to 20.9%. Nevertheless there is no study to investigate on incidence of noise in computer assisted THR with ceramic on ceramic bearing. The purpose of this study was to determine the incidence and risks factors associated with noise. We retrospectively reviewed 200 patients (202 hips) whom performed computer assisted THR (Orthopilot, B. Braun, Tuttlingen, Germany) with ceramic on ceramic bearing between March 2009 and August 2012. All procedures underwent uncemented THR with posterior approach by single surgeon. All hips implanted with PLASMACUP and EXIA femoral stem (B. Braun, Tuttlingen, Germany). All cases used BIOLOX DELTA (Ceramtec, AG, Plochingen, Germany) ceramic liner and head. The incidence and type of noise were interviewed by telephone using set of questionnaire. Patient's age, weight, height, body mass index, acetabular cup size, femoral offset size determined from medical record for comparing between silent hips and noisy hips. The acetabular inclination angle, acetabular anteversion angle, femoral offset, hip offset were reviewed to compare difference between silent hips and noisy hips. The audible noise was reported for 13 hips (6.44%). 5 patients (5 hips) reported click (2.47%) and 8 patients (8 hips) squeaked (3.97%). The mean time to first occurrence of click was 13.4 months and squeak was 7.4 months after surgery. Most common frequency of click was less than weekly (60%) and squeak was 1–4 times per week (50%). Most common activity associated with noise was bending; 40% in click and 75% in squeaking. No patients complained for pain or social problem. Moreover, no patient underwent any intervention for the noise. The noise had not self-resolved in any of the patients at last follow up. Age, weight, height and BMI showed no statistically significant difference between silent hips and click hips. In addition, there was also same result between silent hips and squeaking hips. Acetabular cup insert size and femoral offset stem size the results showed that there was no statistically significant difference between silent hips and click hips, also with squeaking hips. Acetabular inclination, angle acetabular anteversion angle, femoral offset, hip offset the results shown that only acetabular anteversion angle differed significantly between silent hips (19.94±7.78 degree) and squeaking hips (13.46±5.54 degree). The results can conclude that incidence of noise after ceramic on ceramic THR with navigation was 6.44 %. Squeaking incidence was 3.97% and click incidence was 2.47%. The only associated squeaking risk factor was cup anteversion angle. In this study, squeaking hip had cup anteversion angle significant less than silent hip

Navigation in total hip arthroplasty has been shown to improve acetabular positioning and can decrease the incidence of mal-positioned acetabular components. The aim of this study was to assess two surgical guidance systems by comparing intra-operative measurements of acetabular component inclination and anteversion with a post-operative CT scan. We prospectively collected intra-operative navigation data from 102 hips receiving conventional THA or hip resurfacing arthroplasty through either a direct anterior or posterior approach. Two guidance systems were used simultaneously: an inertial navigation system (INS) and optical navigation system (ONS). Acetabular component anteversion and inclination was measured on a post-operative CT. The average age of the patients was 64 years (range: 24-92) and average BMI was 27 kg/m. 2. (range 19-38). 52% had hip surgery through an anterior approach. 98% of the INS measurements and 88% of the ONS measurements were within 10° of the CT measurements. The mean (and standard deviation) of the absolute difference between the post-operative CT and the intra-operative measurements for inclination and anteversion were 3.0° (2.8) and 4.5° (3.2) respectively for the ONS, along with 2.1° (2.3) and 2.4° (2.1) respectively for the INS. There was significantly lower mean absolute difference to CT for the INS when compared to ONS in both anteversion (p<0.001) and inclination (p=0.02). Both types of navigation produced reliable and reproducible acetabular cup positioning. It is important that patient-specific planning and navigation are used together to ensure that surgeons are targeting the optimal acetabular cup position. This assistance with cup positioning can provide benefits over free-hand techniques, especially in patients with an altered acetabular structure or extensive acetabular bone loss. In conclusion, both ONS and INS allowed for adequate acetabular positioning as measured on postoperative CT, and thus provide reliable intraoperative feedback for optimal acetabular component placement

In 2021, Vigdorchik et al. published a large multicentre study validating their simple Hip-Spine Classification for determining patient-specific acetabular component positioning in total hip arthroplasty (THA). The purpose of our study was to apply this Hip-Spine Classification to a sample of Australian patients undergoing THA surgery to determine the local acetabular component positioning requirements. Additionally, we propose a modified algorithm for adjusting cup anteversion requirements. 790 patients who underwent THA surgery between January 2021 and June 2022 were assessed for anterior pelvic plane tilt (APPt) and sacral slope (SS) in standing and relaxed seated positions and categorized according to their spinal stiffness and flatback deformity. Spinal stiffness was measured using pelvic mobility (PM); the ΔSS between standing and relaxed seated. Flatback deformity was defined by APPt <-13° in standing. As in Vigdorchik et al., PM of <10° was considered a stiff spine. For our algorithm, PM of <20° indicated the need for increased cup anteversion. Using this approach, patient-specific cup anteversion is increased by 1° for every degree the patient's PM is <20°. According to the Vigdorchik simple Hip-Spine classification groups, we found: 73% Group 1A, 19% Group 1B, 5% Group 2A, and 3% Group 2B. Therefore, under this classification, 27% of Australian THA patients would have an elevated risk of dislocation due to spinal deformity and/or stiffness. Under our modified definition, 52% patients would require increased cup anteversion to address spinal stiffness. The Hip-Spine Classification is a simple algorithm that has been shown to indicate to surgeons when adjustments to acetabular cup anteversion are required to account for spinal stiffness or flatback deformity. We investigated this algorithm in an Australian population of patients undergoing THA and propose a modified approach: increasing cup anteversion by 1° for every degree the patient's PM is <20°

Background. Rotational acetabular osteotomy (RAO) is an effective treatment option for symptomatic acetabular dysplasia. However, excessive lateral and anterior correction during the periacetabular osteotomy may lead to femoroacetabular impingement. We used preoperative planning software for total hip arthroplasty to perform femoroacetabular impingement simulations before and after rotational acetabular osteotomies. Methods. We evaluated 11 hips in 11 patients with available computed tomography taken before and after RAO. All cases were female and mean age at the time of surgery was 35.9 years. All cases were early stage osteoarthritis without obvious osteophytes or joint space narrowing. Radiographic analysis included the center-edge (CE) angle, Sharp's acetabular angle, the acetabular roof angle, the acetabular head index (AHI), cross-over sign, and posterior wall sign. Acetabular anteversion was measured at every 5 mm slice level in the femoral head using preoperative and postoperative computed tomography. Impingement simulations were performed using the preoperative planning software ZedHip (LEXI, Tokyo, Japan). In brief, we created a three-dimensional model. The range of motion which causes bone-to-bone impingement was evaluated in flexion (flex), abduction (abd), external rotation in flex 0°, and internal rotation in flex 90°. The lesions caused by impingement were evaluated. Results. In the radiographic measurements, the CE angle, Sharp's angle, acetabular roof angle, and AHI all indicated improved postoperative acetabular coverage. The cross-over sign was recognized pre- and postoperatively in each case. Acetabular retroversion appeared in one case before RAO and in three cases after RAO. Preoperatively, there was a tendency to reduce the acetabular anteverison angle in the hips from distal levels to proximal. In contrast, there was no postoperative difference in the acetabular anteversion angle at any level. In our simulation study, bone-to-bone impingement occurred in flex (preoperative/postoperative, 137°/114°), abd (73°/54°), external rotation in flex 0°(34°/43°), and internal rotation in flex 90°(70°/36°). Impingement occurred within internal rotation 45°in flexion 90°in two preoperative and eight postoperative cases. The impingement lesions were anterosuperior of the acetabulum in all cases. Discussion. It is easy to make and assess an impingement simulation using preoperative planning software, and our data suggest the simulation was helpful in a clinical setting, though there were some remaining problems such as approximation of the femoral head center and differences in femur movement between the simulation and reality. In the postoperative simulation there was a tendency to reduce the range of motion in flex, abd, and internal rotation in flex 90°. There was a correlation between acetabular anteversion angle and flex. Since impingement occurred within internal rotation 45°in flexion 90°in eight postoperative simulations, we consider there is a strong potential for an increase in femoroacetabular impingement after RAO

Introduction. Studies of metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) have reported high complication and failure rates due to elevated metal ion levels. These rates were shown to be especially high for the Articular Surface Replacement (ASR) HRA, possibly due to its unique design. Associations between metal ion concentrations and various biological and mechanical factors have been reported. Component positioning as measured by acetabular inclination has been shown to be of especially strong consequence in metal ion production in ASR HRA patients, but few studies have evaluated acetabular anteversion as an independent variable. The primary objective of this study was to evaluate the associations between component orientation, quantified by acetabular inclination and anteversion, and blood metal ions. Secondly, we sought to report whether conventional safe zones apply to MoM HRA implants or if these implants require their own positioning standards. Methods. We conducted a multi-center, prospective study of 512 unilateral ASR HRA patients enrolled from September 2012 to June 2015. At time of enrollment our patients were a mean of 7 (3–11.5) years from surgery. The mean age at surgery was 56 years and 24% were female. All subjects had complete demographic and surgical information and blood metal ions. In addition, each patient had valid AP pelvis and shoot-though lateral radiographs read by 5 validated readers measuring acetabular abduction and anteversion, and femoral offset. A multivariate logistic regression was used with high cobalt or chromium (greater than or equal to 7ppb) as the dependent variable. The independent variables were: female gender, UCLA activity score, age at surgery, femoral head size, time from surgery, femoral offset, acetabular abduction, and acetabular anteversion. Results. The average acetabular inclination angle was found to be 44.7° (20.6°–64.5°), and the average anteversion angle was 24° (0.2°–55.3°) (Figure 1). After controlling for the possible confounding variables, the factors contributing to elevated metal ions (≥ 7 ppb) were found to be time from surgery (OR = 1.29, p = 0.011), high abduction angle (– 55°) (OR = 4.40, p = 0.001), low anteversion angle (0°–10°) (OR = 3.82, p = 0.001), and female gender (OR = 3.45, p = 0.001). Discussion and Conclusion. We found that blood metal ion levels are affected by both acetabular inclination and anteversion (Figure 2). Furthermore, we observed that there was a high degree of variation in the positioning of these implants, and we conclude that those with high inclination and/or low anteversion angle should be most vigilantly monitored

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

Surgeons often target the Lewinnek zone (40°±10° of inclination; 15°±10° of anteversion) for acetabular orientation during total hip arthroplasty (THA). However, matching native anteversion (20°-25°) may achieve optimal stability. The purpose of this study was to (1) determine incidence of early dislocation with increased target acetabular anteversion, and (2) report the accuracy of imageless navigation for achieving target acetabular position in a large, single-surgeon cohort. A posterolateral approach with soft tissue repair was performed in the 553 THA meeting the inclusion criteria. The same imageless navigation system was used for acetabular component placement in all THA. Target acetabular orientation was 40° ± 10° of inclination and 25° ± 10° of anteversion. Computer software was used to measure acetabular positioning on 6-week postoperative anteroposterior pelvic radiographs. Incidence of dislocation within 6 months of surgery was determined. Repeated measures multiple regression using the Generalised Estimating Equations approach was used to identify baseline patient characteristics (age, gender, BMI, primary diagnosis, and laterality) associated with component positioning outside of the targeted ranges for inclination and anteversion. Fisher exact tests were used to examine the relationship between dislocation and component placement in either the Lewinnek safe zone or the targeted zone. All tests were two-sided with a significance level of 0.05. Mean inclination was 42.2° ± 4.9°, and mean anteversion was 23.9° ± 6.5°. 82.3% of cups were placed within the target zone. Variation in anteversion accounted for 67.3% of outliers. Only body mass index was associated with inclination outside the target range (p = 0.017), and only female gender was associated with anteversion outside the target range (p = 0.030). Six THA (1.1%) experienced early dislocation, and 3 THA (0.54%) were revised for multiple dislocations. There was no relationship between dislocation and component placement in either the Lewinnek zone (p = 0.224) or the target zone (p = 0.287). This study demonstrates that increasing target acetabular anteversion using the posterolateral approach does not increase the incidence of early THA dislocation. However, the long-term effects on bearing surface wear and stability must be elucidated. The occurrence of instability even in patients within our target zone emphasises the importance of developing patient-specific targets for THA component alignment

Combined acetabular and femoral anteversion (CA) of the hip following total hip arthroplasty (THA) is critical to the hip function and longevity of the components. However, no study has been reported on the accuracy in restoration of CA of the hip after operation using robotic assistance and conventional free-hand techniques. The purpose of this study was to evaluate if using robotic assistance in THA can better restore native CA than a free-hand technique. Twenty three unilateral THA patients participated in this study. Twelve of them underwent a robotic-arm assisted THA (RIO® Robotic Arm Interactive Orthopedic System, Stryker Mako., Fort Lauderdale, FL, USA) and eleven received a free-hand THA. Subject specific 3D models of both implanted and non-implanted hips were reconstructed using post-operative CT scans. The anteversion and inclination of the native acetabulum and implanted cup were measured and compared. To determine the differences of the femoral anteversion between sides, the non-implanted native femur was mirrored and aligned with the remaining femur of the implanted side using an iterative closest point algorithm. The angle between the native femoral neck axis and the prosthesis neck axis in transverse plane was measured as the change in femoral anteversion following THA. The sum of the changes of the acetabular and femoral anteversion was defined as the change of CA after THA. A Wilcoxon signed rank test was performed to test if the anteversion of the navigation and free-hand THAs were different from the contralateral native hips (α = 0.05). The acetabular anteversion were 22.0°±7.4°, 35.9°±6.5° and 32.6°±22.6° for the native hips, robotic assisted THAs and free-hand THAs, respectively, and the corresponding values of the acetabular inclinations were 52.0°±2.9°, 35.4°±4.4° and 43.1°±7.1°. The acetabular anteversion was increased by 12.2°±11.1° (p=0.005) and 12.5°±20.0° (p=0.102) for the robotic assisted and the free-hand THAs. The femoral anteversion was increased by 6.3°±10.5° (p=0.077) and 11.0°±13.4° (p=0.014) for the robotic assisted and free-hand THAs, respectively. The CA were significantly increased by 18.5°±11.7° (p<0.001) and 23.5°±26.5° (p=0.019) for the robotic assisted and the free-hand THAs. The changes of the CA of the free-hand THAs varied in a larger range than those of the robotic assisted THAs. This study is the first to evaluate the changes in acetabular and femoral anteversions of the hips after robotic assisted and free-hand THAs using the contralateral native hip as a control. The results demonstrate that both the navigation and free-hand THAs significantly increased the CA compared to the contralateral native hips, but the changes of the robotic assisted THAs (18.5°±11.7°) were smaller and varied less than those of the free-hand THAs (23.5°±26.5°). These data suggest that the robotic assisted THA can better restore the native hip CAs with higher repeatability than the free-hand technique. Further studies are needed to investigate the effects of the hip anteversion changes on the in-vivo function of the hip and the long-term outcomes in THA patients

Background:. Numerous studies have reported the importance of acetabular component positioning in decreasing dislocation rates, the risk of liner fractures, and bearing surface wear in total hip arthroplasty (THA). The goal of improving acetabular component positioning has led to the development of computer-assisted surgical (CAS) techniques, and several studies have demonstrated improved results when compared to conventional, freehand methods. Recently, a computed tomography (CT)-based robotic surgery system has been developed (MAKO™ Robotic Arm Interactive Orthopaedic System, MAKO Surgical Corp., Fort Lauderdale, FLA, USA), with promising improvements in component alignment and surgical precision. The purpose of this study was to compare the accuracy in predicting the postoperative acetabular component position between the MAKO™ robotic navigation system and an imageless, CAS system (AchieveCAS, Smith and Nephew Inc., Memphis, TN, USA). Materials and Methods:. 30 THAs performed using the robotic navigation system (robotic cohort) were available for review, and compared to the most recent 30 THAs performed using the imageless, CAS system (CAS cohort). The final, intraoperative reading for acetabular abduction and anteversion provided by each navigation system was recorded following each THA. Einsel-Bild-Roentgen analysis was used to measure the acetabular component abduction and anteversion based on anteroposterior pelvis radiographs obtained at each patient's first, postoperative visit (Figure 1). Two observers, blinded to the treatment arms, independently measured all the acetabular components, and the results were assessed for inter-observer reliability. Comparing the difference between the final, intraoperative reading for both acetabular abduction and anteversion, and the radiographic alignment calculated using EBRA analysis, allowed assessment of the intraoperative predictive capability of each system, and accuracy in determining the postoperative acetabular component position. In addition, the number of acetabular components outside of the “safe zone” (40° + 10° of abduction, 15° + 10° of anteversion), as described by Lewinnek et al., was assessed. Lastly, the operative time for each surgery was recorded. Results:. In the robotic cohort, the mean, absolute difference between the intraoperative reading and the postoperative alignment was 4.3° + 2.3° for acetabular abduction, and 3.2° + 2.3° for acetabular anteversion. In comparison, in the CAS cohort, the mean, absolute difference was 3.7° + 2.8° for acetabular abduction (p = 0.4), and 3.8° + 2.7° for acetabular anteversion (p = 0.4). In both cohorts, all of the acetabular components were placed within 40° + 10° of abduction. In the robotic cohort, 27 of 30 components were placed within 15° + 10° of anteversion, versus 25 of 30 components in the CAS cohort (p = 0.7). The interobserver correlation coefficients for measurement of both the acetabular abduction and anteversion were good (p = 0.83 and 0.79, respectively). A statistically significant difference was appreciated between the two cohorts for operative times, with a mean operative time of 120.2 + 8.9 minutes in the robotic cohort (vs. 73.6 + 17.1 minutes in the CAS cohort, p < 0.01). Discussion:. This study demonstrates the robotic navigation system to require significantly increased operative times, while providing no significant advantage over the imageless, CAS system with regards to predicting the postoperative acetabular component position

INTRODUCTION. Traditionally, acetabular component insertion in direct anterior approach (DAA) total hip arthroplasty (THA) has been performed using fluoroscopic guidance. Handheld navigation systems can be used to address issues of alignment, cup placement and accuracy of measurements. Previous navigation systems have been used successfully in total knee arthroplasty (TKA) and has now been introduced in THA. We investigated the use of a new accelerometer-based, handheld navigation system during DAA THA to compare it to traditional means. This study aims to determine accuracy of acetabular cup placement as well as fluoroscopy times between two groups of patients. METHODS. Data was prospectively collected for a group of consecutive DAA THA procedures using a handheld navigation system (n=45) by a single surgeon. This was compared to data retrospectively collected for a group that underwent the same procedure without use of the navigation system(n=50). The time for use of the navigation system, including insertion of pins/registration, guiding cup position, and removal of pins, was recorded intraoperatively. Postoperative anteroposterior and cross-table lateral radiographs were used to measure acetabular inclination and anteversion angles. Targeted angles for all cases were 40° ±5 for inclination and 20° ±5 for anteversion. Intraoperative fluoroscopy exposure times were obtained from post-anesthesia care unit radiographs. RESULTS. Mean time of pin insertion/registration, cup positioning and removal was 180.5 seconds, 127.7 seconds and 26 seconds, giving a mean total time of 5.6 minutes. There were no significant differences in mean postoperative acetabular inclination angles between the navigation group as compared to the non-navigation group (39.8° vs 40.6°) (p = .2). There were no significant differences in mean postoperative acetabular anteversion angles between the navigation group as compared to the non-navigation group (24.3° vs 23.7°) (p=.5). Mean intraoperative fluoroscopy exposure times were significantly lower in the navigation group as compared to the non-navigation group (12.6 vs 22.2 seconds) (p<.0001). CONCLUSION. The findings demonstrated that a new handheld navigation system required minimal increase in operative time and was as accurate for cup positioning as fluoroscopically assisted DAA THA. Furthermore, there was a 45% reduction in fluoroscopy exposure time. Reduction in fluoroscopy time will lower radiation exposure for the surgeon and patients

Introduction. Optimal implant position is critical to hip stability after total hip arthroplasty (THA). Recent literature points out the importance of the evaluation of pelvic position to optimize cup implantation. The concept of Functional Combined Anteversion (FCA), the sum of acetabular/cup anteversion and femoral/stem neck anteversion in the horizontal plane, can be used to plan and control the setting of a THA in standing position. The main purpose of this preliminary study is to evaluate the difference between the combined anteversion before and after THA in weight-bearing standing position using EOS 3D reconstructions. A simultaneous analysis of the preoperative lumbo pelvic parameters has been performed to investigate their potential influence on the post-operative reciprocal femoro-acetabular adaptation. Material and Methods. 66 patients were enrolled (unilateral primary THAs). The same mini-invasive anterolateral approach was performed in a lateral decubitus for all cases. None of the patients had any postoperative complications. For each case, EOS full-body radiographs were performed in a standing position before and after unilateral THA. A software prototype was used to assess pelvic parameters (sacral slope, pelvic version, pelvic incidence), acetabular / cup anteversion, femoral /stem neck anteversion and combined anteversion in the patient horizontal functional plane (the frontal reference was defined as the vertical plane passing through centers of the acetabula or cups). Sub-analysis was made, grouping the sample by pelvic incidence (<55°, 55°–65°, >65°) and by pre-operative sacral slope in standing position (<35°, 35°–45°, >45°). Paired t-test was used to compare differences between preoperative and postoperative parameters within each subgroup. Statistical significance was set at p < 0.05. Results. In the full sample, mean FCA increased postoperatively by 9,3° (39,5° vs 30,2°; p<0.05). In groups with sacral slope < 35° and sacral slope > 45°, postoperative combined anteversion increased significantly by 11,7° and 12,9°, respectively. In the group with pelvic incidence > 65°, postoperative combined anteversion increased significantly by 14,4°. There was no significant change of combined anteversion in the remaining subgroups. Discussion. In this series the FCA increased after THA, particularly in patients with a low or high sacral slope on the pre-operative evaluation in standing position. This may be related to a greater difficulty for the surgeon in anticipating the postoperative standing orientation of the pelvis in these patients, as they were standardly oriented during surgery (lateral decubitus). Interestingly the combined anteversion was also increased in patients with a high pelvic incidence that is commonly associated with a high sacral slope. Conclusion. Post-operative increase of anatomical cumulative anteversion has been previously reported using anterior approach. The FCA concept based on EOS 3D reconstructions brings new informations about the reciprocal femoro-acetabular adaptation in standing position. Differences found in combined anteversion before and after the surgery show that a special interest should be given to patients with high pelvic incidence and low or high sacral slope, to optimize THA orientation in standing position

Introduction. Prosthetic replacement remains the treatment of choice for displaced femoral neck fractures in the elderly population, with recent literature demonstrating significant functional benefits of total hip arthroplasty (THA) over hemiarthroplasty. Yet the fracture population also has historically high rates of early postoperative instability when treated with THA. The direct anterior approach (DAA) may offer the potential to decrease the risk of postoperative instability in this high-risk population by maintaining posterior anatomic structures. The addition of intraoperative fluoroscopy can improve precision in component placement and overcome limitations on preoperative planning due to poor preoperative radiographs performed in the emergency setting. Methods. We retrospectively reviewed clinical and radiographic outcomes of 113 consecutive patients with displaced femoral neck fractures treated by two surgeons over a five-year period. All underwent surgery via the DAA using fluoroscopic guidance, and were allowed immediate postoperative weight bearing without any hip precautions or restrictions. Charts were reviewed for relevant complications, while radiographs were reviewed for component positioning, sizing, and leg length discrepancy. Mean follow-up was 8.9 months. Results. Mean age was 79.3 years (range, 42 to 101), 73% of patients were women, and mean BMI was 22.6 kg/m. 2. Ninety patients (80%) received THA while 23 (20%) received unipolar or bipolar hemiarthroplasty. Mean acetabular anteversion was 15.0 degrees (range, 4 to 24) and mean abduction was 39.2 degrees (range, 27 to 51) with 95% of acetabular components in the combined safe zone as described by Lewinnek. Mean radiographic leg-length difference was +2.2 mm (range, −4.9 to +8.8mm). There was no femoral stem subsidence of more than 2mm. Only one patient (0.9%) dislocated postoperatively, who was eventually constrained for recurrent posterior instability 3 months following surgery. Delayed wound healing (6.1%) was the most common postoperative complication. Conclusions. The direct anterior approach allows a safe, effective, and reproducible approach for treatment of displaced femoral neck fractures, with very low rate of early postoperative instability compared to historical controls. The use of intraoperative fluoroscopy allows excellent component positioning, sizing, and restoration of leg length in spite of inconsistent preoperative radiographs

Background. Component positioning in total hip arthroplasty (THA) is critical to achieve optimal patient outcomes. Recent literature has shown acetabular component positioning may be inaccurate using traditional techniques. Robotic-assisted THA is a recent platform introduced to decrease the risk of malpositioned components. However, to date, a paucity of data is available comparing the intra-operative component position generated by the navigation system to post-operative radiographs. Purpose. The purpose of this study was to compare the component position measurements of a navigation system, used during robotic-assisted THA, to component position measurements obtained on post-operative radiographs. Methods. Intra-operative component position measurements for acetabular inclination, acetabular anteversion, leg length change, and offset change for 145 patients were recorded. Pre-operative and post-operative radiographs of the same 145 patients were then measured for the same parameters. A comparison of component position provided by the navigation system and radiographic data was then performed. Sub-group analyses of posterior and direct anterior measurements were performed. Results. Correlation between the navigation system and post operative radiographs was within 10° for 95.9% of cases for inclination and 96.6% for anteversion. Correlation within 10 mm of radiographic-measured values occurred in 97.7% of cases for change in leg length and 94.0% for change in global offset. 100% of the cases ended up with radiographic leg length discrepancy of less than 10 mm. Conclusion. The intra-operative component position data obtained from the navigation system utilized during robotic-assisted THA demonstrated correlated well with component position data obtained from radiographs

Management of recurrent instability of the hip requires careful assessment to determine any identifiable causative factors. While plain radiographs can give a general impression, CT is the best methodology for objective measurement. Variables that can be measured include: prosthetic femoral anteversion, comparison to contralateral native femoral anteversion, total offset from the medial wall of the pelvis to the lateral side of the greater trochanter, comparison to total offset on the contralateral side, acetabular inclination, & acetabular anteversion. Wera et al describe potential causes of instability. These are typed into I. Acetabular Component Malposition; II. Femoral Component Malposition; III. Abductor Deficiency; IV. Impingement; V. Late Wear; and VI. Unknown. Acetabular component malposition is the most common cause of instability and so measurement of cup orientation is essential. It is well known that excessive or inadequate anteversion can lead to anterior and posterior dislocation respectively but horizontal components are also associated with posterior dislocation due to deficient posterior/inferior acetabular surface. Similarly, excessive or inadequate femoral anteversion can be easily identified on CT as can insufficient total offset of the reconstructed joint compared to the contralateral side. This can be caused by medialization of the acetabular component. Abductor deficiency can be a soft-tissue cause of instability, but it certainly isn't the only one. Knowledge of the prior surgical exposure can be instructive. Anterior exposures can be prone to deficient anterior capsule just as posterior exposures can be prone to deficient posterior capsule and short rotators, while anterolateral and lateral exposures can be associated with gluteus minimus and gluteus medius compromise. Impingement, whether involving implants, bone, or soft tissue are primarily secondary to the above factors, if osteophytes were properly trimmed at the index procedure. Correction of the incorrect variables is the primary goal of revision for instability and greatly preferable to using salvage options such as dual-mobility or constrained articulations which invoke additional concerns. Ultimately though, such salvage options are necessary if the cause of the instability cannot be determined or can be determined but not corrected. Bracing, while highly inconvenient and sometimes impractical for certain patients, still has a role in specific circumstances. Formal analysis of the unstable prosthetic reconstruction is the key to successful treatment

Introduction. Optimal implant position is the important factor in the hip stability after THA. Both the acetabular and femoral implants are placed in anteversion. While most hip dislocations occur either in standing position or when the hip is flexed, preoperative hip anatomy and postoperative implants position are commonly measured in supine position with CT scan. The isolated and combined anteversions of femoral and acetabular components have been reported in the literature. The conclusions are questionable as the reference planes are not consistent: femoral anteversion is measured according to the distal femoral condyles plane (DFCP) and acetabulum orientation in the anterior pelvic plane (APP)). The EOS imaging system allows combined measurements for standing position in the “anatomical” reference plane or anterior pelvic plane (APP) or in the patient “functional” plane (PFP) defined as the horizontal plane passing through both femoral heads. The femoral anteversion can also be measured conventionally according to the DFCP. The objective of the study was to determine the preoperative and postoperative acetabular, femoral and combined hip anteversions, sacral slope, pelvic incidence and pelvic tilt in patients who undergo primary THA. Material and Methods. The preoperative and postoperative 3D EOS images were assessed in 62 patients (66 hips). None of these patients had spine or lower extremity surgery other than THA surgery in between the 2 EOS assessments. None had dislocation within the follow up time period. Results. Pelvic values. The preoperative sacral slope was 42.4°(11° to 76°) as compared to the postoperative sacral slope (40.3°, −4° to 64°)(p=0.014). The preoperative pelvic tilt was 15.3° (−10° to 44°) as compared to the postoperative tilt (17.2°, −6° to 47°)(p=0.008). The preoperative pelvic incidence was 57.7°(34° to 93°) and globally unchanged as compared to the postoperative incidence (57.5°, 33° to 79°)(p=0.8). Acetabular values. Surgeons increased the anteversion according to the APP by an average of 12.6°(−13° to 53°)(p<0.001). Acetabular anteversion was increased by 14.3° in the PFP (−11° to 51°)(p<0.001). Femoral values. In the DFCP, preoperative neck anteversion was decreased postoperatively by an average of −3,2°(−48° to 33°)(p=0,0942). In the PFP, preoperative neck anteversion was decreased postoperatively by an average of −6,3°(−47° to 17°)(p<0,001). Combined values. According to the classical methods (acetabular orientation in the APP and femoral anteversion in the DFCP), mean preoperative combined anteversion was 36.1° (4° to 86°) and was increased postoperatively to 45.5°(−12° to 98°)(p=0.0003). According to the PFP, mean preoperative combined anteversion was 30,7°(5° to 68°) and was increased postoperatively to 38,8°(−10° to 72°)(p=0,0001). Conclusion. This study reports two methods for the measurement of acetabular and femoral anteversion, “anatomical” according to the APP and DFCP and “functional” according to the PFP. Surgeons tend to increase the anteversion of the acetabular implant and to decrease femoral anteversion during the surgery. The trend is the same for postoperative evolution of values using the “anatomical” or the “functional” methods but numerical discrepancies are explained by significant APP orientation changes. The assessment of the true combined anteversion provides new perspectives to optimize our understanding of THA stability and function