Aims. Pelvic tilt (PT) can significantly change the functional orientation of the acetabular component and may differ markedly between patients undergoing total hip arthroplasty (THA). Patients with stiff spines who have little change in PT are considered at high risk for instability following THA. Femoral component position also contributes to the limits of impingement-free range of motion (ROM), but has been less studied. Little is known about the impact of combined anteversion on risk of impingement with changing pelvic position. Methods. We used a virtual hip ROM (vROM) tool to investigate whether there is an ideal functional combined anteversion for reduced risk of hip impingement. We collected PT information from functional lateral radiographs (standing and sitting) and a supine CT scan, which was then input into the vROM tool. We developed a novel vROM scoring system, considering both seated flexion and standing extension manoeuvres, to quantify whether hips had limited ROM and then correlated the vROM score to component position. Results. The vast majority of THA planned with standing combined anteversion between 30° to 50° and sitting combined anteversion between 45° to 65° had a vROM score > 99%, while the majority of vROM scores less than 99% were outside of this zone. The range of PT in supine, standing, and sitting positions varied widely between patients. Patients who had little change in PT from standing to sitting positions had decreased hip vROM. Conclusion. It has been shown previously that an individual’s unique spinopelvic alignment influences functional cup anteversion. But functional combined anteversion, which also considers stem position, should be used to identify an ideal THA position for impingement-free ROM. We found a functional combined anteversion zone for THA that may be used moving forward to place total hip components. Cite this article: Bone Jt Open 2021;2(10):834–841

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. 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

Introduction. Acetabular component positioning, offset, combined anteversion, leg length, and soft tissue envelope around the hip plays an important role in hip function and durability. In this paper we will focus on acetabular positioning of the cup. Technique. The axis of the pelvis is identified intra-operatively as a line drawn from the highest point of the iliac crest to the middle of the greater trochanter. Prior to reaming the acetabulum, an undersized trial acetabular component is placed parallel and inside the transverse ligament, inside the anterior column and projecting posterior to the axis of the pelvis. This direction is marked and the subsequent reaming and final component placement is performed in the same direction. The lateral opening is judged based on the 45-degree angle from the tear drop to the lateral margin of the acetabulum on anteroposterior pelvic radiographs. The final anteversion of the cup is adjusted based on increased or decreased lumbar lordosis and combined anteversion. Methods. Anteroposterior pelvic radiographs of 100 consecutive patients undergoing posterior THR between September 2010 and March 2011 with this method were evaluated for cup inclination angle and anteversion using EBRA software. Results. There were no malalignments or dislocations. The mean cup inclination angle and anteversion were 41 ± 5.1 degrees (range 37.1 – 48.4) and 22.1 ± 4.8 degrees (range 16.6 – 29.3), respectively. Conclusion. This is a reproducible method of cup positioning and with proper femoral component position and restoring leg length, offset, combined anteversion, and balance soft tissue around the hip. These factors affect the incidence of dislocation, infection, reduced wear, and durability

Introduction. Computer navigation is a highly sophisticated tool in orthopedic surgery for component placement in total hip arthroplasty (THA). A number of recommendations have been published. Although Lewinnek's safe-zone is the best-known among these its significance is questioned in recent years since it addresses the acetabular socket only ignoring the femoral stem. Modern target definitions consider both socket and stem and provide well-defined recommendations for complementary component positioning. We present a new small-sized hand-held imageless navigation system that implies these targets and supports the surgeon in realizing the concept of combined anteversion and combined Target-Zone (cTarget- Zone) in THA and to control leg length and offset without altering the standard surgical work-flow and we report initial results. Methods. The targets for positioning the components of a total hip as expressed by radiographic cup inclination (cRI) and anteversion (cRA), stem antetorsion (sAT) and neck-to-shaft angle (sNSA) are determined for a specific prosthesis system using a computerized 3D-model. The optimizing goal is maximizing the size of the cSafe-Zone providing the largest target zone for an impingement-free prosthetic range of motion (pROM) in order to minimize the risk for dislocation in physiologic and combined movements. Independent parameters like head size, head-to-neck ration and also component orientations like cRI, cRA, sAT and sNSA were varied systematically and the optimal cSafe-Zone was computed in semi-automated batch runs. These optimized prosthesis-specific results were introduced into the software of the hand-held navigation system. This system measures leg length, offset, acetabular and femoral head centers intraoperatively. Results. In contrast to Lewinnek the outline of our cSafe-Zone is not rectangular but polygonal. Its size shows prosthesis-specific maxima. The largest zones are found for optimal sNSA values at 126° +/−4°, optimal ranges for cRI depend on head size and range from 44° to 36°, best sAT range from 10° to 18°, cRA from 18° to 25°. There is a prosthesis- specific linear correlation between sAT and cRA that denotes the combined anteversion. The target value for combined anteversion is not dependent on pelvic tilt but on sNSA. The hand-held navigation system displays all these orienting parameters as well as leg-length and offsets. Furthermore, it supports a virtual reduction work-flow thus accelerating surgery. All these information provide important decision-making details for the surgeon intraoperatively in real-time for augmented quality. Conclusion. The combined Target-Zone provides the basis for patient- and implant-specific control of prosthesis implantation. It includes all important positioning parameters of both total hip components and such gives well-defined individual recommendations for the targets. The new hand-held navigation system (Naviswiss) provides a smart way to direct and control the total hip implantation according to the best combined orientation considering also the concept of combined Safe-Zone. Such it prevents outliers, provides better safety and documents the surgical workflow and the final result of the surgery

Introduction: Acetabular component positioning, offset, combined anteversion, leg length, and soft tissue envelope around the hip plays an important role in hip function and durability. In this paper we will focus on acetabular positioning of the cup. Technique: The axis of the pelvis is identified intra-operatively as a line drawn from the highest point of the iliac crest to the middle of the greater trochanter. Prior to reaming the acetabulum, an undersized trial acetabular component is placed parallel and inside the transverse ligament, inside the anterior column and projecting posterior to the axis of the pelvis. This direction is marked and the subsequent reaming and final component placement is performed in the same direction. The lateral opening is judged based on 45-degree angle from the tear drop to the lateral margin of the acetabulum on anteroposterior pelvic radiographs. The final anteversion of the cup is adjusted based on increase or decrease of lumbar lordosis and combined anteversion. Methods: Anteroposterior pelvic radiographs of 100 consecutive patients undergoing posterior THR between September 2010 and March 2011 with this method were evaluated for cup inclination angle and anteversion using EBRA software. Results: There were no malalignment or dislocation. The mean cup inclination angle and anteversion were 41 ± 5.1 degrees (range 37.1 – 48.4) and 22.1 ± 4.8 degrees (range 16.6 – 29.3), respectively. Conclusion: This is a reproducible method of cup positioning and with proper femoral component position, restores leg length, offset, combined anteversion, and balances soft tissue around the hip. These factors affect the incidence of dislocation, infection, reduced wear, and durability

Combined anteversion angle of acetabular component and femeral neck is an important factor for total hip arthroplasty (THA) as it may affect impingement and dislocation. Previous studies have collected data mainly from direct measurements of bone morphology or manual measurements from 2D or 3D radiolographic images. The purpose of this study was to electronically measure the version angles in native acetabulum and femur in matured normal Caucasion population using a novel virtual bone database and analysis environment named SOMA™. 221 CT scans from a skeletally mature, normal Caucasian population with an age range of 30–95 years old. The population included 135 males and 86 females. CT data was converted to virtual bones with cortical and cancellous boundaries using custom CT analytical sofware. (SOMA™ V.3.2) Auxillary reference frames were constructed and measurements were performed within the SOMA™ design environment. Acetabular Anteversion (AA) angle as defined by Murray. 1. was measured. The acetabular rim plane was constructed by selecting 3 bony land marks from pubis, ilium and ischium. A vector through acetabular center point and normal to the rim plane defined the plane for the AA measurement. The AA was defined as the angle of this plane relative to the frontal (Coronal) plane of the pelvis. The Femoral Neck Anteversion (FNA) angle was measured from the neck axis plane to the frontal (Coronal) plane as defined by the posterior condyles. The neck axis plane was constructed to pass through femoral neck axis perpendicular to the transverse plane. The combined anteversion angle was computed as the summation of acetabular and femoral anteversion angles. Student's t tests were performed to compare gender difference with an assumed 95% confidence level. The mean AA angle for total population was 25.8°, SD=7.95°. The mean AA for male was 24.8°, SD=5.93° and for female was 27.3°, SD=7.14°. P=0.009. The mean FNA angle for total population was 14.3°, SD=6.52°. The mean FNA for male was 13.5°, SD=7.97° and for female was 15.5°, SD=7.80°. P=0.058. The mean combined anteversion angle for total population was 40.1°, SD=10.76°. The mean combined anteversion angle for male was 38.3° SD=10.39 ° and for female was 42.8° SD=10.83 °. P=.0002. The plot of AA as a function of FNA shows weak correlation for both male and female. (Figure 1) The frequency distribution is shown in Figure 2. The results showed the both AA, FNA and combined anteversion angles were significantly smaller in male population than that in female population. The FNA angle of the cementless femoral stem can be smaller than with the natural femur, therefore a higher AA or higher posterior build up may be required for the acetabular component for optimal function of a THA

Introduction. In total hip arthroplasty (THA), it is important to define the coordinate system of the pelvis and femur for standardization in measuring the implant alignment. A coronal plane of the pelvis (functional pelvic coordinates) in supine position has been recommended as the pelvic coordinates for cup orientation and an anatomical plane of the femur (posterior condylar plane: PCP) is widely used as the femoral coordinates to measure stem or femoral anteversion. It has been reported that the pelvic sagittal tilt in supine does not change a lot after THA. However, changes in the axial rotation of the posterior condylar plane after THA have not been well studied. If the horizontal tilt of PCP of the femur in a resting position changes a lot after THA, the combined anteversion theory cannot be functional. Therefore, we evaluated the angulation changes of the posterior condylar plane after THA and analyzed the related factors by using CT images. Methods. Forty patients (5 men and 35 women, mean age 58 years) with hip osteoarthritis who had undergone THA were the subjects of this study. CT images used for measurements were taken preoperatively (preop-CT) and 3 weeks after THA (postop-CT), and more than 2 years after THA (2nd postop-CT). Measurements were done on the reconstructed CT images using 3D viewer software. The axial rotation of the femur was measured as the angle between the posterior condylar line (PCL) and a line through the bilateral anterior superior iliac spines. To analyze the factors relating to the rotational change of the femur, change in femoral anteversion, leg length, and leg medialization after THA were also measured. Surgical approach (posterolateral: 32 cases, direct anterior: 8 cases) was also evaluated as a factor relating to the rotational change. Results. PCL was externally rotated at an average angle of 3.3° at preop-CT, −10.4° at postop-CT, and −7.2° at 2nd postop-CT. There was a significant difference between preop-CT and postop-CT, preop-CT and 2nd postop-CT (p<0.01, respectively). Femoral anteversion decreased 0.5°, the leg was lengthened 11.7mm, and was medialized 8.5mm after THA. In the analysis of the related factors, only the leg length change and the amount of leg medialization significantly correlated with the rotational change between preop-CT and postop-CT (β=−0.367, −0.316, respectively). On the other hand, no factors correlated with the rotational change between preop-CT and 2nd postop-CT. Discussion. PCL at a resting position internally rotated 13.7° after THA and remained 10.5° internally rotated from the preoperative position at more than 2 years after THA. This internal rotation after THA may have occurred by releasing the external contracture caused by osteoarthritis. Because the PCL at a resting position internally rotates approximately 10° after THA, we have to consider this change when we calculate the range of motion of the hip in the combined anteversion theory. Conclusion. PCL at a resting position internally rotates approximately 10°after THA and we may need to consider this change in the combined anteversion theory

INTRODUCTION. Golf is considered low-impact sport, but concerns exist about whether golf swing can be performed in safe manner after THA. The purpose of this study was to clarify dynamic hip kinematics during golf swing after THA using image-matching techniques. METHODS. This study group consisted of eight right-handed recreational golfers with 10 primary THAs. Each operation was performed using a posterolateral approach with combined anteversion technique. Nine of ten polyethylene liners used had elevated portion of 15°. Continuous radiographic images of five trail and five lead hips during golf swing were recorded using a flat panel X-ray detector (Fig. 1) and analyzed using image-matching techniques (Fig. 2). The relative distance between the center of cup and femoral head and the minimum liner-to-stem distance were measured using a CAD software program. The cup inclination, cup anteversion, and stem anteversion were measured in postoperative CT data. Hip kinematics, orientation of components, and cup-head distance were compared between patients with and without liner-to-stem contact by Mann-Whitney U test. RESULTS. At the top of backswing, lead hips showed 26 ± 11° ER, and trail hips showed 24 ± 19° IR. At the end of follow-through, lead hips showed 24 ± 19° IR, and trail hips showed 24 ± 12° ER. The mean cup inclination and anteversion, stem anteversion, and combined anteversion were 40 ± 5°, 18 ± 11°, 33 ± 14°, and 50 ± 8°, respectively. The minimum liner-to-stem distance showed the smallest value of 3 ± 4 mm at the maximum ER. Bone-to-bone and bone-to-implant impingements were not observed in all hips at all phases. The liner-to-stem contact was observed in four hips with elevated liners (two trail and two lead hips; Fig 3). Patients with elevated liner-to-stem contact demonstrated significantly (p < .05) larger maximum ER and larger cup anteversion than patients without contact. The mean cup-head distance was 0.9 ± 0.5 mm of translation. No significant difference was found in the flexion/extension and adduction/abduction at the maximum ER, cup inclination, combined anteversion, and cup-head distance between patients with and without contact. DISCUSSION. Golf swing produced approximately 50° of axial rotations in both lead and trail hips after THA. The mean cup-head distances showed less than 1.0 mm, and there was no significant difference between patients with and without neck-liner contact. Therefore, we consider that dynamic stability without excessive hip rotations or subluxation was demonstrated during golf swing. Despite no evidence of component malpositioning, elevated liner-to-stem contact was observed in 40% of hips with significantly larger ER and cup anteversion. Because the liner-to-stem contact may be a concern with regard to the long-term prognosis following THA, further attention must be given to the anteversion of the components and the use of elevated liner at the time of surgery. To view tables/figures, please contact authors directly

Introduction. To control implant alignments (anteversion and abduction angle of the acetabular cup and antetorsion of the femoral stem) within an appropriate angle range is essentially important in total hip arthroplasty to avoid implant impingement. A navigation system is necessary for accurate intraoperative evaluation of implant alignments but is too expensive and time-consuming to be commonly used. Therefore, a cheaper and easier tool for intraoperative evaluation of the alignments is desired in the clinical field. I presented an idea of marking ruler-like scales on a trial femoral head in the last ISTA Congress. The purpose of this study is to introduce an idea further improved in evaluating the combined implant alignment intraoperatively. Materials and Methods. We can evaluate the combined anteversion (sum of cup anteversion and stem antetorsion) and cup abduction angle by reading the scales at the most proximal point of inner edge of the liner when horizontal and vertical scales are marked on the femoral head appropriately and the hip joint is kept at the neutral position after implant settings and trial reduction. Whether the impingement occurred within the target ROM (Flx 130, IR40@Flx90, Ext 40, ER 40) was judged under specific conditions of the oscillation angle (139), neck-shaft angle of the stem (130), stem adduction angle (7), stem antetorsion (20 or 30), and cup anteversion and abduction angles. Cup anteversion and abduction angles were changed from 0 to 40 and 30 to 50 degrees in 1-degree increments, respectively. Impingement judgment was performed mathematically for each combination of implant alignment based on matrix transformations and trigonometric formulas. Results. Impingement-free combinations of implant alignments were identified using spreadsheet software. Points which indicated impingement-free when they matched with the most proximal point of the inner edge of the liner when the hip joint was kept neutral were plotted on the surface of the head on a 3-dimensional computer graphic software. Thus, the safe zone could be indicated visually on the trial head by a collection of these points. Discussion. We can easily judge whether the implant impingement occurs or not by using this trial head intraoperatively. However, there are several factors which make the judgment inaccurate. First, the safe zone varies according to the stem antetorsion. Second, the position at which the hip is kept intraoperatively is not necessarily neutral. Third, stem adduction angle varies according to the length of the femur. Conclusion. Safe zone mapping on the trial femoral head is low cost and easy method to be introduced in the clinical practice for the purpose of a rough judgment of implant impingement

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

Background. Between 1999 and August 2005, we performed Direct Lateral Approach (DLA) in lateral decubitus position as the main approach for primary total hip arthroplasty (THA). After August 2005, we introduced Direct Anterior Approach(DAA) in supine position. Intraoperative target orientation in primary THA was planned in 40–45°cup abduction, 10–20°cup anteversion, and 10–20° stem anteversion. Precice implant positioning has been considered to be very important for postoperative function and stability. The purpose of this study was to compare the DLA and DAA for implant positioning accuracy. Methods. From 1999 to July 2009, we performed 566 primary THAs(78 male, 488 female). The subjects were divided into two groups of 224 DLA and 342 DAA (72 in early stage and 270 in late stage) The difference of the mean age at surgery and preoperative diagnosis among the groups were not significant. We planned to set the cup anteversion at 20°in DAA early stage and 12.5°in late stage DAA due to the development of postoperative dislocation in several cases with early stage DAA. We measured the cup and stem alignment postoperatively using radiography and computed tomography, and measured the combined anteversion angle by Widmer. Statistical analysis was done using the Bartlett Statistical Test and F-test. The results were expressed as median and interquartile range, with an alpha level set at less than 0.05. Results. Cup abduction angle with DLA was 42.7±6.25 °(average±standard deviation), 42.1±4.1°with early stage DAA and 41.9±5.3°with late stage DAA. There was no significant difference between the approaches with average and standard deviation (SD) of cup abduction. The mean cup anteversion with DLA (17.3±10.0°) was significantly smaller than that with early stage DAA(26.6±8.1°) and late stage DAA(21.0±8.0°). SD of cup anteversion with DLA was significantly larger than that with both DAA groups. The mean stem anteversion was significantly smaller with DLA (18.9±14.3) and late stage DAA (16.7±11.1°) than that with early stage DAA (23.5±11.9°). SD of stem anteversion with DLA was significantly larger than that with both DAA groups. There were 9 hips of dislocation: 5 hips in DLA, 3 in early DAA and one in late DAA. SD of combined anteversion Value with DLA(30.5±13.7) was significantly larger than that with early DAA (40.3±12.2) and late DAA (32.7±11.1.∗∗∗∗∗. Conclusion. Significantly less SD for anteversion of stem and cup was demonstrated with DAA compared with DLA. Stable operative positioning with DAA could yield a more accurate and reliable implantation compared with DLA in lateral position. DAA in supine position was a superior approach for primary THA

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

Proper component alignment is crucial for a successful total hip arthroplasty (THA). Some studies found safe cup orientations and corresponding stem antetorsions based on a defined desired range of motion (ROM) suitable for activities of daily living. These studies either used complex and time consuming 3D simulations or more simple mathematical formulas which cannot be extended to combined motions. With the method introduced in this work, any arbitrary motion can be applied. The ROM specified as the ROM of the femur relative to the pelvis is transformed into the ROM of the prosthesis neck relative to the cup for each cup orientation. For this transformation, the orientation and design of the stem are considered. The comparison of the neck and cup orientations is done using a 2D mapping of a 3D spherical surface which reduces the complexity of the calculation. We found that the femoral antetorsion as well as the neutral stem flexion and adduction have an influence on the resulting safe zone. The result is not just a combined anteversion but a combined orientation. For validating the plausibility of the algorithm, the resulting safe zones are compared to literature. Same results can be achieved using the same input data. Using this technique, a patient-specific safe zone based on the ROM can be derived and adjusted to the stem orientation

Introduction & aims. Correct prosthetic alignment is important to the longevity and function of a total hip replacement (THR). With the growth of 3-dimensional imaging for planning and assessment of THR, the importance of restoring, not just leg length and medial offset, but anterior offset has been raised. The change in anterior offset will be influenced by femoral anteversion, but there are also other factors that will affect the overall change after THR. Consequently, the aim of this study was to investigate the relationship between anterior offset and stem anteversion to determine the extent to which changing anteversion influences anterior offset. Method. Sixty patients received a preoperative CT scan as part of their routine planning for THR (Optimized Ortho, Sydney). All patients received a Trinity cementless shell and a cemented TaperFit stem (Corin, UK) by the senior author through an anterolateral approach. Stem anteversion was positioned intraoperatively to align with cup anteversion via a modified Ranawat test. Postoperatively, patients received a CT scan which was superimposed onto the pre-op CT scan. The difference between native and achieved stem anteversion was measured, along with the 3-dimensional change in head centre from pre-to post-op. Finally, the relationship between change in stem anteversion and change in anterior offset was investigated. Results. Mean change in anterior offset was −2.3mm (−14.0 to 7.0mm). Mean change in anteversion from native was −3.0° (−18.8° to 10.5°). There was a strong correlation between change in anterior offset and change in anteversion, with a Pearson correlation coefficient of 0.89. A 1° increase in anteversion equated to a 0.7mm increase in anterior offset. Conclusions. A change in the anteroposterior position of the femoral head is primarily affected by a change in stem anteversion, with a 1° increase in anteversion equating to a 0.7mm increase in anterior offset. The AP position of the stem in the canal, along with the flexion of the stem will also contribute. Given the well-recognised influence of leg length, medial offset and combined anteversion on restoring hip function, it seems reasonable to assume that anterior offset will also have a significant effect on the biomechanics of the replaced hip

Aims

The aim of this study was to evaluate the suitability of the tapered cone stem in total hip arthroplasty (THA) in patients with excessive femoral anteversion and after femoral osteotomy.

Introduction. One of the objectives of total hip arthroplasty is to restore femoral and acetabular combined anteversion. It is desirable to reproduce both femoral and acetabular antevesions to maximize the acetabular cup fixation coverage and hip joint stability. Studies investigated the resultant of implanted femoral stem anteversion in western populations showed that the implanted femoral stems had only a small portion can meet the desirable femoral anteversion angle. 1. , and anteversion angle increases after the implantation of an anatomical femoral stem with anteverted stem neck comparing to anatomical femoral neck. 2. The purpose of this study was to anatomically measure the anteversion angular difference between metaphyseal long axis and femoral neck in normal Chinese population. The metaphyseal long axis represents the coronal fixation plane of modern cementless medial-lateral cortical fitting taper stem. This angular difference or torsion Δ angle provides the estimation of how much the neck antevertion angle of femoral stem would be needed to match for desirable anatomical femoral neck version. Methods. 140 (77 male and 63 female) anonymous normal adult Chinese CT data with average age of 54.6 (male 54.6, female 54.5, P=0.95) were segmented and reconstructed to 3D models in Trauson Orthopeadic Modeling and Analytics (TOMA) program. Femoral head center, femoral neck axis and center point of diaphyseal canal 100mm bellow calcar formed the femoral neck plane. The metaphyseal stem implantation plane was determined by the center point of medial calcar, proximal canal central axis formed by femoral neck plane and the center point of diaphyseal canal 100mm bellow calcar. [Fig. 1] The angle between two planes was the torsion Δ angle between femoral placement plane and anatomical femoral neck. [Fig. 2] The torsion Δ angles were measured for all 140 cases. The traditional anteversion angle for anatomical femoral neck was also measured by Murphy's method. Student T test was perform to compare the angles for male and female. The 98% confidence level was assumed. Results. The average torsion Δ angle for whole population was 4.9°(0.04°-15.6°), SD=3.52°, male: 4.6° (0.42°-13.9°), SD=3.09°; female: 5.3° (0.04°-15.6°), SD=3.98°. There was no statistical significant difference between genders. P=0.28. All metaphyseal stem placement planes were less anteverted than anatomical femoral neck plane. [Fig. 3] The average anatomical femoral neck anteversion angle for total population was 18.6° (0.27°-42.6°), SD=7.54°; male: 18.6° (0.27°-32.9°), SD=7.37°; female: 18.7° (1.74°-42.6°), SD=7.81°. There was no statistical significance between male and female P=0.92. Only 26% of study population or 37 cases with unadjusted implant neck version had normal anteversion angle of 10°-15° (Tönnis). Discussion. The study suggested femoral stem neck anteversion angle adjustments up to 11° was necessary to match anatomical femoral neck for 94% of cases in Chinese population. And the adjustments of 0°-7° represented the 76% majority of population. This finding was in agreement with the published data in western population. 2. . Significance. Variable femoral stem neck anteversion angles up to 11° are necessary to reproduce the anatomical anteversions for 94% of normal Chinese population. For any figures or tables, please contact the authors directly

Introduction. Pelvic posterior tilt change (PPTC) after THA is caused by release of joint contracture and degenerative lumbar kyphosis. PPTC increases cup anteversion and inclination and results in a risk of prosthesis impingement (PI) and edge loading (EL). There was reportedly no component orientation of fixed bearing which can avoid PI and EL against 20°PPTC. However, dual mobility bearing (DM) has been reported to have a large oscillation angle and potential to withstand EL without increasing polyethylene (PE) wear against high cup inclination such as 60∼65°. Objective. The purpose of this study was to investigate the optimal orientation of DM-THA for avoiding PI and EL against postoperative 20°PPTC. Methods. Our study was performed with computer tomography -based three-dimensional simulation software (ZedHip. LEXI co. Japan). The CT data of hip was derived from asian typical woman with normal hips. Used prosthesises were 50mm cup and 42mm outer head of modular dual mobility system and Accolade II 127°(stryker). Femoral coordinate system was retrocondylar plane with z-axis from trochanteric fossa to intercondylar notch. Cup orientation was described as anatomical definition. The safe zone was calculated by the required hip range of motion which was defined as 130°flexion, 40°extension, 30°external rotation, and 50°internal rotation with 90°flexion and the maximum inclination of DM cup which was 60°in consideration of withstanding EL. Cup orientations withstanding 20°PPTC were defined as the primary cup orientation which changes consistently within the safe zone with the match of 20°PPTC. And among them cup orientation with lowest inclination was defined as the optimal cup orientation. result. The optimal orientations could be identified only within stem anteversion from 15°to 40°. The relationship between the optimal cup orientation and stem anteversion could be automatically identified. The correlation between stem anteversion and cup anteversion was linearly distributed and could be expressed as an approximated line of the formula that (stem anteversion)+(cup anteversion)=36.8. And likewise the relationship between stem anteversion and cup inclination was curved-linerly distributed and could be expressed as an approximated curved line of the formula that (cup inclination)=0.04(stem anteversion). 2. 2.18(stem anteversion)+74.8. Cup orientation calculated by the Widmer's combined anteversion theory is easily deviated from the safe zone by PPTC. The optimal cup orientation calculated in this study could be set more inclination and retroversion than it calculated by the Widmer's theory in contribution of large oscillation angle and admissibility of high inclination cup setting of DM. Therefore it could be possible to withstand 20°PPTC. Conclusion. Performing THA with considering postoperative PPTC is necessary for good long term outcome without dislocation and PE wear. The solution for 20°PPTC after THA is to apply dual mobility bearing and the formula of combined orientation theory calculated in this study

Introduction. In recent literatures dealing with optimisation of prosthetic alignment in total hip arthroplasty (THA), the concept of combined anteversion (CA), sum of acetabular anteversion (AV) and femoral antetorsion (AT), has been addressed. We have been using an image-free THA navigation system?OrthoPilot THAPro?to achieve improved overall alignment with both stem and cup. In the use of this system, we have used the stem-first procedure so-called CA technique. In this technique, the femur was prepared first with the target angle corresponding to the native femoral AT and the cup AV was decided considering CA calculated with the formula of Widmer (37.3°= cup AV + 0.7 stem AT). The purpose of this study was to evaluate the accuracy of CA by using CA technique with image-free navigated THA. Methods. Fifty hips underwent primary THA using OrthoPilot THApro with CA technique. In CA technique, the femur was prepared first and the target angle of AT value was basically determined by for the individual native femoral AT angle. After the femur was prepared, the cup AV was decided based on the formula of Widmer. All included patients underwent postoperative CT examination, and the prosthetic alignment was assessed using the 3D-Template system (Zed Hip, LEXI). Results. In the assessment of accuracy of the navigation systems in 50 consecutive THA's, comparison of intraoperative navigation value and postoperative CT evaluation indicated that the absolute discrepancy of cup AV, and stem AT was 4.5° ± 3.5°and 5.9° ± 4.3° respectively. In the assessment of the cup AV with postoperative CT evaluation, the measured values averaged 20.7° ± 6.2° while AT values averaged 20.9° ± 10.6°. Distribution of AT values showed large SD. By contrast, the average Widmer's CA values (cup AV + 0.7 stem AT) were 35.2° ± 5.7°. In the assessment of overall alignment, the Widmer's CA values were within 37° ± 5° in 40 hips and 37° ± 10° in 46 hips. Conclusion. The present study proposed that the confirming stem AT prior to cup placement could be important to achieve appropriate CA value. CA technique with image-free navigated THA could achieve accurate and consistent control of CA value

Metal-on-metal bearings (MoM) saw an increase in global utilisation in the last decade. This peaked in 2008 in the US, with approximately 35% of bearings being hard-on-hard (metal-on-metal, or ceramic-on-ceramic). Beginning in 2008, reports began to surface regarding local soft tissue reactions and hypersensitivity to MoM bearings. A major implant manufacturer recalled a resurfacing device in 2010 after national joint registries demonstrated higher than expected revision rates. Patients with painful MoM bearings are a difficult diagnostic challenge. The surgeon must go back to basic principles, perform a complete history and physical exam, obtain serial radiographs and basic blood work (ESR, CRP) to rule out common causes of pain and determine if the pain is, or is not, related to the bearing. The Asymptomatic MoM Arthroplasty: Patients will present for either routine follow up, or because of concerns regarding their bearing. It is important to emphasise that at this point the vast majority of patients with a MoM bearing are indeed asymptomatic and their bearings are performing well. The surgeon must take into account: a) which specific implant are they dealing with and what is its track record; b) what is the cup position; c) when to perform metal ion testing; d) when to perform further soft tissue imaging (MARS MRI, Ultrasound); e) when to discuss possible surgery. Painful MoM THA causes not related to the bearing couple: These can be broken down into two broad categories. Causes that are Extrinsic to the hip include spine, vascular, metabolic and malignancy. Causes that are Intrinsic to the hip can either be Extracapsular or Intracapsular. Painful MoM THA causes related to the bearing couple: There are now described a number of possible clinical scenarios and causes of pain that relate to the MoM bearing couple itself: A) Local hypersensitivity reaction without a significant soft tissue reaction; B) Local hypersensitivity reaction with a significant soft tissue reaction; C) Impingement and soft tissue pain secondary to large head effect. Factors related to a hypersensitivity reaction: Some patients, and prostheses, seem to be at a higher risk of developing issues following a MoM bearing, although our understanding of the interplay of these factors is still in evolution: patients at risk include all women and patients with smaller component sizes. Implant factors play a role with some implants having higher wear rates and being more prone to corrosion. Special tests: There is ongoing confusion related to the relative value of the various special tests that patients with a painful MoM undergo. A) Metal Ions - obtaining serum, or whole blood, cobalt and chromium levels is recommended as a baseline test. However, there is no established cutoff level to determine with certainty if a patient is having a hypersensitivity reaction. Metal ions therefore can be used as a clue, but cannot be relied upon in isolation to make a diagnosis. B) MARS MRI - a useful tool for demonstrating soft tissue involvement, but there are many painless, well-functioning MoM implants that have soft tissue reactions, that don't require a revision. In the painful MoM hip an MRI, or ultrasound, is recommended to look for soft tissue destruction or a fluid-filled periprosthetic lesion (pseudotumor). Significant soft tissue involvement is concerning and is commonly an indication for revision in the painful MoM hip. C) CT imaging - can be utilised to help determine cup position and combined anteversion, however, plain radiographs can give a rough estimate of this as well, so routine CT scan evaluations are not currently recommended. The painful MoM bearing, that is demonstrating significant soft tissue involvement is a concerning scenario. Earlier revision, to prevent massive abductor damage, would seem prudent for these patients. The painful MoM bearing with no significant soft tissue changes can probably be followed and reviewed at regular intervals. If the pain persists and is felt to be secondary to a hypersensitivity reaction, then revision is really the only option, although the patient must be cautioned regarding the unpredictable nature of the pain relief