Purpose:. In order to acquire good stability of an arthroplasty hip, the proper placement of the implants, which prevents impingement between the stem neck and the socket, is important. In general, the anteversion of the uncemented femoral stem depends on the relationship between the three-dimensional structure of the proximal femoral canal and the proximal stem geometry. The exact degree of the anteversion will be known just after broaching during the operation. If the stem anteversion could be forecasted, preoperative planning of the socket placement would be relatively easy. Furthermore, when a high degree of anteversion is forecasted, a special femoral stem to reduce it, such as a modular stem, could be prepared. However, we experienced that the preoperatively measured anteversion of the femoral neck using computer tomography (CT) was sometimes different from that of the stem measured during the operation. The purpose of this study was to investigate whether the preoperative measurement would be helpful to predict the stem anteversion by examining the relationship between the anteversion of the femoral neck and the stem. Patients and methods:. A total of 57 primary THAs by one senior surgeon from April 2011 until March 2012 were carried out. Two THAs using a modular stem and one for the hip after previous proximal femoral osteotomy were excluded. The remaining 54 THAs were examined. The used uncemented stems were designed for proximal metaphyseal fixation. CT scans, including the distal femoral condyles as well as the hips, were carried out in all cases preoperatively. The anteversion of the femoral neck was measured as the angle of the maximum longitudinal line of the cross section of the femoral neck to the line connecting the posterior surfaces of both of the distal femoral condyles (Fig. 1). The femoral neck anteversion was measured at three levels (Fig. 1). The stem anteversion was measured just after the femoral broaching during the THA. The relationship between the anteversion angles of the femoral neck and of the stem was examined by using a regression analysis. The institutional review board approved this study. Results:. The anteversion angles of the femoral neck varied widely when they were measured at all of the levels (Table 1). The anteversion angle of the femoral neck was not always identical to that of the stem. There were 32–46% of cases in which the difference between the stem anteversion and the femoral neck anteversion was within 5 degrees. There was a significant relationship between the anteversion of the stem and that of the femoral neck measured at all three levels (Fig. 2). When it was measured just below the femoral head, it was the closest to one, and the p-value was the lowest. Discusssion and Conclusions:. The anteversion of the uncemented stem could be calculated by using the formula to show the relationship between the stem anteversion and the femoral neck antevesion measured preoperatively. The values appeared to be sufficiently correct for making clinical decisions, although a prospective study may be necessary to confirm this

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. Methods. We included patients who underwent THA using Wagner Cone due to proximal femur anatomical abnormalities between August 2014 and January 2019 at a single institution. We investigated implant survival time using the endpoint of dislocation and revision, and compared the prevalence of prosthetic impingements between the Wagner Cone, a tapered cone stem, and the Taperloc, a tapered wedge stem, through simulation. We also collected Oxford Hip Score (OHS), visual analogue scale (VAS) satisfaction, and VAS pain by postal survey in August 2023 and explored variables associated with those scores. Results. Of the 58 patients (62 hips), two (two hips) presented with dislocation or reoperation, and Kaplan-Meier analysis indicated a five-year survival rate of 96.7% (95% CI 92.4 to 100). Mean stem anteversion was 35.2° (SD 18.2°) for the Taperloc stem and 29.8° (SD 7.9°) for the Wagner Cone stem; mean reduction from Taperloc to Wagner Cone was 5.4° (SD 18.8°). Overall, 55 hips (52 patients) were simulated, and the prevalence of prosthetic impingement was lower for the Wagner Cone (5.5%, 3/55) compared with the Taperloc (20.0%, 11/55) stem, with an odds ratio of 0.20 (p = 0.038). Among the 33 respondents to the postal survey (36 hips), the mean scores were VAS pain 10.9, VAS satisfaction 86.9, and OHS 44.7. A multivariable analysis revealed that reduction of stem anteversion from Taperloc to Wagner Cone was more favourable for VAS pain (p = 0.029) and VAS satisfaction (p = 0.002). Conclusion. The mid-term survival rate for THA using the Wagner Cone stem was high, which may be supported by a reduction in prosthetic impingement. The reduction in excessive stem anteversion by using a tapered cone stem was associated with reduced pain and increased patient satisfaction. Cite this article: Bone Jt Open 2024;5(10):858–867

The purposes of this study were to report the accuracy of stem anteversion for Exeter cemented stems with the Mako hip enhanced mode and to compare it to Accolade cementless stems. We reviewed the data of 25 hips in 20 patients who underwent THA through the posterior approach with Exeter stems and 25 hips in 19 patients with Accolade stems were matched for age, gender, height, weight, disease, and approaches. There was no difference in the target stem anteversion (20°–30°) between the groups. Two weeks after surgery, CT images were taken to measure stem anteversion. The difference in stem anteversion between the plan and the postoperative CT measurements was 1.2° ± 3.8° (SD) on average with cemented stems and 4.2° ± 4.2° with cementless stems, respectively (P <0.05). The difference in stem anteversion between the intraoperative measurements and the postoperative CT measurements was 0.75° ± 1.8° with Exeter stems and 2.2° ± 2.3° with Accolade stems, respectively (P <0.05). This study demonstrated a high precision of anteversion for Exeter cemented stems with the Mako enhanced mode and its clinical accuracy was better with the cemented stems than that with the cementless stems. Although intraoperative stem anteversion measurements with the Mako system were more accurate with the cemented stems than that with the cementless stem, the difference was about 1° and the accuracy of intra-operative anteversion measurements was quite high even with the cementless stems. The smaller difference in stem anteversion between the plan and postoperative measurements with the cemented stems suggested that stem anteversion control was easier with cemented stems under the Mako enhanced mode than that with cementless stems. Intraoperative stem anteversion measurement with Mako total hip enhanced mode was accurate and it was useful in controlling cemented stem anteversion to the target angle

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

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

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

We have previously reported on the improved all-cause revision and improved revision for instability risk in lipped liner THAs using the NJR dataset. These findings corroborate studies from the Australian (AOANJRR) and New Zealand (NZOA) joint registries. The optimal orientation of the lip in THAs utilising a lipped liner remains unclear to many surgeons. The aim of this study was to identify impingement-free optimal liner orientations whilst considering femoral stem version, cup inclination and cup version. A cementless THA kinematic model was developed using a 20 degree XLPE liner. Physiological ROM and provocative dislocation manoeuvre analyses were performed. A total of 9 cup positions were analysed (inclination 30–40–50 degrees, anteversion 5-15-25 degrees) and combined with 3 stem positions (anteversion 0-15-30 degrees) and 5 lip orientations (right hip 11 to 7 o'clock). Some lip orientation/component position combinations lead to impingement within the physiological ROM range. Using a lipped liner increases the femoral head travel distance prior to dislocation when impingement occurs in the plane of the lip. In THAs with a cup inclination of 30 and 40 degrees, inferior lip orientations (7–8 o'clock for a right hip) performed best. Superior lip orientation performed best with a cup inclination of 50 degrees. Femoral stem version has a significant effect on the range of movement prior to impingement and hence the preferred lip orientation. The optimal orientation of the lip in lipped liner THA is dependent on the position of both the acetabular and femoral components. In the common component orientation combination of stem anteversion 15, cup inclination 40 and cup anteversion 15, the optimal lip orientation was postero-inferiorly (8 o'clock for a right hip). Preventing impingement during physiological ROM is possible with appropriate lip liner orientation

Introduction. Cross table lateral (CTL) radiographs are commonly used to measure acetabular component anteversion after total hip arthroplasty (THA). CTL measurements may differ by >10 degrees from CT scan measurements, but the reasons for this discrepancy are poorly understood. We compare anteversion measurements made on CTL radiographs and CT scans to identify spinopelvic parameters predictive of inaccuracy. Methods. THA patients (n=47) with preoperative spinopelvic radiographic analysis and postoperative CT scans were retrospectively reviewed. Acetabular component anteversion was measured on post-operative CTL radiographs, and CT scans using 3D reconstructions of the pelvis. Patients were grouped by error (CTL-CT)>10° (n=11) or <10° (n=36), and spinopelvic mobility parameters were compared using t-tests. Correlation between error and mobility parameters was assessed with Pearson coefficient. Results. Patients with CTL error >10° (range 10–14) had stiffer lumbar spines with less lumbar flexion (38° vs 47°, p=0.03), greater sagittal imbalance measured by pelvic incidence-lumbar lordosis mismatch (6° vs −2°, p=0.04), more pelvic extension when seated (pelvic tilt −10° vs −2°, p=0.05), and greater change in pelvic tilt between supine and seated positions (13° vs 4°, p=0.04). The error of CTL measurements showed a positive correlation with increased CTL anteversion (r=0.5, p=0.001), standing lordosis (r=0.23, p=0.05), seated lordosis (r=0.4, p=0.01) and pelvic tilt change between supine and step-up positions (r=0.34, p=0.01). Discussion. Differences in spinopelvic mobility patterns may explain the variable accuracy of acetabular anteversion measurements on CTL radiographs. Patients with stiff spines and increased compensatory pelvic motion have less accurate measurements on CTL radiographs. Flexion of the contralateral hip is required to obtain clear CTL radiographs. In patients with a stiff lumbar spine, this movement may extend the pelvis and increase anteversion of the acetabulum on CTL views. Reliable analysis of acetabular component anteversion in this patient population may require advanced imaging with a CT scan

Introduction. The correct anteversion of the acetabular cup is critical to achieve optimal outcome after total hip arthroplasty. While number of method has been described to measure the anteversion in plane anteroposterior and lateral radiograph, it is still controversial which method provides best anteversion measurement. While many of the previous studies used CT scan to validate the anteversion measured in plane anteroposterior radiograph, this may cause potential bias as the anteversion measured in CT scan reflects true anteversion while the anteversion measurement methods in plane radiograph are design to measure the planar anteversion. Thus, in the current study, we tried to find the optimal anteversion measurement method free from the previously described bias. Material and method. Custom made cup model was developed which enables change in anteversion and inclination. Simple radiograph was taken with the cup in 10° to 70° degree of inclination at 10° increments and for each inclination angle, anteversion was corrected from 0° to 30° at 5° increments. The radiograph was taken with the beam directed at the center of the cup (mimicking hip centered anteroposterior radiograph) and at 9cm medial to the cup (mimicking pelvis anteroposterior radiograph). The measurements were done by two orthopaedic surgeons using methods described by 1) Pradhan et al, 2) Lewinak et al, 3) Widmer et al, and 4) Liaw et al. For each measurements, the anteversion were compared with the actual anteversion. Result. Interoverver correlation (kappa value) were high in all measurements ranging 0.988 to 0.998. Regardless of how the radiograph was taken, Pradhan method was the most accurate measurement method showing difference of 2.17° ± 1.69° and −2.5° ± 1.93° compare to the actual anteversion respectively for hip centered radiograph and pelvis anteroposterior radiograph. The Widmer method showed the least accuracy (pelvis AP : −6.75° ± 4.62°, hip centered AP : −14.84° ± 4.36°). However, when the anteversion were measured in the safe zone with the inclination in 30° to 50° Liaw's method in hip centered radiograph showed the highest accuracy (1.63° ± 1.4°). Conclusion. The study indicates that the Pradhan's method may provide the most accurate anteversion measurement. However, with the hip in 30° to 50° inclination, Liaw's method measured from hip centred radiograph will provide most accurate anteversion measurement

The purpose of this study was to investigate the influence of surgical approach on femoral stem version in THA. This was a retrospective database review of 830 THAs in 830 patients that had both preoperative and postoperative CT scans. All patients underwent staged bilateral THAs and received CT-based 3D planning on both sides. Stem version was measured in the second CT-scan and compared to the native neck axis measured in the first CT-scan, using the posterior condyles as the reference for both. Cases were performed by 104 surgeons using either a direct anterior (DAA, n=303) or posterior (PA, n=527) approach and one of four stem designs: quadrangular taper, calcar-guided short stem, flat taper and fit-and-fill. Sub-analyses investigated changes in version for low (≤5°), neutral (5–25°) and high (≥25°) native version subgroups and for the different implant types. Native version was not different between approaches (DAA = 12.6°, PA = 13.6°, p = 0.16). Overall, DAA stems were more anteverted relative to the native neck axis vs PA stems (5.9° vs 1.4°, p<0.001). This trend persisted in hips with high native version (3.2° vs -5.3°, p<0.01) and neutral native version (5.3° vs 1.3°, p<0.001), but did not reach significance in the low native version subgroup (8.9° vs 5.9°, p=0.13). Quadrangular taper, calcar-guided, and flat taper stem types had significantly more anteversion than native for DAA, while no differences were found for PA. Stems implanted with a direct anterior approach had more anteversion than those implanted with a posterior approach. The smaller surgical field, soft tissue tension and lack of a “tibial” vertical reference frame may contribute to this finding

Introduction. To control anteversion of the acetabular cup and femoral stem within an appropriate angle range is extremely important in total hip arthroplasty. The sum of these angles is called the “combined anteversion” (CA), and a navigation system is necessary for its accurate intraoperative evaluation. However, navigation is too expensive and time-consuming to be commonly used. Therefore, a cheaper and easier tool for intraoperative CA evaluation is desired in the clinical field. I had an idea of marking ruler-like scales on a trial femoral head ball for this purpose. The purpose of this study was to introduce the idea in a computer simulation. Materials and Methods. An acetabular cup, a femoral head, and a femoral stem were designed virtually using three- dimensional computer graphics software (FreeCAD). The head was assembled with the femoral stem, and the axis of the stem was tilted 7 degrees to the vertical axis, referring the angle between mechanical and anatomical axes of the femur. Ruler-like scales and a horizontal line were marked on the surface of the head. The cup inclination angle was fixed at 40 degrees and paired with the head and stem assembly. The cup axis was on the stem–neck plane, which meant that CA was zero before rotating the cup and the stem. The scale at an intersecting point of the inner edge of the cup and the horizontal line was read before and after rotating the cup and the stem. I confirmed if the sum of the rotated angles of the cup and stem and the angle indicated by the scales were consistent when they were rotated at an arbitrary angle. Results. CA was successfully evaluated by the difference in angle indicated by the scales before and after rotation. Discussion. There are several definitions for cup and stem anteversion. The CA evaluated in this study was the sum of anatomical anteversion of the cup and the angle between the neck axis and epicondylar or posterior-condylar axes of the knee projected on the horizontal plane. There are several factors that make the CA evaluation by this method inaccurate. For example, when the cup inclination angle is not 40 degrees, or the pelvis or the femur are not held at the intended position, the CA indicated by the scales is not accurate. It is my future work to assess whether this method is accurate enough to be used in the clinical situation. Conclusion. Marking ruler-like scales on the femoral head would be a low-cost and effective method for rough intraoperative evaluation of CA

INTRODUCTION. In total hip arthroplasty, preoperative planning is almost indispensable. Moreover, 3-dimensional preoperative planning became popular recently. Anteversion management is one of the most important factors in preoperative planning to prevent dislocation and to obtain better function. In arthritic hip patients osteophytes are often seen on both femoral head and acetabulum. Especially on femoral head, osteophytes are often seen at posterior side and its surface creates smooth round contour that assumes new joint surface. (Fig. 1). We can imagine new femoral head center tracing that new joint surface. OBJECTIVES. In the present study, the posterior osteophytes are compared in osteoarthritic patients and other patients. MATERIALS & METHODS. Anteversion and new anteversion which was reduced by osteophyte formation were assessed in 28 hip CAT scans, (22 arthritic hips, 6 avascular necrotic hips). RESULTS. Only in arthritic patients, osteophytes on posterior side were observed. The anteversion was 33.7+/− 13.0 degree in arthritic patients, which was reduce to 29.7+/−13.1 degree. The mean difference was 4.0+/−4.7 degree reduction. In AVN patients the mean anteversion was 21.4 +/− 9.40 in AVN patients. No reduction was observed in AVN patients. DISCUSSION. Osteophytes are often created to make the biomechanical situation better. This phenomenon is possiblly explained that those posterior osteophytes have been formed for proper reduction of excessive anteversion

Introduction: Template use prior to hip arthroplasty is a valuable form of pre-operative planning. The femoral neck anteversion may influence the interpretation of the femoral off-set on plain x-rays. Method: The femoral neck anteversion of a series of adult patients with developmental hip dysplasia has been assessed using CT guided measurement. Using this data and more normal ranges of anteversion we have been able to estimate the effect of anteversion on perceived off-set. Results: Femoral neck anteversion significantly effects the perceived offset at angles of greater than 20 degrees. The average femoral neck anteversion in our series of patients with hip dysplasia was 22 degrees. With a perceived off-set of 40mm on an AP x-ray the actual offset becomes 44mm in a patient when the patient has 25 degrees of anteversion. Conclusion: Femoral neck anteversion is an important factor when considering the appearance of plain hip x-rays. Recognition of this factor may improve the ability of the operating surgeon to assess the correct components pre-operatively

Introduction. Traditional methods of component positioning in total hip replacement (THR) utilize mechanical alignment guides which estimate position relative to the plane of the operating room table. However, variations in pelvic tilt alter the relationship between the anatomic plane of the pelvis and that of the table such that components placed in optimal position relative the table may not land within the classic anatomic “safe zone” described by Lewinnek. It has been suggested that navigation software should incorporate adjustments for the degree of pelvic tilt. Current imageless navigation software has this capability, however there is a paucity of data regarding the accuracy of this technology. Purpose. We aimed to assess the accuracy of intra-operative pelvic tilt adjusted anteversion measurements as compared to unadjusted measurements. Methods. 6-week post-operative Anteroposterior Pelvis radiographs from 27 consecutive primary THR were measured utilizing Ein-Bild-Roentgen-Analyse (EBRA-Cup®) hip analysis software (Figure 1) and a cross-table lateral radiograph (Figure 2). Inclination and anteversion values were recorded and direction of version was confirmed by assessment of cross-table lateral images. Values were compared with intra-operative measurements obtained via BrainLab® imageless navigation. Pelvic tilt adjusted and unadjusted anteversion measurements were recorded. Mean measurement error and standard error of the mean were determined and Pearson correlation coefficients were calculated. Results. Navigated component inclination correlated with EBRA-Cup® derived inclination measurements (r = 0.4308, p = 0.02) with a mean error of 3.8°. Similarly, pelvic tilt adjusted anteversion correlated with EBRA-Cup® derived measurements (r = 0.65, p < 0.001). The mean difference between anteversion measurements was 3.58° and the standard error of the mean was 0.58°. 24 of 27 patients had <6° of difference between the two measurements. Post-operative component position correlated more closely with pelvic tilt adjusted anteversion than with unadjusted values (r = 0.3, p = 0.12). As expected, this was most pronounced in patients with greater than 10 degrees of pelvic tilt (mean error of 11.2° vs. 4.5°). Conclusions. Imageless navigation based anteversion measurements are more accurate when adjusted for pelvic tilt

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

Introduction. Acetabular component orientation is an important determinant of outcome following total hip arthroplasty (THA). Although surgeons aim to achieve optimal cup orientation, many studies demonstrate their inability to consistently achieve this. Factors that contribute are pelvic orientation and the surgeon's ability to correctly orient the cup at implantation. The goal of this study was to determine the accuracy with which surgeons can achieve cup orientation angles. Methods. In this in vitro study using a calibrated left and right sawbone hemipelvis model, participants (n=10) were asked to place a cup mounted on its introducer giving different targets. Measurements of cup orientation were made using a stereophotogrammetry protocol to measure radiographic inclination and operative anteversion (OA). A digital inclinometer was used to measure the intra-operative inclination (IOI) which is the angle of the cup introducer relative to the floor. First, the participant stated his or her preferred IOI and OA and positioned the cup accordingly. Second, the participant had to position the cup parallel to the anteversion of the transverse acetabular ligament (TAL). Third, the participant had to position the cup at IOI angles of 35°, 40° and 45°. Fourth, the participant used the mechanical alignment guide (45° of IOI and 30° of OA) to orient the cup. Each task was analysed separately and subgroup analysis included left versus right side and hip surgeons versus non-hip surgeons. Results. For the first task, hip surgeons preferred smaller IOI and larger OA than non-hip surgeons, but there was no significant difference in accuracy between both groups. When aiming for TAL, both surgeon groups performed similar, but accuracy on the non-dominant side was significantly better compared with the dominant side (mean deviation 0.6° SD 2.4 versus −2.6° SD 2.3) (p=0.004). When aiming for a specific IOI target of 35°, 40° or 45°, non-hip surgeons outperformed hip surgeons (mean deviation form target IOI 1.9° SD 2.7 versus −3.1° SD 3.8) (p<0.0001) with less variance (p=0.03). Contrary to version, accuracy on the dominant side was significantly better compared with the non-dominant side (mean deviation −0.4° SD 3.4 versus −2.1° SD 4.8). When using a mechanical guide, surgeons performed similar (0.6° SD 1.2 versus −0.4° SD 2.1 for inclination p=0.11 and −0.5° SD 2.6 versus −1.8° SD 3.3 for version p=0.22) and these values did not differ significantly from the actual IOI and OA of the mechanical guide. When using a mechanical guide, there was no difference in accuracy between the dominant and non-dominant side. Conclusion. There was no difference in accuracy between hip surgeons and non-hip surgeons when they aimed for their preferred IOI and OA or used a mechanical guide. When aiming for a specific IOI target, non-hip surgeons outperformed hip surgeons. Hip surgeons overestimate IOI and underestimate OA, presumably because this helps to achieve the desired radiographic cup orientation. Regarding accuracy, the non-dominant side was better for version and the dominant side for inclination. When aiming for a specific IOI and OA target, using a mechanical guide is significantly better than freehand cup orientation

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. 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

Purpose. The purpose of this study is to inspect balance of the pelvis in the acetabular operation of total hip arthroplasty (THA) using direct anterior approach (DAA), and it is to examine precision of the acetabular socket setting. Materials and Methods. We performed THA using DAA to 104 patients (114 hips) joints from August 2006 to April 2009 and identified for seventy five patients (eighty four hips) that imaging of the postoperative CT was possible. The orientation of acetabular sockets were performed using an alignment guide which assumed an operating table an axis from August 2006 to September 2008 (A group), and using an alignment guide which assumed a pelvis an axis from October 2008 to May 2009(B group). A group were thirty eight patients (forty four hips), and B group were twenty eight (thirty). There were two men and thirty six women in A group, and one man and twenty seven women in B group. The average age of both groups was 66 years old. The objective angle of the acetabular socket was performed as angle guide of abduction of 45° and anteversion of 20°. The orientation of the acetabular socket converted the angle of postoperative CT into radiographic angle, and measured it. For sixteen hips in B group, both angle guide was used, and there were measured a difference of two angle guide in the acetabular operation as movement of the pelvis. The examination item assumed it the mean values of angle for the acetabular socket in both groups, precision to set up the acetabular socket to planned orientation within ±5 °and a mean difference of two angle guides of sixteen hips in B group. Results. The mean values of abduction for the acetabular socket were 45 °in A group and 43.8 °in B group, and that of anteversion for the acetabular socket were 22.5 °in A group and were 20.9 °in B group. In A group, the precision to set up the acetabular socket to abduction 45±5 °was 91.8%, and that to anteversion 20±5 ° was 71%. Hips that anteversion of the acetabular socket was more than 25° were 13/44 joints. In B group, the precision to set up the acetabular socket to abduction of 45±5 °was 97%, and that to anteversion of 20±5°was 97.5%. The difference of two alignment guide for sixteen hips in B group were mean 5°(0～9°), and anteversion of pelvis decreased. Disccussion. THA using DAA causes a pelvic anteversion during the acetabular preparation and as a result, anteversion of postoperative acetabular sockets increase. It suggests that even if DAA is supine position, the movement of the pelvis occurs. Conclusion. The precision to set up the acetabular socket which we used alignment guide make the pelvis the axis was higher than that used alignment guide make the operating table the axis. In the acetabular preparation using DAA, anteversion of the pelvis occurred mean 5°

Introduction. The midcortical line, the midline between the anterior and the posterior cortical walls has been reported as an intraoperative reference guide for reproducing the true femoral anteversion in cross-sectional computed tomography (CT) image study but we suspected that the version of the midcortical line on the cutting surface is different from that on the axial image. The three-dimensional (3D) CT-based preoperative planning software for THA enabled us to evaluate the cut surface of the femoral neck osteotomy. When we planned the straight non-anatomic stem placement in 20° of anteversion, we noticed that the line connecting the trochanteric fossa and the middle of the medial cortex of the femoral neck (T line) was coincident with the component torsion in almost all cases except those involving secondary osteoarthritis of the hip. Therefore we hypothesised that the T-line would provide an accurate reference guide for anteversion of the femoral component in THA. We performed this study to answer the question: which is the better intraoperative reference guide for reproducing the true femoral anteversion, the midcortical line or the T line?. Materials and methods. The institutional review board allowed a retrospective review of CT images of 33 normal femora (33 patients) in our CT database. We performed virtual THA using the non-anatomic straight stem on the 3D CT-based preoperative planning software at the two different cutting heights of 10mm or 15mm above the lesser trochanter. The anteversion of the stem implanted parallel to the T line or the midcortical line was measured. The true femoral neck anteversion was measured using the single CT slice method reported by Sugano. Results. The mean true femoral anteversion was 16.9°±10.7°. We found strong positive correlations between the anteversion of the stem and the true femoral anteversion using the T-line at each cutting height (r=0.85 and r=0.92 in 10mm and 15mm cutting height respectively). The mean differences between the anteversion of the stem parallel to the T line and the true femoral anteversion were 3.5° (95% confidence interval; 1.38°–5.59°) and 2.7° (95% confidence interval; 1.15°–4.15°) in 10mm and 15mm cutting height respectively. The mean anteversion of the stem parallel to the midcortical line on the cut surface were −2.0° and −1.9° in 10mm and 15mm cutting height respectively and we could not implant the stem in some cases. Discussion. Theoretically, the anteversion of the stem using the T line is close to the true femoral anteversion because the trochanteric fossa is in line with the femoral canal, and the center of the medial cortex of the cutting surface faces the center of the femoral head, if the cutting height is not too low. Conclusion. The T line was a useful intraoperative reference guide for reproducing the true femoral anteversion and the midcortical line on the cut surface of the femoral neck was not a good intraoperative reference guide