Radiographic calculation of anteversion in acetabular prostheses

Functional Acetabular Component Positioning During Direct Anterior Approach Hip Arthroplasty Using a Novel Three-Dimensional Virtual Mesh Imaging System With Fluoroscopy

BACKGROUND

Optimal position of total hip arthroplasty (THA) components is critical for joint mechanics and stability. Acetabular component positioning during supine surgery in direct anterior approach (DAA) THA may be different in the standing position postoperatively, which traditional fluoroscopy is unable to predict. A novel 3-dimensional (3D) image analysis technology (IAT) that uses artificial intelligence to measure the tilt and rotation of the pelvis has enabled prediction of component positioning from supine to standing. The purpose of this study was to compare intraoperative fluoroscopy, non-3D-IAT, and 3D-IAT with postoperative standing radiographs to assess the accuracy of component positioning.

METHODS

From 2022 to 2023, 30 consecutive patients (86.6% women, mean age 59 [range, 55 to 67]) undergoing primary DAA THA with the use of the 3D-IAT were identified. A separate cohort of 148 patients from 2020 to 2021 (85% women, mean age 65 [range, 55 to 69]) who underwent DAA THA with non-3D-IAT was used for comparison. Leg length discrepancy (LLD), cup anteversion, and inclination were manually measured on intraoperative fluoroscopic images and digitally measured using IAT. Follow-up evaluation occurred at 1 month with standing pelvis radiographs measured using Ein Bild Röntgen Analyze-Cup software. Measurements were compared via Wilcoxon signed rank tests where P ≤ .05 indicates significantly different measurements.

RESULTS

Median LLD, inclination, and anteversion measurements via non-3D-IAT and fluoroscopy were significantly different compared to postoperative standing radiographs (P < .001). The 3D-IAT more accurately predicted LLD, abduction, and anteversion, with values not significantly different from postoperative standing measurements (P = .23, P = .93, and P = .36, respectively).

CONCLUSIONS

The use of the 3D-IAT during DAA THA allowed for the more accurate prediction of acetabular component position in the standing position postoperatively.

Liaw's Ellipse Anteversion Method for Distinguishing Acetabular Component Retroversion from Anteversion on Plain Radiographs

Improper acetabulum component position is a significant risk factor for postoperative dislocation after total hip arthroplasty. Several radiographic two-dimensional methods exist for measuring acetabulum component anteversion, but they cannot distinguish between anteversion and retroversion. "Liaw's version," initially proposed as a simple mathematical standardized two-dimensional method, was modified to the computerized ellipse method, proving superior accuracy to traditional two-dimensional methods. In this article, we demonstrated its application in detecting and measuring retroverted acetabulum component. We obtained anteroposterior pelvis radiographs from a patient undergoing total hip arthroplasty on the day of surgery and 2 weeks postoperatively. The computerized ellipse method was used to measure the acetabulum component orientation. Upon comparison, the difference between θ assigned to be retroverted (9.52-8.56 = 0.96) is much smaller than the difference between θ assigned to be anteverted (23.81-18.86 = 4.95), leading us to determine retroversion. This was further confirmed by computed tomography at the 6-week follow-up. We propose that using the computerized ellipse method to measure Liaw's version can be a valuable tool in identifying acetabulum component retroversion on anteroposterior radiographs during routine postoperative follow-up and retrospective assessments of total hip arthroplasty patients.

Could We Expect Postoperative Cup Anteversion after Total Hip Arthroplasty Using Postoperative Plain Anteroposterior and Lateral Radiograph? A Three-Dimensional Experimental Operation Study

BACKGROUND

A postoperative radiograph in total hip arthroplasty (THA) is usually obtained to evaluate the inclination and anteversion of the acetabular components. However, there is no gold-standard method for calculating the exact inclination and anteversion of the acetabular components on post-THA radiographs. We aimed to measure the actual anteversion of the acetabular component on postoperative radiographs by obtaining correlation data between the virtual and actual acetabular component positioning using virtual three-dimensional (3D) surgery.

METHODS

A total of 64 hip scans of 32 patients who underwent lower-extremity computed tomography (CT) were retrospectively reviewed. We reconstructed 3D models of the 64 hips using customized computer software (Mimics). Furthermore, to identify the safe zone of acetabular component position in THA, we performed virtual 3D surgery simulations for five anteversion (-10°, 0°, 10°, 20°, and 30°) and five inclination (20°, 30°, 40°, 50°, and 60°) types. We analyzed the acetabular anatomy using 3D models to measure the radiographic, anatomical, and operative anteversion (RA, AA, OA) and inclination (RI, AI, OI) angles. Additionally, we used the Woo-Morrey (WM) method to calculate the anteversion angle in the reconstructed cross-table lateral (CL) radiographs and determined the correlation between these measurements.

RESULTS

The safe zone of the acetabular component was visualized on post-THA CL radiographs using the WM method of anteversion measurement based on the different anteversions and inclinations of the acetabular component. The AA, RA, OA, OI, and WM differed significantly between males and females (p value < 0.05). As the anatomical inclination or anteversion increased, the WM anteversion measurements also increased. The radiographic anteversion measurement best matched the WM method of measurement, followed by anatomical and operative methods.

CONCLUSIONS

The actual anteversion of the acetabular component after THA can be measured on CL radiographs with the WM method using a 3D virtual program, with good reproducibility.

A novel method for evaluating combined component anteversion in total hip arthroplasty on cross-table lateral hip radiographs

INTRODUCTION

Accurate measurement of combined component anteversion (CA) is important in evaluating the radiographic outcomes following total hip arthroplasty (THA). The aim of the present study was to evaluate the accuracy and reliability of a novel radiographic method in estimating CA in THA.

MATERIALS AND METHODS

The radiographs and computer tomography of patients who underwent a primary THA were retrospectively reviewed, to measure the radiographic CA (CAr), defined as the angle between a line connecting the center of the femoral head to the most anterior rim of the acetabular cup and a line connecting the center of the femoral head to the base of the femoral head to allow a comparison with the CA measured on the CT (CACT). Subsequently, a computational simulation was performed to evaluate the effect of cup anteversion, inclination, stem anteversion, and leg rotation on the CAr and develop a formula that would correct the CAr according to the acetabular cup inclination based on the best-fit equation.

RESULTS

In the retrospective analysis of 154 THA, the average CAr_cor, and CACT were 53 ± 11° and 54 ± 11° (p > 0.05), respectively. A strong correlation was found between CAr and CACT (r = 0.96, p < 0.001), with an average bias of - 0.5° between CAr_cor and CACT. In the computational simulation, the CAr was strongly affected by the cup anteversion, inclination, stem anteversion, and leg rotation. The formula to convert the CAr to CA_cor was: CA-cor = 1.3*Car - (17* In (Cup Inclination) - 31.

CONCLUSION

The combined anteversion measurement of THA components on the lateral hip radiograph is accurate and reliable, implying that it could be routinely used postoperatively but also in patients with persistent complaints following a THA.

LEVEL OF EVIDENCE

Cross-sectional study, Level III.

Integrating model explanations and hybrid priors into deep stacked networks for the "safe zone" prediction of acetabular cup

BACKGROUND

Existing state-of-the-art "safe zone" prediction methods are statistics-based methods, image-matching techniques, and machine learning methods. Yet, those methods bring a tension between accuracy and interpretability.

PURPOSE

To explore the model explanations and estimator consensus for "safe zone" prediction.

MATERIAL AND METHODS

We collected the pelvic datasets from Orthopaedic Hospital, and a novel acetabular cup detection method is proposed for automatic ROI segmentation. Hybrid priors comprising both specific priors from data and general priors from experts are constructed. Specifically, specific priors are constructed based on the fine-tuned ResNet-101 convolutional neural networks (CNN) model, and general priors are constructed based on expert knowledge. Our method considers the model explanations and dynamic consensus through appending a SHapley Additive exPlanations (SHAP) module and a dynamic estimator stacking.

RESULTS

The proposed method achieves an accuracy of 99.40% and an area under the curve of 0.9998. Experimental results show that our model achieves superior results to the state-of-the-art conventional ensemble classifiers and deep CNN models.

CONCLUSION

This new screening model provides a new option for the "safe zone" prediction of acetabular cup.

Achieving Precise Cup Positioning in Direct Anterior Total Hip Arthroplasty: A Narrative Review

Malpositioned implants in total hip arthroplasty are associated with impingement, increased wear, and dislocations, thus precise cup positioning is crucial. However, significant deviations between targeted and actually achieved cup positions have been found even in patients operated by experienced surgeons. When aiming for higher accuracy, various methods based on freehand positioning lead by anatomic landmarks, C-arm fluoroscopy, imageless navigation, or robotic-assisted-surgery have been described. There is a constant development of new products aiming to simplify and improve intraoperative guidance. Both the literature and expert opinions on this topic are often quite controversial. This article aims to give an overview of the different methods and systems with their specific advantages and potential pitfalls while also taking a look into the future of cup positioning in anterior hip replacements.

Cup positioning and its effect on polyethylene wear of vitamin E- and non-vitamin E-supplemented liners in total hip arthroplasty: radiographic outcome at 5-year follow-up

BACKGROUND

Aseptic loosening remains a challenging problem after total hip arthroplasty. Accurate cup placement and supplementation of antioxidants in acetabular liners might reduce material failure rates. The aim of this study is to assess the effect of the cup position on the wear behaviour of UHMWPE-XE and UHMWPE-X liners in vivo using virtual radiographs.

METHODS

We conducted a prospective, randomized, controlled, multicenter trial. Clinical data of 372 probands were analyzed. Anteroposterior pelvic X-rays of 324 patients immediately postoperatively and after 1 and 5 years were evaluated by the RayMatch® analysis software regarding cup position and wear behaviour.

RESULTS

Mean cup anteversion was 20.3° (± 7.4) and inclination was 41.9° (± 7.0) postoperatively. 62.3% of all patients had an anteversion and inclination within the Lewinnek safe zone. Anterior and anterolateral approaches led to significantly higher cup anteversion compared to lateral approaches (27.3° ± 5.5; 20.9° ± 7.2; 17.5° ± 6.6; p < 0.001 and p = 0.001, respectively). Mean anteversion increased to 24.6° (± 8.0) after 1 year (p < 0.001). Only one revision occurred because of implant dislocation. Wear rates from UHMWPE-X and UHMWPE-XE did not differ significantly. Anteversion angles ≥ 25° correlated to increased polyethylene wear (23.7 µm/year ± 12.8 vs. 31.1 µm/year ± 22.8, p = 0.012) and this was amplified when inclination angles were ≥ 50° (23.6 µm/year ± 12.8 vs. 38.0 µm/year ± 22.7, p = 0.062).

CONCLUSION

Anterior approaches lead to the highest inaccuracy of cup placement, but cup positioning outside the Lewinnek safe zone does not necessarily cause higher dislocation rates. Moreover, mean anteversion increased by approximately four degrees within the first year after operation, which is expected to be functional due to a regularization of pelvic tilt after intervention. Mid-term wear rates of UHMWPE-X and UHMWPE-XE liners are comparable, but steep cup positions lead to significantly increased polyethylene wear. In summary, a re-evaluation of target zones for intraoperative cup positioning might be considered. In the long-term reduced oxidative embrittlement could lead to superior wear behaviour of vitamin E-blended liners.

Laser projector method for measuring postoperative acetabular anteversion after total hip replacement

INTRODUCTION

For patients undergoing THR, measuring the postoperative acetabular anteversion precisely plays a pivotal role in the prognosis. However, using elliptical methods mandates computerized equipment that is frequently in shortage in remote areas and developing countries. We invented a laser projector utilizing the ellipse method to measure the acetabular anteversion directly. The aim is to examine the consistency and validity of the laser projector as compared to our original software, Elliversion.

MATERIALS AND METHODS

We retrospectively collected 50 postoperative pelvis radiographs including acetabulum from our institution. One investigator first measured the anteversion of included radiographs through Elliversion software as the control group. Subsequently, two operators independently used the laser projector for measurements in two separate periods with 1-day intervals as the experimental group. Our analysis was comprised of intra- and inter-observer comparisons and reliability, which investigated both the consistency and validity, by using two-sample student's t-test and intraclass correlation coefficient.

RESULTS

There was no significant difference in measuring the anteversion through laser projectors between two operators (p = 0.54), with excellent inter-observer reliability (ICC, 0.967). The estimated effect in the anteversion measurement between the Elliversion and laser projector was also comparable, with the ICC level of 0.984, indicating excellent reliability.

CONCLUSION

Our study reported the consistency and validity of this laser projector as there is no significant difference between Elliversion and Laser projector, notably with excellent intra- and inter-observer reliability. We look forward to helping elevate clinical acumen when doctors provide care to patients after THR, especially in remote areas.

Variability in Acetabular Component Position in Patients Undergoing Direct Anterior Approach Total Hip Arthroplasty Who Have Concomitant Spine Pathology

BACKGROUND

Hip instability following total hip arthroplasty (THA) can be a major cause of revision surgery. Physiological patient position impacts acetabular anteversion and abduction, and influences the functional component positioning. Osteoarthritis of the spine leads to abnormal spinopelvic biomechanics and motion, but there is no consensus on the degree of component variability for THAs performed by anterior approach. Therefore, we sought to present guidelines for changes in acetabular component positioning between supine and standing positions for patients undergoing primary THA by a uniform anterior approach.

METHODS

Perioperative patient radiographs of the pelvis and lumbar spine were collected. Images were used to determine acetabular component positioning and degree of coexisting spinal pathology, categorized as a Lane Grade (LG). Final analysis of variance was performed on a sample size of 643 anterior primary THAs.

RESULTS

From supine to standing position, as the severity of lumbar pathology increased the change in anteversion also increased (LG:0 = -0.11° ± 4.65°, LG:1 = 2.02° ± 4.09°, LG:2-3 = 5.78° ± 5.72°, P < .001). The mean supine anteversion in patients with absent lumbar pathology was 19.72° ± 5.05° and was lower in patients with worsening lumbar pathology (LG:1 = 18.25° ± 4.81°, LG:2-3 = 16.73° ± 5.28°, P < .001).

CONCLUSION

Patients undergoing primary THA by anterior approach with worsening spinal pathology have larger increases in component anteversion when transitioning from supine to standing positions. Consideration should be given to this expected variability when placing the patient's acetabular component.

Usefulness of intraoperative C-arm image intensifier in reducing errors of acetabular component during primary total hip arthroplasty: an application of Widmer's method

Background

Acetabular prosthesis positioning in total hip arthroplasty (THA) is crucial in reducing the risk of dislocation. There has been minimal research on the proper way to put the acetabular components into the safe zone intraoperatively. Assessment of version by intraoperative imaging intensifier is very valuable. The value of Widmer’s method, using the intraoperative C-arm available to determine cup anteversion was assessed.

Methods

One hundred one hips in 91 patients who underwent primary THA were eligible for inclusion. Utilizing intraoperative C-arm images, measurement was performed using the technique described by Widmer. The values obtained using 3D computed tomography postoperatively, which determined the anteversion of the acetabular component, were regarded as the reference standard.

Results

The method of Widmer obtained values similar to those obtained using 3D computed tomography and was considered accurate (n.s.). All 101 hips were positioned in the set target zone. Among the 101 hips, the cup position in nine hips (8.9%) was changed. The dislocation rate in our study was 1.0% with all dislocations occurring in hips placed in the target zone. The mean Harris hip score after THA in 1 year was 94.2 (82-98).

Conclusions

The method of Widmer was accurate using intraoperative imaging intensifier for the measurement of the anteversion of the acetabular component during THA, with reference to the anteversion obtained from the 3D computed tomography. Also, utilizing intraoperative C-arm imaging was very useful because it allowed for correction of the position of the acetabular cup.

Assessment of Acetabular Component Anteversion after Total Hip Arthroplasty: Comparison of Anteroposterior and Cross-Table Lateral Radiographs with Computed Tomography Scans

Background

Several methods of measurement of anteversion of acetabular components after total hip arthroplasty (THA) have been described in the literature using plain radiographs or computed tomography (CT) scans. None of these have proved to be the gold standard. We aimed to study the correlation between the CT and radiographic methods of calculation of acetabulum anteversion.

Methods

CT scans of the pelvis, anteroposterior (AP) and cross-table lateral (CL) radiographs were obtained in 60 patients who underwent THA two weeks after surgery. Anteversion was measured using Widmer method and Liaw method on AP radiographs, and the ischiolateral method on CL radiographs. Anteversion measured on the CT scan was taken as the reference anteversion and the above measurements were analysed for correlation with the measurements on CT scan. Intraclass correlation coefficients (ICCs) were calculated for both intra- and interobserver reliability.

Results

Mean acetabular version on CL radiographs was 53.1 ± 10.7. Mean version on AP radiographs by Widmer method was 21.4 ± 3.6 and by Liaw method was 20.3 ± 4.8. Mean version on CT scans was 26.02 ± 6.8. There was a good correlation between the acetabular version on CT scans with the version on AP radiographs by Widmer method (r = 0.78, p < 0.001) and Liaw method (r = 0.87, p < 0.001). Good correlation was seen between the acetabular version on CL radiographs and CT scans (r = 0.91, p < 0.001). Also, a good correlation was observed between the acetabular version measurements on CL radiographs and AP radiographs by Widmer method (r = 0.81, p < 0.001) or Liaw method (r = 0.70, p < 0.001). Excellent inter- and intraobserver reliability were seen for all the measurements.

Conclusions

Calculation of acetabular component version on AP views as well as CL views of plain radiographs showed a strong correlation with the version measurements on CT scans. Good correlations were observed between different techniques of measurement on radiographs. Therefore, all these measurements can be valid methods for assessment of anteversion.

Changes of acetabular anteversion according to pelvic tilt on sagittal plane under various acetabular inclinations

Improper functional orientation of the acetabular cup can result in improper positions when dynamic pelvic positions are not considered. The purpose of this study was to evaluate changes on acetabular anteversion according to pelvic tilt under various acetabular inclinations. Two artificial pelvic models were selected for this study. Acetabular inclinations on the coronal plane were 25°, 32°, 50°, and 60°. Acetabular anteversion of all components were 15°. Changes of anteversion according to pelvic tilt were measured at angles of 0°, 10°, 20°, 30°, and 40°. Computer Navigation, PolyWare 3D pro, CT, and plain radiography were used to measure each angle. The anatomical anteversions against pelvic tilt were calculated using the following formulae: anatomical anteversion (°) = -14.48Χ + 90.18 (inclination angle 25°); anatomical anteversion (°) = -12.26Χ + 80.10 (inclination angle 32°); anatomical anteversion (°) = -7.468Χ + 61.13 (inclination angle 50°); and anatomical anteversion (°) = -5.328Χ + 44.84 (inclination angle 60°) (Χ: pelvic tilt angle). Radiographic anteversion against pelvic tilt were calculated using the following formulae: radiographic anteversion (°) = -9.50Χ + 57.09 (inclination angle 25°); radiographic anteversion (°) = -8.577Χ + 50.89 (inclination angle 32°); radiographic anteversion (°) = -6.794Χ + 45.73 (inclination angle 50°); radiographic anteversion (°) = -5.226Χ + 33.08 (inclination angle 60°). In conclusion, changes in anteversion according to pelvic tilt were lesser at higher degrees of acetabular inclination.

Vitamin E-blended highly cross-linked polyethylene liners in total hip arthroplasty: a randomized, multicenter trial using virtual CAD-based wear analysis at 5-year follow-up

BACKGROUND

Progressive oxidation of highly cross-linked ultra-high molecular weight (UHMPWE-X) liners is considered to be a risk factor for material failure in THA. Antioxidants such as vitamin E (alpha-tocopherol) (UHMWPE-XE) were supplemented into the latest generation of polyethylene liners. To prevent inhomogenous vitamin E distribution within the polymer, blending was established as an alternative manufacturing process to diffusion. The purpose of the present study was to investigate the in vivo wear behavior of UHMWPE-XE in comparison with conventional UHMWPE-X liners using virtual CAD-based radiographs.

METHODS

Until now, 94 patients from a prospective, randomized, controlled, multicenter study were reviewed at 5-year follow-up. Of these, 51 (54%) received UHMWPE-XE and 43 (46%) UHMWPE-X liners. Anteroposterior pelvic radiographs were made immediately after surgery and at 1 and 5 years postoperatively. The radiographs were analyzed using the observer-independent analysis software RayMatch^® (Raylytic GmbH, Leipzig, Germany).

RESULTS

The mean wear rate was measured to be 23.6 μm/year (SD 13.7; range 0.7-71.8 μm). There were no significant differences between the two cohorts (UHMWPE-X: 23.2 μm/year vs. UHMWPE-XE: 24.0 μm/year, p = 0.73). Cup anteversion significantly changed within the 1st year after implantation independent from the type of polyethylene liner [UHMWPE-X: 18.2-23.9° (p = 0.0001); UHMWPE-XE: 21.0-25.5° (p = 0.002)]. No further significant changes of cup anteversion in both groups were found between year 1 and 5 after implantation [UHMWPE-X (p = 0.46); UHMWPE-XE (p = 0.56)].

CONCLUSION

The present study demonstrates that the addition of vitamin E does not adversely affect the midterm wear behavior of UHMWPE-X. The antioxidative benefit of vitamin E is expected to become evident in long-term follow-up. Cup anteversion increment by 5° within the 1st year is likely a result of the released hip flexion contracture resulting in an enhanced posterior pelvic tilt. Therefore, a reassessment of target values in acetabular cup placement might be considered.

Lewinnek Safe Zone References are Frequently Misquoted

Background

Optimal acetabular component orientation in total hip arthroplasty (THA) is a necessity in achieving a stable implant. Although there has been considerable debate in the literature concerning the safe zone, to date, there has not been any review to determine if these references are consistent with the definition applied by Lewinnek et al. in 1978. Therefore, this article aims to examine the available literature in the PubMed database to determine how often a correct reference to the safe zone as defined by Lewinnek was applied to discussions regarding THA.

Methods

A search for literature in the PubMed database was performed for articles from 1978 to 2019. Search criteria included terms ‘Lewinnek,’ ‘safe zone,’ and ‘total hip arthroplasty.’ Exclusions included abstract-only articles, non-English articles, articles unrelated to THA, and those lacking full content.

Results

A review of literature yielded 147 articles for inclusion. Overall, only 11% (17) cited the Lewinnek article correctly. Forty-five percent (66) of articles referenced measurements in the supine position, 18% (26) referenced other positions, and 37% (55) did not specify. Nineteen percent (28) reported measurements of the acetabular cup orthogonal to the anterior pelvic plane, while 73% (108) did not, and 7% (11) did not specify. Twenty-three percent (34) measured from computed tomography scans instead of other methods.

Conclusions

In the discussion of the safe zone regarding THA, only 11% of articles listed are consistent with the definition established by Lewinnek. This warrants further investigation into a consistent application of the term and its implications for THA implant stability and dislocation rates.

[A comparative study of MAKO robotic arm assisted total hip arthroplasty and traditional total hip arthroplasty through posterolateral approach]

Objective

To investigate the efficacy of total hip arthroplasty (THA) assisted by the MAKO robotic arm via posterolateral approach.

Methods

The clinical data of 70 patients treated with THA via posterolateral approach between March 2017 and March 2019 who met the selection criteria were retrospectively analyzed. According to different treatment methods, the patients were divided into two groups, 35 were treated with MAKO robotic arm assisted THA (MAKO group) and 35 with traditional THA (THA group). There was no significant difference in gender, age, body mass index, disease duration, etiology, perioperative time, preoperative activity of daily living (ADL) scale index, American Society of Anesthesiologists (ASA) classification, walking ability, comorbidities, hemoglobin, and other general data between the two groups ( P>0.05). The operation time, intraoperative blood loss, hospital stay, postoperative acetabular abduction and anteversion angles, postoperative length difference of bilateral lower limbs, and proportions of intraoperative blood transfusion, immediate postoperative loading, wound drainage time more than 2 days, and complications were recorded and compared between the two groups. According to the X-ray films at 6 months after operation, the reduction quality was judged. The forgotten joint score, Harris score, and proportions of independent walking and ADL index increased were used to evaluate the function recovery of patients.

Results

Patients in both groups were followed up 6-18 months, with an average of 8 months. There was no significant difference ( P>0.05) between the two groups in operation time, intraoperative blood loss, hospital stay, acetabular abduction and anteversion angles, and length difference of both lower limbs at 6 months after operation. There was no significant difference in the proportions of intraoperative blood transfusion, immediate postoperative loading, and wound drainage time more than 2 days between the two group ( P>0.05). X-ray reexamination at 6 months after operation showed that there was no significant difference in the reduction quality between the two groups ( Z=4.191, P=0.123). Postoperative complications occurred in 7 patients (20.0%) in the MAKO group and 10 patients (28.6%) in the THA group, showing no significant difference in the incidence of complications between the two groups ( χ ²=2.121, P=0.224). Two patients (5.7%) in the MAKO group and 4 patients (11.4%) in the THA group underwent revision within 6 months, showing no significant difference in the revision rate between the two groups ( χ ²=0.729, P=0.673). At 3 and 6 months after operation, the proportions of independent walking and ADL index increased showed no significant difference between the two groups ( P>0.05). Harris scores in both groups improved significantly when compared with preoperative scores ( P<0.05); there was no significant difference in the forgotten joint scores and Harris scores between the two groups ( P>0.05).

Conclusion

Compared with traditional THA, MAKO robotic arm assisted THA has longer operation time and more intraoperative blood loss, but it has the advantages of accurate positioning and simple operation, and there is no significant difference in short-term postoperative function recovery.

Reduced-dose computed tomography is the most accurate method to measure ceramic hip resurfacing cup version

BACKGROUND

A precise assessment of cup version after hip resurfacing is generally requested, especially in clinical trials or in case of complications.

AIMS

To identify which diagnostic imaging modality, between AP pelvis X-rays, the AP Pelvis CT Scout image and reduced-dose axial CT scan, is the most precise to assess cup version of an all-ceramic hip resurfacing implant in a first-in-human clinical trial.

METHODS

We retrospectively assessed the cup version of the first 20 patients who underwent an experimental all-ceramic hip resurfacing on AP pelvis X-rays (0.8 mSv of radiation), AP pelvis CT scout images (0.016 mSv) and axial CT slices performed using a reduced dose protocol (0.3 mSv). The intra-observer and inter-observer reliabilities were calculated.

RESULTS

Reduced dose Pelvis CT scan was the most precise imaging modality to detect cup version (Pearson Correlation Coefficient, PCC = 0.98, p < 0.001). The AP Pelvis CT Scout image was found to be sufficient to measure cup version within an acceptable margin of tolerance (mean difference ± 4.7° from pelvis CT scan) and highly correlated to axial pelvis CT scan measurements (PCC 0.97, p < 0.001). Analysis of cup version from AP X-rays poorly correlated with measurements from Pelvis CT (PCC 0.59, p = 0.006).

CONCLUSIONS

Due to lower radiation exposure and highest accuracy, reduced dose CT is a valid modality to measure acetabular cup version after ceramic hip resurfacing. Plain X-rays are not accurate nor precise to measure version, whereas high agreement of measurements between AP Pelvis CT Scout and axial pelvis CT scan was found.

Trans-lateral decubitus radiograph of the hip: A new view to measure the anteversion of the femoral stem

BACKGROUND

Malposition of the femoral stem is a risk factor for dislocation after total hip arthroplasty (THA). Currently, two radiological methods are available for the measurement of stem anteversion. However, one method is not applicable in patients with a stiff hip, and the other one cannot differentiate the anteversion and retroversion of the stem. Therefore, we developed a method to measure the stem anteversion and assessed its reliability as well as validity.

METHODS

Trans-lateral decubitus view of the proximal femur was taken with the patient in lateral decubitus position, the hip in extension and the knee in 90° flexion. Hip anteroposterior (AP) view, trans-lateral decubitus view and CT scan of the hip were taken in 36 patients, who underwent THA. Their mean age was 59.8 (27-84) years and the mean body mass index was 25.2 (18.8-30.9) kg/m². The stem neck-femoral shaft angle was measured on hip AP view and the trans-lateral decubitus view. Then, the stem anteversion was calculated using the Ogata-Goldsand formula. We assessed the intra- and inter-observer reliabilities and evaluated the validity by comparing with the measurements on CT scan.

RESULTS

The intra- and inter-observer reliabilities were 0.934 and 0.935, respectively. The calculated stem anteversion (23.72°±8.17°) correlated well with the stem anteversion on CT scan (23.91°±10.25°), especially when the radiological anteversion was <30° (correlation coefficient = 0.729, p = 0.001).

CONCLUSION

We developed a reliable and valid method to measure stem anteversion using hip AP view and trans-lateral decubitus view of the femur. This method can replace conventional radiological methods.

Radiographic assessment of the cup orientation after total hip arthroplasty: a literature review

Optimal acetabular cup orientation is of substantial importance to good long-term function and low complication rates after total hip arthroplasty (THA). The radiographic anteversion (RA) and inclination (RI) angles of the cup are typically studied due to the practicability, simplicity, and ease of interpretation of their measurements. A great number of methods have been developed to date, most of which have been performed on pelvic or hip anteroposterior radiographs. However, there are primarily two influencing factors for these methods: X-ray offset and pelvic rotation. In addition, there are three types of pelvic rotations about the transverse, longitudinal, and anteroposterior axes of the body. Their effects on the RA and RI angles of the cup are interactively correlated with the position and true orientation of the cup. To date, various fitted or analytical models have been established to disclose the correlations between the X-ray offset and pelvic rotation and the RA and RI angles of the cup. Most of these models do not incorporate all the potential influencing parameters. Advanced methods for performing X-ray offset and pelvic rotation corrections are mainly performed on a single pelvic AP radiograph, two synchronized radiographs, or a two-dimensional/three-dimensional (2D-3D) registration system. Some measurement systems, originally developed for evaluating implant migration or wear, could also be used for correcting the X-ray offset and pelvic rotation simultaneously, but some drawbacks still exist with these systems. Above all, the 2D-3D registration technique might be an alternative and powerful tool for accurately measuring cup orientation. In addition to the current methods used for postoperative assessment, navigation systems and augmented reality are also used for the preoperative planning and intraoperative guidance of cup placement. With the continuing development of artificial intelligence and machine learning, these techniques could be incorporated into robot-assisted orthopaedic surgery in the future.

Effect of pelvic tilt and rotation on cup orientation in standing anteroposterior radiographs

BACKGROUND

Individual pelvic tilt and rotation have wide variability that can affect the measurement of cup orientation in anteroposterior (AP) radiographs. The purpose of this study was to analyse the effect of pelvic tilt and rotation on radiographic measurements of cup orientation.

METHODS

A total of 53 patients (63 hips) were included in this study. The patients underwent a computed tomography study with standing AP pelvis radiographs taken both preoperatively and approximately 3 months postoperatively. We used 2-dimensional/3-dimensional matching to measure the pelvic tilt and rotation, and the non-standardised and standardised cup orientation.

RESULTS

There was no difference in the pelvic tilt and rotation between the preoperative and postoperative radiographs. The distribution of the differences between the non-standardised and standardised cup anteversion exhibited a change within 5° in only 34/63 (54%) hips. The pelvic tilt correlated with the difference between the non-standardised and standardised cup anteversion, but the pelvic rotation did not. When all 63 hips were separated into the right and left sides, the pelvic rotation inversely correlated with the pelvic tilt-adjusted difference between the non-standardised and standardised cup anteversion of the right side but directly correlated with that of the left side.

CONCLUSIONS

The current study demonstrated that the measurement of cup anteversion in standing AP radiographs is significantly affected by both the pelvic tilt and pelvic rotation. An improved understanding of the pelvic orientation may eventually allow for desired cup positioning on a patient-specific basis to potentially reduce complications associated with the malposition of the cup.

Intraoperative evaluation of acetabular cup position during anterior approach total hip arthroplasty: are we accurately interpreting?

INTRODUCTION

Intraoperative radiographic evaluation during total hip arthroplasty (THA) has shown to improve the accuracy of acetabular component placement, however, differences in interpretation based on radiographic technique has not been established. This study aims to determine if differences exist in the interpretation of acetabular component abduction and anteversion between different radiographic projections.

METHODS

55 consecutive direct anterior THAs in 49 patients were prospectively enrolled. Target anteversion and abduction was defined by the Lewinnek zone. Fluoroscopy was used to direct acetabular component placement intraoperatively. After final cup implantation, fluoroscopic posterior-anterior hip and pelvis images were obtained for analysis. After completion of the procedure, an anterior-posterior plain pelvis radiograph was obtained in the operating room. Acetabulum component abduction and anteversion were postoperatively determined using specialised software on each of the 3 image acquisition methods.

RESULTS

Average acetabular cup abduction for intraoperative fluoroscopic posterior-anterior hip (FH), intraoperative fluoroscopic posterior-anterior pelvis (FP), and postoperative, standard, anteroposterior pelvis radiographs (PP) was 40.95° ± 2.87°, 38.87° ± 3.82° and 41.73° ± 2.96° respectively. The fluoroscopic hip and fluoroscopic pelvis tended to underestimate acetabular cup abduction compared to the postoperative pelvis (p < 0.001). Average acetabular cup anteversion for FH, FP, and PP was 19.89° ± 4.87°, 24.38° ± 5.31° and 13.36° ± 3.52° respectively. Both the fluoroscopic hip and fluoroscopic pelvis overestimated anteversion compared to the AP pelvis, with a 6.38° greater mean value measurement for FH (p < 0.001), and an 11° greater mean value measurement for FP (p < 0.001).

CONCLUSIONS

Fluoroscopic technique and differences between radiographic projections may result in discrepancies in component position interpretation. Our results support the use of the fluoroscopic posterior-anterior hip as the choice fluoroscopic imaging technique.

Accuracy of planar anteversion measurements using anteroposterior radiographs

Background

Several methods using simple anteroposterior (AP) radiographs have been suggested for the measurement of anteversion of the cup component after total hip arthroplasty. Herein, we compared six widely used anteversion measurement methods using two different types of AP radiograph, the conventional pelvis AP and hip-centered AP radiographs, to identify the measurement method and the type of radiograph that would provide the highest accuracy and reliability.

Methods

We developed two custom-made bi-planar anteversion measurement models for the validation test. The models were designed for pelvis AP and hip-centered AP radiographs, respectively. The radiographs were acquired using the inclination angles of both models, changing from 10° to 70° at 10° increments. For each inclination angle, anteversion was changed from 0° to 30° at 5° increments. The measurements were obtained independently by two orthopedic surgeons blinded from each other’s measurements, using the methods of 1) Pradhan et al., 2) Lewinnek et al., 3) Widmer et al., 4) Liaw et al., 5) Hassan et al., and 6) Ackland et al. The measurements were repeated after 2 months. The accuracy, compared with that of the reference angle, and intra-observer and inter-observer reliabilities of each method were calculated.

Results

The highest accuracy was found when the method of Liaw et al. was used with hip-centered AP radiographs, which showed a difference of 1.37° ± 1.73 from the reference angle. Moreover, regardless of the type of radiograph, the methods by Pradhan et al., Lewinnek et al., and Liaw et al. showed excellent correlations with the reference anteversion. However, substantial differences were found when the methods by Widmer et al., Hassan et al., and Ackland et al. were used, regardless of the type of radiograph used. When anteversion was measured in an inclination between 30° and 50°, the method of Pradhan et al., when used with pelvis AP radiographs, showed the highest accuracy (1.23° ± 0.92°). We also found no significant difference in anteversions between the measurements made on pelvic and hip-centered AP radiographs. Both interobserver and intraobserver reliabilities were high for all the measurements tested.

Conclusions

The methods by Pradhan et al., Liaw et al., and Lewinnek et al. may provide relatively accurate anteversion measurements with high reliability, regardless of the type of radiograph.

A Novel Method for Correcting Pelvic Tilt on Anteroposterior Pelvic Radiographs

Background Anteroposterior (AP) pelvic radiographs remain the standard for pre- and postoperative imaging during total hip arthroplasty (THA), despite the known limitation of plain films, including the inability to adequately account for distortion caused by variations in pelvic orientation such as pelvic tilt. The purpose of this study was to develop a reliable method for correcting pelvic tilt on AP pelvic radiographs in patients undergoing THA. Methods CT scans from 20 patients/cadaver specimens (10 male, 10 female) were used to create 3D renderings, from which synthetic radiographs of each pelvis were generated. For each pelvis, 13 synthetic radiographs were generated, showing the pelvis at between -30° and 30° of pelvic tilt, in 5° increments. On each image, eight unique parameters/distances were measured to determine the most appropriate parameters for the calculation of pelvic tilt. The most reliable and accurate of these parameters was determined via regression analysis and used to create gender-specific nomograms from which pelvic tilt measurements could be calculated. The accuracy and reliability of the nomograms and correction method were subsequently validated using both synthetic radiographs (n=50) and stereoradiographic images (n=58). Results Of the eight parameters measured, the vertical distance between the superior margin of the pubic symphysis and the transischial line (PSTI) was determined to be the most reliable (r=-0.96, ICC=0.94). Using that parameter and applying the associated nomograms to 50 synthetic radiographs of random pelvic tilt, the mean difference between the actual pelvic tilt and that calculated using the correction method was 0.1°±5.1° (p=0.98, r=0.96). In 58 stereoradiographic images, the mean difference between actual and measured pelvic tilt was -0.2°±6.4° (p=0.74, r=0.77). The pooled results indicate no significant difference between actual (2.2°±13.9°) and measured pelvic tilt (2.1°±14.3°, p=0.93, r=0.91). No significant differences were noted based on gender. Conclusions Our method of correcting for pelvic tilt using the vertical distance from the pubic symphysis to the transischial line provides a reliable method for correcting for pelvic tilt on AP pelvic radiographs.

A precise method for determining acetabular component anteversion after total hip arthroplasty

AIMS

Several radiological methods of measuring anteversion of the acetabular component after total hip arthroplasty (THA) have been described. These are limited by low reproducibility, are less accurate than CT 3D reconstruction, and are cumbersome to use. These methods also partly rely on the identification of obscured radiological borders of the component. We propose two novel methods, the Area and Orthogonal methods, which have been designed to maximize use of readily identifiable points while maintaining the same trigonometric principles.

PATIENTS AND METHODS

A retrospective study of plain radiographs was conducted on 160 hips of 141 patients who had undergone primary THA. We compared the reliability and accuracy of the Area and Orthogonal methods with two of the current leading methods: those of Widmer and Lewinnek, respectively.

RESULTS

The 160 anteroposterior pelvis films revealed that the proposed Area method was statistically different from those described by Widmer and Lewinnek (p < 0.001 and p = 0.004, respectively). They gave the highest inter- and intraobserver reliability (0.992 and 0.998, respectively), and took less time (27.50 seconds (sd 3.19); p < 0.001) to complete. In addition, 21 available CT 3D reconstructions revealed the Area method achieved the highest Pearson's correlation coefficient (r = 0.956; p < 0.001) and least statistical difference (p = 0.704) from CT with a mean within 1° of CT-3D reconstruction between ranges of 1° to 30° of measured radiological anteversion.

CONCLUSION

Our results support the proposed Area method to be the most reliable, accurate, and speedy. They did not support any statistical superiority of the proposed Orthogonal method to that of the Widmer or Lewinnek method. Cite this article: Bone Joint J 2019;101-B:1042-1049.

BMCRI method for measuring cup anteversion after total hip replacement

STUDY DESIGN

Prospective clinical study.

BACK GROUND

In total hip replacement the cup placement is critical. Orientation is determined by anteversionand abduction. We have devised a simple geometrical method to calculate anteversion using simple instruments which does not require complicated conversion tables, scientific calculators, trigonometric tables and special x ray equipment.

OBJECTIVES

The aim of study is to evaluate the new method in terms of reliability and validity in comparison with other commonly used radiological methods against CT evaluation.

METHODOLOGY

In 30 hips of 25 consecutive patients, 13 females and 12 males who underwent primary total hip replacement in our institution, the component version in our method was calculated and compared with CT evaluation of angles. The intra and inter observer reliability were assessed.

RESULTS

Average CT measurement was 23.28 for ante version.We found our method had good correlation with CT calculation with average variability of +/_ 3.913800 in planar anteversionand CT methods had excellent intra and inter observer reliability (C.I. = 0.884 to 0.947&0.866 to 0.963).

CONCLUSION

Our method is accurate in comparison with CT (P value > 0.05), which does not need any reference tables, conversiontables, scientific calculators, multiple radiation exposures and not time consuming.

Accuracy of plain antero-posterior radiographic-based methods for measurement of acetabular cup version

INTRODUCTION

Acetabular cup version is crucial for successful total hip arthroplasty (THA). Many methods have been described for measurement of cup version angle. The aim of this study is to assess the accuracy of five commonly used methods for measurement of acetabular cup version in plain antero-posterior views of the pelvis and hip.

MATERIAL AND METHODS

Sixty primary THA cases were subjected postoperatively to plain A-P of the pelvis (AP-P), A-P view of the hip (AP-H), and computed tomography (CT) imaging. The acetabular cup version was measured in AP-P and AP-H by five methods (Lewinnek, Widmer, Hassan et al., Ackland et al., and Liaw et al.). These measurements were compared to the CT measurement.

RESULTS

All plain X-ray methods showed no significant differences from the CT, except those of Hassan et al. in AP-H, and Widmer and Ackland et al. in AP-P.

CONCLUSIONS AND RECOMMENDATIONS

For measurement of acetabular cup version angle, we recommend the use of Lewinnek and Liaw et al. methods both in AP-P and in AP-H, while Hassan et al.'s method is recommended in AP-P only, and Widmer and Ackland et al.'s methods in AP-H only.

Evaluation of Tilt-correction of Anteversion on Anteroposterior Pelvic Radiographs in Total Hip Arthroplasty

Despite inaccuracies due to artifact and variations in patient positioning, anteroposterior (AP) radiographs remain the clinical standard for post-operative evaluation of component placement following total hip arthroplasty (THA). However, cup position, specifically anteversion, can be significantly affected by variations in patient positioning on an X-ray. A major cause of such artifact is unaccounted for pelvic tilt. Several methods for correcting the effects of pelvic tilt on radiographic anteversion have been proposed, with varying degrees of accuracy. The purpose of this study was to evaluate the accuracy and reliability of a commonly referenced method for correcting acetabular cup anteversion in a cohort undergoing total hip arthroplasty and determine its appropriateness for use in this population of patients. Radiographs from patients who underwent primary or revision hip arthroplasty between February 2016 and February 2017 were retrospectively reviewed. Corrected anteversion was calculated by measuring the vertical distance between the symphysis pubis and the sacrococcygeal joint, per the method outlined by Tannast et al. This symphococcygeal distance was then applied to Tannast’s nomograms to calculate the magnitude of pelvic tilt. Corrected and uncorrected anteversion values were compared to anteversion values collected intraoperatively using an imageless computer-assisted navigation device. A total of 71 cases were initially eligible for inclusion in the study. The correction method could not be applied in 44% (31/71) of the cases, chiefly due to difficulties in visualizing the required landmarks. In cases where it could be applied, corrected values correlated very poorly with navigation measurements (r = -0.07). Mean corrected anteversion (36.9°, SD: 7.4°) differed from uncorrected anteversion (25.2°, SD: 7.6°) by an average of 13.5° (p<0.001). Mean navigated anteversion (27.4°, SD: 5.7°) differed from corrected values by an average of 10.8° (p=0.16). The evaluated correction method could not be consistently applied to radiographs and did not reliably correct anteversion due to pelvic tilt in this population of patients undergoing hip arthroplasty. This correction method does not appear to be appropriate for use in this patient population.

Robot-assisted total hip arthroplasty: Clinical outcomes and complication rate

BACKGROUND

The purpose of this study was to report minimum 2-year outcomes and complications for robotic-arm-assisted total hip arthroplasty (THA).

METHODS

Data were prospectively collected and retrospectively reviewed between June 2011 and April 2014. Inclusion criteria were primary robotic-arm-assisted THAs treating idiopathic osteoarthritis with ≥ 2-year follow-up. Demographics, operating time, complications, 2-year outcome scores and satisfaction, and subsequent surgeries were recorded.

RESULTS

There were 181 cases eligible for inclusion, of which 162 (89.5%) had minimum 2-year follow-up. At the latest follow-up, the mean visual analogue scale was 0.7, satisfaction was 9.3, Harris hip score was 91.1 and forgotten joint score was 83.1. Six (3.7%) intraoperative complications and six (3.7%) postoperative complications were reported. No leg length discrepancies (LLDs) or dislocations were reported.

CONCLUSIONS

Robotic-arm-assisted THA demonstrates favourable short-term outcomes and does not result in a higher complication rate compared to non-robotic THA as reported by the literature.

The best method for evaluating anteversion of the acetabular component after total hip arthroplasty on plain radiographs

Background

Several radiological methods for measuring the anteversion of the acetabular component after total hip arthroplasty (THA) exist, and no single standardized method has been established. We evaluated the reliability and accuracy of six widely utilized methods (Liaw et al., Lewinnek et al., Widmer, Hassan et al., Ackland et al., and Woo and Morrey) for measuring anteversion on plain radiographs, using a reference standard in the same definition obtained from the PolyWare programme.

Methods

We reviewed 71 patients who underwent primary unilateral THA. The anteversion of the acetabular component was measured on pelvis AP radiographs using five different methods (Liaw et al., Lewinnek et al., Widmer, Hassan et al., and Ackland et al.) and on cross-table lateral radiographs using the method of Woo and Morrey. The values obtained using the PolyWare programme, which determines the anteversion of the acetabular component by edge detection, were regarded as the reference standard.

Results

Intra- and inter-observer reliabilities were excellent for all methods using plain radiographs, including the PolyWare programme. The method of Liaw et al. obtained values similar to those obtained using the PolyWare programme and was thus considered accurate (P = 0.447). However, values obtained using the other five methods significantly differed from those obtained using the PolyWare programme and were thus considered less accurate (P < 0.001, P < 0.001, P < 0.001, P = 0.007, and P < 0.001, respectively).

Conclusion

The method of Liaw et al. is more accurate than other methods using plain radiographs for the measurement of the anteversion of the acetabular component after THA, with reference to the anteversion obtained from the PolyWare programme.

Quantitative Effect of Pelvic Position on Radiographic Assessment of Acetabular Component Position

BACKGROUND

Intraoperative fluoroscopy aims to improve component position in total hip arthroplasty. Measurement bias related to image quality, however, has not been quantified. We aim to quantify measurement bias in the interpretation of acetabular component position as a function of pelvis and fluoroscopic beam position in a simulated supine total hip arthroplasty model.

METHODS

Posterior-anterior pelvis and hip images were obtained using a previously described pelvic model with known acetabular component position. Pelvic position was varied in 5° increments of pelvis rotation (iliac-obturator) and tilt (inlet-outlet), and in 1 cm increments from beam center in cranial-caudal and medial-lateral planes. Multiple regression analyses were conducted to evaluate the relationship between the resulting bias in interpretation of component position relative to pelvis position.

RESULTS

Anteversion and abduction measurement bias increased exponentially with increasing deviation in rotation and tilt. Greater bias occurred for anteversion than for abduction. Hip centered images were less affected by pelvis malposition than pelvis centered images. Deviations of beam center within 5 cm in the coronal plane did not introduce measurement bias greater than 5°. An arbitrarily defined acceptable bias of ±5° for both abduction and anteversion was used to identify a range of optimum pelvic positioning each for hip and pelvis centered imaging.

CONCLUSION

Accurate measurement of acetabular component abduction and anteversion, especially anteversion, is sensitive to proper pelvic position relative to the chosen radiographic plane. An acceptable measurement bias of ±5° is achieved when the pelvis is oriented within a newly identified range of optimum pelvic positioning.

Hip Spine Relationships: Application to Total Hip Arthroplasty

Lumbosacral orientation in the sagittal plane is of utmost importance, as it plays a critical role in the function of the spine and the hip joints. Equilibrium of the trunk influences the tridimensional orientation of the acetabulum and the functional range of motion of the hips. Each patient is characterized by a “morphological” parameter named incidence angle; its sagittal balance is the consequence of a postural adaptation for other functional parameters (pelvic tilt, sacral slope, lumbar lordosis, acetabular sagittal tilt, functional anteversion). Understanding variations of the sacral slope on lateral pelvic X-rays is essential for planning total hip arthroplasty and identifying patients at risk of impingement, as lumbosacral posture influences functional anteversion of the acetabulum. Posterior pelvic version as in sitting position (sacral slope decrease) is linked to the increase of the functional acetabular anteversion. Anterior pelvic version as in standing position (sacral slope increase) is linked to the decrease of the functional acetabular anteversion.

Standardized fluoroscopy-based technique to measure intraoperative cup anteversion

Direct anterior approach (DAA) with the patient lying supine has facilitated the use of intraoperative fluoroscopy and allows for standardized positioning of the patient. The current study presents a new technique to measure acetabular component anteversion using intraoperative fluoroscopy. The current paper describes a mathematical formula to calculate true acetabular component anteversion based on the acetabular component abduction angle and the c-arm tilt angle (CaT). The CaT is determined by tilting the c-arm until an external pelvic oblique radiograph with the equatorial plane of the acetabular component perpendicular to the fluoroscopy receptor is obtained. CaT is determined by direct reading on the C-arm device. The technique was validated using a radiopaque synbone model comparing the described technique to computed tomography anteversion measurement. The experiment was repeated 25 times. The difference in anteversion between the two measuring techniques was on average 0.2° (range -3.0-3.1). The linear regression coefficients evaluating the agreement between the experimental and control methods were 0.99 (95%CI 0.88-1.10, p < 0.001) and 0.33 (95%CI -1.53-2.20, p = 0.713) for the slope and intercept, respectively. The current study confirms that the described three-step c-arm acetabular cup measuring technique can reproducibly and reliably assess acetabular component anteversion in the supine position, as compared to CT-imaging. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2307-2312, 2017.

The validity and reproducibility of cross table radiographs compared with CT scans for the measurement of anteversion of the acetabular component after total hip arthroplasty

Aims

The aim of this study was to assess the reproducibility and validity of cross table radiographs for measuring the anteversion of the acetabular component after total hip arthroplasty (THA) and to compare it with measurements using CT scans.

Patients and Methods

A total of 29 patients who underwent THA between June 2010 and January 2016 were included. There were 17 men and 12 women. Their mean age was 43 years (26 to 65). Seven patients underwent a bilateral procedure. Thus, 36 THAs were included in the study. Lateral radiographs and CT scans were obtained post-operatively and radiographs repeated three weeks later. The anteversion of the acetabular component was measured using the method described by Woo and Morrey and the ischiolateral method described by Pulos et al and these were compared with the results obtained from CT scans.

Results

The mean anteversion was 18.35° (3° to 38°) using Woo and Morrey’s method, 51.45° (30° to 85°) using the ischiolateral method and 21.22° (2° to 48°) using CT scans. The Pearson correlation coefficient was 0.754 for Woo and Morrey’s method and 0.925 for the ischiolateral method. There was a linear correlation between the measurements using the ischiolateral method and those using CT scans. We derived a simple linear equation between the value of the CT scan and that of ischiolateral method to deduce the CT scan value from that of ischiolateral method and vice versa.

Conclusion

The anteversion of the acetabular component measured using both plain radiographic methods was consistently valid with good interobserver reproducibility, but the ischiolateral method which is independent of pelvic tilt was more accurate. As CT is costly, associated with a high dose of radiation and not readily available, the ischiolateral method can be used for assessing the anteversion of the acetabular component. Cite this article: Bone Joint J 2017;99-B:1006–11.

New cross-table lateral radiography method for measuring acetabular component anteversion in total hip arthroplasty: a prospective study of 93 primary THA

INTRODUCTION

Various methods have been described for measuring acetabular component anteversion. However, accurate measurement of anteversion is difficult. We herein propose a new method using cross-table lateral (CL) radiography performed with the contralateral hip flexed to 45° (45° flexed CL radiography). The main purpose of this study was to evaluate the reliability and validity of this new method.

METHODS

The study group included 93 patients who underwent total hip arthroplasty (THA). All hips were evaluated with computed tomography (CT) and both standard and 45° flexed CL radiographs to measure acetabular component anteversion the week after THA. The intraobserver and interobserver reliability of each measurement was assessed. Plain radiography measurements were compared with reference CT measurements to evaluate their validity.

RESULTS

All measurements had excellent intraobserver and interobserver reliability, and plain radiography measurements correlated well with CT measurements. The mean measurements were 21.9° (3°-39°) with CT, 24.9° (7°-47°; p<0.001) with standard CL radiographs, and 22.5° (7°-43°; p = 0.112) with 45° flexed CL radiographs.

DISCUSSION

The anteversion values measured with our new method were closer to the CT values used as a reference standard than those with standard CL radiographs. Our new method appears to be reliable and valid for measuring acetabular component anteversion.

A cadaver study validating CT assessment of acetabular component orientation: the Perth CT hip protocol

OBJECTIVE

The aim was to develop a CT-based protocol to accurately measure post-operative acetabular cup inclination and anteversion establishing which bony reference points facilitate the most accurate estimation of these variables.

MATERIALS AND METHODS

An all-polyethylene acetabular liner was implanted into a cadaveric acetabulum. A conventional pelvic CT scan was performed and reformatted images created in both functional and anterior pelvic planes. CT images were transferred to a Freedom-Plus Graphics software package enabling an identical, virtual 3D model of the cadaveric pelvis to be created and definitive acetabular cup orientation established. Using coronal and axial slices of the CT scans, acetabular cup inclination and anteversion were measured on five occasions by ten radiographers using differing predetermined bony landmarks as reference points. The intra- and inter-observer variation in measurement of acetabular cup orientation using varying bony reference points was assessed in comparison to the elucidated definitive cup position.

RESULTS AND CONCLUSION

Virtually derived definitive acetabular cup orientation was measured showing cup inclination and anteversion as 41.0 and 22.5° respectively. Mean CT-based measurement of cup inclination and anteversion by ten radiographers were 43.1 and 20.8° respectively. No statistically significant difference was found in intra- and inter-observer recorded results. No statistically significant differences were found when using different bony landmarks. CT assessment of acetabular component inclination and anteversion is accurate, reliable and reproducible when measured using differing bony landmarks as reference points. We recommend measuring acetabular inclination and anteversion from the inferior acetabular wall/teardrop and posterior ischium respectively.

A mathematical method for precisely calculating the radiographic angles of the cup after total hip arthroplasty

We established a mathematical method to precisely calculate the radiographic anteversion (RA) and radiographic inclination (RI) angles of the acetabular cup based on anterior-posterior (AP) pelvic radiographs after total hip arthroplasty. Using Mathematica software, a mathematical model for an oblique cone was established to simulate how AP pelvic radiographs are obtained and to address the relationship between the two-dimensional and three-dimensional geometry of the opening circle of the cup. In this model, the vertex was the X-ray beam source, and the generatrix was the ellipse in radiographs projected from the opening circle of the acetabular cup. Using this model, we established a series of mathematical formulas to reveal the differences between the true RA and RI cup angles and the measurements results achieved using traditional methods and AP pelvic radiographs and to precisely calculate the RA and RI cup angles based on post-operative AP pelvic radiographs. Statistical analysis indicated that traditional methods should be used with caution if traditional measurements methods are used to calculate the RA and RI cup angles with AP pelvic radiograph. The entire calculation process could be performed by an orthopedic surgeon with mathematical knowledge of basic matrix and vector equations.

Plain Radiographs are a Useful Substitute for Computed Tomography in Evaluating Acetabular Cup Version

BACKGROUND

The purpose of this study is to compare acetabular component version measurements from cross-table lateral (XTL) radiographs, anteroposterior pelvis (AP-P) and anteroposterior hip (AP-H) radiographs, and axial pelvic computed tomography (CT) scans.

METHODS

One hundred fifty hips met our inclusion criteria of having a CT, XTL, and AP-P done postoperatively. Version was measured by 2 authors. Pearson regression analysis assessed correlation between versions of the modalities. Analysis of variance testing compared the averages of the values as a whole and based on demographics. When available, comparisons were also done with AP-H radiographs.

RESULTS

Mean version for XTL and CT scan was 21.7° and 23.8°, respectively, whereas that from AP-P and AP-H radiographs was 12.5° and 17.2°, respectively. XTL and AP-H version measures were closely correlated with CT (P = .81), whereas AP-P measurements were only moderately correlated with CT (P = .75). AP-P and AP-H were significantly (P < .05) different from CT, whereas XTL was not (P = .36).

CONCLUSION

The XTL radiograph remains a useful, cheaper, and safer substitute for CT scan when assessing supine version in the postoperative setting.

Cross table lateral radiography for measurement of acetabular cup version

BACKGROUND

Appropriate orientation of the acetabular cup is an important factor for long-term results of total hip arthroplasty. For measurement of cup version cross-table lateral radiography is frequently used, but the reliability has been questioned. We compared cross table lateral radiography with computed tomography in patients that had undergone primary total hip arthroplasty.

METHODS

The study was prospectively done in 117 patients (117 hips). At 3 months after total hip replacement the acetabular version was measured by cross table lateral radiography and compared to measurements by computed tomography.

RESULTS

By cross table lateral radiography acetabular anteversion was on mean 13.9° with a standard deviation of 10.1° as compared to 17.8°±12.6° by computed tomography. Mean difference was -3.8 with a distribution of measurements of ±13 degrees for 95% of the cases.

CONCLUSIONS

Our study shows that cross table radiography provides acceptable information for clinical use, but has limited use for precise analysis of acetabular cup version.

Anteroposterior Radiographs Are More Accurate than Cross-Table Lateral Radiographs for Acetabular Anteversion Assessment: a Retrospective Cohort Study

BACKGROUND

Measuring acetabular anteversion is relevant to routine follow-up of total hip arthroplasties (THAs) and for malfunctioning THAs. Imageless navigation facilitates acetabular component orientation relative to the anterior pelvic plane (APP) or to the APP adjusted for sagittal pelvic tilt (PT). The optimal plain radiographic method for the postoperative assessment of anteversion is not agreed upon.

QUESTIONS/PURPOSES

(1) Do anteversion measurements on plain radiographs correlate more with APP anteversion or PT-adjusted anteversion? (2) Do measurements of anteversion performed on supine anteroposterior (AP) radiographs more accurately reflect intraoperative anteversion values for navigated THA compared to anteversion measured on cross-table lateral (CL) radiographs?

METHODS

Seventy patients receiving primary navigated THA were included. APP and PT-adjusted anteversion were recorded; the latter defined the intraoperative target for anteversion. Postoperative anteversion was measured on supine AP pelvis radiographs with computer software and CL radiographs with conventional methods. Intraoperative measurements were used as the reference standards for comparisons.

RESULTS

Mean intraoperative APP anteversion was 20.6° ± 5.6°. Mean intraoperative PT-adjusted anteversion was 22.9° ± 4.5°. Mean anteversion was 22.7° ± 4.7° on AP radiographs and 27.2° ± 4.2° on CL radiographs (p < 0.001). Only correlations between PT-adjusted anteversion and radiographic assessments of anteversion were significant. The mean difference between PT-adjusted anteversion and anteversion on AP radiographs was -0.2° ± 4.3°, while the mean difference between the PT-adjusted anteversion and anteversion measured on CL radiographs was 4.3 ± 5.1° (p < 0.001).

CONCLUSION

Plain film assessment of anteversion was more accurate on supine AP radiographs than on CL radiographs, which overestimated acetabular anteversion.

Validating a Modified Circle Theorem Method for the Measurement of Acetabular Cup Anteversion on Plain Radiography with Intra-Operative Data from Robotic Assisted Total Hip Arthroplasty

This study aims to validate a modified circle theorem method for the calculation of true version of the acetabular component on anteroposterior x-rays with intra-operative version data derived from robotic assisted total hip arthroplasty (THA). Planar anteversion measurements recorded intraoperatively in 80 THAs were correlated to measurements on anteroposterior radiographs. The mean anteversion of the cohort measured by the robotic system and on plain radiography was 21.2° ± 2.0° and 19.9° ± 3.4° respectively and 97.5% of cases were in a 30% relative error. The correlation between the true and planar measurements of anteversion on plain radiographs was strong (Pearson correlation coefficient of 0.9422). We conclude that the circle theorem method can be validated with data from robotic guided THA.

The reliability and accuracy of measuring anteversion of the acetabular component on plain anteroposterior and lateral radiographs after total hip arthroplasty

There is no single standardised method of measuring the orientation of the acetabular component on plain radiographs after total hip arthroplasty. We assessed the reliability and accuracy of three methods of assessing anteversion of the acetabular component for 551 THAs using the PolyWare software and the methods of Liaw et al, and of Woo and Morrey. All measurements of the three methods had excellent intra- and inter-observer reliability. The values of the PolyWare software, which determines version of the acetabular component by edge detection were regarded as the reference standard. Although the PolyWare software and the method of Liaw et al were similarly precise, the method of Woo and Morrey was significantly less accurate (p < 0.001). The method of Liaw et al seemed to be more accurate than that of Woo and Morrey when compared with the measurements using the PolyWare software. If the qualified lateral radiograph was selected, anteversion measured using the method of Woo and Morrey was considered to be relatively reliable.

Cup version can be accurately measured on the false profile view radiograph

INTRODUCTION

Accurate measurement of cup version on plain radiographs remains difficult due to the two-dimensional projection of an ellipse and difficulty obtaining reproducible radiographs.

PURPOSE

Determine: 1) if the cup angle measured on the false profile view (FPV) could be used to determine radiographic cup version; 2) how patient positioning would affect cup angle measurement on the FPV; 3) if implant cup design affects cup angle measurement.

MATERIALS AND METHODS

Three cup version positions were assessed in a sawbone: 13° (normal); 28° (excessive anteversion) and -2° (retroversion). Cup angle was measured on the FPV at five different degrees of pelvic rotation within each cup version group. Pelvic rotation was quantified using the ratio of the inter-femoral head distance measured on the FPV versus the anteroposterior radiographs (FP/AP ratio). Eighty patients (40 metal-on-polyethylene, 40 metal-on-metal) post-total hip were also assessed. Cup version was assessed with Einzel-Bild-Roentgen-Analysis software (EBRA). R2 was calculated to assess correlation between both measurement methods.

RESULTS

For the sawbone model, an R2 of 0.95 was obtained. For patients, overall R2 was 0.56 with an FP/AP ratio of 0.3-0.49 having an R2 of 0.72. The EBRA anteversion versus cup angle scatterplot had an R2 of 0.72 (95%CI: +/-7.8°). Subgroup analysis revealed no differences between the metal-on-poly and metal-on-metal for cup angle measurements. The intra-class coefficient for intra- and inter-observer reliability for all cases (individual and combined FP/AP groups) was 0.98 to 0.99.

CONCLUSION

The FPV cup angle measurement value provides an accurate measurement of radiographic cup anteversion with well-defined patient position parameters.

Correlation of Structural Bony Abnormalities and Mechanical Symptoms of Hip Joints

PURPOSE

The purpose of this study is to determine structural bony abnormalities predisposing for femoroacetabular impingement by comparison of patients with and without mechanical symptoms.

MATERIALS AND METHODS

We conducted this comparative study on 151 patients (151 hips; mean age 44.8 years; range 16-73 years) with mechanical symptoms with results of multi-detector computed tomography (MDCT) arthrography (the symptomatic group). Each patient was matched with a control who underwent MDCT due to ureter stone (the asymptomatic group) in terms of age, gender, site (right or left), and time at diagnosis. Acetabular evaluations, which included cranial and central anteversion and anterior and lateral center edge angles and femoral measurements, were performed. In addition, we evaluated the prevalence and characteristics of structural bone abnormalities between the two groups.

RESULTS

The prevalence for patients who had at least one structural bony abnormality in the symptomatic and asymptomatic groups was 80.1% (121/151) and 54.3% (82/151), respectively (odds ratio: 3.39, 95% confidence interval: 2.30-5.66; P<0.001). The most common osseous abnormality was the isolated Pincer type in both groups: 89 (73.6%) of 121 hips with an osseous abnormality in the symptomatic group and 57 (69.5%) of 82 hips with an osseous abnormality in the asymptomatic group. By analysis of CT arthrography in symptomatic patients, a labral tear was found in 107 hips (70.9%), and 86 (80%) of these hips had a structural bony abnormality.

CONCLUSION

A significantly greater prevalence rate of structural bony abnormality was observed for the symptomatic group than for the asymptomatic group. These findings are helpful for development of appropriate treatment plans.

An analysis of the best method for evaluating anteversion of the acetabular component after total hip replacement on plain radiographs

Several radiological methods of measuring anteversion of the acetabular component after total hip replacement (THR) have been described. These studies used different definitions and reference planes to compare methods, allowing for misinterpretation of the results. We compared the reliability and accuracy of five current methods using plain radiographs (those of Lewinnek, Widmer, Liaw, Pradhan, and Woo and Morrey) with CT measurements, using the same definition and reference plane. We retrospectively studied the plain radiographs and CT scans in 84 hips of 84 patients who underwent primary THR. Intra- and inter-observer reliability were high for the measurement of inclination and anteversion with all methods on plain radiographs and CT scans. The measurements of inclination on plain radiographs were similar to the measurements using CT (p = 0.043). The mean difference between CT measurements was 0.6° (-5.9° to 6.8°).

Measurements using Widmer’s method were the most similar to those using CT (p = 0.088), with a mean difference between CT measurements of -0.9° (-10.4° to 9.1°), whereas the other four methods differed significantly from those using CT (p < 0.001).

This study has shown that Widmer’s method is the best for evaluating the anteversion of the acetabular component on plain radiographs.

Cite this article: Bone Joint J 2014; 96-B:597–603.

Early clinical and radiographic results of minimally invasive anterior approach hip arthroplasty

We present a retrospective review of the early results and complications in a series of 35 consecutive patients with 43 total hip arthroplasties performed through an anterior muscle sparing minimally invasive approach. We found the early complication rates and radiographic outcomes comparable to those reported from arthroplasties performed via traditional approaches. Complications included dislocation (2%), femur fracture (2%), greater trochanteric fracture (12%), postoperative periprosthetic intertrochanteric fracture (2%), femoral nerve palsy (5%), hematoma (2%), and postoperative iliopsoas avulsion (2%). Radiographic analysis revealed average cup anteversion of 19.6° ± 6.6, average cup abduction angle of 48.4° ± 7, stem varus of 0.9° ± 2, and a mean leg length discrepancy of 0.7 mm. The anterior approach to the hip is an attractive alternative to the more traditional approaches. Acceptable component placement with comparable complication rates is possible using a muscle sparing technique which may lead to faster overall recovery.

Intrarater and Interrater Reliability of the Socket Version Marker in Total Hip Replacement

The aim of this study was to evaluate the intraobserver and interobserver variability in determining the socket version using the wire marker. 100 anteroposterior pelvis radiographs of cemented primary total hip replacements were reviewed by two orthopaedic consultants and registrars, twice. Intrarater and interrater reliability were assessed using Cohen’s kappa. Intrarater kappas for junior doctors were 0.78 and 0.80, 0.73 and 0.62 for Consultants. Interrater kappas were 0.60 between the two Consultants and 0.63 between the two Junior Doctors. The kappas between Consultant A and Junior Doctor A was 0.61, between Consultant A and Junior Doctor B was 0.59, between Consultant B and Junior Doctor A was 0.53 and between Consultant B and Junior Doctor B was 0.46. Intrarater reliability was substantial for the two junior doctors and the two consultants. Interrater reliability was moderate-to-substantial between the two consultants, between the two junior doctors and between each pair of junior doctors/consultants.

Radiological measurement of femoral stem version using a modified Budin method

Version of the femoral stem is an important factor influencing the risk of dislocation after total hip replacement (THR) as well as the position of the acetabular component. However, there is no radiological method of measuring stem anteversion described in the literature. We propose a radiological method to measure stem version and have assessed its reliability and validity. In 36 patients who underwent THR, a hip radiograph and CT scan were taken to measure stem anteversion. The radiograph was a modified Budin view. This is taken as a posteroanterior radiograph in the sitting position with 90° hip flexion and 90° knee flexion and 30° hip abduction. The angle between the stem-neck axis and the posterior intercondylar line was measured by three independent examiners. The intra- and interobserver reliabilities of each measurement were examined. The radiological measurements were compared with the CT measurements to evaluate their validity. The mean radiological measurement was 13.36° (sd 6.46) and the mean CT measurement was 12.35° (sd 6.39) (p = 0.096). The intra- and interobserver reliabilities were excellent for both measurements. The radiological measurements correlated well with the CT measurements (p = 0.001, r = 0.877). The modified Budin method appears reliable and valid for the measurement of femoral stem anteversion.

Reliability and validity of measuring acetabular component orientation by plain anteroposterior radiographs

BACKGROUND

Inaccurate placement of an acetabular cup can cause impingement, dislocation, and accelerated wear. However, there is no universally agreed-on approach to measuring cup position using plain radiographs.

OBJECTIVES/PURPOSES

Our goal was to evaluate the reliability and validity of measuring the orientation of acetabular components on plain anteroposterior (AP) radiographs.

METHODS

We obtained plain AP radiographs and CT scans for 60 patients who underwent 60 primary total hip arthroplasties (THAs). The method devised by Lewinnek et al. was used to measure the orientation of acetabular components on plain AP radiographs, and three-dimensional (3-D) CT scans were used to measure both the radiographic anteversion angle and the inclination angle. Reliability was evaluated by analysis of the agreement between inter- and intraobserver measurements using plain AP radiographs. Measurements on 3-D CT scans were regarded as the reference standard; validity was assessed by comparing radiographic measurements with the CT scans.

RESULTS

Inter- and intraobserver reliability for measuring component orientation on plain AP radiographs was nearly perfect with intraclass correlation coefficients of 0.896 and 0.969 for anteversion and 0.984 and 0.993 for inclination. Measurement of cup inclination angles differed between plain radiographs and CT scans, but the difference was small, and the difference, although statistically significant, probably was not clinically important (2.3° ± 1.8°, p < 0.001). There was no significant difference between the anteversion as measured on CT scan versus that measured on plain radiographs (p = 0.19).

CONCLUSIONS

Measurement of the orientation of acetabular components on plain AP radiographs is reliable and accurate compared with measurement on CT.

Clinical experience with computer navigation in revision total hip arthroplasty

The biomechanically and anatomically correct placement of hip prostheses components is the main challenge in revision hip arthroplasty. The orientation of the cup and stem with the restoration of leg length, offset and hip centre is hampered by the defect situations frequently present. In primary hip arthroplasty, it has been demonstrated that the components can be accurately positioned using computer-navigated procedures. However, such procedures could also be of considerable benefit in revision hip arthroplasty. Systems that not only detect anatomical landmarks using pointers but also use image data for referencing may provide a possible solution for the defect situation. Literature about navigation in revision arthroplasty is very rare. This article comprises general considerations on this subject and presents our experience and possible clinical applications.

Positioning of the acetabular component in cemented prostheses - radiographic calculation

OBJECTIVE

to assess the reliability of the inclination angle and anteversion of acetabular cup component in patients with idiopatic osteoarthritis of the hip, aseptic necrosis and hip neck fracture using trigonometric formula and plain radiographs.

METHODS

66 patients underwent cemented total arthroplasty of 72 hips. The inclination of acetabular component was measured using plain radiograph. The acetabular component anteversion was measured using trigonometric formula.

RESULTS

it was observed that, in the osteoarthritic hips, hip neck fracture and aseptic necrosis, the degree of agreement was highly significant (p < 0.0001), in the measurements of anteversion and inclination angles, among the three assessments, from intra as well as inter-observers. All the agreement pairs were of excellent degree (ICC > 0.80).

CONCLUSION

using plain radiographs and trigonometric formula, the method resulted to be highly accurate and reliable. Besides being easy to be calculated. No significant variation was found in the anteversion and inclination angles when compared with osteoarthritis of the hip, aseptic necrosis and hip neck fracture.