Position of the acetabular cup -- accuracy of radiographic calculation compared to CT-based measurement

Roles of combined femoral and acetabular anteversion in pathological changes of hip dysplasia and hip reconstructive surgery

Combined femoral and acetabular anteversion is the sum of femoral and acetabular anteversion, representing their morphological relationship in the axial plane. Along with the increasing understanding of hip dysplasia in recent years, numerous scholars have confirmed the role of combined femoral and acetabular anteversion in the pathological changes of hip dysplasia. At present, the reconstructive surgery for hip dysplasia includes total hip replacement and redirectional hip preservation surgery. As an important surgery index, combined femoral and acetabular anteversion have a crucial role in these surgeries. Herein, we discuss the role of combined femoral and acetabular anteversion in pathological changes of hip dysplasia, total hip replacement, and redirectional hip preservation surgery.

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.

Prospective comparative evaluation of intraoperative joint stability and component placement between posterior approach to hip and its quadriceps coxae sparing modification for primary hip arthroplasty

Background

Efforts at minimizing the propensity of posterior approach of hip for post-operative dislocation after total hip arthroplasty have been a subject of continual research. We comparatively evaluated the posterior approach to hip and its quadriceps coxae sparing (QCS) modification with regard to joint stability and component placement.Questions/Purposes: (1) Does sparing of Quadriceps Coxae tendons vis a vis their sectioning in posterior approach help in achieving better intraoperative stability? (2) Does sparing of Quadriceps Coxae tendons come in the way of adequate surgical exposure sufficient to place hip components accurately? (3) Does sparing of Quadriceps Coxae tendons result in better early functional outcome?

Methods

Seventy-two patients requiring THA were enrolled prospectively and randomized into two groups: group A (posterior approach) and group B quadriceps coxae sparing (QCS) approach. They were compared for intraoperative joint stability, accuracy of component placement, duration of surgery, blood loss, any event of hip dislocation, and functional outcome.

Results

QCS approach resulted in better intraoperative hip stability as the hips tolerated a higher value of 43.50±3.5⁰ mean internal rotation (at 90⁰ of flexion and 20⁰ of adduction) in this group versus a mean value of 33.50±5.5⁰ in posterior approach group (p < 0.01). No significant difference was observed for femoral version, acetabular inclination, and acetabular version in the two groups (p > 0.05). There was no difference between the two groups in terms of duration of surgery, intraoperative blood loss, and functional outcome at one year (p > 0.05). No event of hip dislocation was observed in QCS approach, whereas, one such event happened in the posterior-approach group.

Conclusion

Preservation of the QC tendons improves the intraoperative stability of THA and they do not cause any hindrance in the exposure required for optimum component placement.

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.

The role of 3-dimensional preoperative planning for primary total hip arthroplasty based on artificial intelligence technology to different surgeons: A retrospective cohort study

Preoperative planning with computed tomography (CT)-based 3-dimensiona (3D) templating has been achieved precise placement of hip components. This study investigated the role of the software (3-dimensional preoperative planning for primary total hip arthroplasty [THA] based on artificial intelligence technology, artificial intelligence hip [AIHIP]) for surgeons with different experience levels in primary THA. In this retrospective cohort study, we included patients, who had undergone THA with the help of the AIHIP, and matched to patients, who had undergone THA without the help of the AIHIP, by age and the doctor who operated on them. The subjects were divided into 4 groups, senior surgeon (Chief of Surgery) with AIHIP group, senior surgeon without AIHIP group, junior surgeon (Associate Chief of Surgery) with AIHIP group and junior surgeon without AIHIP group. The general data, imaging index, clinical outcomes and accuracy of stem size prediction and cup size prediction were retrospectively documented for all patients. There was a significant difference in discrepancy in leg length (P = .010), neck-shaft angle (P = .025) and femoral offset (P = .031) between the healthy side and the affected side, operation duration (P < .001), decrease in hemoglobin (Hb) per 24 hours (P = .046), intraoperative radiation exposure frequency (P < .050) and postoperative complications (overall P = .035) among the patients in junior surgeon group. No significant differences were found between senior surgeon groups with respect to discrepancy in leg length (P = .793), neck-shaft angle (P = .088)and femoral offset (P = .946) between the healthy side and the affected side, operation duration (P = .085), decrease in Hb per 24 hours (P = .952), intraoperative radiation exposure frequency (P = .094) and postoperative complications (overall P = .378). The stem sizes of 95% were accurately estimated to be within 1 stem size, and 97% of the cup size estimates were accurate to within 1 cup size in senior surgeon group with AIHIP. A total of 87% stem sizes were accurately estimated to be within 1 stem size, and 85% cup sizes were accurate to within 1 cup size in junior surgeon group with AIHIP. In conclusion, our study suggests that an AI-based preoperative 3D planning system for THA is a valuable adjunctive tool for junior doctor and should routinely be performed preoperatively.

Validation of a Novel Method of Measuring Cup Orientation using BiPlanar Simultaneous Radiographic Images

BACKGROUND

Accurate acetabular component positioning is paramount to the success of total hip arthroplasty. Two-dimensional imaging alone remains a popular tool for implant position assessment despite known limitations. We investigated the accuracy of a novel method for assessing acetabular component position based upon orthogonal simultaneous biplanar Xray images.

METHODS

There were forty consecutive patients who had a pre-existing total hip arthroplasty (THA) on the contralateral side who underwent both computed tomography (CT) and simultaneous orthogonal biplanar radiographic scans for pre-operative planning of THA. The operative inclination (OI) and operative anteversion (OA) of the acetabular cup were calculated by a new measurement method using the biplanar simultaneous scans. Those measurements were compared to measurement of the cup orientation on CT. The measurements were made by two independent observers. Interobserver correlation coefficients were calculated between the two observers to measure reliability.

RESULTS

The mean error in OA measurement of the acetabular cup between simultaneous orthogonal biplanar radiographic and CT imaging was 0.5° (Standard Deviation (SD): 1.9°, minimum -4.0°, maximum 5.0°), the mean error in OI was 0.0° (SD: 1.7°, minimum -5.0°, maximum 4.0°). The average absolute error was 1.5° for OA, and 1.2° for OI. Interobserver correlation coefficient was 0.83 for OA and 0.93 for OI.

CONCLUSION

The novel method of measuring cup orientation using simultaneous biplanar radiographic scans utilized in this study was accurate and reproducible between observers compared to CT measurements.

Three-Dimensional Morphometry of the Canine Pelvis: Implications for Total Hip Replacement Surgery

OBJECTIVES

 Two-dimensional measurements of acetabular geometry are widely used for the assessment of acetabular component orientation following total hip replacement (THR). With the increasing availability of computed tomography scans, there is an opportunity to develop three-dimensional (3D) planning to improve surgical accuracy. The aim of this study was to validate a 3D workflow for measuring angles of lateral opening (ALO) and version, and to establish reference values for dogs.

METHODS

 Pelvic computed tomography scans were obtained from 27 skeletally mature dogs with no radiographic evidence of hip joint pathology. Patient-specific 3D models were built, and ALO and version angles were measured for both acetabula. The validity of the technique was determined by calculating intra-observer coefficient of variation (CV, %). Reference ranges were calculated and data from left and right hemipelves were compared using a paired t-test and symmetry index.

RESULTS

 Measurements of acetabular geometry were highly repeatable (intra-observer CV 3.5-5.2%, inter-observer CV 3.3-5.2%). Mean (± standard deviation) values for ALO and version angle were 42.9 degrees (± 4.0 degrees) and 27.2 degrees (± 5.3 degrees) respectively. Left-right measurements from the same dog were symmetrical (symmetry index 6.8 to 11.1%) and not significantly different.

CONCLUSIONS

 Mean values of acetabular alignment were broadly similar to clinical THR guidelines (ALO of 45 degrees, version angle of 15-25 degrees), but the wide variation in angle measurements highlights the potential need for patient-specific planning to reduce the risk of complications such as luxation.

Does intraoperative periprosthetic occult fracture of the acetabulum affect clinical outcomes after primary total hip arthroplasty?

INTRODUCTION

The frequency of intraoperative periprosthetic occult fracture of the acetabulum (IPOA) in primary total hip arthroplasty (THA) is relatively high. However, the effect of this fracture on clinical outcome and survival of primary THA remains unknown. This study aimed to determine the impact of IPOA on the outcomes of primary THA during a minimum follow-up of 5 years.

MATERIALS AND METHODS

This retrospective case-control study compared the outcomes of primary THA with or without IPOA during a minimum 5-year follow-up. Thirty-eight patients who underwent primary THA with IPOA (O group) were matched to 76 patients without IPOA (C group) between 2004 and 2013 based on age, sex, body mass index, primary diseases, cup diameter, cup design, and additional dome screw. Both groups underwent the same rehabilitation programs after surgery. We evaluated the Japanese Orthopaedic Association clinical outcomes score; postoperative complications, such as nerve injury, dislocation, heterotopic ossification, iliopsoas impingement, or infection; and radiographic outcomes. Additionally, we performed Kaplan-Meier survival analysis with cup aseptic loosening, cup failure revision, and all-cause revision as the endpoints.

RESULTS

There were no significant differences in the pre- and postoperative clinical scores, postoperative complication rates, and cup sagittal rotation between the two groups. Radiographic evaluations showed no aggravation of cases to overt fractures. Bone ingrowth was observed in all cases, and none of the acetabular cups had a progressive radiolucent line ≥ 2 mm in all the 3 acetabular zones. Ten-year survival rates for cup aseptic loosening and cup failure revision were 100% in both groups; those for all-cause revision were 97.4% (92.0-100%) and 100% in the O and C groups, respectively (p = 0.157).

CONCLUSIONS

Primary THA with IPOA provides favorable mid- to long-term outcomes. On IPOA diagnosis, although radiographic follow-up is necessary, additional treatments or rehabilitation programs are not required. Furthermore, postoperative computed tomography images for the detection of IPOA may be unnecessary.

Image-Less THA Cup Navigation in Clinical Routine Setup: Individual Adjustments, Accuracy, Precision, and Robustness

Background and Objectives: Even after the ‘death’ of Lewinnek’s safe zone, the orientation of the prosthetic cup in total hip arthroplasty is crucial for success. Accurate cup placement can be achieved with surgical navigation systems. The literature lacks study cohorts with large numbers of hips because postoperative computer tomography is required for the reproducible evaluation of the acetabular component position. To overcome this limitation, we used a validated software program, HipMatch, to accurately assess the cup orientation based on an anterior-posterior pelvic X-ray. The aim of this study were to (1) determine the intraoperative ‘individual adjustment’ of the cup positioning compared to the widely suggested target values of 40° of inclination and 15° of anteversion, and evaluate the (2) ‘accuracy’, (3) ‘precision’, and (4) robustness, regarding systematic errors, of an image-free navigation system in routine clinical use. Material and Methods: We performed a retrospective, accuracy study in a single surgeon case series of 367 navigated primary total hip arthroplasties (PiGalileoTM, Smith+Nephew) through an anterolateral approach performed between January 2011 and August 2018. The individual adjustments were defined as the differences between the target cup orientation (40° of inclination, 15° of anteversion) and the intraoperative registration with the navigation software. The accuracy was the difference between the intraoperative captured cup orientation and the actual postoperative cup orientation determined by HipMatch. The precision was analyzed by the standard deviation of the difference between the intraoperative registered and the actual cup orientation. The outliers were detected using the Tukey method. Results: Compared to the target value (40° inclination, 15° anteversion), the individual adjustments showed that the cups are impacted in higher inclination (mean 3.2° ± 1.6°, range, (−2)−18°) and higher anteversion (mean 5.0° ± 7.0°, range, (−15)−23°) (p < 0.001). The accuracy of the navigated cup placement was −1.7° ± 3.0°, ((−15)−11°) for inclination, and −4.9° ± 6.2° ((−28)−18°) for anteversion (p < 0.001). Precision of the system was higher for inclination (standard deviation SD 3.0°) compared to anteversion (SD 6.2°) (p < 0.001). We found no difference in the prevalence of outliers for inclination (1.9% (7 out of 367)) compared to anteversion (1.63% (6 out of 367), p = 0.78). The Bland-Altman analysis showed that the differences between the intraoperatively captured final position and the postoperatively determined actual position were spread evenly and randomly for inclination and anteversion. Conclusion: The evaluation of an image-less navigation system in this large study cohort provides accurate and reliable intraoperative feedback. The accuracy and the precision were inferior compared to CT-based navigation systems particularly regarding the anteversion. However the assessed values are certainly within a clinically acceptable range. This use of image-less navigation offers an additional tool to address challenging hip prothesis in the context of the hip−spine relationship to achieve adequate placement of the acetabular components with a minimum of outliers.

Pelvic tilt impacts cup orientation on CT: how accurate is the gold standard?

BACKGROUND

Computed tomography (CT) is the gold standard for the accurate measurement of cup inclination and anteversion in total hip arthroplasty (THA). However, functional cup position strongly depends on the tilt of the pelvis and thus pelvic tilt in the supine position on the CT table harbors the risk of misinterpretation.

PURPOSE

To evaluate the influence of pelvic tilt on cup measurements in postoperative CT scans.

MATERIAL AND METHODS

This is a secondary outcome analysis of a prospective study. In 123 patients undergoing THA, anatomic cup inclination and anteversion as measured on postoperative 3D-CT scans were compared between: (i) the anterior pelvic plane (APP) resembling neutral pelvic tilt; and (ii) the coronal plane representing the standard planes on CT. Furthermore, the effect of the variation on cup positions within Lewinnek's safe zone in relation to the applied reference plane was assessed.

RESULTS

Mean pelvic tilt in supine position was -3.5° ± 5.6°. This resulted in a mean difference for anteversion between APP und coronal plane of 2.1° ± 3.7° and of 2.1° ± 1.9° for cup inclination, respectively. The change varied up to 20.2° for cup inclination and up 12.2° for cup anteversion. The overall conversion rate for inclination and/or anteversion regarding Lewinnek's safe zone was high at 23.6% (29/123).

CONCLUSION

Pelvic tilt affects cup orientation on CT scans depending on the applied reference plane. Standard CT planes should be corrected regarding pelvic tilt before measurements to avoid errors in measurement.

Augmented Reality- vs Accelerometer-Based Portable Navigation System to Improve the Accuracy of Acetabular Cup Placement During Total Hip Arthroplasty in the Lateral Decubitus Position

BACKGROUND

There have been no studies regarding the effectiveness of augmented reality (AR)-based portable navigation systems compared with accelerometer-based portable navigation systems in total hip arthroplasty (THA).

METHODS

We retrospectively compared THAs performed using an AR-based portable navigation system (n = 45) and those performed using an accelerometer-based portable navigation system (n = 42). All THAs were performed with the patient in the lateral decubitus position. The primary outcome was the absolute difference between cup placement angles displayed on the navigation screen and those measured on postoperative X-ray.

RESULTS

The mean absolute differences were significantly smaller in the AR-based portable navigation system group than the accelerometer-based portable navigation system group in radiographic inclination (2.5° ± 1.7° vs 4.6° ± 3.1°; 95% confidence interval 1.1°-3.2°, P < .0001). Similarly, the mean absolute differences were significantly better in the AR-based portable navigation system group in radiographic anteversion (2.1° ± 1.8° vs 6.4° ± 4.2°; 95% confidence interval 3.0°-5.7°, P < .0001). Neither hip dislocation, surgical site infection, nor other complications associated with use of the navigation system occurred in either group.

CONCLUSION

The AR-based portable navigation system may provide more precise acetabular cup placement compared with the accelerometer-based portable navigation system in THA.

Interobserver and Intraobserver Reliabilities of Three-Dimensional Postoperative Evaluation Software in Total Hip Arthroplasty

BACKGROUND

In primary and revision total hip arthroplasty, to prevent perioperative complications, the prediction of the optimal implant size is essential. Using three-dimensional computed tomography-based postoperative evaluation software, we explored the accuracy and the precision of measurement of the size, alignment, and position of the prosthetic components after total hip arthroplasty.

METHODS

Using postoperative evaluation software, the postoperative computed tomography data from 20 hips in 20 patients were evaluated. The component size, alignment, and three-dimensional positioning of the cup and stem were assessed. The concordance rates of the component, repeatability (intraobserver reliability), and reproducibility (interobserver reliability) of postoperative evaluation were calculated. The radiographic inclination and radiographic anteversion of the cup, anteversion, varus-valgus angle, and flexion-extension angles of the stem were measured for alignment. The implant positioning was measured along three axes, namely, X-axis (transverse), Y-axis (sagittal), and Z-axis (longitudinal).

RESULTS

The concordance rates of all parts are above 94%. The intraobserver and interobserver intraclass correlation coefficients of alignment measurement were very good for both cup (0.879-0.964) and stem (0.973-0.996). The intraobserver and interobserver intraclass correlation coefficients of cup positioning were very good (0.961-0.987) for all axes. The intraobserver and interobserver intraclass correlation coefficients of implant positioning were very good for the stem (0.879-0.995) for all axes.

CONCLUSIONS

Computed tomography-based postoperative evaluation software was able to evaluate the size and position of total hip implants with high reproducibility.

Can we trust combined anteversion and Lewinnek safe zone to avoid hip prosthesis dislocation?

INTRODUCTION

Dislocation is one of the most common complications after primary total hip arthroplasty (THA). Combined anteversion (CA) is currently considered one of the most important measures of stability for THA. Thus, the aim of this study is to determine the association between a correct CA after THA and hip prosthesis dislocation, and to analyze the reliability of the Lewinnek safe zone parameters.

MATERIAL AND METHODS

This is a non-interventional retrospective study, carried out at a tertiary hospital in Spain. 2489 primary THA in 2147 patients between January 2008 and December 2014 were identified. Clinical, biological and radiographic data, including cup inclination and cup and femoral anteversion, were analyzed of all patients who developed a hip prosthesis dislocation.

RESULTS

Thirty-four patients met the eligibility criteria to be analyzed. In 73.5% (25/34) of cases, acetabular anteversion (AV) was correct, with a mean AV of 15.1° ± 9.4°. Femoral anteversion (FA) was considered correct only in 38.2% (13/34) of the dislocated THA, with a mean FA of 8.4° ± 17.2°. Sixteen of these 34 patients (47.0%) presented a correct CA, with a mean CA of 24.2° ± 21.0°. Nineteen hips (55.8%) were within the Lewinnek safe zone. Moreover, eleven patients (32.3%) developed a dislocation even though components were within the Lewinnek safe zone and presented a correct CA.

CONCLUSION

Our findings suggest that even when the THA components are positioned within a correct CA and in the Lewinnek safe zone, hip prosthesis dislocations can occur in a not inconsiderable percentage of the cases. Thus, further radiological and clinical analysis should be done to identify potential reasons for hip prosthesis dislocation.

The area method for measuring acetabular cup anteversion: An accurate and autonomous solution

Several radiological methods of measuring anteversion of the acetabular component after total hip arthroplasty have been described, all time-consuming and with varying reproducibility. This study aimed to compare the recently proposed Area method to true cup anteversion as determined by an accelerometer. This study further applied this method programmatically to autonomously determine radiographic cup orientation using two computer programs, then compared these results to hand and accelerometer measurements. 160 anteroposterior pelvis radiographs were taken of a standard Sawbones® pelvis fitted with a total hip arthroplasty system. The acetabular cup was re-oriented between each radiograph, with anteversion ranging from 0° to 90°. An accelerometer was mounted to the cup to measure true cup anteversion. Radiographic anteversion was independently measured via three methods: by hand, linear image processing, and machine learning. Measurements were compared to triaxial accelerometer recordings. Coefficient of determination (R2) was found to be 0.997, 0.991, and 0.989 for hand measurements, the machine learning, and linear image processing, respectively. The machine learning program and hand measurements overestimated anteversion by 0.70° and 0.02° respectively. The program using linear techniques underestimated anteversion by 5.02°. Average runtime was 0.03 and 0.59 s for the machine learning and linear image processing program, respectively. The machine learning program averaged within 1° of cup orientation given a true cup anteversion less than 51°, and within 2° given an anteversion less than 85°. The Area method showed great accuracy and reliability with hand measurements compared to true anteversion. The results of this study support the use of machine learning for accurate, timely, autonomous assessment of cup orientation.

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.

Electromagnetic navigation system for acetabular component placement in total hip arthroplasty is more precise and accurate than the freehand technique: a randomized, controlled trial with 84 patients

Background and purpose - The accuracy of conventional navigation systems depends on precise registration of bony landmarks. We investigated the clinical use of electromagnetic navigation (EMN), with a unique device for precise determination of the anterior pelvic plane. Patients and methods - We randomly allocated patients scheduled for total hip arthroplasty into 2 groups of 42 patients each. In the study group, cups were placed at the predetermined target angles (inclination: 42.5°; anteversion: 15°) with the support of EMN. In the control group, cups were placed freehand aiming at the same target angles. Postoperatively the true position of the cup was determined using computed tomography scan of the pelvis. Precision (root mean squared error, RMSE) bias (mean bias error, ME), accuracy, and duration of surgery were compared between the methods. Results - Cup anteversion was more accurate and precise in the navigated group. The ME in the navigated and freehand group was -1.7° (95% CI -2.4 to 1.1) and -4.5° (CI -6.5 to 2.5), respectively. The RMSE in the navigated and freehand group was 2.8° (CI 2.3-3.2) and 8.0° (CI 6.3-9.5), respectively. The inclination was also more precise in the navigated group, with the RMSE in the navigated and freehand group at 4.6° (CI 3.4-5.9) and 6.5° (CI 5.4-7.5), respectively. The accuracy of the inclination and the duration of surgeries were similar between the groups. Interpretation - Cup placement with the help of EMN is more precise than the freehand technique and it does not affect the duration of surgery.

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.

Ellipse method for measuring Liaw's anteversion of the acetabular component after total hip arthroplasty

BACKGROUND

Several cup anteversion measurements for post-operative total hip arthroplasty (THA) surgery have been described. We developed the standardized Liaw's trigonometric method to eliminate the influence of patient position, which is the most accurate method for cup anteversion measurement. We then developed an ellipse method using the Elliversion software and reported an interobserver error reduction in 2013. In this study, we attempted to apply this ellipse method in the clinic and compared its accuracy with the standard trigonometric version.

METHODS

In the present study, we attempted to incorporate the ellipse method with Liaw's standardized anteversion in the simulated cup position. We measured standardized Liaw's anteversion for 434 radiographs in the clinic using the ellipse method. Repeated standard deviation (RSD) was calculated for accuracy evaluation. Furthermore, paired t-test was used for comparison with the interobserver and intraobserver errors.

RESULTS

We found that the standardized Liaw's anteversion measured using the ellipse method showed lower RSD than the radiographic version. RSD was 0.795 in the standardized Liaw's anteversion with ellipse method group. The p-values of the paired t-test were all higher than 0.05 when measuring the interobserver and intraobserver errors. It indicated that the ellipse method was a precise and simple tool for cup anteversion measurement.

CONCLUSION

We believe that this ellipse measurement can assist surgeons while placing the acetabulum cup into the precise position and enable early diagnosis of acetabulum loosening.

Quality, but not quantity of physical activity is associated with metal ion concentrations in unilateral hip resurfacing

Little is known about the influence of physical activity (PA) on metal ion concentrations in subjects with metal-on-metal hip arthroplasty. Implant wear is thought to be a function of use and thus of patient activity levels. It is hypothesized that daily habitual PA of patients with hip resurfacing arthroplasty (HRA) is associated with metal ion concentrations. Therefore a study was conducted in patients with a unilateral HRA at 10-years follow-up. Blood metal ion concentrations were determined. An acceleration-based activity monitor was used to measure PA in daily life. The cohort consisted of 12 males (75%) and 4 females (25%) with a median age at surgery of 55.5 ± 9.7 years [43.0-67.9] and a median follow-up of 9.9 ± 1.0 years [9.1-10.9]. The median cobalt and chromium ion concentrations were 25 ± 13 and 38 ± 28 nmol/L. A significant association between sit-stand transfers and high-intensity peaks with cobalt ion concentrations were found. Regarding PA and metal ion concentrations as a proxy of wear in HRA, specific activities like transfers or qualitative aspects of activity behavior like intensity, seem to matter more than the quantity of low-intensity activities like walking or cycling. This suggests that patients may safely engage in such activities to achieve important general health benefits and quality of life.

Are single plane intraoperative and biplanar postoperative radiographic measurements of acetabular cup position the same?

PURPOSE

Supine positioning and the use of fluoroscopy during direct anterior approach total hip arthroplasty (DAA THA) have been reported to improve acetabular component positioning. This study aims to compare 2-dimensional intraoperative radiographic RadLink measurements of acetabular component position with 3-dimensional postoperative 3D SterEOS measurements.

METHODS

Intraoperative fluoroscopy and RadLink (El Segundo, CA, USA) were used to measure acetabular cup position intraoperatively in 48 consecutive patients undergoing DAA THA. Cup position was measured on 6-week postoperative standing EOS images using 3D SterEOS software (EOS Imaging, SA, Paris, France) and compared to RadLink findings using Student's t-test. Safe-zone outliers were identified. We evaluated for measurement difference of > +/- 5°.

RESULTS

RadLink acetabular cup abduction measurement (mean 43.0°) was not significantly different than 3D SterEOS in the anatomic plane (mean 42.6°, p = 0.50) or in the functional plane (mean 42.7°, p = 0.61). RadLink acetabular cup anteversion measurement (mean 17.9°) was significantly different than 3D SterEOS in both the anatomic plane (mean 20.6°, p = 0.022) and the functional plane (mean 21.2°, p = 0.002). RadLink identified 2 cups outside of the safe-zone. However, SterEOS identified 12 (anatomic plane) and 10 (functional plane) outside of the safe-zone. In the functional plane, 58% of anteversion and 92% of abduction RadLink measurements were within +/- 5° of 3D SterEOS.

CONCLUSIONS

Intraoperative fluoroscopic RadLink acetabular anteversion measurements are significantly different than 3D SterEOS measurements, while abduction measurements are similar. Significantly more acetabular cups were noted to be outside of the safe-zone when evaluated with 3D SterEOS versus RadLink.

Analysis of four methods of measuring three-dimensional pelvic tilt in the lateral decubitus position

Proper alignment of acetabular implantation is necessary for good patient outcomes and preventing complications or additional surgeries in total hip arthroplasty (THA). Rotation of the pelvis in lateral decubitus (LD) is typically not accounted for as surgeons use the surgery table as a reference plane to align implants. This study compared four techniques to measure 3D pelvic rotations in LD position using computer models. CT scans of 19 subjects in LD position were used to create 3D pelvis models. Pelvic rotations were measured by three users using four techniques: landmark (LM), defined plane (DP), anterior pelvic plane (APP), and plane of best symmetry (POBS) methods. Measurements were analysed for intra-user reliability and relationships between methods were assessed using intraclass correlation coefficient, standard error of measurement, and coefficient of determination. The POBS method exhibited the highest inter-observer reliability and is recommended as a new measurement technique to measure pelvic rotations before THA surgery. The LM method exhibited low reliability but may be suitable for expert users familiar with pelvic landmarks. The APP method should only be used when the patients' APP planes are known in neutral standing and side-lying postures. The DP method is not recommended due to substantial individual variability. Graphical abstract.

Squeaking and other noises in patients with ceramic-on-ceramic total hip arthroplasty

INTRODUCTION

Noise in ceramic-on-ceramic (CoC) total hip arthroplasty (THA) is a potential symptom of abnormal bearing wear. Squeaking and other prosthetic hip noises are multi-factorial phenomena that can be analysed and may provide prognostic information.

METHODS

46 patients with noisy CoC bearings were investigated using X-ray, computed tomography and joint fluid analysis, and classified into either high or low risk of ceramic liner fracture groups according to previously published guidelines. Noise events from the bearings of 16 high risk cases which were subsequently revised were compared with 30 patients in the low risk control group who did not undergo revision. Noise events were analysed for their physical characteristics using a standardised protocol and classified as either low frequency and short duration 'clicking' or long duration and high frequency 'squeaking'.

RESULTS

The peak frequency of squeaking during forward walking was significantly higher for patients in the case group who were revised, compared with the control group. The patient-reported onset of squeaking (46 months postoperatively) was earlier than short-noise emissions (82 months). In the standardised sequence of movements, short-noise always occurred more frequently than squeaking. Small heads (28 mm) were more likely to develop short-noise, while large heads (⩾32 mm) were more likely to develop squeaking.

DISCUSSION

Noise evaluation may provide additional value for predicting failure of CoC bearings, though some questions should be better investigated in a dedicated prospective trial.

Total Hip Arthroplasty Using Imageless Computer-Assisted Navigation-2-Year Follow-Up of a Prospective Randomized Study

The purpose of this study is to compare computer-assisted to manual implantation-techniques in total hip arthroplasty (THA) and to find out if the computer-assisted surgery is able to improve the clinical and functional results and reduce the dislocation rate in short-terms after THA. We performed a concise minimum 2-year follow-up of the patient cohort of a prospective randomized study published in 2014 and evaluated if the higher implantation accuracy in the navigated group can be seen as an important determinant of success in total hip arthroplasty. Although a significant difference was found in mean postoperative acetabular component anteversion and in the outliers regarding inclination and anteversion (p < 0.05) between the computer-assisted and the manual-placed group, we could not find significant differences regarding clinical outcome or revision rates at 2-years follow-up. The implantation accuracy in the navigated group can be regarded as an important determinant of success in THA, although no significant differences in clinical outcome could be detected at short-term follow-up. Therefore, further long-term follow-up of our patient group is needed.

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.

GeoGebra: A reliable and free software for measuring acetabular cup anteversion on digitalized plain radiographs

OBJECTIVE

Although accurate measurement of cup anteversion in hip replacement requires CT scans, however, its routine application, especially during follow-up, remains economically and ethically unreasonable. Thus, several methods have been devised for making this measurement on plain radiographs. In recent years, several ways have been adopted using software on digital radiographs. We present one such method which uses open access mathematical software GeoGebra.

METHODS

Anteversion was measured on 72 radiographs (36 cemented; 36 uncemented) by three different observers using this software. One observer repeated measurements at three weeks interval.

RESULTS

The intraclass correlation coefficient for interobserver variability and intraobserver variability was 0.982 (0.973-0.989) and 0.986 (0.978-0.991) respectively. There was a significant difference in the reliability of the method for cemented and uncemented cups with higher reliability for cemented cups (p < 0.001).

CONCLUSION

GeoGebra software can be used as a reliable alternative for measuring acetabular cup anteversion on good quality well centred digital radiographs of the pelvis.

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.

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.

Metal ion concentrations after metal-on-metal hip arthroplasty are not correlated with habitual physical activity levels

INTRODUCTION

Metal-on-metal (MoM) hip arthroplasties have shown high clinical failure rates with many patients at risk for a revision and under surveillance for high metal ion concentrations. Implant wear releasing such ions is assumed to be a function of use, i.e. the patient's physical activity. This study aimed to assess whether habitual physical activity levels of MoM patients are correlated with metal ion concentrations and are higher in patients with high (at risk) than in patients with low (safe) metal ion concentrations.

METHODS

A cohort study was conducted of patients with any type of MoM hip prosthesis. Metal ion concentrations were determined using ICP-MS. Habitual physical activity of subjects was measured in daily living using an acceleration-based activity monitor. Outcome consisted of quantitative and qualitative activity parameters.

RESULTS

In total, 62 patients were included. Mean age at surgery was 60.8 ± 9.3 years and follow-up was 6.3 ± 1.4 years. Cobalt concentrations were highly elevated overall (112.4 ± 137.9 nmol/L) and significantly more in bilateral (184.8 ± 106.5 nmol/L) than in unilateral cases (87.8 ± 139.4 nmol/L). No correlations were found between physical activity parameters and metal ion concentrations. Subgroup analysis of patients with low versus high cobalt concentration showed no significant differences in habitual physical activity.

DISCUSSION

No correlation was found between physical activity levels and metal ion concentrations. Implant use by normal habitual activities of daily living seems not to influence metal ion concentrations.

Accuracy of Acetabular Component Positioning Using Computer-assisted Navigation in Direct Anterior Total Hip Arthroplasty

Background 

Appropriate component positioning in total hip arthroplasty (THA) is imperative for long-term survivorship. C-arm fluoroscopy provides visual guidance in the direct anterior approach (DAA), but it is limited by qualitative properties. Conversely, imageless computer-assisted navigation systems (CAS) provide surgeons with intraoperative, three-dimensional (3D) quantitative measurements for cup position, although the accuracy of such systems has not been extensively addressed in the DAA. We evaluated the ability of an imageless CAS to deliver measurements for acetabular cup position with accuracy in the DAA.

Materials and methods 

A retrospective analysis of 69 primary THA procedures was conducted. Acetabular cup position measurements (anteversion and inclination) obtained intraoperatively by imageless navigation were compared to standard, postoperative anteroposterior pelvic radiographic measurements. Statistical comparisons were made using the Bland-Altman technique.

Results 

The mean difference between device and radiographic measurements for anteversion was 3.4° (standard deviation (SD): 4.1°; absolute mean difference (ABS): 4.2°), and 4.0° for inclination (SD: 3.6°; ABS: 4.3°). Bland-Altman analysis demonstrated excellent agreement; 93% (64/69) and 97% (67/69) of anteversion pairings fell within the statistical and clinical limits of agreement, whereas 94% (65/69) and 100% (69/69) of inclination pairings were within the statistical and clinical limits, respectively.

Conclusions 

Measurements obtained intraoperatively for acetabular cup position using imageless navigation in the DAA are agreeable with the current clinical standard.

A new radiographic acetabular cup anteversion measurement method in total hip arthroplasty: a clinical study

BACKGROUND

The acetabular cup positioning is one of the most crucial steps affecting stability and wear rates in total hip arthroplasty. Different methods have been described for determining the anteversion of the acetabular cup in the literature. But there is still not a widely accepted method to assess the acetabular anteversion radiography. The aim of this study is to measure the acetabular anteversion angle on a single pelvis AP radiography with our method which was proven with an experimental study before.

MATERIALS AND METHODS

A total of 15 patients (8 males, 7 females) who underwent total hip arthroplasty and have had a pelvis computed tomography scans in our outpatient clinic were evaluated retrospectively. The anteversion angle was calculated in all of pelvis CT scans. For radiological measurement, the formula defined by the authors in an experimental model previously was used.

RESULTS

Statistically significant difference was not determined between radiographic and CT-based measurements (p = 0.207; p > 0.05). A statistically significant agreement was observed at a level of 98.8% between radiographic and CT-based measurements (ICC = 0.988; 95% CI 0.966-0.996; p < 0.01).

CONCLUSION

Assessment of the acetabular cup anteversion is very important to predict the possible complications after total hip arthroplasty. Although many methods have been defined for this purpose, each of these has advantages and disadvantages. In particular, with computed tomography method, the patient is exposed to excessive radiation, whereas we think that our method is a preferred method due to features not requiring additional equipment, low radiation exposure, being simple, cost-effectiveness, easily applicable and almost 100% accurate.

Gravity-Assisted Navigation System for Total Hip Arthroplasty

In this chapter we propose a new system that allows reliable acetabular cup placement in total hip arthroplasty (THA) when the surgery is operated in lateral approach. Conceptually it combines the accuracy of computer-generated patient-specific morphology information with an easy-to-use mechanical guide, which effectively uses natural gravity as the angular reference. The former is achieved by using a statistical shape model-based 2D-3D reconstruction technique that can generate a scaled, patient-specific 3D shape model of the pelvis from a single conventional anteroposterior (AP) pelvic X-ray radiograph. The reconstructed 3D shape model facilitates a reliable and accurate co-registration of the mechanical guide with the patient's anatomy in the operating theater. We validated the accuracy of our system by conducting experiments on placing seven cups to four pelvises with different morphologies. Taking the measurements from an image-free navigation system as the ground truth, our system showed an average accuracy of 2. 1 ± 0. 7^∘ for inclination and an average accuracy of 1. 2 ± 1. 4^∘ for anteversion.

Customized implants for acetabular Paprosky III defects may be positioned with high accuracy in revision hip arthroplasty

PURPOSE

In revision hip arthroplasty, custom-made implants are one option in patients with acetabular Paprosky III defects.

METHODS

In a retrospective analysis, we identified 11 patients undergoing cup revision using a custom-made implant. The accuracy of the intended position of the implant was assessed on post-operative 3D CT and compared to the pre-operative 3D planning in terms of inclination, anteversion, and centre of rotation. In addition, the accuracy of post-operative plain radiographs for measuring implant position was evaluated in relation to the 3D CT standard.

RESULTS

We found a mean deviation between the planned and the final position of the custom-made acetabular implant on 3D CT of 3.6° ± 2.8° for inclination and of - 1.2° ± 7.0° for anteversion, respectively. Restoration of center of rotation succeeded with an accuracy of 0.3 mm ± 3.9 mm in the mediolateral (x) direction, - 1.1 mm ± 3.8 mm in the anteroposterior (y) direction, and 0.4 mm ± 3.2 mm in the craniocaudal (z) direction. The accuracy of the post-operative plain radiographs in measuring the position of the custom-made implant in relation to 3D CT was 1.1° ± 1.7° for implant inclination, - 2.6° ± 1.3° for anteversion and 1.3 mm ± 3.5 mm in the x-direction, and - 0.9 mm ± 3.8 mm in the z-direction for centre of rotation.

CONCLUSION

Custom-made acetabular implants can be positioned with good accuracy in Paprosky III defects according to the pre-operative planning. Plain radiographs are adequate for assessing implant position in routine follow-up.

Does Intraoperative Fluoroscopy Improve Limb-Length Discrepancy and Acetabular Component Positioning During Direct Anterior Total Hip Arthroplasty?

BACKGROUND

One potential benefit of the direct anterior approach (DAA) for total hip arthroplasty is the ability to use intraoperative fluoroscopy for acetabular cup positioning and limb-length evaluation. Previous studies comparing the use of fluoroscopy with an anterior approach to a posterior approach have reported conflicting results. To our knowledge, no prior study has compared acetabular cup position and limb-length discrepancy (LLD) using a DAA with and without fluoroscopy.

METHODS

We retrospectively reviewed the charts of 298 patients who underwent direct anterior total hip arthroplasty with or without intraoperative fluoroscopy. All procedures were performed by 2 surgeons who use DAA as their primary approach. Preoperative and 6-week postoperative low anteroposterior pelvis and cross-table lateral radiographs were reviewed by 3 independent surgeons. Acetabular cup inclination, anteversion, and LLD were measured and compared.

RESULTS

Thirty-three patients were excluded for inadequate imaging, leaving 125 patients in the fluoroscopy group and 140 patients in the nonfluoroscopy group. Mean inclination, anteversion, and LLD were 39.4° (95% confidence interval [CI], 38.5°-40.2°), 30.2° (95% CI, 29.2°-31.2°), and 1.1 mm (95% CI, 0.1 mm-2.2 mm) for the fluoroscopy group and 39.9° (95% CI, 39.3°-40.5°), 31.1° (95% CI, 30.0°-32.2°), and 0.8 mm (95% CI, -0.1 mm to 1.6 mm) for the nonfluoroscopy group. There was no significant difference in acetabular inclination (P = .35), anteversion (P = .22), or postoperative LLD (P = .64) between groups.

CONCLUSION

This study found no clinically or statistically significant difference in acetabular inclination, anteversion, or LLD between the fluoroscopy and nonfluoroscopy groups. Both surgeons achieved a similar mean acetabular cup position and an equivalent mean LLD.

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.

The reliability of measuring acetabular component position on radiographs using everyday diagnostic imaging software

BACKGROUND

It is standard practice for total hip arthroplasty (THA) patients to have post-operative imaging, and one of the reasons is to assess the adequacy of acetabular component position. Correct positioning of the acetabular component is important for successful outcome in THA. Acetabular component position can be measured from either computed tomography (CT) or plain radiographs. While CT is the gold standard for accurately measuring acetabular component position, radiographs are routinely used for post-operative evaluation. However, measurement of acetabular component position from plain radiographs is not straightforward and numerous methods have been proposed. As most imaging is now digital, the aim of this study was to investigate the reliability of one method to measure acetabular component position using a basic diagnostic imaging software program that is readily available to orthopaedic surgeons.

METHODS

We investigated the reliability Lewinnek's method using a basic Picture Archiving and Communication System program, InteleViewer ™ . We measured 69 post-operative anteroposterior (AP) radiographs of patients who underwent primary THA. Intra-observer and inter-observer reliability for Lewinnek's method was calculated using the intraclass correlation coefficient.

RESULTS

Our results showed excellent intra- and inter-observer reliability for both inclination (0.99, 95% confidence interval (CI): 0.99-1.0; and 0.97, 95% CI: 0.95-0.99) and anteversion (0.99, 95% CI: 0.98-0.99; and 0.93, 95% CI: 0.89-0.96) measurements.

CONCLUSION

This study has shown that using Lewinnek's method, acetabular component position can be reliably measured on post-operative AP digital radiographs using readily available software tools.

Three-dimensional orientation and location-dependent varying rules of radiographic angles of the acetabular cup

AIM

The aim of this study is to demonstrate the varying rules of radiographic angles following varying three-dimensional (3D) orientations and locations of cup using an accurate mathematical model.

METHODS

A cone model is established to address the quantitative relationship between the opening circle of cup and its ellipse projection on radiograph. The varying rules of two-dimensional (2D) radiographic anteversion (RA) and inclination (RI) angles can be analyzed.

RESULTS

When the centre of cup is located above X-ray source, with proper 3D RI/RA angles, 2D RA angle can be equal to its 3D counterpart, and 2D RI angle is usually greater than its 3D counterpart. Except for the original point on hip-centered anterior-posterior radiograph, there is no area on radiograph where both 2D RA and RI angles are equal to their 3D counterparts simultaneously.

DISCUSSION

This study proposes an innovative model for accurately explaining how 2D RA/RI angles of cup are varying following different 3D RA/RI angles and location of cup. The analysis results provide clinicians an intuitive grasp of knowledge about 2D RA/RI angles greater or smaller than their 3D counterparts post-operatively. The established model may allow determining the effects of pelvic rotations on 2D radiographic angles of cup.

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.

Inter- and intra-observer variability of radiography and computed tomography for evaluation of Zurich cementless acetabular cup placement ex vivo

Objective: To evaluate the inter- and intra-observer variability in measurement of the angle of lateral opening (ALO) and version angle measurement using digital radiography and computed tomography (CT).

Methods: Each hemipelvis was implanted with a cementless acetabular cup. Ventrodorsal and mediolateral radiographs were made of each pelvis, followed by CT imaging. After removal of the first cup, the pelves were implanted with an acetabular cup in the contra-lateral acetabulum and imaging was repeated. Three surgeons measured the ALO and version angles three times for each cup from the mediolateral radiographic projection. The same measurements were made using three-dimensional multiplanar reconstructions from CT images. Two anatomical axes were used to measure pelvic inclination in the sagittal plane, resulting in six measurements per cup. Two-way repeated measures analysis of variance evaluated inter- and intra-observer repeatability for radiographic and CT-based measurements.

Results: Version angle based on radio-graphic measurement did not differ within surgeons (p = 0.433), but differed between surgeons (p <0.001). Radiographic measurement of ALO differed within surgeons (p = 0.006) but not between surgeons (p = 0.989). The ALO and version angle measured on CT images did not differ with or between surgeons.

Clinical significance: Assessment of inter-and intra-observer measurement of ALO and version angle was more reproducible using CT images than conventional mediolateral radiography for a Zurich cementless acetabular cup.

Can Surgeons Reduce the Risk for Dislocation After Primary Total Hip Arthroplasty Performed Using the Posterolateral Approach?

BACKGROUND

Hip dislocation is one of the most common postoperative complications after total hip arthroplasty (THA). Potential contributors include patient- and surgical-related factors. We performed a retrospective cohort study to identify risk factors for postoperative dislocation in patients receiving THA via the posterolateral approach.

METHODS

We assessed 1326 consecutive primary THAs performed between 2010 and 2015. Patient information was documented, and plain radiographic films were used to evaluate cup positioning, hip offset, and hip length change. A multiple logistic regression was used to identify risk factors for dislocation. Follow-up was coordinated by the Danish National Patient Registry.

RESULTS

Age and American Society of Anesthesiologists scores were higher in dislocating THA compared with those in the nondislocating THA. Cup anteversion was less in dislocating THA compared with that in nondislocating THA. Independent risk factors for cup dislocation were increased age, body mass index <25 and >30 kg/m², and leg shortening of >5 mm.

CONCLUSION

Surgeons should aim for a shortening of leg length <5 mm to reduce the risk of postoperative dislocation in primary THA. Although anteversion was reduced for dislocating THA, there is likely no universal safe zone for cup positioning. Hip stability is multifactorial, and optimal cup positioning may vary from patient to patient.

Radiographic cup anteversion measurement corrected from pelvic tilt

The purpose of this study was to develop a novel technique to improve the accuracy of radiographic cup anteversion measurement by correcting the influence of pelvic tilt. Ninety virtual total hip arthroplasties were simulated from computed tomography data of 6 patients with 15 predetermined cup orientations. For each simulated implantation, anteroposterior (AP) virtual pelvic radiographs were generated for 11 predetermined pelvic tilts. A linear regression model was created to capture the relationship between radiographic cup anteversion angle error measured on AP pelvic radiographs and pelvic tilt. Overall, nine hundred and ninety virtual AP pelvic radiographs were measured, and 90 linear regression models were created. Pearson's correlation analyses confirmed a strong correlation between the errors of conventional radiographic cup anteversion angle measured on AP pelvic radiographs and the magnitude of pelvic tilt (P < 0.001). The mean of 90 slopes and y-intercepts of the regression lines were -0.8 and -2.5°, which were applied as the general correction parameters for the proposed tool to correct conventional cup anteversion angle from the influence of pelvic tilt. The current method proposes to measure the pelvic tilt on a lateral radiograph, and to use it as a correction for the radiographic cup anteversion measurement on an AP pelvic radiograph. Thus, both AP and lateral pelvic radiographs are required for the measurement of pelvic posture-integrated cup anteversion. Compared with conventional radiographic cup anteversion, the errors of pelvic posture-integrated radiographic cup anteversion were reduced from 10.03 (SD = 5.13) degrees to 2.53 (SD = 1.33) degrees. Pelvic posture-integrated cup anteversion measurement improves the accuracy of radiographic cup anteversion measurement, which shows the potential of further clarifying the etiology of postoperative instability based on planar radiographs.

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.

Acetabular cup position and risk of dislocation in primary total hip arthroplasty

Background and purpose - Hip dislocation is one of the most common complications following total hip arthroplasty (THA). Several factors that affect dislocation have been identified, including acetabular cup positioning. Optimal values for cup inclination and anteversion are debatable. We performed a systematic review to describe the different methods for measuring cup placement, target zones for cup positioning, and the association between cup positioning and dislocation following primary THA. Methods - A systematic search of literature in the PubMed database was performed (January and February 2016) to identify articles that compared acetabular cup positioning and the risk of dislocation. Surgical approach and methods for measurement of cup angles were also considered. Results - 28 articles were determined to be relevant to our research question. Some articles demonstrated that cup positioning influenced postoperative dislocation whereas others did not. The majority of articles could not identify a statistically significant difference between dislocating and non-dislocating THA with regard to mean angles of cup anteversion and inclination. Most of the articles that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in dislocation rate. Alternative target ranges have been proposed by several authors. Interpretation - The Lewinnek safe zone could not be justified. It is difficult to draw broad conclusions regarding a definitive target zone for cup positioning in THA, due to variability between studies and the likely multifactorial nature of THA dislocation. Future studies comparing cup positioning and dislocation rate should investigate surgical approach separately. Standardized tools for measurement of cup positioning should be implemented to allow comparison between studies.

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.

Central X-ray beam correction of radiographic acetabular cup measurement after THA: an experimental study

PURPOSE

Accurate assessment of cup orientation on postoperative radiographs is essential for evaluating outcome after THA. However, accuracy is impeded by the deviation of the central X-ray beam in relation to the cup and the impossibility of measuring retroversion on standard pelvic radiographs.

METHOD

In an experimental trial, we built an artificial cup holder enabling the setting of different angles of anatomical anteversion and inclination. Twelve different cup orientations were investigated by three examiners. After comparing the two methods for radiographic measurement of the cup position developed by Lewinnek and Widmer, we showed how to differentiate between anteversion and retroversion in each cup position by using a second plane. To show the effect of the central beam offset on the cup, we X-rayed a defined cup position using a multidirectional central beam offset. According to Murray's definition of anteversion and inclination, we created a novel corrective procedure to balance measurement errors caused by deviation of the central beam.

RESULTS

Measurement of the 12 different cup positions with the Lewinnek's method yielded a mean deviation of [Formula: see text] (95 % CI 1.3-2.3) from the original cup anteversion. The respective deviation with the Widmer/Liaw's method was [Formula: see text] (95 % CI 2.4-4.0). In each case, retroversion could be differentiated from anteversion with a second radiograph. Because of the multidirectional central beam offset ([Formula: see text] cm) from the acetabular cup in the cup holder ([Formula: see text] anteversion and [Formula: see text] inclination), the mean absolute difference for anteversion was [Formula: see text] (range [Formula: see text] to [Formula: see text] and [Formula: see text] (range [Formula: see text] to [Formula: see text] for inclination. The application of our novel mathematical correction of the central beam offset reduced deviation to a mean difference of [Formula: see text] for anteversion and [Formula: see text] for inclination.

CONCLUSION

This novel calculation for central beam offset correction enables highly accurate measurement of the cup position.

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.

Good vs Poor Results After Total Hip Arthroplasty: An Analysis Method Using Implant and Anatomic Parameters With the EOS Imaging System

BACKGROUND

Existing imaging techniques and single-parameter analyses, in nonfunctional positions, fail to detect the differences between patients with good vs poor results after total hip arthroplasty.

METHODS

The present study developed an analysis method using the EOS full-body, low-dose, biplanar, weightbearing imaging system to compare good vs poor patients after total hip arthroplasty and to report on our preliminary experiences (17 good, 18 poor).

RESULTS

All revision cases were found to have at least 4 high or low implant or anatomic parameters relative to the good group. These included acetabular cup orientation, sagittal pelvic tilt, sacral slope, femoral offset, and neck-shaft angle. Acetabular cup orientation differed significantly between groups.

CONCLUSION

With the EOS system, a large cohort can be studied relatively quickly and at low dose, which could lead to patient-specific guidelines.

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.