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

Cup accuracy and early-term clinical outcomes of a novel, pinless, robotic-assisted total hip arthroplasty system: A first-in-human pilot study

BACKGROUND

Malpositioning of the acetabular cup represents a challenge during total hip arthroplasty (THA). The purpose of this study was to evaluate the accuracy of acetabular cup placement and early postoperative clinical outcomes with a novel, pinless, fluoroscopic-guided, robotic-assisted application for direct anterior (DA) approach THA.

METHODS

This prospective, pre-market phase 2 study enrolled 19 patients undergoing THA for osteoarthritis. Standing anteriorposterior (AP) and lateral radiographs up to 1 year postoperatively were assessed for component fixation and complications. Martell Hip Analysis software was used to assess radiographic acetabular anteversion and inclination from postoperative standing AP pelvis images and the results were compared to target and final component values from the surgical logs. Patient reported outcome measures (PROMs) were collected preoperatively, four weeks, three months, and one year after operation.

RESULTS

Mean absolute difference for anteversion and inclination from respective targets on intraoperative fluoroscopic views was 1.4° ± 1.3° (P = 0.159) and 1.3° ± 1.1° (P = 0.378). The absolute difference between postoperative radiographs and intraoperative target values was 2.91 ± 2.40° (P = 0.019) for anteversion and 3.84 ± 2.57° (P = 0.007) for inclination. The difference in target and postoperative radiographic inclination and anteversion was within 5° in 77.8% of cases, and the cup was within the Lewinnek safe zone in 16 of 18. Oxford Hip Score (OHS) (44.3 ± 4.6 vs. 22.2 ± 11.3), score on Numeric Pain Rating Scale (NRPS) (0.5 ± 1.0 vs. 5.7 ± 2.6), and Hip Osteoarthritis Outcome Score-12 (HOOS-12) Overall Score (91.4 ± 11.2 vs. 42.8 ± 20.1) were significantly improved at one year. At one-year, 88.2% and 11.8% of patients were very satisfied or satisfied.

CONCLUSION

This first-in-human study on THA utilizing a pinless, fluoroscopy-based robotic arm demonstrated high accuracy in terms of radiographic inclination and anteversion, excellent hip-specific functional outcomes and safety one year after operation. Video Abstract.

Radiological assessment of cup anteversion with a novel 3D-printed highly-porous titanium dual mobility cup

BACKGROUND

Cup anteversion after primary total hip arthroplasty (THA) with monobloc dual mobility cups (DMC) is difficult to measure on anterior-posterior (AP) pelvic radiographs because of the implant radiopacity and cup design which do not allow for an accurate visualization of the radiographic projection of the cup equatorial rim and the femoral head. This study aims to radiographically investigate on the reliability and accuracy of different measurement methods for cup anteversion in monobloc DMC THA, by comparing a novel titanium cup with conventional cup designs.

METHODS

97 THAs with a monobloc 3D-printed titanium DMC were radiographically assessed for cup radiographic anteversion (RA) one month postoperatively. RA were measured by three blinded observers through Lewinnek, Woo-Morrey methods and an open access mathematical software (GeoGebra), used as reference method. Intra- and interobserver reliability of RA measurements were evaluated for each method using intraclass correlation coefficient (ICC). Accuracy was assessed comparing Lewinnek and Woo-Morrey methods with GeoGebra. Moreover, further 98 THAs with conventional different brand DMC were radiographically assessed as control group by using the same methods.

RESULTS

ICC for intra- and interobserver reliability for RA measurements with GeoGebra, Lewinnek and Woo-Morrey methods were 0.975-0.980, 0.978 - 0.965, and 0.979 - 0.958, respectively, for the titanium DMC group. Lewinnek resulted more accurate for RA than Woo-Morrey, differing by + 0.4° (p = 0.06) and + 4.4° (p < 0.001) from GeoGebra, respectively. ICC for intra- and interobserver reliability for GeoGebra, Lewinnek and Woo-Morrey methods were 0.848 - 0.756, 0.843 - 0.801, and 0.965 - 0.958, respectively, for the control DMC group. Lewinnek and Woo-Morrey methods differed by -2.3° and + 5.1° from GeoGebra, respectively (p < 0.001).

CONCLUSIONS

RA measurements are more consistent, repeatable and accurate with a titanium DMC than standard DMC, due to the minor radiopacity of the former cup which enable RA measurements on AP radiographs. Conversely, RA measurements of conventional DMC are more consistent but less accurate if performed on cross-table lateral radiographs by Woo-Morrey method than AP radiographs.

Lewinnek zone not "the be-all and end-all" functional planning for acetabular component positioning in total hip arthroplasty

BACKGROUND

Proper positioning of a total hip arthroplasty (THA) plays a crucial role in the success and long-term survivorship of the implant. Cup positioning within the Lewinnek Safe Zone (LSZ) does not, however, avoid implant dislocation. Thus, the concept of a functional cup position has been introduced. The purpose of this study was to assess the discrepancy between LSZ and the acetabular cup position suggested by the patient's specific functional planning. The hypothesis was that a mismatch does exist.

METHODS

One hundred consecutive patients with primary hip osteoarthritis undergoing primary THA with a personalized functional preoperative planning and patient-specific cup implantation system were enrolled. Anatomical and spino-pelvic functional parameters were recorded and, for each patient, a "safe cup orientation" was suggested. The suggested functional safe zone was compared to the LSZ.

RESULTS

The mean suggested inclination was 39° ± 3° (range 32°-45°). The mean suggested anteversion was 21° ± 3° (range 12°-28°). The patient's functional acetabular inclination (AI) corresponded to the LSZ in one of the 100 patients, whereas the acetabular anteversion (AV) was outside the LSZ in 8 of the 100 patients. The mean pelvic tilt while standing and sitting were 0.5° ± 7° (range 21°-45°) and -6° ± 16.7° (range -63°-33°), respectively. The mean pelvic incidence was 52° ± 9.7° (range 33°-83°).

CONCLUSION

When a functional patient's specific preoperative planning is performed, the LZS does not correspond to the patient's functional safe zone in about 8% of patients. The concept of a universal safe zone should be revisited, and a functional personalized safe zone may have to be more widely considered.

A novel method of acetabular component anteversion measurement on plain radiographs

BACKGROUND

Acetabular component anteversion (ACA) markedly impacts the outcome of total hip arthroplasty (THA) and thus is routinely measured on radiographs postoperatively. However, clinical ACA measurement methods are either too complicated or subjective due to three drawbacks: complex calculations, measurement of obscured points, and complex geometric drawings. This study aimed to develop a precise and convenient novel method of measuring ACA on routine radiographs without the three drawbacks and to verify its accuracy and reliability by comparing it against existing methods.

METHODS

A novel geometric principle to measure ACA was developed. Accordingly, a protractor was designed to measure radiographic anteversion (RA) on anteroposterior (AP) hip radiographs. Three researchers measured RA twice, using the protractor, McLaren's, and Pradhan's method on 26 computer-simulated radiographs with pre-set RAs and 20 actual radiographs. Accuracy was assessed by errors on simulated radiographs, and reliability was assessed by results of measurements on simulated and actual radiographs.

RESULTS

The absolute error of the novel method (1.01° ± 1.06°) was lower than McLaren's method (1.34° ± 1.16°) (p < 0.05) and not significantly different from Pradhan's method (1.10° ± 1.02°) (p = 0.392). The protractor's intra-rater and inter-rater reliability were good-to-excellent or excellent and higher or equivalent to the two other methods.

CONCLUSIONS

The novel method avoids the three major drawbacks of conventional methods. Its accuracy is significantly higher than McLaren's method and comparable to Pradhan's. The novel method has higher or non-inferior accuracy and reliability than McLaren's and Pradhan's methods.

Return to surfing following hip arthroplasty

BACKGROUND

To date, no previous studies have explored return to surfing after hip arthroplasty. The objective of this study is to analyse return to a risky activity following hip arthroplasty.

METHODS

A retrospective chart review was conducted on all primary total hip arthroplasties (THA) and hip resurfacing arthroplasties (HRA) performed by the senior author from 2014 to 2021. Patients identified as surfers were contacted to complete a survey including surfing history and patient-reported outcomes.

RESULTS

83 hips in 67 patients were contacted. There were 66 THAs and 17 HRAs. 81 hips were performed through a posterior approach and 2 through an anterior approach. At an average of 67 months, there were no dislocations and no patients reported hip pain while surfing. Time to resume surfing was a median of 16 (range 8-144) weeks. Among 13 patients who did not return to surfing, 8 cited new lifestyle restrictions, 4 attributed it to other arthritic joints, and only 1 patient attributed their limitation to the replaced hip. This group had taken significantly more time off from surfing prior to surgery.

CONCLUSIONS

Return to surfing following THA and HRA is common and safe in our study population with no complications and specifically no dislocations. Patients with other sites of arthritis and patients who have more extensive time away from surfing prior to surgery are less likely to return to sport. While surfing is clearly not without risk, patients can generally expect a high rate of successful return to surfing after hip arthroplasty.

Assessing the Reliability of Postoperative Cross-Table Radiographs Compared to CT Scans for Measuring Acetabular Anteversion Angle Following Total Hip Arthroplasty

AIM

This study aimed to evaluate acetabular anteversion following total hip arthroplasty (THA) using cross-table lateral radiographs and CT scans and to determine the reliability of cross-table lateral radiographs compared to computed tomography (CT) scans for measuring acetabular anteversion.

MATERIALS AND METHODS

We conducted a cross-sectional study of patients undergoing THA at Justice K.S. Hegde Charitable Hospital, Deralakatte, Mangalore, from January 2020 to June 2021. Radiographs are typically taken in both anteroposterior (AP) and lateral views after THA. However, for this study, a cross-table lateral view was used instead of the usual lateral radiograph to measure the angle of anteversion. The anteversion was calculated using the method described by Woo and Morrey. Additionally, CT scans were performed on all patients as part of the study protocol. The anteversion measured in these scans was compared to that in the cross-table radiographs to assess the latter's reliability for routine use. The risk of radiation exposure from CT scans was minimized by adhering to the ALARA (As Low as Reasonably Achievable) principle, with only axial sections of the acetabular cup being scanned.

RESULTS

 The results show that the radiographic acetabular anteversion and CT scan measurements have a mean difference of 0.3036. There is a positive correlation between these measurements. The p-value is not statistically significant (p=0.698). Therefore, the measurements are correlated with each other with a linear relationship (r=0.919). For anteversion measurements using the X-ray method, the mean was 27.16 degrees with a standard deviation of ±9.49. The median was 27.26 degrees, ranging from 10.27 to 42.58 degrees. In comparison, the CT method yielded a mean anteversion of 27.40 degrees with a standard deviation of ±8.50 degrees. The median was 27.64 degrees, ranging from 12.35 to 43.11 degrees.

CONCLUSION

Cross-table lateral radiographs are a reliable and comparable method to CT scans for measuring acetabular anteversion following total hip arthroplasty.

How Relevant Is the Parallax Effect on Low Centered Pelvic Radiographs in Total Hip Arthroplasty

The correct cup position in total hip arthroplasty (THA) is usually assessed on anteroposterior low centered pelvic radiographs, harboring the risk of misinterpretation due to projection of a three-dimensional geometry on a two-dimensional plane. In the current study, we evaluate the effect of this parallax effect on the cup inclination and anteversion in THA. In the course of a prospective clinical trial, 116 standardized low centered pelvic radiographs, as routinely obtained after THA, were evaluated regarding the impact of central beam deviation on the cup inclination and anteversion angles. Measurements of the horizontal and vertical beam offset with two different methods of parallax correction were compared with each other. Furthermore, the effect of parallax correction on the accuracy ofmeasuring the cup position was investigated. The mean difference between the two parallax correction methods was 0.2° ± 0.1° (from 0° to 0.4°) for the cup inclination and 0.1° ± 0.1° (from -0.1° to 0.2°) for the anteversion. For a typically intended cup position of a 45° inclination and 15° anteversion, the parallax effect led to a mean error of -1.5° ± 0.3° for the inclination and 0.6° ± 1.0° for the anteversion. Central beam deviation resulted in a projected higher cup inclination up to 3.7°, and this effect was more prominent in cups with higher anteversion. In contrast, the projected inclination decreased due to the parallax effect up to 3.2°, especially in cups with high inclination. The parallax effect on routinely obtained low centered pelvic radiographs is low and not clinically relevant due to the compensating effect of simultaneous medial and caudal central beam deviation.

Preoperative radiographs to predict component malposition in direct anterior approach total hip arthroplasty

INTRODUCTION

There is conflicting evidence as to whether or not patients undergoing total hip arthroplasty (THA) via the direct anterior approach (DAA) have increased risk of component malposition. The aim of this study was to investigate whether specific preoperative radiographic features were predictive of postoperative component malposition in DAA THA.

PATIENTS AND METHODS

We examined 204 THA operations performed for osteoarthritis via the DAA at a single institution. Preoperative radiographs were analysed with numerous pre-specified measurements and classifications being recorded. Postoperative radiographs were analysed to determine if any of these preoperative radiographic factors correlated with component malposition in regard to cup inclination, cup version, femoral stem coronal alignment, leg-length discrepancy (LLD) and femoral offset discrepancy.

RESULTS

Numerous preoperative factors were associated with component malposition. Coxa profunda was found to be a significant predictor of cup anteversion being outside of the target range (p = 0.0089) and an increased centre-edge angle was a significant predictor for a postoperative LLD (p = 0.0134). A decreased neck-shaft angle (p = 0.0007) and a lower preoperative LLD (p = 0.0019) were both predictive of femoral stem coronal malalignment.

CONCLUSIONS

Preoperative radiographs can be a valuable tool for surgeons in predicting patients at risk of component malposition in DAA THA.

Correlation of Acetabular Anteversion and Thoracic Kyphosis Postoperatively with Proximal Junctional Failure in Adult Spinal Deformity Fused to Pelvis

Objectives

To investigate whether the immediate thoracic kyphosis (TK) and acetabular anteversion (AA) postoperatively are correlated with proximal junctional failure (PJF) in adult spinal deformity (ASD) patients underwent surgical treatment.

Methods

This is a retrospective study. Following institutional ethics approval, a total of 57 patients (49 Female, eight Male) with ASD underwent surgery fused to sacroiliac bone (S1, S2, or ilium) from March 2014 to January 2019 were included. All of those patients were followed up for at least 2 years. Demographic, radiographic and surgical data were recorded. The maximum range of flexion motion (F‐ROM) and extension motion (E‐ROM) actively of hip joints was measured and recorded at pre‐ and postoperation. The sum of F‐ROM and E‐ROM was defined as the range of hip motion (H‐ROM). Receiver operating characteristic (ROC) curve analysis was used to obtain the cut off value of parameters for PJF. A Kaplan–Meier curve and log‐rank test were used to analyze the differences in PJF‐free survival.

Results

In all, 14 patients developed PJF during follow‐up. Comparisons between patients with and without PJF showed significant differences in immediate TK (P < 0.001) and AA (P = 0.027) postoperatively. ROC curve analysis determined an optimal threshold of 13° for immediate AA postoperatively (sensitivity = 74.3%, specificity = 85.7%, area under the ROC curve [AUC] = 0.806, 95% CI [0.686–0.926]). Nineteen patients with post‐AA ≤13° were assigned into the observational group, and 38 patients with post‐AA >13° were being as the control group. Patients in the observational group had smaller H‐ROM (P = 0.016) and F‐ROM (P < 0.001), but much larger E‐ROM (P < 0.001). There were 10 patients showing PJF in the observational group and four in the control group (10/9 vs 4/34, P < 0.001). PJF‐free survival time significantly decreased in the observational group (P = 0.001, log‐rank test). Furthermore, patients in the observational group had much larger TK (post‐TK, P = 0.015). The optimal threshold for post‐TK (sensitivity = 85.7%, specificity = 76.7%; AUC = 0.823, 95% CI [0.672–0.974]) was 28.1° after the ROC curve was analyzed. In the observational group, those patients with post‐TK ≥28.1° had significantly higher incidence of PJF (9/2 vs 1/7, P < 0.001) than those with post‐TK < 28.1°. Moreover, PJF‐free survival time in those patients significantly decreased (P = 0.001, log‐rank test).

Conclusions

ASD patients with acetabular anteversion of ≤13° at early postoperation may suffer significantly restricted hip motion and much higher incidence of PJF during follow‐up, moreover, in those patients, postoperative TK ≥28.1° would be a significant risk factor for PJF developing.

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.

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.

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.

Validation of a Novel Software Measurement Tool for Total Hip Arthroplasty

Background

Preoperative planning and postoperative evaluation of component position in total hip arthroplasty (THA) utilize specialized software that must be able to provide measurements that are both accurate and precise. A new software program for use in THA has recently been developed. We sought to evaluate the accuracy of this new software in comparison with two current, widely used software programs.

Methodology

Postoperative anteroposterior (AP) pelvic radiographs from 135 THA patients were retrospectively reviewed. Reference values for acetabular anteversion, inclination, and leg length were established using validated software programs (TraumaCad^® as the primary reference value [PRV] and OsiriX Lite^TM as the secondary reference value [SRV]). Measurements from the new software program (Intellijoint VIEW^TM) were compared with reference values using Student’s t-test and chi-square test.

Results

For anteversion, mean values for the PRV (27.34° ± 7.27°) and the new software (27.29° ± 7.21°) were not significantly different (p = 0.49). The new software differed from the PRV by a mean of 0.05° ± 0.93°. Similar results were noted for inclination, where the new software differed from the PRV and SRV by -0.13° ± 0.65° and 0.25° ± 1.26°, respectively (mean values: PRV: 43.62° ± 6.02°; SRV: 43.99° ± 6.27°; new software: 43.74° ± 6.17°; p = 0.87), and for leg length, where the new software differed from the PRV and SRV by 0.05 mm ± 0.46 mm and 0.22 mm ± 0.52 mm, respectively (mean values: PRV: 10.61 mm ± 11.60 mm; SRV: 10.77 mm ± 11.70 mm; new software: 10.56 mm ­ ± 11.61 mm; p = 0.98). Measurements were highly correlated across multiple reviewers (intraclass correlation coefficient ≥0.987).

Conclusions

The new software measurement tool is accurate and precise for assessing the acetabular component position and leg length measurements following THA in AP pelvic radiographs compared to currently used image measurement software.

Smartphone-assisted technique in total hip arthroplasty can improve the precision of acetabular cup placement: a randomised controlled trial

BACKGROUND

Malposition of the acetabular component mainly results from intraoperative pelvic motion and manual errors during cup placement. We investigated the outcomes of a device that uses a level indicator application of a smartphone to function as a pelvic tilt goniometer to assess intraoperative motion. The cup positions outside Lewinnek's safe zone were compared between the smartphone-assisted technique and the conventional method that uses a mechanical alignment guide.

METHODS

A randomised controlled trial was conducted among 64 patients receiving primary cementless total hip arthroplasties (THAs) via a posterolateral approach from June 2015 to February 2017. Acetabular components were implanted either by conventional technique (n = 32) or using smartphone technique (n = 32). Inclination and anteversion angles were measured in supine pelvic radiographs.

RESULTS

The inclination angle in the smartphone group was not significantly different from the conventional group (41.2° ± 3.9° vs. 40.3° ± 7.9°, p = 0.567). The anteversion angle was also similar (19.3 ± 3.8° vs 19.1° ± 5.9°, p = 0.856). However, the standard deviation of the angle in the smartphone group was significantly lower for inclination (p < 0.001) and anteversion (p = 0.016). There were 3 outliers (9.4%) in the smartphone group, but 13 (40.6%) in the conventional group (p = 0.008). The risk ratio was 0.23 (95% CI, 0.07-0.73). The risk difference was -0.31 (95% CI, -0.51- -0.11).

CONCLUSION

The smartphone-assisted technique in THA improves the precision of cup placement and decreases the percentage of safe zone outliers.Thai Clinical Trials Registry (ID: TCTR20151123002).

3D simulation of radiographic projections to test and reduce the effect of pelvic tilt on the accuracy of cross-table lateral radiography

Background

Cross-table lateral (CL) radiography is a convenient and feasible method to assess cup version angle (VA) after total hip arthroplasty; However, pelvic tilt (PT) may contribute to its measurement inaccuracy. How PT affects CL radiographic measurements have not been well studied. We sought (1) to determine the effect of the PT on cup version measurement on CL radiography and (2) to develop a method for reducing measurement errors caused by the PT.

Methods

We used 3D technique to construct standard model and capture CL radiography simulation. A linear regression model was created to analyze the relationship between PT and VA. CL radiography and computed tomography (CT) were performed for the enrolled patients after surgery. The consistency between CL and CT measurements were verified by intra-class correlation coefficient (ICC).

Results

There was a high correlation between the VA and PT. For each 1-degree increased in the PT, the VA decreased by 0.76° (R² = 0.995, p < 0.001). Based on the data, we created a corrective formula to convert the radiographic measurements into values approximating the actual VA under a natural pelvic position. The VA measurements corrected by our equation was in high agreement with the CT-measured values with reference to the corresponding PT (ICC = 0.988, p < 0.001), which was in sharp contrast to that without PT control (ICC = 0.454, p = 0.203).

Conclusions

The PT may contribute to cup version measurement inaccuracies on CL radiography. Our mathematical algorithm can serve as a reliable method to improve the accuracy of CL radiography.

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.

Outcomes of conversion THA after failed porous tantalum implant for osteonecrosis of the femoral head: a comparative matched study

BACKGROUND

As a joint-preserving surgery, porous tantalum implantation (PTI) provides an additional treatment option for osteonecrosis of the femoral head (ONFH). However, conversion to a total hip arthroplasty (THA) after failed PTI is considered a challenging procedure. The purpose of this study was to compare the clinical and radiologic outcomes and complications of THA after failed PTI with those of primary THA without any previous surgery for ONFH.

METHODS

This retrospective study included 32 patients undergoing THA after failed PTI and 25 age, sex, and body mass index matched patients who underwent primary THA without any previous surgery for ONFH between December 2009 and March 2014. All patients were followed for at least 36 months. The postoperative clinical and radiological evaluations were based on Harris Hip Score (HHS) and plain radiographs. The independent sample test and the chi-square test were used for the statistical analysis.

RESULTS

The HHS in the PTI group was similar to that in the primary group at the latest follow-up (p = 0.274), but longer operation time and greater intraoperative blood loss were observed in the PTI group (p < 0.001, respectively). No significant differences in radiological parameters and postoperative complications were found between the 2 groups (p > 0.05).

CONCLUSIONS

THA after PTI showed similar clinical and radiological outcomes to primary THA except for longer operation time and greater intraoperative blood loss.

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.

Validity of intraoperative imageless navigation (Naviswiss) for component positioning accuracy in primary total hip arthroplasty: protocol for a prospective observational cohort study in a single-surgeon practice

INTRODUCTION

Optimal outcomes in total hip arthroplasty (THA) are dependent on appropriate placement of femoral and acetabular components, with technological advances providing a platform for guiding component placement to reduce the risk of malpositioned components during surgery. This study will validate the intraoperative data captured using a handheld imageless THA navigation system against postoperative measurements of acetabular inclination, acetabular version, leg length and femoral offset on CT radiographs.

METHODS AND ANALYSIS

This is a prospective observational cohort study conducted within a single-centre, single-surgeon private practice. Data will be collected for 35 consecutive patients (>18 years) undergoing elective THA surgery, from the research registry established at the surgeon's practice. The primary outcome is the agreement between intraoperative component positioning data captured by the navigation system compared with postoperative measurements using CT. A total of ten CT scans will be reassessed for interobserver and intraobserver reliability. The influence of patient and surgical factors on the accuracy of component position will also be examined with multivariable linear regression.

ETHICS AND DISSEMINATION

Ethics approval for this study was provided through a certified ethics committee (Bellberry HREC approval number 2017-07-499). The results of this study will be disseminated through peer-reviewed journals and conference presentations.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry (ANZCTR) Trial ID: ACTRN12620000089932.

Use of smartphone to improve acetabular component positioning in total hip athroplasty: A comparative clinical study

BACKGROUND

The position of the acetabular cup is important to the outcome of total hip athroplasty (THA). We devised an instrument that uses the level indicator application of smartphone together with a mechanical alignment guide to improve the precision of cup placement. This study aims to determine the percentage of acetabular cups positioned in the Lewinnek safe zone comparing between the conventional technique (using a mechanical alignment guide alone) and the smartphone technique (using a mechanical alignment guide combined with the devised instrument and smartphone).

METHODS

A historical controlled trial was conducted among 82 patients who underwent primary THAs through a posterolateral approach. In the conventional group, 41 cups were placed during January 2013 and December 2014, whereas 41 cups in the smartphone group were placed during January 2015 and March 2016. Inclination and anteversion angles were measured in standardized pelvic radiographs. The cup orientation was compared between groups.

RESULTS

The inclination angle in the smartphone group was significantly lower than in the conventional group (40.9° (SD 3.8) vs. 46.3° (SD 6.7), p < 0.001), but the anteversion angle was higher (19.6° (SD 4.4) vs. 16.5° (SD 6.1), p = 0.010). The smartphone group had more cups positioned in the Lewinnek safe zone (90.2% vs. 56.1%, p = 0.001) and longer operative times (136 (SD 27) vs. 119 (SD 23) min, p = 0.011). No significant difference was found for blood loss ( p== 0.384) or dislocation rate ( p = 0.494).

CONCLUSION

Using the computerized function of smartphone could improve the precision of cup positioning. Most cups were placed within a narrow margin inside the Lewinnek safe zone.

Mid-Term Survivorship of a Novel Constrained Acetabular Device

BACKGROUND

Recurrent instability after total hip arthroplasty is a difficult complication. In certain cases, a constrained acetabular device is needed to address these issues. The purpose of this study is to report the midterm outcomes and survivorship of a single novel constrained liner device.

METHODS

A retrospective review as performed on all procedures (except first stage exchange for infection) in which a Freedom Constrained (Zimmer Biomet, Warsaw, IN) liner was used between December 2003 and November 2016. Patients with 2-year minimum follow-up or failure were included, yielding a cohort of 177 patients. Procedures were 130 aseptic revisions, 40 reimplantations following infection eradication, and 7 complex primaries. The constrained mechanism was implanted in 46 hips (26%) to treat active instability and 131 hips (74%) for increased risk of instability and intraoperative instability. Patients had on average 3.4 previous surgeries.

RESULTS

With an average 7.1-year follow-up, 11 hips dislocated (6.2%), and 13 hips (7.3%) were revised for acetabular aseptic loosening, resulting in an overall constrained aseptic or mechanical failure rate of 13.6%. Nineteen hips (10.7%) failed from infection with 58% of these having had a previous infection. Patients with active instability had significantly higher failure for dislocation than patients who were at risk (15.2% vs 3%, P = .01). All-cause survival rate at 7 years was 74.8%, aseptic survival was 83.6%, and survival for instability was 91.8%.

CONCLUSION

Revision for instability remains challenging as many patients have had numerous previous surgeries and at-risk anatomy. Constrained inserts are one option to manage instability, but a high rate of recurrence can still occur.

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.

Comparison of Total Hip Arthroplasty after Two Types of Failed Hip Preserving Procedures with Primary Total Hip Arthroplasty

Objective

Porous tantalum implantation (PTI) and bone impaction grafting (BIG) through a window at the femoral head neck junction are known as two types of joint‐preserving procedures. They provide an alternative option in the treatment of osteonecrosis of the femoral head by providing strong structural support to the subchondral plate. However, when earlier joint‐preserving treatments fail, conversion to a total hip arthroplasty seems to be the final treatment of choice. This emphasizes the importance of joint‐preserving procedures that do not hinder the clinical results of a subsequent total hip arthroplasty. The results of conversion total hip arthroplasty after failed PTI and BIG are still controversial. The purpose of this study was to compare the clinical and radiological outcomes of total hip arthroplasty after failed PTI or BIG surgery with primary total hip arthroplasty.

Methods

Patients at our institution between 2010 and 2014 who underwent total hip arthroplasty after failed PTI or BIG surgery compared to primary total hip arthroplasty were retrospectively reviewed. A total of 27 patients (30 hips) who underwent total hip arthroplasty after failed PTI surgery (group I) were matched according to age, gender and BMI index with 28 patients (30 hips) who underwent total hip arthroplasty after failed BIG surgery (group II) and 30 patients (30 hips) who underwent primary total hip arthroplasty (group III). The clinical results included preoperative and postoperative Harris Hip score, surgery duration, blood loss volume and clinical complications. Radiological follow‐up results included abduction angle and anteversion angle of the acetabular cup, periprosthetic osteolysis, and prosthesis subsidence.

Results

There was no significant difference in the preoperative and postoperative Harris Hip score among the three groups at the latest follow‐up (P = 0.247). The surgery duration was longer and intra‐operative blood loss volume was higher in group I than in group II and group III (P < 0.05, respectively). There was no difference in surgery duration and blood loss volume between group II and group III (P > 0.05). There was no significant difference in radiological follow‐up results among the three groups (P > 0.05). Varying degrees of residual tantalum debris were seen on postoperative radiographs of all group I patients. There was no difference in the incidence of complications among the three groups (P > 0.05).

Conclusions

PTI group had higher blood loss volume and surgery duration than BIG group and primary total hip arthroplasty group. BIG group had no significant differences with primary total hip arthroplasty group in clinical and radiological follow‐up results. There were no significant differences between the three groups in the Harris Hip score and radiological follow‐up results.

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.

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.

Determination of humeral inclination in stemless shoulder arthroplasty using plain radiographs

Plain radiographs of the shoulder are routinely used to assess implant orientation after shoulder arthroplasty. Recently, humeral inclination has come into focus especially in reverse stemless shoulder arthroplasty. But, in X-ray projections not exactly parallel to the base of the humeral component, the humeral inclination angle cannot be determined precisely. Therefore, we established a mathematical algorithm to calculate the humeral neck shaft angle and counterchecked the formula using plain radiographs of a sawbone model containing a humeral head prosthesis. With increasing angles of retroversion, the base of the humeral component forms an ellipse in plain radiographs. Knowing the width and length of the ellipse as well as the inclination angle in a plain radiograph, the exact inclination angle can be determined using the equation reported below. Thus, independent from the viewing angle or angle of retroversion, the inclination angle of a stemless humeral head implant can be estimated with an accuracy of ±1.5-degree deviation. The algorithm proposed may be the basis for further research on the impact of humeral inclination in stemless shoulder arthroplasty.

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.

Advantages of an Anterior-Based Muscle-Sparing Approach in Transitioning From a Posterior Approach for Total Hip Arthroplasty: Minimizing the Learning Curve

BACKGROUND

Enthusiasm for anterior-based approaches for total hip arthroplasty (THA) continues to increase but there is concern for increased complications during the learning curve period associated. This study aimed to investigate if there was a difference in perioperative variables, intraoperative and immediate postoperative complications, or patient-reported outcomes when transitioning from a mini-posterior approach (mPA) to an anterior-based muscle-sparing (ABMS) approach for THA.

METHODS

Retrospective cohort study on the first 100 primary THA cases (n = 96 patients) of the senior author (August 2016 to August 2017) using the ABMS approach. These cases were compared to primary THA cases done the year prior (July 2015 to July 2016, n = 91 cases in 89 patients) using an mPA. Data were extracted and analyzed via gamma regression with robust standard errors and using generalized estimating equation regression.

RESULTS

We found no difference in the estimated blood loss (P = .452) and surgical time (P = .564) between the cohorts. The ABMS cases had a slightly shorter length of stay (P = .001) with an adjusted mean length of stay of 1.53 days (95% confidence interval 1.4-1.6) compared to 1.85 days (95% confidence interval 1.8-1.9) in the mPA cases. There was no difference in the frequency of immediate postoperative complications (all, P > .05). There was no difference in the adjusted mean change in patient-reported outcomes (all P > .05). In the ABMS group, there was no difference in surgical time or physical function computerized adaptive test between the first 20 cases (reference) and each subsequent group of 20 cases (all P > .05).

CONCLUSION

This study demonstrates no associated learning curve for an experienced senior surgeon when switching routine THA approach from mPA to ABMS. We advise careful interpretation of our results, as they may not apply to all surgeons and practices.

LEVEL OF EVIDENCE

Level III Therapeutic Study: retrospective comparative study.

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.

Assessment of acetabular version in total hip arthroplasty: an application of Widmer's technique in a regional setting

BACKGROUND

Acetabular prosthesis positioning in total hip arthroplasty is important in reducing the risk of dislocation. Assessment of version by computed tomography scan is expensive and involves a large radiation dose. We wished to assess the value of Widmer's technique, utilizing readily available radiographs, to determine cup anteversion.

METHODS

Patients who underwent primary total hip arthroplasty by the senior author (AGS) at a single regional hospital over a 5-year period were eligible for inclusion. Measurements were performed using the technique described by Widmer, utilizing standard post-operative radiographs. Statistical analysis was undertaken in SPSS v22. Significance was accepted at P < 0.05.

RESULTS

Assessment included 109 hips in 99 patients; 63 hips with cemented cups and 46 hips with uncemented cups. Mean acetabular anteversion in the cemented group was 11.9° (0-27.7, SD: 7) and in the uncemented group was 14.1° (10.3-32.7, SD: 7.1); this difference trended towards statistical significance (P = 0.09). Test-retest measurements showed high degree of correlation (Pearson test: 0.927, P < 0.001). There were 96 of 109 hips positioned in the Lewinnek safe zone of 5-25° anteversion. The crude dislocation rate in our cohort was 6.4% (7 of 109 hips) with all dislocations occurring in hips placed in the safe zone.

CONCLUSION

Widmer's technique is a reliable method for calculating acetabular version in a regional hospital setting and offers the individual surgeon a ready technique of personal quality control. Cup version was not a significant factor contributing to dislocation rates in our series.

The mean ten-year results of metal-on-metal hybrid hip resurfacing arthroplasty

Aims

This study presents the long-term survivorship, risk factors for prosthesis survival, and an assessment of the long-term effects of changes in surgical technique in a large series of patients treated by metal-on-metal (MoM) hip resurfacing arthroplasty (HRA).

Patients and Methods

Between November 1996 and January 2012, 1074 patients (1321 hips) underwent HRA using the Conserve Plus Hip Resurfacing System. There were 787 men (73%) and 287 women (27%) with a mean age of 51 years (14 to 83). The underlying pathology was osteoarthritis (OA) in 1003 (75.9%), developmental dysplasia of the hip (DDH) in 136 (10.3%), avascular necrosis in 98 (7.4%), and other conditions, including inflammatory arthritis, in 84 (6.4%).

Results

The mean follow-up time was 10.5 years (1 to 20). Using revision for any reason as the endpoint, the overall survivorship at 15 years was 89.4% (95% confidence interval (CI) 86.8 to 91.4). There was a substantial increase between the first and second generation of surgical technique (86.6% vs 90.1%; p = 0.05). Men with idiopathic OA had a 15-year survivorship of 94.5% and women, 82.2% (p = 0.001); gender was not a risk factor after stratification by component size and aetiology. Using revision for excessive wear (ion levels > 7 µg/l associated with symptoms or adverse local tissue reactions) as the endpoint, the 15-year survivorship was 98.5%. Risk factors for revision for all modes of failure were an underlying pathology of hip dysplasia, a contact patch to rim (CPR) distance of 7 mm or less, an age at surgery of 55 years or less, and a femoral component size of 46 mm or less. Specific risk factors for aseptic failure of the femoral component were early surgical technique, a cementless metaphyseal stem, and a body mass index of 24 kg/m2 or less.

Conclusion

HRA is a viable concept; metal-on-metal bearings are well suited for this procedure when a well-designed device is properly implanted. The best results were obtained in men with OA, but survivorship was better for other underlying pathologies and for women after changes were made to the technique of implantation. Lifetime durability is a possible outcome for many patients despite a high level of activity. Cite this article: Bone Joint J 2018;100-B:1424–33.

Correct Assessment of Acetabular Component Orientation in Total Hip Arthroplasty From Plane Radiographs

BACKGROUND

Correct positioning of the cup is an important factor in total hip arthroplasty. Assessing its position from a plain anteroposterior pelvic radiograph is known to be hampered by systemic errors. This study focuses on developing a correction method to adjust for these potential sources of error and to eliminate them based on a 3D geometric analysis.

METHODS

Computed tomography scans of 113 (66 male, 47 female) pelvices were reconstructed and virtually projected onto a plain radiograph with varying rotational and translational positions. Thus cup inclination and anteversion as measured on a 2D-radiograph and in the 3D environment were correlated. Projected offset of the symphysis from the mid-sacrum served as a mean to measure pelvic right/left-rotation. Pelvic tilt was determined from the projected height of the contour of the small pelvis. Correction formulas were verified by projecting a gimbal-mounted artificial pelvis with a cup implanted in a known position.

RESULTS

We found gender-specific formulas that correct for malrotated and off-centered radiographs. Applying these formulas cup inclination was assessed as close as 1.3° (±1.90°) to the true 3D value and cup anteversion as close as 1° (±1.91°) although deviations between directly measured plain values and corrected values rose up to 18°.

CONCLUSION

Inherent effects of central projection and malrotations due to pelvic tilt, pelvic rotation, and noncentered radiographs are corrected. Evaluation of radiographic inclination and anteversion of acetabular cups from plain 2D-radiographs show improved precision. Real values are approached better than 1.3° when applying our correction formulas.

Effect of Pelvic Tilt and Rotation on Cup Orientation in Both Supine and Standing Positions

BACKGROUND

The purpose of this study is to analyze the effect of pelvic tilt and rotation on radiographic measurement of cup orientation.

METHODS

A total of 68 patients (79 hips) were included in this study. The patients had a computed tomography study and approximately 3 months of postoperative standing anteroposterior pelvic radiographs in both supine and standing positions. We used 2-dimensional (2D)/3-dimensional (3D) matching to measure pelvic tilt and rotation, and cup orientation.

RESULTS

There was a wide range of pelvic tilt between individuals in both supine and standing positions. Supine pelvic tilt was different from standing pelvic tilt (P < .05). There were differences in cup anteversion before and after 2D/3D matching in both supine and standing positions (P < .05). Supine and standing pelvic tilt correlated with differences in cup anteversion before and after 2D/3D matching. When all 79 hips were separated into right and left side, pelvic rotation inversely correlated with the pelvic tilt-adjusted difference in anteversion before and after 2D/3D matching of the right side but directly correlated with that of the left side in both supine and standing positions.

CONCLUSION

This study demonstrated that the measurement of cup anteversion on anteroposterior radiographs is significantly affected by both pelvic tilt and pelvic rotation (depending on the side). Improved understanding of pelvic orientation and improved ability to measure pelvic orientation may eventually allow for desired cup positioning to potentially protect against complications associated with malposition of the cup.

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.

The Safe Zone Range for Cup Anteversion Is Narrower Than for Inclination in THA

BACKGROUND

Cup malposition is a common cause of impingement, limitation of ROM, acceleration of bearing wear, liner fracture, and instability in THA. Previous studies of the safe zone based on plain radiographs have limitations inherent to measuring angles from two-dimensional projections. The current study uses CT to measure component position in stable and unstable hips to assess the presence of a safe zone for cup position in THA.

QUESTIONS/PURPOSES

(1) Does acetabular component orientation, when measured on CT, differ in stable components and those revised for recurrent instability? (2) Do CT data support historic safe zone definitions for component orientation in THA?

METHODS

We identified 34 hips that had undergone revision of the acetabulum for recurrent instability that also had a CT scan of the pelvis between August 2003 and February 2017. We also identified 175 patients with stable hip replacements who also had a CT study for preoperative planning and intraoperative navigation of the contralateral side. For each CT study, one observer analyzed major factors including acetabular orientation, femoral anteversion, combined anteversion (the sum of femoral and anatomic anteversion), pelvic tilt, total offset difference, head diameter, age, sex, and body mass index. These measures were then compared among stable hips, hips with cup revision for anterior instability, and hips with cup revision for posterior instability. We used a clinically relevant measurement of operative anteversion and inclination as opposed to the historic use of radiographic anteversion and inclination. The percentage of unstable hips in the historic Lewinnek safe zone was calculated, and a new safe zone was proposed based on an area with no unstable hips.

RESULTS

Anteriorly unstable hips compared with stable hips had higher operative anteversion of the cup (44° ± 12° versus 31° ± 11°, respectively; mean difference, 13°; 95% confidence interval [CI], 5°-21°; p = 0.003), tilt-adjusted operative anteversion of the cup (40° ± 6° versus 26° ± 10°, respectively; mean difference, 14°; 95% CI, 10°-18°; p < 0.001), and combined tilt-adjusted anteversion of the cup (64° ± 10° versus 54° ± 19°, respectively; mean difference, 10°; 95% CI, 1°-19°; p = 0.028). Posteriorly unstable hips compared with stable hips had lower operative anteversion of the cup (19° ± 15° versus 31° ± 11°, respectively; mean difference, -12°; 95% CI, -5° to -18°; p = 0.001), tilt-adjusted operative anteversion of the cup (19° ± 13° versus 26° ± 10°, respectively; mean difference, -8°; 95% CI, -14° to -2°; p = 0.014), pelvic tilt (0° ± 6° versus 4° ± 6°, respectively; mean difference, -4°; 95% CI, -7° to -1°; p = 0.007), and anatomic cup anteversion (25° ± 18° versus 34° ± 12°, respectively; mean difference, -9°; 95% CI, -1° to -17°; p = 0.033). Thirty-two percent of the unstable hips were located in the Lewinnek safe zone (11 of 34; 10 posterior dislocations, one anterior dislocation). In addition, a safe zone with no unstable hips was identified within 43° ± 12° of operative inclination and 31° ± 8° of tilt-adjusted operative anteversion.

CONCLUSIONS

The current study supports the notion of a safe zone for acetabular component orientation based on CT. However, the results demonstrate that the historic Lewinnek safe zone is not a reliable predictor of future stability. Analysis of tilt-adjusted operative anteversion and operative inclination demonstrates a new safe zone where no hips were revised for recurrent instability that is narrower for tilt-adjusted operative anteversion than for operative inclination. Tilt-adjusted operative anteversion is significantly different between stable and unstable hips, and surgeons should therefore prioritize assessment of preoperative pelvic tilt and accurate placement in operative anteversion. With improvements in patient-specific cup orientation goals and acetabular component placement, further refinement of a safe zone with CT data may reduce the incidence of cup malposition and its associated complications.

LEVEL OF EVIDENCE

Level III, diagnostic study.

The Results of Total Hip Arthroplasty After Sugioka Transtrochanteric Anterior Rotational Osteotomy for Osteonecrosis

BACKGROUND

Since Sugioka transtrochanteric anterior rotational osteotomy (ARO) for osteonecrosis of the femoral head (ONFH) changes the morphology of the proximal femur, total hip arthroplasty (THA) after previous ARO is considered a technically demanding procedure. The purpose of this study was to compare the clinicoradiologic outcomes of THA after ARO with those of THA without any antecedent surgery for ONFH.

METHODS

Twenty-four hips in 20 patients who underwent cementless THA after ARO (postosteotomy group) were retrospectively reviewed and compared with patients who underwent cementless THA without any antecedent surgery for ONFH during the same period (primary group). In the postosteotomy group, the mean duration from ARO to THA was 19.7 years. All patients were followed for at least 5 years (mean, 8.3 years; follow-up rate, 78.5%). A clinical assessment was performed preoperatively and at the latest follow-up using the Harris Hip Score. A radiographic examination was performed at 3 months after THA and at the latest follow-up.

RESULTS

The Harris Hip Score at the latest follow-up in the postosteotomy group was equivalent to that in the primary group, but longer operation time and greater intraoperative blood loss were observed in the postosteotomy group. There were no significant differences in postoperative complications, including dislocation (2 hips in each group). The leg lengthening in the postosteotomy group tended to be longer. No hips showed implant malpositioning, loosening, or required any revision surgery.

CONCLUSION

The clinicoradiologic outcomes of THA after ARO are considered to be comparable with those of THA without any antecedent surgery for ONFH.

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.

Correlation between serum metal ion levels and adverse local tissue reactions after Conserve® Plus hip resurfacing arthroplasty

BACKGROUND

Adverse local tissue reactions (ALTR) have been associated with the use of metal-on-metal (MoM) bearings and the monitoring of cobalt (Co) and chromium (Cr) ion levels in blood or serum may be the best way to evaluate in vivo the wear of these bearings. However, the relationship between Co and Cr ion concentrations and the formation of ALTR remains unclear.

METHODS

We investigated the relationship between ALTR and serum Co and Cr ion levels and identified the clinical factors influencing the formation of ALTR in patients treated with MoM hip resurfacing arthroplasties. 228 patients with unilateral Conserve® Plus MoM hip resurfacing had serum metal ion studies performed more than 1 year after surgery. Metal artifact reduction sequence magnetic resonance imaging (MARS MRI) was performed on subjects at risk for ALTR as determined by a screening protocol.

RESULTS

12 patients had ALTR. Logistic regression showed a strong association of ALTR with elevated ion levels and with low (<10 mm) contact patch to rim distance.

CONCLUSIONS

MoM bearings require enough functional coverage of the socket by design and then precise implantation to maximise functional coverage of the femoral ball, enhance lubrication, and avoid edge-loading wear.

Risk factors for wear-related failures after hip resurfacing in patients with a low contact patch to rim distance

Aims

A contact patch to rim (CPR) distance of < 10 mm has been associated with edge-loading and excessive wear. However, not all arthroplasties with a low CPR distance show problems with wear. Therefore, CPR distance may not be the only variable affecting the post-operative metal ion concentrations.

Patients and Methods

We used multiple logistic regression to determine what variables differed between the patients who had high and low cobalt (CoS) and chromium (CrS) serum ion concentrations within a cohort of patients with low (< 10 mm) CPR distances. A total of 56 patients treated with unilateral hip resurfacing arthroplasty (HRA) had CoS and CrS ion studies performed more than one year after surgery. The mean age of the patients at the time of surgery was 51.7 years (29 to 70), with 38 women (68%) and 18 men (32%).

Results

It was seen that 47 patients had low ion levels (< 7µg/L) and nine had high ion levels (≥ 7µg/L). We found increased risks of high wear with decreasing CPR distance.

Conclusion

The use of CPR distance measurements to predict hips at risk for elevated wear is needed for all patients with HRA. We recommend that patients with low CPR distances have at least one serum ion study performed while patients with CPR distance > 10 mm do not need routine ion studies. We believe that patients with low CPR distance and low ions do not need repeat ion studies unless the patient becomes symptomatic or has substantial radiographic changes. Cite this article: Bone Joint J 2017;99-B:865–71.

Total Hip Arthroplasty in the Spinal Deformity Population: Does Degree of Sagittal Deformity Affect Rates of Safe Zone Placement, Instability, or Revision?

BACKGROUND

Changes in spinal alignment and pelvic tilt alter acetabular orientation in predictable ways, which may have implications on stability of total hip arthroplasty (THA). Patients with sagittal spinal deformity represent a subset of patients who may be at particularly high risk of THA instability because of postural compensation for abnormal spinal alignment.

METHODS

Using standing stereoradiography, we evaluated the spinopelvic parameters, acetabular cup anteversion, and inclination of 139 THAs in 107 patients with sagittal spinal deformity. Standing images were compared with supine pelvic radiographs to evaluate dynamic changes in acetabular cup position. Dislocation and revision rates were procured through retrospective chart review. The spinal parameters and acetabular cup positions among dislocators were compared with those who did not dislocate.

RESULTS

The rate of THA dislocation in this cohort was 8.0%, with a revision rate of 5.8% for instability. Patients who sustained dislocations had significantly higher spinopelvic tilt, T1-pelvic angle, and mismatch of lumbar lordosis and pelvic incidence. Among all patients, 78% had safe anteversion while supine, which decreased significantly to 58% when standing due to increases in spinopelvic tilt. Among dislocating THA, 80% had safe anteversion, 80% had safe inclination, and 60% had both parameters within the safe zone.

CONCLUSION

In this cohort, patients with THA and concomitant spinal deformity have a particularly high rate of THA instability despite having an acetabular cup position traditionally thought of as within acceptable alignment. This dislocation risk may be driven by the degree of spinal deformity and by spinopelvic compensation. Surgeons should anticipate potential instability after hip arthroplasty and adjust their surgical plan accordingly.

Contact patch to rim distance: the quintessential tool for metal-on-metal bearing in vivo performance analysis - a review

With metal-on-metal (MoM) bearings, fluid film lubrication is disrupted when the contact patch area between the femoral head and the cup is close to the edge of the acetabular component, making the calculation of the contact patch to rim (CPR) distance a key variable in the study of the performance of MoM bearings. A few research centers have used models of varying complexity to calculate the CPR distance and determine its relationship with assessments of component wear. In this review, we aimed to summarise the current knowledge related to the application of CPR distance calculations in the study of in vivo performance of MoM bearings. Our systematic search of the US National Library of Medicine yielded 9 relevant publications in which 3 different models were used for the computation of the CPR distance. The 3 models show different levels of complexity and their use is mainly dependent upon the size of the subject sample and the nature of the data collected as a dependent variable. The studies reviewed consistently showed a strong inverse correlation between CPR distance and wear or metal ion levels suggesting that any study aiming to determine the risk factors for MoM hip devices needs to include an assessment of CPR distance. Cup anteversion can be measured reliably with various tools and should not be an obstacle to the use of this essential variable that is CPR distance.

Screws are not needed when secure interference fit of uncemented acetabular components is adequate: a 5- to 15-year follow-up with clinical and radiological analysis

PURPOSE

Even with good surgical preparation, adequate primary stability of the acetabular component is not always achieved after primary total hip replacement (THR). We hypothesise that adequate bone preparation for appropriate cortical loading would allow us to avoid screw use.

METHODS

A total of 791 uncemented cups were analysed to compare the need for screws to obtain primary fixation in 5 different designs. Arthritic hips with inflammatory arthritis or severe congenital hip disease were excluded. A press-fit technique was first tried in all hips and screws were only used when strictly needed. Radiological acetabular shape and postoperative cup position were assessed in all hips. The mean follow-up was 9.6 (5-15) years.

RESULTS

Screws were required in 155 hips (19.6%). We could not detect any difference in the percentage of screw use between designs. We found that female patients (odds ratio [OR] 2.06; 95% confidence interval [CI], 1.41-3.02) and cups with a greater distance to the hip rotation centre on the postoperative radiograph (OR 1.69; 95% CI, 1.17-2.45) had a higher risk for screw use. A greater anteversion of the cup had a lower risk for screw use (OR 0.96; 95% CI, 0.94-0.99). At latest follow-up no hips had needed revision for aseptic loosening.

CONCLUSIONS

Good intraoperative technique is not enough to avoid screw use since more accurate cup position and reconstruction of the hip rotation centre are required for an adequate interference fit. A press-fit technique can provide similar mid-term results to screw use in hips without severe deformities.

Mid-term results of ReCap/Magnum/Taperloc metal-on-metal total hip arthroplasty with mean follow-up of 7.1 years

INTRODUCTION

Despite enthusiasm for metal-on-metal bearings, disappointing short- to mid-term outcomes has all but halted the use of this bearing articulation. This review presents mid-term results for the ReCap Magnum total hip replacement.

PATIENTS AND METHODS

This prospective study evaluated 79 ReCap/Magnum/Taperloc total hip replacements with mean follow-up of 7.1 (range 3.7-9.2) years. 43 were female and 36 male. Metal ions were measured and radiographic measurement included a 'margin of safety' angle to quantify risk of edge loading. When a clinical suspicion of adverse reaction to metal debris was present, patients had metal artefact reduction sequence MRI. Harris Hip Score and Oxford Hip Score evaluated functional outcome and SF-12 and EQ-5L-5D assessed quality of life at final follow-up.

RESULTS

7 hips were revised indicating 91.1% survivorship at 7.1 years. Postoperative Harris Hip Score and Oxford Hip Score significantly improved. Females and symptomatic patients predicted increased metal ions. Margin of safety correlated with postoperative Oxford Hip Score. Symptomatic hips and positive MRI showed reduced survivorship.

CONCLUSIONS

Compared to more traditional bearings like metal or ceramic on polyethylene the overall outcome of this ReCap/Magnum/Taperloc study cohort is modest. It is felt that further failures will occur in this group therefore cautious interpretation of the results is justified given the potential for reduced survival outcomes.

Results of the cemented Exeter femoral component in patients under the age of 40 : an update at ten to 20 years' follow-up

AIMS

We carried out a further study of the long-term results of the cemented Exeter femoral component in patients under the age of 40 with a mean follow-up of 13.6 years (10 to 20).

PATIENTS AND METHODS

We reviewed our original cohort of 104 cemented Exeter stems in 78 consecutive patients with a mean age of 31 years (16 to 39). Only one patient was lost to radiological follow-up.

RESULTS

A total of six patients (eight hips) had died for reasons unrelated to their surgery. There had been one further periprosthetic fracture from a fall and one fractured femoral stem. No revisions for aseptic loosening were undertaken during the whole study period. Overall, 11 hips had progressive radiolucent lines in one or more zones. The Kaplan Meier survival percentages at ten and 17 years were 97.1% (95% confidence interval (CI) 91.3 to 99.1) and 92.1% (95% CI 74.1 to 97.8) with revision for any reason as the endpoint, and 100% at both ten and 17 years with aseptic loosening (95% CI 83.8 to 100) as the endpoint. No additional hips were classified as radiologically loose.

CONCLUSION

The Exeter femoral component continues to function satisfactorily in young patients for up to 17 years after surgery. Cite this article: Bone Joint J 2017;99-B:192-8.

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.

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.

Magnetic resonance imaging evaluation of acetabular orientation in normal Chinese children

There are no data regarding the acetabular orientation on magnetic resonance imaging (MRI); this study investigates the changes of acetabular orientation with age in normal Chinese children.We retrospectively analyzed the medical records of children who underwent hip MRI examination at our hospital from January 2009 to December 2015. A total of 180 patients with normal MRI reading of the hip joints were included and were divided into 14 groups according to age: from 6 months of age and then for each year from 1 to 16 years. The bony and cartilage acetabular anteversion angle (AAA), acetabular inclination angle (AIA), and acetabular index (AI) were measured. Total bony and cartilage femoral head coverage angles were measured on axial section total femoral head coverage angle (a-TCA) and coronal section total femoral head coverage angle (c-TCA).The mean bony AAA and AIA were 12.2 ± 2.5° and 50.9 ± 2.5°, respectively; both of them stayed constant from the age of 6 months to 16 years. Similar results were found in cartilage AAA (12.1 ± 2.5°) and AIA (41.2 ± 3.0°). There was no difference between bony and cartilage AAA, but bony AIA was significantly larger than cartilage AIA. Bony AI was 24.1 ± 2.4° at the age of 6 months, decreasing to 12.5 ± 2.3° by 12 to 13 years of age; cartilage AI (5.9 ± 1.7°) maintained a steady value with age. The mean bony a-TCA and c-TCA at 6 months were 117.0 ± 5.8° and 127.5 ± 5.1°, increasing to 144.5 ± 4.6° and 140.7 ± 2.5° at the age of 16 years. However, the cartilage a-TCA (145.2 ± 7.2°) and c-TCA (154.1 ± 5.7°) did not change significantly with age.Both bony and cartilage AAA and AIA remain constant up to the age of 16 years in normal Chinese pediatric population. Although the cartilage coverage of femoral head by the acetabulum remains unchanged with age, the bony coverage of femoral head increases.