Fiabilité limitée du plan pelvien antérieur pour l’implantation assistée par informatique de la cupule d’une prothèse totale de hanche

Influence of acetabular and femoral morphology on pelvic tilt

Aims

The aim of this study was to investigate whether anterior pelvic plane-pelvic tilt (APP-PT) is associated with distinct hip pathomorphologies. We asked: is there a difference in APP-PT between young symptomatic patients being evaluated for joint preservation surgery and an asymptomatic control group? Does APP-PT vary among distinct acetabular and femoral pathomorphologies? And does APP-PT differ in symptomatic hips based on demographic factors?

Methods

This was an institutional review board-approved, single-centre, retrospective, case-control, comparative study, which included 388 symptomatic hips in 357 patients who presented to our tertiary centre for joint preservation between January 2011 and December 2015. Their mean age was 26 years (SD 2; 23 to 29) and 50% were female. They were allocated to 12 different morphological subgroups. The study group was compared with a control group of 20 asymptomatic hips in 20 patients. APP-PT was assessed in all patients based on supine anteroposterior pelvic radiographs using validated HipRecon software. Values in the two groups were compared using an independent-samples t-test. Multiple regression analysis was performed to examine the influences of diagnoses and demographic factors on APP-PT. The minimal clinically important difference (MCID) for APP-PT was defined as > 1 SD.

Results

There were no significant differences in APP-PT between the control group and the overall group (1.1° (SD 3.0°; -4.9° to 5.9°) vs 1.8° (SD 3.4°; -6.9° to 13.2°); p = 0.323). Acetabular retroversion and overcoverage groups showed higher mean APP-PTs compared with the control group (p = 0.001 and p = 0.014) and were the only diagnoses with a significant influence on APP-PT in the stepwise multiple regression analysis. All differences were below the MCID. The age, sex, height, weight, and BMI showed no influence on APP-PT.

Conclusion

APP-PT showed no radiologically significant variation across different pathomorphologies of the hip in patients being assessed for joint-preserving surgery.

Deep learning-based workflow for hip joint morphometric parameter measurement from CT images

Objective.Precise hip joint morphometry measurement from CT images is crucial for successful preoperative arthroplasty planning and biomechanical simulations. Although deep learning approaches have been applied to clinical bone surgery planning, there is still a lack of relevant research on quantifying hip joint morphometric parameters from CT images.Approach.This paper proposes a deep learning workflow for CT-based hip morphometry measurement. For the first step, a coarse-to-fine deep learning model is designed for accurate reconstruction of the hip geometry (3D bone models and key landmark points). Based on the geometric models, a robust measurement method is developed to calculate a full set of morphometric parameters, including the acetabular anteversion and inclination, the femoral neck shaft angle and the inclination, etc. Our methods were validated on two datasets with different imaging protocol parameters and further compared with the conventional 2D x-ray-based measurement method.Main results. The proposed method yields high bone segmentation accuracies (Dice coefficients of 98.18% and 97.85%, respectively) and low landmark prediction errors (1.55 mm and 1.65 mm) on both datasets. The automated measurements agree well with the radiologists' manual measurements (Pearson correlation coefficients between 0.47 and 0.99 and intraclass correlation coefficients between 0.46 and 0.98). This method provides more accurate measurements than the conventional 2D x-ray-based measurement method, reducing the error of acetabular cup size from over 2 mm to less than 1 mm. Moreover, our morphometry measurement method is robust against the error of the previous bone segmentation step. As we tested different deep learning methods for the prerequisite bone segmentation, our method produced consistent final measurement results, with only a 0.37 mm maximum inter-method difference in the cup size.Significance. This study proposes a deep learning approach with improved robustness and accuracy for pelvis arthroplasty planning.

Direct Anatomic Registration in Computer-Assisted Total Hip Arthroplasty Improves Accuracy of Acetabular Cup Alignment

Background

Computer-assisted total hip arthroplasty using direct anatomic registration (DAR) with acetabular center axis software is an alternative method to the indirect anterior pelvic plane method. The software maps the center of hip rotation and orientation of the native acetabulum in 3 dimensions. This study aimed to evaluate the accuracy of acetabular cup alignment using DAR navigation combined with a mechanical guide device (MGD).

Methods

This prospective nonrandomized controlled study included 106 patients who underwent primary cementless total hip arthroplasty through the posterolateral approach. Fifty-four patients in the study group underwent DAR combined with MGD, whereas 52 patients underwent MGD only for acetabular cup positioning. Plain radiographs of both hips and computerized tomographic scans were obtained 2 months postoperatively for the evaluation of acetabular cup inclination and anteversion, respectively.

Results

The acetabular cup alignment in the study group was within the Lewinnek safe zone more than that in the control group (81.5% vs 59.6%, P < .05). The study group had a mean inclination angle of 43.88°° (standard deviation [SD] 5.38) and anteversion angle of 12.82° (SD 5.99), whereas the control group had 41.10° (SD 6.79) and 12.82° (SD 9.53), respectively. There were no significant differences in estimated blood loss, length of stay, and Harris hip scores at preoperative and 3 and 6 months postoperatively, except for the operative time, which was longer in the study group (P < .01). There was 1 posterior hip dislocation in each group.

Conclusions

DAR navigation combined with MGD provides better accuracy for acetabular cup positioning within the Lewinnek safe zone compared with the conventional technique.

A conservative approach to dislocation following total hip arthroplasty: a review of 8606 hips

PATIENTS AND METHODS

We present the data on 8606 total hip arthroplasty (THA) procedures carried out in 7818 patients through a posterior approach between 1998 and 2017.

RESULTS

218 hips (2.5%) suffered at least 1 dislocation with dislocation rates declining from 6.2% from 1998 to 2002 to 1.5% from 2003 to 2017. Overall, 92 hips (1.06%) required revision surgery but of these, only 5 (0.06%) had a full revision of both components with the remaining 87 requiring intervention only on the acetabular side. None have had a pseudo-arthrosis; none were left dislocated and all remain stable to date.

CONCLUSIONS

In patients who have a second dislocation within 3 months of their primary surgery we recommend a spica or long leg cylinder cast to reduce the need for revision surgery. We propose an algorithm to manage instability with less aggressive operative treatment in this often-elderly patient population with the potential for less physiological insult and significant cost savings.

The influence of sagittal pelvic malrotation on transverse acetabular ligament guided cup orientation: a retrospective cohort study

Background

Total hip arthroplasty (THA) candidates frequently present pelvic malrotation. The aim of this study is to analyze how pelvic malrotation influence transverse acetabular ligament (TAL) guided cup orientation and investigate whether pelvic malrotation produce different clinical outcomes after THA.

Methods

We retrospectively reviewed a consecutive series of THA patients (144 hips) who use TAL as a guidance for cup positioning from March 2017 to January 2020. The patients were divided into normal pelvis (NP) group and backward pelvis (BP) group by sagittal pelvic malrotation assessed by APPA, the angle between the vertical and the APP on standing lateral pelvic radiographs preoperatively. Cup anteversion and inclination and that out of the safe zones were measured and compared in two groups. The demographic data, clinical results, and complications of patients were also compared.

Results

Backward pelvic malrotation were found in 60.6 % of this cohort of THA candidates. The mean angle of both inclination and anteversion in BP group were significantly larger than that in NP group. The rate of cup for anteversion and inclination above the safe zone in BP group was significantly larger than that in NP group. There were 4 patients in BP group recording anterior hip dislocation after surgery. Other complications were not observed at last follow-up.

Conclusions

Backward pelvis malrotation may increase TAL guided cup inclination and anteversion, which were inclined to became outlier above the safe zone. This likely increase the rates of dislocation after THA. For the patients with pelvis malrotation, cup positioning should be performed individually instead of guided by TAL.

Accuracy of cup placement in total hip arthroplasty by means of a mechanical positioning device: a comprehensive cadaveric 3d analysis of 16 specimens

INTRODUCTION

We tested whether a mechanical device (such as Hipsecure) to pinpoint the anterior pelvic plane (APP) as a guide can improve acetabular cup placement. To assess accuracy we asked: (1) is the APP an effective guide to position acetabular cup placement within acceptable ° of divergence from the optimal 40° inclination and 15° anteversion; (2) could a mechanical device increase the number of acetabular cup placements within Lewinnek's safe zone (i.e. inclination 30° to 50°; anteversion 5° to 25°)?

METHODS

16 cadaveric specimens were used to assess the 3D surgical success of using a mechanical device APP to guide acetabular cup placement along the APP. We used the Hipsecure mechanical device to implant acetabular cups at 40° inclination and 15° anteversion. Subequently, all cadaveric specimens with implants were scanned with a CT and 3D models were created of the pelvis and acetabular cups to assess the outcome in terms of Lewinnek's safe zones.

RESULTS

The mean inclination of the 16 implants was 40.6° (95% CI, 37.7-43.4) and the mean anteversion angle was 13.4° (95% CI, 10.7-16.1). All 16 cup placements were within Lewinnek's safe zone for inclination (between 30° and 50°) and all but 2 were within Lewinnek's safe zone for anteversion (between 5° and 25°).

CONCLUSION

In cadaveric specimens, the use of a mechanical device and the APP as a guide for acetabular cup placement resulted in good positioning with respect to both of Lewinnek's safe zones.

Influence of pelvic sagittal tilt on 3-dimensional bone coverage in total hip arthroplasty: a simulation analysis

BACKGROUND

In total hip arthroplasty with computer navigation assistance, cup orientation is generally determined according to the coordinate system relative to the functional pelvic plane (FPP). However, there is a large difference in the cup anteversion between a posterior pelvic tilt relative to the computed tomography (CT) table in the sagittal plane and anterior pelvic tilt, even when the cup is set at the same orientation angle according to each FPP. The present study analysed this difference from the viewpoint of 3-dimensional (3D) coverage of the acetabular component (3D coverage) to determine how the 3D acetabular coverage is altered with changes in pelvic sagittal tilt.

METHODS

We analysed 3D-simulated acetabular coverage measured in 3D pelvic models reconstructed from the preoperative CT data of 50 patients. In each patient, we created 5 pelvic models with a sagittal tilt of 10° increments between 20° anterior tilt and 20° posterior tilt relative to the CT table.

RESULTS

We found that 3D coverage decreased as the pelvis tilted posteriorly. Particularly, there were significant differences between the pelvis with 20° anterior tilt and that with neutral tilt (p < 0.001). There was also a difference between the pelvis with neutral tilt and that with a 20° posterior tilt (p < 0.01). The mean decrease in 3D coverage between the pelvis with neutral tilt and that with 20° posterior tilt was 7.2 ± 1.6%.

CONCLUSIONS

We found that 3D coverage differed among pelvis with different sagittal tilts when the cup orientation angle was determined according to FPP.

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.

Standardization of hemipelvis alignment for in vitro biomechanical testing

Although in vitro biomechanical tests are regularly performed, the definition of a suitable reference frame for hemipelvic specimens is still a challenge. The aims of the present study were to: (i) define a reference frame for the human hemipelvis suitable for in vitro applications, based on robust anatomical landmarks; (ii) identify the alignment of a hemipelvis based on the alignment of a whole pelvis (including right/left and male/female differences); (iii) identify the relative alignment of the proposed in vitro reference frame with respect to a reference frame commonly used in gait analysis; (iv) create an in vitro alignment procedure easy, robust and inexpensive; (v) quantify the intra-operator repeatability and inter-operator reproducibility of the procedure. A procedure to univocally identify the anatomical landmarks was created, exploiting the in vitro accessibility of the specimen's surface. Through the analysis on 53 CT scans (106 hemipelvises), the alignment of the hemipelvis based on the alignment of a whole pelvis was analyzed: differences between male/female and right/left hemipelvises were not statistically significant To overcome the uncertainty in the identification of the acetabular rim, a standard acetabular plane was defined. An alignment procedure was developed to implement such anatomical reference frame. The intra-operator repeatability and the inter-operator reproducibility were quantified with four operators, on male and female hemipelvises. The intra-operator repeatability was better than 1.5°. The inter-operator reproducibility was better than 2.0°. Alignment in the transverse plane was the most repeatable. The presented procedure to align hemipelvic specimens is sufficiently robust, standardized, and accessible. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1645-1652, 2018.

The Use of Fluoroscopy During Direct Anterior Hip Arthroplasty: Powerful or Misleading?

BACKGROUND

Direct anterior approach total hip arthroplasty (THA) with fluoroscopic assistance is growing in popularity. Variables such as pelvic tilt, c-arm technique, and patient positioning can affect the perceived fluoroscopic view. This study evaluates the effect of these variables on the position of the acetabular component.

METHODS

Forty-one hips in 40 patients undergoing direct anterior arthroplasty THA with fluoroscopic assistance underwent routine postoperative radiographs and postoperative pelvic computed tomography scan. The acetabular component position as defined by a 3-dimensional reconstruction was compared to the surgeon's intraoperative perception of the component's position and compared to routine postoperative plain radiograph measurements.

RESULTS

Although fluoroscopy was used to create an anteroposterior pelvic radiograph utilizing the coccyx to pubis symphysis distance, a 3D reconstruction created in the same pelvic orientation as the fluoroscopic images confirmed that 39/41 hips were placed with unrecognized excess of anteversion and inclination secondary to imaging the pelvis in extension.

CONCLUSION

Intraoperative imaging during supine direct anterior arthroplasty THA confirms appropriate component placement. Pelvic tilt can greatly affect the perceived position of the acetabular component and cannot be accurately compensated for by assessing the relationship between the coccyx and pubic symphysis due to morphologic variation and orientation. We recommend positioning the c-arm so that the size and shape of the obturator foramen matches the standing preoperative anteroposterior pelvis image. This technique allows for the native standing pelvic tilt to be accounted for intraoperatively and will result in the least variation in intraoperative and postoperative standing acetabular component orientation.

What is the Impact of a Spinal Fusion on Acetabular Implant Orientation in Functional Standing and Sitting Positions?

BACKGROUND

This study used EOS imaging of primary total hip arthroplasty (THA) patients, with and without predating spinal fusion, to investigate (1) the impact of spinal fusion on acetabular implant anteversion and inclination, and (2) whether more extensive spinal fusion (fusion starting above the thoracolumbar junction or extension of fusion to the sacrum) affects acetabular implant orientation differently than lumbar only spinal fusion.

METHODS

Ninety-three patients had spinal fusion (case group), and 150 patients were without spinal fusion (controls). None of the patients experienced dislocation. The change in sacral slope (SS) and cup orientation from standing to sitting was measured.

RESULTS

Mean SS change from the standing to sitting positions was -7.9°in the fusion group vs -18.4°in controls (P = .0001). Mean change in cup inclination from the standing to sitting positions was 4.9°in the fusion group vs 10.2°in controls (P = .0001). Mean change in cup anteversion from standing to sitting positions was 7.1°in the fusion group vs 12.1°in controls (P = .0001). For each additional level of spinal fusion, the change in SS from standing to sitting positions decreased by 1.6(95% confidence interval [CI], 2.2073-1.0741), the change in cup inclination decreased by 0.8(95% CI, 0.380-1.203), and the change in cup anteversion decreased by 0.9(95% CI, 0.518-1.352; P < .001 in all cases).

CONCLUSION

Patients with spinal fusion demonstrated less adaptability of the lumbosacral junction. Longer spinal fusion or inclusion of the pelvis in the fusion critically impacts hip-spine biomechanics and significantly affects the ability to compensate in the standing-to-sitting transition.

Measurement of acetabular inclination and anteversion via CT generated 3D pelvic model

Background

Inclination and anteversion were the main factors that determined the reliability of the acetabulum. Inclination and anteversion measurements included anatomical, operational and radiographic methods. The aim of our present study was to exhibit divergence of inclination and anteversion via the three measurements.

Methods

Inclination and anteversion were defined according to the definitions put forward by Murray. Three-dimensional models of pelvis of CT data were brought forth. Acetabular axis was determined by the rim of acetabula. Reference planes were established by bone landmarks including anterior superior iliac spine, pubic tubercles and sacral crests. Inclinations and anteversions were calculated according to the definitions.

Results

Forty-nine cases were involved in the research. Data of inclination form anatomical, operational and radiographic showed 37.48 ± 11.07, 45.12 ± 14.76 and 48.76 ± 14.36, and anteversion were 18.12 ± 7.59, 24.97 ± 9.68, 14.30 ± 5.64. A substantial deviation was noted in the inclinations (P < 0.01) and anteversions (P < 0.01).

Conclusion

Our findings suggested that the inclinations and anteversions of the three measurements varied, which might in turn interfere the decision of orthopedists.

Computer navigation of the acetabular component in total hip arthroplasty: a narrative review

Total hip arthroplasty (THA) is a common procedure for primary osteoarthritis, but increasing numbers are also being performed for other pathologies such as secondary arthritis, inflammatory arthropathies and trauma. Estimates suggest that around 8.5 million people in the UK are affected by joint pain secondary to arthritis and a rising ageing population has resulted in an increase in THA operations of around 4% per year over the last six years.

Multiple studies have shown that THA provides improved quality of life scores, but there remains the burden of complications which account for 15% of £1bn NHS liability payouts. DaPalma et al analysed the financial impact of complications following THA and found the additional cost of a dislocation within six weeks of surgery is 342% of the primary cost.

Following primary THA, complications may occur as a result of incorrect component positioning of the femoral stem, the acetabular cup or both. It is known that acetabular malposition may lead to increased rates of dislocation, impingement, edge-loading, polyethylene wear, pelvic osteolysis and prosthesis failure.

Acetabular component positioning has been described as the single most important factor in dictating risk of dislocation following THA. Furthermore, instability and dislocation after primary THA is the most common single reason for revision surgery accounting for 22.5% of all revisions and 33% of acetabular revisions.

We outline the currently available methods of acetabular navigation comparing freehand techniques with computer and robotic-assisted navigation of the acetabular component.

Cite this article: Davenport D, Kavarthapu V. Computer navigation of the acetabular component in total hip arthroplasty: a narrative review. EFORT Open Rev 2016;1:279-285. DOI: 10.1302/2058-5241.1.000050.

The Impact of Total Hip Arthroplasty on Pelvic Motion and Functional Component Position is Highly Variable

BACKGROUND

This study's purpose was to determine the impact of THA implantation on pelvic motion, and to assess motion in patients with a history of lumbar fusion or prosthetic dislocation.

METHODS

This was an IRB-approved, prospective investigation of 3 cohorts: (1) patients without a history of lumbar surgery undergoing THA (group A), (2) patients with a lumbar fusion (group B), and (3) patients with a THA prosthetic dislocation (group C). All patients received both standing and sitting lateral pelvis images to measure sacral slope and pelvic tilt in the sagittal plane.

RESULTS

Fifty-eight patients were enrolled (24 group A, 27 group B, and 7 group C), with no differences in age, gender, or body mass index (P = .1-.7). In group A, the mean change in sacral slope from standing to sitting was 22.1° ± 15.2° preoperatively and 19.5° ± 14.8° postoperatively. However, in 13 patients, the difference in pelvic motion from the standing to seated position, from preoperatively to postoperatively, was >5° and in 10 patients, this difference was >10°. The change in standing to sitting sacral slope was significantly less in patients with a lumbar fusion (9.8° ± 8.2°) and history of prosthetic dislocation (12.5° ± 4.7°) vs group A (P < .001 and P = .008).

CONCLUSION

Implantation of a THA can increase or decrease sagittal plane pelvic motion from the standing to seated position with a high degree of variability. Thus, the ability to predict ideal component positioning from preoperative images may be challenging.

A robust method to extract the anterior pelvic plane from CT volume independent of pelvic pose

PURPOSE

The anterior pelvic plane (APP) is commonly used as a reference plane to assess acetabular orientation. However, conventional methods for determining the APP may not be accurate and are prone to user variability. To overcome these issues, we developed a robust method to accurately extract the APP independent of pelvic pose using three-dimensional pelvic computed tomography (CT).

MATERIALS AND METHODS

Twenty-eight studies for suspected nonmusculoskeletal conditions were obtained. The APP was determined by four landmarks that were automatically extracted from user-defined regions of interest (ROIs) with compensation of pelvic pose. The APP defined from these landmarks was quantitatively compared to the APPs determined by an expert and an unskilled. Intraobserver reliability was measured to evaluate the time-interval variability. Finally, we evaluate the robustness of this method to patient posture using an arbitrarily rotated volume. The intraclass correlation coefficients (ICCs) were calculated to determine the interobserver and intraobserver reliabilities.

RESULTS

The ICC values for the four landmarks and the APP were similar between the semiautomated method and expert determination (ICC >0.937). The ICC values for intraobserver reliability over time for our method were all 1, demonstrating high reliability. Furthermore, agreement between the parameters determined from the original volume and the rotated volume was nearly perfect.

CONCLUSIONS

Our method is a useful measurement tool for the APP as it is robust, and the results were similar to an experienced surgeon's determination. Furthermore, it was independent to the direction of the CT slice and more robust than a measurement by an unskilled.

Total Hip Prostheses in Standing, Sitting and Squatting Positions: An Overview of Our 8 Years Practice Using the EOS Imaging Technology

More total hip arthroplasty (THA) is performed worldwide and especially in younger and more active patients compared to earlier decades. One of the focuses of THA research in the future will be on optimizing the radiological follow-up of these patients using 2D and 3D measurements of implants position while reducing the radiation dose delivered.

Low-dose EOS^® imaging is an innovative slot-scanning radiograph system providing valuable information in patient functional positions (standing, sitting and even squatting positions). EOS has been proven accurate and reliable without significant inconvenience caused by the metallic artifacts of implants. The ability to obtain precise data on implant orientation according to the patient posture opens new perspectives for a comprehensive analysis of the pelvic frontal and sagittal balance and its potential impact on implants function and failures.

We report our 8 years experience on our first 300 THA patients using this technology routinely for pre and post op evaluation. Our results will be compared and confronted with the actual literature about this innovative technology. We shall especially emphasize our experience about patients with abnormal posture and the evolution of the subject over time, because the phenomenon of an aging spine is frequently associated with the process of aging hips.

An accurate method of radiological assessment of acetabular volume and orientation in computed tomography spatial reconstruction

Background

Two-dimensional (2D) measurements of acetabular morphology and orientation are well known; there is less information on these acetabular characteristics in three dimensions. One important reason is the lack of standardized reference planes for the pelvis, especially in relation to the spinopelvic unit; another is that no method precisely assesses the acetabulum in three-dimensional (3D) orientation based on its axis rather than on the directions of the edges of the acetabular rim. We present an objective, highly reliable and accurate, axis-based approach to acetabular anthropometry in the measurement of acetabular volume and spatial orientation in both normal and pathologic hips. This was done using reference planes based on the sacral base (SB) and true acetabular axis in 3D computed tomography (CT) pelvic reconstruction.

Methods

Radiological examinations of 30 physiologic pelves (60 acetabula) were included in the study. Reliability and accuracy of the method were verified by comparing acetabular angles in 2D pelvic scans with 3D reconstructions. We also applied the method to two pathologic acetabula.

Results

Comparison of axis position in the horizontal plane revealed significant positive correlations between 2D angle measurements (acetabular anteversion angle [AAA] and anterior acetabular index [AAI]) and 3D measurement of anteversion angle (p < 0.001 and p = 0.012, respectively). In the frontal plane, there was no difference between abduction angle, measured on topogram, and inclination angle, obtained from a 3D model (p = 0.517). In the sagittal plane, there was a significant negative correlation between AAA and acetabular tilt (p < 0.001). Inter- and intra-observer reproducibility was excellent for determination of the sacral-base plane and assessment of volume, with Fleiss κ coefficients of 0.850 and 0.783, respectively, and intraclass correlation coefficients of 0.900 and 0.950, respectively. Inter-observer reproducibility for evaluation of acetabular axis ranged from 0.783 to 0.883, and intra-rater reliability ranged from 0.850 to 0.900 for all 3D angles.

Conclusions

Our method is a new, reliable diagnostic tool for assessing the acetabula in both normal and pathologic hip joints. The sacral-base plane can be used as a stable reference that takes the relationship of the acetabulum to the spinopelvic unit into consideration.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-015-0503-8) contains supplementary material, which is available to authorized users.

Intra- and extra-articular planes of reference for use in total hip arthroplasty: a preliminary study

PURPOSE

Acetabular component malalignment in total hip arthroplasty can lead to potential complications such as dislocation, component impingement and excessive wear. Computer-assisted orthopaedic surgery systems generally use the anterior pelvic plane (APP). Our aim was to investigate the reliability of anatomical landmarks accessible during surgery and to define new potential planes of reference.

METHODS

Three types of palpations were performed: virtual, on dry bones and on two cadaveric specimens. Four landmarks were selected, the reproducibility of their positioning ranging from 0.9 to 2.3 mm. We then defined five planes and tested them during palpations on two cadaveric specimens.

RESULTS

Two planes produced a mean orientation error of 5.0° [standard deviation (SD 3.3°)] and 5.6° (SD 2.7°).

CONCLUSIONS

Even if further studies are needed to test the reliability of such planes on a larger scale in vivo during surgery, these results demonstrated the feasibility of defining a new plane of reference as an alternative to the APP.

Reliability of cup position in navigated THA in the lateral decubitus position using the 'flip technique'

Malpositioning of the acetabular component in total hip arthroplasty (THA) increases the risk of dislocation, reduces the range of motion and may contribute to bearing surface wear. During computer assisted navigation, the anterior pelvic plane is registered intraoperatively by percutaneous palpation, but this may be unreliable. The aim of our study was to evaluate the reliability of imageless navigation in acetabular positioning employing data acquisition in the supine position and surgery in the lateral position ('flip technique'). We report 24 patients affected by primary osteoarthritis undergoing THA in which implants were placed with a conventional free-hand technique using the acetabular transverse ligament for cup orientation. For imageless navigation we used Orthopilot-Aesculap software. All patients had a postoperative computed tomography (CT) scan at three months, using previously validated dedicated software for cup orientation. Data collected using navigation software were compared with CT measurements. The mean acetabular inclination and anteversion recorded intra-operatively using navigation software were respectively 41°5' (SD: 9.61) and 9°5' (SD: 4.01) respectively. The mean inclination and anteversion calculated post-operatively by the CT based image software were 44°2' (SD 5.83) and 14°4' (SD 6.42) respectively. There was a statistically significant difference between the anteversion values (p=0.04). Therefore, the acquisition of parameters in the supine position with surgery performed in the lateral decubitus position creates unreliable data concerning cup anteversion using an imageless navigation system, and therefore the 'flip technique' cannot be recommended.

Study of the three-dimensional orientation of the labrum: its relations with the osseous acetabular rim

Understanding the three-dimensional orientation of the coxo-femoral joint remains a challenge as an accurate three-dimensional orientation ensure an efficient bipedal gait and posture. The quantification of the orientation of the acetabulum can be performed using the three-dimensional axis perpendicular to the plane that passes along the edge of the acetabular rim. However, the acetabular rim is not regular as an important indentation in the anterior rim was observed. An innovative cadaver study of the labrum was developed to shed light on the proper quantification of the three-dimensional orientation of the acetabulum. Dissections on 17 non-embalmed corpses were performed. Our results suggest that the acetabular rim is better represented by an anterior plane and a posterior plane rather than a single plane along the entire rim as it is currently assumed. The development of the socket from the Y-shaped cartilage was suggested to explain the different orientations in these anterior and posterior planes. The labrum forms a plane that takes an orientation in between the anterior and posterior parts of the acetabular rim, filling up inequalities of the bony rim. The vectors V(L) , V(A2) and V(P) , representing the three-dimensional orientation of the labrum, the anterior rim and the posterior rim, are situated in a unique plane that appears biomechanically dependent. The three-dimensional orientation of the acetabulum is a fundamental parameter to understand the hip joint mechanism. Important applications for hip surgery and rehabilitation, as well as for physical anthropology, were discussed.

Acetabular center axis: is it the future of hip navigation?

There are 2 distinct methods of cup navigation in total hip arthroplasty. One predicts orientation of the acetabulum through bony landmarks outside the acetabulum (eg, the anterior pelvic plane); its unreliability is well published. The other identifies acetabular center axis (ACA) and is patient-specific method that is independent of pelvic tilt, making it more reliable. Data from readily palpable acetabular registration points were compared with postoperative pelvic computed tomography images in 137 cases. Findings show that ACA software is accurate in determining acetabular/cup version and inclination. Cup center axis should coincide within 4 mm of ACA to minimize impingement and maximize stability without altering preoperative femoral version.

Influence of the sagittal balance of the spine on the anterior pelvic plane and on the acetabular orientation

The Anterior Pelvic Plane (APP), defined by the anterior superior iliac spines and the pubic tubercle, was commonly used as reference for positioning and postoperative evaluation of the orientation of the acetabular cup in total hip arthroplasty. APP was assumed to be vertical, but was not observed always so, mostly because of associated spinal diseases inducing perturbations in the harmony of the sagittal balance of the pelvi-spinal unit. Consequently a sagittal rotation of the pelvis occurs, and so a tilt of the APP which alters directly the orientation of the cup in upright position. An analysis of the APP tilt related to the sagittal balance of the spine was provided and its implication on the cup orientation. It appeared essential for an individual adjustment of the cup positioning to avoid a functional mal-position which can lead to an increased risk of dislocation and impingement.