Anterior Pelvic Plane: A Potentially Useful Pelvic Anatomical Reference Plane in Assessing the Patients’ Ideal Pelvic Parameters Without the Influence of Spinal Sagittal Deformity

Study Design: Observational study. Objective: This study was aimed at investigating the reliability of anterior pelvic plane (APP) as an anatomical reference plane for assessing the patients’ pelvic incidence in patients with ankylosing spondylitis kyphosis deformity. Methods: The globe kyphosis (GK), lumber lordosis (LL), thoracolumbar kyphosis (TLK), thoracic kyphosis (TK), anatomical cervical 7 sacrum angle (aC7SA), and cervical 7 sacrum angle (C7SA) were measured on full-length spine radiography imagines. The pelvic incidence (PI), anatomical pelvic tilt (aPT), and anatomical sacral slope (aSS) were measured on the pelvic synthesized 2D lateral radiography imagines. Because the angle between APP and vertical line was about 4°, Angle1 and tPT were calculated using the following formulas: Angle1 = aC7SA − 4; PT = aPT + 4. According to the study conducted by Vialle, traditional PT (tPT) was calculated using the following widely accepted formula: tPT = PI * 0.37 − 7. Measured PT (mPT) was also measured on the full-length spine radiography imagines. Results: The data analysis showed that PI, mPT, aSS, aPT, and APPA were 50.83 ± 13.44°, 32.52 ± 4.64°, 41.36 ± 9.46°, 8.56 ± 6.80°, and 23.95 ± 5.17°, respectively. There was no significant difference between the PT and tPT (12.56 ± 6.80, 11.49 ± 4.73; P = .152). So, the results demonstrated that the PT could play the equivalent effect as tPT did for making surgical plans in patients with kyphosis deformity. Conclusion: The pelvic anatomical reference plane had potential to be used in assessing the patients’ ideal pelvic incident without the influence of spinal sagittal deformity. The aPT+4 may represent patients’ postoperative ideal PT.

Alternative Anatomical Landmarks for Anterior Pelvic Plane Determination

The anterior pelvic plane (APP) defined by both anterior superior iliac spines (ASIS) and the pubic symphysis (PS), is used as reference for cup orientation during total hip arthroplasty (THA). However, acquiring the PS and the contralateral ASIS during the intervention with the patient in lateral decubitus position, can be challenging due to the medical devices and the patient abdominal apron. The goal of this study is to find more easily accessible anatomical landmarks, useful for the APP acquisition. Thus we propose to study the variability of the pelvis anatomy in order to identify which landmarks vary with the APP. We built a statistical shape model (SSM) of the pelvis and studied the variability of APP orientation when deforming the SSM along its variation modes. We computed the APP inclination for each deformation and modeled linear relations between the APP inclination and the deformation along the variation modes. We found that the variability in APP inclination is mainly due to 3 variation modes that deform the iliac crest (IC), the posterior superior and anterior inferior iliac spines (PSIS, AIIS). Acquiring those three anatomical landmarks (IC, PSIS and AIIS) with the ipsilateral ASIS, could be a solution to determine more easily the APP for THA in lateral decubitus.

Spinopelvic Characteristics in Acetabular Retroversion: Does Pelvic Tilt Change After Periacetabular Osteotomy?

Background: Acetabular retroversion may lead to impingement and pain, which can be treated with an anteverting periacetabular osteotomy (aPAO). Pelvic tilt influences acetabular orientation; as pelvic tilt angle reduces, acetabular version reduces. Thus, acetabular retroversion may be a deformity secondary to abnormal pelvic tilt (functional retroversion) or an anatomic deformity of the acetabulum and the innominate bone (pelvic ring). Purpose: To (1) measure the spinopelvic morphology in patients with acetabular retroversion and (2) assess whether pelvic tilt changes after successful anteverting PAO (aPAO), thus testing whether preoperative pelvic tilt was compensatory. Study Design: Case series; Level of evidence, 4. Methods: A consecutive cohort of 48 hips (42 patients; 30 ± 7 years [mean ± SD]) with acetabular retroversion that underwent successful aPAO was studied. Spinopelvic morphology (pelvic tilt, pelvic incidence, anterior pelvic plane, and sacral slope) was measured from computed tomography scans including the sacral end plate in 21 patients, with adequate images. In addition, the change in pelvic tilt with aPAO was measured via the sacrofemoral-pubic angle with supine pelvic radiographs at an interval of 2.5 ± 2 years. Results: The spinopelvic characteristics included a pelvic tilt of 4° ± 4°, a sacral slope of 39° ± 9°, an anterior pelvic plane angle of 11° ± 5°, and a pelvic incidence of 42° ± 10°. Preoperative pelvic tilt was 4° ± 4° and did not change postoperatively (4° ± 4°) ( P = .676). Conclusion: Pelvic tilt in acetabular retroversion was within normal parameters, illustrating “normal” sagittal pelvic balance and values similar to those reported in the literature in healthy subjects. In addition, it did not change after aPAO. Thus, acetabular retroversion was not secondary to a maladaptive pelvic tilt (functional retroversion). Further work is required to assess whether retroversion is a reflection of a pelvic morphological abnormality rather than an isolated acetabular abnormality. Treatment of acetabular retroversion should focus on correcting the deformity rather than attempting to change the functional pelvic position.

Reliability of pelvic parameters measurement with sterEOS: preliminary results

SterEOS is a software developed by EOS Imaging® allowing the measurement of 3D orthopaedic parameters on two bi-planar radiographs. The goal of this preliminary study was to assess the reliability of the pelvic measurements. Two observers, a novice and an intermediate user, measured three times these parameters on pre and postoperative EOS images coming from ten patients. Intra- and inter-observer precision have been evaluated with intra-class coefficient (ICC) and Bland-Altman graphs. On preoperative EOS images, a high intra- and inter-observer precision (ICC>0.8) was obtained for the measurement of the femoral head diameter, the femur length, the pelvic version and the pelvic obliquity. The offset, the femoral neck length, the pelvic incidence and the sacral slope measurement had a high intra-observer precision but a lower inter-observer precision. The measurement of the acetabulum inclination and anteversion, the CCD angle, the femur torsion, the pelvic rotation and the anterior pelvic plane inclination had a low intra- and inter-observer precision. Similar results were found on postoperative EOS images. Our results are partially consistent with the literature since authors found high intra- and inter-observer precision for all pelvic parameters. Further studies are therefore needed to evaluate the impact of the observer experience on the reliability of those measurements.

Correlation of tilt of the anterior pelvic plane angle with anatomical pelvic tilt and morphological configuration of the acetabulum in patients with developmental dysplasia of the hip: a cross-sectional study

Background It was previously reported that pelvises with developmental dysplasia of the hip are tilted anteriorly, which increases bony coverage of the femoral head. This study aimed to investigate the correlation between anatomical parameters of the pelvis such as pelvic incidence and anatomical pelvic tilt and functional parameters of the spine and pelvis such as tilt of the anterior pelvic plane. Methods We examined 84 female patients with bilateral developmental dysplasia of the hip who had undergone curved periacetabular osteotomy at author’s institution. Radiographs of the thoracic to lumbar spines and the pelvis were obtained in the standing position to measure spino-pelvic parameters before surgery. Morphological parameters of the acetabulum such as the anterior center-edge (CE) angle, posterior CE angle, lateral CE angle, and acetabular anteversion were measured using a preoperative three-dimensional pelvic model reconstructed from computed tomography images. Pearson’s correlation analysis was conducted to evaluate the relationship of these parameters. Results With regard to correlations between pelvic incidence (PI) and other parameters, the sacral slope (SS) value (r = 0.666) was the highest among functional parameters and the anatomical-SS value (r = 0.789) was the highest among morphological parameters. There were moderate correlations of the anterior pelvic plane angle (APPA) with pelvic tilt (PT) (r = − 0.594) and anatomical-PT (r = 0.646). With regard to correlations between spino-pelvic parameters and bony morphological parameters of the acetabulum, there was a moderate correlation between anatomical-PT and acetabular anteversion (AA) (r = 0.424). There were moderate correlations of APPA with the anterior CE angle (r = − 0.478), posterior CE angle (r = 0.432), and AA (r = 0.565). APPA had a stronger correlation with anatomical-PT (r = 0.646) than with AA. Conclusions The tilt of the pelvis may be more dependent on anatomical-PT, a morphological parameter of the pelvis, than the lateral CE angle, anterior CE angle, posterior CE angle, and acetabular anteversion on bony coverage of the acetabulum. This study is the first to investigate the correlation between functional parameters of the pelvis and spine and morphological parameters of the pelvis and acetabulum besides PI.

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.