Anterior Pelvic Plane Research Articles

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.

The effect of using different coordinate systems on in-vivo hip angles can be estimated from computed tomography images

Measurements of hip kinematics inherently depend on the coordinate system in which they are derived, yet the effect of the coordinate system definition on calculations of hip angles is not well-understood. Herein, hip angles calculated during dynamic activities were compared using coordinate systems described in the literature. In-vivo kinematic data of 24 participants (13 males) were analyzed during gait and the anterior impingement test using dual fluoroscopy and model-based tracking. Two coordinate systems for the pelvis (anterior pelvic plane, International Society of Biomechanics [ISB]) and three coordinate systems for the femur (table top plane with two definitions of the superior-inferior axis, ISB) were evaluated. Bony landmarks visible on computed tomography (CT) images were identified to establish each coordinate system and used as the basis to calculate differences in hip angles between coordinate system pairs. In the analysis during gait, the maximum differences derived from various coordinate system definitions were 6.7° ± 5.5° for flexion, 7.7° ± 2.1° for rotation, and 5.5° ± 0.7° for adduction. For the anterior impingement test, the differences were 8.1° ± 5.9°, 7.1° ± 1.2°, and 5.3° ± 0.7°, respectively. Landmark-based analysis using CT images could estimate these dynamic differences with errors less than 1.0°. Our results indicate that hip angles can be accurately transformed to angles calculated in different coordinate systems by accounting for the inherent bony anatomy. This information may aid in the interpretation of results across biomechanical studies of the hip.

Prevalence of Sagittal Spinal Deformity Among Patients Undergoing Total Hip Arthroplasty

BackgroundThe important relationship between sagittal spinal alignment and total hip arthroplasty (THA) is becoming well recognized. Prior research has shown a significant relationship between sagittal spinal deformity (SSD) and THA instability. This study aims at determining the prevalence of SSD among preoperative THA patients. MethodsA multicenter database of preoperative THA patients was analyzed. Radiographic parameters measured from standing radiographs included anterior pelvic plane tilt, spinopelvic tilt, and lumbar lordosis (LL); pelvic incidence (PI) was measured from computed tomography scans. Lumbar flatback was defined as PI-LL mismatch >10°, balanced as PI-LL of −10° to 10°, and hyperlordosis as PI-LL <−10°. ResultsA total of 1088 patients were analyzed (mean, 64 years; 48% female). And 59% (n = 644) of patients had balanced alignment, 16% (n = 174) had a PI-LL > 10°, and 4% (n = 46) had a PI-LL > 20° (severe flatback deformity). The prevalence of hyperlordosis was 25% (n = 270). Flatback patients tended to be older than balanced and hyperlordotic patients (69.5 vs 64.0 vs 60.8 years, P < .001). Spinopelvic tilt was more posterior in flatback compared to balanced and hyperlordotic patients (24.7° vs 15.4° vs 7.0°) as was anterior pelvic plane tilt (−7.1° vs −2.0° vs 2.5°) and PI (64.1° vs 56.8° vs 49.0°), all P < .001. ConclusionOnly 59% of patients undergoing THA have normally aligned lumbar spines. Flatback SSD was observed in 16% (4% with severe flatback deformity) and there was a 25% prevalence of hyperlordosis. Lumbar flatback was associated with increasing age, posterior pelvic tilt, and larger PI. The relatively high prevalence of spinal deformity in this population reinforces the importance of considering spinopelvic alignment in THA planning and risk stratification.

Does Acetabular Coverage Vary Between the Supine and Standing Positions in Patients with Hip Dysplasia?

Although variation in physiologic pelvic tilt may affect acetabular version and coverage, postural change in pelvic tilt in patients with hip dysplasia who are candidates for hip preservation surgery has not been well characterized, and its clinical importance is unknown. The aim of this study was to determine (1) postural changes in sagittal pelvic tilt between the supine and standing positions; (2) postural changes in the acetabular orientation and coverage of the femoral head between the supine and standing positions; and (3) patient demographic and morphologic factors associated with sagittal pelvic tilt. Between 2009 and 2016, 102 patients underwent pelvic osteotomy to treat hip dysplasia. All patients had supine and standing AP pelvic radiographs and pelvic CT images taken during their preoperative examination. Ninety-five patients with hip dysplasia (lateral center-edge angle < 20°) younger than 60 years old were included. Patients with advanced osteoarthritis, other hip disease, prior hip or spine surgery, femoral head deformity, or inadequate imaging were excluded. Sixty-five patients (64%) were eligible for participation in this retrospective study. Two board-certified orthopaedic surgeons (TT and MF) investigated sagittal pelvic tilt, spinopelvic parameters, and acetabular version and coverage using pelvic radiographs and CT images. Intra- and interobserver reliabilities, evaluated using the intraclass correlation coefficient (0.90 to 0.98, 0.93 to 0.99, and 0.87 to 0.96, respectively), were excellent. Demographic data (age, gender, and BMI) were collected by medical record review. Sagittal pelvic tilt was quantified as the angle formed by the anterior pelvic plane and a z-axis (anterior pelvic plane angle). Using a 2D-3D matching technique, we measured the change in sagittal pelvic tilt, acetabular version, and three-dimensional coverage between the supine and standing positions. We correlated sagittal pelvic tilt with demographic and CT measurement parameters using Pearson's or Spearman's correlation coefficients. Although functional pelvic tilt varied widely among individuals, the pelvis of patients with hip dysplasia tilted posteriorly from the supine to the standing position (mean APP angle 8° ± 6° versus 2° ± 7°; mean difference -6°; 95% CI, -7° to -5°; range -17° to 4.1°; p < 0.001; paired t-test).The pelvis tilted more than 5° posteriorly from the supine to the standing position in 39 patients (60%), and the change was greater than 10° in 12 (18%). In the latter subgroup of patients, the mean acetabular anteversion angle increased (22° ± 5° versus 27° ±5°; mean difference 5°; 95% CI, 4°-6°; p < 0.001) and the mean anterosuperior acetabular sector angle notably deceased from the supine to the standing position (91° ± 11° versus 77° ± 14°; mean difference -14°; 95% CI, -17° to -11°; p < 0.001; paired t-test). Postural change in pelvic tilt was not associated with any of the studied demographic or morphologic parameters, including patient age, gender, BMI, and acetabular version and coverage. On average, the pelvis tilted posteriorly from the supine to the standing position in patients with hip dysplasia, resulting in increased acetabular version and decreased anterosuperior acetabular coverage in the standing position. Thus, assessment with a supine AP pelvic radiograph may overlook changes in acetabular version and coverage in weightbearing positions. We recommend assessing postural change in sagittal pelvic tilt when diagnosing hip dysplasia and planning hip preservation surgery. Further studies are needed to determine how postural changes in sagittal pelvic tilt affect the biomechanical environment of the hip and the clinical results of acetabular reorientation osteotomy. Level IV, diagnostic study.

How do global sagittal alignment and posture change after total hip arthroplasty?

Postural change after total hip arthroplasty (THA) is still a matter of discussion. Previous studies have mainly concentrated on the pelvic motions. We report the post-operative changes of the global sagittal posture using pelvic, spinal, and lower extremities parameters. 139 patients (primary THA, without previous spinal or lower extremity surgery) were included. We measured pelvic parameters [SS, sacral slope; PI, pelvic incidence; PT, pelvic tilt; APP angle, anterior pelvic plane angle] and the global posture parameters (SVA, sagittal vertical angle; GSA, global sagittal angle; TPA, T1 pelvic angle). Patients were categorized into low PI group < 45°, 45° < medium PI < 65°, and high PI > 65°. Mean GSA and SVA decreased post-operatively (p = 0.005 and p = 0.004 respectively). The TPA change was not significant (p = 0.078). In the low PI group, GSA (5.4 ± 5.0 to 4.3 ± 4.0, p = 0.005) and SVA (5.4 ± 4.9 to 4.2 ± 4.1, p = 0.038) decreased with more posterior pelvic tilt. Post-operative TPA was significantly higher (8.4 ± 10.6 to 9.8 ± 10.7; p = 0.048). In the medium PI group, SVA decreased (4.2 ± 4.6 to 3.6 ± 4.5, p = 0.020) with more posterior pelvic tilt. In the high PI group, pelvic and global posture parameters did not evolve significantly. PI is the key determining factor in pelvic tilt modification after THA. Patients with low PI demonstrate significant modification in spine, pelvic, and lower extremities. Pelvic tilt is the main adaptation mechanism for medium incidence patients whereas pelvic tilt does not change in high PI patients after surgery.

Perioperative changes in pelvic tilt after hip resurfacing using a direct lateral approach

Background: Proper positioning of the acetabular component is critical for prevention of dislocation and excessive wear for total hip arthroplasty (THA) and hip resurfacing. Consideration of preoperative pelvic tilt (PT) may aid in acetabular component placement. The purpose of this study was to investigate how PT changes after hip resurfacing, via pre and post-operative radiographic analysis of anterior pelvic plane (APP), and whether radiographic analysis of the APP is a reproducible method for evaluating PT in resurfaced hips. Methods: A consecutive group of 228 patients from a single surgeon who had hip resurfacing were evaluated. We obtained X-rays from an institutional database for these patients who had their surgeries between January 1 st , 2014 to December 31 st , 2016. PT was measured by two observers before and after resurfacing utilizing a standardized radiographic technique. Correlation coefficients were calculated for PT measurements between observers, and pre- and post-surgery. Results: Mean preoperative PT was 0.7° (SD ±6.6°) and 0.4° (SD ±6.1°). Mean post-operative PT was −1.2° (SD ±6.2°) and −1.2° (SD ±6.0°). Correlations between pre and post-operative PT were R=0.829 (P 10°. Intraclass correlation coefficients between observers were R=0.987 (95% CI, 0.963–0.981; P Conclusions: After hip resurfacing arthroplasty (HRA), the mean difference between preoperative and postoperative PT was less than 1°. These results suggest that near-native PT is maintained with consistency after hip resurfacing, a finding that is variable following THA. Since variations in PT affect functional acetabular position, these results support the use of PT measurement in pre-operative planning for hip arthroplasty with a high degree of inter-observer reliability.

Influence of Spinopelvic Alignment on Pelvic Tilt after Total Hip Arthroplasty.

ObjectiveTo evaluate the impact of spinopelvic parameters and hip contracture on change in the pelvic tilt (PT) after Total hip arthroplasty (THA).MethodsOne hundred patients (15 male and 85 female) who underwent THA were included in this prospective study. Radiographic data were obtained preoperatively and 1 year after THA. Radiographic parameters included sagittal anterior pelvic plane (APP), sagittal vertical axis (SVA), sacral slope (SS), pelvic inclination (PI), and lumbar lordosis angle (LL). The APP was defined as the angle between the anterior pelvic plane and the vertical plane. A positive value indicates pelvic retroversion. Postoperative changes in PT were divided into three groups: the PA group (pelvic anteversion, ΔAPP < −5°), the PR group (pelvic retroversion, ΔAPP > 5°), and the PT group (minimal change, ΔAPP ≤ ± 5°). The Kruskal–Wallis test and the Steel–Dwass test were used to compare the preoperative and postoperative spinopelvic parameters among the three groups. The Spearman's rank correlation coefficient was used to evaluate the correlation between ΔAPP and spinopelvic parameters.ResultsMinimal change in pelvic tilt was observed in 59% of patients, while pelvic anteversion was observed in 16% of patients and pelvic retroversion was observed in 25% of patients. There were no significant changes in the spinopelvic parameters, including TK, LL, SVA, LL, SS, and APP after THA. The Femoral angle (FA) was significantly decreased after THA (P < 0.001). Preoperative APP was significantly more retroverted in the PA group than the PR group, and the PT group (6.8 ± 12.2, 0.2 ± 9.9, −8.3 ± 8.3, P < 0.001). Preoperative SS, PI‐LL, and PI were significantly smaller in the PA group than the PT group and the PR group. A significant negative correlation was identified between preoperative APP and ΔAPP (r = −0.418, P < 0.001).ConclusionApproximately 60% of the patients did not have any marked change in PT after THA. Preoperative APP was the only predictive factor associated with marked anterior or posterior change in PT.

\u201cSimple mechanical devices did not improve pelvis positioning in AP pelvis radiographs for reliable assessment of the acetabular orientation\u201d

BackgroundThe aim of this study was to develop two simple positioning devices for anteroposterior pelvis radiographs and to evaluate their effect on accuracy of the radiographs for assessment of the acetabular orientation compared with non-instrumented positioning.MethodsThe superior anterior iliac spines and the pubic symphysis were used as anatomical landmarks to obtain a horizontal orientation of the pelvis according to the anterior pelvic plane. Anteroposterior pelvis radiographs were taken of 11 human cadaveric pelvic bones with each of the positioning devices and without any device. Defined measurements were carried out to objectify the tilt and rotation of the pelvis and to assess the cross-over sign as well as the presence of the ischial spine sign. Computed tomography scans were performed as a standard of reference. Bland-Altman-Plots were used to compare the continuous measurement values and Cohen’s Kappa was applied for the categorical data. Intra- and inter-observer reliability was determined by the intraclass correlation coefficient and Cohen’s Kappa.ResultsThe mean values of the measurements showed a high variability. A low correlation of the measurement values was found between the radiographs of the different positioning methods and the computed tomography scans. The intra- and inter-observer reliability was good (Cohen’s Kappa 0.78 and 0.69; intraclass correlation coefficient 0.99 and 0.98).ConclusionThe use of positioning devices did not lead to more accurate anteroposterior pelvis radiographs compared to non-instrumented positioning. Simple positioning devices do not provide standardized anteroposterior pelvis radiographs for reliable assessment of the acetabular orientation.

Evaluation of anatomical pelvic parameters between normal, healthy men and women using three-dimensional computed tomography: a cross-sectional study of sex-specific and age-specific differences

BackgroundSagittal spinal balance and standing posture are affected by pelvic morphology, especially pelvic incidence (PI). However, it is not difficult to identify the hip center because of overlap of the pelvis, image contrast, and soft tissue artifacts. Measurements of PI are not always suitable in all patients, especially those with osteoarthritis of the hip joint whose femoral head is nonspherical, subluxed, or dislocated. We measured PI, pelvic tilt (PT), and sacral slope (SS) as anatomical parameters using a novel three-dimensional measurement in order to compare the pelvic morphology between normal, healthy men and women.MethodsIn this cross-sectional study, we evaluated 108 Japanese subjects (55 men, 53 women) without low back or knee pain. We used the three-dimensional pelvis model adjusted to the anterior pelvic plane and measured the pelvic parameters. The subjects were stratified by age (< 50 versus ≥ 50 years) and sex. Intraobserver and interobserver reliabilities were calculated with intraclass correlation coefficients.ResultsThere was no significant difference in PI, anatomical-PT, and anatomical-SS between sexes. There was a strong correlation between PI and anatomical-SS in men and women (R = 0.790 and 0.715, respectively). Values of anatomical-PT were lower, and values of anatomical-SS were greater among older subjects than among younger subjects; the value of PI was similar between younger and older subjects. Intraobserver and interobserver mean absolute differences were about 2 mm and 2°, respectively; the intraclass correlation coefficient was > 0.87.ConclusionsWe found a strong correlation between PI and anatomical-SS in men and women. This novel measurement concept may be useful to estimate PI from anatomical-SS because the measurements of PI are not always suitable in all patients, especially those with osteoarthritis of the hip joint whose femoral head is not spherical or whose femoral head is subluxed or dislocated. This is the first report to describe the relationship between PI, anatomical-PT, and anatomical-SS as morphologic parameters with a high interclass correlation coefficient for intraobserver and interobserver reliabilities.

Hip-Spine Syndrome: Acetabular Anteversion Angle Is Associated with Anterior Pelvic Tilt and Lumbar Hyperlordosis in Patients with Acetabular Dysplasia: A Retrospective Study.

Background:Hip-spine syndrome was originally described by Offierski and MacNab, who argued that the flexion deformity of the hip rotated the pelvis forward, causing the spine symptoms. We additionally hypothesized that in patients who have osteoarthritis (OA) of the hip, the pelvis is tilted anteriorly to compensate for the anterior acetabular coverage defect. We investigated the hip factors associated with anterior pelvic tilt (PT) in patients who had OA of the hip due to acetabular dysplasia.Methods:We retrospectively reviewed the medical records of patients who had undergone total hip arthroplasty between January 2009 and December 2017 to identify those who had unilateral secondary OA due to acetabular dysplasia. Patients who had spinal imbalance, a history of spinal or lower limb fracture or surgery, bilateral OA of the hip, or a severely subluxated hip were excluded, leaving 100 eligible patients. We defined the indicators of an anterior acetabular coverage defect, flexion deformity of the hip, and anterior PT as the acetabular anteversion angle (AAA), extension range of motion (ROM), and anterior tilt of the pelvis, respectively. We measured hip factors and spinal parameters on radiographs and the standardized axial and coronal planes on 3-dimensional computed tomography with reference to the anterior pelvic plane. Hip factors associated with PT were investigated.Results:Univariate analysis showed a significant correlation between PT and both AAA (r = –0.389, p < 0.001) and combined anteversion angle (r = –0.272, p = 0.03). Multivariate regression analysis identified AAA (β = –0.385, p < 0.001) and extension ROM (β = 0.212, p = 0.0496) as independent factors associated with PT. Lumbar lordosis and pelvic incidence minus lumbar lordosis were significantly correlated with AAA, but sagittal vertical axis was not.Conclusions:When treating patients who have acetabular dysplasia, surgeons should recognize the relationship between the anterior acetabular coverage and anterior PT. Correcting hyperlordosis of the lumbar spine can induce progression of hip OA because it may decrease the acetabular anterior coverage.

The relationship between global spinal alignment and pelvic orientation from standing to sitting following pedicle subtraction osteotomy in ankylosing spondylitis patients with thoracolumbar kyphosis.

To investigate the relationship between the spinal sagittal alignment and arc of pelvic motion from standing to sitting in ankylosing spondylitis (AS) patients with thoracolumbar kyphosis following pedicle subtraction osteotomy (PSO). AS patients who underwent PSO for thoracolumbar kyphosis from January 2016 to July 2018 were recruited. EOS standing and sitting images were obtained pre- and postoperatively. Radiographic parameters were measured on the sagittal radiographs, including lumbar lordosis, thoracic kyphosis, pelvic incidence, pelvic tilt, sacral slope, sagittal vertical axis (SVA), spinosacral angle, anterior pelvic plane angle (APPA) and knee flexion angle. Thirty-six patients were enrolled. From standing to sitting, APPA was increased by a mean of 14.7° (P < 0.001) and 3.0° (P = 0.083) before and after surgery, respectively. The increase in APPA from standing to sitting was correlated with the standing SVA (R = 0.592, P < 0.001) preoperatively. After PSO, the change in APPA was correlated with the change in SSA in both the standing and sitting position (R = 0.381, P = 0.022 and R = 0.667, P < 0.001, respectively). The APPA from standing to sitting was decreased in 11 patients with standing C7 plumb line posterior to the femoral head postoperatively. In AS patients, pelvic orientation was adjusted by the global spinal alignment. When planning total hip arthroplasty for AS patients, global spinal alignment should be considered to improve the joint stability.

Three-dimensional analysis of acetabular orientation using a semi-automated algorithm

Understanding the morphology of the acetabulum is necessary for preoperative evaluation in hip surgery. The purpose of this study was to (1) establish a novel method for measuring three-dimensional (3D) acetabular orientation, (2) quantify the reliability of this method, and (3) describe relevant characteristics of three-dimensional (3D) acetabular orientation among normal Asian subjects. Computed tomography (CT) scans of the pelvis that had been performed for suspected non-musculoskeletal conditions were obtained from 200 subjects (60 males, 140 females). A novel method was developed to measure 3D acetabular orientation with a semi-automatically determined pelvic coordinate system based on the anterior pelvic plane (APP). To quantify the robustness of our method, we analyzed the results obtained from 20 patients at different times and with different raters and pelvic poses in the same CT volume. To determine morphological differences of the acetabulum by age and sex, we analyzed the parameters of 200 CT volumes. Each intraclass correlation coefficient (ICC) values for intra- and inter-observer reliability were over 0.975 and 0.945, demonstrating high reliability. Furthermore, agreement between the angles determined from the original volume and the rotated volume was nearly perfect (ICCs > 0.956). Multiple linear regression analysis with age and sex as covariates indicated that acetabular inclination was not significantly associated with age (p = 0.687) or sex (p = 0.09). There was also no evidence that acetabular anteversion was associated with age (p = 0.383) or sex (p = 0.53). Our method showed excellent reliability for determining acetabular orientation, as it is robust, fast, and easily applicable to larger populations. In addition, the results of the analysis of acetabular orientation by age and sex can be used as a reference in various diagnostic procedures in orthopedics.

Anterior pelvic plane registration accuracy and cup position measurement using ultrasound- and pointer-based navigation in primary total hip arthroplasty.

Incorrect cup positioning in primary total hip arthroplasty is known as a risk factor for early implant failure. The use of navigation systems leads to more accurate cup positioning. The aim of this study was to compare the registration accuracy of the anterior pelvic plane and the measurement accuracy of the definite cup position for a pointer computer-assisted orthopaedic navigation system (P-CAOS) and an ultrasound-based navigation tool (US-CAOS) in an intra-individual study design. Anterior pelvic plane registration was performed in 44 patients receiving a primary total hip arthroplasty with P-CAOS and US-CAOS. The cup implantation was performed using US-CAOS. Intraoperatively, the cup position was assessed using P-CAOS and US-CAOS. The postoperative cup position was determined via CT scan. Inclination and anteversion errors were calculated using intraoperative values and CT data. All operations were performed by a single, high-volume surgeon using a minimally invasive anterolateral approach. The mean inclination error was 0.9∘ in the US-CAOS group and -1.1∘ in the P-CAOS group. This was not statistically significant. The mean anteversion error was significantly reduced (p< 0.001) in the US-CAOS group (1.4∘) compared to the P-CAOS group (-8.0∘). Significantly more cups (23 of 44; 52%) in the P-CAOS group were outliers regarding to the defined anteversion error range of 15∘± 10∘. Outliers in the US-CAOS group amounted to two (of 44; 5%) (p< 0.001). The number of outliers regarding the inclination error range of 40∘± 10∘, did not differ significantly between the P-CAOS (2; 5%) and US-CAOS (1; 2%) group. We were able to show a systematic anterior pelvic plane registration error in this intraindividual study design. US-CAOS based APP landmark registration showed to be significantly more precise compared to P-CAOS registration. The anteversion error of the cup using US-CAOS showed to be significantly reduced compared to the P-CAOS method.

Dual mobility device reduces the risk of prosthetic hip instability for patients with degenerated spine: A case-control study

IntroductionThe pelvic incidence is an anatomical and biomechanical pelvic parameter determining spine sagittal morphology and kinematics. Stiffening of the lumbo-pelvic complex, a result of degeneration, affects the functional cup positioning, putting prosthetic hip patients at risk of instability. The anti-dislocation dual mobility (DM) device may be clinically advantageous by reducing the risk of prosthetic instability for older patients with spine ageing. Our study aims to answer the following questions: (1) is there a relationship between prosthetic hip instability and the standing cup position, (2) is there a relationships between prosthetic hip instability and the pelvic incidence, (3) is there a relationships between prosthetic hip instability and the severity of the spine degeneration?, (4) is the DM cup device an effective option for reducing the risk of prosthetic instability related to spine degeneration? HypothesisThere is a relationship between prosthetic hip instability and the standing cup position and pelvic parameters. MethodsCase-control study on prospectively collected data since 2009. From 1672 conventional total hip replacements (THR–5.4% dislocation rate) and 1056 DM-THRs (1.1% dislocation rate) performed at our institute since 2009, we created three groups: 33 patients with unstable THR (group 1–case), 41 patients with stable THR (group 2–control), and 42 patients with stable DM-THR (group 3–control). The cup orientation was measured on standing pelvic radiographs and the spino-pelvic parameters were measured on standing EOS™ biplanar images or lateral full spine radiographs. ResultsBy comparing patients from group 1 with those of group 2 we found they had similar cup position (57% versus 51% fitting the safe zone, p=0.58), higher pelvic incidence (58° versus 51°, p=0.01), and more severe spine degeneration (smaller anterior pelvic plane Tilt (2° versus 7° [p=0.002]), a larger pelvic incidence–lumbar lordosis mismatch (17° versus 8° [p=0.005]), and a higher proportion of spino-sacral angle<127° (70% versus 43%, (p=0.02)). Patients from group 3 had similar cup position, pelvic incidence, and spine degeneration compared to patients from group 1. Discussion/ConclusionPatients with spine-hip relation type 2C/D (high pelvic incidence and severe spine degeneration) have an increased risk of instability that is partly compensated for by the use of a DM device. Preoperative screening of patients with abnormal spine-hip relation would improve THR planning and reduce the risk of prosthetic hip instability. The use of a DM device on spine-degenerated elderly patients is probably sound. Level of evidenceIII, case-control study.

Variations in pelvic dimensions: An anatomical and computed tomography study.

The anterior pelvic plane (APP) is a useful anatomical reference with both clinical and research applications in orthopedic surgery and rehabilitation medicine. It is used as a marker for computer-assisted total hip replacement and image-guided assessment of the hip center in clinical gait analysis. Despite its common use, no published data exist on the variations in height and width in an adult population. The aim of this study was to determine the range of dimensions for the anterior pelvic plane found in the Scottish adult population. Thirty-five human cadavers and 100 pelvic computed tomography (CT) scans were examined. Pelvic height and width were measured, and the ratios were determined. The mean width and height for combined cadaver and CT pelves were found to be 238.0 mm (SD 20.1, range 188.3-273.8) and 92.7 mm (SD 10.5, range 71.2-114.7), respectively. The mean width-to-height ratio for all pelves was 2.59 (SD 0.31, range 1.73-3.50). There were no statistically significant differences in means between males and females. The variations of APP dimensions within an adult population are presented. These will be of value in the validation of algorithms for computer navigation and hip joint center calculation in total hip arthroplasty and gait analysis. Furthermore, differences in dimensions between cadaveric and CT measurements have been shown which may have implications for further research and the validity of reference data dependent on data-point acquisition. Clin. Anat. 31:981-987, 2018. © 2018 Wiley Periodicals, Inc.

Measurement System for Attitude of Anterior Pelvic Plane and Implantation of Prothesis in THR Surgery

With the average age of population increasing in the world, the number of total hip replacement (THR) surgeries increases year by year. However, the failure rate of THR surgeries is up to 10% following primary surgery and 28% after revision arthroplasty, which has direct correlation to the implantation angles between prosthesis and pelvis. To improve the implanting accuracy of the prosthesis, we propose a measurement system and estimation algorithms. The system includes three parts: an initial attitude measurement instrument, which is used to determine the initial attitude of the anterior pelvic plane (APP), a real-time attitude measurement instrument, which aims to acquire the real-time attitude of the APP, and an acetabular cup angle measurement instrument, which obtains the relative angles between prosthesis and pelvis. Each of them is based on inertial measurement unit (IMU) and magnetometer. A quaternion-based extended Kalman filter is adopted to fuse the data from IMU and magnetometer to estimate the orientation, and the algorithm calculating the attitude of pelvis and relative angles between pelvis and prosthesis is designed in this paper. The reliability of this system, from the measurement point of view, has been verified by experiments. The experimental results show that the root-mean-square errors of APP attitude and acetabular cup implanting orientation are less than 1.6° and 3° with standard uncertainty of less than 0.22° and 0.17°, respectively. The accuracy of our system meets the requirement of the THR surgeries.

Evaluation of pelvic morphology in female patients with developmental dysplasia of the hip using three-dimensional computed tomography: A cross-sectional study

BackgroundThe purpose of this study is to measure pelvic morphology with respect to the pelvic incidence, pelvic tilt, and sacral slope using 3-dimensional measurement and to compare the pelvic morphology between the normal population and women with developmental dysplasia of the hip (center-edge angle, <25°). We hypothesized that the relationship between pelvic incidence, anatomical pelvic tilt, and anatomical sacral slope would be different between normal subjects and patients with developmental dysplasia of the hip. MethodsWe evaluated 61 healthy women without low back or knee pain and 71 patients with developmental dysplasia of the hip. We used the 3-dimensional pelvis model adjusted to the anterior pelvic plane and measured the pelvic parameters. To determine correlation, we used Pearson's coefficients. To evaluate variation, we used intraclass correlation coefficients. ResultsPelvic incidence and anatomical pelvic tilt were significantly greater by 4° in the group with developmental dysplasia of the hip than in the normal group (p = 0.026 and < 0.001, respectively). The vertical distance from hip axis to the center of the S1 endplate was significantly greater in the group with developmental dysplasia of the hip than in normal group, that is, by 8 mm (p < 0.001). There was a strong correlation between pelvic incidence and anatomical sacral slope in both groups (R = 0.707 and 0.897, respectively). The intraobserver and interobserver mean absolute differences were about 2 mm and 2°, respectively, and the intraclass correlation coefficient was >0.88. ConclusionPelvic incidence and anatomical-pelvic tilt were significantly greater in patients with developmental dysplasia of the hip. We found a strong correlation between the pelvic incidence and anatomical sacral slope in both groups. Therefore, anatomical-sacral slope may be useful for estimating pelvic incidence because it is not easily measured, especially in patients with osteoarthritis of the hip joint.

The anteroposterior axis of the tibia is adjusted to approximately a right angle to the anterior pelvic plane in the standing position in patients with hip dysplasia similar to normal subjects: a cross-sectional study

BackgroundWe previously described that the anteroposterior (AP) axis of the tibia is approximately perpendicular to the transverse axis of the anterior pelvic plane (APP) in the standing position in healthy subjects. The purpose of this study was to investigate the rotational alignment between the APP and clinical epicondylar axis and the AP axis of the tibia relative to pelvic coordination in the standing position in normal subjects and in women with developmental dysplasia of the hip (DDH) to aid decision making for surgeons in the alignment of implants in total hip or knee arthroplasty.MethodsThis study included 77 Japanese women. Twenty-nine in the DDH group underwent curved periacetabular osteotomy; 48 women without lumbago and knee pain were included in the normal group. Femoral neck anteversion (FNA), condylar twist angle, and knee rotation angle were measured in femoral coordination. The angle between the femoral neck axis and clinical epicondylar axis (CEA) was measured, the transverse axis of the APP was also measured, and the angle between the AP axis of the tibia and transverse axis of the APP was calculated.ResultsThere was a moderate negative correlation between FNA and CEA relative to the APP. This finding indicated a trend towards greater FNA leading to more internal rotation. Knee rotation angle (KRA) relative to the APP was 1.65° ± 5.58° in the normal group and − 2.65° ± 7.57° in the DDH group. This finding indicated that the tibia AP axis was approximately perpendicular to the APP in the standing position both in the normal and DDH groups.ConclusionWe found that the tibia AP axis was at approximately a right angle to the transverse axis of the APP in the standing position in both the normal and DDH groups, while the KRA was different in the normal and DDH groups. These findings may prove helpful for positional alignment investigations needed for implantation in total hip or knee arthroplasty and gait analysis.

Which one is more affected by navigation-assisted cup positioning in total hip arthroplasty: Anteversion or inclination? A retrospective matched-pair cohort study in Asian physique.

The purpose of this study was to compare acetabular cup positioning using an imageless navigation-assisted total hip arthroplasty (THA) to a case-matched control group using the conventional technique in Asian physique. Case matching controlled study using retrospectively collected data for THAs was done. Matching criteria were gender, age ± 5 years, and body mass index ± 5 kg/m2. Thirty patients who had navigation THAs were manually matched to a conventional group of 30 patients. After measuring anteversion and inclination on 3-D CT, final cup anteversion was calculated using the mathematical formula (anteversion = arctan [tan (anatomic anteversion) × sin (inclination)]). No significant difference was observed between mean inclination ( p = 0.420), anteversion ( p = 0.697), and the mean deviation from 15° for anteversion ( p = 0.649). However, there was a statistical significant difference for mean deviation from 40° for inclination ( p = 0.027). There was a significant difference in the percentage of correctly placed acetabular cup in safe zones with inclination ( p = 0.039). Although soft tissue overlying the pubic tubercle interfered with registration of the bony landmark and thereby induced inaccuracy of anteversion angles in the navigation group, the use of imageless navigation-assisted technique increases the placement within the safe zone for inclination and enhances the accuracy and the precision of inclination of the acetabular cup relative to the conventional THA rather than anteversion. This finding may be due to the effect of the patient's physique on the anterior pelvic plane (APP)-based reference system of imageless navigation.

Assessment of pelvic tilt in anteroposterior radiographs by means of tilt ratios

In anteposterior (AP) radiographs, cup position in total hip arthroplasty and acetabular anatomy in hip-preserving surgery are highly influenced by pelvic tilt. The sagittal rotation of the anterior pelvic plane is an important measurement of pelvic tilt during hip surgery. Thus, correct evaluation of cup position and acetabular parameters requires the assessment of pelvic tilt in AP radiographs. Changes in pelvic tilt inversely change the height of the lesser pelvis and the obturator foramen in AP radiographs. Tilt ratios were calculated by means of these two parameters in simulated radiographs for ten male and ten female pelvises in defined tilt positions. A tilt formula obtained by exponential regression analysis was evaluated by two blinded investigators by means of 14 simulated AP radiographs of the pelvis with pelvic tilts ranging from + 15° to -15°. No differences were found between male and female tilt ratios for each 5° step of simulated pelvic tilt. Pelvic tilt and tilt ratios correlated exponentially. Using the tilt formula, the two blinded investigators were able to assess pelvic tilt with high conformity, a mean relative error of + 0.4° (SD ± 4.6°), and a mean absolute error of 3.9° (SD ± 2.3°). Neutral pelvic tilt is indicated by a tilt ratio of 0.5 when the height of the lesser pelvis is twice the height of the obturator foramen. The analysis and interpretation of cup position and acetabular parameters may be improved by our method for assessing pelvic tilt in AP radiographs.