Anterior Pelvic Plane Research Articles

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.

A new mini-navigation tool allows accurate component placement during anterior total hip arthroplasty.

IntroductionComputer-assisted navigation systems have been explored in total hip arthroplasty (THA) to improve component positioning. While these systems traditionally rely on anterior pelvic plane registration, variances in soft tissue thickness overlying anatomical landmarks can lead to registration error, and the supine coronal plane has instead been proposed. The purpose of this study was to evaluate the accuracy of a novel navigation tool, using registration of the anterior pelvic plane or supine coronal plane during simulated anterior THA.MethodsMeasurements regarding the acetabular component position, and changes in leg length and offset were recorded. Benchtop phantoms and target measurement values commonly seen in surgery were used for analysis. Measurements for anteversion and inclination, and changes in leg length and offset were recorded by the navigation tool and compared with the known target value of the simulation. Pearson’s r assessed the relationship between the measurements of the device and the known target values.ResultsThe device accurately measured cup position and leg length measurements to within 1° and 1 mm of the known target values, respectively. Across all simulations, there was a strong, positive relationship between values obtained by the device and the known target values (r=0.99).ConclusionThe preliminary findings of this study suggest that the novel navigation tool tested is a potentially viable tool to improve the accuracy of component placement during THA using the anterior approach.

Intra- and Inter-rater Reliability of Navigated Ultrasound in the Assessment of Pelvic Tilt in Symptom-Free Young Adults.

Pelvic tilt is the angle between the anterior pelvic plane and the coronal plane. It affects cup positioning in total hip arthroplasty. The primary objective of this study was to test the intra- and inter-rater reliability of a navigated smart device-based ultrasound system for pelvic tilt assessment. The secondary objective was to test the inter-rater variability of the measurements on a hip phantom. A repeated-measures design was used. Two raters measured the pelvic tilt of 12 symptom-free young adults in upright and supine positions. Additionally, pelvic tilt was measured on a hip phantom. Each rater performed 3 measurements in each body position on the participants and 12 measurements on the hip phantom. Intra- and inter-rater reliability were calculated with the use of intraclass correlation coefficients. The variability in measurements on the hip phantom was assessed by a Bland-Altman analysis of agreement. Intraclass correlation coefficient 95% confidence intervals for intra-rater reliability ranged from good to excellent and moderate to excellent for the supine and upright positions respectively. Intraclass correlation coefficient 95% confidence intervals for inter-rater reliability ranged from poor to excellent for both positions. Hip phantom measurements showed no significant average bias (P > .05) and no significant proportional bias (P > .05). The 95% inter-rater limits of agreement were ±1.3° and ±1.7° for the supine and upright positions, respectively. The intra-rater reliability values achieved were suitable. Intraclass correlation coefficient values for inter-rater reliability remained below an acceptable level. Possible reasons and overcoming strategies were presented. The 95% limits of agreement were good, at less than ±2°.

The effect of seated pelvic tilt on posterior edge-loading in total hip arthroplasty: A finite element investigation.

Edge-loading of a ceramic-on-ceramic total hip replacement can lead to reproducible squeaking and revision. A patient's functional acetabular cup orientation, driven by their pelvic tilt, has been shown to be a significant factor in squeaking during hip flexion. The aim of this study was to investigate the effect of seated pelvic tilt on the contact mechanics at the ceramic bearing surface. A finite element model of a ceramic-on-ceramic total hip replacement was created. The cup was orientated at 40° inclination and 15° anteversion relative to the anterior pelvic plane. The stem was flexed 90° to replicate sitting in a chair. The model was loaded using data from in vivo measurements taken during a sit-to-stand activity. The pelvis was modelled in seven different sagittal positions, ranging from -30° to 30° of pelvic tilt, where a positive value denotes anterior pelvic tilt. Three different head sizes were investigated: 32, 36 and 40 mm. The maximum contact pressure and contact patch to rim distance were determined for each of the 21 simulations. Edge-loading (contact patch to rim distance < 0 mm) occurred with all head sizes when seated pelvic tilt was ≥10° and induced a large increase in contact pressure on the liner, with a maximum pressure exceeding 500 MPa. Edge-loading initiated at seated pelvic tilts of 7°, 9° and 5° for the 32, 36 and 40 mm heads, respectively. Patients with anterior pelvic tilts in the seated position are susceptible to posterior edge-loading. As the position of the pelvis when seated is patient specific, cup orientation should be adjusted on an individual basis to minimise edge-loading.

Implant Orientation Measurement After THA Using the EOS X-Ray Image Acquisition System.

We investigated the accuracy of measuring implant orientation after THA in standing position using EOS system (EOS Imaging Inc., Paris, France). Ninety patients who underwent THA were subjected to this study by comparing angles measured by EOS system and those measured from CT scans using 3D image analyzing software, ZedHip (LEXI, Tokyo, Japan). The radiographic cup inclination and anatomical cup anteversion were measured with respect to the anterior pelvic plane (APP) coordinate. The femoral stem antetorsion was analyzed by measuring the angles between the stem neck axis and the post-condylar axis in the femoral functional axis coordinate.The differences (mean ± SD) (range of 95%CI) between angles measured by EOS system and those from CT scans in the cup inclination, cup anteversion, and stem antetorsion were - 2.3° ± 2.7° (-2.8°∼ - 1.7°), -0.1° ± 5.0° (-1.2°∼0.9°), and - 1.3° ± 6.5° (-2.7°∼0.1°), respectively. Cup inclination measured on 14 hips, cup anteversion measured on 28 hips, and stem antetorsion measured on 27 hips were classified as outliers whose differences were over 5°. Difficulties in defining the reference points for APP correlated with the incidences of the outliers in cup orientation measurements.We could not set new reference points on the 3D bone surface models reconstructed by EOS system, so we have to use reference points defined on 2D images. In addition, the APP coordinate in EOS system was not the same as the standard definition. EOS system may not be used to measure the implant positions after THA until these problems will be improved.

A surface-based approach to determine key spatial parameters of the acetabulum in a standardized pelvic coordinate system

Accurately determining the spatial relationship between the pelvis and acetabulum is challenging due to their inherently complex three-dimensional (3D) anatomy. A standardized 3D pelvic coordinate system (PCS) and the precise assessment of acetabular orientation would enable the relationship to be determined. We present a surface-based method to establish a reliable PCS and develop software for semi-automatic measurement of acetabular spatial parameters. Vertices on the acetabular rim were manually extracted as an eigenpoint set after 3D models were imported into the software. A reliable PCS consisting of the anterior pelvic plane, midsagittal pelvic plane, and transverse pelvic plane was then computed by iteration on mesh data. A spatial circle was fitted as a succinct description of the acetabular rim. Finally, a series of mutual spatial parameters between the pelvis and acetabulum were determined semi-automatically, including the center of rotation, radius, and acetabular orientation. Pelvic models were reconstructed based on high-resolution computed tomography images. Inter- and intra-rater correlations for measurements of mutual spatial parameters were almost perfect, showing our method affords very reproducible measurements. The approach will thus be useful for analyzing anatomic data and has potential applications for preoperative planning in individuals receiving total hip arthroplasty.

High prevalence of acetabular retroversion in asymptomatic adults: a 3D CT-based study.

This study sought to establish the prevalence of the cross over sign (COS) and posterior wall sign (PWS) in relation to the anterior pelvic plane (APP) in an asymptomatic population through reliable and accurate 3D-CT based assessment. Data from pelvic CT scans of 100 asymptomatic subjects (200 hips) undertaken for conditions unrelated to disorders of the hip were available for analysis in this study. A previously established 3D analysis method was applied to assess the prevalence of the COS and PWS in relation to the APP. Of the 200 included hips, 24% (48) presented a positive COS and 5.5% (11) presented a positive PWS. A combination of COS and PWS was observed in 1% (two) of all hips (1%). The high incidence of acetabular retroversion, determined by the COS, shows that this anatomic configuration may not differ in frequency between asymptomatic individuals and patients with symptomatic femoroacetabular impingement (FAI). Patients presenting with hip pain and evidence of FAI should be subjected to strict diagnostic scrutiny and evaluated in the sum of their clinical and radiological presentation. In our cohort of asymptomatic adults, the COS showed a higher incidence than the PWS or a combined COS/PWS. Cite this article: Bone Joint J 2017;99-B:1584-9.

Is anatomic acetabular orientation related to pelvic morphology? CT analysis of 150 healthy pelvises.

Links between sagittal spinal alignment and acetabular orientation attract considerable research attention with the goal of optimising prosthetic cup position. However, whether pelvic incidence (PI) is related to anatomic acetabular orientation remains unknown. We therefore conducted a radiological study with the following objectives: to look for correlations between PI and anatomic acetabular parameters; to describe the sacro-pubic angle (SPA), defined by fixed bony pelvic landmarks, and its relations with acetabular anteversion; and to determine whether anatomical parameters (PI and SPA) correlate with demographic characteristics. PI correlates with anatomical acetabular parameters. We conducted a computed tomography (CT) study of the pelvises of 150 patients free of degenerative disease. Three parameters were measured: anatomic acetabular orientation in the Lewinnek reference plane, PI, and the SPA subtended by the line connecting the midpoint of the sacral endplate to the pubic symphysis and the anterior pelvic plane. Statistical tests were performed to look for correlations among these parameters. Intra-observer and inter-observer reproducibility was considered highly satisfactory (inter-class correlation coefficient, >86% and >82%, respectively). Mean PI was 58.6°±10.2° (range, 32.8°-97.6°), with no significant differences between genders or across age groups. Mean SPA was 34.7°±5.5° (range, 18.3°-49.8°). Mean anatomic acetabular anteversion (AAA) was greater in females (23.4°; range, 11.5°-34.5°) than in males (20°; range, 7.5°-34.5°) (P<0.001). PI did not correlate with any of the acetabular parameters (PI/AAA, r=0.8 and P=0.33; PI/acetabular inclination on the horizontal, r=-0.96 and P=0.24). SPA correlated significantly with both PI (r=0.33 and P<0.001) and AAA (r=0.33 and P<0.001). This CT study of normal pelvises showed that AAA was significantly greater in females and that SPA correlated significantly with both PI and acetabular anteversion. SPA could serve to define the "theoretical" AAA of each individual patient and could thus be incorporated into surgical planning protocols or intra-operative guidance methods for hip replacement surgery. IV, retrospective study with no control group.

Preoperative Ultrasonographic Assessment of the Anterior Pelvic Plane for Personalized Total Hip Replacement.

Correct positioning of the acetabular component is a key factor in minimizing the risk of dislocation after total hip replacement (THR) surgery. A "safe" orientation of the cup is usually defined by 2 angles measured between its geometric axis and the anterior pelvic plane. However, in the current state-of-the-art approach to THR surgery, the intraoperative orientation of the anterior pelvic plane cannot be measured. Even less is known about the functional orientation of the pelvis, which determines the postoperative orientation of the cup during the patient's everyday activities. The aim of this article is to present an original approach to personalized THR surgery, in which the necessary measurements are done preoperatively without interfering with the surgical work flow, and the individual orientation of the cup is obtained without navigation using standard tools that are available in the operating room. To quantify the effect of the anatomic conditions on the final orientation of the cup, we measured the orientation of the anterior pelvic plane in 43 patients scheduled for THR using a newly developed noninvasive method based on ultrasonography and mobile devices. Our results confirm a large variability of the pelvic orientation in both supine and standing positions. We further show how this variability affects the final position of the cup and discuss its consequences for the patient. Finally, we explore a few practical solutions for individualized cup placement, including our own approach, which is based on tilting of the operating table. In this work, we show that the common guidelines used today for cup implantation can only be effectively applied to a small portion of the population. In most cases, it is crucial that the orientation of the cup is readjusted for the particular anatomy of the individual patient.

The anteroposterior axis of the tibia is approximately perpendicular to the anterior pelvic plane in the standing position in healthy Japanese subjects

BackgroundWe previously reported that the clinical epicondylar axis (CEA) was approximately parallel to the transverse axis of the anterior pelvic plane (APP) in the standing position in normal subjects. The purpose of this study was to investigate the rotational alignment between APP in the standing position and the anteroposterior (AP) axis of the tibia relative to pelvic coordination in normal subjects.MethodsThis study included 68 healthy Japanese, 24 males and 44 females, without lumbago and knee pain. Femoral neck anteversion (FNA), condylar twist angle, and knee rotation angle were measured in femoral coordination. The angle between the femoral neck axis and CEA transverse axis of APP was also measured, and the angle between the AP axis of the tibia and the transverse axis of APP was calculated. The mean value of knee rotation angle was 0.23° and 2.06° in male and female subjects, respectively.ResultsThere was a moderate positive correlation between FNA and the femoral axis angle relative to the transverse axis of APP. The knee rotation angle relative to APP was 0.33° and 1.56° in male and female subjects, respectively, and the tibia AP axis was approximately perpendicular to the transverse axis of APP in the standing position. Regarding validation, we obtained high interclass correlation coefficients for both intraobserver and interobserver reliability.ConclusionWe found that the knee rotation angle was almost 0° and that the tibia AP axis was approximately perpendicular to the CEA. The tibia AP axis was also approximately perpendicular to the transverse axis of the APP in standing position.

Morphological Analysis of True Acetabulum in Hip Dysplasia (Crowe Classes I-IV) Via 3-D Implantation Simulation.

The purpose of this study was to investigate the 3-dimensional (3D) morphological features of the true acetabulum in patients with developmental dysplasia of the hip (DDH). Seventy-nine hips-53 in patients with developmental dysplasia of the hip (DDH) and 36 normal hips-were included in the present study. According to the Crowe classification, 26 hips were graded as Class I, 31 were Class II or III, and 22 were Class IV. The anterior pelvic plane was defined to standardize the measurements in the study. A selected virtual cup component was implanted into the true acetabulum of a 3D pelvic model of each hip. The acetabular anteversion angle, effective center-edge (CE) angle, effective Sharp angle, and thickness of the medial wall were measured to provide morphological indices of the true acetabulum. Acetabular sector angles and the component coverage ratio were measured to provide coverage indices. The acetabular anteversion angle increased with the severity of the DDH. Crowe-II/III hips had the smallest effective CE angle and the largest effective Sharp angle. The mean medial wall thickness was greatest in the Crowe-II/III hips (8.72 mm; 95% confidence interval [CI] = 7.52 to 9.92 mm), intermediate in the Crowe-I hips (7.17 mm; 95% CI = 6.24 to 8.11 mm), and smallest in the Crowe-IV hips (6.05 mm; 95% CI = 4.78 to 7.32 mm). The integrated coverage ratio of the Crowe-II/III hips was significantly less than that of the Crowe-I and IV hips. The morphological features of the true acetabulum in patients with DDH can be evaluated comprehensively by using 3D implantation simulation. Segmental bone deficiency was prevalent in the dysplastic hips, especially those in the Crowe-II/III group. Both the severity and the individual morphology of the acetabular dysplasia should be carefully considered in preoperative planning.

Femur first surgical technique: a smart non-computer-based procedure to achieve the combined anteversion in primary total hip arthroplasty

BackgroundThe relevance of prosthetic component orientation to prevent dislocation and impingement following total hip arthroplasty (THA) has been widely accepted. We investigated the use of a non-computer-based surgery to address the reciprocal orientation of the acetabular and femoral components.MethodsIn the femur first technique, the cup is positioned relative to the stem. When the definitive antetorsion of femoral component is fixed, the cup is positioned in a compliant anteversion to the stem. Clinical and radiographic assessments were performed before and 3 months after THA. Radiographic assessment was performed in standing position with the EOS 2D/3D radiography system. 3D images were used to preoperative anterior pelvic plane (APP) angle, postoperative acetabular inclination (AI) and anteversion (AA), and postoperative stem antetorsion. Clinical assessment was performed with Harris Hip Score (HHS).ResultsForty patients (40 hips) underwent primary THA with an average age of 61 years (range, 36–84). Average HHS increased from 43 ± 5 (range, 37–52) preoperatively to 97 ± 6 (range, 86–100) at the last follow-up (P < 0.0001). Average combined anteversion value of cup with liner and stem was 38° ± 9° (range, 12°-55°). Average AI value of cup with liner was 39° ± 6° (range, 30°-55°) in the group with standard stem and 45° ± 7° (range, 39°-58°) in the group with varized stem (P = 0.007). Relationship analysis showed no correlation between the combined anteversion values of the cup with liner and stem with APP angle values (r = 0.26, P = 0.87).ConclusionsFemur first technique allows the surgeon to achieve a combined anteversion ranging from 25° to 50° with a cup inclination ranging from 30° to 50°. The cup is positioned according to the functional plane of the patient regardless the preoperative pelvic tilt.

Correction of Pelvic Tilt and Pelvic Rotation in Cup Measurement after THA - An Experimental Study.

Purpose Accurate assessment of cup orientation on postoperative pelvic radiographs is essential for evaluating outcome after THA. Here, we present a novel method for correcting measurement inaccuracies due to pelvic tilt and rotation. Method In an experimental setting, a cup was implanted into a dummy pelvis, and its final position was verified via CT. To show the effect of pelvic tilt and rotation on cup position, the dummy was fixed to a rack to achieve a tilt between + 15° anterior and -15° posterior and 0° to 20° rotation to the contralateral side. According to Murray's definitions of anteversion and inclination, we created a novel corrective procedure to measure cup position in the pelvic reference frame (anterior pelvic plane) to compensate measurement errors due to pelvic tilt and rotation. Results The cup anteversion measured on CT was 23.3°; on AP pelvic radiographs, however, variations in pelvic tilt (± 15°) resulted in anteversion angles between 11.0° and 36.2° (mean error 8.3°± 3.9°). The cup inclination was 34.1° on CT and ranged between 31.0° and 38.7° (m. e. 2.3°± 1.5°) on radiographs. Pelvic rotation between 0° and 20° showed high variation in radiographic anteversion (21.2°-31.2°, m. e. 6.0°± 3.1°) and inclination (34.1°-27.2°, m. e. 3.4°± 2.5°). Our novel correction algorithm for pelvic tilt reduced the mean error in anteversion measurements to 0.6°± 0.2° and in inclination measurements to 0.7° (SD± 0.2). Similarly, the mean error due to pelvic rotation was reduced to 0.4°± 0.4° for anteversion and to 1.3°± 0.8 for inclination. Conclusion Pelvic tilt and pelvic rotation may lead to misinterpretation of cup position on anteroposterior pelvic radiographs. Mathematical correction concepts have the potential to significantly reduce these errors, and could be implemented in future radiological software tools. Key Points · Pelvic tilt and rotation influence cup orientation after THA. · Cup anteversion and inclination should be referenced to the pelvis. · Radiological measurement errors of cup position may be reduced by mathematical concepts. Citation Format · Schwarz TJ, Weber M, Dornia C et al. Correction of Pelvic Tilt and Pelvic Rotation in Cup Measurement after THA - An Experimental Study. Fortschr Röntgenstr 2017; 189: 864 - 873.

IMU-based Real-time Pose Measurement system for Anterior Pelvic Plane in Total Hip Replacement Surgeries.

With the aging of population, the number of Total Hip Replacement Surgeries (THR) increased year by year. In THR, inaccurate position of the implanted prosthesis may lead to the failure of the operation. In order to reduce the failure rate and acquire the real-time pose of Anterior Pelvic Plane (APP), we propose a measurement system in this paper. The measurement system includes two parts: Initial Pose Measurement Instrument (IPMI) and Real-time Pose Measurement Instrument (RPMI). IPMI is used to acquire the initial pose of the APP, and RPMI is used to estimate the real-time pose of the APP. Both are composed of an Inertial Measurement Unit (IMU) and magnetometer sensors. To estimate the attitude of the measurement system, the Extended Kalman Filter (EKF) is adopted in this paper. The real-time pose of the APP could be acquired together with the algorithm designed in the paper. The experiment results show that the Root Mean Square Error (RMSE) is within 1.6 degrees, which meets the requirement of THR operations.

Influence of pelvic tilt on functional acetabular orientation.

Pelvic tilt influences acetabular orientation (AO). Anatomical AO can be measured in relation to the anterior pelvic plane (APP), functional AO can be calculated relative to table's plane. To assess to what extent functional AO is determined by pelvic tilt and if APP and table plane give equal information for correct AO. AO was evaluated by computed tomography (CT) scans of 138 patients. Pelvic tilt, anatomical and functional AO were measured, differences between the two reference planes were calculated. Anatomical and functional acetabular anteversion (AA) were found to be different in 21% of individuals with an enhanced extent of pelvic tilt. Functional AA was increased compared to anatomical AA at high posterior pelvic tilt (p < 0.001). Enlarged anterior tilting of the pelvis reduced APP-related AA (p < 0.002). Anatomical AA positively correlated with pelvic tilt, particularly in females (p < 0.01, correlation coefficient = 0.698, R2 = 0.523). APP and table plane do not provide equal information about AO at enhanced pelvic tilt. Functional orientation of the acetabulum is dependent on pelvic tilt, which itself is influenced by anatomical AA and should therefore be analyzed for precise AO.

Acetabular and Femoral Anteversions in Standing Position are Outside the Proposed Safe Zone After Total Hip Arthroplasty

BackgroundAlthough most hip dislocations occur in either standing or sitting position, the safe zone for implant position is defined for the supine position. Our goal was to determine preoperative and postoperative pelvis and hip orientations and whether the safe zone defined in supine position can be used to assess standing radiographs. MethodsPreoperative and postoperative three-dimensional EOS images were assessed in 66 total hip arthroplasty patients. None of the patients had dislocation within the follow-up period (12-36 months). The acetabular anteversion (both anterior pelvic plane [APP] and patient functional plane) and the femoral anteversion were measured. The sacral slope, pelvic version, pelvic inclination, and pelvic incidence were also measured. ResultsAcetabular anteversion increased postoperatively in both APP and patient functional plane (P <.001). Femoral neck anteversion decreased postoperatively (P =.0942). Sacral slope was 42.4° (−25.9° to 24°) preoperatively compared with 40.3° (−4.1° to 64.2°) postoperatively (P =.013). Pelvic version changed from 15.2° (−10.4° to 43.8°) to 17.2° (−6° to 46.7°; P = 0.008). Pelvic inclination was 1.12° (−25.9° to 24°) before total hip arthroplasty and −1.2° (−40.7° to 23.4°) postoperatively (P =.005). ConclusionThe acetabular and femoral implant orientations in standing position reside out of the safe zone in most patients. The APP is not vertical in standing position in most patients due to anterior or posterior pelvic tilt. The proposed safe zone in supine position may not be a useful measure in the assessment of standing radiographs of patients with significant anterior or posterior pelvic tilt. Level of EvidenceLevel IV, therapeutic case series study.

Evaluating Surgeon Estimation of Cup Position in Total Hip Arthroplasty: A Cadaver Study

AbstractInaccurate placement of components during total hip arthroplasty (THA) can lead to significant postoperative complications including revision surgery. Traditionally, surgeons grossly estimate component positioning intraoperatively using anatomical landmarks; however, evidence indicates that this surgeon assessment may not be reliable. The purpose of this study was to determine the accuracy of surgeon estimates of component position as compared with imaging (radiographs and computed tomography [CT] scan) and a new surgical navigation system. Three board-certified orthopaedic surgeons each performed four THA procedures on six cadavers (12 hips). Radiographs and CT scans were obtained postoperatively. The “gold standard” measurements of implanted cup anteversion and inclination were derived from three-dimensional renderings created from postoperative CTs. A reference value for cup position was created by aligning the anterior pelvic plane in each rendering coplanar with the CT table. Following each procedure, surgeons provided their estimate of acetabular cup component orientation. Surgeon estimates were compared with data gathered from postoperative radiographs, CT scans, and the navigation device. Surgeon estimates of anteversion and inclination were within 10 degrees of reference values in 64% (7/11) and 82% (9/11) of cases, respectively. Surgeon estimates of anteversion differed from reference values by a mean of 7.6 ± 5 degrees, whereas inclination differed from reference values by a mean of 6.1 ± 5.1 degrees (all means absolute). Radiographic measurements differed from reference values by 7.8 ± 4.3 degrees (p &gt; 0.05) and 2.7 ± 2.3 degrees (p = 0.06) for anteversion and inclination, respectively, whereas CT values differed by 2.5 ± 1.6 degrees (p = 0.004) and 2.3 ± 2.1 degrees (p = 0.04). The navigation system differed from reference values by 4 ± 4 degrees (p = 0.08) and 4.2 ± 3.2 degrees (p = 0.31). Surgeons underestimated anteversion and inclination by 7.7 ± 4.8 degrees and 6.9 ± 4.8 degrees, respectively. Surgeon underestimation was observed in 8/11 (73%) cases, with anteversion underestimated by &gt; 5 degrees in 5/8 (62%) cases and inclination underestimated by &gt; 5 degrees in 4/8 (50%) cases. Our findings suggest that surgeons tend to underestimate both anteversion and inclination and that the accuracy of their estimates is similar to that of radiographs. CT scans and the navigation system were able to provide more accurate measurements of cup position.

Application of Navigated Ultrasound for Assessment of the Anterior Pelvic Plane in Patients With Degenerative Hip Diseases.

Correct positioning of the acetabular cup is the key for successful total-hip replacement. In common clinical practice, the target alignment of the cup is defined with respect to the anterior pelvic plane. In patients with substantial anterior pelvic plane inclination, this condition may lead to inappropriate distribution of the load on the cup, as most of the forces exerted within the hip joint act along the vertical axis. With the known pelvic inclination, it is possible to readjust the position of the cup with respect to the individual posture of the patient. In this work, we present the first clinical evaluation of a new approach to measurement of the pelvic tilt angle using navigated ultrasound. In our method, the ultrasound probe is tracked with an optical localizer implemented on a handheld mobile device. The method was tested by taking preoperative measurements from 20 patients with osteoarthritis in standing, sitting, and supine positions. The mean values of the measured angles were consistent with the corresponding results reported by other authors. Considering the noninvasiveness of the method and affordability of the hardware used in our system, it can be used in preoperative and postoperative measurements of pelvic orientation for supporting surgery planning and evaluation of treatment outcomes.

The Relationship Between Subluxation Percentage of the Femoroacetabular Joint and Acetabular Width in Asian Women with Developmental Dysplasia of the Hip.

Implantation of the acetabular cup insert in the "true" location of the acetabulum is a fundamental principle of total hip arthroplasty for the treatment of secondary osteoarthritis due to developmental dysplasia of the hip (DDH). As knowledge of the morphology of the acetabulum is required for accurate placement, we investigated the relationship between acetabular width and the Crowe classification of subluxation percentage of the hip. We also analyzed factors associated with the acetabular width ratio (AWR), defined as the acetabular width of the dysplastic hip divided by that of the unaffected, contralateral hip. We completed a retrospective review of the preoperative standard anteroposterior radiographs and computed tomography (CT) scans of 207 female patients who underwent primary total hip arthroplasty for unilateral DDH. The "true" acetabular plane was defined on each CT reconstruction as a plane perpendicular to the anterior pelvic plane, parallel to the teardrop line, and passing through the center of the femoral head on the unaffected, contralateral side. The acetabular width was measured for both the affected hip and the contralateral, reference hip on the true acetabular plane, with the acetabular width defined as the distance between the edges of the anterior and posterior walls of the acetabulum. All hips were classified according to the Crowe groupings on the basis of the subluxation percentage of the dysplastic hip; the subluxation percentage increased from groups I to IV, with group IVb showing joint dislocation. The acetabular width decreased from Crowe groups I to IVb, with a negative correlation found between the AWR and the subluxation percentage (Spearman correlation coefficient, ρ = -0.404; p < 0.001). Multivariate regression analysis identified subluxation percentage and femoral neck-shaft angle as independent factors associated with the AWR. Characterization of factors associated with the AWR, namely subluxation percentage and femoral neck-shaft angle, will guide surgeons in correctly implanting the acetabular cup insert during total hip arthroplasty in patients with DDH.

Selection of a surgical approach for total hip arthroplasty according to the depth to the surgical site.

The surgical depths of approaches for total hip arthroplasty (THA) have not been reported previously. In this study, we investigate the relationships between the distances to the centre of the femoral head in different approaches and body mass index (BMI). The study included patients with normal hip joints who presented to our hospital. We used the pelvic coordinate system relative to the anterior pelvic plane and the femur coordinate system relative to the posterior condylar plane. We assessed the anterior, anterolateral, lateral and posterior approaches, and defined each approach line. We evaluated each distance in terms of BMI and gender. 164 hips were assessed. The distance to the centre of the femoral head was the longest in the posterior approach, followed by the lateral, anterolateral, and anterior approaches (p<0.05). Additionally, the distance in each approach increased as patients' BMI increased. The approximated line tilts were almost the same. The correlation coefficients between BMI and the distance to the centre of the femoral head were high in all approaches. In the anterior and anterolateral approaches, men with low BMI had a short distance to the femoral head. The distance for each approach was measured according to the pelvic coordinate system and the femur coordinate system. The results showed no significant differences between them. The distance to the centre of the femoral head is the shortest in the anterior approach, regardless of BMI and gender. The distance in each approach might increase with an increase in BMI. BMI has similar effects in all approaches.