Pelvic Tilt Measurements Research Articles

Inadequate Annotation and Its Impact on Pelvic Tilt Measurement in Clinical Practice.

Accurate pre-surgical templating of the pelvic tilt (PT) angle is essential for hip and spine surgeries, yet the reliability of PT annotations is often compromised by human error, inherent subjectivity, and variations in radiographic quality. This study aims to identify challenges leading to inadequate annotations at a landmark dimension and evaluating their impact on PT. We retrospectively collected 115 consecutive sagittal radiographs for the measurement of PT based on two definitions: the anterior pelvic plane and a line connecting the femoral head's centre to the sacral plate's midpoint. Five annotators engaged in the measurement, followed by a secondary review to assess the adequacy of the annotations across all the annotators. The outcomes indicated that over 60% images had at least one landmark considered inadequate by the majority of the reviewers, with poor image quality, outliers, and unrecognized anomalies being the primary causes. Such inadequacies led to discrepancies in the PT measurements, ranging from -2° to 2°. This study highlights that landmarks annotated from clear anatomical references were more reliable than those estimated. It also underscores the prevalence of suboptimal annotations in PT measurements, which extends beyond the scope of traditional statistical analysis and could result in significant deviations in individual cases, potentially impacting clinical outcomes.

Variations in pelvic tilt during day-to-day activities after total hip arthroplasty measured with an ultrasound system

IntroductionThe pelvis plays a major role in the orientation of total hip arthroplasty (THA) implants and consequently, on the postoperative stability of the new hip joint. The relationship between the spine and pelvis affects the functional orientation of the acetabular cup, although this relationship differs between individuals and the positions encountered in everyday life. We believe this should be factored in when planning the THA procedure. This led us to conduct an in vivo ultrasound study to document the values of pelvic tilt in standing, sitting and lying positions in patients who have advanced hip osteoarthritis, before and after they undergo THA. HypothesisThe pelvic tilt when standing, sitting and lying supine does not change significantly after THA. Materials and methodsThe pelvic tilt, defined as the angle between the anterior pelvic plane and a vertical line was measured using an ultrasound device in 30 patients before the THA procedure and again 6 months later in standing, sitting and lying positions. The measurements were done during an office visit with the patient on an examination table for the lying position, on a chair for the sitting position and with the heels and occiput against the wall for the standing position. ResultsThe preoperative and 6-month postoperative pelvic tilt were –5.6̊±10.4̊ [–30.6̊; 11.7̊] and –5.8̊±7.9̊ [–20.6̊; 10.4̊] (p=0.4129) when standing, –44.5̊±6.10 [–53.8̊; –23.9̊] and –43.5̊±6.9̊ [–54.4̊; –17.3̊] (p=0.5760) when sitting, –88.3̊±5.1̊ [–99.3̊; –78.7̊] and –87.9̊±5.9̊ [–97.6̊; –72.4̊] (p=0.6106) when lying supine, respectively. There was no significant difference in the pelvic tilt before and 6 months after THA procedure. Variations of±5̊; ±5–10̊; ±10–15̊ and 15–20̊ were found in 72% (18); 20% (5); 4% (1) and 4% (1) of patients when lying supine, 56% (14); 36% (9); 8% (2); 0% (0) of patients when standing and 76% (19); 24% (6); 0% (0); 0% (0) when sitting. The mean variation for each patient between the preoperative and 6 months postoperative measurement was 4.8±3.4̊ [0.8̊; 10.4̊] (p=0.4129), 3.5±2.3̊ [0.2̊; 9.1̊] (p=0.5760), and 4.6̊±3.2̊ [1.2̊; 15.4̊] (p=0.6106) for the standing, sitting and lying positions respectively. ConclusionThe pelvic tilt does not significantly change 6 months after THA. Taking into account the various positions used in everyday life may help to optimize the implant position. We have described the use of an affordable, accurate and non-irradiating device that provides fast and easy measurements of pelvic tilt in various positions. Level of evidenceIV.

Validity and application of Doiguchi's pelvic tilt measurement method

BackgroundThe validity of Doiguchi's pelvic tilt measurement method has not been proven. The objective in our study was to validate the method. MethodsOur investigation included 73 total hip arthroplasties (THAs) performed using our cup placement procedure from July 2020 to November 2021. Pelvic tilt formed by the pubic symphysis and sacral promontory (PTPS) in supine and lateral positions was calculated by two methods (the Doiguchi method and the digital reconstructed radiograph (DRR) method using a 3D computer templating system) based on the transverse and longitudinal diameters of the pelvic ring measured immediately before THA. ResultsThere was a strong/moderate correlation in the values of PTPS between the Doiguchi and DRR methods. However, the value of PTPS calculated by the Doiguchi method was significantly lower than that calculated by DRR, and there was a partially direct match. On the other hand, there was no significant difference in the value of PT change from supine to lateral position between the Doiguchi and DRR methods. The PT changes based on both methods were strongly correlated, and the PT change calculated by the Doiguchi method was almost identical to that calculated by the DRR method. ConclusionsDoiguchi's pelvic tilt measurement method was validated for the first time. These results demonstrated that the ratio of the transverse and longitudinal diameters of the pelvic ring was an important factor defining the change in pelvic tilt. The slope in the linear function of the Doiguchi method was found to be almost the correct value, although the intercept of the linear function exhibited individual differences.

The Sacro-femoral-pubic Angle Is Unreliable to Estimate Pelvic Tilt: A Meta-analysis.

The accurate measurement of pelvic tilt is critical in hip and spine surgery. A sagittal pelvic radiograph is most often used to measure pelvic tilt, but this radiograph is not always routinely obtained and does not always allow the measurement of pelvic tilt because of problems with image quality or patient characteristics (such as high BMI or the presence of a spinal deformity). Although a number of recent studies have explored the correlation between pelvic tilt and the sacro-femoral-pubic angle using AP radiographs (SFP method), which aimed to estimate pelvic tilt without a sagittal radiograph, disagreement remains about whether the SFP method is sufficiently valid and reproducible for clinical use. The purpose of this meta-analysis was to evaluate the correlation between SFP and pelvic tilt in the following groups: (1) overall cohort, (2) male and female cohort, and (3) skeletally mature and immature cohorts (young and adult groups, defined as patients older or younger than 20 years). Additionally, we assessed (4) the errors of SFP-estimated pelvic tilt angles and determined (5) measurement reproducibility using the intraclass correlation coefficient. This meta-analysis was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and registered in PROSPERO (record ID: CRD42022315673). PubMed, Embase, Cochrane, and Web of Science were screened in July 2022. The following keywords were used: sacral femoral pubic, sacro femoral pubic, or SFP. The exclusion criteria were nonresearch articles such as commentaries or letters and studies that only investigated relative pelvic tilt rather than absolute pelvic tilt. Although the included studies had different patient recruitment strategies, study quality-wise, they all used an adequate amount of radiographs for landmark annotation and applied a correlation analysis for the relationship between the SFP angle and pelvic tilt. Thus, no risk of bias was found. Participant differences were mitigated via subgroup and sensitivity analyses to remove outliers. Publication bias was assessed using the p value of a two-tailed Egger regression test for the asymmetry of funnel plots, as well as the Duval and Tweedie trim and fill method for potential missing publications to impute true correlations. The extracted correlation coefficients r were pooled using the Fisher Z transformation with a significance level of 0.05. Nine studies were included in the meta-analysis, totaling 1247 patients. Four studies were used in the sex-controlled subgroup analysis (312 male and 460 female patients), and all nine studies were included in the age-controlled subgroup analysis (627 adults and 620 young patients). Moreover, a sex-controlled subgroup analysis was conducted in two studies with only young cohorts (190 young male patients and 220 young female patients). The overall pooled correlation coefficient between SFP and pelvic tilt was 0.61, with high interstudy heterogeneity (I 2 = 76%); a correlation coefficient of 0.61 is too low for most clinical applications. The subgroup analysis showed that the female group had a higher correlation coefficient than the male group did (0.72 versus 0.65; p = 0.03), and the adult group had a higher correlation coefficient than the young group (0.70 versus 0.56; p < 0.01). Three studies reported erroneous information about the measured pelvic tilt and calculated pelvic tilt from the SFP angle. The mean absolute error was 4.6° ± 4.5°; in one study, 78% of patients (39 of 50) were within 5° of error, and in another study, the median absolute error was 5.8º, with the highest error at 28.8° (50 female Asian patients). The intrarater intraclass correlation coefficients ranged between 0.87 and 0.97 for the SFP angle and between 0.89 and 0.92 for the pelvic tilt angle, and the interrater intraclass correlation coefficients ranged between 0.84 and 1.00 for the SFP angle and 0.76 and 0.98 for the pelvic tilt angle. However, large confidence intervals were identified, suggesting considerable uncertainty in measurement at the individual radiograph level. This meta-analysis of the best-available evidence on this topic found the SFP method to be unreliable to extrapolate sagittal pelvic tilt in any patient group, and it was especially unreliable in the young male group (defined as patients younger than age 20 years). Correlation coefficients generally were too low for clinical use, but we remind readers that even a high correlation coefficient does not alone justify clinical application of a metric such as this, unless further subgroup analyses find low error and low heterogeneity, which was not the case here. Further ethnicity-segregated subgroup analyses with age, sex, and diagnosis controls could be useful in the future to determine whether there are some subgroups in which the SFP method is useful. Level III, diagnostic study.

Measurement of pelvic tilt and rotation on AP radiographs using HipRecon: Validation and comparison to other parameters.

In this paper, we present and evaluate HipRecon, a noncommercial software package that simultaneously calculates pelvic tilt and rotation from an anteroposterior pelvis radiograph. We asked: What is the (1) accuracy and precision, (2) robustness, and (3) intra-/interobserver reliability/reproducibility of HipRecon to analyze both pelvic tilt and rotation on conventional AP pelvis radiographs? (4) How does the prediction of pelvic tilt on AP pelvis radiographs using HipRecon compare to established measurement methods? We compared the actual pelvic tilt of 20adult human cadaveric pelvises with the calculated pelvic orientation based on an AP pelvis radiograph using HipRecon software. The pelvises were mounted on a radiolucent fixture and a total of 380 AP pelvis radiographs with different configurations were acquired. In addition, we investigated the correlation between actual tilt and the tilt calculated using HipRecon and seven other established measurement methods. The calculated software accuracy was 0.2 ± 2.0° (-3.6-4.1) for pelvic tilt and 0.0 ± 1.2° (-2.2-2.3, p = 0.39) for pelvic rotation. The Bland-Altman analysis showed values that were evenly and randomly spread in both directions. HipRecon showed excellent consistency for the measurement of pelvic tilt and rotation (intraobserver intraclass-correlation coefficient[ICC]: 0.99 [95% CI: 0.99-0.99] and interobserver ICC 0.99 [95% CI: 0.99-0.99]). Of all eight analyzed methods, the highest correlation coefficient was found for HipRecon (r = 0.98, p < 0.001). In the future, HipRecon could be used to detect changes in patient-specific pelvic orientation, helping to improve clinical understanding and decision-making in pathologies of the hip.

THE “GOOD DOCTOR” PERFORMANCE OF RADIOLOGICAL ANNOTATION: MEASURING PELVIC TILT AS AN EXAMPLE

Human error is usually evaluated using statistical descriptions during radiographic annotation. The technological advances popularized the “non-human” landmarking techniques, such as deep learning, in which the error is presented in a confidence format that is not comparable to that of the human method. The region-based landmark definition makes an arbitrary “ground truth” point impossible. The differences in patients’ anatomies, radiograph qualities, and scales make the horizontal comparison difficult. There is a demand to quantify the manual landmarking error in a probability format.Taking the measurement of pelvic tilt (PT) as an example, this study recruited 115 sagittal pelvic radiographs for the measurement of two PTs. We proposed a method to unify the scale of images that allows horizontal comparisons of landmarks and calculated the maximum possible error using a density vector. Traditional descriptive statistics were also applied.All measurements showed excellent reliabilities (intraclass correlation coefficients &gt; 0.9). Eighty-four measurements (6.09%) were qualified as wrong landmarks that failed to label the correct locations. Directional bias (systematic error) was identified due to cognitive differences between observers. By removing wrong labels and rotated pelves, the analysis quantified the error density as a “good doctor” performance and found 6.77°-11.76° maximum PT disagreement with 95% data points.The landmarks with excellent reliability still have a chance (at least 6.09% in our case) of making wrong landmark decisions. Identifying skeletal contours is at least 24.64% more accurate than estimating landmark locations. The landmark at a clear skeletal contour is more likely to generate systematic errors. Due to landmark ambiguity, a very careful surgeon measuring PT could make a maximum 11.76° random difference in 95% of cases, serving as a “good doctor benchmark” to qualify good landmarking techniques.

EVALUATING PELVIC TILT USING MEASUREMENTS FROM ANTEROPOSTERIOR PELVIC RADIOGRAPHS: A META-ANALYSIS OF SACRO-FEMORAL-PUBIC (SFP) METHOD

Accurate measurement of pelvic tilt (PT) is critical in diagnosing hip and spine pathologies. Yet a sagittal pelvic radiograph with good quality is not always available. Studies explored the correlation between PT and sacro-femoral-pubic (SFP) angle from anteroposterior (AP) radiographs yet demonstrated conflicting conclusions about its feasibilities. This study aims to perform a cohort-controlled meta-analysis to examine the correlation between the SFP angle and PT and proposes an application range of the method.This study searched PubMed, Embase, Cochrane, and Web of Science databases for studies that evaluated the correlation between SFP angle and PT. The Pearson's correlation coefficient r from studies were tabulated and compared. Pooled r for overall and gender/age (teenage or adult) controlled subgroup were reported using Fisher's Z transformation. Heterogeneity and publication bias were evaluated using Egger's regression test for the funnel plot asymmetry.Eleven studies were recruited, with nine reported r (totalling 1,247 patients). The overall pooled r was 0.61 with high inter-study heterogeneity (I2 = 75.95%). Subgroup analysis showed that the adult group had a higher r than the teenage group (0.70 versus 0.56, p &lt; 0.001). Although statistically insignificant (p = 0.062), the female group showed a higher r than the male group (0.72 versus 0.65).The SFP method must be used with caution and should not be used in the male teenage group. The current studies did not demonstrate that the SFP method was superior to other AP landmarks correlating to PT. Identical heterogeneity was observed among studies, indicating that more ethnicity-segregated and gender-specific subgroup studies might be necessary. More data input analysing the errors will be useful.

Repeatability of Inertial Measurement Units for Measuring Pelvic Mobility in Patients Undergoing Total Hip Arthroplasty.

Consideration of pelvic mobility when positioning implants for total hip arthroplasty (THA) has been shown to reduce the risk of complications such as dislocation, squeaking and excessive wear. We aim to test the repeatability of pelvic tilt measurements taken between three positions (standing, flexed-seated and step-up) by an inertial measurement unit (IMU) and hence, evaluate their reliability in screening for high pelvic mobility in patients undergoing THA. The repeated IMU measurements of pelvic tilt were analysed for consistency and compared with measures taken by x-ray analysis. Our study showed greater variation in measures taken by the IMU particularly in the flexed-seated position. The patient's pelvic tilt in this position negatively correlated with their mid-back angle, suggesting the posture of the patient is a source of variation in the flexed-seated position if not kept consistent during assessments. IMUs were overall able to produce accurate and reliable measurements of pelvic tilt; however, protocols will need to be adjusted to factor in a patient's mid-back angle when taking future readings.

Can Pelvic Orientation Be Accurately Predicted Using One Radiographic View Alone?

AbstractPelvic positioning during total hip arthroplasty (THA) can affect the functional position of the acetabular component. A comprehensive understanding of pelvic orientation before THA is necessary to allow for proper cup positioning and mitigate the risks of postoperative complications. Measurements using anteroposterior (AP) radiographs have been described as an effective means of accurately predicting pelvic functional orientation. The purpose of our study was to describe the accuracy of assessing pelvic tilt using AP radiographs alone. An online survey was created and sent to a cohort of fellowship-trained adult reconstruction (AR) surgeons. The survey consisted of 65 standing AP pelvis radiographs. Participants were asked to score each radiograph as (1) anterior pelvic tilt more than 10 degrees, (2) posterior pelvic tilt more than 10 degrees, or (3) neutral. Responses were then compared with measurements of pelvic tilt made on lateral standing pelvic radiographs. Demographic data, such as country of practice, surgical volume, surgical approach, familiarity with spinopelvic mobility, and planning with spinopelvic mobility were evaluated. Categorical variables were compared using chi-squared analysis and analysis of variance. Continuous variables were assessed using unpaired, two-tailed Student's t-tests. A total of 45 surgeons completed the survey. The average correct predictive value of pelvic tilt between all surgeons was 53.2%. Of the responding surgeons, 51.2% performed greater than 100 cases per year. Fifty percent of surgeons reported that they were “not so familiar” or “somewhat familiar” with the principles of spinopelvic mobility. Also, 43.5% of surgeons reported that they did not routinely use spinopelvic mobility principles in THA planning. Pelvic orientation before THA is poorly predicted in our cohort of surveyed fellowship-trained AR surgeons with standing AP pelvis radiographs alone. Given the limited understanding of these principles within our cohort, preoperative evaluation of spinopelvic parameters with AP radiographs may require supplementation with lateral pelvic views to ensure detailed assessment and accurate preoperative planning. This is a prospective survey study and reflects level of evidence II.

Assessing Pelvic Tilt in Patients Undergoing Total Hip Arthroplasty Using Sensor Technology

BackgroundThe purpose of our study was to assess the accuracy of a commercially available wearable sensor in replicating pelvic tilt movement in both the sitting and standing position in patients before total hip arthroplasty.MethodsThis prospective study evaluated patients undergoing a primary unilateral total hip arthroplasty by a single surgeon. Patients were excluded if they had a body mass index (BMI) greater than 40 kg/m2. Two sensors were adhered directly to patients’ skin at S2 and T12. The S2 angle was recorded on the sensor at maximum flexion and extension angles and compared with pelvic tilt measurements on both sitting and standing radiographs. The primary outcomes recorded were patients’ pelvic tilts measured using radiographs (PT-RAD) and sensors (PT-SEN), with Pearson correlation coefficients and intraclass correlation coefficients (ICCs) calculated.ResultsSixty-one patients (35 males and 26 females) with an average age of 61.5 ± 8.5 years and BMI of 26.9 ± 4.1 kg/m2 were analyzed. The mean prestanding PT-RAD and PT-SEN were 1.5 ± 8.3 and 1.0 ± 8.1, respectively, with an ICC of 0.98 (95% confidence interval, 0.96-0.99). The mean presitting PT-RAD and PT-SEN were -21.9 ± 12.5 and -20.9 ± 11.7, respectively, with an ICC of 0.97 (95% confidence interval, 0.95-0.98). The multiple R2 was 0.95 for the prestanding and presitting comparisons. The R2 for all comparisons between PT-RAD and PT-SEN was >0.85, regardless of BMI or sex.ConclusionsAlthough the use of wearable technology may have limitations, based on our results, a wearable sensor is accurate in replicating pelvic tilt movement.

Reliability and Reproducibility of Sacro-Femoro-Pubic Angle Measurements on Anteroposterior Pelvis Radiographs.

BackgroundThe sacro-femoro-pubic (SFP) angle is a surrogate measurement for pelvic tilt obtained on anteroposterior (AP) pelvis radiographs. It is unknown whether the SFP angle can be measured reliably by senior surgeons and trainees alike.MethodsWe conducted an intrareader and interreader reliability study using preoperative AP pelvis radiographs. Using our hospital electronic database, we randomly selected 31 subjects undergoing primary total hip arthroplasty. An attending orthopedic surgeon and two orthopedic surgery residents performed two separate SFP angle measurements for each subject. Intrareader and interreader agreement were measured using intraclass correlation coefficients (ICC).ResultsPairwise intrareader and interreader ICCs ranged from 0.91 to 0.99. Overall ICC was 0.94. Interreader ICCs between the attending surgeon and each orthopedic resident were 0.93 and 0.98, and the ICC between orthopedic residents was 0.91. Interreader mean differences for SFP angle measurements were 2.32 degrees or less: -2.03 (standard deviation: 2.23) and 0.29 (1.64) between the attending surgeon and each orthopedic resident, and 2.32 (2.44) between orthopedic residents.ConclusionSFP angle may be measured reliably on AP pelvis radiographs by senior clinicians and trainees. SFP angle measurement may prove helpful as an alternative to pelvic tilt measurements when lateral pelvic radiographs are not available.

A Novel Method for Correcting Pelvic Tilt on Anteroposterior Pelvic Radiographs.

BackgroundAnteroposterior (AP) pelvic radiographs remain the standard for pre- and postoperative imaging during total hip arthroplasty (THA), despite the known limitation of plain films, including the inability to adequately account for distortion caused by variations in pelvic orientation such as pelvic tilt. The purpose of this study was to develop a reliable method for correcting pelvic tilt on AP pelvic radiographs in patients undergoing THA.MethodsCT scans from 20 patients/cadaver specimens (10 male, 10 female) were used to create 3D renderings, from which synthetic radiographs of each pelvis were generated. For each pelvis, 13 synthetic radiographs were generated, showing the pelvis at between -30° and 30° of pelvic tilt, in 5° increments. On each image, eight unique parameters/distances were measured to determine the most appropriate parameters for the calculation of pelvic tilt. The most reliable and accurate of these parameters was determined via regression analysis and used to create gender-specific nomograms from which pelvic tilt measurements could be calculated. The accuracy and reliability of the nomograms and correction method were subsequently validated using both synthetic radiographs (n=50) and stereoradiographic images (n=58).ResultsOf the eight parameters measured, the vertical distance between the superior margin of the pubic symphysis and the transischial line (PSTI) was determined to be the most reliable (r=-0.96, ICC=0.94). Using that parameter and applying the associated nomograms to 50 synthetic radiographs of random pelvic tilt, the mean difference between the actual pelvic tilt and that calculated using the correction method was 0.1°±5.1° (p=0.98, r=0.96). In 58 stereoradiographic images, the mean difference between actual and measured pelvic tilt was -0.2°±6.4° (p=0.74, r=0.77). The pooled results indicate no significant difference between actual (2.2°±13.9°) and measured pelvic tilt (2.1°±14.3°, p=0.93, r=0.91). No significant differences were noted based on gender.ConclusionsOur method of correcting for pelvic tilt using the vertical distance from the pubic symphysis to the transischial line provides a reliable method for correcting for pelvic tilt on AP pelvic radiographs.

Does Compensatory Anterior Pelvic Tilt Decrease After Bilateral Periacetabular Osteotomy?

The kinetic link among the lumbar spine, pelvic tilt, and the hip has been hypothesized, but this relationship requires further study in acetabular dysplasia. Anecdotal reports suggest that patients may compensate for acetabular dysplasia with an involuntary increase in anterior pelvic tilt; it is not known if this relationship is affected by acetabular reorientation. (1) Does compensatory pelvic tilt decrease on preoperatively obtained standing AP pelvis radiographs compared with those obtained at a minimum of 6 months after bilateral periacetabular osteotomy (PAO)? (2) Does a modified surrogate measurement of pelvic tilt, the pubic symphysis to sacroiliac (PS-SI) index, correlate with a physical synthetic bones model in which pelvic tilt can be directly measured? (3) Can the PS-SI index demonstrate high interrater reliability? We assessed the surgical records of one surgeon, who participates in the longitudinally maintained Academic Network of Conservational Hip Outcomes Research (ANCHOR) registry, for patients who had undergone the second side of a staged bilateral PAO between 2007 and 2016; there were 113 such patients. Of those, 70 (62%) were lost to followup within 6 months of the second PAO or did not have adequate imaging studies, and another three (3%) were excluded for prespecified reasons, leaving 40 (35%) for evaluation in this retrospective study. Standing preoperative and most recent postoperative AP pelvis radiographs were used to measure the Tönnis angle, anterior wall index, posterior wall index, lateral center-edge angle, pubis symphysis-to-sacrococcygeal junction distance, and the PS-SI index. The most recent radiographs were obtained at a mean of 16 ± 6 months after the second PAO. We chose 6 months as the minimum because at this time point, the majority of patients have reached their maximum clinical improvement and are no longer limited by postoperative muscle dysfunction. Statistical analysis was performed using the intraclass correlation coefficient (ICC) for interrater reliability and paired t-tests for assessing change in measurements from pre- to postoperative. Additionally, a model was created using a physical synthetic bones model in which pelvic tilt could be directly measured. This model was secured through bilateral acetabuli on a mount and rotated through 5° increases in pelvic tilt. AP pelvis radiographs were obtained at each point, the PS-SI index was measured, and a regression analysis performed to evaluate for trend. Overall, 37 of 40 patients (93%) had a decrease in pelvic tilt, as measured by the PS-SI index. The mean amount of pelvic tilt as measured by the PS-SI index decreased after surgery when comparing the preoperative with latest radiographs on this parameter (97 ± 14 mm versus 89 ± 13 mm, mean difference 8 ± 9 mm; 95% confidence interval, -11 to -5; range 17 increase to 24 decrease, p < 0.001). A linear relationship between pelvic tilt and PS-SI index (PS-SI index = 5.0° + 3.6° tilt, R = 0.99) was identified in the synthetic bones validation model. Finally, the interrater reliability was found to be excellent for the PS-SI index preoperatively (ICC = 0.986) and postoperatively (ICC = 0.988). We found a modest reduction in anterior pelvic tilt after bilateral PAO. This finding suggests that acetabular reorientation affects pelvic position. In clinical practice, patients with acetabular dysplasia may compensate with dynamic and reversible changes in pelvic tilt. The PS-SI index is a reproducible tool to measure the height of the pelvic inlet as an assessment of pelvic tilt. In the future, clinical studies should evaluate the clinical implications of these radiographic findings, including the assessment of back pain, which although multifactorial may be influenced by pelvic tilt. Level III, therapeutic study.

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.

The Immediate Effects of Posterior Pelvic Tilt with Taping on Pelvic Inclination, Gait Function and Balance in Chronic Stroke Patients*

PURPOSE: The purpose of this study is to identify the immediate effect of posterior pelvic tilt taping on anterior pelvic inclination, gait function, and balance in chronic stroke patients. METHODS: Fourteen chronic stroke subjects were enrolled in this study. Subjects who consented to participate in this cross-over experiment were assigned three interventions: posterior pelvic tilt taping, placebo taping, and no taping, in random order. After tape application, subjects were asked to complete: 1) Anterior pelvic tilt measurement, 2) 10-Meter Walk test, and 3) Limits of stability (LOS) test. To eliminate the learning effect of the tape after tearing off the tape, a 10 minute break was given between posterior pelvic tilt taping intervention and placebo taping intervention. RESULTS: Significant decreases were observed for the anterior pelvic inclination on both sides after posterior pelvic tilt taping application compared with placebo taping and no taping application (p .05). CONCLUSION: Posterior pelvic tilt taping in chronic stroke patients decreases the inappropriate anterior pelvic inclination immediately and improves gait function, but it has little effect on balance.

PELVIC TILT: RELIABILITY OF MEASURING THE STANDING POSITION AND RANGE OF MOTION IN ADOLESCENT ATHLETES

BackgroundStanding pelvic posture remains a common assessment in sports therapy. The palpation technique assessing the relative position of the anterior and posterior superior iliac spines is widely used to quantify...

Visual Observations Compared With Palpation Meter Measurements for Reliable Measurements of Pelvic Tilt and Height Difference

Visual Observations Compared With Palpation Meter Measurements for Reliable Measurements of Pelvic Tilt and Height Difference

Textile-based Micro Electro Mechanical System (MEMS) Accelerometer for Pelvic Tilt Mesurement

This project proposes the application of textile-based MEMS accelerometer for measuring pelvic tilt angle. Textile-based accelerometer provides an alternative to the costly and hazardous radiographic measurement of pelvic tilt. The flexibility of textile structure makes it more advantageous to conform to body contour than rigid digital inclinometer and more accurate than indirect trigonometric measurement. Conventional MEMS devices are usually constructed from silicon-based material, which is expensive and requires access to clean room equipments. Textile material is relatively low-cost, flexible, lightweight, readily available, environmental friendly and easy to use. Silver nanoparticles (AgNPs) are used here as the transducer material to induce piezoresistive effect when stress is applied on the textile. The electrode and resistor parts of the accelerometer were made by stamping different volume of AgNPs on a cotton cloth. Starch ironing method was used to stiffen the textile. The force is applied by the 10g mass attached at the tip of the accelerometer. The working principle of this accelerometer is based on piezoresistive effect generated by the conductive nanomaterials patterned on textile substrate. When a force is applied, the accelerometer experiences mechanical stress which causes change in its resistance. The initial resistance for the accelerometers ranges from 17.00 to 30.97 MΩ. When the tilt angle increases, the relative resistance change also increases in nearly linear behavior. The concept of textile-based accelerometer is proven feasible as there is a transducible effect of resistance change when the sample is tilted.

Defining a reference range of acetabular inclination and center-edge angle of the hip in asymptomatic individuals

Acetabular morphology is an important predictor of the severity of osteoarthrosis and survival of hip prostheses but there is limited data on the normal range of acetabular measurements on plain radiographs. The aim of this project was to determine the statistically normal ranges of acetabular inclination (AI) and center-edge angle (CEA). One hundred coronal CT localizers (50 men and 50 women aged 20-30 years) were included in this study. All the patients underwent CT examination for thoracic or intra-abdominal indications. Patients with pelvic disease, fractures, history of serious trauma, or previous pelvic surgery were excluded. One pair of independent observers measured the AI and pelvic tilt (PT), and a further pair measured the center-edge angle (CEA), using electronic calipers on a high-resolution PACS workstation. AI and CEA measurements were obtained for 200 hips. There was very good intra-class correlation between the observers (r = 0.7-0.8). The mean AI was 38.8° (2SD 32.1-45.5°). That in men was 38.0° (2 SD 31.8-44.1°) and 39.6° (2 SD 32.7-46.8°) in women, which was statistically significantly different (p < 0.001). The mean CEA measurement for all patients was 36.3° (SD 13.8°), for men 37.7° (SD 10.8°) and for women 34.9° (SD 11.4°) with a statistically significant gender difference (p < 0.001). The mean pelvic tilt measurement (sacro-coccygeal-pubic symphysis) was 38.3 mm (2 SD 18.3-58.3 mm) with a significant gender difference (p < 0.001). The results of this study define reference ranges of two common measures of acetabular morphology and confirm statistically significant differences between men and women.

Computer assisted determination of acetabular cup orientation using 2D–3D image registration

2D-3D image-based registration methods have been developed to measure acetabular cup orientation after total hip arthroplasty (THA). These methods require registration of both the prosthesis and the CT images to 2D radiographs and compute implant position with respect to a reference. The application of these methods is limited in clinical practice due to two limitations: (1) the requirement of a computer-aided design (CAD) model of the prosthesis, which may be unavailable due to the proprietary concerns of the manufacturer, and (2) the requirement of either multiple radiographs or radiograph-specific calibration, usually unavailable for retrospective studies. In this paper, we propose a new method to address these limitations. A new formulation for determination of post-operative cup orientation, which couples a radiographic measurement with 2D-3D image matching, was developed. In our formulation, the radiographic measurement can be obtained with known methods so that the challenge lies in the 2D-3D image matching. To solve this problem, a hybrid 2D-3D registration scheme combining a landmark-to-ray 2D-3D alignment with a robust intensity-based 2D-3D registration was used. The hybrid 2D-3D registration scheme allows computing both the post-operative cup orientation with respect to an anatomical reference and the pelvic tilt and rotation with respect to the X-ray imaging table/plate. The method was validated using 2D adult cadaver hips. Using the hybrid 2D-3D registration scheme, our method showed a mean accuracy of 1.0 +/- 0.7 degrees (range from 0.1 degrees to 2.0 degrees) for inclination and 1.7 +/- 1.2 degrees (range from 0.0 degrees to 3.9 degrees) for anteversion, taking the measurements from post-operative CT images as ground truths. Our new solution formulation and the hybrid 2D-3D registration scheme facilitate estimation of post-operative cup orientation and measurement of pelvic tilt and rotation.