Pelvic rotation and tilt can cause misinterpretation of the acetabular index measured on radiographs

Influence of Femoral Position and Pelvic Projection on Norberg Angle Measurements

OBJECTIVE

 Canine hip dysplasia is a common orthopaedic disease in dogs. The Norberg angle value is a measure of hip joint laxity. The aim of this study was to quantify the degree of rotation necessary to consider the radiograph as inadequately positioned and to determine the influence of rotation on the Norberg angle.

STUDY DESIGN

 Three sets of radiographs with different positioning and projections were acquired using 10 canine cadavers. Rotation of the pelvis was simulated by rotating the X-ray tube without changing the position of the patient.

RESULTS

 In dorsoventral projections, the Norberg angle value is increased by 3.2 to 5.8%. Due to rotation along the long axis, the Norberg angle increases on one side and decreases on the contralateral side by approximately the same value. Rotation of greater than 2 degrees in a lateral direction is visually perceived by the observer as tilted. Rotation of the projection in the caudoventral to craniodorsal direction causes mild increase of the Norberg angle (≤1%), while rotation of the projection in a cranioventral to caudodorsal direction causes moderate (≤2%) decrease of the Norberg angle. Rotation of less than -10 degrees (caudoventral to craniodorsal) or greater than 10 degrees (cranioventral to caudodorsal) is visually perceived as tilted.

CONCLUSION

 Tilted images that are subjectively perceived evaluable have only little effect on the Norberg angle and are therefore probably acceptable. Dorsoventral projections can be recognized based on the proximal position of the patella and should be excluded from evaluation, as the Norberg angle value can be falsely increased.

A cross-sectional study evaluating patients' preferences for Salter innominate osteotomy

BACKGROUND

Residual acetabular dysplasia in children after reduction of hip dislocation is often treated using Salter innominate osteotomy to prevent future osteoarthritis. Preventive surgery for asymptomatic patients, which could result in overtreatment, should be carefully applied with consideration of patients' opinions. In this study, we aimed to describe opinions on Salter innominate osteotomy as preventive surgery for children among adult patients who had undergone periacetabular osteotomy for hip pain due to hip dysplasia.

METHODS

A mail-in questionnaire survey was conducted with 77 patients who underwent periacetabular osteotomy. Participants responded whether they would recommend Salter innominate osteotomy as preventive surgery for children and the reason for their opinion. We also performed a patient-based evaluation using the Japanese Orthopaedic Association Hip-Disease Evaluation Questionnaire and assessed clinical outcome measures with the Japanese Orthopedic Association score. Their recommendations and reasons were evaluated, and associations between their opinions and demographic and clinical characteristics were analyzed.

RESULTS

Forty-three patients (56%) responded to the questionnaire. Of these, 10 (23%) patients recommended undergoing Salter innominate osteotomy, 28 (65%) patients did not, and 5 (12%) patients responded they were undecided. No significant association was observed between their opinions and demographic/clinical characteristics evaluated in the survey. The most frequent reason for why they do not recommend Salter innominate osteotomy was related to uncertainty about future hip pain.

CONCLUSIONS

In total, 65% of the study participants did not recommend Salter innominate osteotomy for children with risk of dysplasia in the future. Participants' preferences regarding preventive surgery were not influenced by demographic and clinical characteristics.

A novel approach for screening standard anteroposterior pelvic radiographs in children

Anteroposterior pelvic radiography is the first-line imaging modality for diagnosing developmental dysplasia of the hip (DDH). Nonstandard radiographs with pelvic malposition make the correct diagnosis of DDH challenging. However, as the only method available for screening standard pelvic radiographs, traditional manual assessment is relatively laborious and potentially erroneous. We retrospectively collected 3,247 pelvic radiographs. There were 2,887 radiographs randomly selected to train and optimize the AI model. Then 362 radiographs were used to test the model's diagnostic performance. Its diagnostic accuracy was assessed using receiver operating characteristic (ROC) curves and measurement consistency using Bland-Altman plots. In 362 radiographs, the AI model's area under ROC curves, accuracy, sensitivity, and specificity for quality assessment was 0.993, 99.4% (360/362), 98.6% (138/140), and 100.0% (222/222), respectively. Compared with clinicians, the 95% limits of agreement (Bland-Altman analysis) for pelvic tilt index (PTI) and pelvic rotation index (PRI), as determined by the model, were -0.052-0.072 and -0.088-0.055, respectively.

CONCLUSIONS

The artificial intelligence-assisted method was more efficient and highly consistent with clinical experts. This method can be used for real-time validation of the quality of pelvic radiographs in current picture archiving and communications systems (PACS).

WHAT IS KNOWN

• Nonstandard pediatric radiographs with pelvic malposition make the correct diagnosis of developmental dysplasia of the hip (DDH) challenging. • Traditional manual assessment remains the only method available for screening standard pediatric pelvic radiographs, which is relatively laborious and potentially erroneous.

WHAT IS NEW

• This study proposed an artificial intelligence-assisted model to assess the quality of pediatric pelvic radiographs accurately and efficiently. • We recommend the integration of the model into current picture archiving and communications systems (PACS) for real-time screening of standard pediatric pelvic radiographs.

MRI May Be More Valuable than Pelvic Radiographs in the Assessment of Paediatric Borderline Acetabular Dysplasia

The osseous acetabular index (OAI) and cartilaginous acetabular index (CAI) is often used in diagnosing acetabular dysplasia (AD) in children. We examined the reliability of OAI and CAI in AD diagnostics and compared OAI measurements obtained from radiographs versus MRI. Four raters performed retrospective repeated measurements of the OAI and CAI on pelvic radiographs and MRI scans of 16 consecutive patients (mean age 5 years (2-8)) examined for borderline AD during a period of 2½ years. In MRI, the image selected for analysis by the raters was also registered. Spearman's correlation, scatter plots, and Bland-Altman (BA) plots were analysed for correlation between OAI on pelvic radiographs (OAIR) and MRI scans (OAIMRI), while intra- and interrater reliability was assessed for OAIR, OAIMRI, CAI, and MRI image selection using intraclass correlation coefficients (ICC). ICC values for inter- and intrarater reliability of OAIR, OAIMRI, and CAI were all above 0.65, with no significant differences observed. ICC values (CI) for individual raters' MRI image selection was 0.99 (0.998-0.999). The mean difference (95% CI) between OAIR and OAIMRI was -0.99 degrees (-1.84; -0.16), while the mean absolute difference (95% CI) between OAIR and OAIMRI was 3.68 degrees (3.17; 4.20). Absolute differences between OAIR and OAIMRI was independent of pelvic positioning or time interval between radiographs and MRI scans. OAI and CAI had high Intrarater reliability but mediocre interrater reliability. There was an absolute difference of 3.7 degrees in OAI between pelvic radiographs and MRI scans.

Intra- and interobserver variability of novel magnetic resonance imaging parameters for hip screening and treatment outcomes at age 5 years

BACKGROUND

The outcome measure of neonatal hip screening is usually the radiographic acetabular index.

OBJECTIVE

To assess the feasibility of magnetic resonance imaging (MRI) without sedation and compare the utility of outcome parameters measured from MRI images.

MATERIALS AND METHODS

The invitation for MRI scanning at 5 years of age was incorporated into follow-up for babies who had more than one ultrasound examination during treatment or surveillance.

RESULTS

Diagnostic images were obtained in 132 of 134 children. The mean osseous acetabular index (standard deviation [SD]) was 16.6 (3.3) degrees for the right hip and 17.8 (3.2) for the left; the values for the cartilaginous acetabular index were 3.1 (3) and 3.4 (3.2). The mean downslope of a tangent to the lateral bony acetabular roof was 10.4 (4.5) and 9.0 (4.3) with respect to Hilgenreiner's line and that of a line drawn through the apex to the margin of the acetabulum was 3.7 (4.6) and 3.9 (4.7). Intra- and interobserver variation was greater for measures specific to the lateral acetabular roof than for ossific and cartilaginous indices. There was significant negative correlation between the downslope of the tangent to the lateral roof index and the age at onset of treatment on both sides, but no significant correlation for ossific or cartilaginous acetabular indices or apex-marginal index.

CONCLUSION

MRI without sedation at 5 years of age is feasible as an outcome measure for hip screening programmes. Parameters specific to the lateral acetabulum may better reflect acetabular sufficiency, despite having greater observer variation than cartilaginous and ossific acetabular indices.

Clinical thought-based software for diagnosing developmental dysplasia of the hip on pediatric pelvic radiographs

Background

The common methods of radiographic diagnosis of developmental dysplasia of the hip (DDH) include measuring hip parameters and quantifying the degree of hip dislocation. However, clinical thought-based analysis of hip parameters may be a more effective way to achieve expert-like diagnoses of DDH. This study aims to develop a diagnostic strategy-based software for pediatric DDH and validate its clinical feasibility.

Methods

In total, 543 anteroposterior pelvic radiographs were retrospectively collected from January 2017 to December 2021. Two independent clinicians measured four diagnostic indices to compare the diagnoses made by the software and conventional manual method. The diagnostic accuracy was evaluated using the receiver operator characteristic (ROC) curves and confusion matrix, and the consistency of parametric measurements was assessed using Bland-Altman plots.

Results

In 543 cases (1,086 hips), the area under the curve, accuracy, sensitivity, and specificity of the software for diagnosing DDH were 0.988-0.994, 99.08%-99.72%, 98.07%-100.00%, and 99.59%, respectively. Compared with the expert panel, the Bland-Altman 95% limits of agreement for the acetabular index, as determined by the software, were -2.09°-2.91° (junior orthopedist) and -1.98°-2.72° (intermediate orthopedist). As for the lateral center-edge angle, the 95% limits were -3.68°-5.28° (junior orthopedist) and -2.94°-4.59° (intermediate orthopedist).

Conclusions

The software can provide expert-like analysis of pelvic radiographs and obtain the radiographic diagnosis of pediatric DDH with great consistency and efficiency. Its initial success lays the groundwork for developing a full-intelligent comprehensive diagnostic system of DDH.

Comparison of Transfer Learning Models in Pelvic Tilt and Rotation Measurement in Pediatric Anteroposterior Pelvic Radiographs

The rotation and tilt of the pelvis during anteroposterior pelvic radiography can lead to misdiagnosis of developmental dysplasia of the hip (DDH) in children. At present, no method exists for accurately and conveniently measuring the precise rotation and tilt angles of pelvic on radiographs. The objective of this study was to develop several rotation and tilt measurement models using transfer learning and digital reconstructed radiographs (DRRs), and to compare their performances on pelvic radiographs. Based on the inclusion criteria, 30 of 92 children who underwent 3D hip CT scans at Xijing Hospital from 2015 to 2020 were included in the study. Using DRR techniques, radiographs were generated by rotating and tilting the pelvis in CT datasets at - 12 to 12° (projected every 3°) and were randomized to a 2:1:1 ratio of training dataset, validation dataset, and test dataset. Five pre-trained networks, including VGG16, Xception, VGG19, ResNet50 and InceptionV3 were used to develop pelvic rotation measurement models and tilt measurement models, and these models were trained with training dataset. The callback function was used during the training to slow down the learning rate when learning was stalled. Then, the validation set was used to optimize each model and compare their performances. At last, we tested the final performances of optimal rotation measurement model and optimal tilt measurement model on test dataset. The mean absolute error (MAE) was employed to assess the performance of the models. A total of 2430 pelvic DRRs were collected based on 30 CT datasets. Among 5 pre-trained transfer learning models, VGG16-Tilt achieved the best tilt prediction performance at the same BS and different LR. VGG16-Tilt model achieved its best performance on validation set at LR = 0.001 and BS = 4, and the final MAE on the test set was 0.5250°. In terms of rotation prediction, VGG16-Rotation also achieved the best performance, and it achieved its best performance on validation set at LR = 0.002 and BS = 8. The final MAE of VGG16-Rotation on the test set was 1.0731°. Pretrained transfer learning models worked well in predicting tilt and rotation angles of the pelvis on radiographs in children. Among them, VGG16-Tilt and VGG16-Rotation had the best effect in dealing with such problems despite their simple structures. These models deployed in devices can give orthopedic surgeons a powerful aid in DDH diagnosis.

Rotational abnormalities in dysplastic hips and how to predict acetabular torsion

OBJECTIVES

The aim of this study was to investigate the degree to which conventional radiography can represent the acetabular and femoral rotational alignment profile between dysplastic and borderline-dysplastic hips.

METHODS

A retrospective trial was conducted including 56 borderline-dysplastic and dysplastic hips at a mean age of 28.9 years (range from 18 to 46). Inclusion criteria consisted of symptomatic patients with hip dysplasia undergoing 2-dimensional radiography as well as computed tomography. On radiography, the lateral center edge angle, acetabular hip index, hip lateralization index, acetabular index angle, and the Sharp angle were measured, and the presence of a crossover sign was noted. In computed tomography, the full rotational profile of the lower limb was measured.

RESULTS

Significant correlations were observed in the overall analysis between the anteversion of the acetabulum and the hip lateralization index (mean 0.56, coefficient of regression (CoR) -32.35, p = 0.011) as well as the acetabular index angle with a mean of 11.50 (CoR 0.544, p = 0.018). Similar results were found in the subgroup of dysplastic hips with an acetabular index angle of 13.9 (p = 0.013, CoR 0.74). For the borderline-dysplastic group, no significant correlations between the pelvis radiography and rotational CT were seen.

CONCLUSION

Although the femoral and acetabular torsion cannot be predicted from x-rays, the anteversion of the acetabulum correlates with the acetabular index angle, the hip lateralization index, and eventually the beta angle in dysplastic hips. For borderline-dysplastic hips, such results did not show up, which strongly illustrates the need for computed tomography in these cases.

KEY POINTS

• Much of the current literature focuses on rotational alignment especially with respect to the femur and tibia in healthy patients, although little is known about the acetabular, femoral, and tibial torsion in dysplastic hips. • This is the first study showing significant correlations between the anteversion of the acetabulum and the hip lateralization index as well as the acetabular inclination angle. Also, it is the first study to provide a mechanism for estimation of the torsion of the acetabulum with plain radiography in dysplastic hips. • In borderline-dysplastic hips, no significant correlation was found, which raises the question if a simple x-ray has enough validity to address the acetabular deformity with surgery.

Clinical Impact of Pelvic Malrotation on Radiograph-Based Preoperative Planning for Total Hip Arthroplasty: A Proof-of-Concept and Prudent Prediction of Acceptable Rotation

Introduction

Pelvic rotation (PR) on preoperative radiograph templating can affect various critical measured acetabular angles and potentially outcomes of successful total hip arthroplasty (THA). Optimising anatomical reconstruction of the joint is essential to achieve function, longevity and prevention of complications following surgery. There is limited literature that standardises the degree of acceptable PR on radiograph or its effects on the fitting of acetabular prostheses.

Objective

This study aimed to develop a proof-of-concept that quantifies how PR can affect various acetabular angles used in pre-operative THA templating and to formulate a practicable method of determining if the preoperative PR is acceptable.

Materials and methods

Computerised tomography (CT) models from three control and two THA patients were generated and manipulated in various degrees of PR. CT slices were thickened to simulate radiographs and acetabular angles measured.

Results

The acetabular anteversion distance (AAD) and lateral opening angle (LOA) demonstrated a linear and quadratic relationship with good correlation (R 2 = 0.923, R 2 = 0.710 respectively, p < 0.0001) in relation to PR. Change in area of prosthesis (AOP) demonstrated a good linear correlation (r 2 = 0.774 and r 2 = 0.875, p < 0.0001) with PR. Two novel measurements were used to estimate the degree of PR from a pelvic radiograph; the horizontal distance between pubic symphysis and middle of sacrococcygeal joint (PSSC) and the simplified pelvic rotation ratio (SPRR). A strong correlation between PSSC and SPRR with change in PR was observed (R 2 = 0.970, R 2 = 0.953, p < 0.001).

Conclusion

Preliminary result suggests that an SPRR > 2.0 correlates to PR > 20° with potential to have a clinical impact on preoperative measurements.

Prevalence of radiographic hip dysplasia in Japanese population-based study

OBJECTIVES

The purpose of this study was to measure the indices of radiographic developmental dysplasia of the hip (DDH) in a cross-sectional study of an elderly Japanese population.

METHODS

Hip radiographs of 427 informed, voluntary Japanese community-dwelling individuals (279 female and 148 male) aged 50-96 years-old were obtained from Miyagawa village in Japan through a health screening. The hip radiographs were measured by a custom-written, semi-automated MATLAB program. The center edge (CE) angle, acetabular roof obliquity (ARO), acetabular head index (AHI), and minimum joint space width (mJSW) were measured. We examined the associations between gender, side-of-hip, and age group on radiographic DDH and hip osteoarthritis (OA).

RESULTS

The mean CE angle was 31.0°. The mean ARO was 5.8°. The mean AHI was 88.2%. The mean mJSW was 4.0 mm. Of the total population, 29.9% had DDH and 4.0% had hip OA. Of those who had hip OA, 41.2% were secondary OA, and 58.8% were primary OA. The relationship between DDH and OA was not significant.

CONCLUSION

DDH is unlikely to be an important cause of hip OA in the present population-based study.

Statistical quantification of hip radiograph assessment using Shenton line femur neck length ratio

INTRODUCTION

Identification of a poorly positioned hip radiograph often requires a subjective assessment by the radiographer, which, due to the observer dependency of this method, may have conflicting opinions between radiographers. A quantitative approach may be a better personnel independent approach for assessing an optimally positioned hip radiograph. A Shenton line length femur neck length ratio (SLFLR) could be used to achieve this, which is the aim of this study.

METHODS

Seventy-three (48 digital and 25 analog) optimally positioned non-pathological hip radiographs of asymptomatic patients aged between 20 and 59 years and reported by the consultant radiologist as normal were conveniently selected. Three different radiographers, each blinded to the results of the other two, measured the Shenton line length and the femur neck length with the aid of flexible and straight meter rules for the analog images and inbuilt electronic calipers for the digital images. Bland-Altman method of agreement was used to assess for reproducibility and reliability of the measurements while the 5th, 25th, 75th, and 95th percentiles of the SLFLR were computed.

RESULTS

The mean ± SD SLFLR for both genders were 1.07 ± 0.08 cm (females: 1.06 ± 0.09 and males: 1.08 ± 1.07 cm). The measurements demonstrated high reproducibility and reliability between (interclass correlation coefficient: 0.993) and within (intraclass correlation coefficient: 0.998) radiographers. The 5th, 25th, 75th, and 95th percentile values of the SLFLR are 0.90, 1.03, 1.12, and 1.18.

CONCLUSION

For a hip radiograph to be reported as optimal for patients aged 20-59 years, the SLFLR should be between 0.90 and 1.18. This method is highly reproducible and repeatable and could be adopted for quantitative assessment of radiographs.

IMPLICATIONS FOR PRACTICE

The SLFLR could be used as an additional tool by the radiographer to quantitatively assess for a well-positioned hip radiograph.

Clinical application of artificial intelligence-assisted diagnosis using anteroposterior pelvic radiographs in children with developmental dysplasia of the hip

AIMS

The diagnosis of developmental dysplasia of the hip (DDH) is challenging owing to extensive variation in paediatric pelvic anatomy. Artificial intelligence (AI) may represent an effective diagnostic tool for DDH. Here, we aimed to develop an anteroposterior pelvic radiograph deep learning system for diagnosing DDH in children and analyze the feasibility of its application.

METHODS

In total, 10,219 anteroposterior pelvic radiographs were retrospectively collected from April 2014 to December 2018. Clinicians labelled each radiograph using a uniform standard method. Radiographs were grouped according to age and into 'dislocation' (dislocation and subluxation) and 'non-dislocation' (normal cases and those with dysplasia of the acetabulum) groups based on clinical diagnosis. The deep learning system was trained and optimized using 9,081 radiographs; 1,138 test radiographs were then used to compare the diagnoses made by deep learning system and clinicians. The accuracy of the deep learning system was determined using a receiver operating characteristic curve, and the consistency of acetabular index measurements was evaluated using Bland-Altman plots.

RESULTS

In all, 1,138 patients (242 males; 896 females; mean age 1.5 years (SD 1.79; 0 to 10) were included in this study. The area under the receiver operating characteristic curve, sensitivity, and specificity of the deep learning system for diagnosing hip dislocation were 0.975, 276/289 (95.5%), and 1,978/1,987 (99.5%), respectively. Compared with clinical diagnoses, the Bland-Altman 95% limits of agreement for acetabular index, as determined by the deep learning system from the radiographs of non-dislocated and dislocated hips, were -3.27° - 2.94° and -7.36° - 5.36°, respectively (p < 0.001).

CONCLUSION

The deep learning system was highly consistent, more convenient, and more effective for diagnosing DDH compared with clinician-led diagnoses. Deep learning systems should be considered for analysis of anteroposterior pelvic radiographs when diagnosing DDH. The deep learning system will improve the current artificially complicated screening referral process. Cite this article: Bone Joint J 2020;102-B(11):1574-1581.

How to judge pelvic malposition when assessing acetabular index in children? Three simple parameters can determine acceptability

BACKGROUND

The acetabular index (AI) is the most commonly used parameter for diagnosing hip dysplasia. Pelvic malposition can result in misinterpretation of AI measurement especially in younger children. We aimed to investigate the correlation between pelvic orientation and acetabular index (AI) by using digital reconstructed radiographs (DRRs) and identify reliable parameters predictive of pelvic orientation on plain radiographs.

METHODS

We retrospectively identified 33 children (52 hips) who received dual source CT examinations. Virtual pelvic models were reconstructed after scanning. After orientating in the standard neutral position, the models were rotated and tilted around corresponding axes. DRRs were generated at every 3° during the process. The acetabular index, the horizontal diameter (Dh) and vertical diameter (Dv) of bilateral obturator foramina, the vertical distance (h) between upper border of pubic symphysis, and Hilgenreiner's line were measured on each DRR by two independent observers. Rotation index (Rr = right Dh/left Dh), tilt index (Rt = h/Dv), intra-observer error, and inter-observer error of AI were calculated.

RESULTS

For tilt and rotation up to 12.0°, AI increased with anterior tilt and decreased with posterior tilt. And for rotation, it increased on the side toward which the pelvis rotated and decreased on the opposite side. AI varied dramatically if angulation exceeded 6.0°. Malposition below this limit demonstrated the intra- and inter-observer errors were ± 2.0° and ± 3.0° respectively and caused no significant effect on AI measurement.

CONCLUSIONS

For children up to age 6 years, an acceptable pelvic plain radiograph can be determined when Rt is approximately between 0.9 and 1.4 and Rr between 0.7 and 1.5. For the first time, we have identified parameters derived from a group of subjects which can predict this degree of malposition. The parameters obturator diameters (Dh), obturator height (Dv), and distance (h) between symphysis and Hilgengreiner's line can be feasibly measured on X-ray and employed in clinical practice to assess the acceptability of the pediatric pelvic radiograph prior to measurement of the AI.

Residual hip dysplasia in children: osseous and cartilaginous acetabular angles to guide further treatment-a pilot study

PURPOSE

In case of residual hip dysplasia (RHD) in children, pelvic radiographs are sometimes insufficient to precisely evaluate the entire coverage of the femoral head, when trying to decide on the need for further reconstructive procedures.

METHODS

This study retrospectively compares the bony and the cartilaginous acetabular angle of Hilgenreiner (HTE) of 60 paediatric hips on pelvic MRI separated in two groups. Group 1 included 31 hips with RHD defined by a bony HTE > 20°. Group 2 included 27 hips with a HTE < 20°. They were compared by introducing a new ratio calculated from the square of cartilaginous HTE above the bony HTE on frontal MRI. The normal upper limit for this acetabular angle ratio was extrapolated from the published normal values of cartilaginous HTE and bony HTE in children.

RESULTS

The acetabular angle ratio was statistically significantly increased in the hips with RHD with a mean value of 7.1 ± 4.7 compared to the hips in the control group presenting a mean value of 2.1 ± 1.9 (p < 0.00001).

CONCLUSIONS

This newly introduced ratio seems to be a helpful tool to orientate the further treatment in children presenting borderline RHD.

Variation in pelvic radiography practice: Why can we not standardise image acquisition techniques?

INTRODUCTION

Pelvic radiographs remain an essential investigation in orthopaedic practice. Although it is recognised that acquisition techniques can affect image appearances and measurement accuracy, it remains unclear what variation in practice exists and what impact this could have on decision making.

METHOD

This was a cross sectional survey of UK radiology departments utilising an electronic tool. An introductory letter and link was distributed. Responses were received from 69 unique hospital sites within the specified timeframe, a response rate of 37.9%.

RESULTS

There was no consistent technique for the positioning of patients for pelvic radiographs. The distance varied between 90 and 115 cm and 10 different centering points were described. In relation to leg position, the feet are usually internally rotated (65 of 69 [94.2%]). Only 1 teaching hospital (1 of 69 [1.4%]) uses a weight-bearing position as standard. Orthopaedic calibration devices were not in routine use, with only 21 using on pelvic x-rays (30.4%). Further, the type of device and application criteria were inconsistent.

CONCLUSIONS

To our knowledge this is the first study to directly compare radiographic positioning across hospital sites. Our data demonstrated marked variation in technique for pelvis radiographs with associated implications for clinical decision making. Research is required to determine the standard technique and quality outcome measures to provide confidence in diagnostic interpretation particularly for serial radiographs.

Evaluation of errors in measurements of infantile hip radiograph using digitally reconstructed radiograph from three-dimensional MRI

Purpose

Plain hip radiograph is commonly used for the diagnosis of infantile acetabular dysplasia. Many infants are unable to maintain adequate position during radiography. Besides, the infantile hip is much smaller and has a higher cartilage component in the acetabulum and proximal femur compared with the adult hip. In this study, we developed a digitally reconstructed radiograph synthesized from magnetic resonance imaging (MRI) and investigated errors of hip radiographic measurements in different pelvic positions.

Patients and methods

MRI of both hips was performed in 10 patients (mean age 3.9 years). Three-dimensional (3D) bone models were created from MRI data. We tilted 3D pelvic bone models between 10° anteversion and retroversion and through 10° rotation on the affected and contralateral sides using 3D axes. Following this, we created digitally reconstructed radiographs in each pelvic position and calculated the acetabular index (AI), center-edge angle (CEA), migration percentage (MP), and teardrop distance (TDD).

Results

AI tended to increase with pelvic retroversion and did not change with pelvic rotation. CEA tended to decrease with pelvic retroversion and rotation on the contralateral side. MP increased with pelvic retroversion and rotation on the contralateral side. TDD did not change significantly with pelvic tilt and rotation.

Conclusions

Radiographic measurements of hip in infants were highly influenced by pelvic movement. AI was influenced by pelvic tilt; CEA and MP were influenced by both pelvic tilt and rotation. We need to keep in mind that infantile hip radiographs could have about ±5° errors in AI and CEA.

Correlation between ultrasonic and radiographic imaging of developmental dysplasia of the hip

PURPOSE

The correlation between the degree of developmental hip dysplasia (DDH) measured on ultrasound images compared with that measured on radiographs is not clear. Most studies have compared ultrasonography (US) and radiographic images made at different times of follow-up. In this study the correlation between US images and radiographs of the hip made on the same day was evaluated.

METHODS

US images and radiographs of both hips of 74 infants, who were treated for stable DDH, were reviewed in a retrospective study. Only infants who had an US examination and a radiograph on the same day were included.

RESULTS

The correlation between α-angle of Graf and femoral head coverage on US was strong (p ≤ 0.0001). Weak correlations were found between the acetabular index of Tönnis on radiographs and α-angle of Graf on US (p = 0.049) and between acetabular index of Tönnis on radiographs and femoral head coverage of Morin on US (p = 0.100).

CONCLUSION

This study reports on the correlation between US and radiographic imaging outcomes, both made on the same day in patients for treatment and follow-up of DDH.

LEVEL OF EVIDENCE

IV.

Changes in Pelvic Incidence, Pelvic Tilt, and Sacral Slope in Situations of Pelvic Rotation

STUDY DESIGN

Digitally reconstructed radiograph-based study.

OBJECTIVE

Using a computer-based method to determine what degree of pelvic rotation is acceptable for measuring the pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS). The effectiveness of a geometrical formula used to calculate the angle of pelvic rotation proposed in a previous article was assessed.

SUMMARY OF BACKGROUND DATA

It is unclear whether PI, PT, and SS are valid with pelvic rotation while acquiring a radiograph.

MATERIALS AND METHODS

Ten 3-dimensionally reconstructed models were established with software and placed in a neutral orientation to orient all of the bones in a standing position. Next, 140 digitally reconstructed radiographs were obtained by rotating the models around the longitudinal axis of each pelvis in the software from 0 to 30 degrees at 2.5-degree intervals. PI, PT, and SS were measured. The rotation angle was considered to be acceptable when the change in the measured angle (compared with the "correct" position) was <6 degrees. The rotation angle (α) on the images was calculated by a geometrical formula. Consistency between the measured value and the set angle was assessed.

RESULTS

The acceptable maximum angle of rotation for reliable measurements of PI was 17.5 degrees, and the changes in PT and SS were within an acceptable range (<6 degrees) when the pelvic rotation increased from 0 to 30 degrees. The effectiveness of the geometrical formula was shown by the consistency between the set and the calculated rotation angles of the pelvis (intraclass correlation coefficient=0.99).

CONCLUSIONS

Our study provides insight into the influence of pelvic rotation on the PI, PT, and SS. PI changes with pelvic rotation. The acceptable maximum angle for reliable values of PI, PT, and SS was 17.5 degrees, and the rotation angle of the pelvis on a lateral spinopelvic radiograph can be calculated reliably.

Three-dimensional orientation of the acetabulum

This study was designed specifically to determine the normal acetabular orientation and femoral head covering, and whether these are affected by age or sex. Computed tomographic images of normal Japanese hip joints were used (males 60, females 60; mean age 48.3 years, range 15-79 years). Male and female age profiles were matched. The reconstructed 3-D pelvic images were aligned in the anatomical pelvic coordinate system. The acetabular orientation angles and femoral covering angles were measured in the sagittal, coronal, and horizontal planes. In the sagittal plane, the acetabular orientation angle was operative anteversion (O-av), and the femoral covering angles were the anterior and posterior center-edge angles (ACE and PCE). In the coronal plane, they were the Sharp angle (SA) and the lateral center-edge angle (LCE). In the horizontal plane, they were anatomical anteversion (A-av) and the anterior and posterior sector angles (ASA and PSA). The O-av, SA, and A-av were smaller in the male than the female acetabulum (P < 0.01). SA in both males and females was inversely correlated with age (P < 0.01). Both male PCE and PSA were significantly smaller than those of females, while male ASA was larger than female ASA (P < 0.05). The male acetabulum is directed further outward and downward than the female one. However, this does not indicate that the male acetabulum covers the femoral head more, because there is no significant sex difference in the LCE. Femoral coverage is more posteriorly biased in females than in males owing to pelvic inclination. Clin. Anat. 30:753-760, 2017. © 2017Wiley Periodicals, Inc.

Influence of patient rotational malpositioning on pelvic parameters assessed on lateral radiographs

AIM

To estimate the effect of patients' axial rotation (AR) during pelvic radiograph acquisition, on the reliability and validity of sagittal pelvic parameters.

MATERIALS AND METHODS

Lateral digitally reconstructed radiographs (LDRRs) were obtained from the pelvic computed tomography (CT) scans of eight children and nine adults. Then, the AR of the pelvis was simulated and the corresponding LDRRs were reconstructed at 5°, 10°, 15°, and 20° of the AR. Pelvic parameters were measured digitally on each radiograph. Intra- and interobserver variability were evaluated at each AR position (three operators repeated the measurements three times each). The bias on each clinical parameter, in each AR position, was calculated relatively to the 0° position.

RESULTS

Interobserver variability increased similarly in children and adults with AR. It reached 4.4° for pelvic incidence and 4.7° for the sacral slope at 20° of AR. Biases on radiological parameters increased with AR and exceeded the acceptable threshold of errors when AR reached 10°. A linear regression was established (R²=0.834, p<0.0001) in order to estimate the AR of a patient on a lateral pelvic radiograph based on the measurement of the bifemoral distance normalized to the sagittal pelvic thickness.

CONCLUSIONS

AR of patients during radiograph acquisition can be estimated in clinical practice, which would allow physicians to discard any radiographs where the calculated AR exceeded 10°.

Radiographic Evaluation of Hip Dislocations Necessitating Revision Total Hip Arthroplasty

Although prosthetic hip dislocation is a common reason for revision arthroplasty, few studies have comprehensively evaluated the radiographic factors that may lead to the need for revision. Therefore, the authors radiographically evaluated all prosthetic hip dislocations that were treated at one institution. They then specifically assessed those that required revision surgery. The authors found that the prosthetic center of rotation (pCOR) was located superolateral and inferolateral to the native COR (nCOR) in all patients. Most hips had pCOR distances more than 5 mm from the nCOR. Furthermore, most patients had cup inclination and anteversion angles within Lewinnek's previously defined "safe zone." Determining these similarities and properly planning these procedures may help decrease the instability rate and therefore improve the overall success of this procedure. [Orthopedics.2016; 39(5):e1011-e1018.].

The 'triradiate bump': a novel radiographic sign that may confound assessment of acetabular retroversion

PURPOSE

The triradiate cartilage transiently projects medially within the pelvic brim around the time of triradiate closure, mimicking the ischial spine sign. The purpose of this study was to characterize this newly identified radiographic sign using a longitudinal radiographic study.

METHODS

We identified 72 subjects from a longitudinal radiographic study of healthy adolescents, each with at least four consecutive, annual anterior-posterior radiographs of the left hip, including physeal closure. Images were reviewed to identify the presence of the triradiate bump, the year it was most prominent, and the number of years relative to triradiate closure after which it had completely remodeled.

RESULTS

The transient medial projection of the triradiate cartilage (triradiate bump) was identified in 26/40 (65 %) females and 22/32 (69 %) males (p = 0.74). The medial projection of the triradiate cartilage was most prominent at 10.8 ± 0.8 years of age in females and 12.6 ± 0.7 years of age in males (p < 0.001). The triradiate cartilage projected medially a mean of 4.7 ± 0.8 or 5.1 ± 1.4 mm for females and males, respectively (p = 0.29), but remodeled completely in all cases around triradiate closure.

CONCLUSIONS

The transient medial projection of the triradiate cartilage within the pelvic brim, the 'triradiate bump sign', is a common radiographic finding in healthy adolescents around the time of closure of the triradiate cartilage that may mimic the ischial spine sign. These two signs can be distinguished as the projection of the ischial spine is located more inferiorly within the pelvic brim and the triradiate bump has a horizontal limb of radiolucency extending to its medial border.

Progression of Hip Dysplasia in Mucopolysaccharidosis Type I Hurler After Successful Hematopoietic Stem Cell Transplantation

BACKGROUND

Dysostosis multiplex contributes substantially to morbidity in patients with Hurler syndrome (mucopolysaccharidosis type I Hurler phenotype [MPS I-H]), even after successful hematopoietic stem cell transplantation (HSCT). One of the hallmarks of dysostosis multiplex in MPS I-H is hip dysplasia, which often requires surgical intervention. We sought to describe in detail the course of hip dysplasia in this group of patients, as assessed by radiographic analysis, and to identify potential outcome predictors.

METHODS

Longitudinal data were obtained from digitally scored pelvic radiographs of patients with MPS I-H using OrthoGon software for parameters including, but not limited to, the acetabular index, migration percentage, Smith ratio, and neck-shaft angle. Scoring was performed independently by two blinded observers. Additional information on genotype, enzyme replacement therapy pre-HSCT, donor chimerism, and enzyme activity post-HSCT were obtained. General trends and potential correlations were calculated with mixed-model statistics.

RESULTS

Fifty-two patients (192 radiographs) were included in this analysis. Intraobserver and interobserver variation analysis showed an intraclass correlation coefficient ranging from 0.78 to 1.00. Among the twenty-one patients with follow-up beyond the age of five years, the acetabular index was in the range of severe hip dysplasia in up to 86% of the patients. Severe coxa valga was seen in 91% of the patients. Lateral and superior femoral displacement were highly prevalent, with the migration percentage outside the reference range in up to 96% of the patients. Finally, anterior pelvic tilt increased with age (p = 0.001). No correlations were identified between clinical parameters and radiographic findings.

CONCLUSIONS

Our study shows that progressive acetabular dysplasia as well as coxa valga and hip displacement are highly prevalent and progressive over time in patients with MPS I-H, despite successful HSCT. These data may provide essential natural history determinations for the assessment of efficacy of new therapeutic strategies aimed at improving skeletal outcomes in patients with MPS I-H.

Analysis of pelvic rotation on the standard hip ventrodorsal extended radiographic view

OBJECTIVES

To study the symmetry of the iliac horizontal diameter (IHD) maximum obturator foramen width (OFW), ischiatic femoral overlap (IFO), pelvic horizontal radius (PHR), femoral head diameter (FHD), and obturator foramen area (OFA) parameters in the normal hip extended radiographic view and to evaluate the correlation of pelvic rotation with the magnitude of asymmetry of these parameters.

METHODS

Nine canine cadavers from adult, large and giant breeds were radiographed in standard hip extended views and with 2°, 4° and 6° degrees of rotation. The variables IHD, OFW, IFO, PHR, FHD, and OFA were analysed in radiographs.

RESULTS

The IHD measurements exhibited repeatability, bilateral symmetry and 95% of confidence interval of asymmetry in different pelvic rotations without superposition (p <0.05); OFW and IFO exhibited repeatability, bilateral symmetry and a small superposition in 95% of confidence interval of asymmetry according different pelvic rotations; PHR, FHD and OFA exhibited repeatability, bilateral symmetry and unacceptable superposition in 95% of confidence interval of asymmetry depending on pelvic rotation.

CLINICAL SIGNIFICANCE

The IHD is the recommended variable and OFW is an acceptable variable in order to evaluate slight pelvic rotation. The data may be used in qualitative analyses of hip extended radiographic views. In the future, complementary studies should be performed to evaluate the impact of degree of pelvic rotation on the hip dysplasia score.

Influence of Ankle Position and Radiographic Projection Angle on Measurement of Supramalleolar Alignment on the Anteroposterior and Hindfoot Alignment Views

BACKGROUND

Using digitally reconstructed radiographs (DRRs), we determined how changes in the x-ray beam projection angle from the horizon, tibiotalar joint angle, and axial rotation of the foot influenced measurements of the medial distal tibial angle (MDTA) on the anteroposterior (AP) and hindfoot alignment views (HAV).

METHODS

Seven cadaver foot-ankle specimens were scanned by computed tomography (CT) at fixed tibiotalar joint positions, ranging from 15 degrees of dorsiflexion to 25 degrees of plantarflexion. DRRs were created from each CT scan to simulate alterations in the horizontal projection angle (0 to 25 degrees) and foot axial rotation (-30 to 30 degrees). The MDTA was measured on each DRR and compared with that quantified on the baseline HAV and AP view.

RESULTS

Altering the horizontal projection angle by ≥5 degrees and >10 degrees significantly altered the MDTA for the AP view and the HAV, respectively. Shifting dorsiflexion and plantarflexion caused minor changes in the MDTA that were only statistically significant for the HAV. Axial rotation significantly changed the MDTA on both views, but deviations were more pronounced for the HAV.

CONCLUSIONS

Compared with the HAV, the MDTA on the AP view was less sensitive to changes in foot-ankle position. However, increasing the tilt of the x-ray beam from the horizon altered the MDTA on the AP view substantially.

CLINICAL RELEVANCE

To avoid misinterpretation of the MDTA, we recommend using the AP view to quantify supramalleolar alignment as it is less sensitive to changes in positioning of the foot-ankle. When acquiring an AP film, the x-ray beam should be directed along the horizon to ensure consistent assessment of the MDTA across patients.

Medial percutaneous hemi-epiphysiodesis improves the valgus tilt of the femoral head in developmental dysplasia of the hip (DDH) type-II avascular necrosis

BACKGROUND AND PURPOSE

Avascular necrosis (AVN) is a major cause of disability after treatment of developmental dysplasia of the hip (DDH), leading to femoral head deformity, acetabular dysplasia, and osteoarthritis in adult life. Type-II AVN is characterized by retarded growth in the lateral aspect of the physis or by premature lateral fusion, which produces a valgus deformity of the head on the neck of the femur. We investigated the effect of medial percutaneous hemi-epiphysiodesis as a novel technique in the treatment of late-diagnosed type-II AVN.

PATIENTS AND METHODS

9 patients (11 hips) with a diagnosis of type-II AVN who underwent medial percutaneous hemi-epiphysiodesis after the surgical treatment for DDH were included in the study. 10 patients (12 hips) with the same diagnosis but who did not undergo hemi-epiphysodesis were chosen as a control group. Preoperative and postoperative articulotrochanteric distances, head-shaft angles, CE (center-edge) angles, and physeal inclination angles were measured. The treatment group underwent medial hemi-epiphysodesis at a mean age of 8 years. The mean ages of the treatment group and the control group at final follow-up were 14 and 12 years respectively. The mean duration of follow-up was 5.7 years in the treatment group and 8.3 years in the control group.

RESULTS

Preoperative articulotrochanteric distance, head-shaft angle, and functional outcome at the final follow-up assessment were similar in the 2 groups. However, preoperative and postoperative CE angles and physeal inclination angles differed significantly in the treatment group (p < 0.05). The final epiphyseal valgus angles were better in the treatment group than in the control group (p = 0.05). The treatment group improved after the operation.

INTERPRETATION

Medial percutaneous epiphysiodesis performed through a mini-incision under fluoroscopic control is a worthwhile modality in terms of changing the valgus tilt of the femoral head.

Normal values of bony, cartilaginous, and labral coverage of the infant hip in MR imaging

BACKGROUND

Magnetic resonance imaging (MRI) is becoming more popular in the evaluation of residual hip dysplasia. Normal values of the bony, cartilaginous, and labral coverage in MRI are not published. The aim of our study was to establish reference values for normal hips at different ages and to assess the interobserver variability of such measurements.

METHODS

MRIs of 115 normal hips in 73 children were analyzed. The bony, cartilaginous, and labral acetabular index (AI bone/cartilage/labrum) was measured in the coronal plane just posterior to the inferior branch of the triradiate cartilage. To determine interobserver variability, measurements were made by 3 different observers. Percentile graphs were established from the Student t distribution of the measurements grouped by 2 years of age.

RESULTS

Global interobserver variability for the measurement of the AI bone was excellent [intraclass correlation coefficient (ICC)=0.88]. For the AI cartilage and labrum the ICC was somewhat lower (ICC 0.78) but still rated as good. Age-dependent percentile graphs of the AI bone, cartilage, and labrum are presented. Although the AI bone decreased during childhood, the AI cartilage as well as the AI labrum stays relatively constant with the 50 percentile around 5 degrees for the AI cartilage and -5 degrees for the AI labrum. The 90 percentile is around 10 degrees for the AI cartilage and 0 degrees for the AI labrum.

CONCLUSIONS

We present percentile graphs of age-related normal values. Although bony coverage increases during childhood, cartilaginous and labral coverage stay constant. We think that measuring an AI cartilage above 10 degrees or an AI cartilage above 0 degrees might be a good additional parameter to classify hips into the group of residual dysplasia.

CLINICAL RELEVANCE

The knowledge of normal values for cartilaginous and labral coverage is a valuable adjunct in decision-making for secondary surgery in residual dysplasia. This was a retrospective cross-sectional study.

Bony abnormalities of the hip joint: a new comprehensive, reliable and radiation-free measurement method using magnetic resonance imaging

OBJECTIVES

To develop comprehensive and reliable radiation-free methods to quantify femoral and acetabular morphology using MRI.

METHODS

32 hips (16 subjects, 6 with intra-articular hip disorder (IAHD); 10 controls) were included. A 1.5T magnetic resonance system was used to obtain 3D fat suppressed gradient echo images at the pelvis and distal femora. After acquisition, pelvic images were post-processed to correct for coronal, axial and sagittal rotation. Measurements performed included acetabular version (AV), femoral version (FV), lateral center edge angle (LCEA), femoral neck angle (FNA) and alpha angle (AA) at 3, 2, 1 and 12 o'clock. Two experienced raters, a musculoskeletal radiologist and an orthopaedic physical therapist, and a novice rater, a research assistant, completed reliability testing. Raters measured all hips twice with minimum 2 weeks between sessions. Intraclass Correlation Coefficients were used to determine rater reliability; standard error of measurements was reported to estimate the reasonable limits of the expected error in the different raters' scores.

RESULTS

Interrater reliability was good to excellent for all raters for AV, FV, FNA, and LCEA (ICCs: 0.82-0.98); good to excellent between experienced raters (ICCs: 0.78-0.86) and poor to good between novice and experienced raters (ICCs: 0.23-0.78) for AA. Intrarater reliability was good to excellent for all raters for AV, FV and FNA (ICCs: 0.93-0.99); for one experienced and novice rater for LCEA (ICCs: 0.84-0.89); moderate to excellent for the experienced raters for AA (ICCs: 0.72-0.89). Intrarater reliability was poor for the second experienced rater for LCEA (ICC: 0.56), due to a single measurement error and for the novice rater for AA (ICCs: 0.17-0.38).

CONCLUSION

We described MRI methods to comprehensively assess femoral and acetabular morphology. Measurements such as AV, FV and FNA and the LCEA can be made reliably by both experienced and novice raters, however the AA measurement was reliable only among experienced raters.

Development of the osseous and cartilaginous acetabular index in normal children and those with developmental dysplasia of the hip

The purpose of this study was to investigate the development of the osseous acetabular index (OAI) and cartilaginous acetabular index (CAI) using MRI. The OAI and CAI were measured on the coronal MR images of the hip in 81 children with developmental dysplasia of the hip (DDH), with a mean age of 19.6 months (3 to 70), and 241 normal control children with a mean age of 5.1 years (1 month to 12.5 years). Additionally the developmental patterns of the OAI and CAI in normal children were determined by age-based cross-sectional analysis.

Unlike the OAI, the normal CAI decreased rapidly from a mean of 10.17° (sd 1.60) to a mean of 8.25° (sd 1.90) within the first two years of life, and then remained constant at a mean of 8.04° (sd 1.65) until adolescence. Although no difference in OAI was found between the uninvolved hips in children with unilateral DDH and normal hips (p = 0.639), the CAI was significantly different between them both (p < 0.001). The normal CAI has fully formed at birth, and is maintained constantly throughout childhood. The CAI in the unaffected hips in children with unilateral DDH is also mildly dysplastic.

Evaluation of femoral head coverage following Chiari pelvic osteotomy in adolescents by three-dimensional computed tomography and conventional radiography

INTRODUCTION

Currently, the cover of the femoral head was mainly assessed using conventional plain films after Chiari pelvic osteotomy in most studies. The purpose of the current study was to observe whether the femoral head coverage measured by three-dimensional computed tomography (3D-CT) was consistent with the radiographic findings.

PATIENTS AND METHODS

A total of 24 patients (24 hips) with an average age of 11.5 years, underwent Chiari osteotomy due to acetabular dysplasia, and 15 subjects (30 hips) of normal control with a mean age of 12 years were involved in the study. The pre- and postoperative coverage of femoral head was measured by using conventional plain film and 3D-CT on the anterior 1/4, middle 1/2, and posterior 1/4 coronal plane. The anterolateral, mediolateral and posterolateral coverage measured by 3D-CT were compared with the coverage measured by plain radiograph, and which were also compared with the normal control individuals.

RESULTS

The postoperative anterolateral, mediolateral coverage measured by 3D-CT was significantly smaller than that measured by radiography (P < 0.01). No significant difference was found between the 3D-CT measurements on the posterolateral coverage and the radiographic results. The anterolateral femoral head coverage in the patients following Chiari pelvic osteotomy was also smaller than that in the normal control individuals (P = 0.026). In contrast, the postoperative posterolateral coverage in the patients was more excessive than that in the normal control individuals (P = 0.001).

CONCLUSION

Conventional radiographs may show sufficient cover of the femoral head after Chiari osteotomy, whereas in fact, the cover may be not perfect, especially on the anterolateral part. Therefore, the postoperative 3D-CT is beneficial for evaluating the outcome of Chiari osteotomy, especially when the anterolateral coverage o

Evaluation of pelvis slope and flattening on children gymnasts by Biophotogrammetry technique

This work proposes to detect possible affections or abnormalities in pelvic belt region in a group of rhythmic gymnastics due to the need for studies in the field of biomechanics and structural evaluation of human being. The methodology for this study used a tool called Biophotogrammetry. This technique has analyzed, through scanned images, the structural pelvic girdle bone profile of 64 practitioners of rhythmic gymnastics. The results of this study have presented weighted averages of 45.07±9.78° between the right pelvic slope (RPS) and left pelvic slope (LPS) and 91.74±2.50° for flattening of the pelvis (FP). Therefore, it is concluded that the Biophotogrammetry technique provides data related to the gold standard radiography test, used as reference for the pelvic girdle measurements.

Can excessive lateral rotation of the ischium result in increased acetabular anteversion? A 3D-CT quantitative analysis of acetabular anteversion in children with unilateral developmental dysplasia of the hip

BACKGROUND

The purposes of this study were to observe whether increased acetabular anteversion was a universal finding and whether excessive lateral rotation of the ischium was correlated with increased acetabular anteversion.

METHODS

We retrospectively reviewed 90 patients with unilateral developmental dysplasia of the hip (DDH), including 77 female patients and 13 male patients with an average age of 18 months (range, 6 to 60 mo). A total of 31 children were involved in the normal control group, including 14 girls and 17 boys with an average age of 21 months (range, 7 to 48 mo). The acetabular anteversion angle (AA), pubic relative length (PRL), ischiac relative distance (IRD), lateral rotational angle of the ischium (IA), and pubic rotational angle were compared between the affected hips and the unaffected hips in the unilateral DDH group and between the right hips and left hips in the normal control group.

RESULTS

No retroverted acetabulum was found in any hip. No significant differences in AA, IA, pubic rotational angle, IRD, and PRL were found between the left and right hips in the normal control group. However, the PRL was shorter in the affected hips than in the unaffected hips (P < 0.05). The average IA, AA, and IRD in the affected hips were larger than that in the unaffected hips (P < 0.05). The IA was positively correlated with AA and IRD in the DDH group.

CONCLUSIONS

Increased acetabular anteversion in affected hips is a universal finding in unilateral DDH. The deficiency of the anterior wall in the acetabulum is not a unique reason for increased acetabular anteversion in unilateral DDH, because it is also correlated with excessive lateral rotation of the ischium.

LEVEL OF EVIDENCE

IV.

Does medial rotational deformity of the whole pelvis universally exist in unilateral DDH?

INTRODUCTION

There are no reports on the morphologic features of the entire pelvis in the subgroup of dislocation of hips according to the classification system of Tönnis. In addition, the correlation of excessive medial rotation of the lower pelvis with the increased acetabular anteversion was uncertain in the children with unilateral developmental dysplasia of the hip (DDH).

PATIENTS AND METHODS

In the study, 74 patients with unilateral DDH and 31 subjects of normal control were involved, and the images of three-dimensional computed tomography (3D-CT) were retrospectively reconstructed to compare the acetabular anteversion angle (AA), the rotational angle of the upper pelvis (URA), and the rotational angle of the lower pelvis (LRA). The correlation of the AA with LRA was analyzed.

RESULTS

In the group of grade II and IV, though the LRA was increased on the dislocated side as compared with the unaffected side (P < 0.05), the URA did not differ between the two sides (P > 0.05). There was positive correlation between AA and LRA on the dislocated side in the group of grade II, III, and IV.

CONCLUSION

The excessive medial rotation of whole pelvis on the dislocated side was not universally presented in unilateral DDH. The excessive medial rotational deformity of the lower pelvis could induce increased acetabular anteversion. An individualized treatment plan based on the accurate assessment of morphologic features of the whole pelvis and the exact understanding for underlying causes of acetabular anteversion through 3D-CT should be considered to avoid complications during surgery.