Computed Tomography Scans in Patients With Young Adult Hip Pain Carry a Lifetime Risk of Malignancy

3.0T magnetic resonance imaging-based hip bone models for femoroacetabular impingement syndrome are equivalent to computed tomography-based models

This study aimed to compare three-dimensional (3D) proximal femoral and acetabular surface models generated from 3.0T magnetic resonance imaging (MRI) to the clinical gold standard of computed tomography (CT). Ten intact fresh-frozen cadaveric hips underwent CT and 3.0T MRI scans. The CT- and MRI-based segmented models were superimposed using a validated 3D-3D registration volume-merge method to compare them. The least surface-to-surface distance between the models was calculated by a point-to-surface calculation algorithm using a custom-written program. The variables of interest were the signed and absolute surface-to-surface distance between the paired bone models. One-sample t-tests were performed using a signed and absolute test value of 0.16 mm and 0.37 mm, respectively, based on a previous study that validated 1.5T MRI bone models by comparison with CT bone models. For the femur, the average signed and absolute surface-to-surface distance was 0.18 ± 0.09 mm and 0.30 ± 0.06 mm, respectively. There was no difference in the signed surface-to-surface distance and the 0.16 mm test value (t = 0.650, p = 0.532). However, the absolute surface-to-surface difference was less than the 0.37 mm test value (t = -4.025, p = 0.003). For the acetabulum, the average signed and absolute surface-to-surface distance was -0.06 ± 0.06 mm and 0.26 ± 0.04 mm, respectively. The signed (t = -12.569, p < 0.001) and absolute (t = -8.688, p < 0.001) surface-to-surface difference were less than the 0.16 mm and 0.37 mm test values, respectively. Our data shows that 3.0T MRI bone models are more similar to CT bone models than previously validated 1.5T MRI bone models. This is likely due to the higher resolution of the 3T data.

A Novel Digital Templating Method for Total Hip Arthroplasty in Patients With Unilateral Hip Arthrosis

BACKGROUND

Identification of the hip center of rotation (HCOR) before total hip arthroplasty (THA) is crucial for achieving optimal implant position and size, and for restoring native biomechanics around the hip joint. Current techniques for determining the HCOR in cases of abnormal hip anatomy are limited and unreliable. This study presents a novel technique using open-access software for preoperative THA templating for patients with significantly abnormal hip anatomy due to unilateral hip arthrosis. The aim is to reliably predict the HCOR and acetabular implant size compared with a traditional intraoperative method.

MATERIALS AND METHODS

This retrospective study involved 20 patients with unilateral hip arthrosis who underwent THA. Preoperative templating was performed using the experimental technique, and the position of the HCOR was measured on preoperative and postoperative radiographs. The positions of the predicted and actual HCOR were compared, along with the inclination and size of the acetabular component.

RESULTS

The difference between the predicted and actual HCOR positions was insignificant (0.43±0.22 mm vertically and 0.18±0.20 mm horizontally), and there was a positive correlation between them (r=0.78, P<.005; r=0.72, P<.005). The agreement between the predicted and actual acetabular implant sizes was 85%, with near-perfect interobserver agreement (Cohen's kappa=0.827).

CONCLUSION

This novel technique provides a reliable method for predicting HCOR and acetabular implant size for THA in cases of unilateral hip arthrosis. This technique may help optimize biomechanics and improve outcomes in challenging cases. Further research and validation are warranted to establish its broader applicability. [Orthopedics. 2024;47(3):e139-e145.].

MR-based Bony 3D models enable radiation-free preoperative patient-specific analysis and 3D printing for SCFE patients

Objectives

Slipped capital femoral epiphyses (SCFE) is a common pediatric hip disease with the risk of osteoarthritis and impingement deformities, and 3D models could be useful for patient-specific analysis. Therefore, magnetic resonance imaging (MRI) bone segmentation and feasibility of 3D printing and of 3D ROM simulation using MRI-based 3D models were investigated.

Methods

A retrospective study involving 22 symptomatic patients (22 hips) with SCFE was performed. All patients underwent preoperative hip MR with pelvic coronal high-resolution images (T1 images). Slice thickness was 0.8-1.2 mm. Mean age was 12 ± 2 years (59% male patients). All patients underwent surgical treatment. Semi-automatic MRI-based bone segmentation with manual corrections and 3D printing of plastic 3D models was performed. Virtual 3D models were tested for computer-assisted 3D ROM simulation of patients with knee images and were compared to asymptomatic contralateral hips with unilateral SCFE (15 hips, control group).

Results

MRI-based bone segmentation was feasible (all patients, 100%, in 4.5 h, mean 272 ± 52 min). Three-dimensional printing of plastic 3D models was feasible (all patients, 100%) and was considered helpful for deformity analysis by the treating surgeons for severe and moderate SCFE. Three-dimensional ROM simulation showed significantly (p < 0.001) decreased flexion (48 ± 40°) and IR in 90° of flexion (-14 ± 21°, IRF-90°) for severe SCFE patients with MRI compared to control group (122 ± 9° and 36 ± 11°). Slip angle improved significantly (p < 0.001) from preoperative 54 ± 15° to postoperative 4 ± 2°.

Conclusion

MRI-based 3D models were feasible for SCFE patients. Three-dimensional models could be useful for severe SCFE patients for preoperative 3D printing and deformity analysis and for ROM simulation. This could aid for patient-specific diagnosis, treatment decisions, and preoperative planning. MRI-based 3D models are radiation-free and could be used instead of CT-based 3D models in the future.

The impact of data augmentation and transfer learning on the performance of deep learning models for the segmentation of the hip on 3D magnetic resonance images

Different pathologies of the hip are characterized by the abnormal shape of the bony structures of the joint, namely the femur and the acetabulum. Three-dimensional (3D) models of the hip can be used for diagnosis, biomechanical simulation, and planning of surgical treatments. These models can be generated by building 3D surfaces of the joint's structures segmented on magnetic resonance (MR) images. Deep learning can avoid time-consuming manual segmentations, but its performance depends on the amount and quality of the available training data. Data augmentation and transfer learning are two approaches used when there is only a limited number of datasets. In particular, data augmentation can be used to artificially increase the size and diversity of the training datasets, whereas transfer learning can be used to build the desired model on top of a model previously trained with similar data. This study investigates the effect of data augmentation and transfer learning on the performance of deep learning for the automatic segmentation of the femur and acetabulum on 3D MR images of patients diagnosed with femoroacetabular impingement. Transfer learning was applied starting from a model trained for the segmentation of the bony structures of the shoulder joint, which bears some resemblance to the hip joint. Our results suggest that data augmentation is more effective than transfer learning, yielding a Dice similarity coefficient compared to ground-truth manual segmentations of 0.84 and 0.89 for the acetabulum and femur, respectively, whereas the Dice coefficient was 0.78 and 0.88 for the model based on transfer learning. The Accuracy for the two anatomical regions was 0.95 and 0.97 when using data augmentation, and 0.87 and 0.96 when using transfer learning. Data augmentation can improve the performance of deep learning models by increasing the diversity of the training dataset and making the models more robust to noise and variations in image quality. The proposed segmentation model could be combined with radiomic analysis for the automatic evaluation of hip pathologies.

Femoral Head Osteonecrosis: Computed Tomography Not Needed to Identify Collapse When Using the Association Research Circulation Osseous Staging System

Background

The 2019 Revised Association Research Circulation Osseous (ARCO) Staging Criteria for Osteonecrosis of the Femoral Head (ONFH) only requires plain radiographs and magnetic resonance imaging (MRI) to diagnose and stage ONFH; however, the effectiveness of the 2019 ARCO criteria in the absence of computed tomography (CT) scans has not been investigated. Therefore, the purpose of this study was to evaluate whether CT scanning is a necessary modality for diagnosing/staging ONFH using the ARCO staging system. More specifically, do CT scans help differentiate pre- and post-collapse lesions more than MRI scans?

Methods

A study was conducted on 228 ONFH patients diagnosed between January 1, 2008, and December 31, 2018, at a single academic medical center. CT and MRI scans were reviewed by the senior author and other contributors. The ONFH classification was compared between the 2 scans to determine if CT scans were able to further differentiate staging of collapsed lesions vs MRI scans.

Results

A diagnosis of ONFH was made by MRI first in 57% (129/228) while 21% (48/228) used MRI and CT simultaneously. Only 22% (51/228) of cases were diagnosed by CT scans first. There were no cases where collapse was found by a CT scan that were not diagnosed by standard x-rays and/or MRIs.

Conclusions

CT scans are not a useful adjunct for diagnosing or treating ONFH and are not necessary if MRI is ordered when using the Revised ARCO Staging System for ONFH diagnosis.

Hounsfield Unit-Calculated Bone Mineral Density Loss Following Combat-Related Lower Extremity Amputations

BACKGROUND

After combat-related lower extremity amputations, patients rapidly lose bone mineral density (BMD). As serial dual x-ray absorptiometry (DXA) scans are rarely performed in this setting, it is difficult to determine the timeline for bone loss and recovery or the role of interventions. However, a strong correlation has been demonstrated between DXA BMD and computed tomography (CT) signal attenuation. We sought to leverage multiple CT scans obtained after trauma to develop a predictive model for BMD after combat-related lower extremity amputations.

METHODS

We reviewed amputations performed within the United States military between 2003 and 2016 in patients with multiple CT scans. We collected pertinent clinical information, including amputation level(s), complications, and time to weight-bearing. The primary outcome measure was the development of low BMD, estimated in Hounsfield units (HU) from CT scans with use of a previously validated method. One hundred and twenty-eight patients with 613 femoral neck CT scans were available for analysis. A least absolute shrinkage and selection operator (LASSO) multiple logistic regression analysis was applied to determine the effects of modifiable and non-modifiable variables on BMD. A random-effects model was applied to determine which factors were most predictive of low BMD and to quantify their effects.

RESULTS

Both amputated and non-amputated extremities demonstrated substantial BMD loss, which stabilized approximately 3 years after the injury. Loss of BMD followed a logarithmic pattern, stabilizing after 1,000 days. On average, amputated limbs lost approximately 100 HU of BMD after 1,000 days. Other factors identified by the mixed-effects model included nonambulatory status (-33.5 HU), age at injury (-3.4 HU per year), surgical complications delaying weight-bearing (-21.3 HU), transtibial amputation (20.9 HU), and active vitamin-D treatment (-19.7 HU).

CONCLUSIONS

Patients with combat-related lower extremity amputations experience an initially rapid decline in BMD in both intact and amputated limbs as a result of both modifiable and non-modifiable influences, including time to walking, amputation level, surgical complications, and age. The paradoxical association of vitamin-D supplementation with lower HU likely reflects this treatment being assigned to patients with low BMD. This model may assist with clinical decision-making prior to performing lower extremity amputation and also may assist providers with postoperative decision-making to optimize management for prophylaxis against osteoporosis.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Combining the advantages of 3-D and 2-D templating of total hip arthroplasty using a new tin-filtered ultra-low-dose CT of the hip with comparable radiation dose to conventional radiographs

BACKGROUND

Inaccurately scaled radiographs for total hip arthroplasty (THA) templating are a source of error not recognizable to the surgeon and may lead to inaccurate reconstruction and thus revision surgery or litigation. Planning based on computed tomography (CT) scans is more accurate but associated with higher radiation exposure. The aim of this study was (1) to retrospectively assess the scaling deviation of pelvic radiographs; (2) to prospectively assess the feasibility and the radiation dose of THA templating on radiograph-like images reconstructed from a tin-filtered ultra-low-dose CT dataset.

METHODS

120 consecutive patients were retrospectively analyzed to assess the magnification error of our current THA templates. 27 consecutive patients were prospectively enrolled and a radiographic work-up in the supine position including a new tin-filtered ultra-low-dose CT scan protocol was obtained. THA was templated on both images. Radiation dose was calculated.

RESULTS

Scaling deviations between preoperative radiographs and CT of ≥ 5% were seen in 25% of the 120 retrospectively analyzed patients. Between the two templates trochanter tip distance differed significantly (Δ2.4 mm, 0-7 mm, p = 0.035)), predicted femoral shaft size/cup size was the same in 45%/41%. The radiation dose of the CT (0.58 mSv, range 0.53-0.64) was remarkably low.

CONCLUSION

Scaling deviations of pelvic radiographs for templating THA may lead to planning errors of ≥ 3 mm in 25% and ≥ 6 mm in 2% of the patients. 2-D templating on radiograph-like images based on tin-filtered ultra-low-dose CT eliminates this source of error without increased radiation dose.

LEVEL OF EVIDENCE

Retrospective and prospective comparative study, Level III.

Periacetabular osteotomy with intraoperative computer-assisted modalities: a systematic review

The role of intraoperative computer-assisted modalities for periacetabular osteotomy (PAO), as well as the perioperative and post-operative outcomes for these techniques, remains poorly defined. The purpose of this systematic review was to evaluate the techniques and outcomes of intraoperative computer-assisted modalities for PAO. Three databases (PubMed, CINAHL/EBSCOHost and Cochrane) were searched for clinical studies reporting on computer-assisted modalities for PAO. Exclusion criteria included small case series (<10 patients), non-English language and studies that did not provide a description of the computer-assisted technique. Data extraction included computer-assisted modalities utilized, surgical techniques, demographics, radiographic findings, perioperative outcomes, patient-reported outcomes (PROs), complications and subsequent surgeries. Nine studies met the inclusion criteria, consisting of 208 patients with average ages ranging from 26 to 38 years. Intraoperative navigation was utilized in seven studies, patient-specific guides in one study and both modalities in one study. Three studies reported significantly less intraoperative radiation exposure (P < 0.01) in computer-assisted versus conventional PAOs. Similar surgical times and estimated blood loss (P > 0.05) were commonly observed between the computer-assisted and conventional groups. The average post-operative lateral center edge angles in patients undergoing computer-assisted PAOs ranged from 27.8° to 37.4°, with six studies reporting similar values (P > 0.05) compared to conventional PAOs. Improved PROs were observed in all six studies that reported preoperative and post-operative values of patients undergoing computer-assisted PAOs. Computer-assisted modalities for PAO include navigated tracking of the free acetabular fragment and surgical instruments, as well as patient-specific cutting guides and rotating templates. Compared to conventional techniques, decreased intraoperative radiation exposure and similar operative lengths were observed with computer-assisted PAOs, although these results should be interpreted with caution due to heterogeneous operative techniques and surgical settings.

A radiomics approach to the diagnosis of femoroacetabular impingement

Introduction

Femoroacetabular Impingement (FAI) is a hip pathology characterized by impingement of the femoral head-neck junction against the acetabular rim, due to abnormalities in bone morphology. FAI is normally diagnosed by manual evaluation of morphologic features on magnetic resonance imaging (MRI). In this study, we assess, for the first time, the feasibility of using radiomics to detect FAI by automatically extracting quantitative features from images.

Material and methods

17 patients diagnosed with monolateral FAI underwent pre-surgical MR imaging, including a 3D Dixon sequence of the pelvis. An expert radiologist drew regions of interest on the water-only Dixon images outlining femur and acetabulum in both impingement (IJ) and healthy joints (HJ). 182 radiomic features were extracted for each hip. The dataset numerosity was increased by 60 times with an ad-hoc data augmentation tool. Features were subdivided by type and region in 24 subsets. For each, a univariate ANOVA F-value analysis was applied to find the 5 features most correlated with IJ based on p-value, for a total of 48 subsets. For each subset, a K-nearest neighbor model was trained to differentiate between IJ and HJ using the values of the radiomic features in the subset as input. The training was repeated 100 times, randomly subdividing the data with 75%/25% training/testing.

Results

The texture-based gray level features yielded the highest prediction max accuracy (0.972) with the smallest subset of features. This suggests that the gray image values are more homogeneously distributed in the HJ in comparison to IJ, which could be due to stress-related inflammation resulting from impingement.

Conclusions

We showed that radiomics can automatically distinguish IJ from HJ using water-only Dixon MRI. To our knowledge, this is the first application of radiomics for FAI diagnosis. We reported an accuracy greater than 97%, which is higher than the 90% accuracy for detecting FAI reported for standard diagnostic tests (90%). Our proposed radiomic analysis could be combined with methods for automated joint segmentation to rapidly identify patients with FAI, avoiding time-consuming radiological measurements of bone morphology.

Ligamentum Flavum Rupture by Epidural Injection Using Ultrasound with SMI Method

The loss of resistance (LOR) method has been used exclusively to identify epidural space. It is difficult to find the epidural space without the risk of dural puncture. Various devices have been developed to improve the accuracy of the LOR method; however, no method has overcome the problems completely. Therefore, we devised a ligamentum flavum rupture method (LFRM) in which the needle tip is placed only on the ligamentum flavum during the epidural injection, and the injection pressure is used to rupture the ligamentum flavum and spread the drug into the epidural space. We confirmed the accuracy of this method using ultrasound with superb microvascular imaging (SMI) to visualize the epidural space. Here, we report two cases of 63-year-old and 90-year-old males. The 63-year-old patient presented with severe pain in his right buttock that extended to the posterior lower leg. The 90-year-old patient presented with intermittent claudication every 10 min. LFRM was performed, and SMI was used to confirm that the parenteral solution had spread into the epidural space. Our results indicate that LFRM can be used for interlaminar lumbar epidural steroid injections.

CT Scans and Cancer Risks: A Systematic Review and Dose-response Meta-analysis

BACKGROUND

There is still uncertainty on whether ionizing radiation from CT scans can increase the risks of cancer. This study aimed to identify the association of cumulative ionizing radiation from CT scans with pertaining cancer risks in adults.

METHODS

Five databases were searched from their inception to November 15, 2020. Observational studies reporting cancer risks from CT scans in adults were included. The main outcome included quantified cancer risks as cancer case numbers in exposed/unexposed adult participants with unified converted measures to odds ratio (OR) for relative risk, hazard ratio. Global background radiation (2.4 mSv per year) was used as control for lifetime attribution risk (LAR), with the same period from incubation after exposure until survival to 100 years.

RESULTS

25 studies were included with a sum of 111,649,943 participants (mean age: 45.37 years, 83.4% women), comprising 2,049,943 actual participants from 6 studies with an average follow-up period as 30.1 years (range, 5 to 80 years); 109,600,000 participants from 19 studies using LAR. The cancer risks for adults following CT scans were inordinately increased (LAR adults, OR, 10.00 [95% CI, 5.87 to 17.05]; actual adults, OR, 1.17 [95%CI, 0.89 to 1.55]; combined, OR, 5.89 [95%CI, 3.46 to 10.35]). Moreover, cancer risks elevated with increase of radiation dose (OR, 33.31 [95% CI, 21.33 to 52.02]), and multiple CT scan sites (OR, 14.08 [95% CI, 6.60 to 30.05]). The risk of solid malignancy was higher than leukemia. Notably, there were no significant differences for age, gender, country, continent, study quality and studying time phrases.

CONCLUSIONS

Based on 111.6 million adult participants from 3 continents (Asia, Europe and America), this meta-analysis identifies an inordinately increase in cancer risks from CT scans for adults. Moreover, the cancer risks were positively correlated with radiation dose and CT sites. The meta-analysis highlights the awareness of potential cancer risks of CT scans as well as more reasonable methodology to quantify cancer risks in terms of life expectancy as 100 years for LAR.

PROSPERO TRIAL REGISTRATION NUMBER

CRD42019133487.

Association Between Low-Dose Methotrexate Exposure and Melanoma: A Systematic Review and Meta-analysis

Importance

Methotrexate is widely used for the treatment of inflammatory disorders, including rheumatoid arthritis. Studies suggest that methotrexate may be associated with an increased risk of melanoma.

Objective

To determine whether methotrexate exposure is associated with an increased risk of cutaneous melanoma.

Data Sources

MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov were searched from inception to May 12, 2022, for eligible studies.

Study Selection

Case-control studies, cohort studies, or randomized clinical trials (RCTs) were included if they examined the odds or risk of cutaneous melanoma in individuals exposed to low-dose methotrexate in comparison with individuals unexposed. No language limitations were applied.

Data Extraction and Synthesis

Two independent reviewers extracted data on study characteristics and outcome data. The Meta-analysis of Observational Studies in Epidemiology guidelines were followed. To assess study quality, the Cochrane risk of bias tool was used for RCTs, and the Joanna Briggs Institute Checklist was used for cohort and case-control studies. Odds ratio from case-control studies and relative risk or hazard ratio from cohort studies or RCTs were pooled, and a random-effects model meta-analysis was conducted.

Main Outcomes and Measures

Prespecified outcome was the odds ratio, hazard ratio, or risk ratio of cutaneous melanoma comparing low-dose methotrexate exposure with nonexposure.

Results

Seventeen studies (8 RCTs, 5 cohort studies, 4 case-control studies) were eligible for inclusion, and of these, 12 studies with 16 642 cases of melanoma were pooled in the primary analysis. Indications for methotrexate included rheumatoid arthritis, psoriasis, psoriatic arthritis, and inflammatory bowel disease and were unknown in 5 studies. Compared with unexposed individuals, study participants with methotrexate exposure had a small increased risk of melanoma (pooled relative risk, 1.15; 95% CI, 1.08-1.22), but this did not persist in a sensitivity analysis excluding the largest study (pooled relative risk, 1.11; 95% CI, 1.00-1.24). Subgroup analyses according to comparator group (comparing methotrexate exposure with either immunomodulator alone vs immunomodulator and methotrexate) or the indication for methotrexate being rheumatoid arthritis provided similar risk estimates. Using geographical population melanoma incidence rates, a number needed to harm of 18 630 was calculated in Australia, and 41 425 in North America.

Conclusions and Relevance

In this systematic review and meta-analysis, low-dose methotrexate exposure was associated with an increased melanoma risk, but the absolute risk increase could be considered negligible.

A systematic approach to CT evaluation of non-arthritic hip pain

Bone morphology has been increasingly recognized as a significant variable in the evaluation of non-arthritic hip pain in young adults.

Increased availability and use of multidetector CT in this patient population has contributed to better characterization of the osseous structures compared to traditional radiographs.

Femoral and acetabular version, sites of impingement, acetabular coverage, femoral head–neck morphology, and other structural abnormalities are increasingly identified with the use of CT scan.

In this review, a standard CT imaging technique and protocol is discussed, along with a systematic approach for evaluating pelvic CT imaging in patients with non-arthritic hip pain.

Direct Visualization of Cervical Interlaminar Epidural Injections Using Sonography

In this case series, we describe a novel ultrasound (US)-guided cervical interlaminar epidural steroid injections (CILESIs) procedure that does not depend on the loss-of-resistance method for epidural space identification. A needle is introduced into three US-identified structures (triple bar sign), the interspinal ligament, ligamentum flavum, and dura mater. The injectants are monitored using superb microvascular imaging during injection. Here, we demonstrate the use of US-guided CILESIs in nine cases and propose the use of sonography, rather than conventional methods, for easier and safer cervical epidural injections. Sonography for direct visualization of cervical epidural injection may allow for outpatient injections.

Diagnosis of Lumbar Transverse Process Fractures in Orthopedic Clinics Using Sonography

Sonography is conventionally used to diagnose fractures by identifying cortical discontinuity in the bone. However, its usefulness for diagnosing lumbar transverse process fractures (LTPFs) remains unknown. In this series, we describe static and stress sonography findings during manual application of compression stress on the lateral lumbar vertebrae in 17 patients with LTPFs. Features of LTPFs on static sonography included cortical discontinuity (89.3%), hematoma (71.4%), step-off deformity (67.9%), and focal reverberation echo (78.6%). All LTPFs were confirmed on stress sonography. Thus, stress sonography should be considered for the detection of LTPFs when there is at least one static sonographic fracture sign.

Accuracy of pelvic measurements on virtual radiographic projections based on computed tomography scans compared to conventional radiographs pre- and postoperatively

BACKGROUND

The anteroposterior (ap) radiograph of the pelvis is decisive in the diagnosis of different pathologies of the hip joint. Technical advantages have reduced the radiation dose of pelvic CT to levels comparable to radiographs. The purpose of this study was to validate if standard radiographic parameters (lateral center edge angle, medial center edge angle, acetabular index, acetabular arc, extrusion index, crossover sign and posterior wall sign) can accurately be determined on radiograph-like projections reconstructed from the CT dataset pre- and postoperatively.

METHODS

A consecutive series of patient with symptomatic dysplasia of the hip and a full radiologic workup (radiographs and CT scan pre- and postoperatively) who underwent periacetabular osteotomy were included. Standard radiographic parameters were compared between radiographs and radiograph-like projections by two authors pre- and postoperatively.

RESULTS

A total of 16 hips (32 radiographs/32 radiograph-like projections) were included in the study. No significant difference was found between the radiographs and radiograph-like images for all parameter for both examiners. ICC between radiograph and radiograph-like projections for all investigated parameters showed good to excellent reliability (0.78-0.99) pre- and postoperatively.

CONCLUSION

Radiograph-like projections show comparable results to radiographs with regard to the important investigated parameters (lateral center edge angle, medial center edge angle, acetabular index, acetabular arc, extrusion index, crossover sign and posterior wall sign). Thus, ultra-low-dose CT scans may reduce the need for conventional radiographs in pre- and postoperative analyses of 3-dimensional hip pathologies in the future, as the advantages increasingly outweigh the disadvantages.

Editorial Commentary: Low-Radiation Dose 3-Dimensional Computed Tomography Scan Reconstruction Is the Best Way to Visualize the Anterior Inferior Iliac Spine-For Now

Femoroacetabular impingement comes in several anatomic variations that may coexist, and subspine impingement is a commonly discussed cause of indirect extra-articular hip pathology. Although a classification system to identify and understand anterior inferior iliac spine morphology has been in place for some time, attempts have been made to visualize and understand the anatomy based on other imaging modalities. Standard radiographs are a common part of the initial patient evaluation pathway, along with thorough history taking and physical examination findings. Magnetic resonance imaging scans are obtained typically to evaluate the soft tissue, muscle, ligaments, articular cartilage, and labrum for pathology. For many hip preservation surgeons, a computed tomography scan with 3-dimensional reconstruction is standard protocol for patients who progress along the treatment pathway toward a surgical procedure because understanding the complex hip anatomy is key to successful surgical treatment. Many hip arthroscopy patients are in their young adult years, and we always attempt to reduce the amount of radiation exposure. Eliminating this computed tomography scan and using standard-of-care magnetic resonance imaging to simplify patient care, reduce radiation, and reduce health care costs would certainly be beneficial to our hip preservation patients.

Three-Dimensional Magnetic Resonance Imaging Bone Models of the Hip Joint Using Deep Learning: Dynamic Simulation of Hip Impingement for Diagnosis of Intra- and Extra-articular Hip Impingement

Background:

Dynamic 3-dimensional (3D) simulation of hip impingement enables better understanding of complex hip deformities in young adult patients with femoroacetabular impingement (FAI). Deep learning algorithms may improve magnetic resonance imaging (MRI) segmentation.

Purpose:

(1) To evaluate the accuracy of 3D models created using convolutional neural networks (CNNs) for fully automatic MRI bone segmentation of the hip joint, (2) to correlate hip range of motion (ROM) between manual and automatic segmentation, and (3) to compare location of hip impingement in 3D models created using automatic bone segmentation in patients with FAI.

Study Design:

Cohort study (diagnosis); Level of evidence, 3.

Methods:

The authors retrospectively reviewed 31 hip MRI scans from 26 symptomatic patients (mean age, 27 years) with hip pain due to FAI. All patients had matched computed tomography (CT) and MRI scans of the pelvis and the knee. CT- and MRI-based osseous 3D models of the hip joint of the same patients were compared (MRI: T1 volumetric interpolated breath-hold examination high-resolution sequence; 0.8 mm³ isovoxel). CNNs were used to develop fully automatic bone segmentation of the hip joint, and the 3D models created using this method were compared with manual segmentation of CT- and MRI-based 3D models. Impingement-free ROM and location of hip impingement were calculated using previously validated collision detection software.

Results:

The difference between the CT- and MRI-based 3D models was <1 mm, and the difference between fully automatic and manual segmentation of MRI-based 3D models was <1 mm. The correlation of automatic and manual MRI-based 3D models was excellent and significant for impingement-free ROM (r = 0.995; P < .001), flexion (r = 0.953; P < .001), and internal rotation at 90° of flexion (r = 0.982; P < .001). The correlation for impingement-free flexion between automatic MRI-based 3D models and CT-based 3D models was 0.953 (P < .001). The location of impingement was not significantly different between manual and automatic segmentation of MRI-based 3D models, and the location of extra-articular hip impingement was not different between CT- and MRI-based 3D models.

Conclusion:

CNN can potentially be used in clinical practice to provide rapid and accurate 3D MRI hip joint models for young patients. The created models can be used for simulation of impingement during diagnosis of intra- and extra-articular hip impingement to enable radiation-free and patient-specific surgical planning for hip arthroscopy and open hip preservation surgery.

Quantification of Acetabular Coverage on 3-Dimensional Reconstructed Computed Tomography Scan Bone Models in Patients With Femoroacetabular Impingement Syndrome: A Descriptive Study

Background

Accurate assessment of osseous morphology is imperative in the evaluation of patients with femoroacetabular impingement syndrome (FAIS) and hip dysplasia. Through use of computed tomography (CT), 3-dimensional (3D) reconstructed hip models may provide a more precise measurement for overcoverage and undercoverage and aid in the interpretation of 2-dimensional radiographs obtained in the clinical setting.

Purpose

To describe new measures of acetabular coverage based on 3D-reconstructed CT scan bone models.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Preoperative CT scans were acquired on the bilateral hips and pelvises of 30 patients before arthroscopic surgical intervention for FAIS. Custom software was used for semiautomated segmentation to generate 3D osseous models of the femur and acetabulum that were aligned to a standard coordinate system. This software calculated percentage of total acetabular coverage, which was defined as the surface area projected onto the superior aspect of the femoral head. The percentage of coverage was also quantified regionally in the anteromedial, anterolateral, posteromedial, and posterolateral quadrants of the femoral head. The acetabular clockface was established by defining 6 o'clock as the inferior aspect of the acetabular notch. Radial coverage was then calculated along the clockface from the 9-o'clock to 5-o'clock positions.

Results

The study included 20 female and 10 male patients with a mean age of 33.6 ± 11.7 years and mean body mass index of 27.8 ± 6.3. The average percentage of total acetabular coverage for the sample was 57% ± 6%. Acetabular coverages by region were as follows: anteromedial, 78% ± 7%; anterolateral, 18% ± 7%, posterolateral, 33% ± 13%, and posteromedial, 99% ± 1%. The acetabular coverage ranged from 23% to 69% along the radial clockface from 9 to 5 o'clock.

Conclusion

This study demonstrated new 3D measurements to characterize acetabular coverage in patients with FAIS and elucidated the distribution of acetabular coverage according to these measurements.

Consistency of 3D femoral torsion measurement from MRI compared to CT gold standard

Background

Several hip and knee pathologies are associated with aberrant femoral torsion. Diagnostic workup includes computed tomography (CT) and magnetic resonance imaging (MRI). For three-dimensional (3D) analysis of complex deformities it would be desirable to measure femoral torsion from MRI data to avoid ionizing radiation of CT in a young patient population. 3D measurement of femoral torsion from MRI has not yet been compared to measurements from CT images. We hypothesize that agreement will exist between MRI and CT 3D measurements of femoral torsion.

Methods

CT and MRI data from 29 hips of 15 patients with routine diagnostic workup for suspected femoroacetabular impingement (FAI) were used to generate 3D bone models. 3D measurement of femoral torsion was performed by two independent readers using the method of Kim et al. which is validated for CT. Inter-modalitiy and inter-reader intraclass correlation coefficients (ICC) were calculated.

Results

Between MRI and CT 3D measurements an ICC of 0.950 (0.898; 0.976) (reader 1) respectively 0.950 (0.897; 0.976) (Reader 2) was found. The ICC (95% CI) expressing the inter-reader reliability for both modalities was 0.945 (0.886; 0.973) for MRI and 0.957 (0.910; 0.979) for CT, respectively. Mean difference between CT and MRI measurement was 0.42° (MRI – CT, SD: 2.77°, p = 0.253).

Conclusions

There was consistency between 3D measurements of femoral torsion between computer rendered MRI images compared to measurements with the “gold standard” of CT images. ICC for inter-modality and inter-reader consistency indicate excellent reliability. Accurate, reliable and reproducible 3D measurement of femoral torsion is possible from MRI images.

Femoral Neck Hounsfield Units as an Adjunct for Bone Mineral Density After Combat-Related Lower Extremity Amputation

OBJECTIVES

To correlate femoral neck Hounsfield units (HUs) measured on a computed tomography (CT) scan to dual-energy x-ray absorptiometry (DEXA) T-scores allowing evaluation of bone mineral density (BMD) over time after lower extremity trauma-related amputation.

DESIGN

Retrospective cohort study.

SETTING

United States military trauma referral center.

PATIENTS

Military combat-related lower extremity amputees with both DEXA and CT scans within 6 months of each other.

INTERVENTION

None.

MAIN OUTCOME MEASURES

Correlation between femoral neck comprehensive mean HUs and BMD and HUs threshold for low BMD.

RESULTS

Regression model correlation (r) between CT HU and DEXA T-score was r = 0.84 [95% confidence interval (CI) 0.52-0.94] and r = 0.81 (95% CI 0.57-0.92) when CT imaging was separated from DEXA by less than 4 and 5 months, respectively. Beyond 5 months separation, correlation decreased to r = 0.60 (95% CI 0.29-0.80). Using a receiver operator characteristic curve for mean comprehensive HUs to determine low BMD with 4-month cut-off, a threshold of 151 HUs was 97% sensitive and 84% specific to identify low BMD, whereas 98 HUs was 100% sensitive and 100% specific to identify osteoporosis.

CONCLUSION

Using opportunistic CT, clinicians can reliably estimate BMD in trauma-related amputees. This information will inform providers making decisions regarding weightbearing and bisphosphonate therapy to limit further loss. Future phases of this study will aim to use this correlation to study the effects of weightbearing advancement timing, bisphosphonate therapy, and interventions on the natural history of bone density after amputation.

LEVEL OF EVIDENCE

Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Pelvic bone CT: can tin-filtered ultra-low-dose CT and virtual radiographs be used as alternative for standard CT and digital radiographs?

Objectives

To compare ultra-low-dose CT (ULD-CT) of the osseous pelvis with tin filtration to standard clinical CT (CT), and to assess the quality of computed virtual pelvic radiographs (VRs).

Methods

CT protocols were optimized in a phantom and three pelvic cadavers. Thirty prospectively included patients received both standard CT (automated tube voltage selection and current modulation) and tin-filtered ULD-CT of the pelvis (Sn140kV/50mAs). VRs of ULD-CT data were computed using an adapted cone beam–based projection algorithm and were compared to digital radiographs (DRs) of the pelvis. CT and DR dose parameters and quantitative and qualitative measures (1 = worst, 4 = best) were compared. CT and ULD-CT were assessed for osseous pathologies.

Results

Dose reduction of ULD-CT was 84% compared to CT, with a median effective dose of 0.38 mSv (quartile 1–3: 0.37–0.4 mSv) versus 2.31 mSv (1.82–3.58 mSv; p < .001), respectively. Mean dose of DR was 0.37 mSv (± 0.14 mSv). The median signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of bone were significantly higher for CT (64.3 and 21.5, respectively) compared to ULD-CT (50.4 and 18.8; p ≤ .01), while ULD-CT was significantly more dose efficient (figure of merit (FOM) 927.6) than CT (FOM 167.6; p < .001). Both CT and ULD-CT were of good image quality with excellent depiction of anatomy, with a median score of 4 (4–4) for both methods (p = .1). Agreement was perfect between both methods regarding the prevalence of assessed osseous pathologies (p > .99). VRs were successfully calculated and were equivalent to DRs.

Conclusion

Tin-filtered ULD-CT of the pelvis at a dose equivalent to standard radiographs is adequate for assessing bone anatomy and osseous pathologies and had a markedly superior dose efficiency than standard CT.

Key Points

• Ultra-low-dose pelvic CT with tin filtration (0.38 mSv) can be performed at a dose of digital radiographs (0.37 mSv), with a dose reduction of 84% compared to standard CT (2.31 mSv).

• Tin-filtered ultra-low-dose CT had lower SNR and CNR and higher image noise than standard CT, but showed clear depiction of anatomy and accurate detection of osseous pathologies.

• Virtual pelvic radiographs were successfully calculated from ultra-low-dose CT data and were equivalent to digital radiographs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00330-021-07824-x.

Hip Dysplasia

Acetabular dysplasia represents a structural pathomorphology associated with hip pain, instability, and osteoarthritis. The wide spectrum of dysplasia anatomically refers to a 3-dimensional volumetric- and surface area-based insufficiency in coverage and is classified based on the magnitude and location of undercoverage. Borderline dysplasia has been variably defined and leads to management challenges. In symptomatic dysplasia, treatment addresses coverage with periacetabular osteotomy. Concomitant simultaneous or staged hip arthroscopy has significant advantages to address intra-articular pathology. In nonarthritic individuals, there is evidence PAO alters the natural history of dysplasia and decreases the risk of hip arthritis and total hip arthroplasty.

A Novel Three-Dimensional-Printed Ultrasound-Guided Hip Arthrocentesis Model

When evaluating patients with hip pain, clinicians may be trained to both evaluate for a hip effusion and perform ultrasound-guided arthrocentesis to evaluate the etiology of the effusion. We present a novel 3-dimensional-printed hip arthrocentesis model, which can be used to train clinicians to perform both tasks under ultrasound guidance. Our model uses a combination of a 3-dimensional-printed hip joint, as well as readily available materials such as an infant Ambu (Ballerup, Denmark) bag, syringe, intravenous line kit, and silicone. We present our experience so that others may use and adapt our model for their training purposes.

MRI-based 3D models of the hip joint enables radiation-free computer-assisted planning of periacetabular osteotomy for treatment of hip dysplasia using deep learning for automatic segmentation

Introduction

Both Hip Dysplasia(DDH) and Femoro-acetabular-Impingement(FAI) are complex three-dimensional hip pathologies causing hip pain and osteoarthritis in young patients. 3D-MRI-based models were used for radiation-free computer-assisted surgical planning. Automatic segmentation of MRI-based 3D-models are preferred because manual segmentation is time-consuming.To investigate(1) the difference and(2) the correlation for femoral head coverage(FHC) between automatic MR-based and manual CT-based 3D-models and (3) feasibility of preoperative planning in symptomatic patients with hip diseases.

Methods

We performed an IRB-approved comparative, retrospective study of 31 hips(26 symptomatic patients with hip dysplasia or FAI). 3D MRI sequences and CT scans of the hip were acquired. Preoperative MRI included axial-oblique T1 VIBE sequence(0.8 mm³ isovoxel) of the hip joint. Manual segmentation of MRI and CT scans were performed. Automatic segmentation of MRI-based 3D-models was performed using deep learning.

Results

(1)The difference between automatic and manual segmentation of MRI-based 3D hip joint models was below 1 mm(proximal femur 0.2 ± 0.1 mm and acetabulum 0.3 ± 0.5 mm). Dice coefficients of the proximal femur and the acetabulum were 98 % and 97 %, respectively. (2)The correlation for total FHC was excellent and significant(r = 0.975, p < 0.001) between automatic MRI-based and manual CT-based 3D-models. Correlation for total FHC (r = 0.979, p < 0.001) between automatic and manual MR-based 3D models was excellent.(3)Preoperative planning and simulation of periacetabular osteotomy was feasible in all patients(100 %) with hip dysplasia or acetabular retroversion.

Conclusions

Automatic segmentation of MRI-based 3D-models using deep learning is as accurate as CT-based 3D-models for patients with hip diseases of childbearing age. This allows radiation-free and patient-specific preoperative simulation and surgical planning of periacetabular osteotomy for patients with DDH.

Standard Versus Low-Dose Computed Tomography for Assessment of Acetabular Fracture Reduction

OBJECTIVE

First, to assess the impact of varying computed tomography (CT) radiation dose on surgeon assessment of postfixation acetabular fracture reduction and malpositioned implants. Second, to quantify the accuracy of CT assessments compared with the experimentally set displacement in cadaver specimens. We hypothesized that a CT dose would not affect the assessments and that CT assessments would show a high concordance with known displacement.

METHODS

We created posterior wall acetabular fractures in 8 fresh-frozen cadaver hips and reduced them with varying combinations of step and gap displacement. The insertion of an intra-articular screw was randomized. Each specimen had a CT with standard (120 kV), intermediate (100 kV), and low-dose (80 kV) protocols, with and without metal artifact reduction postprocessing. Reviewers quantified gap and step displacement, overall reduction, quality of the scan, and identified intra-articular implants.

RESULTS

There were no significant differences between the CT dose protocols for assessment of gap, step, overall displacement, or the presence of intra-articular screws. Reviewers correctly categorized displacement as anatomic (0-1 mm), imperfect (2-3 mm), or poor (>3 mm) in 27.5%-57.5% of specimens. When the anatomic and imperfect categories were condensed into a single category, these scores improved to 52.5%-82.5%. Intra-articular screws were correctly identified in 56.3% of cases. Interobserver reliability was poor or moderate for all items. Reviewers rated the quality of most scans as "sufficient" (60.0%-72.5%); reviewers more frequently rated the low-dose CT as "inferior" (30.0%) and the standard dose CT as "excellent" (25%).

CONCLUSION

A CT dose did not affect assessment of displacement, intra-articular screw penetration, or subjective rating of scan quality in the setting of a fixed posterior wall fracture.

1.5 T magnetic resonance imaging generates accurate 3D proximal femoral models: Surgical planning implications for femoroacetabular impingement

The objective of this study was to validate three-dimensional (3D) proximal femoral surface models generated from a 1.5 T magnetic resonance imaging (MRI) by comparing these 3D models to those derived from the clinical "gold standard" of computed tomography (CT) scan and to ground-truth surface models obtained by laser scans (LSs) of the excised femurs. Four intact bilateral cadaveric pelvis specimens underwent CT and MRI scans and 3D surface models were generated. Six femurs were extracted from these specimens, and the overlying soft tissues were removed. The extracted femurs were then laser scanned to produce a ground-truth surface model. A 3D-3D registration method was used to compare the signed and absolute surface-to-surface distances between the 3D models. Absolute agreement was evaluated using a 95% confidence interval (CI) derived from the precision of the LS ground-truth. Paired samples t tests and Kolmogrov-Smirnov tests were performed to compare the differences between the signed and absolute surface-to-surface distances between the models. The average signed surface-to-surface distances for the MRI vs LS and MRI vs CT models were 0.07 and 0.16 mm, respectively. These differences fell within the 95% CI of ±0.20 mm indicating absolute agreement between the surface models generated from these modalities. The signed surface-to-surface distance was significantly smaller for MRI vs LS ground truth model as compared with the CT vs LS model. Femoral models derived from a 1.5 T MRI scan demonstrated absolute agreement with the clinical gold standard of CT-derived models and were most like LS ground truth models of the excised femurs.

Guidelines for the assessment of bone density and microarchitecture in vivo using high-resolution peripheral quantitative computed tomography

INTRODUCTION

The application of high-resolution peripheral quantitative computed tomography (HR-pQCT) to assess bone microarchitecture has grown rapidly since its introduction in 2005. As the use of HR-pQCT for clinical research continues to grow, there is an urgent need to form a consensus on imaging and analysis methodologies so that studies can be appropriately compared. In addition, with the recent introduction of the second-generation HrpQCT, which differs from the first-generation HR-pQCT in scan region, resolution, and morphological measurement techniques, there is a need for guidelines on appropriate reporting of results and considerations as the field adopts newer systems.

METHODS

A joint working group between the International Osteoporosis Foundation, American Society of Bone and Mineral Research, and European Calcified Tissue Society convened in person and by teleconference over several years to produce the guidelines and recommendations presented in this document.

RESULTS

An overview and discussion is provided for (1) standardized protocol for imaging distal radius and tibia sites using HR-pQCT, with the importance of quality control and operator training discussed; (2) standardized terminology and recommendations on reporting results; (3) factors influencing accuracy and precision error, with considerations for longitudinal and multi-center study designs; and finally (4) comparison between scanner generations and other high-resolution CT systems.

CONCLUSION

This article addresses the need for standardization of HR-pQCT imaging techniques and terminology, provides guidance on interpretation and reporting of results, and discusses unresolved issues in the field.

High-Resolution Maxillofacial Computed Tomography Is Superior to Head Computed Tomography in Determining the Operative Management of Facial Fractures

BACKGROUND

Computed tomography of the head (CTH) and maxillofacial bones (CTMF) can be performed concurrently, but CTMF is frequently ordered separately, after facial fractures identified on CTH scans. This study aims to evaluate whether obtaining additional CTMF after CTH changes operative management of patients with facial trauma.

MATERIALS AND METHODS

A retrospective chart review was performed of all patients with facial trauma who presented to our level 1 trauma center between January 2009 and May 2019. CTH and CTMF were reviewed for each patient. Fracture numbers and patterns were compared to determine if CTMF provided additional information that necessitated change in management, based on predetermined criteria.

RESULTS

A total of 1215 patients were assessed for facial trauma. Of them, 899 patients underwent both CTH and CTMF scans. CTH identified 22.7% less fractures than CTMF (P < 0.001); specifically, more orbital, nasal, naso-orbito-ethmoid, zygoma, midface, and mandible fractures (P < 0.001). Of all patients 9.2% (n = 83) of patients with nonoperative fractures on CTH were reclassified as operative on CTMF; 0.6% (n = 5) with operative patterns on CTH were reclassified as nonoperative on CTMF, and 18.1% (n = 163) experienced a changed in their operative plan though operative fractures were seen on both imaging modalities. Additional findings seen on CTMF delegated change in the operative plan in 27.9% (n = 251) of cases.

CONCLUSIONS

CTMF scans are necessary to determine operative intervention. As CTH and CTMF are constructed from the data, physicians should consider ordering both scans simultaneously for all patients with facial trauma to limit radiation exposure, control costs, and avoid delays in care.

The Effect of Modality and Landmark Selection on MRI and CT Femoral Torsion Angles

Background Assessment of femoral torsion at preoperative hip imaging is commonly recommended. However, it is unclear whether MRI is as accurate as CT and how different methods affect femoral torsion measurements. Purpose To compare MRI- and CT-based assessment of femoral torsion by using four commonly used measurement methods in terms of agreement, reproducibility, and reliability and to compare femoral torsion angles between the four different measurement methods. Materials and Methods This retrospective study evaluated patients with hip pain who underwent CT and 3-T MRI of the hip including sequences of the pelvis and distal condyles between May 2017 and June 2018. The four measurement methods differed regarding the landmark levels for the proximal femoral reference axis and included measurements at the level of the greater trochanter, femoral neck, base of the femoral neck, and level of the lesser trochanter. Intraclass correlation coefficients (ICCs) were calculated, and Bland-Altman analysis was performed. Results Forty-five patients (mean age ± standard deviation, 19 years ± 5; 27 female) and 57 hips were evaluated. Inter- and intrarater reliability were excellent for each of the four CT- and MRI-based measurement methods (ICC range, 0.97-0.99). Mean difference between CT- and MRI-based measurement ranged from 0.3° ± 3.4 (P = .58) to 2.1° ± 4.1 (P < .001). Differences between CT and MRI were within the corresponding ICC variation for all four measurement methods. Mean torsion angles were greater by 17.6° for CT and 18.7° for MRI (all P < .001) between the most proximal to the most distal measurement methods. Conclusion MRI- and CT-based femoral torsion measurements showed high agreement and comparable reliability and reproducibility but were dependent on the level of selected landmarks used to define the proximal reference axis. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Zoga in this issue.

Standing CT of the equine head: Reducing radiation dose maintains image quality

Multiple published studies involving computed tomographic (CT) examinations of the equine head utilise a wide range of mAs parameters for image acquisition. This prospective, experimental study assessed the effects of lowering mAs during CT image acquisition on image quality and scatter radiation on 10 cadaver equine heads. Each head was scanned three times at 300, 225, and 150 mAs, with all other scanning parameters remaining constant between series. An anthropomorphic phantom was positioned adjacent to each equine head during image acquisition, mimicking a human bystander, with an ionization chamber attached to the phantom at eye level. Each series was reconstructed using filtered back projection, using medium (H30) and high (H80) frequency reconstruction algorithms. Quantitative image quality assessment was performed by calculating signal to noise ratio (SNR) and contrast to noise ratio (CNR). Two qualitative image quality assessments were performed independently by three blinded board certified veterinary radiologists with a 4 week interval, using a visual grade analysis model adapted from peer reviewed medical literature. Ionization chamber measurements, calculated volume CT dose index (CTDIvol), and dose-length product (DLP) were recorded. Halving radiation dose during image acquisition from 300 to 150mAs resulted in comparable image quality between series. There was a statistically significant and linear relationship between mAs and scatter radiation to the bystander; halving mAs during image acquisition resulted in halving of scatter radiation. Results of this cadaveric study support the use of lower mAs settings during standing CT examinations of the equine head.

Patient-Specific 3-D Magnetic Resonance Imaging-Based Dynamic Simulation of Hip Impingement and Range of Motion Can Replace 3-D Computed Tomography-Based Simulation for Patients With Femoroacetabular Impingement: Implications for Planning Open Hip Preservation Surgery and Hip Arthroscopy

BACKGROUND

Femoroacetabular impingement (FAI) is a complex 3-dimensional (3D) hip abnormality that can cause hip pain and osteoarthritis in young and active patients of childbearing age. Imaging is static and based on 2-dimensional radiographs or computed tomography (CT) scans. Recently, CT-based 3D impingement simulation was introduced for patient-specific assessments of hip deformities, whereas magnetic resonance imaging (MRI) offers a radiation-free alternative for surgical planning before hip arthroscopic surgery.

PURPOSE

To (1) investigate the difference between 3D models of the hip, (2) correlate the location of hip impingement and range of motion (ROM), and (3) correlate diagnostic parameters while comparing CT- and MRI-based osseous 3D models of the hip in symptomatic patients with FAI.

STUDY DESIGN

Cohort study (Diagnosis); Level of evidence, 2.

METHODS

The authors performed an institutional review board-approved comparative and retrospective study of 31 hips in 26 symptomatic patients with FAI. We compared CT- and MRI-based osseous 3D models of the hip in the same patients. 3D CT scans (slice thickness, 1 mm) of the entire pelvis and the distal femoral condyles were obtained. Preoperative MRI of the hip was performed including an axial-oblique T1 VIBE sequence (slice thickness, 1 mm) and 2 axial anisotropic (1.2 × 1.2 × 1 mm) T1 VIBE Dixon sequences of the entire pelvis and the distal femoral condyles. Threshold-based semiautomatic reconstruction of 3D models was performed using commercial software. CT- and MRI-based 3D models were compared with specifically developed software.

RESULTS

(1) The difference between MRI- and CT-based 3D models was less than 1 mm for the proximal femur and the acetabulum (median surface distance, 0.4 ± 0.1 mm and 0.4 ± 0.2 mm, respectively). (2) The correlation for ROM values was excellent (r = 0.99, P < .001) between CT and MRI. The mean absolute difference for flexion and extension was 1.9°± 1.5° and 2.6°± 1.9°, respectively. The location of impingement did not differ between CT- and MRI-based 3D ROM analysis in all 12 of 12 acetabular and 11 of 12 femoral clock-face positions. (3) The correlation for 6 diagnostic parameters was excellent (r = 0.98, P < .001) between CT and MRI. The mean absolute difference for inclination and anteversion was 2.0°± 1.8° and 1.0°± 0.8°, respectively.

CONCLUSION

Patient-specific and radiation-free MRI-based dynamic 3D simulation of hip impingement and ROM can replace CT-based 3D simulation for patients with FAI of childbearing age. On the basis of these excellent results, we intend to change our clinical practice, and we will use MRI-based 3D models for future clinical practice instead of CT-based 3D models. This allows radiation-free and patient-specific preoperative 3D impingement simulation for surgical planning and simulation of open hip preservation surgery and hip arthroscopic surgery.

Editorial Commentary: Low-Dose Hip Computed Tomography Sharpens the Saw for Hip Preservation: Can It Cut the Tree?

Computed tomography scans provide excellent visualization of complex hip deformities and assist in the diagnosis and surgical planning of hip preservation surgery. The dose of harmful ionizing radiation can be reduced while preserving reasonable image quality. Low-dose hip computed tomography can be used successfully for preoperative planning. Readers should consider strategies to reduce the radiation dose from computed tomography scans and consider magnetic resonance imaging arthrograms for assessment of cartilage and labral status before hip preservation surgery.

Effect of initial emergency room imaging choice on time to hip reduction and repeat imaging

OBJECTIVES

Hip dislocations are highly morbid injuries necessitating prompt reduction and post-reduction assessment for fracture and incarcerated fragments. Recent literature has questioned the need for initial pelvic radiographs for acute trauma patients, resulting in computed tomography (CT) scans as the initial evaluation. This study investigates the relationship between choice of pre-reduction imaging and treatment of acute hip dislocations.

DESIGN

Retrospective Case-Control.

SETTING

Single Academic Level I Trauma Center.

METHODS

All acute hip dislocations from 2011 to 2016 were reviewed. Exclusion criteria were diagnosis of dislocation at another facility, death prior to reduction, emergent surgical or ICU intervention, and periprosthetic dislocation. Patients were grouped by those with only a radiograph prior to reduction, Group I, versus those with a pre-reduction CT scan, Group II. The primary outcomes were time to reduction and the acquisition of a second CT scan.

RESULTS

Of the 123 hip dislocations identified, 35 patients were excluded, mostly for transfer with a known dislocation. Group I included 29 patients and Group II included 59 patients. The mean time to reduction was 74 min in Group I and 129 min in Group II for a difference of 55 min (p < 0.001). The rate of repeat CT scan was 0 in Group I versus 48 (81%) in Group II (p < 0.001).

CONCLUSION

Initial trauma pelvic radiography prior to CT is still important in the setting of suspected hip pathology to decrease time to hip reduction and unnecessary radiation exposure.

LEVEL OF EVIDENCE

Prognostic Level III.

Editorial Commentary: Invisible, Odorless, and Deadly: Do Computed Tomography Scans in Young Patients With Hip Pain Cause Cancer?

Does imaging of the pelvis using a set of radiographs and computed tomography (CT) cause cancer? A computer-based simulation study using 5 different imaging and radiation dose protocols has calculated the lifetime risk of malignancy for young adults for pelvic radiographs and CT scans. The cumulative lifetime-attributable risk of cancer was 0.2% for males and 0.35% for females. This appears low but the numbers needed to harm were 952 for males and 564 for females. However, the authors have based their calculations on the linear no-threshold model, which is controversial, and a linear relationship between dose and risk may not exist.