Myles Mabee

Three-Dimensional Intercondylar Notch Volumes in a Skeletally Immature Pediatric Population: A Magnetic Resonance Imaging–Based Anatomic Comparison of Knees With Torn and Intact Anterior Cruciate Ligaments

PURPOSE To determine whether 3-dimensional notch volume, measured with magnetic resonance imaging (MRI), differs significantly between knees with torn and intact anterior cruciate ligaments (ACLs) after sports injury in a skeletally immature pediatric population. METHODS MRI studies of 50 pediatric patients (age range, 10 to 17 years) with ACL tears were compared with 50 age- and sex-matched intact-ACL control patients. All patients had open physes and underwent MRI after a sports injury. Notch volume was calculated through manual segmentation of notch boundaries seen on axial 1.5-T proton density-weighted images. Two-dimensional (2D) measurements (notch width and notch width index) were made on coronal proton density-weighted MRI studies. Notch volume was compared between groups by use of the Mann-Whitney U test. Pearson correlation coefficients were also calculated between indices. RESULTS Notch volume was significantly lower in knees with ACL tears than in control knees (5.5 ± 1.1 cm(3)v 6.4 ± 1.5 cm(3), P = .002), whereas 2D notch width and notch width index did not differ significantly between these groups. Girls had significantly smaller notch volumes than boys (5.4 ± 1.2 cm(3)v 6.5 ± 1.3 cm(3), P < .001). Notch volume was not correlated with age but was moderately correlated with 2D notch width (r = 0.485, P < .001). CONCLUSIONS In adolescent patients with sports injuries, the 3-dimensional notch volume was significantly smaller in knees with ACL tears than in intact-ACL control knees. Notch volume was also significantly smaller in girls than in boys and did not vary significantly with age. LEVEL OF EVIDENCE Level III, case-control study.

Potential for Change in US Diagnosis of Hip Dysplasia Solely Caused by Changes in Probe Orientation: Patterns of Alpha-angle Variation Revealed by Using Three-dimensional US

PURPOSE To use three-dimensional ( 3D three-dimensional ) ultrasonography (US) to quantify the alpha-angle variability due to changing probe orientation during two-dimensional ( 2D two-dimensional ) US of the infant hip and its effect on the diagnostic classification of developmental dysplasia of the hip ( DDH developmental dysplasia of the hip ). MATERIALS AND METHODS In this institutional research ethics board-approved prospective study, with parental written informed consent, 13-MHz 3D three-dimensional US was added to initial 2D two-dimensional US for 56 hips in 35 infants (mean age, 41.7 days; range, 4-112 days), 26 of whom were female (mean age, 38.7 days; range, 6-112 days) and nine of whom were male (mean age, 50.2 days; range, 4-111 days). Findings in 20 hips were normal at the initial visit and were initially inconclusive but normalized spontaneously at follow-up in 23 hips; 13 hips were treated for dysplasia. With the computer algorithm, 3D three-dimensional US data were resectioned in planes tilted in 5° increments away from a central plane, as if slowly rotating a 2D two-dimensional US probe, until resulting images no longer met Graf quality criteria. On each acceptable 2D two-dimensional image, two observers measured alpha angles, and descriptive statistics, including mean, standard deviation, and limits of agreement, were computed. RESULTS Acceptable 2D two-dimensional images were produced over a range of probe orientations averaging 24° (maximum, 45°) from the central plane. Over this range, alpha-angle variation was 19° (upper limit of agreement), leading to alteration of the diagnostic category of hip dysplasia in 54% of hips scanned. CONCLUSION Use of 3D three-dimensional US showed that alpha angles measured at routine 2D two-dimensional US of the hip can vary substantially between 2D two-dimensional scans solely because of changes in probe positioning. Not only could normal hips appear dysplastic, but dysplastic hips also could have normal alpha angles. Three-dimensional US can display the full acetabular shape, which might improve DDH developmental dysplasia of the hip assessment accuracy.

MRI Anatomy of the Tibial ACL Attachment and Proximal Epiphysis in a Large Population of Skeletally Immature Knees Reference Parameters for Planning Anatomic Physeal-Sparing ACL Reconstruction

Background: To aid in performing anatomic physeal-sparing anterior cruciate ligament (ACL) reconstruction, it is important for surgeons to have reference data for the native ACL attachment positions and epiphyseal anatomy in skeletally immature knees. Purpose: To characterize anatomic parameters of the ACL tibial insertion and proximal tibial epiphysis at magnetic resonance imaging (MRI) in a large population of skeletally immature knees. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The ACL tibial attachment site and proximal epiphysis were examined in 570 skeletally immature knees with an intact ACL (age, 6-15 years) using 1.5-T proton density–weighted sagittal MRI; also measured were the tibial anteroposterior diameter; anterior, central, and posterior ACL attachment positions; vertical height of the epiphysis; and maximum oblique epiphyseal depth extending from the ACL tibial attachment center to the tibial tuberosity. Results: In adolescents (11-15 years of age), the center of the ACL’s tibial attachment was 51.5% ± 5.7% of the anteroposterior diameter of the tibia, with no significant differences between sexes or age groups (P > .05 in all cases). Mean vertical epiphyseal height was 15.9 ± 1.7 mm in the adolescent group, with significant differences between 11-year-olds (15.2 ± 1.5 mm) and 15-year-olds (16.6 ± 1.6 mm), P < .001, and between males (16.6 ± 1.5 mm) and females (14.8 ± 1.4), P < .001. Mean maximum oblique depth was 30.0 ± 5.3 mm, with a significant difference between 11-year-olds (26.7 ± 4.9 mm) and 15-year-olds (32.7 ± 5.1 mm), P < .001, and between males (29.7 ± 6.4 mm) and females (27.8 ± 5.2 mm), P < .001. The maximum oblique depth occurred at a mean angle of ~50°, and this angle did not change with age or sex. There was a significant moderate correlation (r = 0.39, P < .001) between epiphyseal vertical height and maximum oblique depth. Conclusion: The center of the ACL tibial attachment was consistently near 51% of the anteroposterior diameter, regardless of age or sex. The vertical depth of the tibial epiphysis was ~16 mm in adolescents. Maximum oblique depth from ACL attachment was ~30 mm, occurring at a mean angle ~50° regardless of age or sex. The normative values for tibial ACL attachment and epiphyseal anatomy presented here may be helpful in selecting candidates for surgery and in planning surgical approaches for pediatric ACL reconstruction.

Reproducibility of Acetabular Landmarks and a Standardized Coordinate System Obtained from 3D Hip Ultrasound

Two-dimensional (2D) ultrasound detection of developmental dysplasia of the hip (DDH) is limited by variation in acetabular appearance and alpha angle measurements, which change with position of the ultrasound probe. Three-dimensional (3D) ultrasound captures the entire acetabular shape, and a reproducible “standard central plane” may be generated, from two landmarks located on opposite ends of the acetabulum, for measurement of alpha angle and other indices. Two users identified landmarks on 51 3D ultrasounds, with ranging severity of disease, and inter- and intra-observer reproducibility of landmark and “standard plane” locations was compared; landmarks were chosen within 2 mm, and the “standard plane” rotation was reproducible within 10° between observers. We observed no difference in variability between alpha angles measured on the “standard plane” in comparison with 2D ultrasound. Applications of the standardized 3D ultrasound central plane will be to fuse serial ultrasounds for follow-up and development of new indices of 3D deformity.

Toward automated classification of acetabular shape in ultrasound for diagnosis of DDH

BACKGROUND AND OBJECTIVES The diagnosis of Developmental Dysplasia of the Hip (DDH) in infants is currently made primarily by ultrasound. However, two-dimensional ultrasound (2DUS) images capture only an incomplete portion of the acetabular shape, and the alpha and beta angles measured on 2DUS for the Graf classification technique show high inter-scan and inter-observer variability. This variability relates partly to the manual determination of the apex point separating the acetabular roof from the ilium during index measurement. This study proposes a new 2DUS image processing technique for semi-automated tracing of the bony surface followed by automatic calculation of two indices: a contour-based alpha angle (αA), and a new modality-independent quantitative rounding index (M). The new index M is independent of the apex point, and can be directly extended to 3D surface models. METHODS We tested the proposed indices on a dataset of 114 2DUS scans of infant hips aged between 4 and 183 days scanned using a 12MHz linear transducer. We calculated the manual alpha angle (αM), coverage, contour-based alpha angle and rounding index for each of the recordings and statistically evaluated these indices based on regression analysis, area under the receiver operating characteristic curve (AUC) and analysis of variance (ANOVA). RESULTS Processing time for calculating αA and M was similar to manual alpha angle measurement, ∼30s per image. Reliability of the new indices was high, with inter-observer intraclass correlation coefficients (ICC) 0.90 for αA and 0.89 for M. For a diagnostic test classifying hips as normal or dysplastic, AUC was 93.0% for αA vs. 92.7% for αM, 91.6% for M alone, and up to 95.7% for combination of M with αM, αA or coverage. CONCLUSIONS The rounding index provides complimentary information to conventional indices such as alpha angle and coverage. Calculation of the contour-based alpha angle and rounding index is rapid, shows potential to improve the reliability and accuracy of DDH diagnosis from 2DUS, and could be extended to 3D ultrasound in future.

An index for diagnosing infant hip dysplasia using 3-D ultrasound: the acetabular contact angle

BackgroundDevelopmental dysplasia of the hip (DDH) is a common condition that is highly treatable in infancy but can lead to the lifelong morbidity of premature osteoarthritis if left untreated. Current diagnostic methods lack reliability, which may be improved by using 3-D ultrasound.ObjectiveConventional 2-D US assessment of DDH has limitations, including high inter-scan variability. We quantified DDH on 3-D US using the acetabular contact angle (ACA), a property of the 3-D acetabular shape. We assessed ACA reliability and diagnostic utility.Materials and methodsWe prospectively collected data from January 2013 to December 2014, including 114 hips in 85 children divided into three clinical diagnostic groups: (1) normal, (2) initially borderline but ultimately normal without treatment and (3) dysplastic requiring treatment. Using custom software, two observers each traced acetabula twice on two 3-D US scans of each hip, enabling automated generation of 3-D surface models and ACA calculation. We computed inter-observer and inter-scan variability of repeatability coefficients and generated receiver operating characteristic (ROC) curves.ResultsThe 3-D US acetabular contact angle was reproduced 95% of the time within 6° in the same scan and within 9° in different scans of the same hip, vs. 9° and 14° for the 2-D US alpha angle (P < 0.001). Areas under ROC curves for diagnosis of developmental dysplasia of the hip were 0.954 for ACA and 0.927 for alpha angle.ConclusionThe 3-D US ACA was significantly more reliable than 2-D US alpha angle, and the 3-D US measurement predicted the presence of DDH with slightly higher accuracy. The ACA therefore shows promising initial diagnostic utility. Our findings call for further study of 3-D US in the diagnosis and longer-term follow-up of infant hip dysplasia.

Ultrasound Quantification of Acetabular Rounding in Hip Dysplasia: Reliability and Correlation to Treatment Decisions in a Retrospective Study

Currently, acetabular rounding is only subjectively assessed on ultrasound for developmental dysplasia of the hip. We tested whether acetabular rounding can be quantified reliably and can distinguish between hips requiring and not requiring treatment. Consecutive infants (n = 90) suspected of having dysplasia of the hip, seen at a pediatric orthopedic clinic, were separated into four diagnostic categories (normal, borderline but resolved, treated by brace, treated surgically). Acetabular rounding was assessed by semi-quantitative grade (0 = nil, 1 = mild, 2 = moderate, 3 = severe) by three observers and by direct measurement of acetabular radius of curvature (AROC) by two observers. Inter-observer reliability of rounding grade was poor (κ = 0.30-0.37). AROC had an inter-observer intra-class correlation coefficient of 0.84 and coefficient of variation of 29%-34%. Mean AROC was significantly higher for hips requiring treatment than for those not requiring treatment (3.3 mm vs. 1.6 mm, p = 0.007). AROC reliably quantifies an observation currently being made subjectively by radiologists and surgeons, and may be useful as a supplementary ultrasound index of dysplasia of the hip in future prospective studies.

A Validation Study of a Novel 3-Dimensional MRI Modeling Technique to Identify the Anatomic Insertions of the Anterior Cruciate Ligament

Background: Anatomic single bundle anterior cruciate ligament (ACL) reconstruction is the current gold standard in ACL reconstructive surgery. However, placement of femoral and tibial tunnels at the anatomic center of the ACL insertion sites can be difficult intraoperatively. We developed a “virtual arthroscopy” program that allows users to identify ACL insertions on preoperative knee magnetic resonance images (MRIs) and generates a 3-dimensional (3D) bone model that matches the arthroscopic view to help guide intraoperative tunnel placement. Purpose: To test the validity of the ACL insertion sites identified using our 3D modeling program and to determine the accuracy of arthroscopic ACL reconstruction guided by our “virtual arthroscopic” model. Study Design: Descriptive laboratory study. Methods: Sixteen cadaveric knees were prescanned using routine MRI sequences. A trained, blinded observer then identified the center of the ACL insertions using our program. Eight knees were dissected, and the centers of the ACL footprints were marked with a screw. In the remaining 8 knees, arthroscopic ACL tunnels were drilled into the center of the ACL footprints based on landmarks identified using our virtual arthroscopic model. Postprocedural MRI was performed on all 16 knees. The 3D distance between pre- and postoperative 3D centers of the ACL were calculated by 2 trained, blinded observers and a musculoskeletal radiologist. Results: With 2 outliers removed, the postoperative femoral and tibial tunnel placements in the open specimens differed by 2.5 ± 0.9 mm and 2.9 ± 0.7 mm from preoperative centers identified on MRI. Postoperative femoral and tibial tunnel centers in the arthroscopic specimens differed by 3.2 ± 0.9 mm and 2.9 ± 0.7 mm, respectively. Conclusion: Our results show that MRI-based 3D localization of the ACL and our virtual arthroscopic modeling program is feasible and does not show a statistically significant difference to an open arthrotomy approach. However, additional refinements will be required to improve the accuracy and consistency of our model to make this an effective tool for surgeons performing anatomic single-bundle ACL reconstructions. Clinical Relevance: Arthroscopic anatomic single-bundle ACL reconstruction is the current gold standard for ACL reconstruction; however, the center of the ACL footprint can be difficult to identify arthroscopically. Our novel modeling can improve the identification of this important landmark intraoperatively and decrease the risk of graft malposition and subsequent graft failure.

Developmental Hip Dysplasia Diagnosis at Three-dimensional US: A Multicenter Study

Purpose To validate accuracy of diagnosis of developmental dysplasia of the hip (DDH) from geometric properties of acetabular shape extracted from three-dimensional (3D) ultrasonography (US). Materials and Methods In this retrospective multi-institutional study, 3D US was added to conventional two-dimensional (2D) US of 1728 infants (mean age, 67 days; age range, 3-238 days) evaluated for DDH from January 2013 to December 2016. Clinical diagnosis after more than 6 months follow-up was normal (n = 1347), borderline (Graf IIa, later normalizing spontaneously; n = 140) or dysplastic (Graf IIb or higher, n = 241). Custom software accessible through the institutions research portal automatically calculated indexes including 3D posterior and anterior alpha angle and osculating circle radius from hip surface models generated with less than 1 minute of user input. Logistic regression predicted clinical diagnosis (normal = 0, dysplastic = 1) from 3D indexes (ie, age and sex). Output represented probability of hip dysplasia from 0 to 1 (output: >0.9, dysplastic; 0.11-0.89, borderline; <0.1, normal). Software can be accessed through the research portal. Results Area under the receiver operating characteristic curve was equivalently high for 3D US indexes and 2D US alpha angle (0.996 vs 0.987). Three-dimensional US helped to correctly categorize 97.5% (235 of 241) dysplastic and 99.4% (1339 of 1347) normal hips. No dysplastic hips were categorized as normal. Correct diagnosis was provided at initial 3D US scan in 69.3% (97 of 140) of the studies diagnosed as borderline at initial 2D US scans. Conclusion Automatically calculated 3D indexes of acetabular shape performed equivalently to high-quality 2D US scans at tertiary medical centers to help diagnose DDH. Three-dimensional US reduced the number of borderline studies requiring follow-up imaging by over two-thirds.

Hip segmentation from MRI volumes in infants for DDH diagnosis and treatment planning

Diagnosis and surgical management of Developmental Dysplasia of the Hip (DDH) relies on physical examination and 2D ultrasound scanning. Magnetic Resonance Imaging (MRI) can be used to complement existing techniques and could be advantageous in treatment planning due to its larger field of view. In this paper we propose a semi-automatic method to segment surface models of the acetabulum from MRI images. The method incorporates clinical knowledge in the form of intensity priors which are integrated into a Random Walker (RW) formulation. We use a modified RW framework which compensates for incomplete or blurred boundaries in the image by using information from neighboring slices in the sequence incorporated as node weights. We conducted a pilot study to evaluate the segmentation on a set of 10 infant hip MRI sequences using a 1.5 Tesla MR scanner. Contours obtained from the semi-automated segmentation were compared against manually segmented hip contours using Dice Ratio (DR), Hausdorff Distance (HD) and Root Mean Square (RMS) distance. The proposed method gave values of (DR = 0.84 ± 0.5, HD =3.0 ± 0.7, RMS =1.9 ± 0.3) and (DR=0.86 ± 0.2, HD=3.0 ± 0.1, RMS= 2.0 ± 0.6) for right and left acetabular contours respectively which was higher than the corresponding values obtained from conventional RW segmentation. The execution time of the segmentation algorithm was less than ~4 seconds on a 3.5 GHz CPU.