Can 3D ultrasound identify trochlea dysplasia in newborns? Evaluation and applicability of a technique

https://doi.org/10.1016/j.ejrad.2015.03.015Get rights and content

Highlights

  • We evaluated a possible screening method for trochlea dysplasia.

  • 3D ultrasound was used to perform the measurements on standardized axial planes.

  • The evaluation of the technique showed comparable results to other studies.

  • This technique may be used as a screening technique as it is quick and easy to perform.

Abstract

Femoro-patellar dysplasia is considered as a significant risk factor of patellar instability. Different studies suggest that the shape of the trochlea is already developed in early childhood. Therefore early identification of a dysplastic configuration might be relevant information for the treating physician. An easy applicable routine screening of the trochlea is yet not available. The purpose of this study was to establish and evaluate a screening method for femoro-patellar dysplasia using 3D ultrasound. From 2012 to 2013 we prospectively imaged 160 consecutive femoro-patellar joints in 80 newborns from the 36th to 61st gestational week that underwent a routine hip sonography (Graf). All ultrasounds were performed by a pediatric radiologist with only minimal additional time to the routine hip ultrasound. In 30° flexion of the knee, axial, coronal, and sagittal reformats were used to standardize a reconstructed axial plane through the femoral condyle and the mid-patella. The sulcus angle, the lateral-to-medial facet ratio of the trochlea and the shape of the patella (Wiberg Classification) were evaluated. In all examinations reconstruction of the standardized axial plane was achieved, the mean trochlea angle was 149.1° (SD 4.9°), the lateral-to-medial facet ratio of the trochlea ratio was 1.3 (SD 0.22), and a Wiberg type I patella was found in 95% of the newborn. No statistical difference was detected between boys and girls. Using standardized reconstructions of the axial plane allows measurements to be made with lower operator dependency and higher accuracy in a short time. Therefore 3D ultrasound is an easy applicable and powerful tool to identify trochlea dysplasia in newborns and might be used for screening for trochlea dysplasia.

Introduction

The early identification of deformities and anatomical abnormalities is important information for clinicians to give advice to the parents, organize follow-up or to initiate treatment, all in the effort to prevent future problems and subsequent irreversible damage. Especially in pediatric orthopedics due to the partially guidable growth of the bone and the rapid development of technical orthotics more and more treatment methods become available. One of the screening techniques that had a notable impact on the natural history of a developmental abnormality was the ultrasound screening of the hip developed by Graf [1]. Today, techniques have further improved but modern screening techniques necessitate being quick, cost-effective, safe, and easily applicable.

Femoro-trochlea dysplasia is known to be one of the most important predisposing factors for the development of femoro-patellar instability in children and adults [2]. Instability of the patella with recurrent dislocations results in high patient morbidity and serves as a risk factor for osteo-arthritis [3]. Flattening of the lateral femoral condyle and enlargement of the bony sulcus angle more than 145° predispose to relocation of the patella [3]. In 1950, Gray and Gardener described the surface morphology of the knee which had already been determined very early in utero [4]. These findings were supported by studies on deceased fetuses [5]. Therefore early identification of trochlea dysplasia might be useful to prevent the sequel of patellar instability. In newborns neither radiographs, nor MRI is an optimal imaging modality. Most bony structures are not ossified yet so the definitive form of the femoro-patellar joint is not visible on radiographs. The limitations of MRI for screening purposes in newborns are availability, costs, and need of sedation. Ultrasound allows identification of multiple structures: cartilage, muscles, ligaments and their attachments, and the bone [6], [7]. It is a safe and quick image modality. However, quality and interpretation of the images is an issue and the technique is user dependent. First experiences with an ultrasound using a 3-dimensional system (3D) for screening of hip dysplasia showed a faster and simpler determination of a standard plane [8].

The aim of this study was to establish and evaluate the applicability of a 3D ultrasound screening method for early detection of femoro-patellar dysplasia in newborns, which is reliable, quick, and easy applicable.

Section snippets

Materials and methods

The study was approved by the Ethics Commission of the University Children's Hospital and the Cantonal Ethics Committee. Prospectively all healthy term born babies with no known other syndromes, who were planned for the regular hip-screening ultrasound were included in the study. Hip screening ultrasounds are an established examination at our center. All children at six weeks of age undergo clinical examination of the hip and hip ultrasound. Informed consent was taken prior to the examination.

Results

In total 80 babies (50 boys and 30 girls) from the 36th to 61st gestational week received the additional ultrasound examination of both knees. One hundred and sixty femoro-patellar articulations were analyzed. An initial learning curve was observed but the additional time to the normal hip ultrasound examination was about 1–2 min. All newborn tolerated the procedure without any noticeable discomfort, no sedation used or needed in any of the cases. The best results of image acquisition were

Discussion

To our knowledge, our study is the first to evaluate the applicability of 3D ultrasound as a screening tool for femoro-patellar dysplasia in newborns. Compared with cross-sectional imaging ultrasound 3D ultrasound is relatively inexpensive and easily available. Most importantly reformats of a standardized plane may be less operator dependent then B-mode ultrasound. Sonographic examination of the femoro-patellar articulation can be performed in a short time, there is no need for sedation, and it

Conclusion

3D ultrasound can identify femoro-patellar dysplasia in newborns and has the potential for the use as a screening tool. Standardized axial planes lower the user dependency, allow a more accurate and reproducible long term follow-up, and documentation of the trochlea development. In addition it may provide a guide for the success of new therapeutic options (braces, cast, and physiotherapy) in femoro-patellar dysplasia. However, today therapeutic options are still missing to address the problem

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