Bipositional MR imaging vs. arthrography for the

Journal of Clinical Imaging 26 (2002) 342 – 346

Bipositional MR imaging vs. arthrography for the evaluation of femoral head sphericity and containment in Legg–Calve´ –Perthes disease ¨ stu¨n Aydingo¨zb,*, M. Cemalettin Aksoya, Rahmi Can Akgu¨na Muharrem Yazicia, U a

Department of Orthopaedics and Traumatology, Hacettepe University School of Medicine, 06100 Ankara, Turkey b Department of Radiology, Hacettepe University School of Medicine, 06100 Ankara, Turkey Received 20 February 2002

Abstract Eleven hips of 10 patients with Legg – Calve´ – Perthes disease (LCPD) were examined by arthrography and magnetic resonance (MR) imaging. Arthrogram and MR images were obtained with the hips in neutral position and in 20° flexion – abduction and internal rotation. Modified arthrographic index (AI) was used for the evaluation of sphericity and acetabulum head index (AHI) was used for the assessment of containment. According to AI, there is no significant difference between the arthrograms and coronal MR imaging, but the difference between the coronal and sagittal MR imaging was significant. There was no statistical difference between the arthrograms and MR measurements in terms of AHI. Anterior flattening of the femoral head and the effect of hip flexion in the containment at the sagittal plane could be demonstrated clearly in sagittal MR imaging. Even if there was significant flattening in coronal plane, the sphericity of the head was preserved in the sagittal plane. Bipositional MR imaging is comparable to arthrography for the demonstration of sphericity and containment of the femoral head in both coronal and sagittal planes in LCPD. D 2002 Elsevier Science Inc. All rights reserved. Keywords: Legg – Calve´ – Perthes disease; Arthrography; MR imaging

1. Introduction The most important prognostic factors in Legg –Calve´ – Perthes disease (LCPD) are the patient age at disease onset and the severity of the hip joint deformity [1]. Ismail and Macnicol [2] have shown that the severity of femoral head involvement and sphericity determined by arthrography are the most reliable parameters in terms of final outcome. Determining the relationship between the contours of the femoral head and the acetabulum in various positions is of the utmost importance in choosing the method of treatment. Because most of the femoral head is composed of cartilage in early childhood, X-rays do not provide sufficient information. This relationship can be dynamically imaged by arthrography, which for years has been used in deciding on treatment in LCPD [1]. However, this method requires general anesthesia and the intraarticular injection of a contrast material; moreover, the gonads are exposed to radiation. * Corresponding author. Cevher Sok. 2-3 Kurtulus¸, 06600 Ankara, Turkey. Tel.: +90-312-305-2958; fax: +90-312-312-7071. ¨ . Aydingo¨z). E-mail address: [email protected] (U

In recent years, magnetic resonance (MR) imaging has become a popular technique in LCPD for a variety of purposes [3]. With MR imaging, it is possible to diagnose synovial changes and alterations in bone marrow in the early stages and even to determine the prognosis. MR imaging has many important advantages, e.g., being noninvasive, not requiring anesthesia, providing high soft tissue contrast, and enabling multiplanar investigations. The main disadvantage is that standard MR imaging is a static examination and is therefore inadequate for imaging the relationship between the joints in various positions. The purpose of this study was to obtain bipositional images using a closed (instead of open) MR unit and, by comparing these images with arthrographic findings, to investigate whether MR imaging can be used as an alternative to arthrography in LCPD.

2. Materials and methods Eleven hips of 10 LCPD patients (nine males and one female, average age: 6, age range: 3– 11 years) examined by MR imaging and arthrography were assessed retrospec-

0899-7071/02/$ – see front matter D 2002 Elsevier Science Inc. All rights reserved. PII: S 0 8 9 9 - 7 0 7 1 ( 0 2 ) 0 0 4 4 6 - 1

M. Yazici et al. / Journal of Clinical Imaging 26 (2002) 342–346

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Fig. 1. Patient’s position during MR imaging. Neutral (A) and abduction – flexion – internal rotation (B).

tively. Widespread femoral head involvement (Catterall stages 3 or 4) was determined in all patients and all were in the fragmentation phase.

Arthrography was carried out under general anesthesia with fluoroscopic guidance. A minimum of four images was obtained (neutral anterior – posterior, abduction – internal

Fig. 2. Calculation of the AI in arthrography (A) and MR imaging (B). Ratio between the radius and the distance of the center to the most depressed superolateral point.

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rotation, adduction, and lateral). For MR imaging, a 0.5-T MR system (Philips Gyroscan, The Netherlands) was used. T1-weighted spin echo coronal (TR/TE 500/20 ms, 256 256 matrix, field of view 19 cm, 4-mm section thickness, 0.4-mm intersection spacing) and coronal and sagittal T2weighted gradient echo (TR/TE 600/27 ms, flip angle 35°, 256 256 matrix, field of view 21 cm, 4-mm section thickness, 0.4-mm intersection spacing) images were obtained. After examination in the neutral position was completed, each child’s hip was brought to 20° of abduction – flexion and internal rotation and the investigation was repeated (Fig. 1). Arthrography and MR imaging were carried out within a week of each other in all patients. Both arthrograms and MR images were assessed with regard to the containment and the severity and localization of the deformity at the femoral head. Hinge abduction at the femoral head was also assessed. The arthrographic index (AI) modified by Shigeno and Evans [4] was used for the objective evaluation of femoral head sphericity in MR images and arthrograms taken in the neutral position (Fig. 2). The ratio between

the radius and the distance from the superolateral corner, where the head is most depressed, to the center was calculated. For the assessment of containment, the acetabulum head index (AHI) recommended for arthrography by Moberg et al. [5] was used (Fig. 3). The index was calculated for both the bone and the labral corner. The ratio of the width of the head to the distance between the medial margin of the head and the most lateral point of the acetabulum was calculated separately for the bone and the labrum. The AI was also used for objective evaluation of the sphericity in the sagittal MR images. The Wilcoxon signed rank test was used for statistical comparison. A P value of < .05 was considered significant. Measurements were evaluated by linear regression analysis.

3. Results The femoral head was markedly flattened in the coronal plane in eight patients and in the sagittal plane in two patients.

Fig. 3. Calculation of the AHI in arthrography (A) and MR imaging (B). Bony AHI = BI/OI 100 and labral AHI = LI/OI 100 (I: inner, B: bone, L: labrum, O: outer).


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Fig. 4. Anterior extrusion of the femoral head and the effect of flexion position on the joint relationship in sagittal MR. Neutral (A) and at flexion – abduction – internal rotation (B).

In two patients, the indentation that was formed by the acetabulum on the superolateral part of the head was observed to be typical. The hinging of the femoral head on abduction in these patients appeared as medial dye-pooling in arthrograms, and as an increase in the distance of the medial joint on MR imaging. Overall, arthrography and MR images were identical with respect to the relationship between femoral head contours and the joint. The AI was measured at 0.82 (range 0.62 – 0.96) on arthrograms, 0.82 (range 0.65 – 0.95) on coronal MR imaging, and 0.88 (range 0.68 – 0.96) on sagittal MR imaging. There was no statistically significant difference between the arthrogram and coronal MR imaging, and an excellent correlation was determined ( P = .858, r 2 = .97). However, the difference between coronal and sagittal MR index values was significant ( P = .003, r 2 = .55). On arthrograms, the AHI, measured with the edge of the bone and labrum as reference points, were 71 (range 60 – 82) and 84 (range 73– 92), respectively. On MR imaging, bony AHI was measured as 69 (range 58 –78) for bony corner and 84 (range 72– 92) for labral corner. No statistical difference

was found with respect to the measurements made using the edge of the bone and the edge of the cartilage as reference points ( P = .215 and P = .878, respectively).

4. Discussion LCPD generally affects children 4 – 10 years of age. In this disease, the etiology of which is not completely known, the blood supply to the femoral head epiphysis is temporarily disturbed. Necrosis occurs in the epiphysis, decreasing the bone integrity and causing deformity in the femoral head and thus disrupting the congruity between the femoral head and the acetabulum [1,2]. The lower the age at onset, the lower the risk of deformity. Another factor having a positive effect on the final outcome is the protection of the femoral head in the active phase of the disease. The prognosis is bad in older children (9+ years) and in cases where the femoral head loses its sphericity and the congruity between the acetabulum and the femoral head is deformed. The primary goal in the treatment

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of LCPD, which is a self-limiting process, is to preserve the joint congruity until the active disease has run its course, at the same time maintaining the containment of the femoral head by the acetabulum at maximum. Therefore, awareness of the state of congruity and containment during the active phase of the disease is of great importance in tailoring a therapy program [1]. Arthrography is traditionally a much-used technique for imaging both the true shape of the head and the congruity of the joint in different hip positions. Although excellent dynamic imaging of hip anatomy is possible by arthrography, the frequency of its use is limited by disadvantages such as the requirement of general anesthesia, intraarticular injection of a contrast material, and the use of ionizing radiation [2]. While it is possible to obtain images in the lateral plane, sagittal images are not as informative as coronal images because of the superposition of other bone structures with the hip joint. With MR imaging, LCPD can be diagnosed in the early term, and the extent of alterations in the epiphysis and metaphysis can be determined with certainty, and a preliminary prognosis can be made. Another important advantage of MR imaging is its multiplanar capability [3]. No intraarticular procedure is necessary, nor is general anesthesia, though children may be lightly sedated. However, a static MR imaging examination does not provide answers to all the questions of concern in LCPD. In recent years, a number of reports have been published in radiological literature stating that, with open-system MR imaging units, dynamic images would be possible in Perthes patients and that the information obtained from these images would be similar to arthrographic findings [6,7]. These studies were conducted with patients in the lateral decubitus position. Open-system MR imaging is not available everywhere and the image quality is inferior to that of conventional MR imaging units. In the present study, images were obtained with a conventional MR imaging unit and with the patients in the supine position. The data obtained from MR imaging analysis are very similar with respect to both general observation and objective parameters. Since neither sphericity values nor the AHI was significantly different between the two imaging methods, MR imaging appears to be a good alternative to arthrography. The degree of postoperative containment was clearly demonstrated by 20° abduction –internal rotation and flexion images obtained in a position simulating surgery (varus – derotation– extension osteotomy or triple pelvic osteotomy).

It is known that the anterior and lateral parts of the head are generally involved in LCPD. The femoral head extrudes anteriorly as well as laterally. Therefore, when treatment is being planned, anterior, as well as lateral, containment should be targeted [8]. In our study, the effects of deformity and hip flexion in the sagittal plane on containment were demonstrated in detail with MR imaging (Fig. 4). Sagittal images showed that, even if there was necrosis in the anterior part and the femoral head extruded anteriorly, the sphericity in this plane was better preserved than in the coronal plane and the head takes on a cylindrical appearance. This finding is in agreement with previously reported findings in the literature [4,9]. In conclusion, bipositional images obtained by closedsystem MR imaging are an alternative to arthrography for imaging the femoral head, the degree of its involvement, and its relationship to the acetabulum. The advantages of MR imaging are that it is noninvasive, does not require radiation, provides excellent soft tissue detail, and enables simultaneous examination of the sagittal plane.

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