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Evaluation and Classification

Arthrogram in Legg-Calvé-Perthes Disease

Milani, Carlo PhD; Dobashi, Eiffel Tsuyoshi PhD

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Journal of Pediatric Orthopaedics: September 2011 - Volume 31 - Issue - p S156-S162
doi: 10.1097/BPO.0b013e318223b441
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Abstract

One hundred years have passed since the first citations of Legg-Calvé-Perthes disease (LCPD), and many studies have been carried out during this period. Between 1966 and 2010, Medline carried 1763 references and between 1950 and 2010, Pubmed indexed 2020 scientific papers, excluding books, chapters in books, and papers presented at events. However, it seems that even today, there are many doubts regarding LCPD that are yet to be discussed.

The current conceptualization of this disease is that of an idiopathic necrosis of the proximal femur epiphysis (PFE) that can be totally or partially involved. However, its etiology has still not been fully elucidated despite many studies on the disease.

Treatment should be initiated as early as possible, that is, as soon as the diagnosis has been made, as the configuration of the femoral head (FH) is essential for the prognosis of the hip articulation during LCPD evolution.1–4 The treatment, whether conservative or surgery, is always based on the concept of “containment,” that is, maintaining the FH inside the acetabulum socket throughout the entire evolution of the disease.5–8

To avoid problems ranging from incipient osteoarthritis to the complete degeneration of the affected hip, it is necessary that the PFE remains spherical up to its skeletal maturity during the course of the disease.4,9

RADIOGRAPHIC STUDIES

Although LCPD affects skeletally immature hips, in the majority of institutions, its diagnosis is carried out using conventional x-rays, patient history and clinical examination.10,11

Unfortunately, a radiographic examination (ie, x-ray) only imparts information on the ossified parts of the acetabulum and the FH, but it does not allow us to assess the cartilaginous structure of the hip joint.4,12–14

For this reason, our lack of knowledge of the PFEs cartilaginous structure limits radiographic examination conclusions and, at times, leads to an incorrect interpretation of the position of the FH in relation to the acetabulum, which is fundamental information for determining which therapeutic measures to adopt.

Moreover, in LCPD cases, the so-called early radiographic signals only appear at the advanced stage of the disease, as a considerable loss of trabecular bone is necessary before radiographic abnormalities become evident. This occurs about 6 months after the first infarction of the affected FH.15,16

The prognosis to determine the future of the hip affected by LCPD is performed by analyzing the lesion extension of the PFE ossific nucleus and the lateral subluxation of the FH.17–19 These 2 factors, associated with the stage of the disease, are important parameters in the choice of treatment and in the prognosis of the joint in question.12 However, conventional radiography does not give us information on these 2 factors.15,20–22 Therefore, it becomes necessary to resort to other examinations, such as pneumoarthrography (PAG) and magnetic resonance imaging (MRI), to evaluate the optimal treatment with greater certainty.7,13,23–26

LAREDO'S ARTHROGRAPHIC CLASSIFICATION

Hip arthrography is a diagnostic technique of great importance because it allows a precise and detailed analysis of the morphological aspects of the cartilaginous portion of the FH and acetabulum.10,24,27 In our institution, it has been possible to observe the importance of hip arthrography in LCPD based on a study carried out by Laredo in 1985.28 In 1992,27 based on experiences using arthrography to address this disease, Laredo studied 87 patients (for a total of 105 hips) with LCPD and idealized the arthrographic classification on which the form and size of the FH and its position in the labrum are based. The Laredo classification includes 5 groups. Group I indicates a normal hip; diagnosis is made according to clinical history, physical examination, and scintigraphy. Group II indicates an FH larger than normal but still spherical, with extrusion present at the neutral position and absent at 30 degrees abduction and slight internal rotation. Normally, groups I and II do not present risk and can be treated by conservative therapy, but must be closely observed. Group III indicates an FH larger than normal and ovoid, with extrusion present at 30 degrees abduction and slight internal rotation; this is a hip with early arthrographic risk. Group IV indicates an FH larger than normal and flattened, whereas the labrum loses its concavity and becomes elevated and straightened; extrusion is present at 30 degrees abduction and slight internal rotation, with hinge abduction present. This describes a hip with late arthrographic risk. Finally, group V indicates an FH larger than normal and saddle shaped, whereas the labrum is elevated and sometimes everted, with abnormal pooling of contrast medium at the saddle deformity area. Extrusion is present at 30 degrees abduction and slight internal rotation. This describes a hip with severe late arthrographic risk (Figs. 1–5).

FIGURE 1
FIGURE 1:
Laredo group I: Normal hip. A, Anteroposterior view. B, Thirty degrees abduction and internal rotation.
FIGURE 2
FIGURE 2:
Laredo group II: femoral head larger than normal but still spherical. A, Anteroposterior view. B, Thirty degrees abduction and internal rotation.
FIGURE 3
FIGURE 3:
Laredo group III: femoral head ovoid and larger than normal. A, Anteroposterior view. B, Thirty degrees abduction and internal rotation.
FIGURE 4
FIGURE 4:
Laredo group IV: femoral head flattened and larger than normal. A, Anteroposterior view. B, Thirty degrees abduction and internal rotation.
FIGURE 5
FIGURE 5:
Laredo group V: hinge abduction. A, Anteroposterior view. B, Thirty degrees abduction and internal rotation.

According to this classification, the collapse of the FH in patients who are carriers of LCPD would start in the hip, which he classified as group III. Therefore, according to the researcher, we should focus on this deformity, which he called a “hip at premature arthrographic risk,” to achieve the best results.

The grading systems developed by Catterall,10 Salter-Thompson,29 and Herring et al30 consider femoral lesion extension in the x-ray. The arthrographic classification is based on the shape and size of the femoral proximal epiphysis. We adopted this method because it can be applied in the very beginning of the disease and throughout its entire course to detect early FH deformities. The Salter-Thompson classification29 is applied only in the necrotic phase, and subchondral fracture is not frequently seen. In our series, we observed subchondral fracture in 20% of the cases. When the affected hip is classified as Laredo's group III, it corresponds to Salter-Thompson's B. Along the fragmentation phase, Laredo groups III, IV, and V correspond to Catterall's III or IV and Herring's B, B/C, or C. With regard to the final outcome, applying our protocol of treatment, when the hip is classified as Laredo's I, II, or III, 68% of them will correspond to classes I or II according to Stulberg et al.17 We observed in our series that 87% of the hips classified as Laredo IV or V have strict correlation with Stulberg et al17 classes III and IV.

OUR EXPERIENCE RESULTS AND DISCUSSION

One of our studies was carried out in 2000 at the Universidade Federal de São Paulo, Brasil, in association with the Orthopaedic Paediatric Discipline of the Montpellier Faculty and included 60 patients that were carriers of unilateral LCPD. On applying the Laredo classification, we observed that 26 (78.79%) of the 33 hips in the necrosis phase belonged to Laredo groups III, IV, and V, whereas 10 (76.93%) of the 13 hips in the fragmentation phase were of groups III, IV and (Table 1). In conclusion we observed that 60% of the hips evaluated by PAG had not an appropriate femoral head coverage by the acetabulum. This fact was not noticed by simple pelvis x-ray.

TABLE 1
TABLE 1:
Correlation of the 4 Laredo Classes

To confirm this finding, we measured the acetabulum head index (AHI) using the Heyman-Herdon methodology31 on the x-rays and the respective PAG for the 60 patients examined. We verified that the indices measured on normal hips by radiography were significantly larger than those measured by PAG. The x-ray AHI value for the normal hips was 0.9564 with a standard deviation (SD) of 0.0807, whereas the PAG-AHI value for normal hips was 0.8418 with an SD of 0.0591. For pathological hips, the x-ray AHI value was 0.8721 with an SD of 0.1176, and the PAG AHI value was 0.7565 with an SD of 0.807. However, to obtain normality with respect to AHI in the radiographies, we should apply an SD value between 0.8757 and 1.0371. For normality of AHI in arthrographies, values between 0.7827 and 0.09009 were obtained (Table 2). In this way, we would be able to define hip subluxation as a radiography AHI lower than 87.57% and a PAG AHI lower than 78.27%. As a consequence, we found 10 hips covered by both x-ray and PAG, 30 hips not covered by x-ray and PAG, and 20 hips (33%) covered by x-ray but not covered by PAG.

TABLE 2
TABLE 2:
Average Measurements of the Acetabular Head Index and SD From Plain X-ray and PAG of 60 Hips and the Results Applying the Wilcoxon Test

This discrepancy was defined by Laredo as “arthrographic radiography dissociation.” In other words, 33% of hips analyzed using x-rays probably did not receive the correct treatment.

In the same study, we measured the angle that the labrum forms with Hilgenreiner's line (Fig. 6) in the PAG of the 60 hips studied in relation to Laredo's classification. Labrum angles that were classified as groups I and II were considered as a single group because there was no significant difference between them.

FIGURE 6
FIGURE 6:
Labrum angle (LA) in the arthrogram.

Under this configuration, the comparison of the labrum angle among the 4 groups (I/II, III, IV, and V) showed significant differences (P<0,001) among them (Table 3). There is an inverse association between the labrum angle and the Laredo classification; that is, the higher the classification is, the lower the angle is (Fig. 7). Moreover, it is precisely in groups III, IV, and V that the labrum angle changes significantly in relation to groups I and II. Thus, we again stress the need for the containment of the labrum angle of these hips in the region of 26 degrees.

TABLE 3
TABLE 3:
Averages and Standard Deviations (SD) of All the Measurement Values in Degrees of the Angle of the Labrum in 60 Pathologic Hips and 54 Normal Contralateral Hips Distributed in 4 Categories, According to Laredo
FIGURE 7
FIGURE 7:
Mean measurements of all labrum angle values obtained from the pneumoarthrography in 60 pathologic hips and 54 contralateral normal hips.

In this study, the extrusion of the FH was analysed by using the simple x-ray and PAG applying the method described by Dickens and Menelaus.32 This way we determined 4 significant distinct groups based on the Laredo's classification. In the pathological hips, these results were observed both for the measurements obtained from the radiographies and for those obtained from the PAG. For normal hips, no significant differences were noted across the 4 groups with either PAG or radiography. In the PAG of the pathological hips, extrusion was significantly different from group III onward, whereas in the radiographies, differences were only significant in groups IV and V (Table 4).

TABLE 4
TABLE 4:
Averages and SD of the Values of the Femoral Head Extrusion Measured in the PAG With Regard to the 4 Groups Determined From Laredo

This finding validates 2 facts. First, hip radiography on LCPD does not mirror the anatomical reality of the FH affected by the disease in absolute terms.11,18,33–36 Second, it is precisely Laredo's group III that shows the head exiting its protection zone in the acetabulum bone rim such that deformation will occur with absolute certainty if not addressed in a timely manner.10,32

Researchers such as Axer and Schiller,20 Gershuni,15 and Kamegaya et al33 showed good results through the utilization of PAG because they were able to give early FH cover when it was still under subluxation.

With regard to treatment, the conservative one is applied in cases with arthrographic classification groups I and II, and the patient is periodically clinically controlled. Another arthrographic examination can be performed if the patient's clinical pattern suggests a worsening of conditions. In group III, when the FH is contained in the acetabulum, the proximal femoral varus osteotomy is indicated and, when the proximal femur is considered containable, the Salter's osteotomy is used. In group IV, in which the proximal femur is uncontained but still congruent with the acetabulum, Chiari's osteotomy or the shelf procedure can be indicated. In group V, the hinge abduction hip is treated by valgus osteotomy of the proximal femur.

In 2004, Ishida et al37 studied the Salter Osteotomy results in the treatment of 32 patients (37 hips) at skeletal maturity and observed that the hips classified as group III showed better results in relation to groups IV and V. This result supports the understanding that it is important to provide effective coverage to the FH before it becomes severely deformed to create a more favorable biomechanical environment for the PFE to remodel during the course of the disease.38

Many researchers have confirmed the superimposition of the MRI coronal images in relation to PAG (Fig. 8).25,26,34,39–41 Indeed, all findings can be verified by MRI. Moreover, this approach has some advantages, as is noninvasive, and provides an early diagnosis.

FIGURE 8
FIGURE 8:
Superimposing the magnetic resonance image (MRI) in relation to pneumoarthrography (PAG). A, MRI. B, PAG.

The major disadvantages of MRI are its cost and lack of availability, especially in developing countries. In our institution, the waiting time for an MRI examination is several months for selective patients, which renders treatment based on this examination generally unfeasible.

THE IMPORTANCE OF DYNAMIC ARTHROGRAPHY

Various researchers have confirmed the usefulness of dynamic arthrography in their papers,5,37,42,43 although some have stated that information from dynamic arthrography did not change their surgical treatment protocol.36,44,45

At our Institution, we use dynamic PAG during surgery because it allows us to assess the congruence of the joint and choose the best position of the FH in relation to the acetabulum.

The important is the protocol of the examination procedure. According to Kaelin,46 we must analyze and choose the position that offers the best congruency and stability. For each position, it is necessary to examine the form of the osseous and cartilaginous cotyle and the shape of the osseous and cartilaginous FH, specifically noting irregularities in cartilage thickness and cephalic sphericity, especially in the zone of greater loading.

If the congruence of the hip is present, we will not note a contrast between the head and the acetabulum. We should consider the position of the FH in relation to the acetabulum rather than what we find on the outside. In fact, in most cases there is a coxa magna in most cases, and in such cases, the acetabular cotyle would not be able to cover the FH entirely.

It is also important to study the images in traction and under pressure to simulate gait. If the hip is unstable, the head will subluxate laterally in the cranial direction at the moment of pressure.

The evaluation of suave and harmonious movements without brusque maneuvers is also important.

FINAL CONSIDERATIONS

Despite all the methodologies and image examinations developed over the last 30 years, such as ultrasound, scintigraphy, computerized tomography, and magnetic resonance, we believe that PAG remains an important technique, especially in countries where the availability of newer equipment is limited. In our view, dynamic arthrography is currently the best method for establishing the ideal position for the FH in relation to the acetabulum when surgical treatment in indicated for LCPD.

ACKNOWLEDGMENTS

The authors thank Alain Dimeglio for his hospitality in Montpellier, Brauns & Brauns Language Consultancy for their English support and Sheila Ribeiro de Campos Solla for her editorial assistance in the preparation of this manuscript.

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Keywords:

Legg-Calvé-Perthes disease; pneumo-arthrogram; hip; children

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