Is the Acetabulum Retroverted in SCFE? A Study of Acetabular Morphology in Indian Children with SCFE

Abstract

Background

Acetabular morphology has always been an area of interest in patients with slipped capital femoral epiphysis (SCFE). Acetabular retroversion in SCFE is proposed as a pre-disposing factor and also can predispose the hip to pincer impingement. But there is controversial data in literature regarding the acetabular morphology. All available data are from the West and we present the first study on acetabular morphology in Indian children with SCFE.

Methods

CT scans of 29 patients with SCFE were collected from our database and anteversion was measured as described by Dandachli et al. Lateral central edge angle (LCEA) was measured in the standard AP radiographs of the pelvis. There were 20 boys and 9 girls with a mean age of 13.5. Seven patients had right side SCFE, eighteen had left side SCFE, and four had bilateral involvement. Measurements were done in 33 affected hips and compared with 25 normal hips.

Results

The mean AVsup and AVcen of affected hips were 6.59° and 13.51°, respectively, and that in normal hips were 8.36° and 14.04° (p > 0.05). The mean LCEA was 23.05° on the affected hips and 25.45° on the normal hips (p > 0.05). The AVsup showed retroversion in 24.24% (8/33) of the affected hips and 20% (5/25) of the normal hips. Though the mean version was less in SCFE hips, it was not statistically significant.

Conclusion

Our study documents that 25% of hips with SCFE had acetabular retroversion. However, this was not significantly high compared to the contralateral hips.

Introduction

Slipped capital femoral epiphysis (SFCE) is a common adolescent hip disorder with lot of controversies right from its causation to the management [1–3]. The morphology of the acetabulum in patients with SCFE has been studied previously. Increased lateral CE angle in patients with SCFE has been reported by Kitadai et al. [4]. There are controversial reports on the version of acetabulum in SCFE patients. Though some of the authors have reported it to be normal [5, 6] more recent reports suggests that acetabular is retroverted in patients with SCFE [7–9]. In situ screw fixation which still remains the gold standard for treatment can results in a typical pistol-grip deformity of the proximal femur and this can lead to symptomatic femoro-acetabular impingement. The presence of retroverted acetabulum would theoretically predispose to increased incidence of femoro-acetabular impingement. All the available data on the acetabular morphology are from the West and there are no data reported on the acetabular morphology in Indian children with SCFE. With this background, this study was done to answer the following questions: (1) what is the morphology of acetabulum in Indian children with SCFE? (2) Is there a significant difference in the morphology compared to the unaffected side?

Acetabulum has a complex three-dimensional morphology and trying to study this with two-dimensional imaging may not represent the true morphology. However, measuring the morphological data from a 3-D image could be technically difficult. Dandachli et al. has validated a 2D CT quantifying method of acetabular version, which provides an acetabular version angle that corresponds to the average acetabular version of the superior half of the acetabulum [10]. He has also reported that this method of analysis correlates well with the three-dimensional analysis. This study was done to analyze the acetabular morphology using this new validated method of measuring acetabular version on the CT of both the unaffected and affected hips of patients with slipped capital femoral epiphysis (SCFE) and also by measuring the lateral center–edge angle (LCEA) on plain radiographs of the pelvis.

Methods

With formal Institutional Review Board approval, the database of our Institution was searched for all patients admitted with a diagnosis of SCFE from January 2012 to December 2015. All the patients with SCFE, who had CT Pelvis preoperatively were included in the study irrespective of the method of treatment. All patients who did not have CT pelvis were excluded from the study.

Using Syngo CT Workstation, software version VE26A and Syngo version VE31H, each CT Pelvis was temporarily reconstructed in 3D to obtain a standard position of the pelvis. The 3D pelvis was then reoriented to a standard position by aligning the left and right ASIS in the axial view, aligning the superior portion of the right and left iliac spines in the coronal plane, and finally by aligning the pubic symphsis and the ASIS in the sagittal plane to correct the pelvic tilt. Once reoriented, the CT was reconstructed into 2 mm thickness/0.6 mm intersection gap axial and coronal cuts (Fig. 1a).

Fig. 1.

a Coronal cut section of the reoriented CT scan showing the levels of the axial cuts. b Anteversion measurement of the acetabulum in the second cut called as the superior 1/4th cut (AVsup). There significant retroversion of the affected left hip. c Anteversion measurement of the acetabulum in the third cut which is called as the central (AVsup)

In the reoriented CTs, the acetabular version was measured in two axial cuts; (1) axial cut corresponding to the centre of femoral head (AV_cen) (Fig. 1b) and (2) axial cut corresponding to superior one-fourth of the acetabular dome (AV_sup) (Fig. 1c) as described by Dandachli et al. It was proved by Dandachli that the axial cut through superior one-fourth of the line joining the acetabular roof and inferior pelvic tear drop had 93% correlation to the 3D measurement gold standard described. The lateral center–edge angle of Wiberg (LCEA) was measured using a standard AP X-ray of the pelvis (Fig. 2). All the measurements were done in the affected SCFE hip and normal hip. All the measurements were done by two different observers on two different occasions and the inter-observer error rate was calculated. The inter-observer agreement was excellent with an intraclass correlation co-efficient of 0.84. Statistical analysis was done using SPSS Version 25 and student t test was employed to find out if there is any significant difference between the groups. A negative AVsup value was considered as significant retroversion and Chi square test was done to find out if there was significant difference in retroversion among SCFE and normal hips.

Fig. 2.

X-ray of the pelvis with both hips showing the measurement of LCEA on both the hips

Results

We had 29 patients meeting our inclusion and exclusion criteria who were taken up as the study cohort. There were 20 boys and 9 girls with a mean age of 13.5. Seven patients had right side SCFE, eighteen had left side SCFE, and four had B/L involvement. Measurements were done in 33 affected hips and compared with 25 contralateral normal hips.

Acetabular Version at the Superior One-Fourth Cut (AV_sup)

The mean version (AV_sup) of the SCFE affected hip was 6.59° (SD 8.70) and that on the normal hip was 8.36° (SD 8.26). The distribution of AVsup in SCFE hips and normal hips is shown is the histogram (Fig. 3). There was no significant difference in AV_sup of the affected SCFE hip compared to unaffected hip (p > 0.05).

Fig. 3.

Histogram showing the AVsup in a normal hips, b SCFE hips

Acetabular Version at the Central Cut (AV_cen)

The mean version (AV_cen) of the SCFE hips was 13.52° (SD 4.37) and that of the normal hips was 14.04° (SD 4.59). There was no significant difference in AV_cen of the affected SCFE hip compared to unaffected hip (p > 0.05).

A negative value of the AVsup was considered as significant retroversion and we analysed all the retroverted hips in both the groups. The AVsup showed retroversion in 24.2% (8/33) of the SCFE affected hips and 20% (5/25) of the normal hips as revealed by the scatter plot in Fig. 4. The p value by Chi square test was 0.70 and this difference was not significant statistically. When we analysed the bilateral SCFE hips separately, though the mean version was 1.7°, only three of them had true retroversion as shown in the scatter plot in Fig. 4. One patient had retroversion on both hips, while other patient had retroverted acetabulum on the severely affected side.

Fig. 4.

Scatter plot showing the AVsup plotted in normal hips, SCFE hips, and bilateral SCFE hips

LCEA

The mean LCEA of the SCFE hip was 23.05° (SD 6.43) and that on the normal hip was 25.45° (SD 6.70). There was no significant difference in LCEA in the hips affected with SCFE compared with the normal hips (p > 0.05).

Discussion

SCFE is one of the most common pediatric hip disorders and the association between femoro-acetabular impingement and SCFE has been well established [11, 12]. Impingement may result from morphological changes in the femoral head and neck as well as in the acetabulum. The literature about acetabular morphology in SCFE is still controversial. Some of the studies have shown the acetabular version to be normal [5, 6] while a few recent studies have demonstrated acetabular retroversion in those hips affected with SCFE [7–9].

Previous studies have used 2D CT axial cut corresponding to center of femoral head to measure the anteversion or the cross-over sign on the plain radiographs as an indirect indicator of retroverted acetabulum [6, 7, 9]. Measurements made using these methods may not be the right representation of the complex three-dimensional morphology of the acetabulum. Although 3D CT is a very popular and widely available imaging tool, measurements on 3D CT is cumbersome. Our use of 3D CT in this study was limited to reorienting the pelvis to a standard anatomical position. In a recent study, Dandachli et al. has proved that measurement of acetabular version at the superior fourth of the acetabulum correlates well with the values measured in 3D CT and that this is a more sensitive method to measure the version of the acetabulum [10]. In this study, we have used this method to assess the version of acetabulum in patients with SCFE.

In our series, we defined retroversion as those hips with true retroversion with a negative version. We purposefully excluded those with version < 15° or the so-called relatively retroverted hips from the analysis as this would skew the results spuriously. In a similar study by Monazzam et al. the mean AV_sup in the age-matched controls was 6.68° and thus in this age group, the relative retroversion is the normal version and not an abnormal morphology [8].

The acetabular version (AV_sup), measured at the superior one-fourth cut of the acetabulum was 6.59° on the affected hip and 8.36° on the unaffected hip. This was different from the previous data published from the West which showed decreased version in the affected hips [8]. Though the version on the affected hip was less compared to unaffected hip, this was not statistically significant and there was no significant retroversion. This finding was also in contrast to the findings published by Sankar et al. which showed retroversion of the acetabulum on the affected as well as the unaffected hip in patients with SCFE [7]. However, the methodology in their study was based on the cross-over sign on the antero-posterior radiograph of the pelvis. When we analysed the incidence of retroversion in SCFE affected hips, we found that 24.5% of them had retroversion which shows that one in every four patients with SCFE hip had retroverted morphology. However, we did notice that about 20% of hips without SCFE also had retroversion.

In our study, the mean acetabular version (AV_cen) at the center of head of femur in SCFE patients affected hip was 13.52°. This was similar to the values reported in the previous study by Monazzam et al. which had a mean AV_cen of 13.67° [8]. There was no significant difference in the AV_cen between the affected and normal hips.

The LCEA represents the lateral coverage of the femoral head and an increased LCEA is an overcovered hip which can lead to femoro-acetabular impingement. In our series, there was no significant increase in LCEA in SCFE hips compared to the contralateral hips. Kitadai et al. reported similar findings in his study which showed no significant difference in LCEA between affected and contralateral normal hips [4]. However, when compared with age-matched normal population, the LCEA in SCFE was higher in their series.

This is the first study to report the acetabular morphology in children affected with SCFE in Indian patients and about 25% of the affected hips had retroverted acetabulum in our study. This indicates that one in every four hips with SCFE has the potential morphology to develop symptomatic FAI later. The major limitation of our study is that we were not able to compare the acetabular version in SCFE patients with that in normal population, as we did not have CT scan of the pelvis for age-matched controls. Such a comparison in future would throw us more light on whether there is any significant change in the acetabular morphology in children affected by SCFE.

Compliance with Ethical Standards

Conflict of Interest

The authors declare that they have no conflict of interest.

Ethical Standard Statement

This article does not contain any studies with human or animal subjects performed by the any of the authors.

Informed Consent

For this type of study, informed consent is not required.