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SELECTED PROCEEDINGS FROM THE 2020 BERNESE HIP SYMPOSIUM GUEST EDITOR: KLAUS-ARNO SIEBENROCK MD

CORR Insights®: How Common Is Femoral Retroversion and How Is it Affected by Different Measurement Methods in Unilateral Slipped Capital Femoral Epiphysis?

Siebenrock, Klaus A. MD

Author Information
Clinical Orthopaedics and Related Research: May 2021 - Volume 479 - Issue 5 - p 960-961
doi: 10.1097/CORR.0000000000001704

Where Are We Now?

Based on my experiences, slipped capital femoral epiphysis (SCFE) does not represent a uniform and consistent pattern of disease in the growing hip. In my view, there are several facets to SCFE and multiple causes for developing the disease in adolescence, including obesity, endocrinal imbalance, and hereditary syndromes [3, 4].

Abnormalities in anatomical morphologies such as a vertical orientation of the proximal femoral growth plate or, as has been discussed more recently, a less prominent epiphyseal tubercle, have been associated with a higher risk for developing a clinically relevant SCFE [6].

The current study by Schmaranzer and colleagues [7] found that torsional malalignment of the femur, especially low femoral antetorsion and/or femoral retroversion, represents a risk factor for developing an SCFE. The authors examined five different and previously described measurement methods for femoral torsion. The results showed that each method will lead to a different angle defining femoral torsion. The more distal a landmark of the proximal femur, the higher the measured femoral torsion will be and vice versa [7]. Thus, in any study analyzing femoral torsion angles, it is mandatory to report the applied measurement method as well.

The current study also found a higher prevalence of femoral retrotorsion in patients presenting with SCFE [7]. Thus, femoral retrotorsion may represent another etiological factor for developing an SCFE. The prevalence of femoral retroversion in patients with SCFE ranged from 47% to 91% in the study, depending on the measurement method used. In addition, femoral retrotorsion was higher on the symptomatic and affected side in patients with SCFE.

I commend Schmaranzer and colleagues [7] for using the femoral head center as a reference point, which in SCFE is typically rotated posteriorly and distally. Using the femoral head center as a reference point is advantageous for surgeons treating moderate-to-severe capital slips because there is a posterior bowing of the femoral neck that inevitably will render the neck orientation unreliable and underestimate the true retroversion. Based on their findings, I believe any surgeon planning a corrective osteotomy for a chronic SCFE needs modern imaging (preferably MRI) to accurately include femoral malrotation.

Where Do We Need To Go?

We need to expand our understanding of the underlying pathoanatomy that results in the development of SCFE. Mechanical factors and malalignment of the hip and lower limb potentially play an important role in the development of SCFE. Apart from endocrine and potential hereditary factors, analysis of anatomical features like orientation of the physis, femoral torsion, and the size of the epiphyseal tubercle have to be included to identify patients at risk for developing SCFE.

There is also a need for a uniform measurement method to describe femoral malalignment. Although all of the evaluated measurement methods presented in the current study showed a high intra- and interobserver reliability [7], the authors’ preferred measurement method was taken from a previous study [5], which used the femoral head center as both a rotational center and a horizontal cut through the upper part of the lesser trochanter. Thus, the torsion of the entire proximal femur (intertrochanteric region, femoral neck, and head center) is included in the measured angle. This approach represents the closest we have come to measure the anatomical version of the femur [5]. Knowing the precise anatomical femoral version by using this method [5] allows a more accurate planning for surgical correction.

It would be worth trying to develop a scoring system (including elements like BMI, endocrine disturbances, low femoral torsion, and vertical orientation of the growth plate, for example) with the goal of being able to predict contralateral SCFE. This would be done to refine our indications for pinning of the asymptomatic contralateral side in patients with unilateral SCFE. Finally, the study points to a need to analyze the anatomical aspects of young patients with SCFE. We need to determine whether obesity, frequently seen in patients with SCFE, is linked to femoral retroversion.

How Do We Get There?

Apart from endocrine and potential hereditary factors, we need to evaluate anatomical features more carefully, which may promote the development of an SCFE. In my view, MRI imaging of the hip is the preferred way to improve our understanding of underlying anatomical pathologies. Recently developed three-dimensional MRI acquisition techniques can measure femoral torsion without any contrast or radiation exposure for the young patient.

Femoral torsion seems to be a predictive factor for developing an SCFE. Since femoral torsion is affected by different measurement methods, there is a need for a uniform measurement method. My recommendation is to use the method described by Murphy et al. [5] for two reasons: (1) the inclusion of the entire proximal femur (from calcar to the head) represents the most comprehensive understanding of the head and neck deformity—especially important in SCFE; (2) the measurement has shown to represent most closely the true anatomical femoral version.

In patients with SCFE, MRI scans will be helpful also for the evaluation of the asymptomatic contralateral side, which does not necessarily represent “normal” anatomical morphology [1]. Gradual posterior and inferior rotation of the femoral head at the asymptomatic side may lead to subsequent symptoms. Symptoms may be caused by an acute-on-chronic SCFE or as a minor variant by a decreased offset leading to a painful cam deformity. Thus, developing a scoring system and evaluating the endocrine, hereditary factors, and (patho)anatomical factors including acetabular retroversion [2] is the way to go. This could potentially predict a contralateral SCFE or even define hips at risk for SCFE.

Finally, in their study, Schmaranzer et al. [7] found an association between obesity and femoral retroversion. The development of MRI studies during growth in an asymptomatic population as well as in patients with SCFE could help us potentially determine whether obesity is linked to femoral retroversion or whether it represents just an incidental finding.

References

1. Fraitzl CR, Käfer W, Nelitz M, Reichel H. Radiological evidence of femoroacetabular impingement in mild slipped capital femoral epiphysis: a mean follow-up of 14.4 years after pinning in situ. J Bone Joint Surg Br. 2007;89:1592-1596.
2. Kienle KP, Keck J, Werlen S, Kim YJ, Siebenrock KA, Mamisch TC. Femoral morphology and epiphyseal growth plate changes of the hip during maturation: MR assessments in a 1-year follow-up on a cross-sectional asymptomatic cohort in the age range of 9-17 years. Skeletal Radiol. 2012;41:1381-1390.
3. Liu RW, Fraley SM, Morris WZ, Cooperman DR. Validity and clinical consequences of a rotational mechanism for slipped capital femoral epiphysis. J Pediatr Orthop. 2016;36:239-246.
4. Madhuri V, Arora SK, Dutt V. Slipped capital femoral epiphysis associated with vitamin D deficiency: a series of 15 cases. Bone Joint J. 2013;95-B:851-854.
5. Murphy SB, Simon SR, Kijewski PK, Wilkinson RH, Griscom NT. Femoral anteversion. J Bone Joint Surg Am. 1987;69:1169-1176.
6. Novais EN, Millis MB. Slipped capital femoral epiphysis: prevalence, pathogenesis, and natural history. Clin Orthop Relat Res. 2012;470:3432-3438.
7. Schmaranzer F, Kallini JR, Ferrer MG, et al. How common is femoral retroversion and how is it affected by different measurement methods in unilateral slipped capital femoral epiphysis? Clin Orthop Relat Res. 2021;479:947-959.
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