A new method using ultrasound for measuring femoral anteversion (torsion): technique and reliability

Femoral anteversion: significance and measurement

Femoral neck anteversion (FNA) is the angle between the femoral neck and femoral shaft, indicating the degree of torsion of the femur. Differences in FNA affect the biomechanics of the hip, through alterations in factors such as moment arm lengths and joint loading. Altered gait associated with differences in FNA may also contribute to the development of a wide range of skeletal disorders including osteoarthritis. FNA varies by up to 30° within apparently healthy adults. FNA increases substantially during gestation and thereafter decreases steadily until maturity. There is some evidence of a further decrease at a much lower rate during adulthood into old age, but the mechanisms behind it have never been studied. Development of FNA appears to be strongly influenced by mechanical forces experienced during everyday movements. This is evidenced by large differences in FNA in groups where movement is impaired, such as children born breech or individuals with neuromuscular conditions such as cerebral palsy. Several methods can be used to assess FNA, which may yield different values by up to 20° in the same participant. While MRI and CT are used clinically, limitations such as their cost, scanning time and exposure to ionising radiation limit their applicability in longitudinal and population studies, particularly in children. More broadly, applicable measures such as ultrasound and functional tests exist, but they are limited by poor reliability and validity. These issues highlight the need for a valid and reliable universally accepted method. Treatment for clinically problematic FNA is usually de-rotational osteotomy; passive, non-operative methods do not have any effect. Despite observational evidence for the effects of physical activity on FNA development, the efficacy of targeted physical activity remains unexplored. The aim of this review is to describe the biomechanical and clinical consequences of FNA, factors influencing FNA and the strengths and weaknesses of different methods used to assess FNA.

Femoral Anteversion Measured by Ultrasonography and Radiography

Radiographic and real-time ultrasound measurements of femoral anteversion were compared in an anatomic study of 20 dried adult femurs. The real anteversion (AV) angle was determined by biplanar radiography. In four ultrasound measurements, the linear transducer was kept either horizontal or tilted. The measuring lines were either the anterior tangent of the femoral head—greater trochanter or the anterior tangent of the femoral neck. With the tilted transducer, the correlation between the head-trochanter AV angle and the real AV angle was high (r=0.9452), and slightly less when the anterior neck AV angle was used (r=0.9142). The clinical relevance is that the tilted transducer technique with the head-trochanter tangent is recommended for AV screening in patients with clinical signs of increased femoral anteversion. In adults 8.5° has to be subtracted in order to obtain an approximation of the real AV angle.

The effect of varus and valgus osteotomies on femoral version

BACKGROUND

Although seldom described, varus and valgus osteotomies of the proximal femur can affect femoral version. The magnitude of the effect can be predicted with an understanding of the distinction between femoral version and femoral neck inclination. The purpose of this study was to elucidate this relationship.

METHODS

Version, inclination, apparent neck-shaft angle, and true neck-shaft angle were defined and measured in 72 preserved femora.

RESULTS

Average values were 19.8+/-11.8 degrees for version versus 14.5+/-10.1 degrees for inclination (P=0.004), giving a mean difference of 27% between version and inclination, with greater discrepancy with increasing neck-shaft angle. There were high correlations between measured inclination and inclination calculated using version and apparent neck-shaft angle (r=0.96) and true neck-shaft angle (r=0.97), validating our formulaic relationship between these variables.

CONCLUSIONS

We present and validate the concept of inclination, and its relationship with version and neck-shaft angle. This explains the mechanism for a varus osteotomy decreasing anteversion, and a valgus osteotomy increasing anteversion.

CLINICAL RELEVANCE

With an understanding of these concepts, a surgeon can incline the femoral neck axis to achieve a desired amount of version, for any given neck-shaft angle. Without this understanding, precise control of the version and neck-shaft angle is difficult.

[Determining the femoral antetorsion angle with a fluoroscopy-based optoelectronic navigation system: a precision analysis]

According to the literature, differences in torsion of 15 degrees and more develop in 20-30% of cases after intramedullary nailing of femoral shaft fractures. A computer-assisted method makes it possible to determine the antetorsion angle during surgery. In this experimental study, the precision of the measurements obtained with the navigation system were checked with a femur model and compared with a CT reference method. The measurements are carried out on a femur model that is equipped with a rotation device in the middle of the shaft. Nine reproducible angles can be set. Two investigators each conduct the measurements of the antetorsion angle ten times. A comparison is drawn between the absolute values of the antetorsion angle measured and the difference values of the adjoining positions. When comparing the absolute values of the navigation and reference systems, the mean deviations of both methods are around 1 degrees (0.35; 1.75) and comparing the differences 0.5 degrees (-0.2; 1.17). The maximum deviation of the absolute values of the CT reference method amounts to 6.4 degrees . Under experimental conditions, measurement of the femoral antetorsion angle proved to be sufficiently precise for clinical specifications in comparison to a CT reference method.

Validity and reliability of existing and modified clinical methods of measuring femoral and tibiofibular torsion in healthy subjects: use of different reference axes may improve reliability

Previous studies have evaluated reliability and validity of clinical measurements of femoral and tibiofibular torsion, however, the results are conflicting, warranting an alternative method. The authors developed modified methods of measuring femoral and tibiofibular torsion using different reference axes, and validity and reliability of the modified and existing methods were examined in healthy subjects. Reference values were established using magnetic resonance imaging (MRI) for the validity study. There were significant differences between all clinical methods and corresponding MRI outcomes (P <0.05), whereas Pearson's correlation coefficients between the clinical methods and MRI ranged from 0.67-0.92. For modified methods, intraclass correlation coefficients were 0.89-0.97, whereas those of existing methods were 0.75-0.81. Modified methods were more precise, with standard error of measurements (SEM) of 1.5-2.9 degrees , compared to existing methods (SEM=4.0-5.1 degrees). These results indicate that clinical methods available currently do not accurately measure true torsion of the femur and tibia. Nevertheless, the clinical methods may be useful for screening and descriptive purposes as indices of true torsion, and use of different reference axes could improve their reliability.

The measurement of the rotational deformities with computed tomography in femoral shaft fractures of the children treated with early spica cast

Twenty-eight children with femoral shaft fractures, treated with early spica cast, were evaluated with computed tomography (CT), for their femoral shaft rotational deformities. The femoral torsion angles were measured on both sides. If the torsion angle of the fractured side was more than the other side, it was considered as an internal rotational deformity and if it was less, it was considered as an external rotational deformity. Internal rotational deformities were detected in nine cases and external rotational deformities were detected in 17 cases. Rotational deformity was not observed in two cases. Four cases, with a rotational deformity more than 10 degrees, were corrected with a gypsotomy through the level of the fracture. We concluded that a rotational deformity, which is an important complication in conservative treatment of the femoral shaft fractures in children, can be determined exactly with CT and corrections on the spica cast can be made with a gypsotomy.

Angle of torsion of the femur and its correlates

Unpaired femora (171), devoid of gross pathology and grouped by gender (94 male and 77 female) and side (88 left and 83 right), were used to measure the angle of femoral torsion and the maximum femur length and to score the degree of prominency of the superior cervical tubercle, intertrochanteric line, quadrate tubercle, linea aspera, and adductor tubercle. The angle of torsion ranged from -9 to +35 degrees with a mean of +12.3 degrees. The means were not significantly different either by gender or side. The angle correlated negatively with superior cervical tubercle, intertrochanteric line, and adductor tubercle (P < 0.001), positively with quadrate tubercle (P < 0.001) but not with linea aspera, neck-shaft angle, or length of femur. Bony prominences were significantly more apparent in males. There was no significant association between prominency and side. The torsion seems to be brought about by muscular activity and capsular and ligamentous strain at the hip. This study suggests to clinicians the possibility of correction of torsion defects in certain hip diseases of growing children by suitable alteration in posture of the lower extremity.

Measurement of tibial torsion--a new technique applicable to ultrasound and computed tomography

A new method for measuring tibial torsion is described which can be applied to both ultrasound (US) and computed tomography (CT). The method has been validated in dry tibiae by comparison with direct measurements and with Jend's established CT method. In clinical practice a good statistical level of agreement has been demonstrated between the values obtained from US and CT scans. Both compared well with values obtained using Jend's CT technique. The use of US avoids exposure to radiation and is therefore suited to studying young subjects and controls and making repeat measurements.