Is there a correlation between the femoral anteversion angle and the elasticity of the hip muscles in cases of intoeing gait due to increased femoral anteversion angle?

Intoeing gait is a deformity seen during walks or runs. The causes of intoeing gait have been defined in the literature as metatarsus adductus, internal tibial torsion (ITT), and increased femoral anteversion angle (FAA) in healthy children⁽¹⁾. Metatarsus adductus is a condition where the anterior part of the foot faces inward. ITT is a condition where the tibia is rotated inwards. ITT is the most common cause of this deformity. Increased femoral anteversion is detected by an increase in the femoral anteversion angle. These causes often regress spontaneously in healthy children over time and rarely require surgical intervention⁽¹⁾. Increased FAA refers to the orientation of the femoral neck relative to the femoral condyles. Increased FAA leads to gait disorders, and can also cause hip dislocation and subluxation^{(2, 3, 4)} . The FAA decreases from 30–40° in newborns to 10–15° around the age of 8 years⁽⁵⁾.

SWE applies vibrations to the tissues with focused ultrasound waves. Shear wave velocities can be measured from Doppler frequency modulation of simultaneously transmitted ultrasound waves. Young’s modulus of elasticity is then measured as a function of shear wave velocity (SWV). As the tissue stiffness rises, the shear wave velocity passing through the tissue also increases⁽⁶⁾. Studies in the literature have shown that SWE and shear modulus measurement values are highly correlated with the strength of a muscle to withstand changes in length when compressed⁽⁷⁾.

The aim of this study was to evaluate the correlation between the FAA and elasticity of the hip muscles in children with intoeing gait due to increased FAA, using SWE.

There was an excellent congruence between the femoral anteversion angle measurements performed by the two observers and a good consistency between the muscle elastography evaluations. Iliopsoas, adductor magnus, gluteus maximus, gluteus medius muscles elasticity values and femoral anteversion values are summarized in Tab. 1 for each observer.

The congruence between the measurements performed by the two observers is shown in Tab. 2.

Pearson’s correlation analysis performed between the femoral anteversion angle measurements and muscle elastography measurements made by Observer 1 and Observer 2 is shown in Tab. 3. As can be seen, while there was a moderate significant correlation between the FAA measurements and the elasticity values of the iliopsoas and adductor magnus muscles for both observers, there was no similar correlation with other muscle elasticity measurements.

The study aimed to evaluate the hip muscles by elastography in patients with intoeing gait due to femoral anteversion.

Femoral anteversion can result from stiff hip muscles due to the position of the fetus in the uterus. It also tends to occur in patient families⁽⁹⁾.

Kong et al., in their study of children aged 4–6 years with recently diagnosed intoeing gait, performed 3D CT at the time of diagnosis, and reported that a decrease in the FAA was observed for 18 months⁽¹⁰⁾. In the study of Faulks et al., 95% of the cases were diagnosed as benign intoeing gait and were followed up. The cases in the present study were also benign intoeing gait, and they were planned to be followed up for the FAA⁽¹⁾.

Both in vitro and in vivo studies have demonstrated that the measurement of elastic shear modulus is strongly associated with localized passive muscle tension during stretching⁽¹¹⁾.

Dubois et al. observed higher shear modulus values in the muscles involved in knee joint motion and plantar flexion of the foot when stretched compared to rest⁽¹²⁾. Saeki et al. found that the shear modulus values of ankle plantar flexion muscles increased with dorsiflexion⁽¹³⁾.

Berrigan et al., in their studies on hamstring muscles, showed that joint and muscle position affected shear modulus values⁽⁷⁾. In their study, Andrade et al. found that the maximum dorsiflexion angle of the ankle was affected by the hip angle position, whereas the ankle torque and the passive tension of the gastrocnemius muscle did not change for an equivalent ankle angle⁽¹¹⁾.

In their study, Umehara et al. reported that adding hip rotation to the stretching position with hip adduction and extension might have little effect on tensor fascia lata lengthening, and stretching at knee flexion above 90° could effectively lengthen the tensor fascia lata⁽¹⁴⁾.

Gluteal muscle contracture has been linked to a decrease in the hip flexion passive adduction angle and a rise in the mean shear wave velocity in contracture strips in three individuals, as revealed in a study by Guo et al.⁽¹⁵⁾. Ogawa et al. reported that the hip flexion angle might affect the amount of muscle elongation in the stretched muscle; however, it remains unclear how the hip joint angle affects the stretching of the adductors⁽¹⁶⁾. Studies in the literature show that conditions affecting joint angle and position can impact muscle tension. From this perspective, it is reasonable to conclude that joint position is affected in the circumstances affecting muscle tension. However, as far as we know, there are not enough elastographic studies on which muscle groups can be influential and/or affected in the FAA.

Analan et al. used the hip migration index (MI) on anteroposterior pelvic radiographs to assess hip muscle elasticity. The iliopsoas and adductor magnus muscles were discovered to have a strong connection with the MI. We detected a moderate correlation between the iliopsoas muscle and the adductor magnus muscle in the present study. Analan et al. found a weak correlation between the MI and other hip muscles⁽¹⁷⁾. In the present study, we identified a weak correlation between the FAA and other hip muscles.

Previous studies have investigated biomechanical changes during gait in children with genu varum. However, there was no study evaluating biomechanical changes in the hip muscles in the context of increased femoral anteversion angle with intoeing gait in children. In a study by Jafarnezhadgero et al., a corrective training program may contribute to slow joint degeneration, improved mobility and daily living activities in children with genu varum⁽¹⁸⁾. Our study may benefit from a corrective training program for children’s increased femoral anteversion angle with intoeing gait.

An important limitation of the study was the small number of participants. As a result, elastography changes throughout patient follow-up could not be examined.

In conclusion, iliopsoas muscle and adductor magnus muscle elasticity values were found to be correlated with the FAA. It might be beneficial to conduct further studies with more extensive patient series in the future. Based on their findings, physical therapy methods effective on the iliopsoas muscle and adductor magnus muscle elasticity can be developed.