Children presenting with an in-toeing or out-toeing gait are one of the most common pediatric foot problem seen by physiatrists. Although a lot of research for in-toeing and out-toeing gait, etiologies of these conditions are still debated. But there are many opinions that the structural conditions giving rise to in-toeing or out-toeing can be correlated with the age of onset.

Tibial torsion has also been known as one of the important structural problems in in-toeing or out-toeing gait [1,2,3,4]. The most common measurement methods of the tibial torsion are the classical physical examinations (CPE) and computed tomography (CT) scan. In many studies, CT scan has been proven to the point of validity and reliability for the causal analysis of tibial torsion [5,6,7]. However, to conduct a CT scan is difficult to use, expensive and rarely available in the clinical setting for every child with in-toeing and out-toeing gait or to monitor each stage of progress. For routine clinical evaluation, CPE remains the primary method for assessment. To be useful, this examination should give acceptably reproducible results that can be compared with an established range of normal values [8].

Thus, this study attempted to develop a new instrument for the CPE of the thigh-foot angle (TFA) measurement which is one of the most popular examinations of tibial rotational problems. Moreover, this study intended to evaluate the validity and reliability of the new instrument.

The main aims of this study were to evaluate whether the newly developed TFS could be used for valid and reliable measurements, i.e., if a constant value could be obtained from repeated measurements. Since measurement error is decreased when the validity and reliability of instruments are improved, consistent results are possible when conducting serial measurements in outpatient clinics. It will also be an enormous help in providing counsel to parents of children with orthopedic issues or to plan further treatment.

Common lower extremity abnormalities in children can be attributed to two types of rotational problems, i.e., pronation and supination. There are three types of deformity it has metatarsus adducts or abductions, internal or external tibial torsion, and increased femoral anteversion or retroversion. An accurate diagnosis can be made by carefully documenting the medical history of each pediatric patient and by performing a CPE in order to ascertain the torsional profile of the lower extremities. Charts of normal values and values with two standard deviations for each component of the torsional profile are available. In most cases, the abnormality improved with time. A careful physical examination, explanation of the natural history, and serial measurements are important in order to develop an individualized treatment plan [3].

In-toeing and out-toeing gaits can appear in one or more parts of the lower extremities, including from the hip joint to the femur, knee joint, tibia, ankle joint and foot [1,11,12]. Most in-toeing and out-toeing gaits do not require correction; however, an altered gait beyond the normal range, i.e., above two standard deviations of the torsional profile may result in long-term disability or restricted movement, e.g., arthritis, restriction of normal functions such as pain after exercise and a tendency for frequent falls. Therefore, it is important to accurately diagnose the causes of in-toeing and out-toeing gaits in children and to develop a treatment plan that takes into account changes that may occur as they grow up to become adults [1,10].

The tibial torsion has been known as a major factor among many other causes for the development of intoeing and out-toeing gaits [1,2,3,4]. It affects males and females equally and is often asymmetrical with the left side affected more than the right side. The exact cause is unknown but is believed to be the intrauterine position, sleeping in the prone position after birth, and sitting on the feet. Internal tibial torsion gradually improves on its own by the time the child reaches 8 years of age in 90% of the cases [13].

Internal or medial tibial torsion can manifest as an intoeing gait and is commonly associated with congenital metatarsus varus, genu valgum, or femoral anteversion. Lateral tibial torsion is less common than medial rotation and is often associated with a calcaneovalgus foot. It can be compensatory to persistent femoral anteversion and idiopathic or secondary to a tight iliotibial band [3,13,14]. Physical examination, X-ray, ultrasound, CT scan, and magnetic resonance imaging (MRI) have been used in the clinical setting to identify the causes of tibial torsion in children [15,16,17,18,19]. CT scans and MRI techniques are good imaging strategies for visually assessing the torsional profile of the tibia; however, both techniques are expensive and, in the case of CT scans, serial measurements carry with it a risk of exposing the pediatric patient to excessive radiation.

Since Staheli and his colleagues [8,20] described rotational profile, the TFA and transmalleolar axis (TMA) have been used predominantly to measure tibial torsion. Even if one study showed the validity and reliability were better the TMA than TFA compare to CT scan [21], the other study showed almost physical examinations using goniometer may not accurately reflect the tibial axis due to various posture of fibula [22], and according to Kim et al. [23], there is a low correlation between CPE and CT measurements.

A TMA measurement is difficult because it is difficult to set the mid-point of each medial and lateral malleolus of the ankle in physical examination, and it may vary depending on the measurement posture of the patient in the sagittal and transverse plane, i.e., the overall measurement may not accurately reflect the rotational profile of the tibia. So, the most popular clinical method for evaluating tibial torsion is by measuring the TFA with the child lying prone [8,20,24]. A TFA measurement is easier than the TMA in the physical examination, and we wanted to see if consistency in serial measurements could be obtained that it was more valid and reliable in comparison with the CT scan. For this reason, we chose TFA, taking into account factors such as ease of use, cost, safety, and availability. The TFA between the axis of the foot and the axis of the thigh should be measured with the child lying prone, knees flexed to 90°, and ankle neutral. The thigh axis is a line from the ischial tuberosity through the mid-point of the popliteal fossa, and the foot axis is a line from mid point of heel through second web space. Intoeing angles are given negative values while out-toeing angles are given positive values. The angle describes the status of the tibial torsion [8,24,25].

Periodic observations of the tibial torsion should be done to see if problems resolve on their own or worsen with time. Ideally, these TFA measurements should be reproducible and easy enough to be done properly by inexperienced physicians. Also, most studies of normal TFA measurements have been conducted in Western countries rather than the Far East region or in Korea. Future large-scale studies will need to take into account racial differences and a comprehensive examination will need to be done, i.e., the study method and instruments used by examiners to reduce errors in measurement values will have to be assessed during such an investigation. The aim of this study was to develop a measurement instrument that could improve the validity, inter-test and interpersonal reliabilities in TFA measurements performed on performed for children with the tibial torsion.

In this study, a less experienced examiner showed an error in repeated measurement could obtain similar value with the P-TFA when measuring the TFA with TFS; also, both inter-test and inter-personal reliability of all examiners increased with TFS. As described above, this study suggests a way to compensate for the low reproducibility and accuracy which is the fault of the classical physical examination, shows that the validity and reliability of physical examination are increased with TFS.

Accurate and reproducible TFA and TMA measurement values cannot be obtained if the knee joint cannot be kept at a 90° angle or if there is internal or external rotation of the hip joint. Thus, these changes in the position of the sagittal and transverse plane may generate measurement errors during repeated measurements. To solve this problem, the knee joint was kept bent at an angle of 90o by the main board of the TFS, internal and external rotation of hip was fixed after the wing was adjusted to left and right sides according to the sliding rod in order to measure the TFA in a more accurate position. Thus, it was possible to decrease the measurement error and the reproducibility was increased by measuring the TFA with TFS. Periodic follow-up examinations in an outpatient clinic facilitated the collection of data to be used in a future large-scale study.

Limitations of the study are that we enrolled a small number of patients in the study and that the validity was based on the TFA on the photo. Considering these limitations, a follow-up study should include more pediatric patients. Also, it is desirable to conduct a study to compare the imaging study, such as ultrasound, CT scan, and MRI.

In conclusion, TFS, which is a newly designed instrument developed for TFA measurement performed on children with intoeing and out-toeing gaits, may be more helpful to less experienced examiners.