Foot deformity in infants is the most common congenital anomaly of the musculoskeletal system. Multi-parametric assessment is mandatory for proper diagnosis and subsequently adequate therapeutic procedures. The assessment includes both clinical examination and imaging modalities [4].
In the pediatric age group, the tarsal bones lack ossification, which limits the use of conventional radiographic techniques. US has emerged as a useful imaging modality for assessing foot deformities as it has the benefit of visualizing cartilaginous structures. Additionally, US can be repeated as much as we can in cases of correctable deformities, such as club foot, before and after cast application without radiation exposure. Also, US allows dynamic scanning of the foot in different planes [1].
This study was designed to compare the role of ultrasound and plain radiography in the evaluation of pediatric foot deformities and our findings reveal that both radiographic and sonographic parameters were significantly different between patients and controls.
In this study, thirty patients were recruited from the orthopedics outpatient clinic over a period of 11 months. The mean age of the enrolled patients was 7.81 ± 26.6 months with an age range between 7 days and 10 years. Thirteen of the thirty patients were females (56.7%), and seventeen were males (43.3%). Half of the patients were with bilateral deformity (50%). Twenty-six feet were right side (57.7%), and nineteen were left side (42.3%). Nineteen of the thirty patients diagnosed with club foot deformity (63.3%), and ten were diagnosed with vertical talus (33.3%) and only was diagnosed with tarsal coalition (3.3%).
Despite the fact that clubfoot is one of the most prevalent foot deformities, there is no commonly agreed approach for its conclusive assessment. The majority of clubfoot evaluations remain clinical; however, none of the recognized clinical classification systems have been completely satisfactory. As a result, there is a growing need for the development of an imaging tool that could evaluate patients and monitor treating foot abnormalities in young infants.
Radiographic assessment
Radiographic views were easily obtained from all patients. However, in approximately one-third of patients, it was difficult to draw the long axis of talus and calcaneus due to small and round ossific nuclei. This difficulty has also been noted by Bhargava et al. [4] in their study. In contrast, Simons et al. [5] included only older patients with well-formed ossific centers, allowing adequate drawing of the talus and calcaneus axes. Simons et al. [5] had proposed the AP talocalcaneal angle and the lateral talocalcaneal angle as an indicator of varus and equinus, respectively.
In our study, the AP talocalcaneal angle was significantly decreased in patients (22.21 ± 13.17 degrees) compared to the controls (32.83 ± 4.4 degrees) (P value < 0.0001). Also, the degree of angle reduction was proportionate to the degree of varus deformity. Our findings were consistent with the results of the study conducted by Simons et al. [5] who found a significant difference between cases and controls like our study. This goes also in line with Ippolito et al. [6] who found that the degree of angle correction can be used in the follow-up of the conservative treatment in patients with a club foot. In contrast, Bhargava et al. [4] reported that the AP T-C angle was the least informative and did not vary significantly between patients and controls.
The lateral talocalcaneal angle was significantly decreased in our cases (30.13 ± 15.84 degrees) compared to the controls (39.03 ± 4.72 degrees) (P value < 0.006). Bhargava et al. [4] reported similar values for these angles with P value: 0.003.
Furthermore, the tibiocalcaneal angle was significantly increased in patients compared to the controls (P value < 0.0001), with a mean value of 101.30 ± 12.05 degrees and 80.5 ± 6.5 degrees in patients and controls, respectively, which was in accordance to the results of the study conducted by Goyal et al. [7].
Sonographic assessment (as in Fig. 5)
A variety of sonographic images were used in our study. As a result, all aspects of the foot, including the medial, lateral, dorsal, and posterior, were assessed. A dynamic examination of talonavicular movement was performed in addition to static views.
Regarding the medial view, the MMN distance was significantly shorter compared to the controls (P value < 0.001) in both neutral and dorsiflexion positions, as shown in Figs. 6, 7 and 8. The mean value for MMN in the neutral position was 9.8 ± 2.7 mm and 13.9 ± 3.5 mm in our cases and controls, respectively. The MMN distance is clinically relevant as an indicator of talonavicular malalignment, which is one of the most significant components of clubfoot. In our study, the lower the MMN distance, the greater the soft tissue thickness (P value < 0.001) with a concurrent increase in deformity grade. This finding is consistent with the studies conducted by Bhargava et al. [4], Shiels et al. [8], and Johansson et al. [9, 10], who reported that the MMN distance was 5.3 ± 2.8 mm in patients and 11.9 ± 2.6 mm in the controls. In contrast, our finding is inconsistent with the results published by Aurell et al. [11], who reported the MMN distance to be twice as much in patients compared to controls (mean value of 11.6 ± 2 mm in patients and 4.8 ± 1.2 mm in controls).
On the lateral view, the C–C distance was 5.87 ± 1.66 mm in patients and1.40 ± 1.1 mm in the controls, showing that this distance was significantly longer in patients (P value < 0.001) (Fig. 7). This finding is of great importance because it is difficult to detect this distance through clinical examinations and plain X-rays due to its latent ossification. Consequently, sonographic assessment can be significantly helpful in detecting the medial deviation of cuboid in early cases. However, it should be noted that our values are different from the ones reported by Bhargava et al. [4] and Aurell et al. [11], who reported mean C–C distances of 3.4 ± 2.0 mm and 2.5 ± 1.3 mm in patients, respectively, and 0.8 ± 1 mm and 1.0 ± 1.1 mm in the controls.
The posterior sagittal view was useful in evaluating the tibiocalcaneal relationship. The tibiocalcaneal distance (tcal distance) was a direct indicator of equinus. In our study, the tcal distance was reduced significantly in patients, especially in patients with increased severity of equinus deformity (P value < 0.001). More specifically, our findings revealed a mean tcal distance of 11.5 mm in neutral and 13.23 mm in maximum dorsiflexion in patients and 16.83 mm and 18.57 mm, respectively, in the controls. These results are close to the values found by Gigante et al. [12] with a mean tcal distance of 9 mm in neutral and 10.5 mm in maximum dorsiflexion in patients, and 10 mm and 20 mm, respectively, in the controls. These values were also reported by Chawla et al. [13], who found a tibiocalcaneal distance of 11.25 mm in their study group.
Contrary to the studies we included in this comparison, which focused solely on the club foot, our study had a wider scope as we included patients with tarsal coalition and vertical talus.
Ten of our cases were found to be vertical talus. Although plain radiographs (antero-posterior and lateral radiographs) suggested this diagnosis, this condition was confirmed by U/S.
Radiographs, as the ones shown in Figs. 9, 10, are useful to assess the talocalcaneal angle shown on the antero-posterior view of the foot, which was increased in all patients. The malalignment of the long axis of the talus and the first metatarsal leads to the assumption of navicular dislocation on the head of the talus.
Ultrasound has emerged as a useful diagnostic modality for cases of congenital vertical talus. In all our patients, we found dorsal dislocation of the navicular on the head of the talus, which does not decrease with plantar flexion as opposed to oblique talus (Fig. 11). Due to the fact that the navicular bones are not ossified, in mild cases, plain X-rays cannot confirm this condition, and thus, ultrasound is very useful in such cases. In contrast, severe cases are obvious to detect and confirm with different modalities.
Only one case with tarsal coalition was found in this study which showed a fibrous connection between the cuneiform bones that was not evident in plain X-rays, but was detected by ultrasound.
The main limitation of this study was that there were no reference values for the normal angles measured in different pediatric age groups. Also, we could not do follow-up for the patients, post-treatment, as we could not retain data or get back them for research purposes. Finally, in patients with rigid equinus, the dynamic examination was significantly painful, and thus, it was necessary to prolong the examination time in order to calm the patient down.