Congenital talipes equinovarus is a three-dimensional malformation of leg, ankle and foot immediately visible at birth. It is characterized by forefoot adducts, midfoot cavus, hindfoot varus and equinus of ankle. To assess the severity of the abnormalities, several pediatric orthopedists used clinical-functional scores (such as the Pirani scores or the Dimeligo scores) as well as radiological data. Despite the widespread use of analytical radiography in clubfoot, Surendra et al concluded that radiographic assessment of clubfoot was not a trustworthy tool due to significant intraobserver and interobserver variability. Conventional radiographs were radioactive, unreliable, not easily reproducible, and imprecise in assessing and classifying the severity of clubfoot. Meanwhile, because the tarsal bones of these patients are not totally ossified and are primarily cartilaginous, we can't utilize X-ray to assess the relationship between the tarsal bones.
Clubfoot with good cosmetic and functional healing, according to Blakeslee, may have several covert tarsal joint impingements, dislocations, or subluxations that are not apparent on clinical examination or radiographs. Furthermore, X-ray has not made visualization of the talonavicular relationships possible. With the long-term follow-up of Ponseti-treated clubfoot cases, the investigators found an increase in the recurrence rate of clubfoot, which ranged from 1.9–45%. Ponseti suggested that the recurrence of clubfoot may be due to inadequate repositioning of the tarsal bones alignment, which was not diagnosed with clinical or radiological examinations in early childhood. The level of correction can be seen clearly on MRI, which can also reveal complications and relapses before skeletal maturity. Although there have been several reports on MRI findings of tarsal bone abnormalities of clubfoot, MRI studies on the level of correction after the Ponseti method are scarce and have not been reported in China[14, 15, 16, 17, 18, 19, 20]. Therefore, we decided to objectively evaluate the effectiveness of the Ponseti method for the correction of clubfoot using MRI.
To describe the equinus deformity of clubfoot, the sagittal talocalcaneal angle and sagittal tibiocalcaneal angle were measured in this study. Before Ponseti treatment, the sagittal talocalcaneal angle was reported to be 28 ± 6° in normal foot and 5 ± 9° in clubfoot on MRI by Downey(P < 0.05). The mean sagittal talocalcaneal angle in our study was 29.9° in treated clubfoot and 27.4° in normal foot(P > 0.05). The mean sagittal tibiocalcaneal angle was 68.7° in corrected clubfoot and 72.4° in normal foot(P > 0.05). The results of our MRI revealed that the Ponseti method was successful enough in correction of equinus deformity of clubfoot. Pekindil reported the mean sagittal talocalcaneal angle 36.0° in normal foot and 31.4° in treated side(P > 0.05). Amhad also reported the mean sagittal tibiocalcaneal angle 80.2° in normal side and 91.6° in corrected side(P > 0.05). These measurements were consistent with the findings of our study. An MRI protocol was devised to illustrate the tarsal bones changes that occur with the Ponseti method of the treatment by Pirani, though these changes were qualitative rather than quantitative. They discovered that Ponseti method corrected not only the aberrant relationships of the tarsal bones, but also the abnormal shapes of the individual tarsal osteochondral anlages.
The coronal tibiocalcaneal angle was used to assess the varus deformity of the clubfoot. Satio found that the coronal tibiocalcaneal angle was 0 ± 13.8° in the clubfoot before treatment and14 ± 4.6° in the normal foot(P < 0.001). Our results of coronal tibiocalcaneal angle were for normal and corrected foot were statistically insignificant. We believed that Ponseti method successfully corrected the varus deformity of clubfoot. Pirani et al also observed that the abnormal relationship between the calcaneus and tibia of clubfoot had returned to normal in the coronal plane during the third cast fixation phase .
When compared to normal children, the onset of navicular ossification was found to be delayed in children with clubfoot, and the navicular bone was not apparent on radiographs until they were 3–5 years old. However, it was easy to see the navicular cartilage in the sagittal plane of MRI. If a substantial cavus deformity cannot be treated by stretching the plantar fascia, Carroll believed that extrusion of the dorsolateral navicular bone will occur, leading to talonavicular subluxation. In our study, 1 of 15 (6.7%) of the corrected clubfoot had dorsal talonavicular subluxation. Its rate has been reported as 25% by Ahmad. In the MRI transverse plane, we found that 1 corrected clubfoot had lateral talonavicular subluxation, which has never been repored in previous studies. We speculated that the navicular bone had developed from medial displacement to lateral subluxation due to overcorrection of the Ponseti method and cast fixation. MRI can identify these insidious complications much earlier than X-ray.
Adducts deformity of clubfoot related measurements were transverse talonavicular angle, transverse talar neck angle and transverse talocalcaneal angle. To our knowledge, it was difficult to identify the longitudinal axis of the talar body in the transverse plane of MRI. The longitudinal axis of the talar body was defined as a line perpendicular to the transmalleolar line passing through the center of the medial and lateral malleoli. Before treatment, Downey reported that the mean transverse talar neck angle was 44.0° for clubfoot and 30.8° for normal foot (P < 0.01). And the mean transverse talocalcaneal angle was 22.8° in clubfoot versus 10.1° in normal foot(P < 0.05). These findings were consistent with the adducts deformity of clubfoot described by Ponseti et al. In our study, only transverse talonavicular angle of these three measurements for normal foot and corrected clubfoot were statistically significant. Kamegaya performed plaster fixation on children with clubfoot, they reported 21.0 ± 9.5° for normal foot and 44.2 ± 15.9° for treated clubfoot regarding the transverse talonavicular angle(P < 0.05). We believed that the navicular bone still has a medial displacement despite of the satisfactory appearance and functional activity of the clubfoot after Ponseti method. The transverse talonavicular angle showed that the adducts deformity of clubfoot has not been completely corrected.
Ponseti noticed that the clubfoot had a strong tendency to relapse regardless of the approach used to obtain correction. Among the relapsed deformities, the most common is the recurrence of equinus deformity of ankle, followed by adducts deformity. The recurrence of clubfoot, according to Ponseti, was caused by non-compliance with braces, which might result in an abnormal relationship between the tarsal bones.. In our study, even though the clinical correction and the motion of the foot and ankle are satisfactory, the talonavicular angle on transverse images of MRI showed statistical differences, suggesting that the adducts deformity may be incompletely corrected and therefore additional follow-up is required to rule out the possibility of adducts deformity recurrence. At the same time, residual deformity is present in up to 20% of clubfoot treated by the Ponseti method. We speculated that the reason may be aberrant articular morphology. With MRI, we can detect these small variations in time so as to take targeted treatment and avoid residual abnormalities.
Several limitations of our study should be mentioned. First, the sample size was small. Second, long term follow-up with a larger number of cases will be needed to exclude the possibility of recurrence of clubfoot. Third, the cost of MRI examination is too expensive and using them in the neonatal period is challenging because the infant must be sedated. At last, because the thickness of the MRI scan is 3–4 mm, it will cause errors in the measurement results when selecting slices.