This prospective longitudinal study included a consecutive cohort and aimed to evaluate the development of foot length and foot growth in children with clubfoot from 2 to 7 years of age. The study cohort is representative with respect to unilateral and bilateral involvement, gender distribution, and relapse rate [24–29]. We found that clubfeet were shorter than reference feet at all ages. However, clubfeet growth after the age of 2 years was similar to the growth of reference feet. Children with unilateral clubfeet, with a greater difference in foot length at initial measurement, relapsed more frequently and had poorer motion quality at 7 years of age.
Muller et al. analyzed foot length development in 10,000 typically developed children and found an average increase in foot length of 51 mm between ages 2 and 7 years . These results are consistent with our findings where reference feet grew at an average of 53 mm between ages 2 and 7 years and clubfeet grew an average of 49 mm. Even though clubfeet were smaller compared with reference feet, the percentage foot length growth of reference feet and clubfeet was similar between 2 and 7 years of age. This could partly be explained by decreased bone hypoplasia as suggested by Beck et al. . They found that bone hypoplasia decreased with age when evaluating children with clubfeet between the ages 2 to 4. In our study, a minor growth slowdown was observed in all clubfeet at ages 3.5 to 4.5 years, possibly caused by the absence of daily stretching when the orthosis treatment ended (Table 2).
The relapse rate in this study was 32%. Previous studies have reported relapse rates ranging from 3.7% up to 53% depending on the initial treatment method, bracing protocol, follow-up time, and relapse criteria [24–28]. Most (87%) of the relapses in this study were observed after completion of orthosis treatment. This coincides with increased variation in foot length and foot growth, indicating the importance of daily stretching to prevent relapse. Thus, careful follow-up of clubfoot development after ending orthosis treatment is imperative to detect early relapse.
Small clubfeet have been associated with difficulties at initial correction and increased risk of relapse [4, 6, 7]. We found that a greater difference in foot length at baseline in children with unilateral clubfeet was related to an increased number of relapses and worse motion quality score at the age of 7. These findings indicate that foot length at the age of 2 years could be used as a prognostic tool. Estimating the exact relationships between foot length at an early age and risk of relapse and poor motion quality later in life could be of value for clinical treatment and follow-up planning. In addition to the predictive value of systematically measuring foot length, foot drawings are an easy and inexpensive method to monitor foot growth and shape, providing informative visual feedback on clubfoot development. Furthermore, it is easily understood by both patients and parents.
As multiple comparisons were made, the Bonferroni correction was applied. Without this correction, the differences in length and growth between clubfeet with and without relapse were significant at around the ages of 3 to 5 years, when most of the relapses occurred (Tables 3 and 4). This finding is consistent with our clinical observation that clubfeet growth occasionally slows down during relapse and normalizes after appropriate intervention. However, we cannot exclude the possibility that a type 2 error occurred when foot length and FLG% were compared .
In this study, the contralateral feet were used as reference feet, which could be considered a limitation . However, the reference feet in our study did not differ in size from typically developing feet as described in the literature . The intra- and interrater reliability have not yet been established for measurements made using the foot drawing method. In our study, the same assessors performed all drawing (HA) and length measurements (EM) to minimize operator error.
Another limitation is that the treatment methods used in our cohort are not gold standard and the results need to be confirmed in children treated within the strict Ponseti protocol. On the other hand, clubfeet in our study showed the same growth rate as reference feet, indicating generalizable results.