Lengthening of Achilles Tendon from the Percutaneous Tenotomy Procedure in Ponseti’s Method

Background Talipes equinovarus is one of the common congenital disease of foot deformity of newborn. Initial treatment is often with the Ponseti method. Studies have demonstrated that radiographic measurements can be made with clubfoot. The purposes of this study were to document the amount of Achilles tendon lengthening obtained from PAT in Ponseti’s method and to analyze the factors that might impact on the amount of equinus correction. Methods This is a retrospective study carried out from 2002 to 2006. Sixteen feet of twelve children that received percutaneous Achilles tendon tenotomy (PAT) for the treatment of congenital clubfoot were included. Assessments before and after treatment were performed using Dimeglio system. The foot length from toe to heel at the time of PAT, the pre- and post-PAT ankle dorsiexion and post-casting lateral view of foot were obtained. The Pearson correlation coecient was used to establish relationships between pre-, post-PATT and post-casting Tibio-calcaneal angle (TCA) and Achilles tendon length(ATL). Results The TCA before, after PATT, and after casting were -9.3, 27.4 and 18.4degrees. The ATL before, after PATT, and after casting were 22.7, 31.3, and 28.3mm. The overall lengthening of Achilles tendon was 5.7% of the foot length. The pre-PATT TCA was correlated with post-PATT and post-casting TCA. The pre-PATT ATL was correlated with post-PATT ATL and post-casting ATL. Conclusion Post-PAT correction effect is negatively correlated with the pre-PAT severity of equinus. The comparison between post-PAT and post-casting TCA could be used to check the quality of casting in the Ponseti method.


Introduction
Congenital talipes equinovarus (CTEV) is one of the most common congenital foot-deformity diseases in newborns. Over the centuries, it has been treated by various modalities ranging from extensive operative release to more conservative methods. With the use of the Ponseti technique, the number of patients who undergo radical soft tissue release has decreased, and the Ponseti method has become the gold standard of care for the treatment of congenital club foot. The Ponseti method includes clubfoot assessment, cast correction, percutaneous Achilles tenotomy (PAT), bracing, and tendon transfer if needed. The majority of clubfeet managed with the Ponseti method do not require further treatment. However, some series may require repeat casting, repeat tenotomy, or operative reconstruction for residual or recurrent deformity. 4,11 Clinicians have tried to nd factors for predicting which feet may eventually require additional intervention. 15,19 Two clubfoot scores have been widely used: the Pirani score and Dimeglio score. 2,5 The scoring systems are appropriate for classifying the severity of club foot, it has not been mentioned whether the clinical ndings can be utilized for predicting further operative intervention. Ponseti recommended the evaluation of infant clubfoot by physical examination, but many orthopedic surgeons still rely on imaging methods such as ultrasound and radiographs for decision-making. 13,14 Several studies have demonstrated that reliable radiographic measurements can be made on the feet of children with clubfoot. 16,17 The purpose of this study was to document the amount of Achilles tendon lengthening obtained from PAT in Ponseti's method for the treatment of clubfoot, as well as to analyze the factors that might impact the amount of equinus correction.

Methods
This retrospective study was carried out after obtaining approval from the institutional ethical committee. The study included 16 feet of 12 children who received PAT as part of Ponseti's method for the treatment of CTEV from November 2002 to October 2006. All included patients had idiopathic clubfoot, and patients with any syndromic stigmata were excluded. Cases of atypical, complex clubfoot or those that received any previous treatment were excluded. All patients were treated by a single orthopedic surgeon and were regularly followed up for at least two years following the initial cast correction.
The patient data collected included sex, birthday, age at the start of treatment, side of involvement, and cast times. Assessments were performed before and after treatment using the Dimeglio system. The Dimeglio classi cation system includes four aspects of deformity: equinus, varus, rotation, and forefoot medial deviation. Each is scored on a scale of one to four with four additional categories: depth of posterior crease, medial crease, cavus, and muscle power. The individual scores can be 0 or 1, and the maximum total score is 20. 3 In this study, we followed the protocol outlined in the Ponseti method, including the core principles and technical details of casting, PAT, brace type, and brace protocol. Residual equinus is de ned as <5 degrees of ankle dorsi exion when the foot is fully abducted and is treated with PAT. The foot length from toe to heel at the time of PAT was measured during surgery. The pre-PAT and post-PAT ankle dorsi exion lateral view and post-casting lateral view of the foot were obtained in the operation room with an image intensi er.
The calcaneal axis was de ned as the long axis of the ossi ed os calcis in a lateral view. The neutral tibiocalcaneal angle (TCA) was de ned as a 90-degree angle of the tibia and the calcaneal axes. Positive values indicate dorsi exion, and negative values indicate plantar exion. The length of the Achilles tendon was calculated as follows. The proximal margin of the Achilles tendon was de ned by a line perpendicular to the tibia axis and tangential to the distal margin of the primary ossi cation center of the tibia. The distal margin of the Achilles tendon was de ned by the longitudinal axis of the calcaneus. The Achilles tendon length (ATL) between the upper and lower margins was measured from the midpoint of the retro-tibial and retrocalcaneal soft tissue space ( Figure 1).
The Pearson correlation coe cient was used to establish relationships between the severity of deformity (Dimeglio classi cation) and the amount of correction (TCA change and ATL). Correlation analysis was also performed between the pre-PAT and post-PAT tibio-calcaneal angles to document whether the Achilles tendon is the only contributor to the equinus deformity of the foot. A p-value less than 0.05 was considered statistically signi cant.

Results
A total of 16 feet of 12 patients were included in the study. Four were girls, and eight were boys. The average age of these patients who started the Ponseti method was 37.3 ± 39.9 days, and the average Dimeglio score was 11.8±2.7. Each deformed foot underwent manipulation and casting with an average of 5.2 ± 2.3 times. The age when they received PAT was 96.0 ± 67.7 days. The average TCA before PAT was -8.5 ± 10 degrees. After PAT, the improvement of TCA was 30.8 ± 10.4 degrees. After the application of a long leg cast, the TCA improvement became 22.8 ± 10.4 degrees. After PAT, the ATL was 8.5 ± 2.5 mm (7.8 ± 2.0% of the foot length).
TCA before PAT, after PAT, and after the cast were compared with each other, and a strong correlation was noted ( Table 2). The lengthening of the Achilles tendon before PAT, after PAT, and after the cast also revealed strong correlations with each other ( Table 3). As shown in Table 4 Noncompliance with an abduction orthosis is widely accepted as the primary risk factor for recurrence, but a signi cant relationship has not yet been established between the compliance and relapse of the deformity. 4,6,7,18 Several studies have shown that residual equinus deformity (the extent of ankle dorsi exion) before and after Achilles tenotomy are related to a higher need for future operative intervention. 9,10,12 Kang et al. indicated that lateral TCA measured by radiographs is more objective than physical examination only and is also a predictor for the necessity of performing PAT. 10 All our TCAs measured by radiographs after PAT were over 10 degrees and did not receive further intervention. However, a limitation of this study is that the post-casting ankle/foot lateral view was not taken at the same rotation angle as the pre-PAT and post-PAT lateral views due to the external rotation of the long leg cast near 70 degrees in the Ponseti method.
In conclusion, we revealed that the average lengthening of ATL after PAT was 8.5 mm, the average correction of TCA after PAT was 30.8 o , and the average dorsi exion of 8 o was lost after casting. A lower pre-PAT TCA correlates with lower post-PAT and post-casting TCA. Furthermore, lower pre-PAT ATL correlates with a lower post-PAT and post-casting ATL. This means that the post-PAT correction effect is negatively correlated with the pre-PAT severity of equinus. The comparison between the post-PAT and post-casting TCA could be used to check the quality of casting in the Ponseti method. TCAs after PAT were all over 10 degrees, and no cases needed further operation in our study. Long-term follow up is necessary to document the nal equinus correction.

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Authors' contributions -Wei Ning, Chang analyzed and interpreted the patient data regarding the foot length, angle measurement and analysis under image intensi er. Yu Cheng, Lai performed the physical examination of the clubfoot, and Yen Chang, Lin was a major contributor in writing the manuscript. All authors read and approved the nal manuscript.