Do cast characteristics influence the post Achilles tenotomy treatment outcomes in Ponseti method?

The post tenotomy Ponseti cast is retained for three weeks. In a few children, the cast appears soiled especially at its proximal extent and sometimes, at the knee and foot sections as well. Some of these children manifest deterioration of the previously achieved clinical ankle dorsiflexion. This study aimed at investigating the characteristics of post tenotomy cast at follow up to study their influence on ankle dorsiflexion.

The study included 25 children with bilateral idiopathic clubfeet under the age 1 year treated with Ponseti method who also underwent percutaneous Achilles tenotomy for both feet (50 limbs). The cast characteristics evaluated were extent till groin, knee and ankle intactness along with firmness of plantar surface. Clinical ankle dorsiflexion was measured immediate post tenotomy and at follow up. Odds ratios were calculated to establish relationship between ankle dorsiflexion and cast characteristics.

The mean child's age was 3.7 months. The immediate post tenotomy ankle dorsiflexion was 15.2° and at follow up was 14.2° (p = 0.0029). Sixteen casts (32 %) were found short near the groin edge at follow up. Out of these, 9 limbs (56 %) had lower ankle dorsiflexion measurements than those achieved immediate post tenotomy. Statistically, the likelihood of lost dorsiflexion was heightened 87 times with recessed groin margin compared to the intact casts (p = 0.003). Although the odds ratio of deterioration of ankle dorsiflexion with plantar surface break was even higher (odds ratio 160; p < 0.0001), isolated plantar breaks without cast recession near the groin were not observed in any of the limbs.

The deteriorated cast characteristics at follow up may be responsible for loss of achieved ankle dorsiflexion immediately post tenotomy. The post tenotomy cast should be monitored better to keep its integrity and extent intact.