The talar axis-first metatarsal base angle in CVT treatment: a comparison of idiopathic and non-idiopathic cases treated with the Dobbs method

Purpose Congenital vertical talus (CVT) appears as an idiopathic or non-idiopathic deformity. In this study, we analysed the talar axis-first metatarsal base angle (TAMBA) values of idiopathic and non-idiopathic CVT cases treated with the Dobbs method. Materials and methods Between January 2007 and July 2012, 20 cases of CVT were treated, starting with a manipulation, casting and a minimally invasive surgical approach. We analysed retrospectively the TAMBA values in idiopathic and non-idiopathic CVT. As a new indicator for the mobility in the talonavicular complex, we used the difference of the TAMBA in neutral position and the TAMBA in plantarflexion. TAMBA measurements of CVT successfully treated with the Dobbs method were compared to TAMBA values of CVT unsuccessfully treated using a minimally invasive approach. Results Out of 20 CVT, 14 were successfully treated with the Dobbs method. Of these 14, five feet were non-idiopathic and nine feet were idiopathic. Six feet did not have complete correction following the Dobbs protocol, and were associated with arthrogryposis or caudal regression syndrome. The initial TAMBA in idiopathic feet ranged from 70 to 110 degrees (mean 88 degrees). The TAMBA in non-idiopathic feet ranged from 75 to 128 degrees (mean 105). Feet successfully treated with the Dobbs method had an initial TAMBA between 74 and 110 degrees (mean 87 degrees). Feet unsuccessfully treated with the Dobbs method had an initial TAMBA between 95 and 128 degrees (mean 118 degrees). The measurement difference between the TAMBA in neutral and plantarflexion positions in cases unsuccessfully treated with the Dobbs method were smaller compared to values of feet successfully treated with the Dobbs method. These differences were statistically significant (p < 0.0001). Conclusion In our series, the success of the Dobbs method in CVT treatment depended on the flexibility in the talonavicular complex. The TAMBA value and TAMBA difference (TAMBA neutral minus TAMBA plantarflexion) express the flexibility in the talonavicular joint and could be predictive for the success of a minimally invasive treatment. Only in a few cases is the success of the Dobbs method limited. These feet are associated with a TAMBA greater than 120 degrees in neutral position and, particularly, a TAMBA difference smaller than 25 degrees.