Limb Angular Deformity Correction Using Dyna-ATC: Surgical Technique, Calculation Method, and Clinical Outcome

Abstract

PurposeDyna-ATC is a unilateral external fixator with angulator, lengthener, and translator, which allows for angular correction and compensation of the secondary displacement during angular correction. The purpose of this study is to introduce surgical technique and calculation methods and to evaluate the clinical outcome of angular deformity correction using Dyna-ATC.Materials and MethodsThe amounts of secondary displacement were calculated with the distances between axis of correction of angulation, Center of Rotational Angulation, and osteotomy and the amount of angular deformity. The rate of angular correction was determined to distract the corticotomy at 1 mm/day. Clinical and radiographic evaluation was performed on 13 patients who underwent deformity correction using Dyna-ATC. There were 8 proximal tibia vara, 1 tibia valga, 2 varus and 4 valgus deformities on distal femur. One patient underwent pelvic support femoral reconstruction. Concomitant lengthening was combined in all femur cases. Mean age at surgery was 17.5 years (7 to 64).ResultsAll but one achieved bony healing and normal alignment with the index procedure. Mean mechanical axis deviation improved from 31.9 mm to 3.0 mm. The average amount of angular correction was 11.0° on tibiae and 10.0° on femora. The average length gain on femora was 6.4 cm, and the healing index averaged to 1.1 mo/cm. One patient underwent quadricepsplasty and one patient had three augmentation surgeries due to poor new bone formation.ConclusionWe believe that Dyna-ATC is a useful alternative to bulky ring fixators for selective patients with angular deformity less than 30 degrees in the coronal plane around the knee joint.

One-stage Surgical Treatment of Simultaneous Osteotomy and Asymmetric Lengthening on Short Femur with Severe Deformity of Genu Valgus

“…However, clinical treatment of these types remains to be difficult. Thus, supracondylar femur osteotomy and 8-plate hemi epiphysiodesis are used to treat severe articulation genu angulation deformities during the later periods in the first stage 9–12 , and bone lengthening is performed in the second stage 13,14 . This therapy involves complicated process of long treatment cycle, high expenses and severe trauma, and the short femur deformity is regarded to be more severe if the angulation deformity is treated.…”

Simplified Calculation for Corrective Osteotomies of Long Bones

“…For cuneiform osteotomies of long bones, the calculation of the wedge dimensions, whether a subtraction- or addition-type, have been classically performed using trigonometric methods, which ensures great precision, considering that cylinder wedges are geometrically compatible with triangles in the uniplanar analysis. 11 - 13 Other forms of programming involve the direct method, in which the wedge dimensions are measured on the radiographic film, which also lead to good results, despite being more subject to deviations from the radiographic magnification, besides possible measurement errors that can affect the intervention's outcome. 14 …”