Correction of Blount's disease by a multi-axial external fixation system.

Background: Blount's disease is a multi-planar deformity affecting the pediatric population which leads to varus alignment of the lower extremities. The Multi-Axial Correction (MAC) monolateral external fixation system (Biomet, Parsippany, NJ, USA) is a non-circular fixator that was developed as a response to the technical difficulty for both patients and physicians of placing, managing, and tolerating a circular fixator. The purpose of this study was to determine the efficacy of the MAC system for the treatment of pediatric patients with Blount's disease.
Methods: A retrospective analysis of 17 consecutive patients with surgically corrected Blount's disease using the MAC system with tibial and fibular osteotomies was identified. Patient charts and radiographs at three different time points (pre-operative, fixator removal, and final follow-up) were reviewed. The mechanical axis deviation (MAD), tibial-femoral angle (TFA), medial proximal tibial angle (MPTA), and posterior proximal tibial angle (PPTA) were measured in the MAC group at the three time points mentioned previously. The total wear time, total operative time, and post-operative complications were noted.
Results: The MAC system was able to correct the deformity of Blount's disease as measured by a decrease in the MAD (40.2 +/- 29.3 mm; P </= 0.001) and TFA (15.9 +/- 13.7 degrees ; P </= 0.001), as well as an increase in the MPTA (15.7 +/- 14.6 degrees ; P = 0.001) at the time of fixator removal. The correction was maintained for these parameters at the time of final follow-up (P </= 0.025). The absolute values obtained at final follow-up for MAD (20.5 +/- 12.7 mm medial), TFA (8.0 +/- 4.1 degrees varus), and MPTA (83.7 +/- 8.1 degrees ) after correction with the MAC system were close to what is considered as normal for these indices. The most common complications noted were superficial pin tract infections and/or cellulitis, with no patients having nerve palsy, compartment syndrome, non-union, or leg length discrepancies. The total time that the fixator was on the patients prior to removal was 130.6 days (standard deviation [SD] = 44.8). The mean operative time was 120.6 min (SD = 21.2).
Conclusions: Correction of Blount's disease with osteotomy of the tibia and fibula as well as dynamic fixation with the MAC system achieved deformity correction as measured by radiographic indices with minimal intra- and post-operative complications. The ease of application and adjustment of the MAC system makes it an attractive option for Blount's deformity correction.