Substantiation for the use of orthopedic hexapod for the femur lengthening over the nail

Relevance. During femur lengthening over the nail we have a specific problem - jamming of the nail in the medullary canal. A possible solution is the use of an orthopedic hexapod. Aim: to determine the indications for the use of orthopedic hexapod in the femur lengthening over the nail and to test the technique in the clinic. Material and Methods: To calculate the risk of nail jamming, a circular approximation of the medullary canal area behind the osteotomy level was used. The channel radius was calculated based on measurements of the chord length and height from an X-ray image. Using a system of quadratic equations with a given radius of the nail and a calculated radius of the channel, the risk of jamming was determined depending on the magnitude of the elongation. The use of orthopedic hexapod, which allows a fragment to be moved along a given trajectory, was tested in 10 patients. Results: Calculations were made of the risks and coordinates of jamming during lengthening in a straight line for nail with a radius of 2000 mm and 3000 mm and channel radii from 1200 mm to 3800 mm, which are presented in the form of tables for practical work. It was determined that if the radius of the channel is less than the radius of the nail, then first there will be a conflict along the outer surface of the bend (anterior cortical plate). If it is possible to pass this area with forced distraction, then the conflict is eliminated and after a certain distance it will manifest itself from the opposite side. If the radius of the canal is greater than the radius of the nail, then there will be no conflict in the region of the anterior cortical plate, but then there will be conflict along the posterior surface. In clinical approbation, the calculated lengthening was performed in all cases without increasing the rate of distraction. Conclusion. Indications for the use of orthopedic hexapod are: lengthening more than 40 mm; the presence of torsional deformation or bending of the diaphysis in the frontal plane; the threat of jamming before the end of the planned lengthening; all cases when the radius of the channel exceeds the radius of the nail.