Experimental identification of the corrective capabilities of the spring technique in addressing multiapical femoral deformities

Background. The technique of multiapical deformities correction with several orthopedic hexapods (one for each apex of deformity) is accepted as a standard one. However, usage of two or more hexapods on one segment is uncomfortable for the patient. Besides, software calculation for each of them is difficult and laborious for an orthopedic surgeon. Application of only one orthopedic hexapod with one software calculation is the advantage of the spring technique (ST) of multiapical deformities correction. However, its application is hindered by the fact that the corrective capabilities of this technique have not been studied yet. The aim of the study was to identify by the bench test the corrective capabilities of the spring technique and compare them with the capabilities of the standard one. Methods. The bench test was performed using plastic models of the femur. One-ring modules were used to fix each of the bone fragments. Foam rubber discs were used to imitate soft tissues. The mobile ring was moved relative to the base one in translation, angulation, distraction and rotation. The movement was stopped if one of the struts reached its minimum or maximum length, as well as if one of them touched a frame, transosseous elements or “soft tissues”. The Mann-Whitney U-test was used for statistical analysis. Results. When using all the six struts equipped with standard threaded rods, the corrective capabilities of the spring technique are 58-97% (on average 72%) lower than of the standard one. When replacing 2-6 (depending on the type of motion) threaded rods with longer ones, the capabilities of ST increases by 36-466% (on average 257%). This provides better result for ST in translation (in three directions), varus and recurvation angulation. Conclusions. Corrective capabilities of the spring technique in 5 out of 11 types of motions are better than the capabilities of the standard technic if struts of the orthopedic hexapod are equipped with threaded rods of greater length.