BIOMECHANICAL JUSTIFICATION FOR EXTERNAL FIXATION OF THE PELVIS USING RODS WITH DIFFERENT THREAD HANDS

Abstract

Background. External fixation devices (EFD) have found wide application in pelvic fractures treating, but it is not always that strength characteristics of these devices make it possible to realize early rehabilitation. Objective. the biomechanical justification for external pelvic osteosynthesis with use of rods having different thread hands on the basis of analysis of the stress-strain state (SSS) of the “EFD – pelvis” system and an experimental study of the strength of threaded connections of different rods and the pelvic bone under the effect of alternate cyclic loads. Materials and Methods. Was analyzed the SSS of the “EFD – pelvis” system verified in an experimental study of the strength of threaded connections of different rods and the pelvic bone under the effect of alternate cyclic loads. Results. Standing on a single basis in the AVF rods with the same thread, there are torques directed in different directions: on the right - clockwise (screwing in), on the left - counterclockwise (screwing out).A change in the thread direction does not lead to change in the moment values, but directions of the action of the moments of force for the left rod will correspond to the direction of its screwing both in the left- and right-sided one-support position. Conclusions. Bar-connected rods with a differently directed thread create a reciprocally interlocking structure, which counteracts self-unscrewing. Such a structure significantly increases the strength of connection of an EFD with the pelvic bone and creates conditions for an effective use of the early rehabilitation of patients with pelvic fractures.