IN-VITRO BIOMECHANICAL STUDY OF A DORSO-LUMBO-SACRAL-POSTERIOR SUPPLEINSTRUMENTATION WITH VARIABLE SECTION

This study is designed to analyse the behavior, in the sagittal plane, of a complete human dorso-lumbar rachis, made rigid by the posterior instrumentation used for the treatment of scoliosis, on subjects suffe ring from DMD (Duchenne Muscular Dystrophy). The object of this analys is is to demonstrate the reliability of early surgery made possible by new instrumentation. Close review of the literature shows that the cu rrently used Harrington, or Luque instrumentations lead to mechanical complications, especially rod breaking, at the thoraco-lumbar junction . 8 specimens were non-destructively tested in-vitro. Compression and flexion were applied. For each test, rachis movements with and then wi thout instrumentation, and also rod restraints were noted. The results show a linear stiffness multiplied bg 8.3 in flexion and 11.6 in exte nsion. The maximum restraint recorded for physiological displacements is 77 MPa. This remains largely under the fatigue-breaking limit of th e metal used (stainless steel hammer-hardened-316 L, Young's modulus = 200,000 MPa, Poisson's ratio = 0.21, endurance limit = 350 MPa at 5x1 0(6) cycles). The results of this study encourage us to continue and d evelop early surgery in children affected by myopathy, with fixation o f the complete rachis, including a lumbo-sacral arthrodesis and a supp le dorsal part of the mounting, in the sagittal plane.