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Mechanical consequences of rod contouring and residual scoliosis in sublaminar segmental instrumentation
Author(s) -
Johnston Charles E.,
Ashman Richard B.,
Sherman Michael C.,
Eberle Charles F.,
Herndon William A.,
Sullivan J. Andrew,
King Andrew G. S.,
Burke Stephen W.
Publication year - 1987
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.1100050207
Subject(s) - rod , materials science , stiffness , ultimate tensile strength , contouring , scoliosis , bracing , implant , deformity , stress (linguistics) , axial symmetry , structural engineering , orthodontics , brace , composite material , surgery , medicine , engineering drawing , linguistics , philosophy , alternative medicine , pathology , engineering
The mechanical performance of contoured Luque rods in a neuromuscular model of spine deformity was examined to define an upper limit of deformity above which rod stresses would exceed the endurance limit for 316L stainless steel and therefore predict fatigue. Bovine constructs varying from 0–120° scoliosis were loaded axially, with strain recordings obtained at the apex of the curve. Relatively low loads produced enough tensile stress to contemplate implant fatigue in all except the nondeformed (0°) construct. Construct stiffness was found to decrease rapidly in spines with greater than 38° deformity. In addition, data on patients who had suffered rod fracture from four different centers were found to compare favorably with experimental observations. We conclude that the vulnerability of Luque rod constructs to implant failure, from a mechanical standpoint, is greater than is generally assumed. Cross‐linking of rods was found to increase stiffness. Methods to decrease tensile stresses in the implants and increase stiffness include external immobilization, larger diameter rods, and procedures to enhance correction.