Study Design. Combinations of metal implants (stainless steel (SS), titanium (Ti), and cobalt chrome (CC)) were placed in porcine\r\nspines. After 12 months, tissue response and implant corrosionwere compared between mixed and singlemetal junctions.Objective.\r\nModel development and an attempt to determine any detriment of combining differentmetals in posterior spinal instrumentation.\r\nMethods. Yucatan mini-pigs underwent instrumentation over five unfused lumbar levels. A SS rod and a Ti rod were secured with\r\nTi and SS pedicle screws, SS and Ti crosslinks, SS and CC sublaminar wires, and Ti sublaminar cable.The resulting 4 SS/SS, 3 Ti/Ti,\r\nand 11 connections between dissimilar metals per animal were studied after 12 months using radiographs, gross observation, and\r\nhistology (foreign body reaction (FBR), metal particle count, and inflammation analyzed). Results. Two animals had constructs\r\nin place for 12 months with no complications. Histology of tissue over SS/SS connections demonstrated 11.1 �± 7.6 FBR cells, 2.1 �±\r\n1.7 metal particles, and moderate to extensive inflammation. Ti/Ti tissue showed 6.3 �± 3.8 FBR cells, 5.2 �± 6.7 particles, and no to\r\nextensive inflammation (83% extensive). Tissue over mixed components had 14.1 �± 12.6 FBR cells and 13.4 �± 27.8 particles. Samples\r\nsurrounding wires/cables versus other combinations demonstrated FBR (12.4 �± 13.5 versus 12.0 �± 9.6 cells, P = 0.96), particles (19.8\r\n�± 32.6 versus 4.3 �± 12.7, P = 0.24), and inflammation (50% versus 75% extensive, P = 0.12). Conclusions. A nonfusion model was\r\ndeveloped to study corrosion and analyze biological responses. Although no statistical differences were found in overlying tissue\r\nresponse to single versus mixed metal combinations, galvanic corrosion between differing metals is not ruled out. This pilot study\r\nsupports further investigation to answer concerns when mixing metals in spinal constructs.
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