Abstract
PurposeThere is little information available regarding the cage diameter that can provide the most rigid construct reconstruction after total en bloc spondylectomy (TES). The aim of this study was thus to determine the most appropriate titanium mesh cage diameter for reconstruction after spondylectomy.MethodsA finite element model of the single level lumbar TES was created. Six models of titanium mesh cage with diameters of 1/3, 1/2, 2/3, 3/4, 4/5 of the caudad adjacent vertebra, and 1/1 of the cephalad vertebra were tested for construct stiffness. The peak von Mises stress (MPa) at the failure point and the site of failure were measured as outcomes. A cadaveric validation study also conducted to validate the finite element model.ResultsFor axial loading, the maximum stress points were at the titanium mesh cage, with maximum stress of 44,598 MPa, 23,505 MPa, 23,778 MPa, and 16,598 MPa, 10,172 MPa, 10,805 MPa in the 1/3, 1/2, 2/3, 3/4, 4/5, and 1/1 diameter model, respectively. For torsional load, the maximum stress point in each of the cages was identified at the rod area of the spondylectomy site, with maximum stress of 390.9 MPa (failed at 4459 cycles), 141.35 MPa, 70.098 MPa, and 88.972 MPa, 42.249 MPa, 15.827 MPa, respectively. A cadaveric validation study results were coincided with the finite element model results.ConclusionThe most appropriate mesh cage diameter for reconstruction is 1/1 the diameter of the lower endplate of the adjacent cephalad vertebra, due to its ability to withstand both axial and torsional stress. According to the difficulty of large size cage insertion, a cage diameter of more than half of the upper endplate of the caudad vertebrae is acceptable in term of withstand stress. A cage diameter of 1/3 is unacceptable for reconstruction after total en bloc spondylectomy.
Highlights
Total en bloc spondylectomy (TES) is a procedure aimed at total removal of spinal tumors [1, 2]
The 1/1 diameter cage exhibited the greatest stiffness under an axial compression load of 1000 N until failure
The 1/3 diameter model failed at a von Mises stress value of 390.9 with only 4459 cycles of 5 N-M torsional load
Summary
Total en bloc spondylectomy (TES) is a procedure aimed at total removal of spinal tumors [1, 2]. Successful TES results in a lower local recurrence rate and better prognosis in primary spinal tumor and secondary spinal metastasis patients [3,4,5,6,7]. Achieving total resection with TES results in structural spinal nstability, which requires circumferential reconstruction using pedicular screws and rods and anterior column reconstruction using an autologous bone graft [2, 8,9,10]. Even with rigid stabilization and fixation, hardware failure is a late post-operative complication in TES. Bandiera et al reported a 7% hardware failure in TES patients and proposed that it might be due to short segment fixation and late imbalance of the spinal column. Park et al found that 37.5% of TES patients experienced titanium rod fracture, which occurred at an average of 29.2 months and that lumbar location and history of radiation therapy were risk factors for implant failure [11]
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