Biomechanical Analysis of Revision Strategies for Rod Fracture in Pedicle Subtraction Osteotomy

BACKGROUND: Pseudoarthrosis after pedicle subtraction osteotomy (PSO) can require revision surgery due to posterior rod failure, and the stiffness of these revision constructs has not been quantified. OBJECTIVE: To compare the multidirectional bending stiffness of 7 revision strategies following rod failure. METHODS: Seven fresh-frozen human spines (T11-pelvis) were tested as follows: (1) posterior instrumentation from T12-S1 (excluding L3) with iliac fixation and L3 PSO; (2) inline connectors after rod breakage at L3 (L2 screws removed for access); (3) cross-links connecting rods above and below inline connectors; satellite rods (4) parallel, (5) 45 degrees anterior, and (6) 45 degrees posterior to original rods; 45 degrees posterior with cross-links connecting (7) original and (8) satellite rods. Groups 3 to 8 were tested in random order. Nondestructive pure moment flexion-extension (FE), lateral bending (LB), and axial rotation (AR) tests were conducted to 7.5 Nm; 3D motion tracking monitored the primary range of motion. RESULTS: Addition of inline connectors alone restored stiffness in FE and LB (P > .05), but not in AR (P,.05). Satellite rods (groups 4 to 6) restored stiffness in FE and LB (P > .05), but not in AR (P,.05) and were not significantly different from one another (P > .05). The addition of cross-links (groups 3, 7, and 8) restored stiffness in all bending modes (P > .05) and were significantly greater than inline connectors alone in AR (P > .05). CONCLUSION: The results suggest that these revision strategies can restore stiffness without entire rod replacement. Failure of AR stiffness restoration can be mitigated with cross-links. The positioning of the satellite rods is not an important factor in strengthening the revision.