title: Biomechanical analysis of revision strategies for rod fracture in pedicle subtraction osteotomy.
abstract: 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° anterior, and (6) 45° posterior to original rods; 45° 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Biomechanical Testing Facility, Orthopaedic Trauma Institute, San Francisco General Hospital, San Francisco, California 94110, USA. jscheer@ucsd.edu
authors.forename: Justin K
authors.initials: JK
authors.lastname: Scheer
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Tang
authors.forename: Vedat
authors.initials: V
authors.lastname: Deviren
authors.forename: Jenni M
authors.initials: JM
authors.lastname: Buckley
authors.forename: Murat
authors.initials: M
authors.lastname: Pekmezci
authors.forename: R Trigg
authors.initials: RT
authors.lastname: McClellan
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Ames
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010027:Osteotomy / Q000379:methods*; D017063:Outcome Assessment, Health Care; D012086:Reoperation / Q000379:methods*; D016103:Spinal Fractures / Q000601:surgery*; D013123:Spinal Fusion / Q000379:methods*