Biomechanical analysis of L5/S1 complex and sacroiliac joints on the stability of lumbo-iliac fixation

English Keywords:Lumbo-sacral instability  Sacroiliac joint resection  Iliac screw fixation  Lumbo-iliac fixation  Biomechanics

English Abstract:

  【Abstract】 Objectives: To explore the biomechanical effects of L5/S1 complex and sacroiliac joints on the stability of lumbo-iliac fixation construct, and to provide evidences for the rational reconstruction. Methods: Seven fresh L2-pelvic specimens harvested from donated adult cadavers were used in this study. After testing the initial state simulated by L3-L5 pedicle screw fixation, L3-iliac fixation and sequential joint resections were performed on the same specimen as follows: group A, L3-iliac fixation using bilateral iliac screws; group B, bilateral L5/S1 facetectomy; group C, L5/S1 discectomy; group D, left side sacroiliac joint resection. Biomechanical testing was performed on a material testing machine under 600N compression and 7Nm torsion loading modes for construct stiffness evaluation. Results: The compressive stiffness of initial state was (332±103)N/mm, group A-D obtained(122±15.5)%, (118.3±10.5)%, (81.1±7.7)% and (59.2±8.6)% of the initial compressive stiffness, respectively. No significant difference was detected between group A and B(P>0.05); furthermore, the two groups showed significantly higher compressive stiffness than the initial state(P<0.05); group C and D exhibited lower compressive stiffness than group A, B and the initial state(P<0.05); there was significant difference between group C and D(P<0.05). The torsional stiffness of initial state was (2.47±0.88)Nm/deg. Group A-D acquired (128±14.3)%, (120±12.6)%, (78.4±13.2)% and (62.9±11.3)% of the initial torsional stiffness, respectively. Group B obtained sufficient torsional stiffness compared to group A(P>0.05); both group A and B exhibited notably higher torsional stiffness than all the other three groups(P<0.05). Significant differences were demonstrated among group C, D and initial state(P<0.05). Conclusions: L5/S1 discectomy and one-side sacroiliac joint resection significantly decrease the stability of lumbo-iliac fixation construct. Therefore, anterior support of spine and pelvic continuity reconstruction is important in the lumbo-iliac stability.