A biomechanical comparison of different types of lumbopelvic fixation.
METHODS
Comparative biomechanical testing in calf spines.


OBJECTIVE
To biomechanically evaluate 4 techniques of lumbosacral fixation.


BACKGROUND
Pelvic fixation is a problematic area, and currently, the preferred method of pelvic fixation is controversial. Clinically, iliac screws have demonstrated decreased rod breakage rates, and better correction of pelvic obliquity than unthreaded rods (Galveston technique), but several modern methods of iliac fixation have not been compared.


METHODS
A total of 32 male calf spines were tested under axial rotation, flexion/extension, and lateral bending. Following intact testing, specimens were instrumented in the following groups: group 1-Modified Galveston technique with rods connected directly to iliac screws (no S1 fixation); group 2-S1 screws and iliac screws with offset connectors distal to S1; group 3-S1 screws and iliac screws with offset connectors coupled to the longitudinal rod between L6 and S1; and group 4-S1 and S2 screws without iliac fixation. Pedicle screws were placed from L3 to L6. Following nondestructive testing, specimens were fixed at the cephalad aspect of the construct and flexed to failure, with peak failure moment (Nm).


RESULTS
Group 1 demonstrated significantly more flexion/extension than groups 2, 3, 4 (P<0.001). There were no significant differences between groups for lateral bending or axial rotation at L3-S1 or L6-S1. During destructive testing, group 4 showed a significant reduction in peak failure compared to group 1 (P<0.001), group 2 (P=0.001), and group 3 (P<0.001). There was no significant difference between groups 1, 2, and 3 and all specimens failed at the distal fixation.


CONCLUSIONS
With extension of instrumentation across the lumbosacral junction, our results indicate significant improvement in stability with the use of S1 screws and iliac screw fixation. Furthermore, there does not appear to be any significant difference in the location of the connector for the iliac screw.
Tis
John E
JE
Department of Orthopaedics and Rehabilitation, Walter Reed Army Medical Center, Washington, DC, USA. jtis1@aol.com
Helgeson
Melvin
M
Lehman
Ronald A
RA
Dmitriev
Anton E
AE
D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws / Q000009:adverse effects / Q000592:standards / Q000639:trends; D002417:Cattle; D004868:Equipment Failure; D007085:Ilium / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery; D016268:Internal Fixators / Q000009:adverse effects / Q000592:standards* / Q000639:trends; D004204:Joint Dislocations / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D007593:Joint Instability / Q000503:physiopathology / Q000517:prevention & control / Q000601:surgery; D008159:Lumbar Vertebrae / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D023421:Models, Animal; D010384:Pelvic Bones / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D016059:Range of Motion, Articular / Q000502:physiology; D019651:Plastic Surgery Procedures / Q000295:instrumentation / Q000379:methods; D012447:Sacrum / Q000033:anatomy & histology / Q000502:physiology / Q000601:surgery*; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D013168:Spondylolisthesis / Q000473:pathology / Q000503:physiopathology / Q000601:surgery; D016474:Weight-Bearing / Q000502:physiology