Effect of sacral and iliac instrumentation on strains in the pelvis. A biomechanical study.
METHODS
This study is a biomechanical study on human cadaver pelves using strain gauges to measure strains at different locations in response to different load states.


OBJECTIVE
To examine the changes in strains, at different sites on the pelvis, and after instrumentation of the lumbosacral joint and the lumbosacroiliac joint.


BACKGROUND
Pelvic girdle pain after long instrumented fusions to the sacrum has been described and studied along with sacroiliac and pubic instability. Fractures of the pelvic rami or the iliac wing have been reported in patients after surgical fusions that incorporated the sacrum and sacroiliac joint.


METHODS
Pelves with lumbar spine attached had three axis rosette strain gauges cemented to specific sites on the pelves (ilium [correction of ileum] and rami). Specimens were tested in different configurations involving lumbosacral and sacroiliac instrumentation. Iliac bone harvest was also tested. Strain values were computed and compared for each configuration.


RESULTS
The "Galveston" and "sacral" instrumentation configurations caused significant stress shielding in pelves under all compression loads applied. Axial rotations on the instrumented specimens caused higher strains at all sites. Harvesting of bone from the ilium did not alter the strains seen at the different sites.


CONCLUSIONS
This study suggests significant stress shielding provided by sacro and sacroiliac instrumentation systems, supporting the possibility of development of device-related osteopenia that may predispose patients to late, insufficiency-type fractures as their activity increases. The rigid instrumentation of the lumbosacral spine was found to increase the stress during torsion, which may lead to failure during activity.
Wood
K B
KB
Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, USA.
Schendel
M J
MJ
Ogilvie
J W
JW
Braun
J
J
Major
M C
MC
Malcom
J R
JR
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D007085:Ilium / Q000502:physiology* / Q000637:transplantation; D008159:Lumbar Vertebrae / Q000502:physiology; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000502:physiology*; D012446:Sacroiliac Joint / Q000502:physiology; D012447:Sacrum / Q000502:physiology*; D013314:Stress, Mechanical; D014102:Torsion Abnormality; D016474:Weight-Bearing / Q000502:physiology