Biomechanical comparison of three methods of sacral fracture fixation in osteoporotic bone.
METHODS
Biomechanical cadaveric bench study.


OBJECTIVE
To measure motion at the fracture site in an osteoporotic cadaveric sacral insufficiency fracture model before and after fracture creation, after fixation (via 1 of 3 fixation techniques), and after cyclic loading and to compare those values with motion of the intact pelvis.


BACKGROUND
Sacral insufficiency fractures occur frequently in the elderly and pose treatment challenges. Screw fixation and sacroplasty have been proposed as possible treatments. There is little information about the stabilization provided by these treatments.


METHODS
We potted 18 osteoporotic cadaveric pelves, mounted them on a materials testing machine, measured sacroiliac (SI) joint motion with a vertical load applied to the lumbar spine, and created simulated sacral insufficiency fractures. Then, we measured fracture site motion under load and repaired the fracture using 1 of 3 techniques: a unilateral SI screw, a bilateral SI screw, or sacroplasty. A vertical compressive load (10-350 N) was applied cyclically at 0.5 Hz to the lumbar spine of the repaired specimens for 5000 cycles. Kinematic analysis was conducted prefracture, postfracture, postrepair, and after cyclic loading.


RESULTS
Postfracture, there was a significant increase in motion relative to the intact SI joint. After fixation, the average motion in all 3 groups was similar to that of the intact pelvis. After cyclical loading, motion increased in all groups. No significant differences were found between treatments.


CONCLUSIONS
All 3 fixation methods resulted acutely in motion similar to that of the intact pelvis. Although motion increased as a function of cyclical loading, no significant differences were found between fixation methods. All 3 repair methods reduced fracture site motion, but clinical studies are needed to determine if each method relieves pain and provides sufficient fixation for fracture healing.
Mears
Simon C
SC
International Center for Orthopaedic Advancement, Department of Orthopaedic Surgery, The Johns Hopkins Bayview Medical Center, 4940 Eastern Ave., Baltimore, MD 21224, USA. ehenze1@jhmi.edu
Sutter
Edward G
EG
Wall
Simon J
SJ
Rose
David M
DM
Belkoff
Stephen M
SM
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena / Q000502:physiology; D001863:Bone Screws / Q000592:standards; D002102:Cadaver; D005260:Female; D005592:Fracture Fixation / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D016268:Internal Fixators / Q000592:standards; D008953:Models, Anatomic; D010024:Osteoporosis / Q000150:complications*; D016059:Range of Motion, Articular / Q000502:physiology; D012446:Sacroiliac Joint / Q000033:anatomy & histology / Q000502:physiology; D012447:Sacrum / Q000293:injuries* / Q000503:physiopathology / Q000601:surgery*; D016103:Spinal Fractures / Q000209:etiology / Q000503:physiopathology / Q000601:surgery*; D013314:Stress, Mechanical; D054854:Vertebroplasty / Q000379:methods; D016474:Weight-Bearing / Q000502:physiology