Fri., 10/5/12 Pelvis & Acetabulum, PAPER #60, 3:23 pm OTA-2012
Transiliac-Transsacral Screw Safe Zone Diameter in 1091 Sacrums
John J. Lee, MD; Alex Martusiewicz, MD; James A. Goulet, MD;
University of Michigan, Department of Orthopedic Surgery, Ann Arbor, Michigan, USA
Background/Purpose: Iliosacral screw fixation from an iliac cortex to the sacral body for posterior pelvic disruptions may not provide adequate stabilization in certain injury patterns and in the osteoporotic. Longer transiliac-transsacral screws spanning across the sacrum and bilateral iliac cortices may provide increased stability and can be placed percutaneously with a low complication rate. Placement of these screws, however, is technically challenging due to the small window, or safe zone, which these screws must traverse to avoid devastating neurovascular injury. Pelvic dysmorphism and other anatomic variations may preclude the safe placement of these screws. We present the results of a novel method for measuring the safe zone for transiliac-transsacral screw placement in the upper and second sacral segments.
Methods: 1091 adult (≥18 years old) pelvis CT scans obtained from our trauma registry were morphometrically analyzed automatically with MATLAB software. Each pelvis was oriented in the anatomic position, bisected, and the left and right sides were analyzed separately, assuming the sacrum to be perfectly symmetric. If a unilateral sacral fracture was present, the uninjured side was used for analysis. Patients with bilateral sacral fractures were excluded. A maximum diameter intraosseous cylinder that traversed the sacrum perpendicular to the sagittal plane was calculated for the upper and second sacral segments. Pelvises were grouped into a normal or a lumbarized group depending on the absence or presence of a lumbarized S1. Safe zone diameters for normal and lumbarized were compared. A safe zone diameter of 10 mm was used as the critical threshold for safe placement of a large cannulated screw (6.5 mm to 8.0 mm).
Results: Data are presented as mean (±standard deviation). Of 1091 patients, 672 (62%) were male and 419 (38%) female. Mean age was 36 (±16) years. 64 (5.9%) were identified as lumbarized. Safe zone diameters in normal was 14.0 (±3.9) mm in S1 and 10.7 (±3.7) mm in S2 and in the lumbarized, 17.2 (±3.7) mm in S1 and 9.7 (±2.5) mm in S2 (P <0.0001 for S1 between groups). Of normal pelvises, 17% were below the critical safe threshold in S1 and 38% in S2, whereas in the lumbarized pelvises 3% were below in S1 and 51% in S2. Of the normal pelvises that cannot take an S1 screw, 34% can safely take an S2 screw. 6% of normal pelvises can safely take two large cannulated screws in the upper sacral segment while 18% could do so in the lumbarized group. Second sacral segments in either group cannot accept two large screws.
Conclusion: 83% of normal pelvises and 97% of lumbarized S1 pelvises can accept a large cannulated transiliac-transsacral screw safely in S1 while 62% of normal and 49% of lumbarized pelvises can accept a large cannulated screw safely in S2. This method is superior to prior methods in that the pelvis is analyzed three-dimensionally with an intraosseous cylinder.
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• The FDA has not cleared this drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an “off label” use). ◆FDA information not available at time of printing. Δ OTA Grant.