**THE PILON CONCEPT OF PELVIC ANCHORAGE FOR SPINAL INSTRUMENTATION IN THE HUMAN CADAVER

Richard Schwend,
Romuald Sluyters
and Jan Najdzionek Children's Hospital, Buffalo, New York, USA

INTRODUCTION AND PURPOSE:
We have observed substantial and straight columns of bone in the pelvis, connecting the acetabula to the sacrum. The purpose of this study was to describe the anatomy of the pelvic columns and to evaluate the strength in flexion of iliac bolt instrumentation of the entire columns compared to standard Galveston technique.

MATERIALS AND METHODS:
Twenty adult cadaveric pelvices were used. Each specimen was oriented in the CT scanner to obtain a cross section image of the pelvic columns, which begin from just caudal to the posterior iliac spines and end above the acetabula at the anterior inferior iliac spines. Two different instrumentation techniques were used. Standard Galveston pelvic fixation with a ¼ inch rod extending 8 cm into the pelvis was compared to a 15 cm long, 8 mm ilicac bolt placed within the length of the entire pelvic column, connected to ¼ inch spinal rods. Both constructs had two rigid cross links between the rods. Testing in flexion, a clinically relevant direction of failure, was performed for each construct with the MTS model 881 at 5 NM/sec until failure occurred.

RESULTS:
The rectangular shaped pelvic columns averaged 15.2 (SD 0.8) cm in length, 2.5 (SD 0.3) cm in width and were consistently straight. The orientation of each axis was 22 degrees from the sagittal plane. For the Galveston technique, failure occurred at a mean of 682 (SD 217) Nm. The iliac bolt construct failed at a mean of 2153 (SD 1370) Nm (p < 0.004). For both techniques, failure occurred with the instrumentation migrating cephalad and breaking through the outer posterior surface of the ilium.

CONCLUSION:
The human pelvis has substantial and straight columns of bone extending from the posterior iliac spines, traversing above the sciatic notches, and ending just above each acetabula at the anterior inferior iliac spines. The shape resembles a weight bearing long bone such as the tibia. Analogous to the architectural pilon, intra–medullary instrumentation of the entire length of these pelvic columns provides significantly stronger anchorage for spinal instrumentation compared to standard Galveston technique.

** The FDA has not cleared a drug and/or medical device for the use described in this presentation. (i.e., the drug or medical device is being discussed in an “off–label: use).