Abstract
Background: Certain pelvic fractures with posterior shearing force lesions raise a difficult problem for stabilisation. Assemblies bridging the two sacroiliac joints and anchored in the vertebral pedicles have been proposed to overcome this difficult osteosynthesis problem. But this type of fixation bridges intact joints. We used an original computer-assisted osteosynthesis technique in a patient with an unstable non-union of a displaced fracture passing through the S1 pedicle and the sacral foramina associated with major pubic disjunction.
Case report: The instability of the half-pelvis led to pubalgia and movement of the non-union focus which in turn led to S1 sciatalgia preventing the sitting position. The fracture and the displacement could not be treated initially because of open visceral lesions which required definitive colostomy and a long period of intensive care. The technical problem was to stabilise the pelvis with a posterior osteosynthesis which could not use the S1 pedicle. The fixation had to be sufficiently rigid to compensate for the impossible anterior fixation of the pubic symphesis.
Operative technique: The original solution was to bridge the non-union transversally using two spinal bars (CD instrumentation) applied on the healthy side with two polyaxial screws in S1 (in the pedicle and the wing) and on the non-union side with two polyaxial screws inserted in the iliac wing passing between the internal and external corticals. The assembly was completed with two transiliosacral screws passing through S1 and S2 after demounting and avivement of the non-union.
Discussion: The computer superposed a virtual image of the instruments on the CT images allowing precise insertion of the two iliac screws which had to pass between the bone tables over a long trajectory. The two transiliosacral screws could thus be inserted into S1 and S2 percutaneously with minimal neurological risk. Monitoring the progression allowed safe avivement of the nonunion to the anterior border of the sacrum. The final assembly thus associated four screws and two bars on the posterior part of the sacrum and two anterior screws, enabling perpendicular compression of the nonunion while maintaining the spine and contralateral sacroiliac joint. At five years, the patient remains free of dysesthesia and can sit and walk with little limitation.
Conclusion: This particular case illustrates perspective computer-assisted osteosynthesis methods.
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