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Surgically Relevant Anatomy of Marfan Vertebrae
Myung-Jin Cha1, William ElNemer, Paul D Sponseller
1Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, MD.
Background:
Understanding vertebral anatomy is crucial for the secure fixation of spinal instrumentation. Using MRI and CT scans can identify safe locations for pedicle screw insertion and/or discover underlying pathologies such as dural ectasia. In this study, we explored Marfan vertebrae morphology and compared it to that of idiopathic scoliotic vertebrae. We investigated whether the pedicles and laminae of patients with Marfan syndrome (1) would differ from those with idiopathic scoliosis (IS) and (2) would be affected by the position in the curve and by dural ectasia.
Methods:
Using MRI and CT scans, the morphologies of 134 vertebrae from T1 to L5 were measured in 16 Marfan patients with spine deformity. The morphologies of 140 vertebrae in 20 patients with IS were measured in the same fashion. They were then compared with each other.
Results:
Marfan pedicle channels were significantly thinner than those with idiopathic scoliosis ( P <0.001). This difference increased significantly from cranial to caudal. Type D pedicles (<2 mm wide) were found in 34% of Marfan and 9% of IS patients ( P <0.001). Marfan type D pedicles were found in 36% of atypical locations (outside the concave apex). Pedicle width significantly correlated with both vertebral level and distance from the apex. Pedicles became progressively thinner than IS pedicles at descending levels of the spine. Pedicle width and laminar thickness measurements on CT and MRI did not differ significantly. The average thickness of the Marfan lamina was significantly thinner (by a mean of 1 mm) than that of the IS lamina ( P <0.001). Marfan patients with dural ectasia had significantly thinner laminae in the lumbar spine than those without ( P =0.023).
Conclusions:
Marfan spines were associated with thinning of fixation sites, most pronounced at the curve apex. Laminar thinning was more common on the concavity and with dural ectasia. Radiographs often overestimate the width. Therefore, preoperative MRI or CT is helpful when operating on Marfan spine with pedicle screws and laminar hooks.
Level Of Evidence:
Level III-retrospective cohort study.
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