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In the adult spine, which of the following pedicles have the smallest average transverse diameter.
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Of the levels listed, T6 has the smallest pedicle diameter.
Knowledge of pedicle diameter is important when placing pedicle screws. On average, thoracic pedicle diameter is maximal at T1 and T12, and gradually "dips" to its smallest diameter at the T4 to T6 region.
Scoles et al. performed an anatomic study of 50 normal adult vertebral columns ranging in age from 20 to 40 years at the time of death. They found the average pedicle diameter was smallest at T6 and largest at L5.
Ofiram et al. is an anatomic study of 100 patients comparing the pedicle isthmic width from T10 to L1 using magnetic resonance imaging. In this area they found the smallest pedicle isthmic width was at L1, while T12 had the largest pedicle width in the thoracolumbar junction.
Illustration A shows the finding of pedicle diameter in the Scoles et al study, with the smallest diameter being at T6. Illustration B shows a composite average of multiple studies and depicts the average pedicle diameter from C1 to the sacrum. Notice the "dip" in thoracic diameter from T4 to T6. Notice and additional dip in the lumbar spine at L1, so the diameter of T12 is actually greater than that of L1.
Answer 1: T1 has the largest pedicle diameter in the upper cervicothoracic spine. It is an important fixation point in cervicothoracic fusions.
Answer 3: On average T12 has the largest diameter in the thoracolumbar region,.
Answer 4 & 5: Lumber pedicle diameter continues to increase in the caudal direction, making L5 the largest diameter in the lumbar spine.
Scoles PV, Linton AE, Latimer B, Levy ME, Digiovanni BF.
Spine (Phila Pa 1976). 1988 Oct;13(10):1082-6. PMID: 3206263 (Link to Abstract)
Ofiram E, Polly DW, Gilbert TJ, Choma TJ
Spine. 2007 Jan;32(1):49-54. PMID: 17202892 (Link to Abstract)
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