A CT-based study of the thoracic spine pedicle and pedicle-rib unit morphometry in a Kenyan population

Abstract

Background: The use of pedicle screws in thoracic spine fixation is guided by the morphometric characteristics of the thoracic pedicle and thoracic pedicle-rib unit.

Objective: To document the dimensions of the thoracic pedicle and the pedicle-rib  unit in a Kenyan population.

Methods: Demographic factors, thoracic pedicle dimensions and thoracic pedicle-rib unit dimensions of 97 patients were studied.

Results: The outer transverse diameter of the thoracic pedicles of T1 to T12 varied between 4.5mm and 8.4mm. The pedicle-rib unit diameter was 8.2mm larger. The thoracic pedicle chord length varied between 36.2m and 43.7mm. The pedicle-rib unit chord length was 12.7mm longer. The thoracic pedicle transverse angle decreased from 41.6⁰ at T1 to 2.6⁰ at T12. The thoracic pedicle-rib unit’s transverse angle decreased from 48.6⁰ at T1 to 20.4⁰ at T12.

Conclusions: The optimal thoracic pedicle screw diameter size is 6.5mm. Optimal pedicle screw lengths are: 35mm at T1 to T5 level, 40mm at T6 to T11 levels and 45mm at T12 level. Optimal medial angulation of the screw during placement is: 40⁰ at T1, 25⁰ at T2, 15⁰ at T3 to T5, 10⁰ at T6 to T10, 50at T11 and 15⁰ at T12.

Keywords: Thoracic pedicle morphometry, Diameter