A dry bone study of thoracic spine pedicle transverse diameters in a Kenyan population

Abstract

Background: The size of the pedicle screw utilized in spinal fixation is determined by the transverse diameter of the pedicle at the isthmus. This diameter has not been documented in dry bone specimens in an African population.

Objective: To determine the outer transverse diameter of the thoracic pedicles at the isthmus using a vernier caliper in a Kenyan population, and compare this with published literature.

Methods: One hundred thoracic spine cadaveric specimens were studied at the National Museums of Kenya. The diameters of both right and left pedicles at the isthmus of all the twelve thoracic vertebrae in each specimen were measured directly using a vernier caliper. The results were summarized with measures of central tendency and compared with results from previous studies using the student’s t-test.

Results: The mean transverse diameter of the pedicle measured at the isthmus was: 7.2mm at T1, 5.3mm at T2, 4.3mm at T3, 3.7mm at T4, 3.7mm at T5, 4.0mm at T6, 4.4mm at T7, 4.3mm at T8, 5.0mm at T9, 5.9mm at T10, 7.4mm at T11 and 7.6mm at T12. The overall range was 1.3mm to 12.3mm. These measurements were much smaller than those of European and American studies; but were comparable to those in Indian studies.

Conclusions: The trend in diameter between T1 and T12 within a specimen is like in previous studies. The variability in pedicle diameter between specimens is marked, denoting heterogeneity in the study population.

Recommendations: The pedicle diameter variability precludes a recommendation of the appropriate pedicle screw diameter to be used in surgery. Further studies on the influence of demographic factors on pedicle transverse diameter are recommended.

Keywords: Thoracic pedicle morphometry, Diameter