Establishment of parameters for congenital thoracic stenosis: a study of 700 postmortem specimens.

BACKGROUND: Congenital thoracic stenosis (CTS) occurs when the bony anatomy of the canal is smaller than expected in the general population. The diagnosis currently is made based on the clinical impression from subjective radiographic studies, and the normal values for CTS have not been established. QUESTIONS/PURPOSES: We provided a statistical definition for CTS based on objective measurements of thoracic spine specimens and explored parameters that might predict CTS.
METHODS: We selected 700 adult skeletal specimens from the Hamann-Todd Collection in the Cleveland Museum of Natural History (Cleveland, OH, USA). We used calipers to measure the sagittal canal diameter (SCD), interpedicle distance (IPD), and pedicle length (PL). At each level, canal area was calculated using a geometric formula, a standard distribution was created, and values two SDs below the mean were considered congenitally stenotic. Corresponding values of SCD and IPD of the stenotic specimens were studied. The values of SCD and IPD predicting CTS with highest sensitivity and specificity were tabulated.
RESULTS: At each level, CTS was defined as: T1, 160 mm(2); T2, 135 mm(2); T3, 131 mm(2); T4, 130 mm(2), T5, 129 mm(2), T6, 127 mm(2); T7, 127 mm(2); T8, 129 mm(2); T9, 130 mm(2); T10, 132 mm(2); T11, 140 mm(2); and T12, 173 mm(2). A SCD less than 15 mm and an IPD less than 18.5 mm were predictive of CTS at each level with sensitivities and specificities of 80% to 100%.
CONCLUSIONS: We statistically defined CTS at each level. A SCD less than 15 mm or IPD less than 18.5 mm predicted the presence of CTS at all levels. CLINICAL RELEVANCE: In a symptomatic patient, on routine radiologic examination, a physician should suspect stenosis of the thoracic canal if the SCD and IPD are less than 15 and 18.5 mm respectively. As a spinal deformity surgeon, the canal area is especially relevant when considering a possible canal intrusion by implants.