Objective: In this study, we performed anatomic and computed tomography (CT) measurements of C2 lamina in Chinese people in order to provide the anatomic and radiographic data, and to verify the clinical applicability of trans-lamina screws to this population.
Methods: The anatomic and radiographic measurement was conducted on two separate groups, group A and group B. In group A, a total of 96 human adult (male 51, female 45) cadaver spines were included. The minimal height (H1), thickness (T), length (L1) of C2 lamina, height of the root of lamina (H2), distance from the entry point to the lateral rim of lamina (L2) and to the lateral rim of lateral mass (L3) were bilaterally measured using high precision calipers. The spino-laminar angles (angle A) were also included. In group B, a total of 112 volunteers (male 58, female 54) without upper cervical abnormality were enrolled. Angle A, H1, T, L1, H2, L2 and L3 were bilaterally measured using plain X-rays and reconstruction CT. All measurements were taken at the thinnest part of the lamina in the axial and coronal plane.
Results: All the measurements (except angle A) in males were significantly higher than those in females (P < 0.05). There was no significant difference in the values of bilateral laminae between group A and group B (P > 0.05). The thickness of 45% specimens was less than 6 mm. The length of lamina in all specimens was less than 2.5 cm, while only 5% of the specimens had a length of >3 cm from the entry point to the rim of lamina. The length from the entry point to the lateral rim of lateral mass was between 2.5 and 4.6 cm. In contrast, the length of only 5% specimens was longer than 4 cm.
Conclusions: The preoperative radiographic evaluation is very important to determine the suitable size of screws. The diameter of screws is mainly restricted by the thickness of C2 lamina. It is safe to use screws with a length of 2.5-3.0 cm for Chinese people. The radiographic measurement method we used is simple, accurate and reliable for preoperative measurement.