Ultrasound in the assessment of cranial bone thickness

Preoperative knowledge of skull thickness before harvesting cranial bone grafts would be ideal to help minimize intracranial complications. Previous research has demonstrated regional variations in calvaria; however, accurate preoperative and intraoperative methods of skull thickness measurement are not available. The aim of this research represents the first attempt to examine the reliability of ultrasound to determine cranial bone thickness. Four previously studied calvarial sites were marked in 10 adult male cadaveric skulls. The individual points were insonified using an A-mode ultrasonic transducer operating in pulse-echo mode. The times of flight of the waves propagating in the bone samples were compared with caliper measurements. The mean difference in cranial bone thickness was 0.16 mm, with a standard deviation of 0.09 mm. Student's t-test failed to reveal any statistically significant differences between caliper and ultrasonic measurements (p = 0.569) and Pearson's correlation coefficient supported an extremely strong and positive relationship between the two modalities (r > 0.992). Multiple linear regression models predicted that calvarial thickness could be accurately predicted by ultrasound without consideration of cadaveric specimen or sampling point location (R2 = 0.988). The convergent values between ultrasonic and caliper measurements suggest that this modality can accurately and reliably determine skull thickness. A-mode ultrasound can have significant implications in guiding the harvest of in situ split cranial bone grafts, the placement of osseointegrated implants, skull anthropometrics, and related craniomaxillofacial applications.