Instrumentation for intraoperative measurement of cervical spine stiffness

There is scant information on in vivo cervical biomechanics. The majority of limited data available in this area has been obtained using cadaver studies. With this in mind, simple instrumentation for analysing intraoperative cervical motion segment stiffness (load-axial displacement) was developed. The instrumentation consists of a displacement and strain transducer equipped vertebral retractor to be used with Caspar pins during anterior cervical surgery. Paramount to instrument design was incorporation of components complimentary to high electrical and mechanical repeatability, electrical safety, and creation of a sterile barrier. Preliminary studies conducted on a cadaver with this device revealed C3-C4 axial displacements (millimeters) of 1.735, 2.688, and 4.024 using, respectively, loads (newtons) of 44.482, 88,964, and 133.446. These results suggest this technique will be useful in assessing intraoperative spinal stability.