Percutaneous screw fixation is increasingly being used as a minimally invasive fixation method for treating lumbar and thoracic spine disorders. However, this method is rarely used to treat the cervical spine because of its small dimensions and proximity to neurovascular structures. Holly and Foley [4
] reported on the percutaneous placement of a posterior cervical screw in their cadaver study and achieved highly accurate screw placement using 3D image-based navigation. They did not observe any serious injury to the VA or spinal cord in the cadavers following this procedure. Thus, intraoperative, 3D image-based navigation is required for the percutaneous procedure, while preoperative, 3D-CT-based navigation is inappropriate because of the need for point or surface registration with open exposure. With regard to intraoperative, 3D image-based navigation, we have previously reported on the use and limitations of the Iso-C3D-based (Siemens, Medical Solutions, Erlangen, Germany) and O-arm-based navigation systems separately for the placement of cervical pedicle screws (CPSs) [5,6
]. In particular, O-arm offers high-resolution 2D/3D images that facilitate the accurate and safe insertion of CPS via high-quality navigation, along with other substantial benefits towards cervical spinal instrumentation. These high-resolution images are required for the application of percutaneous screw fixation to the cervical spine. Furthermore, the correct position to fix the reference arc is thought to be the next challenge related to navigation inaccuracy and the complete percutaneous procedure. In general, when using intraoperative, 3D image-based navigation, the reference arc is fixed to the spinal level being instrumented. Sugimoto et al. [7
] reported a case of hangman's fracture treated using the percutaneous procedure with a small midline incision. They used Iso-C3D-based navigation and the reference arc was attached to the spinous process of the axis. Contrarily, in the present case, the reference arc was attached to the halo ring because of the instability of the C2 spinous process. Under the current guidelines for image-guided placement of instrumentation to the upper cervical spine, attaching a reference arc to the headholder, such as the halo ring, is a controversial topic. However, Nottmeier and Young [8
] reported that the image-guided placement of occipitocervical instrumentation using a reference arc attached to a headholder is safe and accurate as long as all the screw holes are drilled with image guidance before tapping the bone and placing the instrumentation [8
]. They also pointed out the intersegmental movement that can occur when tapping the holes or placing the screws, as well as the spreading force of the posterior cervical wound caused by the retractor system. Percutaneous screw fixation, without attaching the reference arc to the instrument level, was free from this spreading force induced by the retractor system.
There are several limitations to the clinical application of this technique. First, this technique is limited to certain types of cervical pathology, such as the cervical trauma typically associated with hangman's fractures. Although most type I fractures can be treated conservatively, it has been suggested that type IIa and type III fractures require surgery [9
]. Rajasekaran et al. [10
] described intraoperative, 3D image-based navigation for transpedicular screw fixation as an effective standard open procedure for treating type II hangman's fractures. Type III fractures, combined with bilateral facet dislocation, often require open reduction and fusion of the C2 and C3 vertebrae. Thus, type II and IIa fractures present optimal conditions for the application of the percutaneous technique demonstrated in this case. Second, this technique requires a more detailed preoperative examination of the cervical region than the open procedure because of the varied morphological characteristics of cervical pedicles and the vertebral artery. Moreover, when the fracture involves the transverse foramen, bringing the fracture back into anatomical alignment may, rarely, compromise the vasculature. In order to prevent this complication, intraoperative CT angiography can provide early detection. Finally, this technique requires thorough knowledge of spinal anatomy and a great deal of experience in open procedures. If an unexpected complication arises, such as serious neurovascular injury, the surgeon must be able to immediately revert to an open method. Despite these limitations, percutaneous posterior screw fixation has several advantages. Direct access to the target site is the main advantage. Because the entry point of the pedicle screw is deep and angulated in the axial plane, it is easier to insert the screw percutaneously than it is in the open procedure using the midline approach. The force of the paraspinal muscles toward the center from the far lateral side can cause the misinsertion of screws. Moreover, the minimal invasiveness of this method can result in reduced operative time, blood loss, postoperative pain and risk of infection, leading to a much quicker recovery. We believe that the percutaneous technique for posterior cervical screw fixation has many advantages and is reliable for treating carefully selected patients, assuming that the surgeon has sufficient experience of performing open surgeries. The preliminary results of this case are promising, but proper evaluation will require more extensive studies.