Since the 1940s, vertebral and pedicle screw fixation have been developed and became increasingly popular among spine surgeons [16]. Although there is increasing use of modern imaging modalities as an aid for pedicular screw insertion, we introduce this study to document the validity of free-hand technique alone for accurate screw insertion.
Our motivation for this study was the limited resources of modern techniques used for pedicular screw insertion in our locality, so we turned back to surgical skills alone.
The definition of free-hand technique refers to the surgical technique that uses bone landmarks for screw insertion without the assistance of any imaging intraoperatively [17].
Although most experienced surgeons prefer using the free-hand pedicle screw insertion technique based on anatomic landmarks, this technique has a variable pedicle perforation rate between 1.7 and 54.7% [18, 19].
The most common reason for the nerve root irritation and injury is breaching of the medial and the inferior cortex of the pedicle.
Assisted methods broadly include functional measures such as intraoperative neural monitoring and anatomic measures such as computed tomography (CT) and fluoro-based and O-arm-based navigation systems [7,8,9,10,11].
Gelalis et al. [17] mentioned that the screws positioned with free-hand technique tend to perforate the cortex medially, whereas the screws placed with CT navigation guidance seem to perforate more often laterally, and he attributed that to the inaccuracy in determining the midline by the navigation technique. Tow et al. [1] founded lateral breach as the most common type in both free hand (62% of violations) and navigation groups (64.5%).
CT was used as the preferred method for detection of pedicular screw position postoperatively [20,21,22] as bony anatomy is best evaluated with CT.
In our study with the use of this technique, only three screws out of 144 (about 0.02) screws were not 100% intrapedicular; although their violation to the pedicular cortex was less than 2 mm, it was neither medial nor inferior that is because screw insertion under direct vision prevents the occurrence of this.
We think that is one of the advantages of our technique because medial and inferior violations of the pedicle never occurred as we always revise the screw direction if it appears intraoperatively to violate medial or inferior pedicular cortex.
Xu et al. [23] compared the accuracy of pedicle screw fixation in cadaveric thoracic spine with the use of Roy-Camille technique compared to partial laminectomy technique, and he found that the last technique is better regarding accuracy of pedicle screw insertion.
Gertezbein et al., [24], stated that there is a safety zone of 4 mm medial to the pedicle, 2 mm extradural and 2 mm in subarachnoid space medial to the pedicle from T10 to L4.
Our opinion is that this safety zone is not constant in all patients because the pathology present strongly affected the relation between the pedicle and the dura.
In vivo and in vitro studies showed variations of malpositioned pedicular screws in lumbar spine to be 5 to 41% and from 3 to 55% in the dorsal spine due to differences in pedicular anatomy between the dorsal and lumbar zones [25,26,27,28].
We think that 0.02 pedicle violation (99.98% accuracy) is one of the best rates in pedicular screw insertion compared to all previous studies, simply because direct visualization permits immediate correction of the screw position intraoperatively without the use of any monitoring modality except the surgeon’s eyes.
Previous studies with 100% accuracy used modern neuronavigation systems with CT like Girardi et al [29] CT navigation (Stealth navigation system, Microsoft Inc., Redmond, Washington) and Carl et al. [30] CT navigation (GE navigational research computer software GE Medical Systems, Milwaukee, WI, USA).
Comparing our results with other studies using the traditional free-hand technique, the results of pedicle screw accuracy varies from 69 to 74% [24, 31,32,33,34].
We usually decompress the neural elements before screw insertion, contrarily to many authors who put screws then do decompression like Girardi et al. [29]. The decompress first technique is the secret for good visualization during screw insertion.
Medial pedicle violation more than 4 mm puts the roots in high risk of injury, and it is agreed between spine surgeons that medial violation less than 2 mm is safe [35, 36]; although Ebraheim et al. [6] found the distance between the dural sleeve and medial pedicle surface to be only 1.5 mm, Roy-Camille et al. [2] mentioned it to be 2 to 3 mm.
Our intraoperative observation about the distance between the root sleeve and the medial and inferior pedicular surfaces depends mainly on the pathology present. Disc herniation and degree of spondylolisthesis affect the root position in relation to the pedicle.
The main advantages of free-hand technique for pedicle screw insertion are the shorter operative time and avoidance or minimizing radiation exposure to the patient and the surgical team [37].We agree with this opinion because the mean time needed for screw insertion was 3.5 min and we use only one fluoroscopic view after completion of all screw insertions, while it was 6.6 min (3.3 to 12.5 min) with the use of CT-guided navigation by Girardi et al. [29].
We routinely decompress the roots first by removal of any offending tissues either bony or soft tissues before insertion of the screws.
According to many previous studies, there is difficulty in assessing correct pedicle screw position with the use of conventional roentgenography [38,39,40].
Titanium screws cause less artifact in CT and MRI; all our screws were titanium so screw artifact was very minimal.
