Precision and safety of percutaneous pedicle screws

Inserting percutaneous pedicle screws is done with the help of fluoroscopic guidance and is used to treat various spinal conditions.  It offers many benefits like reducing intraoperative bleeding, preserving muscle function, and decreasing postoperative pain, leading to a faster recovery compared to traditional open method of pedicle screw fixation.

Although this technique is relatively safer with a lower risk of nerve damage, concerns arise regarding its accuracy and safety when compared to the conventional open method.

Literature has shown that the rates of perforation using the conventional open method range from 1.5% to 25%, while cadaveric studies have documented a similar variability, ranging from 1.6% to 29%. The accuracy of screw placement with navigation assistance is 95.2%, which is significantly higher than the 90.3% accuracy rate without navigation.

Percutaneous pedicle screw placement aided by computer navigation is a viable option instead of relying exclusively on fluoroscopic guidance for the procedure. The rate of perforations in pedicle screws ranges from 3.0% to 7.3% when computer-assisted techniques were used for percutaneous screw placement.

While navigated percutaneous pedicle screw placement offers several benefits, the use of fluoroscopic guidance for screw placement remains the primary practical technique in many centers because of the cost and availability constraints of computer-assisted devices.

Despite differences in factors such as age, the number of screws used per patient, the number of stabilized levels, screw density, and the underlying cause of the spinal condition, there was no significant difference in the rate of screw perforation between the two groups. This is because the technique used in both groups was very similar, and therefore, the rate of screw perforation was not affected by these factors.

There are three areas in the spine where screw perforation rates were highest: T1, the mid-thoracic region (T4-T7), and the lumbosacral junction (L5 and S1).

The highest rate of perforation was at T1 (33.3%), followed by S1 (19.4%) and T4 (18.6%). The T1 vertebra has the highest angulation among the upper thoracic vertebrae in the axial plane, which makes it technically more difficult to insert screws accurately.

Also, it is challenging to obtain a clear lateral view on the image intensifier due to the obstruction caused by the patient’s shoulder joint, scapula, and humerus. The mid-thoracic region has the narrowest pedicular width which increases the risk of perforations.

During a procedure, it has been observed that the narrowest pedicle width is found at T4 or T5 in the mid-thoracic region, which increases the risk of perforation. At the lumbosacral junction, anatomical variations in L5 and S1 result in increased perforation rates compared to upper lumbar vertebral levels with rounded bodies and “cylindrical canal” configurations.

The wider triangular body of L5 and S1 increases the risk of lateral and anterior perforations when the medial angulations of pedicle screws are inadequate, and the “trefoil canal” configuration results in a higher risk of medial perforations. In this configuration, the narrowest part of the pedicle is at the same level as the posterior border of the vertebral body, which increases the risk of perforation when a pedicle screw with a larger diameter than the trocar is inserted.

It is recommended that additional precautions be taken when inserting percutaneous pedicle screws in these three regions. Inserting percutaneous pedicle screws under fluoroscopic guidance is a safe procedure and has comparable accuracy to conventional open techniques.

However, it requires different technical skills and precautions. This method offers new options for fixing various spinal disorders and has the potential to preserve muscular attachments, resulting in better muscular function and final outcomes.

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