Clinical Study

Clinically significant pedicle screw malposition is an underestimated cause of radiculopathy

Loosening of pedicle screws is a frequently observed complication in spinal surgery. Because additional stabilization procedures such as cement augmentation or lengthening of the instrumentation involve relevant risks, optimal stability of the primarily implanted pedicle screw is of essential importance. The aim of the present study was to investigate the effect of increasing the screw diameter on pedicle screw stability.

A total of 10 human cadaveric vertebral bodies (L4) were included in the present study. The bone mineral density was evaluated using quantitative computed tomography and the pedicle diameter using computed tomography. The vertebrae underwent instrumentation using 6.0-mm × 45-mm pedicle screws on 1 side and screws with the largest possible diameter (8–10-mm × 45-mm) on the other side. Fatigue testing was performed by applying a cyclic loading (craniocaudal sinusoidal 0.5 Hz) with increasing peak force (100 N + 0.1 N/cycle) until screw head displacement of 5.4 mm was reached.

The mean fatigue load was 334 N for the 6-mm diameter screws and was increased significantly to 454 N (+36%) for the largest possible diameter screws (P < 0.001). With an increase in the fatigue load by 52%, this effect was even more pronounced in vertebrae with reduced bone density (bone mineral density <120 mg/cm³; n = 7; P < 0.001). The stiffness of the construct was significantly greater in the largest diameter screw group compared with the standard screw group during the entire testing period (start, P < 0.001; middle, P < 0.001; end, P = 0.009).

Increasing the pedicle screw diameter from a standard 6-mm screw to the largest possible diameter (8–10 mm) led to a significantly greater fatigue load.

To provide data about surgical workflow, accuracy, complications, radiation exposure, and learning curve effect in patients who underwent minimally invasive (MIS) transforaminal lumbar interbody fusion with navigation coupled with mobile intraoperative computed tomography.

A retrospective analysis was performed of data from consecutive patients who underwent single- or double-level MIS transforaminal lumbar interbody fusion at a single institution; mobile intraoperative computed tomography combined with a navigation system was used as the sole intraoperative imaging method to place pedicular screws; decompression and interbody fusion were performed through a 22-mm tubular retractor. Clinical data, perioperative complications, accuracy of pedicular screw placement, and radiation exposure were analyzed. A learning curve effect on surgical time and accuracy was assessed.

A total of 408 screws in 100 patients were analyzed. In all cases, spinal navigation allowed for identification of pedicular trajectories and greatly facilitated nerve root decompression through the MIS approach. Overall accuracy according to Heary classification was 95.3%. Nineteen screws (4.7%) presented a minor lateral breach (<2 mm), not clinically significant. Surgical time, blood loss, and patient radiation exposure compared favorably with reported values from other series using three-dimensional navigation. A learning curve effect on surgical time, but not on screw accuracy, was identified.

MIS transforaminal lumbar interbody fusion can now be performed without any radiation exposure to the surgeon and operating room staff, with almost absolute accuracy during screw positioning and tubular decompression. A learning curve effect on surgical time, but not on overall screw accuracy, may be expected.

To compare the effective dose (ED) and image quality (IQ) of O-arm cone-beam CT (Medtronic, Minneapolis, MN, USA) and Airo multi-slice CT (Brainlab AG, Munich, Germany) for intraoperative-CT (i-CT) in spinal surgery.

The manufacturer-defined protocols available in the O-arm and Airo systems for three-dimensional lumbar spine imaging were compared.

Organ dose was measured both with thermo-luminescent dosimeters and GafChromic films in the Alderson Radiation Therapy anthropomorphic phantom.

A subjective analysis was performed by neurosurgeons to compare the clinical IQ of the anthropomorphic phantom images acquired with the different i-CT systems and imaging protocols.

Image uniformity, noise, contrast-to-noise-ratio (CNR), and spatial resolution were additionally assessed with the Catphan 504 phantom.

O-arm i-CT caused 56% larger ED than Airo due to the high definition (HD) imaging protocol.

The noise was larger for O-arm images leading to a lower CNR than that measured for Airo. Moreover, scattering and beam hardening effects were observed in the O-arm images. Better spatial resolution was measured for the O-arm system (9 lp/cm) than for Airo (4 lp/cm).

For all the investigated protocols, O-arm was found to be better for identifying anatomical features important for accurate pedicle screw positioning.

According to phantom measurements, the HD protocol of O-arm offered better clinical IQ than Airo but larger ED. The larger noise of O-arm images did not compromise the clinical IQ while the superior spatial resolution of this system allowed a better visibility of anatomical features important for pedicle screw positioning in the lumbar region.

Pedicle screw insertion is a common procedure in spine surgery, and freehand, fluoroscopic, and robotic-assisted techniques all are used. These are indirect methods that use fluoroscopy, and direct visualization of canal involvement has not been possible. However, owing to the development of high-definition imaging modalities, delicate procedures that use endoscopy are possible.

A 47-year-old man presented with severe radiating pain in his leg after undergoing L5-S1 level endoscopic transforaminal lumbar interbody fusion and percutaneous pedicular screw fixation. The patient then underwent an endoscopy-assisted technique for violated spinal canal and screw revision in which the misplaced screw was directly visualized using endoscopy and the trajectory of the misplaced screw was changed. With 30° endoscopy, we directly visualized the screw thread and root compression. Then with 0° endoscopy, we changed the screw trajectory inside the pedicle with an anatomic landmark. The patient's radiating pain was completely relieved after revision of the malpositioned screw. Postoperative imaging showed the revised screw trajectory inside the pedicle.

Endoscopy-assisted pedicle screw insertion does not require an additional incision, and early recovery after the procedure is possible. Accurate diagnosis of canal pathology and treatment are possible with direct visualization using endoscopy.

Robotic guidance (RG) and navigation (NV) have been shown to reduce radiologic and clinically relevant pedicle screw malpositions. It remains unknown if there are any additional benefits to these techniques in intraoperative and perioperative end points.

We conducted a systematic review in MEDLINE, Embase, Scopus, and the Cochrane Library and identified controlled studies comparing RG, NV, and freehand (FH) thoracolumbar pedicle screw insertion and carried out random-effects meta-analyses.

Thirty-two studies (24,008 patients) were included. Only 8 studies (26%) were randomized, and study quality was rated as very low or low in 24 cases (77%). Compared with NV, FH procedures showed longer length of hospital stay (Δ, 0.7 days; 95% confidence interval, 0.2–1.2; P = 0.006) and more overall complications (odds ratio, 1.6; 95% confidence interval, 1.3–1.9; P < 0.001). No statistically significant differences among RG and FH were identified, likely because of lack in statistical power (all P > 0.05). In particular, both RG and NV did not show increased intraoperative radiation use, as determined by seconds of fluoroscopy, compared with FH (both P > 0.05).

It seems that navigation may offer potential benefits in perioperative outcomes such as length of hospital stay and overall complications, without significant increase in intraoperative radiation, which cannot yet be said for robotic guidance. The findings must be interpreted with caution, because the evidence is severely limited in both quantity and quality. Further evaluation will establish any demonstrable intraoperative or perioperative benefits to computer assistance, which may warrant the high costs often associated with these devices.

Various computer-based guidance systems have been devised to reduce costly screw-related complications, yet their clinical effectiveness has never been comparatively assessed in a meta-analysis. We aimed to evaluate the incidence of clinically relevant pedicle screw revisions among robot-guided, navigated, and freehand spinal instrumentation.

Controlled trials comparing robot-guided, navigated, or freehand spinal instrumentation for any indication and that specifically reported the proportion of patients who experienced pedicle screw revisions were included. Estimates were pooled using random-effects meta-analyses. Sensitivity analyses including zero-event trials and assessing per screw incidences were carried out.

Among 37 studies (7095 patients), intraoperative revisions in robot-guided (odds ratio [OR], 3.6; 95% confidence interval [CI], 0.7–19.4; P = 0.14) and navigated (OR, 1.5; 95% CI, 0.3–7.2; P = 0.64) procedures were comparable to freehand. Although postoperative revisions were reduced in robot-guided (OR, 0.3; 95% CI, 0.1–0.9; P = 0.04) and navigated (OR, 0.3; 95% CI, 0.2–0.5; P < 0.001) procedures, statistical significance was lost in sensitivity analyses for robotic guidance, but not for navigation. The pooled incidence of malpositioned screws requiring postoperative revision was 2.1%.

Based on the available data in the peer-reviewed literature, computer assistance in the form of robotic guidance or navigation has the potential to reduce the incidence of costly and clinically relevant postoperative revisions for screw malposition. It is essential to further investigate on a higher level of evidence if the clinical benefits of computer assistance warrant the high acquisition and maintenance costs inherent to these systems.