Assessment of Surgical Procedural Time, Pedicle Screw Accuracy, and Clinician Radiation Exposure of a Novel Robotic Navigation System Compared With Conventional Open and Percutaneous Freehand Techniques: A Cadaveric Investigation.

STUDY DESIGN: Cadaveric study. OBJECTIVE: To evaluate accuracy, radiation exposure, and surgical time of a new robotic-assisted navigation (RAN) platform compared with freehand techniques in conventional open and percutaneous procedures. METHODS: Ten board-certified surgeons inserted 16 pedicle screws at T10-L5 (n = 40 per technique) in 10 human cadaveric torsos. Pedicle screws were inserted with (1) conventional MIS technique (L2-L5, patient left pedicles), (2) MIS RAN (L2-L5, patient right pedicles), (3) conventional open technique (T10-L1, patient left pedicles), and (4) open RAN (T10-L1, patient right pedicles). Output included (1) operative time, (2) number of fluoroscopic images, and (3) screw accuracy. RESULTS: In the MIS group, compared with the freehand technique, RAN allowed for use of larger screws (diameter: 6.6 ± 0.6 mm vs 6.3 ± 0.5 mm; length: 50.3 ± 4.1 mm vs 46.9 ± 3.5 mm), decreased the number of breaches >2 mm (0 vs 7), fewer fluoroscopic images (0 ± 0 vs 108.3 ± 30.9), and surgical procedure time per screw (3.6 ± 0.4 minutes vs 7.6 ± 2.0 minutes) (all P < .05). Similarly, in the open group, RAN allowed for use of longer screws (46.1 ± 4.1 mm vs 44.0 ± 3.8 mm), decreased the number of breaches >2 mm (0 vs 13), fewer fluoroscopic images (0 ± 0 vs 24.1 ± 25.8) (all P < .05), but increased total surgical procedure time (41.4 ± 8.8 minutes vs 24.7 ± 7.0 minutes, P = .000) while maintaining screw insertion time (3.31.4 minutes vs 3.1 ± 1.0 minutes, P = .650). CONCLUSION: RAN significantly improved accuracy and decreased radiation exposure in comparison to freehand techniques in both conventional open and percutaneous surgical procedures in cadavers. RAN significantly increased setup time compared with both conventional procedures.

Three-dimensional assessment of robot-assisted pedicle screw placement accuracy and instrumentation reliability based on a preplanned trajectory.

OBJECTIVE: Robotic spine surgery systems are increasingly used in the US market. As this technology gains traction, however, it is necessary to identify mechanisms that assess its effectiveness and allow for its continued improvement. One such mechanism is the development of a new 3D grading system that can serve as the foundation for error-based learning in robot systems. Herein the authors attempted 1) to define a system of providing accuracy data along all three pedicle screw placement axes, that is, cephalocaudal, mediolateral, and screw long axes; and 2) to use the grading system to evaluate the mean accuracy of thoracolumbar pedicle screws placed using a single commercially available robotic system. METHODS: The authors retrospectively reviewed a prospectively maintained, IRB-approved database of patients at a single tertiary care center who had undergone instrumented fusion of the thoracic or lumbosacral spine using robotic assistance. Patients with preoperatively planned screw trajectories and postoperative CT studies were included in the final analysis. Screw accuracy was measured as the net deviation of the planned trajectory from the actual screw trajectory in the mediolateral, cephalocaudal, and screw long axes. RESULTS: The authors identified 47 patients, 51% male, whose pedicles had been instrumented with a total of 254 screws (63 thoracic, 191 lumbosacral). The patients had a mean age of 61.1 years and a mean BMI of 30.0 kg/m2. The mean screw tip accuracies were 1.3 ± 1.3 mm, 1.2 ± 1.1 mm, and 2.6 ± 2.2 mm in the mediolateral, cephalocaudal, and screw long axes, respectively, for a net linear deviation of 3.6 ± 2.3 mm and net angular deviation of 3.6° ± 2.8°. According to the Gertzbein-Robbins grading system, 184 screws (72%) were classified as grade A and 70 screws (28%) as grade B. Placement of 100% of the screws was clinically acceptable. CONCLUSIONS: The accuracy of the discussed robotic spine system is similar to that described for other surgical systems. Additionally, the authors outline a new method of grading screw placement accuracy that measures deviation in all three relevant axes. This grading system could provide the error signal necessary for unsupervised machine learning by robotic systems, which would in turn support continued improvement in instrumentation placement accuracy.

Pedicle screw accuracy assessment in ExcelsiusGPS® robotic spine surgery: evaluation of deviation from pre-planned trajectory.

BACKGROUND: The ExcelsiusGPS® (Globus Medical, Inc., Audubon, PA) is a next-generation spine surgery robotic system recently approved for use in the United States. The objective of the current study is to assess pedicle screw accuracy and clinical outcomes among two of the first operative cases utilizing the ExcelsiusGPS® robotic system and describe a novel metric to quantify screw deviation. METHODS: Two patients who underwent lumbar fusion at a single institution with the ExcelsiusGPS® surgical robot were included. Pre-operative trajectory planning was performed from an intra-operative CT scan using the O-arm (Medtronic, Inc., Minneapolis, MN). After robotic-assisted screw implantation, a post-operative CT scan was obtained to confirm ideal screw placement and accuracy with the planned trajectory. A novel pedicle screw accuracy algorithm was devised to measure screw tip/tail deviation distance and angular offset on axial and sagittal planes. Screw accuracy was concurrently determined by a blinded neuroradiologist using the traditional Gertzbein-Robbins method. Clinical variables such as symptomatology, operative data, and post-operative follow-up were also collected. RESULTS: Eight pedicle screws were placed in two L4-L5 fusion cases. Mean screw tip deviation was 2.1 mm (range 0.8-5.2 mm), mean tail deviation was 3.2 mm (range 0.9-5.4 mm), and mean angular offset was 2.4 degrees (range 0.7-3.8 degrees). All eight screws were accurately placed based on the Gertzbein-Robbins scale (88% Grade A and 12% Grade B). There were no cases of screw revision or new post-operative deficit. Both patients experienced improvement in Frankel grade and Karnofsky Performance Status (KPS) score by 6 weeks post-op. CONCLUSION: The ExcelsiusGPS® robot allows for precise execution of an intended pre-planned trajectory and accurate screw placement in the first patients to undergo robotic-assisted fusion with this technology.

Biomechanical assessment of anchored cervical interbody cages: comparison of 2-screw and 4-screw designs.

BACKGROUND: A new anchored cervical interbody polyetheretherketone spacer was devised that uses only 2 integrated variable-angle screws diagonally into the adjacent vertebral bodies instead of the established device that uses 4 diagonal fixed-angle screws. OBJECTIVE: To compare in vitro the stability provided by the new 2-screw interbody spacer with that of the 4-screw spacer and a 4-screw anterior plate plus independent polyetheretherketone spacer. METHODS: Three groups of cadaveric specimens were tested with 2-screw anchored cage (n = 8), 4-screw anchored cage (n = 8), and standard plate/cage (n = 16). Pure moments (1.5 Nm) were applied to induce flexion, extension, lateral bending, and axial rotation while measuring 3-D motion optoelectronically. RESULTS: In all 3 groups, the mean range of motion (ROM) and lax zone were significantly reduced relative to the intact spine after discectomy and fixation. The 2-screw anchored cage allowed significantly greater ROM (P < .05) than the standard plate during flexion, extension, and axial rotation and allowed significantly greater ROM than the 4-screw cage during extension and axial rotation. The 4-screw anchored cage did not allow significantly different ROM or lax zone than the standard plate during any loading mode. CONCLUSION: The 2-screw variable-angle anchored cage significantly reduces ROM relative to the intact spine. Greater stability can be achieved, especially during extension and axial rotation, by using the 4-screw cage or standard plate plus cage.

Radiographic assessment of thoracolumbar fractures based on axial zones.

STUDY DESIGN: Retrospective study of computed tomography imaging of patients with thoracolumbar (TL) fractures. OBJECTIVE: To propose an axial model of spinal fractures based on the osteoligamentous continuity of the TL spinal segments in the axial plane and to determine the correlation between the 3-column theory and the proposed axial zone model. SUMMARY OF BACKGROUND DATA: Predicting spinal instability of TL fractures is based on several radiologic and clinical parameters. Efforts to refine fracture classification schemes to better predict instability continue. METHODS: Computed tomography scans of 229 consecutive patients who presented with TL fractures between March 2005 and April 2007 were reviewed. TL fractures were classified according to both the Denis 3-column theory and the proposed axial zone model. The incidence of column and axial zone injuries was determined. On the basis of these results, a treatment algorithm was developed. RESULTS: Zone disruption in surgical fractures was distributed as follows: 24 (96%) involved zone A, 25 (100%) involved zone B, 17 (68%) involved zone C, and 15 (60%) involved zone D. All surgical fractures involved 2 or more zones. Zone B was involved in all surgical fractures. The likelihood of surgical intervention increased as the number of zones increased, especially if the injury was a 2-column or 3-column injury. CONCLUSIONS: The current 3-column theory of spinal stability does not account for the axial component of an injury. Application of our proposed "axial zone model" may enhance the ability to predict stability, depending not only on the number of columns, but also on the number of zones involved in the injuries. Further clinical and biomechanical studies are warranted to validate this model.

Health care burden of cervical spine fractures in the United States: analysis of a nationwide database over a 10-year period.

OBJECT The objective of this work was to search a national health care database of patients diagnosed with cervical spine fractures in the US to analyze discharge, demographic, and hospital charge trends over a 10-year period. METHODS Clinical data were derived from the Nationwide Inpatient Sample (NIS) for the years 1997 through 2006. The NIS is maintained by the Agency for Healthcare Research and Quality and represents a 20% random stratified sample of all discharges from nonfederal hospitals within the US. Patients with cervical spine fractures with and without spinal cord injury (SCI) were identified using the appropriate ICD-9-CM codes. The volume of discharges, length of stay (LOS), hospital charges, total national charges, discharge pattern, age, and sex were analyzed. National estimates were calculated using the HCUPnet tool. RESULTS Approximately 200,000 hospitalizations were identified. In the non-SCI group, there was a 74% increase in hospitalizations and charges between 1997 and 2006, but LOS changed minimally. There was no appreciable change in the rate of in-hospital mortality (< 3%), but discharges home with home health care and to skilled rehabilitation or nursing facilities increased slightly. In the SCI group, hospitalizations and charges increased by 29 and 38%, respectively. There were no significant changes in LOS or discharge status in this group. Spinal cord injury was associated with increases in LOS, charges, and adverse outcomes compared with fractures without SCI. Total national charges associated with both groups combined exceeded $1.3 billion US in 2006. CONCLUSIONS During the studied period, increases in hospitalizations and charges were observed in both the SCI and non-SCI groups. The percentage increase was higher in the non-SCI group. Although SCI was associated with higher adverse outcomes, there were no significant improvements in immediate discharge status in either group during the 10 years analyzed.

The minipterional craniotomy: technical description and anatomic assessment.

OBJECTIVE: To describe a modification of the pterional approach (PT), the minipterional craniotomy (MPT), and compare the anatomic exposure provided by these two approaches. METHODS: The anatomic exposure offered by the MPT and PT were compared in eight sides of cadaver heads using a computerized tracking system, a robotic microscope, and an image-guidance system. The area of surgical exposure, angular exposure, and anatomic limits of each craniotomy were evaluated. Three recently operated clinical cases (EGF) are also reported. RESULTS: There were no statistical differences in the total area of surgical exposure between the two craniotomies (PT, 1524.7 +/- 305 mm; MPT, 1469.7 +/- 380.3 mm; P > 0.05) or among the ipsilateral, middle, and contralateral components of the area (P > 0.05). There were no differences in angular exposure along the longitudinal and transverse axis angles for the three selected targets, the bifurcations of internal carotid and middle cerebral arteries, and the anterior communicating artery (P > 0.05). Except for the distal portion of the operculoinsular compartment of the sylvian fissure, no significant differences in the limits of the surgical exposure through the PT and MPT were apparent on the image-guidance system. CONCLUSION: The MPT craniotomy provides comparable surgical exposure to that offered by the PT. The advantages of the MPT include reduction of tissue trauma and bony removal, a decrease in surgical time, and improved cosmetic outcomes.

Biomechanical assessment of anterior lumbar interbody fusion with an anterior lumbosacral fixation screw-plate: comparison to stand-alone anterior lumbar interbody fusion and anterior lumbar interbody fusion with pedicle screws in an unstable human cadaver model.

STUDY DESIGN: Human lumbosacral cadaveric specimens were tested in an in vitro biomechanical flexibility experiment using physiologic loads in 5 sequential conditions. OBJECTIVE: To determine the biomechanical differences between anterior lumbar interbody fusion (ALIF) using cylindrical threaded cages alone or supplemented with an anterior screw-plate or posterior pedicle screws-rods. SUMMARY OF BACKGROUND DATA: Clinically and biomechanically, stand-alone ALIF performs modestly in immobilizing the unstable spine. Pedicle screws improve fixation stiffness significantly, but supplementary anterior instrumentation has not been studied. METHODS: There were 7 specimens tested: (1) intact, (2) after discectomy and facetectomy to induce moderate rotational and translational hypermobility, (3) with 2 parallel ALIF cages, (4) with cages plus a triangular anterior screw-plate, and (5) with cages plus pedicle screws-rods. Pure moments without preload induced flexion, extension, lateral bending, and axial rotation; linear shear forces induced anteroposterior translation. Angular and linear motions were measured stereophotogrammetrically, and range of motion (ROM) and stiffness were quantified. RESULTS: Compared to the destabilized spine, interbody cages alone reduced ROM by 77% during flexion, 53% during extension, 60% during lateral bending, 69% during axial rotation, and 71% during anteroposterior shear (P < 0.001, analysis of variance/Fisher least significant difference). Addition of an anterior plate or pedicle screws-rods, respectively, further reduced ROM by 8% or 13% during flexion (P = 0.21), 21% or 28% during extension (P = 0.15), 5% or 25% during lateral bending (P = 0.04), 11% or 18% during axial rotation (P = 0.13), and 18% or 18% during anteroposterior shear (P = 0.17). Compared to stand-alone ALIF, both the anterior screw-plate and pedicle screw-rod fixation reduced vertebral ROM to less than 1.2 degrees of rotation and less than 0.1 mm of translation. CONCLUSIONS: The anterior screw-plate and pedicle screws-rods both substantially reduced ROM and increased stiffness compared to stand-alone interbody cages. There was no significant difference in the amount by which the supplementary fixation devices limited flexion, extension, axial rotation, or anteroposterior shear; pedicle screws-rods better restricted lateral bending.