New method for intraoperative determination of proper screw insertion or screw malposition

Feasibility of anterior pedicle screw fixation in lumbosacral spine: a radiographic and cadaveric study

Background

The anterior pedicle screw (APS) technique for L5 and S1 is crucial for proper anterior lumbar interbody fusion (ALIF). This study aimed to determine the projection, screw trajectory angle, and bone screw passageway length (BSPL), as well as the screw insertion regularity and the operating area within which it is safe to perform insertion.

Methods

Forty patients with low back pain, all of whom had lumbar computed tomography scans available, was included in this retrospective analysis. Radiographic parameters were measured, including: the distances from the projection to the upper endplate, lower endplate, and midline; the transverse and sagittal screw angles; and the BSPL. In addition, 10 fresh adult cadaveric lumbosacral spine segments were selected to determine the safe anatomic area in which to operate. Finally, APSs were inserted in L5 and S1 to determine the regularity of APS insertion.

Results

We measured the anterior projection parameters, including: the distances to the upper endplate (L5: 12.5±1.3 mm; S1: 4.54±0.87 mm), lower endplate (L5: 17.3±1.6 mm), and midline (L5: 6.6±0.7 mm; S1: 6.6±0.6 mm); the screw trajectory angle, including the transverse screw angle (L5: 25.3±2.8°; S1: 25.7±2.6°), sagittal screw angle (L5: 17.1±1.7°; S1: 22.4±1.1°); and the BSPL (L5: 48.6±3.5 mm; S1: 48.0±3.5 mm). The regularity of APS insertion in L5 and S1 was determined. Upon the needle reaching a point in the lateral view, it reached the corresponding point in the anteroposterior (AP) view. The anatomic parameters of the safe operating area were as follows: the distance from the abdominal aortic bifurcation to the L5 lower edge (40.50±9.40 mm); the distance from the common iliac vein confluence to the L5 lower edge (27.80±8.60 mm); and the horizontal distance from the inner edge of the common iliac vein to the L5 lower edge (37.50±1.30 mm). We also determined the distance between S1 holes (29.30±1.30 mm), the L5/S1 intervertebral height (17.20±1.50 mm), and the safe operating area (2,058.20±84.30 mm²).

Conclusions

This study has determined the projection, screw trajectory angle, and BSPL of APSs in L5 and S1, their insertion regularity, and the area in which the operation can be safely performed.

True accuracy of percutaneous pedicle screw placement in thoracic and lumbar spinal fixation with a CT-based navigation system: Intraoperative and postoperative assessment of 763 percutaneous pedicle screws

PURPOSE

To investigate intraoperative reinsertion of percutaneous pedicle screw (PPS) with intraoperative CT-based navigation and to evaluate the rate of deviation of PPS at postoperative radiographic examination.

METHODS

Seven hundred sixty-three screws were inserted in 138 patients. We investigated the rate of occurrence of intraoperative PPS reinsertion after the diagnosis of screw deviation by fluoroscopy and the causes of each screw deviation. The subsequent distribution of PPS deviation was evaluated by postoperative CT. We also assess the difference in variance between the group judged to be PPS misplaced intra-/postoperatively (IOD group/POD group) and appropriate PPS placement (ND group).

RESULTS

Among all the screws inserted, 10 (1.3%) were diagnosed as being deviated by fluoroscopy during surgery, and 74 (9.7%) screws were found to be deviated at postoperative CT evaluation. We found more pedicle screw mismatch in the POD group than in the ND group (52.7 vs 11.0%, P < 0.001). The distance between the screw and the reference was greater in the IOD group than that in the ND group (1.4 ± 1.2 vs 2.4 ± 1.1 vertebral levels, P = 0.016). In one patient in the IOD group, a motor function deficit was observed postoperatively.

CONCLUSION

PPS fixation under intraoperative CT-based navigation did not prevent screw deviation completely. It is necessary to consider errors that occur during surgery and to confirm placement with real-time assistance such as fluoroscopy even in a surgery performed under CT navigation assistance.

Do intraoperative radiographs in scoliosis surgery reflect radiographic result?

It is often difficult to predict postoperative radiographic curve magnitude and balance parameters while performing intraoperative correction during scoliosis surgery. We asked whether there was a radiographic correlation between intraoperative long-cassette scoliosis film and postoperative standing radiographs of adolescent idiopathic scoliosis with pedicle screw instrumentation. We retrospectively reviewed 44 patients with adolescent idiopathic scoliosis who underwent posterior instrumentation with pedicle screws. We made preoperative, intraoperative (after instrumentation and correction), and standing postoperative radiographic measurements (eg, curve magnitudes, coronal and sagittal balance, disc angles) and compared those for the intra- and postoperative radiographs. The intraoperative long-cassette scoliosis film correlated with the immediate postoperative standing film for all curve correction and balance parameters. The routine use of a long-cassette intraoperative scoliosis film provides the surgeon with a valuable tool to guide intraoperative decision-making and foreshadows the correction and balance obtained on the immediate postoperative film.

LEVEL OF EVIDENCE

Level IV, retrospective study. See Guidelines for Authors for a complete description of levels of evidence.

A novel computer-assisted technique for pedicle screw insertion

BACKGROUND

Commercially available systems for computer-assisted pedicle screw placement are prohibitively expensive, even in advanced countries. The advantage of the great accuracy of computer-assisted systems for pedicle screw insertion makes them highly desirable and essential for current spinal surgeries.

METHODS

We have tried to develop a new software for pedicle screw placement, based on paired point matching.

RESULTS

The newly developed software is much less expensive and is an excellent educational tool. Its accuracy has been established by a cadaveric study, described in this paper.

CONCLUSIONS

The cadaveric study supports the view that computer-assisted pedicle screw fixation using the newly developed software is superior to the conventional fluoroscopic method, especially with regard to the thoracic spine, where a higher degree of accuracy is needed. Further clinical studies are planned and the software needs further refinement for complex clinical situations.