Transpedicle instrumentation in the degenerative spine

A deep learning framework for segmentation and pose estimation of pedicle screw implants based on C-arm fluoroscopy

PURPOSE

Pedicle screw fixation is a challenging procedure with a concerning rates of reoperation. After insertion of the screws is completed, the most common intraoperative verification approach is to acquire anterior-posterior and lateral radiographic images, based on which the surgeons try to visually assess the correctness of insertion. Given the limited accuracy of the existing verification techniques, we identified the need for an accurate and automated pedicle screw assessment system that can verify the screw insertion intraoperatively. For doing so, this paper offers a framework for automatic segmentation and pose estimation of pedicle screws based on deep learning principles.

METHODS

Segmentation of pedicle screw X-ray projections was performed by a convolutional neural network. The network could isolate the input X-rays into three classes: screw head, screw shaft and background. Once all the screw shafts were segmented, knowledge about the spatial configuration of the acquired biplanar X-rays was used to identify the correspondence between the projections. Pose estimation was then performed to estimate the 6 degree-of-freedom pose of each screw. The performance of the proposed pose estimation method was tested on a porcine specimen.

RESULTS

The developed machine learning framework was capable of segmenting the screw shafts with 93% and 83% accuracy when tested on synthetic X-rays and on clinically realistic X-rays, respectively. The pose estimation accuracy of this method was shown to be [Formula: see text] and [Formula: see text] on clinically realistic X-rays.

CONCLUSIONS

The proposed system offers an accurate and fully automatic pedicle screw segmentation and pose assessment framework. Such a system can help to provide an intraoperative pedicle screw insertion assessment protocol with minimal interference with the existing surgical routines.

Outcomes and complications following posterior long lumbar fusions exceeding three levels

The outcomes and complications of posterior-only lumbar instrumented long fusions exceeding three segments with selective segmental transforaminal lumbar interbody fusion for the treatment of degenerative lumbar scoliosis, kyphosis, or both combined with spondylolisthesis were analyzed to investigate risk factors associated with surgical instrumentation failure. Fifteen consecutive patients with degenerative lumbar scoliosis, kyphosis, or both combined with spondylolisthesis were studied retrospectively. There were 5 male and 10 female patients, with a mean age of 71.8 years. All the patients were followed for a mean duration of 19.4 months postoperatively. Radiographic evaluation included coronal Cobb angle, lumbar lordosis (LL) angle, pelvic incidence (PI), and pelvic tilt (PT). The clinical outcomes were assessed by means of Japanese Orthopedic Association (JOA) score. Patients were divided into two groups: group 1—7 patients with surgical complications; group 2—8 patients without complications. The preoperative and postoperative coronal Cobb's angle were not significantly different between groups 1 and 2. The LL highly correlated with developing surgical complications. There were statistically significant differences in preoperative and postoperative LL and the mean difference between PI and the LL (PI–LL) between groups 1 and 2. Linear correlation and regression analysis showed that there was no correlation between JOA score and the coronal Cobb angle in degenerative scoliosis patients. However, we found a positive correlation between JOA and LL. Our series of long lumbar fusions had a high complication and instrumentation failure. Creating adequate LL angle in harmony with PI was a key to prevent surgical complications and attain neurological improvement.

Stress analysis in a pedicle screw fixation system with flexible rods in the lumbar spine

Breakage of screws has been one of the most common complications in spinal fixation systems. However, no studies have examined the breakage risk of pedicle screw fixation systems that use flexible rods, even though flexible rods are currently being used for dynamic stabilization. In this study, the risk of breakage of screws for the rods with various flexibilities in pedicle screw fixation systems is investigated by calculating the von Mises stress as a breakage risk factor using finite element analysis. Three-dimensional finite element models of the lumbar spine with posterior one-level spinal fixations at L4—L5 using four types of rod (a straight rod, a 4 mm spring rod, a 3 mm spring rod, and a 2 mm spring rod) were developed. The von Mises stresses in both the pedicle screws and the rods were analysed under flexion, extension, lateral bending, and torsion moments of 10 N m with a follower load of 400 N. The maximum von Mises stress, which was concentrated on the neck region of the pedicle screw, decreased as the flexibility of the rod increased. However, the ratio of the maximum stress in the rod to the yield stress increased substantially when a highly flexible rod was used. Thus, the level of rod flexibility should be considered carefully when using flexible rods for dynamic stabilization because the intersegmental motion facilitated by the flexible rod results in rod breakage.

Bilateral interlaminar fenestration and unroofing for the decompression of nerve roots by using a unilateral approach in lumbar canal stenosis

BACKGROUND

Conventional laminectomy is a simple procedure that provides adequate decompression in cases of lumbar spinal canal stenosis. However, with this surgical modality, important posterior osteoligamentous elements necessary for spinal stability are lost; and it is often accompanied by damage to the facet joint. Bilateral interlaminar fenestration and unroofing of the intervertebral foramen to achieve decompression of the nerve roots by using a unilateral microsurgical approach in lumbar spinal canal stenosis are less invasive compared with conventional laminectomy.

METHODS

We carried out bilateral interlaminar fenestration and unroofing of the intervertebral foramen to decompress the stenosed nerve roots under a microscope by using a unilateral approach. In particular, we performed the decompression of the contralateral nerve root with this surgical method by using a Caspar retractor. Surgery was performed on 47 patients (18 women and 29 men; 29-85 years; median age, 62 years). All cases were with single-level lumbar spinal canal stenosis and bilateral radiculopathy.

RESULTS

The mean preoperative NCOS was 29.8 (range, 8-48). The mean NCOS after a postoperative period of 3 months was 79.9 (range, 32-100). After a postoperative period of 2 years, the mean NCOS increased to 83.2 (range, 32-100). The satisfaction measures indicated that the procedure was "very successful" in 45 cases, providing "almost complete relief"; "fairly successful" in one case, providing "a good deal of relief"; and "not very successful" in another case, affording "only a little relief."

CONCLUSIONS

This unilateral, minimally invasive decompression provided satisfactory results.

Facet joint violation during pedicle screw insertion: a cadaveric study of the adult lumbosacral spine comparing the two pedicle screw insertion techniques

This article analyses the incidence of facet joint violation by pedicle screws inserted via the two most commonly used techniques, intersection and mammillary. Pedicle screws were inserted on each side of fresh-frozen human cadevaric specimen lumbosacral spines using the two techniques. All facet joints which were violated were found to be on the right side, where the mamillary process technique was employed. The incidence of facet joint violation was higher in the mammillary technique, which was statistically significant. The intersection technique appears to be safer than the mamillary with respect to violation of the adjacent superior facet joint.

Complications per et postopératoires immédiates des arthrodèses lombaires et lombosacrées

PURPOSE OF THE STUDY

Incidence of complications following lumbar or lumbosacral fusion is still an imprecise notion. The aim of this prospective observational study was to determine the frequency of intraoperative and early postoperative complications after this procedure and to analyze favoring factors.

MATERIAL AND METHODS

Twenty-one orthopedic units participated in this study which included 872 patients who underwent lumbar or lumbosacral fusion procedures involving the sector limited by L1 and S1. A minimum of 6 months follow-up was required for inclusion. Four types of complications were studied: general complications, infection, neurological and meningeal complications, mechanical problems. The following preoperative and intraoperative parameters were recorded: epidemiological and morphological data, history of lumbar spine surgery, comorbid conditions, indication for surgery, and technical aspects of the fusion. Two types of analysis were performed. The first was a descriptive analysis designed to determined the overall incidence of complications and the incidence of each type of complication. A multivariate analysis was then performed in order to determine factors influencing occurrence of complications.

RESULTS

Mean follow-up was 13 months, mean age of the cohort was 51 +/- 15.5 years. Prior lumbar surgery was noted in 12% of the patients. A decompression procedure was associated in 40% of the patients due to lumbar stenosis. Posterolateral arthrodesis was used in 71% of the patients and 91% were instrumented. Most of the fusions were short, involving one or two levels. One or more intraoperative or early postoperative complications were observed in 200 patients (23%). The incidences of the four types of complications expressed in percent of the total cohort were 9.7%, 5.6%, 8.6%, and 3.6% for general, infectious, neurological and meningeal, and mechanical complications respectively. Three factors exhibited a significant correlation with occurrence of complications, irrespective of the type: excess weight, presence of several comorbid conditions, and extent of the zone of fusion.

CONCLUSION

This study enabled a precise assessment of the incidence of complications subsequent to lumbar or lumbosacral fusion: 23%. The incidence of serious complications requiring a reoperation was 14.7%. This finding, together with the factors found to influence occurrence of these complications should be kept in mind when determining indications for lumbar or lumbosacral fusion.

Update on use of instrumentation in lumbar spine disorders

The past 20 years have witnessed significant changes in the indications for and use of instrumentation in lumbar spine surgery. Absolute indications for surgical instrumentation include cases of clearly defined instability that commonly occur in the setting of trauma, tumour and infection. Relative indications for instrumentation must consider the clinical context and individual patient characteristics but may include cases of spondylolisthesis, junctional stenosis and pseudarthrosis. The use of instrumentation in the surgical treatment of degenerative disc disease is prevalent but remains highly controversial. Pedicle screws and interbody cages represent alternative forms of instrumentation with substantial clinical evidence supporting their safety and efficacy when applied in the correct clinical settings. Minimally invasive and computer-assisted surgical techniques have shown promising early results but must be subject to longer-term scrutiny. The development of prosthetic disc replacements is an exciting area of research, but clinical results have not approached the success currently enjoyed by hip and knee prostheses, and these devices should be considered experimental. One of the goals of instrumentation is to enhance the rate of spinal fusion. However, achievement of solid radiographic fusion does not guarantee a clinically successful outcome and, conversely, excellent results can be obtained in the setting of radiographic pseudarthrosis. The most important determinant of favourable surgical outcome is appropriate patient selection through a sound understanding of surgical indications.