INTRODUCTION

 

Harrington and Tullos¹ deserve credit for the first deliberate attempt to put pedicle screws through the isthmus of the pedicle. Their report, published in 1969, described the attempted reduction of two cases of high-grade spondylolisthesis. Pioneering the use of pedicle-screw internal fixation proceeded in France and Switzerland during the 1970s. Clinical success with the screws was reported during the 1980s by investigators including Cotrel and Dubousset², Dick³, Roy-Camille⁴, and Louis.⁵

Steffee et al.⁶ developed the variable-screw-placement (VSP) plate, which permitted pedicle screws to be placed according to individual patient anatomy. This device provided much more clinical latitude than the Roy-Camille plate, which had fixed screw-hole distances for application of the screws.⁷

Transpedicular screw application is commonly used and has been very successful for posterior fixation in spinal instability due to trauma, tumor, scoliosis, and degenerative disease. It can be used even when the posterior elements of the spine are absent or injured.

The insertion of pedicle screws remains challenging, because of the variability in width, height, and orientation of spinal pedicles and the proximity of nerve roots. This is even more so the case in the thoracic spine, due to the small pedicular diameter and the proximity of the pleura and the spinal cord.⁸

To ensure precise screw positioning, it is essential that the surgeon have an intimate knowledge of spinal anatomy and be able to localize the bony and neural structures accurately. This requires a melding of directly visualized anatomic landmarks, proprioceptive feedback, and radiographically acquired data. In some centers, electrophysiological monitoring and image-based navigation are also used to improve the surgeon’s accuracy

The high number of intraoperative complications including screw misplacement, pedicle fractures, non-tightness of the nobs and non-anatomical rod bendings indicates that pedicle screw placement is a technically demanding procedure. To avoid such errors this procedure should be performed only by well-trained spinal surgeons who undertake these operations regularly.⁹

               Aim of the study is to review the different complications that can occur during thoracic and lumbar transpedicular fixation procedures, and track back the causes weather operator or device related and the possibilities of their prevention.

 

PATIENTS AND METHODS

 

Sixty three patients, 40 males (63.5%) and 23 females (36.5%) performed transpedicular screw fixation of the thoracic or the lumbar spine and were followed up for a period of at least 9 months between the years 2006 and 2008. 38 patients (60.3 %) suffered spinal fractures due to trauma, 8 patients (12.7 %) suffered pathological spine fractures due to tumors and 17 patients (27 %) suffered from different grades of spondylolisthesis ranging from II – IV. All the patients have had plain radiographs postero-anterior and lateral views, CT scan and MRI done prior to the procedure. For the Traumatic fractures of the spine, we used Frankel grading for spinal cord injury (Table 1) to access the neurological state and the White and Panjabi criteria to access the stability (Table 2).

 

Table 1. Frankel grading for spinal cord injury.

 

A	Complete (no sensory or motor function is preserved)
B	Incomplete (Sensory, but no motor function is preserved below the neurological level)
C	Incomplete (Motor function is preserved below the neurological level, and the majority of key muscles below the neurological level have a muscle power grade of <3)
D	Incomplete (Motor function is preserved below the neurological level, and the majority of key muscles below the neurological level have a muscle power grade of ≥3)
E	Normal (sensory & motor function is normal)

 

Table 2. White and Panjabi criteria for assessment of the stability.

 

Condition	Points assigned
Loss of integrity of anterior (and middle) column Loss of integrity of posterior column(s) Acute resting translational deformity Acute resting angulation deformity Acute dynamic translation deformity exaggeration Acute dynamic translation deformity exaggeration Neural element injury Acute disk narrowing at level of suspected pathology Dangerous loading anticipated	2 2 2 2 2 2 3 1 1

 A score of 5 points or more implies the presence of instability

 

Three hundred-six pedicle screws (226 lumbar, 80 thoracic) were placed under fluoroscopic guidance with 126 rods and 22 cross connectors. The pedicle screws were inserted into the spinal segments T4–S1. Intraoperative neurophysiological monitoring, navigation or other types of guidance tools were not used in this study.

All patients underwent internal fixation by posterior approach. Laminectomy to decompress spinal cord or spinal roots was carried out at the involved level and bone was saved to be used as bone graft for fusion. Pedicles were localized using anatomical landmarks and intraoperative imaging. Polyaxial and monoaxial screws were inserted through pedicles into vertebral bodies’ according to the affected levels under fluoroscopic guidance. Rod contouring was employed in all the cases. The cortical bone of the transverse processes was roughened to make it suitable for bone graft. The bone already saved while doing laminectomy was broken into small fragments and was placed over roughened cortical bone. The wound was then closed in layers after keeping a redivac drain.

The patients were kept on broad-spectrum antibiotics and analgesics for one week. The drain was removed on the next or 2^nd day of surgery. Post operative plain X-rays were done on the 3rd postoperative day and if there is any doubt about the screws’ position or any apparent complaint of the patient then a CT scan was done. The neurological status of the patients and any other complications were noted up to nine months.

 

RESULTS

 

There were 63 patients who were managed with pedicle screws fixation for thoracic, lumbar and thoracolumbar junction lesions including traumatic fractures, pathological fractures and spondylolythesis. There were 40 males (63.5%) and 23 females (36.5%). The age range was 14 to 55 years (mean age of 33 years). 38 patients (60.3 %) suffered spinal fractures due to trauma, 8 patients (12.7 %) suffered pathological spine fractures due to tumors and 17 patients (27 %) suffered from different grades of spondylolisthesis ranging from II – IV.

Eight patients (12.6%) showed one or more intraoperative (operator related) or post operative (device related) complications.

The first complication was screw misplacement which occurred in 4 patients (6.2 %), two of which has suffered permanent neural injury due to a medial misplaced screw causing direct injury to the cord or related spinal root, the other 2 patients had the misplaced screw laterally placed to the pedicle, in other words; within the medial portion of the transverse process. The 4 patients had a redo surgery within one to two weeks of the initial surgery.

Screw loosening occurred in 1 patient (1.5 %), the patient was found to have spinal osteoporosis, the other 3 screws were well fit and the loose screw was replaced by another one with larger diameter and secured with bone cement within its trajectory.

Rod breakage occurred in 2 patients (3.1 %) and was detected after 6 months of the initial surgery in one patient and 9 months in the other (Figures 1 and 2).

Neural injury occurred in 2 patients (3.1 %), these 2 patients had a misplaced screw which was replaced within one week postoperative and by the ninth months follow up showed improvement of the neurological deficit in one patient with partial foot drop grade III (became grade IV) and no improvement in the other patient with complete foot drop.

 

    

 

Figure 1. Plain X-ray dorso-lumbar spine A-P and lateral views showing breakage of the left rod.

 

     

 

Figure 2. plain x-ray dorso-lumbar spine A-P and lateral views

showing rod replacement with application of a cross connector

 

 

Nonunion occurred in 2 patients (3.1%), detected by breakage of a single rod in one patient and both rods in the other after more than 6 months of the initial surgery, both patients showed non union (failure of fusion) of the bone graft placed between the transverse processes indicating insufficient bone graft or inadequate decortication of the transverse processes. A redo surgery was undertaken with new rod placement and reapplication of artificial bone graft mixed with spinous process obtained bone after good decortication of the transverse processes.

Deep wound infection occurred in 1 patient (1.5%), the patient was 30 years old female with 2^nd degree spondylolythesis and with no other medical diseases and no signs of being immunocompromised, the patient presented with severe agonizing back pain radiating to both lower limbs on movement after less than one week of the surgery and after being initially well immediately postoperative. ESR proved to be 95 at the 1^st hour and CRP was 96, follow up MRI showed severe discitis with paraspinal fluid collection assumed to be pus. Medical treatment was applied for about 6 weeks with antibiotics and complete immobilization aided by lumbosacral belt support and complete resolution was obtained after 3 months.

The other 55 patients had an uneventful postoperative follow up and most of them experienced improvement of their neurological deficits with physiotherapy.

 

DISCUSSION

 

Pedicle screw placement is a well-known and increasingly performed technique used to achieve fixation and fusion in thoracolumbar surgery. Since its first introduction by Harrington and Tullos in 1969¹ and further development by Roy-Camille et al.⁴, Louis⁵, and Steffee et al.⁶ in the late 1980s, it has become the mainstay of spinal instrumentation. This technique is used for degenerative, neoplastic, infectious, and malformative pathologies associated with axial instability. Despite technical advances over the last few decades, pedicle screw insertion is still associated with a risk of complications. Among them, the most commonly reported complication is screw malpositioning, with an overall incidence of 0%–42% in the literature.¹⁰ Fortunately, more serious screw-related complications, such as neurological, visceral, or vascular, are very rare.¹¹

In this study, sixty three patients, 40 males (63.5%) and 23 females (36.5%) performed transpedicular screw fixation of the thoracic or the lumbar spine and were followed up for a period of at least 9 months between the years 2006 and 2008. 38 patients (60.3%) suffered spinal fractures due to trauma, 8 patients (12.7%) suffered pathological spine fractures due to tumors and 17 patients (27%) suffered from different grades of spondylolisthesis ranging from II – IV. 8 patients (12.6%) showed one or more intraoperative (operator related) or post operative (device related) complications. The first complication was screw misplacement which occurred in 4 patients (6.2%).

The ideal pedicle screw should have a maximum diameter and length without breaching the pedicle’s cortical layer or that of the vertebral body, and it should converge.¹²

Nevertheless, a satisfactory outcome can also be achieved despite suboptimal screw placement and vice versa. For example, a screw that just barely touches the lower border of the pedicle may cause a clinically apparent radiculopathy and it may require revision. On the other hand, a screw that lies inside the spinal canal may produce no symptoms at all. Therefore, the evaluation of successful fusion surgery should always include a clinical assessment in addition to an appraisal of screw position. A recent meta-analysis with 130 studies involving a total of 37,337 pedicle screws by Kosmopoulos and Schizas¹³ found a mean misplacement rate of 8.7%. Furthermore, additional surgical procedures may be required to repair injuries related to screw problems, with a mean incidence of up to 20.8%.¹⁴ Different techniques have been proposed to improve accuracy, including standard fluoroscopy guidance, computer or robotic assistance, navigation systems, or specific pedicle tools as PediGuard (Spine Vision SA).¹⁵

Nonetheless, experienced spine surgeons have shown the ability to insert screws in the thoracolumbar region with a low incidence of screw misplacement simply by respecting the anatomical landmarks.¹⁶

Although minor misplacement poses little risk of injury, a displacement greater than 4 mm is associated with a high risk of injury to vital structures depending on the instrumented level.¹⁷

Screw loosening occurred in 1 patient (1.5%). Poor bone density (osteoporosis), excessive strain on the implant, residual sagittal imbalance, screw hole preparation technique, torque of insertion, screw purchase, and direction of screw placement may influence the pullout strength of pedicle screws. Tapping the screw hole or additional sublaminar hooks may increase pullout strength.¹⁸

A continuous lucency at the screw-bone interface surrounded by a thin sclerotic zone on the anteroposterior radiograph indicates loosening. The solution is to replace the screw with a larger diameter one or use of bone cement into the trajectory and rapidly insert the screw before cement consolidation.¹⁹

Rod breakage occurred in 2 patients (3.1%). Both patients had long segment fixation for lumber fractures. It often indicates a delay infusion. In such cases, there is an absolute indication to revise the implant. The revision should correct the biomechanical reasons for breakage. The fusion strategy and the fixation extension should be reconsidered, and a successful union must be achieved. The constructs’ stiffness may be improved by inserting anterior devices, by switching from titanium to stainless steel, or by inserting additional cross-links to the system.²⁰

Neural injury: The overall incidence of nerve root or spinal cord injury is rare, ranging between 0.6% and 11%.40 in this study, it occurred in 2 patients (3.1%). Improvement of the neurological deficit occurred in one patient with partial foot drop grade III (became grade IV) and no improvement in the other patient with complete foot drop.

Although a transitory self-limiting neurapraxia is more common, the incidence of a permanent neurological deficit is rare. Pihlajämaki et al. found a permanent foot drop in 3 of 102 patients, which was only attributable to screw misplacement in 1 of the patients.²¹ A new neurological deficit or a new postoperative pain requires careful evaluation of postoperative images to rule out a conflict with a screw, in which case surgical revision is necessary. The planning of the revision procedure should be as complete and precise as possible, because a second misplacement will not be acceptable. A new trajectory within the pedicle should be planned, according to the previous entry point and the target. During the procedure, the misplaced screw is exposed and removed. In such cases, the application of intraoperative CT scanning or navigation is recommended.¹⁹

The new trajectory within the pedicle may create a larger hole, which may cause insufficient purchase of the subsequent screw. For such cases, a rescue procedure must always be available. The surgeon can choose either a larger salvage screw or skip the level and extend the fixation to more levels. Alternatively, the purchase can be augmented by means of PMMA injection. The cement may be injected into the new trajectory and the screw rapidly inserted before cement consolidation.

Deep wound infection occurred in one patient (1.5%) and was completely cured with antibiotics, immobilization in belt and bed rest for six weeks. Patients who showed no improvement should be subjected to system removal.

 

Conclusion

Our study has shown that the incidence of intraoperative complications(operator related) and post operative (device related) fatigue failures of the transpedicular screw-rod devices is directly related to the experience of the surgeon undergoing the operation and so these surgeries should be hand-held by only well trained and spine oriented surgeons.

 

[Disclosure: Authors report no conflict of interest]

 

REFERENCES

 

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