The use of pedicle-screw internal fixation for the operative treatment of spinal disorders

Can computer-assisted surgery reduce the effective dose for spinal fusion and sacroiliac screw insertion?

BACKGROUND

The increasing use of fluoroscopy-based surgical procedures and the associated exposure to radiation raise questions regarding potential risks for patients and operating room personnel. Computer-assisted technologies can help to reduce the emission of radiation; the effect on the patient's dose for the three-dimensional (3-D)-based technologies has not yet been evaluated.

QUESTIONS/PURPOSES

We determined the effective and organ dose in dorsal spinal fusion and percutaneous transsacral screw stabilization during conventional fluoroscopy-assisted and computer-navigated procedures.

PATIENTS AND METHODS

We recorded the dose and duration of radiation from fluoroscopy in 20 patients, with single vertebra fractures of the lumbar spine, who underwent posterior stabilization with and without the use of a navigation system and 20 patients with navigated percutaneous transsacral screw stabilization for sacroiliac joint injuries. For the conventional iliosacral joint operations, the duration of radiation was estimated retrospectively in two cases and further determined from the literature. Dose measurements were performed with a male phantom; the phantom was equipped with thermoluminescence dosimeters.

RESULTS

The effective dose in conventional spine surgery using 2-D fluoroscopy was more than 12-fold greater than in navigated operations. For the sacroiliac joint, the effective dose was nearly fivefold greater for nonnavigated operations.

CONCLUSION

Compared with conventional fluoroscopy, the patient's effective dose can be reduced by 3-D computer-assisted spinal and pelvic surgery.

LEVEL OF EVIDENCE

Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Pedicle screw placement in the thoracic spine: a comparison study of computer-assisted navigation and conventional techniques

The technique of computer-assisted pedicle screw installation and its clinical benefit as compared with conventional pedicle screw installation was evaluated. Twenty-two patients had thoracic screw insertion under 3-dimentional computer-assisted navigation (92 screws) and 20 patients under conventional fluoroscopic control (84 screws). The 2 groups were compared for accuracy of screw placement, screw insertion time by postoperative thin-cut computed tomography scans, and statistical analysis. The cortical perforations were graded by 2-mm increments. In the computer group, 88 (95.65%) were grade I (good), 4 (4.35%) were grade II (<2 mm), and 0 were grade III (>2 mm) violations. There were 4 cortical violations (3.57%). In the conventional group, there were 14 cortical violations (16.67%), 70 (83.33%) were grade I (good), 11 (13.1%) were grade II (<2 mm), and 3 (3.57%) were grade III (>2 mm) violations (P<.001). The number (19.57%) of upper thoracic pedicle screws (T1-T4) inserted under 3-dimensional computer-assisted navigation was significantly higher than that (3.57%) by conventional fluoroscopic control (P<.001). Average screw insertion time in the conventional group was more than in the computer group (P<.001). Three-dimensional computer-assisted navigation pedicle screw placement can increase accuracy, reduce surgical time, and be performed safely and effectively at all levels of the thoracic spine, particularly the upper thoracic spine.

Ball tip technique for thoracic pedicle screw placement in patients with adolescent idiopathic scoliosis

Object

The aim in this study was to evaluate the efficacy of the ball tip technique in placing thoracic pedicle screws (TPSs), as compared with the conventional freehand technique, in both a cadaveric study and a clinical study of patients with adolescent idiopathic scoliosis. Although posterior spinal surgery using TPSs has been widely applied, these screws are associated with the potential risk of vascular, pulmonary, or neurological complications. To further enhance the accuracy and safety of TPS placement, the authors developed the ball tip technique.

Methods

After creating an appropriate starting point for probe insertion, a specially designed ball tip probe consisting of a ball-shaped tip with a flexible metal shaft is used to make a guide hole into the pedicle. Holding the probe with the fingertips while using an appropriate amount of pressure or by tapping it gently and continuously with a hammer, one can safely insert the ball tip probe into the cancellous channel in the pedicle.

In a cadaveric study, 5 spine fellows with similar levels of experience in placing TPSs applied the ball tip or the conventional technique to place screws in 5 cadavers with no spinal deformities. The incidence of misplaced screws was evaluated by dissecting the spines. In a clinical study, 40 patients with adolescent idiopathic scoliosis underwent posterior surgery with TPS placement via the ball tip or conventional technique (20 patients in each treatment group). The accuracy of the TPS placements was evaluated on postoperative axial CT scanning.

Results

In the cadaveric study, 100 TPSs were evaluated, and the incidence of misplaced screws was 14% in the ball tip group and 34% in the conventional group (p = 0.0192). In the clinical study, 574 TPSs were evaluated. One hundred seventy-one intrapedicular screws (67%) were recognized in the conventional group and 288 (90%) in the ball tip group (p < 0.01). In the conventional and ball tip groups, the respective numbers of TPSs with a pedicle breach of ≤ 2 mm were 20 (8%) and 15 (5%), those with a pedicle breach of > 2 mm were 32 (13%) and 9 (3%; p < 0.01), and those located in the costovertebral joints were 32 (13%) and 7 (2%).

Conclusions

In both cadaveric and clinical studies the ball tip technique enhanced the accuracy of TPS placement as compared with the conventional freehand technique. Thus, the ball tip technique is useful for the accurate and safe placement of TPSs in deformed spines.

The effect of starting point placement technique on thoracic transverse process strength: an ex vivo biomechanical study

Background

The use of thoracic pedicle screws in spinal deformity, trauma, and tumor reconstruction is becoming more common. Unsuccessful screw placement may require salvage techniques utilizing transverse process hooks. The effect of different starting point placement techniques on the strength of the transverse process has not previously been reported. The purpose of this paper is to determine the biomechanical properties of the thoracic transverse process following various pedicle screw starting point placement techniques.

Methods

Forty-seven fresh-frozen human cadaveric thoracic vertebrae from T2 to T9 were disarticulated and matched by bone mineral density (BMD) and transverse process (TP) cross-sectional area. Specimens were randomized to one of four groups: A, control, and three others based on thoracic pedicle screw placement technique; B, straightforward; C, funnel; and D, in-out-in. Initial cortical bone removal for pedicle screw placement was made using a burr at the location on the transverse process or transverse process-laminar junction as published in the original description of each technique. The transverse process was tested measuring load-to-failure simulating a hook in compression mode. Analysis of covariance and Pearson correlation coefficients were used to examine the data.

Results

Technique was a significant predictor of load-to-failure (P = 0.0007). The least squares mean (LS mean) load-to-failure of group A (control) was 377 N, group B (straightforward) 355 N, group C (funnel) 229 N, and group D (in-out-in) 301 N. Significant differences were noted between groups A and C, A and D, B and C, and C and D. BMD (0.925 g/cm² [range, 0.624-1.301 g/cm²]) was also a significant predictor of load-to-failure, for all specimens grouped together (P < 0.0001) and for each technique (P <0.05). Level and side tested were not found to significantly correlate with load-to-failure.

Conclusions

The residual coronal plane compressive strength of the thoracic transverse process is dependent upon the screw starting point placement technique. The funnel technique significantly weakens transverse processes as compared to the straightforward technique, which does not significantly weaken the transverse process. It is also dependent upon bone mineral density, and low failure loads even in some control specimens suggest limited usefulness of the transverse process for axial compression loading in the osteoporotic thoracic spine.

Biomechanical and histological evaluation of an expandable pedicle screw in osteoporotic spine in sheep

Transpedicular fixation can be challenging in the osteoporotic spine as reduced bone mineral density compromises the mechanical stability of the pedicle screw. Here, we sought to investigate the biomechanical and histological properties of stabilization of expandable pedicle screw (EPS) in the osteoporotic spine in sheep. EPSs and standard pedicle screws, SINO screws, were inserted on the vertebral bodies in four female ovariectomized sheep. Pull-out and cyclic bending resistance test were performed to compare the holding strength of these pedicle screws. High-resolution micro-computed tomography (CT) was performed for three-dimensional image reconstruction. We found that the EPSs provided a 59.6% increase in the pull-out strength over the SINO screws. Moreover, the EPSs withstood a greater number of cycles or load with less displacement before loosening. Micro-CT image reconstruction showed that the tissue mineral density, bone volume fraction, bone surface/bone volume ratio, trabecular thickness, and trabecular separation were significantly better in the expandable portion of the EPSs than those in the anterior portion of the SINO screws (P < 0.05). Furthermore, the trabecular architecture in the screw-bone interface was denser in the expandable portion of the EPS than that in the anterior portion of the SINO screw. Histologically, newly formed bone tissues grew into the center of EPS and were in close contact with the EPS. Our results show that the EPS demonstrates improved biomechanical and histological properties over the standard screw in the osteoporotic spine. The EPS may be of value in treating patients with osteoporosis and warrants further clinical studies.

Tratamento cirúrgico da escoliose em pacientes com amiotrofia espinhal com parafusos pediculares (instrumental de 3ª geração) e complicações precoces

OBJETIVO: avaliar a utilização de artrodese via posterior com parafusos pediculares para correção da escoliose em pacientes com amiotrofia espinhal. MÉTODOS: realizou-se um estudo retrospectivo de 16 pacientes com amiotrofia espinhal submetidos à artrodese via posterior exclusiva, com parafusos pediculares. Foi avaliado o perfil geral dos pacientes e o potencial de correção do ângulo de Cobb e da obliquidade pélvica, além das complicações precoces. RESULTADOS: o ângulo de Cobb pré-operatório foi em média de 94,6º (65 a 132º), no pós-operatório de 40,4º (2 a 70º), percentual de correção de 57,2%. A obliquidade pélvica pré-operatória foi em média 34,7º (25 a 56º), no pós-operatório foi para 11,3º (0 a 20º), com percentual de correção de 67,4%. Cinco pacientes tiveram complicações precoces (31,2%) com boa resolução. CONCLUSÕES: o tratamento cirúrgico da escoliose em pacientes com amiotrofia espinhal por meio de artrodese via posterior utilizando parafusos pediculares tem grande potencial de correção da deformidade coronal e da obliquidade pélvica, sem grandes complicações no pós-operatório precoce.

Reformatted computed tomographic evaluation of the thoracic pedicle in a Chinese population for the surgical application of transpedicular screw placement

PURPOSE

To study the transverse thoracic pedicle diameter of a Chinese population and to determine the feasibility and safety of transpedicular screw fixation.

METHODS

The authors studied the transverse pedicle diameter of the T1-T12 of the thoracic spine in a Chinese population using reformatted computed tomography. The data were compared with Caucasians and other Asians.

RESULTS

The mean outer pedicle widths of the thoracic spine from T1 to T12 were 8.43, 6.65, 5.20, 4.44, 4.50, 4.87, 5.04, 5.32, 5.66, 6.65, 8.08 and 8.27 mm in males and 7.91, 6.03, 4.55, 3.91, 4.05, 4.31, 4.39, 4.60, 5.13, 5.67, 7.21 and 7.50 mm in females, respectively. Female patients have smaller dimensions compared with male patients. A significant percentage of patients have an outer pedicle width of less than 4.5 mm from T3 to T8, which is not suitable for transpedicular screw fixation with a 3.5 mm screw.

CONCLUSIONS

The results of this study suggest that transpedicular screw fixation may not be suitable for the mid-thoracic regions in most Chinese females and that modified pedicle screw techniques or modified type of fixation is required in these patients. CT evaluation is a must before this procedure is performed.

Complications of pedicle screw fixation in scoliosis surgery: a systematic review

STUDY DESIGN

Systematic review.

OBJECTIVE

To review the published literature on the use of pedicle screws in pediatric spinal deformity to quantify the risks and complications associated with pedicle screw instrumentation, particularly in the thoracic spine.

SUMMARY OF BACKGROUND DATA

The use of pedicle screws in adolescent scoliosis surgery is common. Although many reports have been published regarding the use of pedicle screws in pediatric patients, there has been no systematic review on the risks of complications.

METHODS

PubMed, Ovid Medline, and Cochrane databases were searched for studies reporting the use of thoracic pedicle screws in pediatric deformity. We excluded articles dealing with neuromuscular scoliosis or bone dysplasia to focus mostly on adolescent thoracic idiopathic scoliosis and the likes. We then searched for cases reports dealing with thoracic pedicle screws complications.

RESULTS

This systematic review retrieved 21 studies with a total of 4570 pedicle screws in 1666 patients. The mean age of the patients was 17.6 years; 812 patients were women and 252 were men, and 5 studies did not identify sex. Overall, 518 (4.2%) screws were reported as malpositioned. However, in studies in which postoperative computed tomography scans were done systematically, the rate of screw malpositioning was as high as 15.7%. The reported percentage of patients with screw malpositioned is around 11%. Eleven patients underwent revision surgery for instrumentation malposition. Other complications reported include loss of curve correction, intraoperative pedicle fracture or loosening, dural laceration, deep infection, pseudarthrosis, and transient neurologic injury. There were no major vascular complications reported in these 21 studies. We could identify 9 case report articles dealing with complications of pedicle screws. Such complications were mostly either vascular (10 cases) or neurologic (4 cases), without any irreversible complications.

CONCLUSION

Malposition is the most commonly reported complication of thoracic pedicle screw placement, at a rate of 15.7% per screw inserted with postoperative computed tomography scans. The use of pedicle screws in the thoracic spine for the treatment of pediatric deformity has been reported to be safe despite the high rate of patients with malpositioned screws (11%). Major complications, such as neurologic or vascular injury, were almost never reported in this literature review of case series. Cases reports on the other hand have started to identify such complications.

Accuracy of pedicle screw placement in the lumbosacral spine using conventional technique: computed tomography postoperative assessment in 102 consecutive patients

OBJECT

The goal of this study was to determine the incidence of screw misplacement and complications in a group of 102 patients who underwent transpedicle screw fixation in the lumbosacral spine with conventional open technique and intraoperative fluoroscopy. The results are compared with published data.

METHODS

Cases involving 102 consecutive patients (424 inserted screws) were reviewed. Surgery was performed in all cases by the same surgeon's team, using the same implant, and all results were assessed by means of a specific CT protocol. The screw position was assessed by the authors and an independent observer. Screw position was classified as correct when the screw was completely surrounded by the pedicle cortex, as "cortical encroachment" (questionable violation) if the pedicle cortex could not be visualized, and as "frank penetration" when the screw was outside the pedicular boundaries. Frank penetration was further subdivided as minor (when the edge of the screw thread was up to 2.0 mm outside the pedicle cortex), moderate (2.1-4 mm), and severe (> 4 mm). The incidence of intra- and postoperative complications not related to screw position as well as hardware failures were also registered, with a minimum follow-up duration of 8 months.

RESULTS

The rate of frank pedicle screw misplacement was 5%. The rate of minimal or questionable pedicle wall violation was 2.8%. Among the frank misplacements, 6 were classified as minor, 12 as moderate, and 3 as severe penetration. Two patients (2%) had radicular pain and neurological deficits (inferomedial and inferolateral minor misplacement at L-4 and L-5, respectively), and 5 patients (4.9%) complained only of radicular pain. At the follow-up examination all patients had completely recovered their neurological function and radicular pain was resolved in all cases. The complications not related to screw malposition were 2 pedicle fractures (2% of patients), 1 nerve root injury (1%), and 1 dural laceration (1%). Five patients (4.8%) had postoperative anemia and required transfusions. Superficial or deep wound infection was noted in 3 patients (2.9%). Late hardware failure occurred in 2 patients (2%). One patient developed adjacent segmental instability and required additional surgery to extend the fusion.

CONCLUSIONS

Our rates of screw misplacement and complications compare favorably with the lowest rates of the series in which conventional technique was used and are close to the rates reported for image-guided methods. The risk of malpositioning may be reduced with careful preoperative surgical planning, accurate knowledge of the spinal anatomy, surgical experience, and correct indication for conventional surgery. The conventional technique still remains a practical, safe, and effective surgical method for lumbosacral fixation.

Iso-C3D navigation assisted pedicle screw placement in deformities of the cervical and thoracic spine

BACKGROUND

Pedicle screw instrumentation of the deformed cervical and thoracic spine is challenging to even the most experienced surgeon and associated with increased incidence of screw misplacement. Iso-C3D based navigation has been reported to improve the accuracy of pedicle screw placement, however, there are very few studies assessing its efficacy in the presence of deformity. We conducted a study to evaluate the accuracy of Iso-C3D based navigation in pedicle screw fixation in the deformed cervical and thoracic spine.

MATERIALS AND METHODS

We inserted 98 cervical pedicle screws (18 patients) and 242 thoracic pedicle screws (17 patients) using Iso-C3D based navigation for deformities of spine due to scoliosis, ankylosing spondylitis, post traumatic and degenerative disorders. Two independent observers determined and graded the accuracy of screw placement from postoperative computed tomography (CT) scans.

RESULTS

Postoperative CT scans of the cervical spine showed 90.8% perfectly placed screws with 7 (7%) grade I pedicle breaches, 2 (2%) grade II pedicle breaches and one anterior cortex penetration (< 2mm). Five lateral pedicle breaches violated the vertebral artery foramen and three medial pedicle breaches penetrated the spinal canal; however, no patient had any neurovascular complications. In the thoracic spine there were 92.2% perfectly placed screws with only six (2%) grade II pedicle breaches, eight (3%) grade I pedicle breaches and five screws (2%) penetrating the anterior or lateral cortex. No neuro-vascular complications were encountered.

CONCLUSION

Iso-C3D based navigation improves the accuracy of pedicle screw placement in deformities of the cervical and thoracic spine. The low incidence of pedicle breach implies increased safety for the patient.

The accuracy of multi-slice three-dimensional computerized tomography on the verification of the pedicle screw trajectory

The purpose of our study was to determine the diagnostic power of three-dimensional reformatted multi-slice computerized tomography (CT) images on misplaced pedicle screws in spinal surgery. Eighty-four consecutive patients with 458 screws in situ were investigated prospectively using both axial CT slices and reformatted images after operation by two blinded investigators. All the screw misplacements were documented and the differences between the two imaging modalities were recorded. Axial CT slices were able to show only 23 of 60 misplaced pedicle screws; multislice CT was three times more powerful in the diagnosis of pedicle screw complications in spinal surgery (p<0.05). We concluded that multi-slice CT reconstruction should be the primary diagnostic tool after screw implantation in the human spine.

Safety of thoracic pedicle screw application using the funnel technique in Asians: a cadaveric evaluation

The objective of this cadaveric study is to determine the safety and outcome of thoracic pedicle screw placement in Asians using the funnel technique. Pedicle screws have superior biomechanical as well as clinical data when compared to other methods of instrumentation. However, misplacement in the thoracic spine can result in major neurological implications. There is great variability of the thoracic pedicle morphometry between the Western and the Asian population. The feasibility of thoracic pedicle screw insertion in Asians has not been fully elucidated yet. A pre-insertion radiograph was performed and surgeons were blinded to the morphometry of the thoracic pedicles. 240 pedicle screws were inserted in ten Asian cadavers from T1 to T12 using the funnel technique. 5.0 mm screws were used from T1 to T6 while 6.0 mm screws were used from T7 to T12. Perforations were detected by direct visualization via a wide laminectomy. The narrowest pedicles are found between T3 and T6. T5 pedicle width is smallest measuring 4.1 +/- 1.3 mm. There were 24 (10.0%) Grade 1 perforations and only 1 (0.4%) Grade 2 perforation. Grade 2 or worse perforation is considered significant perforation which would threaten the neural structures. There were twice as many lateral and inferior perforations compared to medial perforations. 48.0% of the perforations occurred at T1, T2 and T3 pedicles. Pedicle fracture occurred in 10.4% of pedicles. Intra-operatively, the absence of funnel was found in 24.5% of pedicles. In conclusion, thoracic pedicle screws using 5.0 mm at T1-T6 and 6.0 mm at T7-T12 can be inserted safely in Asian cadavers using the funnel technique despite having smaller thoracic pedicle morphometry.

Polyaxial screws for lumbo-iliac fixation after sacral tumor resection: experience with a new technique for an old surgical problem

BACKGROUND

Although numerous reports have been published about various methods for reconstruction after sacrectomies, there are still biomechanical and technical dilemmas that are unaddressed. This report describes the experience at authors' institution of five cases in which polyaxial pedicle screws construct has been successfully used for lumbo-iliac fixation after sacral tumor resection.

METHODS

Five cases of sacral tumors, two of Ewing's sarcoma and three of giant cell tumor (GCT) underwent surgical resection and then reconstruction was done with hardware using vertical rods placed alongside the spine bilaterally, transfixing monoaxial and polyaxial pedicle screws in lower lumbar levels and polyaxial screws into the ilium bilaterally. Cross links were also used to connect the two vertical members, thus enhancing biomechanical stability of the construct. Use of autologous bone grafts was relied upon to fill the gap created by sacral resection.

RESULTS

No instrumentation failure was noted and the continuity of the spine and pelvis was well established with the instrumentation and auto grafts. In follow up of these patients (1-3 years), no complications were seen.

CONCLUSION

Polyaxial pedicle screws fixation is an effective technique to transmit axial load from spine to the appendicular bone and can be used safely in patients in whom sacral integrity is compromised after surgical resection. However, the long term benefits of this technique need to be evaluated.

The ipsilateral lamina-pedicle angle: can it be used to guide pedicle screw placement in the sub-axial cervical spine?

Pedicle screws in the sub-axial spine are infrequently used because of concerns over their safety and difficulty in placement, despite their superior pullout strength. In the sub-axial cervical vertebrae, we have observed that the lamina appears to project at right angles to the ipsilateral pedicle axis. The aim of this investigation was to confirm the lamina orientation as a reliable landmark for pedicle screw placement. 80 digital cervical spine CT were analysed. The angle formed by the ipsilateral outer lamina cortex to the pedicle axis was recorded. A total of 398 vertebrae were analysed from patients with a mean age of 39.5 years (range 18-78). Average axial lamina-pedicle angle ranged from 96.6 degrees at C3 to 87.2 degrees at C7 in males, and from 95.6 degrees to 87.5 degrees in females. The angle formed by the posterior cortex of the lamina and the ipsilateral pedicle shows a high level of consistency for sub-axial cervical vertebrae ranging from 96 degrees at C3 to 87 degrees at C7. Although the angle is not exactly 90 degrees at all levels as hypothesised, the orientation of the lamina, nevertheless, forms a useful reference plane for insertion of pedicle screws in the sub-axial cervical spine.

Biomechanical evaluation of a new fixation device for the thoracic spine

The technology used in surgery for spinal deformity has progressed rapidly in recent years. Commonly used fixation techniques may include monofilament wires, sublaminar wires and cables, and pedicle screws. Unfortunately, neurological complications can occur with all of these, compromising the patients' health and quality of life. Recently, an alternative fixation technique using a metal clamp and polyester belt was developed to replace hooks and sublaminar wiring in scoliosis surgery. The goal of this study was to compare the pull-out strength of this new construct with sublaminar wiring, laminar hooks and pedicle screws. Forty thoracic vertebrae from five fresh frozen human thoracic spines (T5-12) were divided into five groups (8 per group), such that BMD values, pedicle diameter, and vertebral levels were equally distributed. They were then potted in polymethylmethacrylate and anchored with metal screws and polyethylene bands. One of five fixation methods was applied to the right side of the vertebra in each group: Pedicle screw, sublaminar belt with clamp, figure-8 belt with clamp, sublaminar wire, or laminar hook. Pull-out strength was then assessed using a custom jig in a servohydraulic tester. The mean failure load of the pedicle screw group was significantly larger than that of the figure-8 clamp (P = 0.001), sublaminar belt (0.0172), and sublaminar wire groups (P = 0.04) with no significant difference in pull-out strength between the latter three constructs. The most common mode of failure was the fracture of the pedicle. BMD was significantly correlated with failure load only in the figure-8 clamp and pedicle screw constructs. Only the pedicle screw had a statistically significant higher failure load than the sublaminar clamp. The sublaminar method of applying the belt and clamp device was superior to the figure-8 method. The sublaminar belt and clamp construct compared favorably to the traditional methods of sublaminar wires and laminar hooks, and should be considered as an alternative fixation device in the thoracic spine.

Thoracic pedicle screws: comparison of start points and trajectories

STUDY DESIGN

Experimental design using cadaveric computerized tomography (CT) scans and a computer-assisted image guidance system to compare various thoracic pedicle screw start points and trajectories.

OBJECTIVE

To compare described thoracic pedicle screw start points and trajectories to determine which allows strictly intrapedicular screw placement with the most margin of error.

SUMMARY OF BACKGROUND DATA

Thoracic pedicle screws are being used in a variety of spinal conditions to include fracture, tumor, and deformity. Optimal thoracic pedicle screw start points have received increasing attention in the literature. Optimal thoracic pedicle trajectory is still undetermined.

METHODS

Using fine cut CT scans of 3 cadaveric male specimens (aged 65-70 years) loaded onto a computer-assisted image guidance system, 966 pedicle screws, were virtually inserted. The effective pedicle diameter (EPD) and maximum insertional arc (MIA) was assessed using 3 different trajectories and start points: (1) straight ahead, (2) straight forward, and (3) anatomic. EPD was measured by placing a maximum-sized virtual screw, using a specific trajectory, without cortical violation of the pedicle and/or the vertebral body. The MIA was assessed by measurement of the angle formed by the most superiorly and inferiorly directed 0.1-mm virtual screw through a given start point without violation of the pedicle cortex and obtaining at least 50% vertebral body purchase.

RESULTS

Mean EPD in the sagittal plane was 7.6 +/- 0.3 (SEM) mm for the straight forward trajectory and 9.1 +/- 0.3 (SEM) mm for the anatomic trajectory, a 20% increase (P < 0.0005). Mean EPD in the axial plane was 4.1 +/- 0.2 (SEM) mm for the straight ahead trajectory and 5.0 +/- 0.2 (SEM) mm for the anatomic trajectory, a 22% increase (P < 0.0005). EPD was found to be statistically different based on the trajectory used for placement in both the axial and sagittal planes in the upper (T1-T4), middle (T5-T8), and lower (T9-T12) thoracic spine. Mean MIA in the sagittal plane was 18.7 +/- 1.1 (SEM) for straight ahead start points, 25.8 degrees +/- 0.8 degrees (SEM) for straight forward start points, and 30.2 degrees +/- 0.8 degrees (SEM) for anatomic start points, a 38% increase (P < 0.0005) in MIA compared with straight ahead and a 17% increase (P < 0.0005) in MIA compared with straight forward. Mean MIA in the axial plane was 17.8 degrees +/- 0.6 degrees (SEM) for straight ahead and anatomic start points, and 18.6 degrees +/- 0.6 degrees (SEM) for straight forward start points. This difference was not statistically significant (P = 0.086). MIA was found to be statistically different based on start points used in the sagittal, but not the axial plane, in the upper, middle, and lower thoracic spine.

CONCLUSION

EPD and MIA are trajectory (EPD) and start point (MIA) dependent. In the axial plane, anatomic EPD was greater than straight ahead EPD. In the sagittal plane, anatomic EPD was greater than straight forward EPD. Using anatomic start points in the sagittal plane, a greater MIA is achievable. These data suggest that in the diminutive thoracic pedicle or when a larger screw is needed, an anatomic trajectory using anatomic start points may allow a larger bone channel for intrapedicular placement of instrumentation.

Effect of micrometer-scale roughness of the surface of Ti6Al4V pedicle screws in vitro and in vivo

BACKGROUND

Titanium implants that have been grit-blasted and acid-etched to produce a rough microtopography support more bone integration than do smooth-surfaced implants. In vitro studies have suggested that this is due to a stimulatory effect on osteoblasts. It is not known if grit-blasted and acid-etched Ti6Al4V implants also stimulate osteoblasts and increase bone formation clinically. In this study, we examined the effects of micrometer-scale-structured Ti6Al4V surfaces on cell responses in vitro and on tissue responses in vivo.

METHODS

Ti6Al4V disks were either machined to produce smooth surfaces with an average roughness (Ra) of 0.2 microm or grit-blasted, resulting in an Ra of 2.0, 3.0, or 3.3 microm. Human osteoblast-like cells were cultured on the disks and on tissue culture polystyrene. The cell number, markers of osteoblast differentiation, and levels of local factors in the conditioned media were determined at confluence. In addition, Ti6Al4V pedicle screws with smooth or rough surfaces were implanted into the L4 and L5 vertebrae of fifteen two-year-old sheep. Osteointegration was evaluated at twelve weeks with histomorphometry and on the basis of removal torque.

RESULTS

The cell numbers on the Ti6Al4V surfaces were lower than those on the tissue culture polystyrene; the effect was greatest on the roughest surface. The alkaline-phosphatase-specific activity of cell lysates was decreased in a surface-dependent manner, whereas osteocalcin, prostaglandin E(2), transforming growth factor-beta1, and osteoprotegerin levels were higher on the rough surfaces. Bone-implant contact was greater around the rough-surfaced Ti6Al4V screws, and the torque needed to remove the rough screws from the bone was more than twice that required to remove the smooth screws.

CONCLUSIONS

Increased micrometer-scale surface roughness increases osteoblast differentiation and local factor production in vitro, which may contribute to increased bone formation and osteointegration in vivo. There was a correlation between in vitro and in vivo observations, indicating that the use of screws with rough surfaces will result in better bone-implant contact and implant stability.

The contralateral lamina: a reliable guide in subaxial, cervical pedicle screw placement

We have assessed the clinical observation that the angle of the contralateral lamina matches the angle required from the sagital plane for the placement of pedicle screws in the subaxial cervical spine. Fifty-four randomly chosen axial CT scans taken between December 2003 and December 2004 were examined. Subjects were excluded if the scan showed signs of fracture, tumour or gross abnormality. The digitised images were analysed on the Philips PACS system using SECTRA software. One hundred and sixty-eight individual vertebrae were assessed between C3 and C7. The following were measured; the angle of the pedicle relative to the sagital plane, the smallest internal and external diameter of the pedicles and the angle of the lamina. Angular measures had a CV% of 3.9%. The re-measurement error for distance was 0.5 mm. Three hundred and thirty-six pedicles were assessed in 25 females and 29 males. Average age was 48.2 years (range 17-85). Our morphologic data from live subjects was comparable to previous cadaveric data. Mean pedicle external diameter was 4.9 mm at C3 and 6.6 mm at C7. Females were marginally smaller than males. Left and right did not significantly differ. In no case was the pedicle narrower than 3.2 mm. Mean pedicle angle was 130 degrees at C3 and 140 degrees at C7. The contralateral laminar angle correlated well at C3, 4, 5 (R (2) = 0.9, C3 P = 0.002, C4 P = 0.06, C5 P = 0.0004) and was within 1 degrees of pedicle angle. At C6, 7 it was within 11 degrees . In all cases a line parallel to the lamina provided a safe corridor of 3 mm for a pedicle implant. The contralateral lamina provides a reliable intraoperative guide to the angle from the sagital plane for subaxial cervical pedicle instrumentation in adults.

Does the direction of pedicle screw rotation affect the biomechanics of direct transverse plane vertebral derotation?

STUDY DESIGN

In vitro biomechanical investigation using human cadaveric vertebrae.

OBJECTIVE

Evaluate the biomechanical differences in transverse plane vertebral body derotation maneuvers of thoracic pedicle screws in both medial and lateral directions.

SUMMARY OF BACKGROUND DATA

Thoracic pedicle screws are thought to have better vertebral rotation control and better segmental scoliosis correction compared to hooks and wires. Little data exists regarding the biomechanical stability of pedicle screws when derotated in either medial or lateral directions.

METHODS

Vertebral bodies (T4-L5) from 12 cadavers were instrumented with appropriate length pedicle screws while measuring insertion torque. Each body was anchored for independent loading in medial or lateral directions. Each screw was rotated around a rod using a constant length lever arm (30.5 cm) rigidly attached to the screw head simulating the posterior vertebral derotation maneuver. Yield torques (Nm) were analyzed using a one-way analysis of variance (P < 0.05).

RESULTS

Yield torques for both directions were significantly related to screw insertion torque (both P < 0.01). There were no statistical differences in yield torque between medial (12.0 +/- 4.9 Nm) or lateral (11.5 +/- 5.1 Nm) directions. There were no significant differences after normalization for insertion torque or screw length. Tests rotating the screw tip laterally demonstrated structural failure in the following percentages (anterolateral failure = 67%, posterior element failure = 33%, additional screw bending = 42%). Rotation medially demonstrated structural failures in the following percentages (canal penetration = 51%, posterior element failure = 49%, additional screw bending = 44%).

CONCLUSION

From these data, a surgeon performing a direct vertebral derotation using a 30 cm (12 in) lever would need to apply roughly 40 N (9 lbs) to causeanatomic failure. Adolescent patients would likely tolerate a greater force without bone failure given a greater bone density, yet, extreme caution is still recommended to prevent screw rotation either medially into the spinal canal or laterally into the chest.

Increasing bending strength and pullout strength in conical pedicle screws: biomechanical tests and finite element analyses

STUDY DESIGN

Comparative in vitro biomechanical study and finite element analysis.

OBJECTIVES

To investigate the bending strength and pullout strength of conical pedicle screws, as compared with conventional cylindrical screws.

SUMMARY OF BACKGROUND DATA

Transpedicle screw fixation, the gold standard of spinal fixation, is threatened by screw failure. Conical screws can resist screw breakage and loosening. However, biomechanical studies of bending strength have been lacking, and the results of pullout studies have varied widely.

METHODS

Ten types of pedicle screws with different patterns of core tapering and core diameter were specially manufactured with good control of all other design factors. The stiffness, yielding strength, and fatigue life of the pedicle screws were assessed by cantilever bending tests using high-molecular-weight polyethylene. The pullout strength was assessed by pullout tests using polyurethane foam. Concurrently, 3-dimensional finite element models simulating these mechanical tests were created, and the results were correlated to those of the mechanical tests.

RESULTS

In bending tests, conical screws had substantially higher stiffness, yielding strength, and fatigue life than cylindrical screws (P<0.01), especially when there was no step at the thread-shank junction. In pullout tests, pullout strength was higher in screws with a conical core and smaller core diameter and also in situations with higher foam density (P<0.01). In finite element analysis, the maximal deflection and maximal tensile stress were closely related to yielding strength (r=-0.91) and fatigue life (r=-0.95), respectively, in the bending analyses. The total reaction force was closely related to the pullout strength in pullout analyses (r=0.84 and 0.91 for different foam densities).

CONCLUSIONS

Conical screws effectively increased the bending strength and pullout strength simultaneously. The finite element analyses reliably predicted the results of the mechanical tests.

Operative treatment of adolescent idiopathic scoliosis with posterior pedicle screw-only constructs: minimum three-year follow-up of one hundred fourteen cases

STUDY DESIGN

Preoperative review of a prospective study, single institution, consecutive series. OBJECTIVE.: To analyze the intermediate-term follow-up of consecutive adolescent idiopathic scoliosis (AIS) patients treated with pedicle screw constructs.

SUMMARY OF BACKGROUND DATA

There have been no reports of the intermediate-term findings in North America following posterior spinal fusion with the use of pedicle screw-only constructs.

METHODS

One hundred and fourteen consecutive patients having a minimum 3-year follow-up (mean 4.8 +/- 1.1; range, 3.0-7.3 years) with AIS were evaluated. The average age at surgery was 14.9 +/- 2.2 years. Radiographic measurements included preoperative (Preop), postoperative (PO), 2-year (2 years), and final follow-up (FFU). A chart review evaluated PFTs, Scoliosis Research Society scores, presence of thoracoplasty, Risser sign, Lenke classification, and complications.

RESULTS

The most frequent curve pattern was Lenke type 1 (45.6%), followed by type 3 (21.9%). The average main thoracic curve measured 59.2 degrees +/- 12.2 SD Preop, and corrected to 16.8 degrees +/- 9.9 PO (P < 0.0001). Sagittal thoracic alignment (T5-T12) decreased from 25.8 degrees to 15.5 degrees at FFU (P = 0.05). Nash-Moe grading for apical vertebral rotation (AVR) in the proximal thoracic curve decreased from 2.0 Preop to 1.1 at FFU (P < 0.0001), and AVR in the thoracolumbar/lumbar spine decreased from 1.6 Preop to 1.1 at FFU (P < 0.0001). Importantly, the horizontalization of the subjacent disc measured -8.3 degrees Preop which decreased to -0.9 degrees PO (P < 0.001). PFT follow-up averaged 2.4 years with a 7.1% improvement in FVC (P = 0.004) and 8.8% in FEV1 (P < 0.0001). SRS scores averaged 83.0% at latest follow-up. Age, gender, Risser sign, or complications did not have a significant effect on outcomes. There were 2 cases of adding-on, 3 late onset infections, 1 with a single pseudarthrosis, but no neurologic complications.

CONCLUSION

This is the largest (N = 114), consecutive series of North American patients with AIS treated with pedicle screws having a minimum of 3-year follow-up. The average curve correction was 68% for the main thoracic, 50% for the proximal thoracic, and 66% for the thoracolumbar/lumbar curve at final follow-up.

Comparison of radiographic outcomes for the treatment of scoliotic curves greater than 100 degrees: wires versus hooks versus screws

STUDY DESIGN

A retrospective comparative study.

OBJECTIVE

To compare the efficacy and safety of several different anchors in the apical levels of scoliotic curves > or = 100 degrees using radiographic outcomes and clinical complications.

SUMMARY OF BACKGROUND DATA

To the best of our knowledge, no reports have compared various anchors at the apical level for correction of scoliosis curves > or = 100 degrees.

METHODS

Sixty-eight scoliosis patients (44 neuromuscular, 21 idiopathic, and 3 congenital) with major curves > or = 100 degrees (mean, 112.7 degrees; range, 100 degrees -159 degrees ) who underwent segmental spinal instrumentation and fusion with different anchors in the apical level were analyzed. All patients had a minimum 2-year follow-up (mean, 4.0 years; range, 2.0-10.5) and were divided into Group W (sublaminar wires n = 26), Group H (hooks n = 18), Group A (anterior vertebral screws n = 7), and Group PS (pedicle screws n = 17) based on the type of apical anchor used. Radiographic parameters and complications were investigated.

RESULTS

The 4 groups did not demonstrate any significant differences in gender, age at surgery, preoperative major Cobb angle, or curve flexibility (all P > 0.05). However, the PS group demonstrated a shorter follow-up period compared with the other 3 groups (P < 0.05). The PS group demonstrated the greatest correction rate, smallest loss of correction (P < 0.05), and greatest amount of correction of the apical vertebral translation (P < 0.0005) at ultimate follow-up. There were 4 cases (5.9%) of pseudarthrosis (3 in Group W, 1 in Group H; P > 0.05), 6 cases (8.8%) of implant failure (4 in Group W, 2 in Group H; P > 0.05). Despite one (1.5%) intraoperative neurologic complication (differences among groups, P > 0.05), there was no permanent neurologic deficit.

CONCLUSION

All 4 constructs were able to achieve and maintain acceptable correction safely without permanent neurologic deficit and all demonstrated acceptable implant failure rate. Pedicle screw constructs in the apical levels demonstrated the best coronal correction, smallest loss of correction, and greatest amount of apical vertebral translation correction of the major Cobb angle compared with the other constructs without neurologic complications.

Free-hand pedicle screw placement during revision spinal surgery: analysis of 552 screws

STUDY DESIGN

: A retrospective study.

OBJECTIVE

: To evaluate the safety of free-hand pedicle screw placement during revision surgery at levels with a solid posterior fusion mass and/or identified pseudarthroses of the thoracic and lumbosacral spine.

SUMMARY OF BACKGROUND DATA

: Placement of pedicle screws into previous fusion masses or pseudarthrosis levels of the spine is challenging because of the loss of anatomic landmarks. We are aware of no study focusing on screw placement without any type of radiographic or navigational assistance.

METHODS

: Thirty-seven patients underwent revision spinal surgery with posterior spinal instrumentation and fusion using 552 transpedicular screws by a single surgeon from 1994 to 2003. Among 552 screws, 184 were inserted into virgin levels, 60 were inserted into the vertebral body through previous screw holes, 208 were inserted into fusion masses, and 100 were inserted into pseudarthrosis levels. We used the quadrangulation method to gain pedicle access in a prior fusion mass after diligent exposure of any and all visible anatomic landmarks. All screws were analyzed using radiographs, intraoperative monitoring data, and clinical outcomes.

RESULTS

: There were 29 women and 8 men. The mean age of patients at the time of surgery was 38 + 6 years (range, 8-75 years). Six screws were removed intraoperatively according to the triggered electromyography criteria and 4 of them were repositioned after checking the integrity of the pedicle by a careful probing technique (1.09%). Six screws were removed after checking the intraoperative radiographs and 5 screws were misplaced, as noted, in postoperative radiographs (1.99%). Two patients underwent revision surgery at 3 days and 6 weeks after initial surgery, respectively, for root decompression at the osteotomy site although screw positions were correct.

CONCLUSION

: The free-hand technique of thoracic and lumbosacral pedicle screw placement in revision spinal surgery is reliable and safe when using the quadrangulation method of gaining pedicle access in a prior fusion mass or at pseudarthrosis levels.

Comparison of open versus percutaneous pedicle screw insertion in a sheep model

Minimally invasive surgery has become more and more important for the treatment of traumatic spine fractures. Besides, some clinical studies, objective data regarding the possible lower damage to the surrounding tissue of the spine is still missing. Here we report a sheep model where we compared a percutaneous versus an open approach for dorsal instrumentation with pedicle screws to the spine. Twelve skeletally mature sheep underwent bilateral pedicle screw fixation at the L4-L6 level. Forty-eight pedicle screws were bilaterally inserted into the pedicles and connected with rods using either an open dorsal standard or a percutaneous approach. Operation time, blood flow, compartment pressure, radiation time, loss of blood, laboratory findings and EMG were evaluated to objectify possible advantages for the percutaneous operation technique. Loss of blood and the distribution of CK-MM as a marker for muscle damage were significantly lower in the percutaneous group. However, radiation time was significantly longer in the percutaneous group. Other parameters like compartment pressure, blood flow and also measurement of the EMG at different time points did not reveal significant differences. Based on the results we found in the present study, percutaneous screw insertion can bring moderate advantages but it should be noted that essential functional deficits to the muscle could not be detected.

Micro-CT evaluation and histological analysis of screw-bone interface of expansive pedicle screw in osteoporotic sheep

OBJECTIVE

To investigate the properties of screw-bone interface of expansive pedicle screw (EPS) in osteoporotic sheep by micro-CT and histological observation.

METHODS

Six female sheep with bilateral ovariectomy-induced osteoporosis were employed in this experiment. After EPS insertion in each femoral condyle, the sheep were randomly divided into two groups: 3 sheep were bred for 3 months (Group A), while the other 3 were bred for 6 months (Group B). After the animals being killed, the femoral condyles with EPS were obtained, which were three-dimensionally-imaged and reconstructed by micro-CT. Histological evaluation was made thereafter.

RESULTS

The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within the spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT with the same thresholds. The three-dimensional (3-D) parameters, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), were significantly better in expansive sections than non-expansive sections (P less than 0.05). Histologically, newly-formed bony trabeculae crawled along the expansive fissures and into the center of EPS. The newly-formed bones, as well as the bones at the bone-screw interface, closely contacted with the EPS and constructed four compartments.

CONCLUSIONS

The findings of the current study, based on micro-CT and histological evaluation, suggest that EPS can significantly provide stabilization in osteoporotic cancellous bones.

The effect of different insertion points on the security of pedicle screw fixation in bovine vertebrae

STUDY DESIGN

Cyclic loading of pedicle screws inserted into bovine vertebrae was applied and the security of fixation was assessed as a function of the point of insertion of the screws.

OBJECTIVE

To determine which point of insertion is associated with more secure fixation using 2 commonly selected insertion points.

SUMMARY OF BACKGROUND DATA

The strength of pedicle screw fixation depends on several factors, some of these have been studied. The present study looked at the difference in fixation security resulting from the use of 2 different insertion points to obtain a more stable fixation and to reduce the risk of loosening.

METHODS

Pedicle screws were inserted through a different insertion point on each side of the vertebra, one lateral to the superior articular process and one through the superior articular process and into the pedicle. They were tested by applying cyclic loading in a craniocaudal direction and the vertical displacement was measured. Permanent migration of the screw through the bone was compared using repeated measures analysis of variance.

RESULTS

Screws inserted lateral to the process were associated with significantly less displacement than those placed through the process (P = 0.02).

CONCLUSION

Using bovine vertebrae, different points of insertion of pedicle screws were associated with different security of fixation. However, further tests using human vertebrae are recommended to confirm the above results.

Computed tomography evaluation of pedicle screws placed in the pediatric deformed spine over an 8-year period

STUDY DESIGN

A retrospective review.

OBJECTIVE

To evaluate the incremental accuracy of pedicle screws used in spinal deformity via a free-hand technique at a single institution over an 8-year period.

SUMMARY OF BACKGROUND DATA

The in vivo accuracy of free-hand pedicle screws placed throughout the deformed spine as evaluated by computed tomography (CT) scanning is unknown over a long time period.

METHODS

A total of 1023 pedicle screws inserted from T1 to L4 in 60 patients (928 screws in 54 scoliosis patients and 95 screws in 6 kyphosis patients) over an 8-year period were investigated via postoperative CT scans. Patients were divided into 3 groups (group I = 1998-1999, group II = 2001-2002, and group III = 2005). All pedicle screws were inserted via the free-hand technique using anatomic landmarks, specific entry sites, neurophysiologic, and radiographic confirmation. Pedicle screw position on CT scan was graded as acceptable versus violated, defined as the screw axis being outside the pedicle wall.

RESULTS

One hundred seven of 1023 pedicle screws (10.5%) demonstrated significant mediolateral pedicle wall violations (19 medial vs. 88 lateral, P = 0.001). groups I and III had significantly higher lateral wall violations than group II (P < 0.05) as did the kyphotic spines (vs. scoliotic spine, P < 0.05). There were significantly more screws placed in the periapical region over time (P < 0.0001), with left-sided lateral violations (T5-T8) increasing from group II to group III, while the number of medial violations significantly decreased with time (P < 0.0001). Pedicle screws placed on the right side showed a significant decrease in accuracy from group II to group III (P = 0.03). The average transverse angle of the acceptable screws was 15.3 degrees which was significantly different from the medial (23.0 degrees , P < 0.001) and lateral (10.6 degrees , P < 0.001) violations between group I and group II. No screws demonstrated neurologic, vascular, or visceral complications.

CONCLUSION

Overall accuracy of acceptable screws using the free-hand pedicle screw placement technique in the deformed spine was 89.5%, without any neurologic, vascular, or visceral complications over an 8-year period. The rate of medial violations decreased with time, as the number of screws placed in the periapical region increased.

Instrumented ligamentotaxis and stabilization of compression and burst fractures of dorsolumbar and mid-lumbar spines

BACKGROUND

Controversy continues regarding the best treatment for compression and burst fractures. The axial distraction reduction utilizing the technique employing the long straight rod or curved short rod without derotation to reduce fracture are practised together with short segment posterolateral fusion (PLF). Effects of the early postoperative mobilization without posterolateral fusion on reduction maintenance and fracture consolidation were not evaluated so far. The present prospective study is designed to assess the effectiveness of i) reduction and restoration of sagittal alignment, ii) no posterolateral fusion on the reduced, fractured vertebral body and injured disc, iii) fracture consolidation and iv) the fate of the unfused cephalad and caudal injured motion segments of the fractured vertebra.

MATERIALS AND METHODS

The study includes 15 Denis burst and two Denis type D compression fractures between T(12) and L(3). The lordotic distraction technique was used for ligamentotaxis utilizing the contoured short rods and pedicle screw fixator. Three vertebrae including the fractured one were fixed. The patients after surgery were braced for ten weeks with activity restriction for 2-4 weeks. The patients were evaluated for change in vertebral body height, sagittal curve, reduction of retropulsion, improvement in neural deficit. The unfused motion segments, residual postoperative pain and bone and metal failure were also evaluated.

RESULTS

The preoperative and postreduction percentile vertebral heights at, zero (immediate postoperative), at three, six and 12 months followup were 62.4, 94.8, 94.6, 94.5 and 94.5%, respectively. The percentages of the intracanal fragment retropulsion at preoperative, and postoperative at zero, 3, 6 and 12 months followup were 59.0, 36.2,, 36.0, 32.3, and 13.6% respectively. The preoperative and postreduction percentile loss of the canal dimension and at zero, three, six and 12 months were 52.1, 45.0, 44.0, 41.0 and 29% respectively suggesting that the under-reduced fragment was being resorbed gradually by a remodeling process. The mean initial kyphosis of 33° became mean 2° immediately after reduction and mean 3° at the final followup. The fractured vertebral bodies consolidated in an average period of ten weeks (range 8-14 weeks). The restored disc heights were relatively well maintained throughout the observation period. All paraparetic patients recovered neurologically. There were no postoperative complications.

CONCLUSION

Instrument-aided ligamentotaxis for compression and burst fractures utilizing the short contoured rod derotation technique and the instrumented stabilization of the fractured spine are found to be effective procedures which contribute to the fractured vertebral body consolidation without recollapse and maintain the motion segment function.

Evidence-based medicine analysis of all pedicle screw constructs in adolescent idiopathic scoliosis

STUDY DESIGN

: Focus paper.

OBJECTIVE

: To evaluate the current evidence-based medicine (EBM) literature in the use of pedicle screw constructs in patients with adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND

: EBM has evolved over the past 20 years to provide a framework for the evaluation of therapy and the application of that assessment to a particular patient or a disease. Application of EBM analysis to spinal instrumentation, and specifically to pedicle screw constructs, is challenging.

METHODS

: Cochrane database, Ovid Medline, and PubMed were searched using the terms "pedicle screws" and "adolescent idiopathic scoliosis." The reference list of the major papers by authors Lenke, Suk, and Kim were hand searched. Relevant articles were retained if they described a pedicle screw construct to correct AIS or compared pedicle screw constructs with another technique. Articles that did not have patients with adolescent idiopathic scoliosis in their subject groups or did not use pedicle screws as a part of their deformity correction were excluded from the study.

RESULTS

: Based on the search strategy described above, 40 articles met the inclusion criteria and were selected for review in this manuscript. Of these, 32 studies are retrospective reviews including 2 studies that do not define their data collection technique. Six studies have a prospective study design, 1 is a case report, and 1 is a cadaveric study.

CONCLUSION

: In the absence of evidence from randomized trials, surgeons must rely on the best available information to guide patient management decisions. Although there have been many publications on the topic of all pedicle screw constructs in AIS, evidence regarding the advantage of all pedicle screw constructs remain limited to case series, biomechanical studies, and expert opinions.

Thoracic pedicle screw placement: analysis using anatomical landmarks without image guidance

STUDY DESIGN

Prospective laboratory study analyzing the technique of pedicle screw placement in a cadaveric model.

OBJECTIVES

To determine whether a freehand technique without image guidance can be used to safely place pedicle screws in the thoracic spine.

SUMMARY OF BACKGROUND DATA

The use of thoracic pedicle screws for the treatment of spinal deformity has been gaining increased acceptance among surgeons. Although these implants improve deformity correction, there is still concern regarding the risks to neurological and vascular structures and regarding the experience level needed to use this implant. This study was designed to determine whether these implants could be placed safely without imaging modalities.

METHODS

Six fresh cadaveric specimens were instrumented from vertebral segments T4-T11. Ninety-six screws were placed along the anatomical axis of the pedicle. Pedicles were dissected to determine the wall violations, the position of neural structures, and the lateral coverage of the pedicle by the rib head.

RESULTS

Ninety-seven percent of screws had less than 1 mm of wall violation, with 84 screws (87.5%) fully contained within the pedicle. Four screws (4.16%) violated the medial cortex. No violations occurred superiorly, inferiorly, or anteriorly. Nerve roots were in contact with the inferior pedicle wall at all levels. The average distance from nerve to the superior pedicle ranged from 3.85 to 5.04 mm.

CONCLUSIONS

Placing pedicle screws along the anatomical axis without image guidance produced a low level of pedicle wall disruption. This technique uses a reproducible start point at each level, and the results are equal to or better than those of other cadaveric studies that have used guidance systems.

Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: part 2--Evaluation of system accuracy

OBJECTIVE

To evaluate the accuracy of a novel bone-mounted miniature robotic system for percutaneous placement of pedicle and translaminar facet screws.

METHODS

Thirty-five spinal levels in 10 cadavers were instrumented. Each cadaver's entire torso was scanned before the procedure. Surgeons planned optimal entry points and trajectories for screws on reconstructed three-dimensional virtual x-rays of each vertebra. Either a clamp or a minimally invasive external frame was attached to the bony anatomy. Anteroposterior and lateral fluoroscopic images using targeting devices were obtained and automatically registered with the virtual x-rays of each vertebra generated from the computed tomographic scan obtained before the procedure. A miniature robot was mounted onto the clamp and external frame and the system controlled the robot's motions to align the cannulated drill guide along the planned trajectory. A drill bit was introduced through the cannulated guide and a hole was drilled through the cortex. Then, K-wires were introduced and advanced through the same cannulated guide and left inside the cadaver. The cadavers were scanned with computed tomography after the procedure and the system's accuracy was evaluated in three planes, comparing K-wire positions with the preoperative plan. A total of fifty-five procedures were evaluated.

RESULTS

Twenty-nine of 32 K-wires and all four screws were placed with less than 1.5 mm of deviation; average deviation was 0.87 +/- 0.63 mm (range, 0-1.7 mm) from the preoperative plan in this group. Sixteen of 19 K-wires were placed with less than 1.5 mm of deviation. There was one broken and one bent K-wire. Another K-wire was misplaced because of collision with the previously placed wire on the contralateral side of the same vertebra because of a mistake in planning, resulting in a 6.5-mm deviation. When this case was excluded, average deviation was 0.82 +/- 0.65 mm (range, 0-1.5 mm).

CONCLUSION

These results verify the system's accuracy and support its use for minimally invasive spine surgery in selected patients.

Accuracy analysis of pedicle screw placement in posterior scoliosis surgery: comparison between conventional fluoroscopic and computer-assisted technique

STUDY DESIGN

The accuracy of pedicle screw placement was evaluated in posterior scoliosis surgeries with or without the use of computer-assisted surgical techniques.

OBJECTIVE

In this retrospective cohort study, the pedicle screw placement accuracy in posterior scoliosis surgery was compared between conventional fluoroscopic and computer-assisted surgical techniques.

SUMMARY OF BACKGROUND DATA

There has been no study systemically analyzing the perforation pattern and comparative accuracy of pedicle screw placement in posterior scoliosis surgery.

METHODS

The 45 patients who received posterior correction surgeries were divided into 2 groups: Group C, manual control (25 patients); and Group N, navigation surgery (20 patients). The average Cobb angles were 73.7 degrees and 73.1 degrees before surgery in Group C and Group N, respectively. Using CT images, vertebral rotation, pedicle axes as measured to anteroposterior sacral axis and vertebral axis, and insertion angle error were measured. In perforation cases, the angular tendency, insertion point, and length abnormality were evaluated.

RESULTS

The perforation was observed in 11% of Group C and 1.8% in Group N. In Group C, medial perforations of left screws were demonstrated in 8 of 9 perforated screws and 55% were distributed either in L1 or T12. The perforation consistently occurred in pedicles in which those axes approached anteroposterior sacral axis within 5 degrees . The average insertion errors were 8.4 degrees and 5.0 degrees in Group C and Group N, respectively, which were significantly different (P < 0.02).

CONCLUSION

The medial perforation in Group C occurred around L1, especially when pedicle axis approached anteroposterior sacral axis. This consistent tendency was considered as the limitation of fluoroscopic screw insertion in which horizontal vertebral image was not visible. The use of surgical navigation system successfully reduced the perforation rate and insertion angle errors, demonstrating the clear advantage in safe and accurate pedicle screw placement of scoliosis surgery.

Imaging assessment of lumbar pedicle screw placement: sensitivity and specificity of plain radiographs and computer axial tomography

STUDY DESIGN

This is a diagnostic study in which cadavers were evaluated by imaging and dissection after pedicle screw placement.

OBJECTIVE

This study was designed to evaluate the accuracy of plain radiographs and/or CT in determining pedicle instrumentation.

SUMMARY OF BACKGROUND DATA

One biomechanical advantage provided by pedicle screws fixation is improved fusion rates. The accuracy of pedicle screw placement has relied on radiograph and CT. Our goal is to evaluate the accuracy of these methods.

METHODS

Cadaveric lumbar spines were exposed by a posterior approach. Titanium pedicle screws were inserted. Radiographs and CTs were obtained. The spines were then dissected to examine screw location. A blinded examiner reviewed the imaging. Screws were considered misaligned if they were extrapedicular or had evidence of cortical perforation.

RESULTS

The sensitivity of radiographs, CT, and combined is 93.9%, 94%, and 98.7%, respectively. The specificity of radiograph, CT, and combined is 12.5%, 36.7%, and 40.7%, respectively. The positive predictive value for radiograph, CT, and combined is 83.2%, 88.1%, and 90.4%, respectively. The negative predictive value for radiograph, CT, and combined is 30.8%, 55.9%, and 84.6%, respectively. The accuracy of radiograph, CT, and combined is equal to 79.4%, 84.4%, and 90%, respectively.

CONCLUSION

Patients who present with significant complaints of pain or neurologic deficits, optimal determination of pedicle screw positions is with the combination of radiographs and CT. Furthermore, routine evaluation of patients' status post pedicle screw fixation can be reliable obtained with radiographs. The biomechanical advantage of pedicle screw fixation has improved fusion rates and diminished the number of levels required for stability. Despite the widespread clinical use of pedicle screw fixation, there is relatively little literature concerning accuracy. This study was designed to evaluate the accuracy of plain radiographs and/or CT in determining the proper position of pedicle screws.

Pullout resistance of thoracic extrapedicular screws used as a salvage procedure

BACKGROUND CONTEXT

Extrapedicular screws are placed more laterally than intrapedicular screws and pass through the transverse process or rib head before entering the vertebral body. These screws are sometimes placed to salvage failed pedicle screws, but the change in pullout resistance of extrapedicular screws after salvage has not been quantified.

PURPOSE

To quantify the pullout resistance of thoracic extrapedicular screws compared with intrapedicular screws and the pullout resistance of newly inserted screws compared with extrapedicular screws used as salvage for failed intrapedicular screws.

STUDY DESIGN

In vitro paired comparison of screw pullout resistance in isolated thoracic vertebrae.

METHODS

Tapered monoaxial pedicle screws were inserted in the left or right pedicle of 11 human cadaveric thoracic vertebrae. An extrapedicular screw was inserted on the contralateral side. Both screws were pulled out axially at 0.5 mm/s using a servohydraulic test frame while applied load was recorded. Then a fresh extrapedicular screw was inserted as a salvage screw on the intrapedicular screw side and pulled out.

RESULTS

In uncompromised vertebrae, the pullout strength of extrapedicular screws was 80+/-32% of that of intrapedicular screws (p=.073, repeated-measures one-way analysis of variance/Tukey). Salvage screws restored pullout strength to 65+/-30% of that of intrapedicular screws (p=.003).

CONCLUSIONS

Extrapedicular screws provided comparable but slightly lower pullout resistance to intrapedicular screws in uncompromised vertebrae. They are therefore a feasible salvage technique when a compromised pedicle precludes reinsertion of an intrapedicular screw, but the salvage screw is significantly weaker than the original screw.

Comparison of thoracic pedicle screw to hook instrumentation for the treatment of adult spinal deformity

STUDY DESIGN

Retrospective, case-control, matched cohort.

OBJECTIVE

Compare the radiographic and clinical outcomes of adult spinal deformity patients treated with thoracic pedicle screw (TPS) or thoracic hook constructs.

SUMMARY OF BACKGROUND DATA

The efficacy of TPS instrumentation for pediatric spinal deformity correction has been established. Little is known about TPS use in adult spinal deformity.

METHODS

Fifty-six patients (average age, 49 years; average follow-up, 3.58 years) were treated with TPS or thoracic hook constructs for coronal (n = 20) or sagittal (n = 36) plane deformities. Patients were evaluated radiographically and with SRS scores.

RESULTS

Coronal deformities treated with TPS demonstrated improved main thoracic curve correction compared with hook constructs at last follow-up (24.8 degrees vs. 13.8 degrees; P < 0.05), despite having larger (59.8 degrees vs. 44.9 degrees; P < 0.05) and more rigid preoperative curves (29.3% vs. 44.9% correction on side-bending radiographs; P < 0.001). Sagittal deformities treated with TPS constructs demonstrated greater thoracolumbar kyphosis correction than hook constructs at last follow-up (12.1 degrees vs. 2.5 degrees; P < 0.05). No TPS patient had a thoracic pseudarthrosis. Four hook patients (14%) had thoracic pseudarthroses.

CONCLUSIONS

TPS instrumentation allows greater coronal and sagittal plane correction and may reduce the risk of thoracic pseudarthrosis compared with hook constructs when treating adult spinal deformities.

Randomized clinical study to compare the accuracy of navigated and non-navigated thoracic pedicle screws in deformity correction surgeries

STUDY DESIGN

Randomized clinical trial (level I evidence).

OBJECTIVE

To compare the accuracy of non-navigation and Iso-C based navigation in pedicle screw fixation in thoracic spine deformities.

SUMMARY OF BACKGROUND DATA

Thoracic pedicle screw insertion for spinal deformity correction can be associated with increased pedicle breaches. Iso-C based navigation has been reported to improve the accuracy of pedicle screw placement, but its use in the presence of deformity has not been reported.

METHODS

Twenty-seven patients with scoliosis and 6 patients with kyphosis had a total of 478 thoracic pedicle screws. The average Cobb angle was 58.4 degrees +/- 8 degrees (range 50 degrees -80 degrees), and the mean kyphotic angle was 54.6 degrees +/- 4 degrees (range 51 degrees -76 degrees). By random allocation, 17 patients had screw insertion under navigation (242 screws) and 16 under fluoroscopic control (236 screws). The 2 groups were compared for accuracy of screw placement, time for screw insertion, and the number of times the C-arm had to be brought into the field. Two independent blinded observers determined accuracy using postoperative computed tomography assessments.

RESULTS

There were 54 (23%) pedicle breaches in the non-navigation group as compared to only 5 (2%) in the navigation group (P < 0.001). Thirty-eight screws (16%) in the non-navigation group had penetrated the anterior or lateral cortex compared to 2 screws (0.8%) in the navigation group. Average screw insertion time in the non-navigation group was 4.61 +/- 1.05 minutes (range 1.8-6.5) compared to 2.37 +/- 0.72 minutes (range 1.16-4.5) in navigation group (P < 0.01). The C-arm had to be moved into the operation field on an average of 1.5 +/- 0.25 times (range 1-3) per screw. With single screening data, an average of 11.4 pedicles (range 9-14) could be visualized without necessity to bring the C-arm into operating field again.

CONCLUSIONS

Iso-C navigation increases accuracy, and reduces surgical time and radiation in thoracic deformity correction surgeries.

Role of intraoperative Iso-C based navigation in challenging spine trauma

BACKGROUND

Pedicle screw fixation is the most preferred method of stabilizing unstable spinal fractures. Pedicle screw placement may be difficult in presence of fractured posterior elements, deformed spine, gross instability and spinal pathology. Challenging spine-fracture fixation is defined as the presence of one or more of the following: 1) obscured topographical landmarks as in ankylosing spondylitis, 2) fractures in occipitocervical or cervicothoracic regions and 3) preexisting altered spinal alignment. We report a series of pedicle screw insertion with guidance of navigation in difficult fixation problems..

MATERIALS AND METHODS

Fourteen patients [hangman's fracture (n=3), odontoid fracture (n=4), C1C2 fracture (n=1) and spinal fracture with coexistent ankylosing spondylitis (n=6)] underwent posterior stabilization. Intraoperatively after surgical exposure, images were acquired by Iso-C 3D C-arm and transferred to navigation system. Instrumentation was performed with navigational assistance. Postoperatively, placements of pedicle screws were evaluated with radiographs and CT scan.

RESULTS

Sixty-seven pedicle screws (cervical, n=33; thoracic, n=6; lumbar, n=26; sacral n=2) and 15 lateral mass screws were inserted with navigation guidance. The average time of image data acquisition by Iso-C 3D C-arm and its transfer to workstation was 4 minutes (range, 2-6 minutes). Postoperative CT scan revealed ideal placement of screws in 63 pedicles (94%), grade 1 cortical breaches (<2 mm) in 3 pedicles (4.5%) and grade 2 cortical breach (2-4 mm) in one pedicle (1.5%). There were no neurovascular complications. Deep infection was encountered in one case, which settled with debridement.

CONCLUSIONS

Intraoperative Iso-C 3D C-arm based navigation is a useful adjunct while stabilizing challenging spinal trauma, rendering feasibility, accuracy and safety of pedicle screw placement even in difficult situations.

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.

Selective posterior thoracic fusions for adolescent idiopathic scoliosis: comparison of hooks versus pedicle screws

STUDY DESIGN

A retrospective review of adolescent idiopathic scoliosis (AIS) patients with major thoracic-compensatory lumbar C modifier curves treated with a selective posterior fusion using an all-hook construct versus pedicle screw construct.

OBJECTIVES

To compare the clinical and radiographic results of selective posterior thoracic fusion using hooks versus pedicle screws in patients with major thoracic-compensatory lumbar C modifier AIS curves.

SUMMARY OF BACKGROUND DATA

Although spontaneous lumbar curve correction often occurs following a selective thoracic spinal fusion, there are few reports that focus on selective posterior thoracic spinal fusion in the presence of a lumbar C modifier curve.

METHODS

Sixty-six consecutive patients with major thoracic-compensatory lumbar C modifier AIS curves underwent selective posterior thoracic fusion to T12 or L1 at a single institution (1987-2001). Hooks were used for instrumentation in 32 patients and pedicle screws were used in 34 patients. Patients were evaluated at a minimum 2-year follow-up. To test for differences between groups analysis of covariance (ANCOVA) was used.

RESULTS

There was no statistical difference between the preoperative thoracic and lumbar Cobb values for the hook group versus the pedicle screw group. The amount of correction obtained surgically of the thoracic Cobb and the amount of spontaneous lumbar Cobb correction were significantly greater in the pedicle screw group (P < 0.001). The incidence of postoperative coronal decompensation, with a greater than 20 mm shift to the left of the C7 plumbline, was higher in the hook group (13 patients) as compared with the pedicle screw Group 4 patients (P < 0.005). There were no complications or reoperations in either group.

CONCLUSION

Selective thoracic fusion of main thoracic-compensatory lumbar C modifier AIS curves with pedicle screws allowed for better thoracic correction and less postoperative coronal decompensation than seen with hooks.

Anterior/posterior spinal instrumentation versus posterior instrumentation alone for the treatment of adolescent idiopathic scoliotic curves more than 90 degrees

STUDY DESIGN

A retrospective review of patients with adolescent idiopathic scoliosis (AIS), with curves more than 90 degrees treated with either a combined anterior/posterior spinal fusion or a posterior spinal fusion alone.

OBJECTIVES

To assess the results of spinal fusion for AIS curves >90 degrees and determine whether the use of a posterior-only approach with an all-pedicle screw construct can decrease the need for anterior release surgery.

SUMMARY OF BACKGROUND DATA

Treatment of AIS curves >90 degrees often consists of anterior release and posterior fusion to improve coronal correction and fusion rate. However, the use of pedicle screws has allowed improved coronal curve correction rates even in large curves, which may decrease the need for anterior release surgery.

METHODS

A total of 54 consecutive patients with AIS with curves >90 degrees who underwent a spinal fusion procedure at 1 institution between 1987 and 2001, with either a combined anterior/posterior spinal fusion (hooks and screws) or a posterior spinal fusion alone with an all-pedicle screw construct, were included for analysis. All patients had a minimum 2-year follow-up (mean 6.0; range 2.0-14.5), and were analyzed radiographically as well as with pulmonary function tests. Statistical analyses were performed between groups using the Wilcoxon-Mann-Whitney tests.

RESULTS

There were 20 patients treated with an anterior/posterior spinal fusion and 34 with a posterior spinal fusion alone. There were no statistically significant differences between the groups for gender, age, number of levels fused, preoperative coronal/sagittal Cobb measurements, coronal curve flexibility, or amount of postoperative coronal Cobb correction. There was less of a negative effect on pulmonary function in the group treated with posterior spinal fusion versus the group treated with a combined anterior/posterior spinal fusion (P < 0.005). There were no complications/reoperations in either group.

CONCLUSION

In this patient population with often restrictive preoperative pulmonary function, a posterior-only approach with the use of an all-pedicle screw construct has the advantage of providing the same correction as an anterior/posterior spinal fusion, without the need for entering the thorax and more negatively impacting pulmonary function.

Esophageal injury from thoracic pedicle screw placement in a polytrauma patient: a case report and literature review

The authors present a case report illustrating a visceral complication that may occur as result of thoracic pedicle screw placement. The case describes the previously unreported occurrence of esophageal impingement secondary to anterior vertebral body perforation by a pedicle screw at the third thoracic vertebra. This case highlights the challenge of thoracic pedicle screw placement and the importance of preoperatively measuring the maximum anterior-posterior dimension of the vertebral body.

A novel "four-rod technique" for lumbo-pelvic reconstruction: theory and technical considerations

STUDY DESIGN

Surgical technique with case example.

OBJECTIVE

To report on a novel technique that allows for the placement of 4 separate longitudinal rods across the lumbo-pelvic junction.

SUMMARY OF BACKGROUND DATA

Despite advances in surgical techniques and instrumentation, lumbo-pelvic fixation remains a significant challenge. Fusions to the pelvis create long lever arms and generate high forces across the lumbosacral junction, resulting in high rates of screw pullout and implant fracture. In the attempt to achieve better bony fixation, techniques described include the use of bone cement, hydroxyapatite, and expandable screws. Although this process has decreased the incidence of screw pullout, it has not addressed the problem of rod fracture at the lumbo-pelvic junction.

METHOD

There are 4 separate longitudinal rods placed across the lumbo-pelvic junction that couples proximal lumbar screw anchors to 4 separate pelvic fixation points. Proximal lumbar fixation anchors are based on alternating Roy-Camille "straight ahead" screws and Magerl "lateral to medial converging" pedicle screws. There are 4 distal pelvic fixation anchors used based on 1 pair of Galveston-like screws and 1 pair of proximal iliac wing screws.

RESULTS

Early results of both ex vivo and in vivo reconstruction show that careful insertion of the lumbar and pelvic screws allows for divergent placement of the pedicle screw heads in a manner that 2 longitudinal rods can be placed per side, resulting in a total of 4 longitudinal rods across the lumbo-pelvic junction. Selection of cross-links in various combinations allows for additional axial and torsional stability, depending on the desired reconstruction.

CONCLUSION

Longer follow-up is necessary, and biomechanical and finite element studies are needed to show long-term efficacy of this technique, however, early results indicate that such a construct is feasible. Furthermore, depending on the general medical condition of the patient, immediate postoperative weight bearing is possible and reasonable.

Surgical complications of posterior lumbar interbody fusion with total facetectomy in 251 patients

OBJECT

Previous studies of surgical complications associated with posterior lumbar interbody fusion (PLIF) are of limited value due to intrastudy variation in instrumentation and fusion techniques. The purpose of the present study was to examine rates of intraoperative and postoperative complications of PLIF using a large number of cases with uniform instrumentation and a uniform fusion technique.

METHODS

The authors reviewed the hospital records of 251 patients who underwent PLIF for degenerative lumbar disorders between 1996 and 2002 and who could be followed for at least 2 years. Intraoperative, early postoperative, and late postoperative complications were investigated. Intraoperative complications occurred in 26 patients: dural tearing in 19 patients and pedicle screw malposition in seven patients. Intraoperative complications did not affect the postoperative clinical results. Early postoperative complications occurred in 19 patients: brain infarction occurred in one, infection in one, and neurological complications in 17. Of the 17 patients with neurological complications, nine showed severe motor loss such as foot drop; the remaining eight patients showed slight motor loss or radicular pain alone, and their symptoms improved within 6 weeks. Late postoperative complications occurred in 17 patients: hardware failure in three, nonunion in three, and adjacent-segment degeneration in 11. Postoperative progression of symptomatic adjacent-segment degeneration was defined as a condition that required additional surgery to treat neurological deterioration.

CONCLUSIONS

The most serious complications of PLIF were postoperative severe neurological deficits and adjacent-segment degeneration. Prevention and management of such complications are necessary to attain good long-term clinical results.

Residual mobility of instrumented and non-fused segments in thoracolumbar spine fractures

The surgical management of thoracolumbar fractures presents potential benefits. However, the surgery solve the instability by fusion of mobile segments. We incorporate in our treatment algorithms, the use of restricted arthrodesis at injured levels, regardless of longer instrumentations, as well as the use of non-fused transitory stabilizations, based on the conviction that in non-fused segments without traumatic disc injury, mobility persists once the instrumentation is removed. The goals of this study were to compare the mobility of non-fused segments after hardware removal to a normal range of motion and to find prognostic pre-op imaging patterns. We reviewed 21 consecutive patients who underwent surgery with preservation of mobile segments (non-fused segments included in the construction) in order to recover mobility after removal of instrumentation, performed between 1995 and 2001. All patients were treated by indirect reduction with posterior transpedicular instrumentation. Clinical and radiological outcome was analyzed after an average follow-up of 46.6 months. Satisfactory subjective outcome results were obtained in 94.7%. The dynamic radiological follow-up study showed 75% (21 segments) with normal or decreased range of motion (ROM) and 25% (7 segments) without mobility. The non-fused segments with hardware removal before 10 months of evolution presented a normal or decreased mobility in 83.2% while the segments with hardware removal after 10 months showed 68.8% of mobility. The intervertebral disc (IVD)'s with normal initial MRI morphology preserved their mobility in 81.9%. Complications occurred in four patients: two superficial wound infections and two patients presented a late fracture of one USS Schanz. The results of this study prove that in thoracolumbar fractures, non-fused spinal segments included in pedicular instrumentation maintained mobility in a high percentage once the hardware is removed. 75% of the segments presented a normal or decreased ROM.

Comparative analysis of pedicle screw versus hybrid instrumentation in posterior spinal fusion of adolescent idiopathic scoliosis

STUDY DESIGN

A retrospective matched cohort study.

OBJECTIVE

To comprehensively compare the 2-year postoperative results of posterior correction and fusion with segmental pedicle screw instrumentation versus with hybrid (proximal hooks and distal pedicle screws) constructs in adolescent idiopathic scoliosis (AIS) treated at a single institution.

SUMMARY OF BACKGROUND DATA

Despite the reports of satisfactory correction and maintenance of scoliotic curves by pedicle screw instrumentation, there have been no reports on the comprehensive comparison of AIS treatment after segmental pedicle screw instrumentation versus hybrid instrumentation.

MATERIALS AND METHODS

A total of 58 AIS patients that underwent posterior fusion with hybrid instrumentation (29) or pedicle screw (29) instrumentation at a single institution were sorted and matched according to four criteria: similar patient age, fusion levels, identical Lenke curve type, and identical operative methods. Patients were compared at 2-year follow-up according to radiographic changes, operative time, intraoperative blood loss, pulmonary function tests, and SRS-24 outcome scores.

RESULTS

The two cohorts were well matched. The preoperative major Cobb angle averaged 62 degrees in the screw group and 60 degrees in the hybrid group. Average major curve correction was 70% in the screw group and 56% in the hybrid group (P = 0.001). At 2-year follow-up, major curve correction was 65% and 46%, respectively (P < 0.001). At 2-year follow-up, thoracic sagittal Cobb angle changes between T5 and T12 were 9.0 degrees decrease in the screw group and 2.4 degrees decrease in the hybrid group compared with preoperative (P = 0.024). There were no differences in the lowest instrumented vertebra below the lower end vertebra (P = 0.56), operative time (P = 0.14), and average estimated blood loss (P = 0.54). Two years following surgery, the screw group demonstrated improved percent predicted pulmonary function values compared with that of the hybrid group (FVC; 81% --> 81% in screw group vs. 85% --> 79% in hybrid group P = 0.08, FEV1; 73% --> 79% in screw group vs. 79% --> 75% in hybrid group, P = 0.006). Postoperative total SRS-24 scores were similar in both groups (hybrid group: 99 vs. screw group: 95) (P = 0.19). There were no neurologic complications related to hybrid or pedicle screw instrumentation.

CONCLUSION

Pedicle screw instrumentation offers a significantly better major curve correction and postoperative pulmonary function values without neurologic problems compared with hybrid constructs. Both instrumentation methods offer similar junctional change, lowest instrumented vertebra, operative time, and postoperative SRS-24 outcome scores in the operative treatment of AIS.