Comparative results between conventional and computer-assisted pedicle screw installation in the thoracic, lumbar, and sacral spine

Computer Assisted Pelvic Surgery: Registration Based on a Modified External Fixator

A fundamental step in Computer Assisted Surgery (CAS) is the registration, when the preoperative virtual data and the corresponding operative anatomy of the region of interest are merged. To provide exact landmarks for anatomical registration, a tubular external fixator was modified. Two intact pelvic bones (one artificial foam pelvis and one cadaver specimen) were used for the experimental setup. Registration was carried out using a standardized protocol for anatomy-based registration in the control group; anatomical registration was achieved using a modified external fixator in the study group. This external fixator had titanium fiducials wedged into the fixator carbon tubes serving as landmarks for paired-point registration. The tubes were used for surface registration. The standard anterior pelvis fixator assembly was augmented with additional bilateral tubes oriented towards the posterior, enabling registration of the sacroiliac areas. The accuracy of registration was checked by "reversed verification", where the examiner used only the screen display to control the virtual position of the pointer tip in relation to selected landmarks. By virtual matching, the real distance was measured with a digital caliper. We defined the verification as "accurate" when the residual distance was less than 1 mm; "acceptable" when it was between 1 mm and 2 mm; and "insufficient" when it exceeded 2 mm. The paired T-test with significance levels of p < 0.05 was used for statistical analysis. The anatomical registration based on the external fixator landmarks was statistically as accurate as that obtained using anatomical landmarks on the pelvic bone. This study concludes that the external fixator, a conventional tool in the management of acute traumatic pelvic instability, can also be useful for landmark registration in CAS.

Functional outcome of computer-assisted spinal pedicle screw placement: a systematic review and meta-analysis of 23 studies including 5,992 pedicle screws

A number of studies have shown increased accuracy of pedicle screw placement in spine with the help of computer-assisted navigation. The literature is lacking in regard to functional benefit derived from this technique. The aim of this systematic review was to look at the functional outcomes following computer-assisted pedicle screw placement in spine. A 'Dialog Datastar' search was used using optimized search strategy covering the period from 1950 to July 2009; 23 papers were finally included which met our inclusion criteria. We report on a total of 1,288 patients with 5,992 pedicle screws. The comparison of neurological complications in two groups demonstrated an odds ratio of 0.25 (95% CI 0.06, 1.14) in favour of using navigation for pedicle screw insertion (p = 0.07). Comparative trials demonstrated a significant advantage in terms of accuracy of navigation over conventional pedicle screw insertion with a relative risk of 1.12 (95% CI 1.09, 1.15) (p < 0.00001). Navigation does not show statistically significant benefit in reducing neurological complications and there was insufficient data in the literature to infer a conclusion in terms of fusion rate, pain relief and health outcome scores.

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.

Universal Clamp system in thoracolumbar spinal fixation: technical note

BACKGROUND

The Universal Clamp is a polyester band passed under the lamina and connected to a rod by a titanium clamp that has been recently reported as an alternative for replacing screws and hooks for thoracolumbar spinal diseases. To date, there is no report of an evaluation of the effectiveness and safety of posterior fixation and fusion using this technique.

METHODS

This study was a prospective evaluation of a cohort of 18 patients with thoracolumbar disorders that were surgically treated between November 2006 and June 2007 with Universal Clamps for spinal fixation. Fifteen cases were traumatic fractures with others two with degenerative severe stenosis and one kyphotic stenosis. Levels treated were thoracolumbar in 15 cases, thoracic in two cases, and lumbar in one case. Seventeen patients underwent correction and instrumentation using a hybrid construct of screws and clamps, while one patient underwent fixation using Universal Clamps only. Intraoperative evoked potentials were monitored in all cases. One patient had infection that resolved after antibiotic therapy without implant removal. No neurological adverse event was seen. There was no rod breakage or clamp loosening during a follow-up of 12 months.

CONCLUSIONS

The polyester band is soft and flexible, and the anterior-posterior spinal canal space occupied by the band is less than by sublaminar wire steel cable, thus avoiding direct spinal cord trauma during sublaminar passage. The flat configuration of the cable distributes the load over a larger contact area under the lamina compared to metal wires without producing imaging artefacts in postoperative imaging. This preliminary report demonstrates the efficacy and safety of this technique for the stabilization of thoracolumbar spinal disorders.

Joint-preserving limb salvage surgery under navigation guidance

BACKGROUND

Recently, the navigation system has been introduced to orthopedic oncology. It can apply MRI and/or CT images to intraoperative visualization. We performed navigation-assisted limb salvage surgeries on patients with a malignant bone tumor of the metaphysis of the long bone or the iliac bone while preserving the adjacent joint.

METHODS

When preoperative chemotherapy was estimated to be effective by imaging studies and the residual remaining epiphysis was expected to be more than 1 cm long after tumor resection with 1-2 cm of surgical margin, joint-preserving surgery was performed under navigation guidance. We carried out CT and MRI data fusion to use MR images as an intraoperative guide. A deep frozen strut allograft was placed in the defect for the restoration of anatomical continuity.

RESULTS

Resection margin measured on pathological examination was in accordance with that of the preoperative plan. The functional scores of all patients were satisfactory. There was no evidence of recurrence on the regional radiographs and CT on the chest until the last follow-up.

CONCLUSION

Navigation-assisted surgery can be indicated for limb salvage and it can help to preserve the adjacent joint in selected cases.

Evaluation of thoracic pedicle screw placement in adolescent idiopathic scoliosis

Pedicle screw fixation is a challenging procedure in thoracic spine, as inadvertently misplaced screws have high risk of complications. The accuracy of pedicle screws is typically defined as the screws axis being fully contained within the cortices of the pedicle. One hundred and eighty-five thoracic pedicle screws in 19 patients that were drawn from a total of 1.797 screws in 148 scoliosis patients being suspicious of medial and lateral malpositioning were investigated, retrospectively. Screw containment and the rate of misplacement were determined by postoperative axial CT sections. Medial screw malposition was measured between medial pedicle wall and medial margin of the pedicle screw. The distance between lateral margin of the pedicle screw and lateral vertebral corpus was measured in lateral malpositions. A screw that violated medially greater than 2 mm, while lateral violation greater than 6 mm was rated as an "unacceptable screw". The malpositions were medial in 20 (10.8%) and lateral in 34 (18.3%) screws. Medially, nine screws were rated as acceptable. Of the 29 acceptable lateral misplacement, 13 showed significant risk; five to aorta, six to pleura, one to azygos vein and one to trachea. The acceptability of medial pedicle breach may change in each level with different canal width and a different amount of cord shift. In lateral acceptable malpositions, the aorta is always at a risk by concave-sided screws. This CT-based study demonstrated that T4-T9 concave segments have a smaller safe zone with respect to both cord-aorta injury in medial and lateral malpositions. In these segments, screws should be accurate and screw malposition is to be unacceptable.

Image-guided pedicle screw insertion accuracy: a meta-analysis

Improved pedicle screw insertion accuracy has been reported with the assistance of computer tomography-based navigation. Studies also indicated that fluoroscopy-based navigation offers high accuracy and is comparable to CT-based assistance. However, different population characteristics and assessment methods resulted in inconsistent conclusions. We searched OVID, Springer, and MEDLINE databases to conduct a meta-analysis of the published literature specifically looking at accuracy of pedicle screw placement with different navigation methods. Subgroups and descriptive statistics were determined based on the subject type (in vivo or cadaveric), navigational method, and spinal level. A total number of 7,533 pedicle screws were summarised in our database with 6,721 screws accurately inserted into the pedicles (89.22%). Overall, the median placement accuracy for the in vivo CT-based navigation subgroup (90.76%) was higher than that with the use of two-dimensional (2D) fluoroscopy-based navigation (85.48%). We concluded that CT-based navigation could provide a higher accuracy in the placement of pedicle screws for all subgroups presented. In the lumbar level, 2D fluoroscopy-based navigation was comparable with CT-based navigation. Discrepancy between the two navigation types increased in the thoracic level for the in vivo populations, where there was less potential in the use of 2D fluoroscopy-based navigation than CT-based navigation.

Computer-assisted pelvic tumor resection: fields of application, limits, and perspectives

The treatment of malignant tumors involving the pelvic area is a challenging problem in musculoskeletal oncology due to the complex pelvic anatomy and the often large tumor size at presentation. The use of navigation systems has effectively increased surgical precision aiming at optimal preservation of pelvic structures without compromising oncologic outcome by means of improved visibility of the surgical field, and enabling intraoperative display and 3D reproduction of preoperatively determined pelvic osteotomy and resection levels. In the following sections, current developments in computer-assisted pelvic surgery are reviewed and possible fields of application, as well as limitations of navigation systems, are discussed.

Real time noninvasive assessment of external trunk geometry during surgical correction of adolescent idiopathic scoliosis

Background

The correction of trunk deformity is crucial in scoliosis surgery, especially for the patient's self-image. However, direct visualization of external scoliotic trunk deformity during surgical correction is difficult due to the covering draping sheets.

Methods

An optoelectronic camera system with 10 passive markers is used to track the trunk geometry of 5 scoliotic patients during corrective surgery. The position of 10 anatomical landmarks and 5 trunk indices computed from the position of the passive markers are compared during and after instrumentation of the spine.

Results

Internal validation of the accuracy of tracking was evaluated at 0.41 +/- 0.05 mm RMS. Intra operative tracking during surgical maneuvers shows improvement of the shoulder balance during and after correction of the spine. Improvement of the overall patient balance is observed. At last, a minor increase of the spinal length can be noticed.

Conclusion

Tracking of the external geometry of the trunk during surgical correction is useful to monitor changes occurring under the sterile draping sheets. Moreover, this technique can used be used to reach the optimal configuration on the operating frame before proceeding to surgery. The current tracking technique was able to detect significant changes in trunk geometry caused by posterior instrumentation of the spine despite significant correction of the spinal curvature. It could therefore become relevant for computer-assisted guidance of surgical maneuvers when performing posterior instrumentation of the scoliotic spine, provide important insights during positioning of patients.

Pneumothorax complicating "in-out-in" thoracic pedicle screw placement for kyphotic deformity correction in a child

The authors describe a rare case of pneumothorax as a complication of thoracic pedicle screw placement in an 11-year-old girl undergoing posterior segmental instrumentation for a kyphotic deformity. Spontaneous pneumothorax after posterior fusion for adolescent idiopathic scoliosis has been reported in the orthopedic literature; however, to the best of the authors' knowledge, pneumothorax directly related to pedicle screw placement for spinal deformity has not been previously described. The authors discuss the anatomical and technical aspects leading to this complication and the lessons learned from it.

Transpedicular screw fixation in the thoracic and lumbar spine with a novel cannulated polyaxial screw system

Objective:

Transpedicular screws are commonly and successfully used for posterior fixation in spinal instability, but their insertion remains challenging. Even using navigation techniques, there is a misplacement rate of up to 11%. The aim of this study was to assess the accuracy of a novel pedicle screw system.

Methods:

Thoracic and lumbar fusions were performed on 67 consecutive patients for tumor, trauma, degenerative disease or infection. A total of 326 pedicular screws were placed using a novel wire-guided, cannulated, polyaxial screw system (XIA Precision^®, Stryker). The accuracy of placement was assessed postoperatively by CT scan, and the patients were followed-up clinically for a mean of 16 months.

Results:

The total medio-caudal pedicle wall perforation rate was 9.2% (30/326). In 19 of these 30 cases a cortical breakthrough of less than 2 mm occurred. The misplacement rate (defined as a perforation of 2 mm or more) was 3.37% (11/326). Three of these 11 screws needed surgical revision due to neurological symptoms or CSF leakage. There have been no screw breakages or dislocations over the follow up-period.

Conclusion:

We conclude that the use of this cannulated screw system for the placement of pedicle screws in the thoracic and lumbar spine is accurate and safe. The advantages of this technique include easy handling without a time-consuming set up. Considering the incidence of long-term screw breakage, further investigation with a longer follow-up period is necessary.

Accuracy and safety of pedicle screw placement in neuromuscular scoliosis with free-hand technique

It is a retrospective analytic study of 1,009 transpedicular screws (689 thoracic and 320 lumbosacral), inserted with free-hand technique in neuromuscular scoliosis using postoperative CT scan. The aim of paper was to determine the accuracy and safety of transpedicular screw placement with free-hand technique in neuromuscular scoliosis and to compare the accuracy at different levels in such population. All studies regarding accuracy and safety of pedicle screw in scoliosis represent idiopathic scoliosis using various techniques such as free-hand, navigation, image intensifier, etc., for screw insertion. Anatomies of vertebrae and pedicle are distorted in scoliosis, hence accurate and safe placement of pedicle screw is prerequisite for surgery. Between 2004 and 2006, 37 consecutive patients, average age 20 years (9-44 years), of neuromuscular scoliosis were operated with posterior pedicle screw fixation using free-hand technique. Accuracy of pedicle screws was studied on postoperative CT scan. Placement up to 2 mm medial side and 4 mm lateral side was considered within-safe zone. Of the 1,009 screws, 273 screws were displaced medially, laterally or on the anterior side showing that 73% screws (68% in thoracic and 82.5% in lumbar spine) were accurately placed within pedicle. Considering the safe zone, 93.3% (942/1009, 92.4% in thoracic and 95.3% in lumbar spine) of the screws were within the safe zone. Comparing accuracy according to severity of curve, accuracy was 75% in group 1 (curve <90 degrees ) and 69% in group 2 (curve >90 degrees) with a safety of 94.8 and 91.2%, respectively (P = 0.35). Comparing the accuracy at different thoracic levels, it showed 67, 64 and 72% accuracy in upper, middle and lower thoracic levels with safety of 96.6, 89.2 and 93.1%, respectively, exhibiting no statistical significant difference (P = 0.17). Pedicle screw placement in neuromuscular scoliosis with free-hand technique is accurate and safe as other conditions.

SEGMENTAL SPINAL INSTRUMENTATION IN THE MANAGEMENT OF SCOLIOSIS

SPINAL INSTRUMENTATION FOR the correction of spinal deformity began with Harrington and his rod system. The use of the Harrington rods was limited, however, because of the need for long-segment instrumentation, distraction, and the potential for hood dislodgment and construct failure. Luque subsequently introduced the next generation of spinal fixation techniques via the concept of segmental instrumentation; his use of sublaminar wires allowed the construct to be fixated to the spine at every level. This arrangement allowed greater control over correction of spinal deformities and significantly lessened the incidence of hardware dislodgment. Modern instrumentation systems, including the use of pedicle screws, permit even greater control of the spine in multiple planes during deformity correction. Newer strategies have decreased the incidence of neurological injury during implant application and provide greater stability. A review of segmental fixation, including surgical techniques, is provided in this article.

Financial analysis of circumferential fusion versus posterior-only with thoracic pedicle screw constructs for main thoracic idiopathic curves between 70 degrees and 100 degrees

PURPOSE

Reports on thoracic pedicle screw (TPS) constructs have demonstrated their safety and efficacy; however, concerns exist regarding their increased cost. This is a review of adolescents with main thoracic scoliosis surgically treated with anterior release and posterior fusion or posterior fusion only. The objectives were to compare the radiographic outcomes and financial data of two surgical treatments: anterior/posterior spinal fusion (APSF) versus posterior spinal fusion (PSF-TPS) alone with TPSs, in patients with large 70-100 degrees main thoracic adolescent idiopathic scoliosis (AIS) curves.

METHODS

We identified 43 patients with main thoracic Lenke type 1-4 AIS curves between 70 and 100 degrees who had been treated with either APSF or PSF-TPS.

RESULTS

Both groups had equivalent radiographic corrections postoperatively. The PSF-TPS group patients had higher implant charges, but the APSF group had higher surgeon procedural charges, operating room charges, anesthesia charges, and inpatient room charges. Total charges were $75,295 for the APSF group and $71,236 for the PSF-TPS group (P > 0.05). Analyses of two subgroups of the APSF group, anterior release via thoracotomy versus VATS and same-day versus staged surgeries, failed to change any of the above findings.

CONCLUSION

Based on this financial analysis, there was no statistically significant differences between the APSF and PSF-TPS groups, with equivalent radiographic corrections.

A CT-free, intra-operative planning and navigation system for minimally invasive anterior spinal surgery - an accuracy study

OBJECTIVE

A comprehensive study was performed to evaluate the accuracy of a newly developed CT-free, intra-operative planning and navigation system for anterior spine surgery.

MATERIALS AND METHODS

Instruments and an image intensifier were tracked using the SurgiGATE navigation system. A laboratory study was performed on 27 plastic vertebrae. Fiducial markers were implanted in the vertebrae for accuracy evaluation purposes, and a dynamic reference base was placed on the vertebrae to establish a patient coordinate system (P-COS). Two fluoroscopic images were used for intra-operative planning. The graft bed plan was recorded in P-COS, followed by surgical formation of the graft bed, which was visualized. To evaluate the accuracy, the vertebrae were scanned with CT, and the markers were used to calculate an accurate paired-point registered transformation between the CT coordinate system and P-COS.

RESULTS

Using the new SPO module, accurate planning and navigation of a resection of the vertebral body is possible using two fluoroscopic images. The overall mean error between the planned resection volume and the actual resection was 0.98 mm. In addition, the module can serve as an educational tool for training spine surgeons.

CONCLUSIONS

The new fluoroscopy-based system can be used safely for accurate performance of anterior resection during spondylodesis. New methods for safe and accurate registration during anterior spine surgery need to be developed.

Computer-assisted pedicle screw placement for thoracolumbar spine fracture with separate spinal reference clamp placement and registration

BACKGROUND

The objective of the study was to improve the accuracy of computer-assisted pedicle screw installation in the spine. This study evaluates the accuracy of computer-assisted pedicle screw placement with separate spinal reference clamp placement and registration on each instrumented vertebra for thoracolumbar spine fractures.

METHODS

Postoperative radiographs and CT scans assessed the accuracy of pedicle screw placement in 21 adult patients on each instrumented vertebra. Screw placements were graded as good if the screws were placed in the central core of the pedicle and the cancellous portion of the body. Screw placements were graded as fair if the screws were placed slightly eccentrically, causing erosion of the pedicular cortex, and with less than a 2-mm perforation of the pedicular cortex. Screw placements were graded as poor if screws were placed eccentrically with a large portion of the screw extending outside the cortical margin of the pedicle and with more than a 2-mm perforation of the pedicular cortex.

RESULTS

A total of 140 image-guided pedicle screws were placed in 21 patients: 78 in the thoracic and 62 in the lumbar spine. Of the 140 pedicle screw placements, 96.4% (135/140) were categorized as good; 3.6% (5/140), fair; and 0% were poor. All 5 fair placement screws were placed in the thoracic spine without any mobility.

CONCLUSION

Separate registration increases accuracy of screw placement in thoracolumbar pedicle instrumentation. Separate spinal reference clamp placement in the instrumented vertebra provides real-time virtual imaging that decreases the possibility of downward displacement during manual installation of the screw.

Current concepts and applications of computer navigation in orthopedic trauma surgery

Navigation has become widely integrated into regular endoprosthetic procedures, but clinical use of navigation systems in orthopaedic trauma has only been implemented in a few indications. Navigation systems enable an accuracy of 1 mm or 1 degree. Navigation can achieve higher precision when it is combined with different imaging modalities, including preoperative computer tomography (CT), intraoperative CT, two-dimensional fluoroscopy, and, recently, intraoperative three-dimensional fluoroscopy. The precision of the navigation system can be influenced by the surgeon as well as by the camera system, type of reference marker, and the registration process. Recent developments in orthopedic trauma navigation allow for bilateral femoral anteversion measurements, noninvasive registration of an uninjured thigh, and intraoperative three-dimensional fluoroscopy-based pedicle screw placement. Although the use of navigation has provided initial positive results in trauma care, prospective clinical studies remain to be performed.

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.

Fluoroscopy-based navigation system in spine surgery

The variability in width, height, and spatial orientation of a spinal pedicle makes pedicle screw insertion a delicate operation. The aim of the current paper is to describe a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and three-dimensional optical localizers in order to reduce radiation exposure while increasing accuracy and reliability of the surgical procedure for pedicle screw insertion. Instrumentation using transpedicular screw fixation was performed: in a first group, a conventional surgical procedure was carried out with 26 patients (138 screws); in a second group, a navigated surgical procedure (virtual fluoroscopy) was performed with 26 patients (140 screws). Evaluation of screw placement in every case was done by using plain X-rays and post-operative computer tomography scan. A 5 per cent cortex penetration (7 of 140 pedicle screws) occurred for the computer-assisted group. A 13 per cent penetration (18 of 138 pedicle screws) occurred for the non computer-assisted group. The radiation running time for each vertebra level (two screws) reached 3.5s on average in the computer-assisted group and 11.5s on average in the non computer-assisted group. The operative time for two screws on the same vertebra level reaches 10 min on average in the non computer-assisted group and 11.9 min on average in the computer-assisted group. The fluoroscopy-based (two-dimensional) navigation system for pedicle screw insertion is a safe and reliable procedure for surgery in the lower thoracic and lumbar spine.

Complications of thoracic pedicle screws in scoliosis treatment

STUDY DESIGN

A retrospective study.

OBJECTIVE

To analyze complications with thoracic pedicle screws in scoliosis treatment at our Department over a 3-year period (1999-2001).

SUMMARY OF BACKGROUND DATA

The use of pedicle screws remains controversial for thoracic scoliosis for fear of complications.

METHODS

A total of 115 consecutive patients who underwent posterior fusion using 1035 transpedicular thoracic screws were reviewed. All patients presented a main thoracic scoliosis with a mean Cobb angle of 75.4 degrees (range, 60 degrees -105 degrees ). For thoracic screw placement, a mini-laminotomy technique was used, inserting a spatula inside the vertebral canal to palpate the borders of the pedicle. Postoperative CT scan was used in 25 patients (21.7%) to study a total of 311 screws, when the screw position was questionable.

RESULTS

An independent spine surgeon retrospectively reviewed medical records and radiographs of the patients, at a mean follow-up of 4 years. There were 18 screws misplaced (1.7%) in a total of 13 patients (11.3%). Screw malposition was symptomatic only in 1 patient (pleural effusion and fever) and asymptomatic in the other 12 cases (10.4%). Other complications included intraoperative pedicle fractures in 15 patients (13%), dural tears (without neurologic complications) in 14 cases (12.1%), and superficial wound infections in 2 (1.7%). Another operation for screw removal was performed in 5 patients (4.3%), due to pleural effusion (in 1 case), asymptomatic late lateral loosening of a malpositioned screw (in 1), and the possible future risks related the intrathoracic screw position despite the lack of any symptoms (in 3). Two cases (1.7%) were retreated due to wound infection, without removing instrumentation. There was no loss of correction at follow-up.

CONCLUSIONS

The thoracic pedicle screw placement in scoliosis patients requires utmost caution. The mini-laminotomy technique was beneficial in increasing safety of the procedure with an acceptable incidence of complications.

Minimally invasive spine surgery: a historical perspective

Minimally invasive spine surgery has gained considerable momentum and increased acceptance among spine surgeons throughout the years. An understanding and awareness of the development of minimally invasive spine surgery and its role in the operative treatment of various spine conditions is imperative. This article provides a succinct historical perspective of the development of spine surgery from the more traditional, open procedures to the use of more "minimal access" or minimally invasive spine surgery procedures.

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.

Image-guided spinal surgery

BACKGROUND

The purpose of this review is to present a comprehensive summary of commonly used methods of spinal image guidance, including the benefits and limitations of this novel technology.

METHODS

The relevant medical literature was examined, supplemented by the author's laboratory and clinical experience with image-guided spinal surgery.

RESULTS

Spinal image guidance has undergone significant evolution and rapid technological advancement in recent years. Image guidance provides three-dimensional visualization of the spine that can be used for preoperative planning and intraoperative navigation. There are three commonly used methods of spinal image guidance: preoperative CT-based, fluoroscopy-based, and 3D fluoroscopy. Each of these methods demonstrates lower rates of spinal implant misplacement than non-image-guided techniques.

CONCLUSIONS

Image guidance provides highly accurate intraoperative navigation and the medical literature suggests that this technology increases the safety of a variety of routine and complex spinal procedures.

A new mechatronic assistance system for the neurosurgical operating theatre: implementation, assessment of accuracy and application concepts

OBJECTIVE

To introduce a new robotic system to the field of neurosurgery and report on a preliminary assessment of accuracy as well as on envisioned application concepts. Based on experience with another system (Evolution 1, URS Inc., Schwerin, Germany), technical advancements are discussed.

MATERIAL/METHODS

The basic module is an industrial 6 degrees of freedom robotic arm with a modified control element. The system combines frameless stereotaxy, robotics, and endoscopy. The robotic reproducibility error and the overall error were evaluated. For accuracy testing CT markers were placed on a cadaveric head and pinpointed with the robot's tool tip, both fully automated and telemanipulatory. Applicability in a clinical setting, user friendliness, safety and flexibility were assessed.

RESULTS

The new system is suitable for use in the neurosurgical operating theatre. Hard- and software are user-friendly and flexible. The mean reproducibility error was 0.052-0.062 mm, the mean overall error was 0.816 mm. The system is less cumbersome and much easier to use than the Evolution 1.

CONCLUSIONS

With its user-friendly interface and reliable safety features, its high application accuracy and flexibility, the new system is a versatile robotic platform for various neurosurgical applications. Adaptations for different applications are currently being realized.

[Percutaneous dorsal versus open instrumentation for fractures of the thoracolumbar border. A comparative, prospective study]

STUDY DESIGN

A prospective clinical study.

OBJECTIVE

To evaluate whether a percutaneous dorsal instrumentation of thoracolumbar fractures prevents irreversible damage to the spinal muscles.

METHODS

A total of 57 patients with thoracolumbar fractures (Th12-L4) were divided into two groups, comparable in terms of gender, fracture level, classification and surgical concept. In the first, 24/57 patients were treated using an open procedure (OP-G); in the second, 33/57 were treated via percutaneous dorsal instrumentation (PER-G). Fracture localisation and classification, accuracy of pedicle screw placement, perioperative blood loss, OR- and image converter time as well as muscle damage (needle-EMG) were evaluated.

RESULTS

OR- and image converter time as well as the accuracy of pedicle screw placement were not statistically different between groups. The difference in perioperative blood loss [43 (10-90) ml (PER-G) vs [870 (570-1,200 ml (OP-G)] was statistically significant (P <0.005). Needle EMG revealed no muscle damage, and the physiological activity and muscle potentials were normal (PER-G). In the OP-G, polyphasic EMG signals were most common (80%), a sign of the drop-out of numerous motor units.

CONCLUSIONS

The open procedure caused permanent and significant damage to the strongest extensors of the autochthonus back musculature, the m. multifidus, which results from multisegment combined damage to the r. posterior nervi spinalis and muscle fibres. In contrast, percutaneous placement of an internal fixative reduces perioperative access morbidity causing little iatrogenic damage to back muscles and only a minor perioperative blood loss.

Pedicle screw insertion: computed tomography versus fluoroscopic image guidance

Computed tomography image-guided surgery (CTGS) clearly improves the accuracy of pedicle screw insertion. Recent reports claim that a fluoroscopy-guided system (FGS) offered high accuracy and easy application. However, the superiority of either technique remains unclear in clinical application. This study compares the accuracy of pedicle screws installed using CTGS with that of screws installed using FGS. Seventy-four screws inserted using FGS in 13 patients and 76 screws inserted using CTGS in 11 patients were compared. The study population included ten cases of vertebral fracture, five cases of degenerative spondylolisthesis, three cases of spondylolytic spondylolisthesis, two cases of tuberculous spondylitis, two cases of failed earlier back surgery and two case of ankylosing spondylitis with pseudarthrosis. The installed vertebral levels ranged from T8 to S1. Screw positions were assessed with postoperative radiographs and computed tomography. Sixty-nine (93.2%) screws were correctly placed in the FGS group, and seventy-three (96.1%) screws were correctly placed in the CTGS group (P=0.491). The results indicated that both image-guided systems offer high accuracy. However, the fluoroscope image-guided system could be considered the primary tool for lower thoracic and lumbosacral pedicle placement because it enables real-time navigation and does not require a preoperative CT scan.

Image guided surgery: New technology for surgery of soft tissue and bone sarcomas

AIM

Providing the surgical oncologist with a new means of performing safe and radical sarcoma surgery with the help of image guidance technology.

METHOD

Two patients with pelvic sarcomas were operated upon with the help of an intra-operative navigation system. The technology of image guided surgery is described in one patient with a retroperitoneal sarcoma invading the bony pelvis and another patient with a chondrosarcoma of the iliac crest.

RESULTS

We show that this new procedure enables optimal radical surgical resection with minimal treatment related morbidity or loss of function.

CONCLUSION

Image guided surgery is a new technical tool in sarcoma surgery.

Pedicle screw placement accuracy: a meta-analysis

STUDY DESIGN

A meta-analysis of the published literature was conducted specifically looking at accuracy and the postoperative methods used for the assessment of pedicle screw placement in the human spine.

OBJECTIVES

This study specifically aimed to identify postoperative methods used for pedicle screw placement assessment, including the most common method, and to report cumulative pedicle screw placement study statistics from synthesis of the published literature.

SUMMARY OF BACKGROUND DATA

Safety concerns have driven specific interests in the accuracy and precision of pedicle screw placement. A large variation in reported accuracy may exist partly due to the lack of a standardized evaluation method and/or the lack of consensus to what, or in which range, is pedicle screw placement accuracy considered satisfactory.

METHODS

A MEDLINE search was executed covering the span from 1966 until 2006, and references from identified papers were reviewed. An extensive database was constructed for synthesis of the identified studies. Subgroups and descriptive statistics were determined based on the type of population, in vivo or cadaveric, and separated based on whether the assistance of navigation was employed.

RESULTS

In total, we report on 130 studies resulting in 37,337 total pedicle screws implanted, of which 34,107 (91.3%) were identified as accurately placed for the combined in vivo and cadaveric populations. The most common assessment method identified pedicle screw violations simply as either present or absent. Overall, the median placement accuracy for the in vivo assisted navigation subgroup (95.2%) was higher than that of the subgroup without the use of navigation (90.3%).

CONCLUSIONS

Navigation does indeed provide a higher accuracy in the placement of pedicle screws for most of the subgroups presented. However, an exception is found at the thoracic levels for both the in vivo and cadaveric populations, where no advantage in the use of navigation was found.

Assessment of CAOS as a training model in spinal surgery: a randomised study

The objectives of this study were (1) to quantify the benefit of computer assisted orthopaedic surgery (CAOS) pedicle screw insertion in a porcine cadaver model evaluated by dissection and computed tomography (CT); (2) to compare the effect on performance of four surgeons with no experience of CAOS, and varying experience of pedicle screw insertion; (3) to see if CT with extended windows was an acceptable method to evaluate the position of the pedicle screws in the porcine cadaver model, compared to dissection. This was a prospective, randomised, controlled and blinded porcine cadaver study. Twelve 6-month-old porcine (white skinned Landrace) lumbar spines were scanned pre-operatively by spiral CT, as required for the CAOS computer data set. Computer randomisation allocated the specimens to one of four surgeons, all new to CAOS but with different levels of experience in spinal surgery. The usual anatomical landmarks for the freehand technique were known to all four surgeons. Two pedicles at each vertebral level were randomly allocated between conventional free hand insertion and an electromagnetic image guided surgery (NAVITRAK) and 6.5 mm cancellous AO screws inserted. Post-operatively, spiral CT was blindly evaluated by an independent radiologist and the spine fellow to assess the accuracy of pedicle screw placement, by each method. The inter- and intra-observer reliability of CT was evaluated compared to dissection. The pedicle screw placement was assessed as perfect if within the pedicle along its central axis, or acceptable (within < 2 mm from perfect), and measured in millimetres from perfect thereafter. One hundred and sixty-six of 168 pedicles in 12 porcine spines were operated on. Complete data were present for 163 pedicles (81 CAOS, 82 freehand). In the CAOS group 84% of screws were deemed acceptable or perfect, compared to 75.6% with the freehand technique. Screw misplacement was significantly reduced using CAOS (P = 0.049). Seventy-nine percent of CAOS screws were ideally placed compared with 64% with a conventional freehand technique (P = 0.05). A logistic linear regression model showed that the miss placed pedicle screw rate was significantly reduced using CAOS (P = 0.047). CAOS benefited the least experienced surgeons most (the research registrars acceptable rate increased from 70 to 90% and the spine fellow from 76 to 86%). CAOS did not have a statistically significant effect on the experienced consultant spine surgeon increasing from 70 to 79% (P = 0.39). The experienced general orthopaedic surgeon did not benefit from CAOS (P = 0.5). CT compared to dissection showed an intra-observer reliability of 99.4% and inter-observer reliability of 92.6%. The conclusions of this study were as follows: (1) an increased number of pedicle screws were ideally placed using the CAOS electromagnetic guidance system compared to the conventional freehand technique; (2) junior surgeons benefited most from CAOS; (3) we believe CAOS (Navitrak) with porcine lumbar spines evaluated by post operative CT, represents a useful model for training junior surgeons in pedicle screw placement; (4) experienced spine surgeons, who have never used CAOS, may find CAOS less helpful than previously reported.

Intraoperative electromyography monitoring in minimally invasive transforaminal lumbar interbody fusion

Object

Minimally invasive transforaminal lumbar interbody fusion (TLIF) is an increasingly popular method for achieving lumbar decompression and fusion. The procedure is technically more demanding than open fusion, with correspondingly more theoretical risk of complication. The authors describe the use of intraoperative electromyography (EMG) as an adjunct to surgery to reduce the risk of complications.

Methods

Between August 2005 and April 2006, 25 consecutive patients underwent minimally invasive TLIF in which a total of 105 pedicle screws were placed. Intraoperative EMG was performed and included passive recordings during decompression and interbody graft placement, as well as active recording during the placement of the pedicle access needle and testing of the pedicle tap. A uniform protocol for active monitoring was used, with the pedicle access needle set at 7 mA. To assess hardware placement, all patients underwent postoperative radiography and 20 underwent postoperative computed tomography (CT) scanning.

In no patient did the authors observe significant EMG activation during decompression. In five cases, intermittent nerve root firing was noted after the interbody graft was placed, but this did not correlate with any postoperative deficits. Using the active stimulation protocol, 76.2% of screw placements required one or more changes to the trajectory of the pedicle access needle. With successful placement of the pedicle access needle, in all 105 screws, the pedicle tap nerve root stimulation threshold was greater than 15 mA. Postoperative radiography was performed in all patients and CT scanning was performed in 20 patients (with 85 screws being placed). Postoperative imaging revealed only three cases of pedicle breach. In all cases, the breach was at the lateral wall of the pedicle and not thought to be clinically relevant.

Conclusions

A continuous stimulation pedicle access needle alerts the surgeon to incorrect medial trajectories and may lead to safer pedicle cannulation. As a result of electrophysiological feedback, the pedicle access needle trajectory was altered in 76.2% of the reported cases. The use of the authors’ protocol resulted in a 0% incidence of clinically relevant malpositioned hardware and a low overall neurological complication rate. Intraoperative nerve root monitoring is a useful adjunct to minimally invasive TLIF.

Clinical Accuracy of Cervicothoracic Pedicle Screw Placement

OBJECTIVE

Posterior transpedicular fixation at the cervicothoracic junction (CTJ) is increasing in popularity. However, the clinical accuracy of pedicle screw placement at the CTJ has not been specifically assessed.

METHODS

Between January 2000 and July 2004, 60 consecutive patients underwent a variety of posterior spinal procedures necessitating pedicle screw placement at C7, T1, and T2. Thirty-two patients had cervicothoracic screws (3.5 to 4.5 mm) placed by an "open" technique (laminectomies or lamino-foraminotomies) and 28 patients with either a closed (before any decompression) 2-dimensional (n=19, fluoroscopy) or 3-dimensional (n=9, CT) computer-assisted technique. Screws were independently assessed for pedicle breach on postoperative CT and scored using a points-based classification system.

RESULTS

The total number of screws placed was 86, 63 and 45 in the open, closed-2-dimensional and closed-3-dimensional groups, respectively. Overall, 61(70.9%), 51(81%), and 40(89%) screws were completely within the pedicle. In the open group, the majority of pedicle breaches were more than 2 mm [n=3 (<2 mm), n=20 (2-4 mm), n=2 (>4 mm)]. Screw violation occurred laterally 11/25(44%), medially 3/25(12%), inferiorly 7/25(28%), and superiorly 4/25(16%). In the closed technique, all breaches were lateral. Seventeen screws (n=11-2-dimensional, n=5-3-dimensional) breached the pedicle by a margin of less than 2 mm and 1 screw (2-dimensional) by 2 to 4 mm. Pedicle screw accuracy was significantly improved with computer-assisted techniques. However, there was no significant difference between the 2-dimensional and 3-dimensional techniques. For all patients, there were no clinically significant screw misplacements, nor any need for screw revision.

CONCLUSIONS

Computer-assisted surgery allows for more accurate placement of pedicle screws at the CTJ. Although a higher proportion of major pedicular breaches occurred in the "open lamina/lamino-foraminotomy" group, no screws required revision in either group.

Fluoroscopic computer-assisted pedicle screw placement through a mature fusion mass: an assessment of 24 consecutive cases with independent analysis of computed tomography and clinical data

STUDY DESIGN

Observational matched cohort study with computed tomography (CT) analysis of pedicle screw placement.

OBJECTIVE

Assess the clinical accuracy of computer-assisted fluoroscopy for the placement of thoracolumbar pedicle screws through a mature posterolateral fusion mass.

SUMMARY OF BACKGROUND DATA

Pedicle screw placement through an amorphous posterolateral fusion mass intuitively carries a higher risk of pedicle wall violation.

METHODS

Postoperative CT scans of 102 pedicle screws placed through a mature posterolateral fusion mass (n = 10 [T10-T12]; n = 92 [L1-S1]) were independently assessed and compared with a matched control (nonobscured anatomy) group. All screws were placed before any decompression using the FluoroNav system.

RESULTS

In the fusion mass group, overall 81.4% of screws were completely within the pedicle. Seven medial and 12 lateral pedicle breaches occurred. Relative to the total number of screws, pedicle breaches were graded II (<2 mm) in 13.5%, III (2-4 mm) in 2.9%, and IV (>4 mm) in 2.0% of screws. The number and direction of pedicle breaches were not significantly different when compared with the control group. There were no clinically significant screw misplacements in either group.

CONCLUSIONS

The use of computer-assisted fluoroscopy is safe and effective for the placement of thoracolumbar (T10-S1) pedicle screws through a posterolateral fusion mass without performing laminoforaminotomies.

Inserting pedicle screws in the upper thoracic spine without the use of fluoroscopy or image guidance. Is it safe?

Several studies have looked at accuracy of thoracic pedicle screw placement using fluoroscopy, image guidance, and anatomical landmarks. To our knowledge the upper thoracic spine (T1-T6) has not been specifically studied in the context of screw insertion and placement accuracy without the use of either image guidance or fluoroscopy. Our objective was to study the accuracy of upper thoracic screw placement without the use of fluoroscopy or image guidance, and report on implant related complications. A single surgeon inserted 60 screws in 13 consecutive non-scoliotic spine patients. These were the first 60 screws placed in the high thoracic spine in our institution. The most common diagnosis in our patient population was trauma. All screws were inserted using a modified Roy-Camille technique. Post-operative axial computed tomography (CT) images were obtained for each patient and analyzed by an independent senior radiologist for placement accuracy. Implant related complications were prospectively noted. No pedicle screw misplacement was found in 61.5% of the patients. In the remaining 38.5% of patients some misplacements were noted. Fifty-three screws out of the total 60 implanted were placed correctly within all the pedicle margins. The overall pedicle screw placement accuracy was 88.3% using our modified Roy-Camille technique. Five medial and two lateral violations were noted in the seven misplaced screws. One of the seven misplaced screws was considered to be questionable in terms of pedicle perforation. No implant related complications were noted. We found that inserting pedicle screws in the upper thoracic spine based solely on anatomical landmarks was safe with an accuracy comparable to that of published studies using image-guided navigation at the thoracic level.

Qualitative and quantitative accuracy of CAOS in a standardized in vitro spine model

Pedicle breach with screw implantation is relatively common. For clinical application of computer-assisted orthopaedic surgery, it is important to quantitatively know the accuracy and localization of any guidance modality. We ascertained the accuracy of computed tomography and C-arm-based navigated drilling versus conventional fluoroscopy using an artificial thoracic and lumbar spine model. The 3.2-mm diameter transpedicle drilling target was the center of a 4-mm steel ball fixed in the anterior left pedicle axis. After drilling, we used computed tomography to verify the position of the steel ball and the canal and visually explored for cortex perforation. Quantitative vector calculation showed computed tomography-based navigation had the greatest accuracy (median, d(thoracic) = 1.4 mm; median, d(lumbar) = 1.8 mm) followed by C-arm navigation (median, d(thoracic) = 2.6 mm; median, d(lumbar) = 2 mm) and the conventional procedure (median, d(thoracic) = 2.2 mm; median, d(lumbar) = 2.7 mm). Visual examination showed a decreased perforation rate in navigated drillings. We found no correlation between pedicle breaches and inaccurate drilling. The data suggest computer-assisted orthopaedic surgery cannot provide sub-millimeter accuracy, and complete prevention of pedicle perforation is not realistic.

Screw position after double-rod anterior spinal fusion in idiopathic scoliosis: an evaluation using computerized tomography

STUDY DESIGN

A retrospective evaluation of screw position after double-rod anterior spinal fusion in idiopathic scoliosis using computerized tomography (CT).

OBJECTIVE

To evaluate screw position and complications related to screw position after double-rod anterior instrumentation in idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Anterior instrumentation and fusion in idiopathic scoliosis is gaining widespread use. However, no studies have been published regarding the accuracy of screw placement and screw-related complications in double-rod and double-screw anterior spinal fusion and instrumentation in idiopathic thoracolumbar scoliosis surgery.

METHODS

CT examinations were performed after surgery in 17 patients with idiopathic scoliosis. At each instrumented level, the position of the screw and the plate relative to the spinal canal, relative to the neural foramen, and relative to the aorta was measured. Complications related to screw position were registered.

RESULTS

A total of 189 screws in 17 patients were evaluated. Malposition occurred in 23% (16 patients) of the total number of screws. Three screws (2 patients) were partially in the spinal canal (1%). This resulted in pain in the right leg in 2 patients. However, electromyography showed no abnormalities. At three levels (3 patients), there was contact between the instrumentation and the aorta. However, no vascular complications occurred. A total of 113 screws (10 patients) were placed under fluoroscopic control and 76 screws (7 patients) were placed without use of fluoroscopy. Less screw malposition was observed in the group in which fluoroscopic control was used (19% vs. 30%, not significant).

CONCLUSIONS

Screw placement in double-rod anterior spinal fusion in idiopathic scoliosis seems to be technically demanding, and the use of fluoroscopic control results in less frequent malposition. The risk of neurologic and vascular complications is low.

The safety of fluoroscopically-assisted thoracic pedicle screw instrumentation for spine trauma

BACKGROUND

Pedicle screw fixation is considered biomechanically superior to other stabilization constructs. However, the potential for severe complications have discouraged its use in the thoracic spine. Our goal is to determine the incidence of major perioperative complications following the placement of thoracic pedicle screws using anatomic landmarks and intraoperative fluoroscopy in patients with spine fractures.

METHODS

Retrospective review of 245 consecutive patients with spine fractures requiring pedicle screw fixation between T1 and T10 at a regional Level I trauma center between 1995 and 2001. Database and medical record review were used to identify the incidence of major perioperative complications. A major complication was defined as a potentially life-threatening vascular injury, neurologic deterioration, pneumothorax or hemothorax, and tracheoesophageal injury. Patients were monitored for these complications from the time of surgery until discharge.

RESULTS

In all, 1,533 pedicle screws were placed between T1 and T10 in 245 patients. No patient sustained a major complication related to screw placement. Three patients (1.2%) required a secondary procedure for prophylactic revision of four (0.26%) malpositioned screws.

CONCLUSIONS

This study supports the safety of pedicle screws in the thoracic spine using preoperative imaging evaluation, standard posterior element landmarks and intraoperative fluoroscopy.

Intraoperative adverse events and related postoperative complications in spine surgery: implications for enhancing patient safety founded on evidence-based protocols

STUDY DESIGN

Prospective observational study.

OBJECTIVE

To assess the incidence and clinical consequence of intraoperative adverse events from a wide variety of spinal surgical procedures.

SUMMARY OF BACKGROUND DATA

In this study, adverse events were defined as any unexpected or undesirable event(s) occurring as a result of spinal surgery. A complication was defined as a disease or disorder, which, as a consequence of a surgical procedure, will negatively affect the outcome of the patient. We hypothesized that most adverse events would not result in complications that would be normally flagged through traditional practice audit approaches. By defining the incidence and types of adverse events seen in a spine surgical practice, we hope to develop preventative approaches to enhance patient safety.

METHODS

All postoperative clinical sequelae (i.e., complications) were prospectively identified, classified as to type, and graded (0 [none] to IV [death]) in 700 consecutive patients who underwent spine surgery (excluding > 300-day surgery microdiscectomies) at a university center from January 2002 to June 2003. To confirm data accuracy and assess the clinical sequelae of any adverse events, the medical records of these 700 patients were reviewed.

RESULTS

The overall incidence of intraoperative adverse events was 14% (98/700). A total of 23 adverse events led to postoperative clinical sequelae for an overall intraoperative complication incidence of 3.2% (23/700). Specific adverse events included dural tears (n = 58), spinal instrumentation-related events (n = 12), blood loss exceeding 5000 mL (n = 10), anesthesia/medical (n = 4), suspected or actual vertebral artery injury (n = 3), approach-related events (n = 3), esophageal/pharyngeal injury (n = 2), and miscellaneous (n = 6).

CONCLUSIONS

Adverse events can frequently occur (14%) during spinal surgery, however, the majority (76.5%) are not associated with complications. Improved patient safety can only be maximized by independent practice audit and the development of prospective methods to record adverse event data so that enhanced, evidence-based, clinical protocols can be developed.

Miniature robotic guidance for spine surgery — introduction of a novel system and analysis of challenges encountered during the clinical development phase at two spine centres

BACKGROUND

Instrumented spinal fusion surgery is increasingly performed. Breaching of the pedicle occurs in 3-55% of screws; clinically significant screw misplacements occur in 0-7% of all transpedicular screw placements. Several techniques have reduced this incidence but none gained popularity due to cost as well as staff issues. Surgical robots offer distinct added value in accuracy and minimal invasiveness. The aim of this study is to introduce the SpineAssist--a novel spine surgery miniature robot, to discuss the various reasons that had prevented full success with its use, to identify patients related, technical related, and surgeon related issues, and to offer ways to avoid them.

METHODS

The SpineAssist miniature robotic system is presented, including a short description of the system, its mode of action and a short summary of the surgical procedure.15 patients had undergone lumbar fusion procedures using the robotic system as part of clinical trials in two Israeli spine centres. A group of 9 procedures was identified within this prospective cohort. This group represents a wide array of technical challenges and human errors which were encountered during the clinical development phase of the SpineAssist. These 9 cases were conducted in two different sites by different surgical teams, over a period of 9 months, with an average interval of 7 weeks between consecutive cases. The cases were analysed for patient, system, surgeon and technical issues causing the difficulty. Conclusions were drawn as to how to avoid these hurdles in the future.

RESULTS

In six cases the system operated smoothly, resulting in accurate screws placement according to the pre-operative plan, this was confirmed by a post-operative CT scan. Technical and surgical challenges which are associated with the system early development stage were encountered during 9 procedures. On the technical side, the following phenomena were evident: 1) failure of the software to automatically achieve satisfying CT-to-fluoro image registration and 2) failure of the hospital's peripheral equipment/logistics preventing registration. On the clinical side of things, the following issues were encountered: 1) failure to avoid excessive pressure on the guiding arm caused by surrounding soft tissues, leading to a shift in the entry point and trajectory of the tool guide. 2) a surgeon applying too much force on the tool guide at the tip of the robotic arm, causing deviation from plan. 3) pre-operative plan out of the reach of the robot arm and 4) attachment of the clamp to the spinous process in a suboptimal orientation.

CONCLUSIONS

It is expected that following a steep learning curve in the range of 5-10 cases, recommended to take place within 2-3 weeks time, the surgical team will gain sufficient experience in operating the SpineAssist miniature robotic device in order to achieve excellent surgical results. The system may be used for wide range of applications including but not limited to pedicle screws, trans-facet and trans-laminar screws, biopsy needles, vertebroplasty or kyphoplasty tools and more. The preoperative plan has to be logical, intraoperative fluoro images taken with care, gentle surgical technique must be kept - maintaining the integrity of the posterior elements, and avoiding pressure between the robot arms and the soft tissues. During the clinical development phase discussed in this study, both teams used an early version of the system. Based on the results of this study several significant software and hardware improvements have already been implemented. It is our hope that describing and analysing our findings will help in planning and preparing for the clinical utilization of the SpineAssist system in future sites and will shorten their learning curve. By the time this article is published wider clinical experience will have been gathered and we expect to soon follow up with an analysis of clinical utilization of this system in a larger study group.

Computer assisted pedicle screw fixation: clinical experience with a newly developed software

We have used software, recently developed at Cochin University of Science and Technology, to perform computer assisted pedicle screw placement in forty pedicles of ten patients with fractured thoracolumbar vertebrae from January 2002 to February 2004. A pre-operative CT scan section at the pedicle level is taken one vertebra above and one below the involved vertebra. The dicom image is converted into a bitmap image and reference lines are drawn through the transverse processes and the spinous processes. The screw trajectory is drawn in the image at the most suitable path of the pedicle. Intraoperatively reference pins are placed exactly at the same areas in the transverse processes and the spinous processes. The intraoperative image is live captured using a camera and is matched with the preoperative image and the awl is advanced into the pedicle corresponding to the screw trajectory in the CT image. Out of forty pedicles instrumented in ten patients using computer assistance, the pedicle wall violation as demonstrated with 1 mm thin CT scans was less than AMIOT Grade 2. Ideal placement was noted in 80% and clinically insignificant perforation (Grade 2&3) in the rest. Computer assisted pedicle screw fixation appears to be a good technique for the accurate placement of pedicle screws in fractured vertebrae.

Pedicle screw fixation of the thoracic spine: an in vitro biomechanical study on different configurations

STUDY DESIGN

An in vitro biomechanical study of different pedicle screw configuration usage on the thoracic spine using a cadaveric model.

OBJECTIVES

To investigate the degree of motion afforded different pedicle screw configurations in the thoracic spine using a cadaveric model with 2 different degrees of intrinsic stability.

SUMMARY OF BACKGROUND DATA

Recently, thoracic pedicle screws have become an alternative to hook and wire fixation, and have gained popularity. Clinically, pedicle screw use has ranged from application to every segment, to skipping every other level. There exists no clear consensus as to which strategy is most appropriate.

METHODS

The load-displacement behavior of 6 different constructs was determined on 8 fresh frozen cadaver spine specimens (T4-T12). Each construct was evaluated on 2 destabilization models, including minimum destabilization (bilateral facetectomy) and maximum destabilization (facetectomy and annulotomy). Pure moments were applied, and the resultant range of motion for each scenario was determined.

RESULTS

Facetectomy did not significantly destabilize the thoracic spine. Annulotomy and facetectomy created gross instability that rendered testing of this destabilization model impossible. All constructs significantly reduced the range of motion compared to intact or facetectomized specimens (P < or = 0.001). When different constructs were compared to each other, a pattern of continuously increasing stability emerged, with the "maximum" construct being the most stable and "minimum" configuration being the least, with varying degrees of statistical significance.

CONCLUSIONS

Our results suggest that the most important factor for the acute postoperative stability of spinal fixation is the degree of preoperative or iatrogenic destabilization. The minimum amount of pedicle screws provides adequate stability when there is minimal destabilization of the spine. On the other hand, when anterior column release has been performed or instability exists before surgery, segmental pedicle screw fixation may be necessary to achieve adequate stability.

Clinical and radiological results after parapedicular screw fixation of the thoracic spine

OBJECT

The proximity of thoracic pedicles to the spinal cord and neurovascular structures has prompted numerous efforts to obtain proper screw placement. The aim of this study was to evaluate the feasibility and efficacy of thoracic parapedicular (intercostovertebral) screw fixation by following anatomical landmarks and using fluoroscopy.

METHODS

Thoracic parapedicular screw fixation was performed in 41 patients (328 screws). Postoperative computerized tomography scans were obtained in all cases to analyze the position of each screw with respect to the pedicle rib unit, the spinal canal, and the vertebral body (VB) according to a proposed novel grading system. Additionally, screw convergence angles were calculated for each instrumented level. There was no additional morbidity associated with parapedicular screw insertion. In a single case a screw suspected of entering the spinal canal was revised without causing neurological damage. The remaining screws were placed entirely within the pedicle rib unit and VB without breaching the neural foramina, pleura, or vascular structures.

CONCLUSIONS

Thoracic and thoracolumbar instability can be treated adequately and safely by using parapedicular screw fixation guided by anatomical landmarks and fluoroscopic imaging. The use of computer-aided navigation may be beneficial but does not appear to be mandatory.