Computer-assisted thoracic pedicle screw placement: an in vitro feasibility study.

STUDY DESIGN: In this cadaveric study, a computer-assisted image guidance system was tested for accuracy of thoracic pedicle screw placement. OBJECTIVES: Evaluate the system's accuracy for thoracic pedicle screw placement in vitro. SUMMARY OF BACKGROUND DATA: The effective use and reliability of pedicle screw instrumentation in providing short-segment stabilization and correction of deformity is well known in the lumbar spine. Pedicle screw placement in the thoracic spine is difficult because of the small dimensions of the thoracic pedicles and risk to the adjacent spinal cord and neurovascular structures. Investigators have shown the improved accuracy of computer-assisted lumbar pedicle screw placement; but the accuracy of computer-assisted thoracic pedicle screw placement, which is becoming more widely used, has not been shown. METHODS: In five human cadavers, 120 thoracic pedicle screws were placed with computer-assisted image guidance. The largest clinically feasible screw was used based on the cross-sectional dimensions of each pedicle. The accuracy was assessed by postoperative computed tomography and visual inspection. RESULTS: The overall pedicle cortex violation was 23 of 120 pedicles (19.2%). Nine violations (7.5%) were graded as major and 14 (11.7%) as minor. A marked and progressive learning curve was evident with the perforation rates that decreased from 37.5% in the first cadaver to 4.2% in the last two cadavers. CONCLUSIONS: Accurate thoracic pedicle screw placement is feasible with computer-assisted surgery. However, as with any other new surgical technology, the learning curve must be recognized and incorporated into the necessary fundamental knowledge and experience for these procedures.

Treatment of posttraumatic syringomyelia with extradural decompressive surgery.

The authors review the management of five patients with posttraumatic syringomyelia (PTS) associated with an uncorrected spinal deformity. Patients with evidence of progressive neurological deterioration underwent ventral spinal decompressive surgery. The mean patient age at the time of injury was 39 years, and the time between injury and the diagnosis of PTS ranged from 2 to 22 years. Mechanisms of injury consisted of fracture/subluxations in three patients and burst fractures in two. All patients experienced delayed neurological deterioration consistent with PTS. Magnetic resonance imaging revealed ventral deformities, and the spinal canal stenosis ranged from 20 to 50% (mean 39%). All patients underwent ventral epidural spinal decompressive surgery to correct the bone deformity and restore the spinal canal. The mean follow-up period was 38 months. The decompressive intervention was initially successful in treating the neurological deterioration in all patients. Symptoms resolved completely in four patients, and the other experienced neurological improvement. Postoperative magnetic resonance imaging revealed a reduction in the size of syrinx cavity in the patients whose symptoms resolved and no change in the remaining patient. Two patients required a subsequent second-stage posterior intradural exploration and duraplasty for recurrence of symptoms and/or syrinx. Posttraumatic spinal deformity may cause spinal canal stenosis and alter subarachnoid cerebrospinal fluid (CSF) flow in certain patients. Ventral epidural spinal decompressive surgery may result in neurological improvement and a reduction of the syrinx cavity, avoiding the need for placement of a shunt or other intradural procedures. However, some patients will also require reconstruction of the posterior subarachnoid space with duraplasty if the ventral decompressive procedure achieves only partial restoration of the subarachnoid CSF flow.

New software applications for interchangeable instrumentation in spinal stereotaxis.

Computer image-guided surgery has been widely accepted because it allows the surgeon to track an instrument through unvisualized critical structures of a patient in real-time, thus minimizing the risk of injury. Current spinal and cranial image-guided surgery is, however, limited by the lack of surgical instruments and software applications that would allow rapid interchange of useful instruments to perform the procedures. Most image-guided systems utilize a single standard probe or a few pre-defined instruments that are not necessarily useful for performing the actual surgical procedure. Present image-guided technology for screw placement in spinal surgery utilizes the standard probe only to confirm the entry point location and view the planned trajectory of the screw. The surgeon then resumes the procedure using standard surgical instruments to drill, tap and place screws without the benefit of image guidance. Our clinical laboratory experience with spinal image-guided surgery indicates that there is potential for error between each of these procedural steps of screw placement. Despite accurately locating an entry point, any deviation in the trajectory during drilling of a pilot hole, tapping or screw placement may result in significant errors in screw placement and potential neurovascular injury. We have developed custom software applications and universal hardware adaptation devices for spinal image-guided surgery that allow the use of standard instruments for intraoperative guidance. Utilizing universal dynamic registration hardware and software, standard surgical instruments are adapted for real-time image guided surgery. An array of light emitting diodes can be attached to essentially any rigid instrument with a definable tip and then calibrated to the system for intraoperative use. Laboratory tests using a cadaveric model indicate a difference in accuracy of less than 1.0 mm between the standard probe and a dynamically registered custom instrument and an absolute mean error of less than 2.0 mm for the image-guided system which is clinically insignificant in most cases. This technology is a significant step forward as it allows the surgeon to use a full array of instruments with image guidance and will ultimately make spinal and intracranial surgery safer and more accurate.

Universal calibration of surgical instruments for spinal stereotaxy.

PURPOSE: To describe new software applications and interchangeable instrumentation enabling the use of standard surgical instruments with image-guided systems for stereotactic spinal procedures. CONCEPT: The ability to adapt essentially any surgical instrument for stereotactic procedures will improve the safety and accuracy of image-guided spinal surgery. RATIONALE: Using universal dynamic registration hardware and software, standard surgical instruments are adapted for real-time image-guided surgery. The Radionics Optical Tracking System (Radionics, Inc., Burlington, MA) has custom software applications and universal hardware adaptation devices for spinal stereotaxy that allows the use of standard instruments for intraoperative guidance. An array of light-emitting diodes can be attached to essentially any rigid instrument with a definable tip and can then be calibrated to the system for intraoperative use. Stereotactic guidance of a drill, tap, and screwdriver may improve screw placement accuracy in spinal surgery because every step of the procedure can be monitored in real time. DISCUSSION: Most stereotactic systems have only a standard probe or limited instruments for localization, targeting, and tracking a procedure. The surgeon then resumes the operation using standard surgical instruments without the benefit of image guidance for the key steps of the procedure. Because each surgical step for screw placement in the spine has a potential for error, use of multiple instruments that can be interchanged for real-time image-guided spinal surgery may increase the accuracy and safety of spinal instrumentation procedures. These techniques can also be applied to intracranial image-guided surgery.

Thoracoscopic sympathectomy: techniques and outcomes.

Thoracic sympathectomy is an important option in the treatment of palmar hyperhidrosis and pain disorders. Earlier surgical procedures were highly invasive with known morbidity, acceptable outcome, and established recurrence rates that were the limitations to considering surgical treatment. Thoracoscopic sympathectomy is a minimally invasive procedure that allows detailed visualization of the sympathetic ganglia and minimal postoperative morbidity; however, outcome studies of this technique have been limited. The authors treated 39 patients with 60 thoracoscopic procedures, and the outcomes in this small series were equivalent to previously established open surgical techniques; however, operative moribidity rates, hospital stay, and time of return to normal activity were substantially reduced. Complications and recurrence of symptoms were also comparable to previous reports. Overall patient satisfaction and willingness to repeat the operative procedure ranged from 66 to 96% in all patients. Patients and physicians can consider minimally invasive thoracoscopic sympathectomy procedures as an option to treat sympathetically mediated disorders because of the procedure's reduced morbidity and at least equivalent outcome rates in comparison to other treatments.

Stereotactic radiosurgery for glioblastoma: a final report of 31 patients.

From February 1989 to December 1992, 31 patients who presented with an initial pathological diagnosis of glioblastoma multiforme underwent tumor debulking or biopsy, stereotactic radiosurgery, and standard radiation therapy as part of their primary treatment. Presenting characteristics in the 22 men and nine women included a median age of 57 years, Karnofsky Performance Scale score median of 80, and median tumor volume of 16.4 cm3. Stereotactic radiosurgery delivered a central dose of 15 to 35 Gy with the isocenter location, collimator size, and beam paths individualized by means of three-dimensional software developed at the University of Wisconsin. The peripheral isodose line varied from 40% to 90% with a median of 72.5% and a mode of 80%. The mean follow-up period was 12.84 months with a median of 9.5 months. Statistical analysis was performed using Kaplan-Meier analysis and log-rank comparison of risk factor groups. The parameters of age, initial Karnofsky Performance Scale score, and biopsy were significantly different in patient survival from debulking; but no difference was noted between single and multiple isocenters and patterns of steroid requirement. Radiographic recurrences were divided by location into the following categories: central (within central stereotactic radiosurgery dose), 0; peripheral (within 2 cm of central dose), 19; and distant (> 2 cm), 4. There is no evidence of recurrence in five surviving patients. Actuarial 12-month survival was 37%, with a median survival of 9.5 months. These values are similar to previous results for surgery and standard radiotherapy alone. The results suggest that the curative value of radiosurgery is significantly limited by peripheral recurrences.

The effect of hemoglobin and its metabolites on energy metabolism in cultured cerebrovascular smooth-muscle cells.

Cerebral arteries in spasm have been found to contain low levels of adenosine triphosphate (ATP), and it has been postulated that this change in levels results from hypoxia produced by arterial encasement in clotted material. This study was undertaken to determine whether any of four blood-derived agents, ferrous hemoglobin, methemoglobin, hemin, or bilirubin, is capable of reducing energy levels in cerebral artery smooth-muscle cells. Twenty-four-hour exposure of cultured canine basilar artery cells to ferrous hemoglobin and bilirubin led to a significant decline in ATP levels (to 8.9 nmol/mg protein and 2.8 nmol/mg protein, respectively) versus control (16.6 nmol/mg protein); methemoglobin and hemin showed no effect. Bilirubin but not hemoglobin was found to interfere with electron transport and with creatine phosphokinase activity in intact cells; however, bilirubin showed no inhibitory effect on this enzyme in cell-free conditions. The findings indicate that hemoglobin and bilirubin may be responsible for diminished energy levels in cerebral arteries. These observations also suggest that bilirubin may exert its effect on ATP by impairing mitochondrial function.

Stereotactic radiosurgery for glioblastoma multiforme.

From February 1989 to August 1992, 26 patients who presented with an initial pathological diagnosis of glioblastoma multiforme underwent tumor debulking (17) or biopsy (9), stereotactic radiosurgery (SR) and standard radiation therapy (dose range 50-66 Gy) as part of their primary tumor therapy. Presenting characteristics included median age of 55 years (range 20-79), Karnofsky Performance Score (KPS) median 82.5 (20-100), and median tumor volume 18.6 cm3 (2.2-59.7). SR collimator size ranged from 2.25 to 4 cm with a central dose of 15-35 Gy. Isocenter location, collimator size and beam paths were individualized using three-dimensional software such that the maximum possible solid angle was subtended without exceeding a 20% tumor dose gradient. The mean follow-up was 10.9 months (6-19.5) with a median of 9.5 months. Statistical analysis was performed using Kaplan-Meier actuarial analysis developing predicted 12-month survival rates. There were no significant differences noted in patient survival for the parameters of biopsy versus debulking, single versus multiple isocenters, age, initial KPS, and patterns of steroid requirement. Radiographic recurrences were divided by location into central (within central SR dose) = 0, peripheral (within 1 cm of central dose) = 16, and distant (< 1 cm) = 4. Predicted 12-month survival was 24%, with a median survival of 9.5 months. These values are similar to previous results for surgery and standard radiotherapy alone [1]. The results suggest that radiosurgery, when used as a mode of primary therapy, offers little or no benefit in quality of life or survival as recurrences occur immediately outside or distant to the central SR field.