Fatal cardiac tamponade associated with posterior spinal instrumentation. A case report

STUDY DESIGN: Case report of a fatal complication of pedicle screw instrumentation and review of the literature. OBJECTIVE: To describe the clinical and postmortem findings in a 35-year-old man who sustained a T11 burst fracture that was managed by transpedicular posterior instrumentation and who died 12 days after surgery of cardiac tamponade caused by a prick injury of the right coronary artery. SUMMARY OF BACKGROUND DATA: Posterior pedicle screw instrumentation is considered a safe and effective method for stabilizing a spinal motion segment. Nevertheless, there are several rare but significant complications that may occur. This is the first report of a heart tamponade after transpedicular screw insertion. METHODS: A 35-year-old man was treated for a T11 burst fracture with posterior transpedicular stabilization. The surgery was uncomplicated. RESULTS: Twelve days after the intervention, the patient died of cardiogenic shock. Postmortem examination showed a heart tamponade of 350 mL blood originating in a prick injury of the right coronary artery. Histologic findings showed evidence that the injury was caused during surgery by a Kirschner wire. CONCLUSION: There are numerous possible intraoperative complications in posterior pedicle screw fixation, such as nerve root and spinal cord injuries. This case of a fatal heart tamponade after transpedicular screw insertion is rare. It shows that the surgeon must be aware of potential risks associated with such a procedure and have a comprehensive three-dimensional understanding of the anatomic structures involved.     

Use of cervicothoracic junction pedicle screws for reconstruction of complex cervical spine pathology

STUDY DESIGN: A retrospective review of 21 patients in which cervical pedicle screw fixation was used at C7 with or without upper thoracic pedicle screw fixation. OBJECTIVE: To evaluate the use of pedicle screw placement in the lower cervical spine. SUMMARY OF BACKGROUND DATA: The use of posterior cervical spine fixation, including lateral mass fixation, has become increasingly popular in recent years. However, lateral mass fixation at C7 is often hindered by lack of substantial high quality bone. The end level of long cervical spine constructs is frequently C7 or T1. Dissatisfaction with lateral mass fixation at C7 and T1 led the authors to use lower cervical pedicle screw fixation for several cervical spine disorders. METHODS: Twenty-one patients who had undergone cervical pedicle screw fixation at C7 were reviewed retrospectively. There were 12 males and 9 females, with an average age of 52 years. All pedicle screws were placed, after direct palpation of the pedicle, with a right angle nerve hook after laminoforaminotomy at C7. RESULTS: There were no neurologic complications related to pedicle screw placement, and no patient was symptomatically worse after the operation. Six patients with root pathology improved. Of 14 patients with cervical myelopathy, 12 improved at least one Nurick grade, and 2 had no improvement. There were no failures of fixation or complications related to pedicle fixation at a minimum of 1 year follow-up. CONCLUSION: Pedicle screws in C7 placed with laminoforaminotomy and palpation technique appears to be safe and efficacious. Excellent fixation can be achieved.     

Internal fixation of the spine in traumatic and scoliotic cases. The potential of pedicle screws

Internal fixation techniques are in common used to stabilize vertebral fractures and correct severe scoliosis. Consolidation of injured vertebrae with neighbouring intact vertebra is the goal in the former case whilst fusion of the vertebrae in a corrected position is aimed at in the latter case. Degenerative spine diseases are not considered in this paper. Classical instrumentation consists of rods (e.g., Cotrel-Dubousset, Harrington, Luque-Galveston) attached to the bone by means of hooks or wires. More recently, transpedicular screws are introduced as an alternative bone/implant interface. Comparing the results of several studies, the posterior pedicle screw based devices demonstrate the ability to produce the most rigid constructs. However, the insertion of pedicle screws implicates a relatively high complication risk and its success strongly depends on the experience of the surgeon. Incorrect drilled holes or malplacement of the screws can result in nerve root injuries and fracture of the pedicle. Studies reported complication ratios up to 30% with substantial neurological implications. A certain degree of automation of the critical actions may be necessary to enhance the safety of pedicle screw insertion. Two techniques of computer assisted spine surgery are compared. Both techniques permit a computer assisted surgical planning based on CT images. During operation the first system permanently observes the position of the drill relative to the spine and informs the surgeon on the deviation of the actual drill path to the planned drill path. The second system uses a pre-operative surgical planning to design and construct a mechanical drill guide, fitting perfectly on the patient's spine.     

Impact of chronic cough on quality of life

STUDY DESIGN: The biomechanical influence of in situ setting hydroxyapatite cement was examined for use in pedicle screw revision surgery. Pull-out testing of control and pedicle screws augmented with hydroxyapatite cement was performed in human cadaver vertebrae. OBJECTIVES: To determine the immediate effect of using hydroxyapatite cement to augment revision pedicle screws after failure of the primary pedicle screw fixation. SUMMARY OF BACKGROUND DATA: The potential problems associated with using polymethylmethacrylate to augment revision pedicular instrumentation have prompted the search for other solutions. The introduction of resorbable hydroxyapatite pastes may have provided new biocompatible solutions for pedicle screw revision. METHODS: Ten human cadaver vertebrae were instrumented with 6.0-mm pedicle screws in each pedicle. The screws were loaded to failure in axial tension (pull-out). The failed pedicles then were instrumented with 7.0-mm pedicle screws, either augmented with hydroxyapatite cement or nonaugmented, which also were loaded to failure. Finally, the nonaugmented 7.0-mm screw hole was reinstrumented with a hydroxyapatite cement-augmented, 7.0-mm pedicle screw and loaded to failure. RESULTS: The pull-out strength of the 7.0-mm, hydroxyapatite cement-augmented screws was 325% (P = 2.9 x 10(-5)) of that of the 6.0-mm control screws, whereas the strength of the 7.0-mm nonaugmented screws was only 73% (P = 2.0 x 10(-2)) of that of the 6.0-mm control screws. The 7.0-mm screws augmented with hydroxyapatite cement also were able to salvage 7.0-mm pull-out sites to 384% (P = 6.9E-5) of the pull-out strength of the 7.0-mm nonaugmented screws. CONCLUSIONS: Hydroxyapatite cement may be a mechanically viable alternative to polymethyl methacrylate for augmenting revision pedicular instrumentation and should be considered for future experimental, animal, and clinical testing.     

Computer-aided pedicle screw placement using frameless stereotaxis

STUDY DESIGN: In vitro assessment of accuracy and reliability of frameless stereotaxis for insertion of pedicle screws in human cadaveric lumbar spine. OBJECTIVES: To assess a new method of targeting and placing pedicle screws in a human cadaver study. SUMMARY OF BACKGROUND DATA: Pedicle screw instrumentation is common. Complications may occur from improper placement of screws. Even when performed by experienced spinal surgeons, improper placement can occur in 5.2% of pedicles instrumented. Development of computer-guided methods of pedicle screw insertion may decrease this complication rate. METHODS: The technique used preoperative computed tomography scans together with a commercial neurosurgical navigational computer system to assist in placing guidewires in the pedicles. A section of human cadaver spine was first scanned and the data transferred to the workstation. The image data set and physical specimen were then registered by using an instrumented articulated arm to identify selected points on the specimen and randomly sample surface points. Eight highly repeatable locations on each vertebral body were found to be suitable for registration, but better overall accuracy was obtained when surface matching was used in combination with these points. Under guidance of image on the computer, Kirschner wires were inserted into the pedicles of four vertebral bodies. The spine was rescanned, and the planned and resulting positions of the wires compared. RESULTS: The average distance between the planned and resulting wire entry point was 1.2 mm, with an average difference in planned and resulting trajectories of 6.0 degrees. CONCLUSIONS: Computer-aided pedicle screw instrumentation is feasible. Further technical points require clarification before widespread use is possible.     

Pedicle screw fixation for arthrodesis of the lumbosacral spine in the elderly. An outcome study

STUDY DESIGN: An analysis of the outcome and effectiveness of instrumented arthrodesis of the lumbosacral spine in elderly patients conducted using a review of records, assessment of fusion via plain radiographs, and a two-part questionnaire. OBJECTIVE: To ascertain the outcome and efficacy of instrumented arthrodesis of the lumbosacral spine in patients 60 years of age and older. BACKGROUND DATA: From 1987 to 1991, 38 patients of at least 60 years of age underwent instrumented arthrodesis of the lumbosacral spine using the Wiltse or Selby pedicle screw fixation system (Advanced Spine Fixation Systems, Inc., Irvine, CA). Patients were considered for surgery only after attempts at conservative management, including physical therapy, medication, injection blocks, and home exercises, had proven unsuccessful. METHODS: Follow-up examinations were performed 3 months, 6 months, 1 year, and 2 years after surgery. Fusion was assessed using plain radiographs, including flexion-extension films. Inpatient and outpatient records were reviewed, and a two-part questionnaire was used to establish the effect of surgery on function and lifestyle. Thirty patients responded to the questionnaire. Follow-up observation of the patients ranged from 25 to 56 months. The mean age was 73.8 years (range, 60-90 years). RESULTS: The mean co-morbidity was 1.7. Based on the authors' method of evaluation of fusion, the fusion rate was 92%. Fifty-seven percent of the patients reported excellent or good results, 26% reported fair results, and 17% reported poor results. Functional gains of 50% or more were reported by 71% of the respondents. Female patients had significantly more complications than male patients, but reported comparable outcomes. CONCLUSION: Despite the increase in age, co-morbidity, and associated risk of perioperative complications inherent in this population, an outcome comparable with that of younger patients is reported.     

In vitro simulation. Early results of stereotaxy for pedicle screw placement

STUDY DESIGN: Frameless stereotaxy with doppler ultrasound and three dimensional computer model registration is assessed in vitro for pedicle screw placement. OBJECTIVE: To identify feasibility of pedicle screw navigation and placement using this technology. SUMMARY OF BACKGROUND DATA: Inaccurate pedicle screw placement can lead to neurovascular injury or suboptimal fixation. Present techniques in pedicle screw placement involve only confirmation of hole orientation. METHOD: Forty-four pedicle screws were placed in lumbosacral models and cadaver specimens. Accuracy was assessed with a computed tomography scan and vertebral cross sectioning. RESULTS: All screws were intrapedicular. Accuracy of anterior cortical fixation was 1.5 mm, with a range of 2.5 mm. CONCLUSION: In vitro frameless stereotaxy is accurate for pedicle screw placement. This technology adds a component of navigation to pedicle screw placement.     

Transcutaneous or transconjunctival peribulbar anesthesia?

The complications of 648 consecutively inserted Universal AO pedicle screws (140 in the thoracic spine and 508 in the lumbar spine) performed by one surgical team to treat 91 patients with spinal problems, were reviewed. The spinal pathology consisted of: scoliosis (34 patients), degenerative lower lumbar spinal disease (25 patients), neoplastic spinal disease (11 patients), thoracic kyphosis (8 patients), spinal fractures (7 patients), lumbo-sacral spondylolisthesis (3 patients), and osteomyelitis (3 patients). Intraoperative complications were: screw misplacement (n = 3), nerve root impingement (n = 1), cerebrospinal fluid leak (n = 2) and pedicle fracture (n = 2). Postoperative complications were; deep wound infection (n = 4), screw loosening (n = 2) and rod-screw disconnection (n = 1). The conclusion was that pedicle screw fixation has an acceptable complication rate and neurological injury during this procedure is unlikely.     

Carbonated apatite cement augmentation of pedicle screw fixation in the lumbar spine

STUDY DESIGN: Biomechanical testing with human cadaveric lumbar vertebral bodies was used to determine the utility of an injectable carbonated apatite cancellous bone cement for improving the structural performance of pedicle screws subjected to axial pull-out or transverse cyclic loading. OBJECTIVES: To ascertain whether augmentation with a carbonated apatite cement can enhance pedicle screw fixation in the lumbar spine. SUMMARY OF BACKGROUND DATA: The beneficial effects of polymethylmethacrylate augmentation on pedicle screw pull-out strength have been demonstrated. Cancellous bone cement, however, may provide an attractive alternative in this application, as it is remodelable, biocompatible, and nonexothermic. METHODS: Forty-three cadaveric lumbar vertebral bodies were instrumented with pedicle screws. In 20 of these specimens, axial pull-out strength was compared between the control screws and those augmented with cancellous bone cement. In the remaining 23 specimens, the screws were loaded in the superior-inferior direction with a peak displacement of +/- 1 mm at a frequency of 3 Hz for 5000 cycles. Three parameters were calculated from the force-versus-time data: 1) the energy dissipated, 2) the peak force at the start of the test, and 3) the peak force at the end of 5000 cycles. RESULTS: The pull-out strength of the augmented pedicles averaged 68% greater than that of the control side. In response to cyclic loading, all measures of bio-mechanical performance improved 30-63%. CONCLUSIONS: The data suggest that augmentation with this carbonated apatite cancellous bone cement can enhance immediate screw fixation.     

Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement

STUDY DESIGN: Pedicle screws were pulled out of human cadaveric vertebrae before and after augmentation with polymethylmethacrylate or in situ-setting calcium phosphate cement. The fixation strength of screws augmented with calcium phosphate cement was compared with that of screws augmented with polymethylmethacrylate. OBJECTIVES: To determine whether a new in situ-setting calcium phosphate cement might be suitable for augmenting the fixation of pedicle screws. The principle objective was to compare the pull-out resistance of screws augmented with calcium phosphate cement with the pull-out behavior of screws augmented with polymethylmethacrylate. Polymethylmethacrylate augmentation was chosen as the standard because of its current clinical use. Five types of screws were tested to determine whether screw design had an effect on the efficacy of augmentation. SUMMARY OF BACKGROUND DATA: Although many factors affect the pull-out resistance of pedicle screws, a key determinant of their performance is the strength of their attachment to the spine. In elderly, osteopenic patients, the screw-bone interface is especially at risk for stripping during insertion or pull-out after surgery. In these patients, polymethylmethacrylate has been used to augment pedicle screw fixation, although its use is not without risk. In situ-setting calcium phosphate cements may provide an alternative to polymethylmethacrylate in this application. Like polymethylmethacrylate, calcium phosphate cements can be injected into the prepared screw hole. They have the added advantage of being resorbed and replaced during healing and normal bone remodeling. METHODS: Thirty human lower lumbar vertebrae (L3-L5) were implanted bilaterally with one of five types of pedicle screws (n = 6 for each screw type). The screws were pulled out 3.0 mm at 0.25 mm/sec with a servohydraulic materials testing machine. The 3.0-mm pull-out distance, which was slightly longer than one thread pitch, was designed to strip the screw-bone interface but to leave the pedicle otherwise intact. After the initial testing, the screws in each vertebrae were removed, and the screw tracks were filled with 2.0 cc of polymethylmethacrylate (one side) or calcium phosphate cement (contralateral side). After augmentation, the screws were reinserted, and the cements were allowed to harden for 24 hours. Postaugmentation testing followed the protocols for preaugmentation testing, and the pull-out resistance of screws augmented with calcium phosphate cement was compared with the pull-out resistance of screws augmented with polymethylmethacrylate. RESULTS: Mechanically, calcium phosphate cement compared favorably with polymethylmethacrylate for augmenting pedicle screws. Both restored the strength of the screw-bone interface: across all screw types, the average increase in pull-out strength was 147% with polymethylmethacrylate augmentation and 102% with calcium phosphate cement. There were no significant differences because of screw type with either type of augmentation. CONCLUSIONS: The in situ-setting calcium phosphate cement investigated in this study compared favorably with polymethylmethacrylate in a single-cycle, pull-out test of augmented pedicle screws in senile trabecular bone. With further evaluation, this cement may offer an alternative to polymethylmethacrylate for the enhancement of pedicle screw fixation clinically.     

Revision pedicle screws. Bigger, longer shims--what is best?

STUDY DESIGN: To evaluate the effect of change in screw dimensions and hole augmentation in pedicle screw revisions, the insertional torque was determined, and results were compared with those in control specimens in an in vitro study using cadaveric thoracolumbar spines. OBJECTIVES: To determine the best method of salvage for failed pedicle screws, by evaluating the insertional torque after placing a larger diameter or longer screw into a stripped hole. Use of a shim and use of larger and longer screws were also investigated. Finally, the effect on insertional torque of simply removing and replacing a pedicle screw in its original hole was investigated. SUMMARY OF BACKGROUND DATA: The effects of using bigger or longer screws and shims to salvage failed pedicles have been studied. The interaction between how much larger, how much longer, and inserting with or without shims, has not been well studied. Optimizing reinsertional torque through the use of bigger screws risks exceeding the pedicle capacity. Using longer screws risks violation of the anterior vertebral body, thereby placing the great vessels and viscera at risk. By knowing the relative contribution of increase in length and diameter, the surgeon can optimize the risk-benefit ratio. METHODS: Eight cadaveric spines from T10 to S1 were harvested. The specimens underwent radiographic screening and bone densitometry. A modified Latin square randomization was designed to evaluate the screw diameters and lengths. Each pedicle was its own control. A 35- x 6.5-mm screw was used as a control. Test screws were placed after pedicle screw hole failure was achieved and documented by stripping. For the test screws, the diameters were increased by 1 mm and 2 mm, the lengths were increased by 5 mm and 10 mm. Shims were added randomly. The peak insertional torque was measured for each control screw and test screw placement. In addition, during each screw placement, the screw was removed and replaced to determine the effect. RESULTS: Insertional torque, after the pedicle screw is removed and replaced in the same hole, was decreased by 34% (P < 0.000005). Increasing the diameter of the salvage screw by 2 mm caused the insertional torque to be increased by 8.4% of the original. Increasing the length of the screw did not improve the salvage screw insertional torque. There was an interaction effect for the 1-mm increase in diameter and the increase in length. At this diameter, increasing the length had a significant effect (P = 0.009) on the salvage torque. Using a shim created no improvement in salvage insertional torque (P = 0.77). There was a poor linear correlation between torque and bone mineral density (r = 0.18) in these osteoporotic specimens. CONCLUSIONS: Removing and replacing a pedicle screw in its original hole substantially decreases its mechanical fixation. For pedicle salvage, increasing the diameter causes the greatest restoration of strength. Shims had no effect in pedicle salvage in osteoporotic specimens.     

Accuracy of using computed tomography to identify pedicle screw placement in cadaveric human lumbar spine

STUDY DESIGN: Utility of using computed tomography to predict pedicle screw misplacement. OBJECTIVE: This study defines the sensitivity and specificity of predicting pedicle screw placement by experienced clinicians using a CT scan image. SUMMARY OF BACKGROUND DATA: In clinical and research settings, the method most commonly used to evaluate pedicle screws placement has been computed tomography. However, no current literature describes the accuracy of this method of evaluating screw placement. METHOD: Cobalt-chrome and titanium alloy pedicle screws of identical size were placed in six cadaveric human lumbar spine. Wide laminectomy was performed to allow complete visualization of the pedicles. Three consecutive lumbar levels were instrumented in each spine, giving 36 pedicle screw placements to identify. The instrumented spines were imaged, and four orthopaedic spine surgeons and a musculoskeletal radiologist were asked to read the images to identify the accuracy of screw placement within the pedicles. RESULTS: The sensitivity rate of identifying a misplaced screw was 67 +/- 6% for cobalt-chrome screws compared with 86 +/- 5% for titanium screws (P < 0.005). The specificity rates of radiographic diagnosis of misplaced pedicle screws were 66 +/- 10% for cobalt-chrome screws and 88 +/- 8% for titanium screws (P < 0.005). Similarly, a statistically significant difference was found in the sensitivity rates of identifying screws placed correctly in the pedicle: 70 +/- 10% for cobalt-chrome screws versus 89 +/- 8% for titanium screws (P < 0.005). Overall accuracy rates were 68 +/- 7% for cobalt chrome screws versus 87 +/- 3% for titanium screws (P < 0.002). CONCLUSION: Reliance on the computed tomography scan data alone in determining accuracy of pedicle screws can lead to inaccuracies in both clinical and research conditions.     

Nitric oxide as a regulatory factor in sleep-wakefulness mechanisms

Most screws used in fracture fixation necessitate a separate step for tapping of the screw hole. Titanium screw systems have been developed in which the screws can be inserted directly after a drill hole is made. These self-tapping screws thereby eliminate an operative step. A retrospective study was conducted that evaluated all wrist and hand procedures performed between January 1992 and December 1994 by 1 surgeon using screw fixation. The results of 39 cases treated with standard tapped titanium screws were compared with 28 cases treated with self-tapping titanium screws. Nearly identical union and complication rates were obtained in each group. Comparable results can be obtained with self-tapping screw fixation, which limits the number of instruments needed, eliminates an operative step, and thereby may diminish operative risk and shorten operative time.     

Spinal instrumentation with a low complication rate

BACKGROUND: Spinal instrumentation has become an increasing part of the armamentarium of neurosurgery and neurosurgical training. For noncontroversial indications for spine fusion the arthrodesis rate seems to be better. For both noncontroversial and controversial indications, the reported complication rate with spinal instrumentation tends to be greater than that with noninstrumented spine surgeries. These reported complications include a 2-3% neurologic injury rate, 3-45% reoperation rate for implant failure, and inflection rates of 5-10%. Therefore, we report on 299 cases that have undergone spinal instrumentation placed exclusively by neurosurgeons with a very low complication rate. METHODS: Two hundred ninety-nine consecutive spinal instrumentation cases performed exclusively by neurosurgeons at Indiana University Medical Center were analyzed for complications related to spinal instrumentation. The spinal instrumentation placed consisted of 195 anterior cervical locking plates, 22 cases of posterior cervical instrumentation, 9 cases of combined anterior locking plates with posterior cervical instrumentation, 14 anterior thoracolumbar plates, 51 posterior thoraco-lumbar instrumentation cases, and 8 combined anterior/posterior thoracolumbar instrumentation cases. RESULTS: The mean follow-up is 40 months (6-95). There was one perioperative death unrelated to the spinal instrumentation. There were no neurologic injuries and there has been no hardware infection to date. There were two dural tears, three superficial wound infections, and three minor wound breakdowns successfully treated. Hardware complications included three cervical plate/screw extrusions reoperated, one cervical plate fracture reoperated, one posterior cervical screw backout not reoperated, one case of broken pedicle screw not reoperated, one vertebral body failure not reoperated, and one posterior rod case reoperated for excessive rod length and protrusion. The overall complication rate attributable to placement of spinal instrumentation was 10/299 (3%) with a reoperation rate of 2%. The arthrodesis rate was 298/299 (99%). CONCLUSION: The complication rate for using spinal instrumentation can be less than previously reported. Lessons learned and discussed should reduce the rate even more. Spinal instrumentation is a safe and useful adjunct to fusion in treating degenerative, traumatic, infectious, and neoplastic diseases of the spine.     

Residual intersegmental spinal mobility following limited pedicle fixation of thoracolumbar spine fractures with the fixateur interne

The Fixateur Interne has been proposed for limited pedicle fixation of thoracolumbar spine fractures with the assumption that motion in the nontraumatized spinal segments could be maintained. To date, no data exist that both localize and quantitate spinal mobility about the fractured vertebra. Voluntary maximum lateral flexion and extension radiographs were obtained on patients with unstable thoracolumbar spine fractures at a minimum of 2 years after Fixateur Interne instrumentation (implant was removed after 1 year). Residual intersegmental motion was measured at levels adjacent to both the vertebra fracture and the fixation. Fifty-nine patients were reviewed, and the posterior vertebral body angle demonstrated a mean total sagittal motion of 2.98 degrees. Cephalad and caudal to the fractured vertebra, a mean of 1.34 degrees and 3.08 degrees, respectively, of residual motion was noted; cephalad and caudal to the previously instrumented segment a mean of 3.22 degrees and 6.88 degrees, respectively, was measured. The authors conclude that residual mobility is most evident at the caudal end of the instrumented segment, removed from the fractured vertebra. The level with end plate disruption becomes essentially ankylosed, with or without a fusion.     

Safety and accuracy of transarticular screw fixation C1-C2 using an aiming device. An anatomic study

STUDY DESIGN: In this anatomic study, the safety and accuracy of C1-C2 transarticular screw placement was tested in a normal anatomic situation in cadaver specimens using a specially designed aiming device. OBJECTIVES: To assess the safety and accuracy of transarticular screw placement using the technique described by Magerl and a specially designed aiming device. SUMMARY OF BACKGROUND DATA: Transarticular C1-C2 screw fixation has been shown to be biomechanically superior to posterior C1-C2 wiring techniques. Several clinical series have been reported in the literature. However, no previous study assessing the accuracy or safety of this technique has been published. Structures at risk are the vertebral arteries, spinal canal, and the occiput-C1 joint. METHODS: Five frozen human cadaveric specimens were thawed and instrumented with 10 C1-C2 transarticular screws, according to the technique described by Magerl but using a specially designed aiming device described by the senior author (Jeanneret). After screw placement, the accuracy of screw positioning and the distance of the screws from the spinal canal, vertebral arteries, and atlanto-occipital joint were determined by anatomic dissection and radiographic analysis. RESULTS: The structure at greatest risk was the atlanto-occipital joint, with one screw found to be damaging the joint. Vertebral artery or spinal canal penetration was not observed in any of the specimens. Screw length averaged 45 mm and, with proper length, the screw tip was found to be located approximately 7.5 mm behind the anterior tubercle of C1 on lateral radiographs. CONCLUSIONS: This anatomic study demonstrates that C1-C2 transarticular screw fixation can be performed safely in a normal anatomic situation by surgeons who are familiar with the pertinent anatomy. The aiming device allowed safe instrumentation in all patients. In case of an irregular anatomic situation (e.g., congenital abnormalities or trauma), computed tomographic scan with sagittal reconstruction is recommended-in particular, to obtain information about the course of the vertebral artery.     

The dynamic hip screw with support plate--a reliable osteosynthesis for highly unstable "reverse" trochanteric fractures?

ORIF management of unstable trochanteric fractures of type A3 of the A0 classification is difficult because of lateral dislocation of the proximal fractured segments, particularly when only the sliding hip-screw is used for fixation. A connectable butt-press plate was recently developed in order to prevent this type of dislocation. We review the results with this fixation technique in 22 elderly patients with an average age of 76 years who presented with highly unstable trochanteric fracture of the A3 type. Three patients died of diseases unrelated to the trauma or operation before the fractures had healed. The other 19 were followed prospectively until fracture healing had occurred. Complaints, leg shortening and changes in the CCD angle were recorded. Furthermore, the mobility score was determined. Although the patients were able to bear full weight after the operation, no lateral dislocation of fragments was observed. Only 1 patient had a varus dislocation of 5 degrees until the fracture had consolidated. This was due to severe osteopenia and subsequent dislocation of the screw within the femoral head. No pseudarthrosis, osteitis or rotational malalignment was noted. Five of the surviving patients had a lower mobility score after fracture healing as compared to the status before the fracture was sustained. On the basis of this review, we recommend the use of this new connectable buttress plate with sliding hip screws because it provides sufficient fixation of highly unstable fractures of type A3.     

Complications of pediatric thoracolumbar and lumbar pedicle screws

STUDY DESIGN: This was a retrospective review of 223 consecutive cases (1986-1996) from one institution where 759 thoracolumbar and lumbar pedicle screws were used in the treatment of various pediatric spinal disorders in patients less than 18 years of age. OBJECTIVES: To determine the incidence of short- and long-term (> 2 years follow-up) complications in this group of patients-specifically, complications related to instrumentation and those directly attributable to pedicle screws in these pediatric patients. SUMMARY OF BACKGROUND DATA: Although much has been written regarding the use of pedicle screws in the adult population, no published study has examined complication rates with regard to thoracolumbar and lumbar pedicle screws placed for pediatric spinal disorders. METHODS: A retrospective review of 223 consecutive cases involving 759 pedicle screws placed for a variety of pediatric spinal disorders was performed. Complications were divided into short term and long term (> 2 years follow-up) and into those relating to instrumentation and those relating to pedicle screws specifically. RESULTS: Short-term complication occurred in 5 patients (2.2%) for a total of 17 screws ultimately removed. Only two of these patients had screws removed for lumbar radicular complaints. No residual sequellae resulted. No long-term (> 2 years postoperative) complications were noted. CONCLUSION: Low short- and long-term complication rates specific for pediatric pedicle screws suggests that for properly trained spinal surgeons, pedicle screws fixation in the pediatric population can be performed safely to treat a variety of spinal disorders.     

Coexistence of enkephalin- and tyrosine hydroxylase-like immunoreactivities in nerve fibers of the temporomandibular joint capsule of the guinea pig

This case report describes the intraoperative improvement of somatosensory evoked potentials (SEPs) during the removal of a broached pedicle screw that had been placed in an unmonitored procedure 1 month earlier. Postoperatively, there was improved neurologic function and reversal of the neurologic deficit that had been caused by the first procedure. To our knowledge, this is the first report of a correlation of intraoperative SEP improvement with improved postoperative neurologic function after neurologic deficit because of nerve irritation or compression from a pedicle screw. Nerve damage occurs in about 15% of patients who undergo instrumentation after lumbar fusion. The potential utility of neurophysiologic methods during initial screw placement is suggested and supported, as proper use of such intraoperative tools may have prevented the need for the second procedure.     

Biomechanical comparison of C1-C2 posterior fixations. Cable, graft, and screw combinations

STUDY DESIGN: Four combinations of cable-graft-screw fixation at C1-C2 were compared biomechanically in vitro using nondestructive flexibility testing. Each specimen was instrumented successively using each fixation combination. OBJECTIVES: To determine the relative amounts of movement at C1-C2 after instrumentation with various combinations of one or two transarticular screws and a posterior cable-secured graft. Also to determine the role of each component of the construct in resisting different types of loading. SUMMARY OF BACKGROUND DATA: Spinal stiffness increases after instrumentation with two transarticular screws plus a posterior wire-graft compared with a wire-graft alone. Other C1-C2 cable-graft-screw combinations have not been tested. METHODS: Eight human cadaveric occiput-C3 specimens were loaded nondestructively with pure moments, and nonconstrained motion at C1-C2 was measured. The instrumented states tested were a C1-C2 interposition graft attached with multistranded cable; a cable-graft plus one transarticular screw; two transarticular screws alone; and a cable-graft plus two transarticular screws. RESULTS: The transarticular screws prevented lateral bending and axial rotation better than the posterior cable-graft. The cable-graft prevented flexion and extension better than the screws. Increasing the number of fixation points often significantly decreased the rotation and translation (paired t test; P < 0.05). Axes of rotation shifted from their normal location toward the hardware. CONCLUSIONS: It is mechanically advantageous to include as many fixation points as possible when atlantoaxial instability is treated surgically.