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.     

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.     

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.     

Adding posterior lumbar interbody fusion to pedicle screw fixation and posterolateral fusion after decompression in spondylolytic spondylolisthesis

STUDY DESIGN: This is a retrospective study analyzing 76 patients treated by decompression, pedicle screw instrumentation, and fusion for spondylolytic spondyiolisthesis with symptomatic spinal stenosis. OBJECTIVES: To verify the advantages of adding posterior lumbar interbody fusion to the usual posterolateral fusion with pedicle screw instrumentation. SUMMARY OF BACKGROUND DATA: Stabilization after decompression of spondylolytic spondylolisthesis is difficult because of a lack of fusional bone bases, gap between the transverse process bases, and incompetent anterior disc support. Posterior lumbar interbody fusion offers anterior support, reduction, and a broad fusion base. METHODS: Forty patients were treated with posterolateral fusion, and 36 were treated with additional posterior lumbar interbody fusion. They were compared for union, reduction of the deformity, and clinical results. RESULTS: The patients were followed up for more than 2 years. Nonunion was observed in three patients who underwent posterolateral fusion (7.5%), and no cases of nonunion was found in patients who underwent posterior lumbar interbody fusion. Reduction of slippage was 28.3% in those who underwent posterolateral fusion and 41.6% in those who had posterior lumbar interbody fusion (P = 0.05). In the posterolateral fusion group, eight patients (20%) had recurrence of deformity, with loss of reduction more than 50%. Hardware failures occurred in two patients who had posterolateral fusion. There was no major neurologic complications in both groups. Both groups had satisfactory results in more than 90% of patients, with marked improvement of claudication. However, subjective improvement of back pain by Kirkaldy-Willis criteria revealed differences in the excellent results. An excellent result was reported by 45% in the posterolateral fusion group and by 75% in posterior lumbar interbody fusion group. CONCLUSIONS: The addition of posterior lumbar interbody fusion to posterolateral fusion after a complete decompression and pedicle screw fixation is a recommended procedure for the treatment of spondylolytic spondylolishesis with spinal stenosis.     

Ultra-low magnetic resonance tomography of thoracic and lumbar spine osteochondrosis

The paper presents the results of tomographic studies of 119 patients with clinical manifestations of radiculopathy or radiculomyelopathy. MR tomography was performed on the Magnaview unit ("Instrumentarium", Finland) at field intensity 0.04 T. The analysis of T1- and T2-weighted sagittal tomograms providing MRT picture of osteochondrosis and various hernias shows that osteochondrosis involves several disks simultaneously while their bulging towards the vertebral canal is multiple. The severity of the hernia in some cases does not closely agree with degeneration degree or the decline of the vertebral disk height. However there is a close correlation between the size and direction of the hernia on the one hand and the clinical manifestations on the other hand.     

Pedicle instrumentation in the thoracic spine. A morphometric and cadaveric study for placement of screws

The aim of this study was to examine the possible effects of local application of a potent immunosuppressive drug, cyclosporin A (CsA), on fibroblast proliferation in vitro. Rabbit subconjunctival fibroblasts were cultured and incubated with varying doses of CsA (from 0.5 to 5%). Growth inhibition curves were obtained, and cell attachment and reversibility of drug-induced growth inhibition were studied. None of the doses stimulated fibroblast proliferation. CsA inhibited fibroblast proliferation depending on the dose and duration of application. Also, drug-induced growth inhibition decreased depending on dose and duration of application. While the dosage which led to 50% inhibition was found to be 7.2 mg/ml, 4% and higher doses had toxic effects.     

Translaminar screw fixation of the lumbar and lumbosacral spine. A 5-year follow-up

STUDY DESIGN: In a retrospective study, the long-term results of translaminar facet screw fixation of the lumbar and lumbosacral spine are reviewed. OBJECTIVES: To evaluate the clinical results, fusion rates and complications of this posterior fusion technique in various conditions of the lumbar spine. SUMMARY OF BACKGROUND DATA: Posterior fusion of the lumbar and lumbosacral spine is one of the possible methods to relieve pain and eliminate instability in degenerative conditions. Data in the literature support the use of internal fixation to optimize the rate of fusion. METHODS: Posterior lumbar and lumbosacral fixation with translaminar screws and fusion in 173 patients with degenerative changes with or without compressive syndromes including failed back syndromes, monosegmental hypermobilities, and posttraumatic conditions were investigated. Fixation and fusion with translaminar screws was performed in 57% monosegmentally, in 40% across two segments and in 2% over three segments. Decompressive surgery was performed in addition in 52% and nucleotomy in 30% of the cases. Clinical and radiologic assessment with flexion/extension x-rays was performed in 145 (83%) patients by two independent orthopedic surgeons. After an average follow-up of 68 months (range, 52-83). RESULTS: Ninety-four percent of the patients showed solid bony fusion in the radiologic follow-up. Loosening of the screws was noted in 3%, and two screws were broken without apparent motion on the functional x-rays. Pain scores decreased from 7.6 before surgery to 2.9 after surgery on a 10-point pain scale. The results were further analyzed according to Stauffer and Coventry with 99 good results, 70 satisfactory results, and 4 bad results. CONCLUSIONS: Translaminar screw fixation offers an immediate postoperative stability of the lumbar and lumbosacral spine and enhances fusion. In the present series no neurologic complications were noted. It represents a useful and inexpensive technique for short segment fusion of the nontraumatic lumbar and lumbosacral spine.     

Functional imaging of the brain using computed tomography

Data from rapid-sequence CT scans of the same cross section, obtained following bolus injection of contrast material, were analyzed by functional imaging. The information contained in a large number of images can be compressed into one or two gray-scale images which can be evaluated both qualitatively and quantitatively. The computational techniques are described and applied to the generation of images depicting bolus transit time, arrival time, peak time, and effective width.     

Preoperative assessment of advanced gastric carcinoma using computed tomography

OBJECTIVES: The role of computed tomography (CT) for the staging of gastric carcinoma is controversial. The purpose of this study was to evaluate the utility of CT in assessing the perigastric spread of advanced gastric carcinoma. METHODS: The study included 56 patients who underwent dynamic CT and laparotomy for the treatment of node-positive gastric adenocarcinoma. Preoperative CT findings were compared with surgical findings, and diagnostic accuracy was estimated. RESULTS: Sensitivity, specificity, and accuracy of preoperative CT in determining the perigastric tumor spreads were 33, 97, and 73% in pancreatic invasion, 36, 97, and 70% in level III lymph node involvement, and 89, 98, and 96% in liver metastasis. Peritoneal dissemination was not detected in 15 of 56 patients (27%), and stage IV disease was not diagnosed correctly in 18 of 40 patients (45%). CONCLUSIONS: Radiologists and surgeons must remember that pancreatic invasion, extended lymph node metastasis, and peritoneal dissemination are sometimes overlooked in CT examination in patients with advanced gastric carcinoma.     

Internal fixation of the thoracic and lumbar spine using Roy-Camille plates

Thirty patients underwent fixation of the thoracic and lumbar spine from 1986 to 1990 using the Roy-Camille pedicular screw fixation system. The spine was stabilized for a variety of pathologic entities including fracture, tumor, spondylolisthesis, postlaminectomy instability, and pseudarthrosis. All but one patient obtained solid fusion based on radiographic and clinical criteria with an average follow up of 19.5 months. All patients reported subjective improvement in preoperative pain levels. There were no neurologic complications associated with the surgical procedure. Roy-Camille plate fixation appears to offer a stable surgical construct in the treatment of thoracic and lumbar spine instability.     

Accuracy of single-energy quantitative computed tomography in the assessment of bone mineral density of cervical vertebrae

Earlier studies have shown that single-energy quantitative computed tomography (SEQCT) is a reliable method for bone mineral density (BMD) measurements in thoracic and lumbar vertebrae. Moreover, SEQCT has proved to be a useful parameter in the selection of appropriate implants in cervical spondylodesis. The aim of this study was to determine the accuracy of SEQCT in cervical vertebrae BMD measurement. BMD with reference to calcium hydroxyapatite (Ca10[PO4]6[OH]2) was assessed by SEQCT in 100 human vertebral bodies of the cervical spine. Bone cylinders were then cut from the appropriate region of interest. The cylinder volume was determined by the liquid displacement technique. The density of the mineral component was measured following incineration at 1100 degrees C for 24 h. The calculated BMD was correlated with the SEQCT values, resulting in a coefficient of r = 0.79 (P < 0.01). Mean SEQCT values were significantly lower than those determined by direct density assessment (t-test for coupled sampling, P < 0.02). This result was in agreement with studies on thoracic and lumbar vertebrae. These data suggest that SEQCT can reliably measure BMD in the cervical spine.     

Precise biopsy investigation of the kidney using computed axial tomography

Computed axial tomography (CAT) allows pinpoint renal localization for percutaneous renal biopsy. A method for using CAT is described. This method may also be used for accurate localization of masses in the retroperitoneal space, lung, kidney, liver, bone or pancreas.     

Accuracy of single-photon emission computed tomography myocardial perfusion imaging in patients with stents in native coronary arteries

Strategies to noninvasively evaluate patients after coronary stenting have not been evaluated. To determine the accuracy of single-photon emission computed tomography (SPECT) myocardial perfusion imaging in patients after coronary stenting, 209 patients who had undergone stenting followed by late stress SPECT myocardial perfusion imaging were evaluated. Quantitative coronary angiography was performed in 33 patients following SPECT imaging. SPECT restenosis was defined as a reversible or fixed defect within the stented vascular territory. Angiographic restenosis was examined using 2 definitions: total area narrowing > or =50% or > or =70% of the stent site or stented artery. The SPECT and angiographic findings were concordant in 22 of 33 stented vascular territories using the 50% definition of restenosis and in 29 of 33 stented territories using the 70% definition. Use of the 70% definition of restenosis resulted in improved accuracy of SPECT to detect a significant stenosis in the stented artery. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of SPECT were 95%, 73%, 88%, 89%, and 88% respectively. In patients with positive SPECT scans, the most significant stenosis in the stented artery was outside the stent site in 50% of cases. SPECT imaging appears to be accurate to predict significant stenosis in the stented artery, although the most severe stenosis is frequently distant from the stent site.     

Accuracy of cortical and trabecular bone measurements with peripheral quantitative computed tomography (pQCT)

In order to assess the accuracy of peripheral QCT (Stratec XCT 960) we analysed scans of the European Forearm Phantom and another phantom consisting of K2HPO4 encased in aluminium tubes to simulate cortical walls. Additionally 14 cadaveric forearm specimen scans were compared to CT scans acquired on a GE9800Q. The accuracy for density assessment of the European Forearm Phantom was better than 3%. A small increase in density was observed with increasing thickness of the aluminium wall (10% for each mm). Density measurements within the wall were confounded by limited spatial resolution. For a thickness of less than 4 mm, the density within the wall was underestimated by up to 40%. The measurement of mineral content was not influenced by this effect and showed an accuracy error of less than 6%. The agreement of density measurements on the different CT systems was very strong (R2 > 0.96; RMSE < 6.2%). Our findings suggest that the Stratec pQCT scanner very accurately measures volumetric trabecular and total bone mineral densities at the distal radius while the assessment of cortical density is associated with considerable inaccuracies due to limited spatial resolution.     

Adaptation of the lumbar spine to different positions in bicycle racing

STUDY DESIGN: A radiologic and electromyographic study was done of the adaptation of the lumbar spine to high-performance cycling. OBJECTIVES: To evaluate changes in the lumbar spine produced by different cycling positions on different types of bicycles used during competition. METHODS: Three professional cyclists were observed to evaluate changes in the lumbar spine. Radiographs were obtained of the different positions adopted by the cyclists during competition, and changes in the angles of the lumbar spine were measured. An electromyographic study was done of the abdominal, lumbar, and thoracic paravertebral muscles. RESULTS: The cyclists' positions involved a change from discal lordosis to kyphosis. To obtain a more aerodynamic position, the cyclists flexed the hip and made the pelvis horizontal without changing disc angles. The contraction of paravertebral lumbar muscles was proportional to pedalling intensity and decreased in more aerodynamic positions. The tone of the paravertebral thoracic muscles depended on the extent of cervical hyperextension. Abdominal muscles remained relaxed in all bicycle positions and with all pedalling intensities. CONCLUSIONS: The changes observed could modify the normal biomechanics of the lumbar spine, but the overall mechanical load on the spine is reduced by shifting weight onto the upper limbs. The imbalance that occurs between the activity of flexor and extensor muscles could cause lumbar pain in persons without proper physical preparation.     

Measurement of lumbar spine flexion-extension using a low-field open-magnet magnetic resonance scanner

RATIONALE AND OBJECTIVES: The authors investigated the feasibility of using a low-field open-magnet magnetic resonance (MR) scanner to acquire functional flexion-extension images for range of motion (ROM) measurements on the lumbar spine. METHODS: Seventeen healthy subjects with no symptoms of back pain (age range, 22-59 years) were scanned in a low-field open-magnet MR scanner in the flexed, neutral, and extended positions. Each image was downloaded to a computer workstation for subsequent flexion-extension, lordosis, and ROM measurement. RESULTS: Data from two subjects were not analyzed because their images did not show all the lumbar vertebrae. For the remaining 15, there was a large variation in the magnitude of the ROM values (range, 9 degrees-70 degrees; mean 36.4 degrees, SD 16.5 degrees). However, there was a significant correlation between age and ROM (r = -0.63; P < 0.05). CONCLUSIONS: The low-field open-magnet MR scanner provides a method for noninvasive imaging of the lumbar spine, allowing the subject freedom of movement in the horizontal plane. This enables functional flexion-extension images of the lumbar spine to be acquired.     

Exposures to patient and personnel in computed axial tomography

Distribution of radiation exposure circumcranially for patients undergoing brain scanning with EMI computed tomographic equipment was measured using thermoluminescent dosimeters. The exposures are found to lie in the range of 1-5 R depending on position relative to tube motion. The maximum exposure of 5 R in CT scanning lies between the estimated exposure of 1.2 R for skull radiography and approximately 10 R for angiographic examination. Measured exposures are reported corresponding to locations of the patients' eyes, thyroid, chest and gonads, and at various locations in the vicinity of the unit.     

The initial results of lumbar dual-energy x-ray absorptiometry (DEXA) compared to double-energy quantitative computed tomography (DE-QCT)

Bone density measurements were performed on 51 patients with suspected osteoporosis. We used DE-QCT and DEXA. The methods were compared with regard to deviation from normal. In 29 of the 51 patients there was more than half standard deviation and in 12 of the 51 cases there was more than a full standard deviation.     

Detection of small hepatocellular carcinomas in cirrhotic livers using iodised oil computed tomography

The chromosome dicentric aberrations in the lymphocytes and levels of antibodies to human thyroid microsomal antigen in the serum of the children lived in the area of Bryansk Province suffered from the Chernobyl accident was examined. Correlation between those tests was not estimated: the autoantibodies were revealed in group with dicentrics and without those in 4.0% and 4.5% of cases correspondingly. Antimicrosomal antibodies were revealed more frequently (5.0%) and in higher titers in the children from the more polluted Bryansk Province than in those from Kaluga Province (3.1%). These data can testify about the role of inside radiation of thyroid gland in appearance of autoimmune thyroiditis signs.