Study of Two-Photon Exchange via the Beam Transverse Single Spin Asymmetry in Electron-Proton Elastic Scattering at Forward Angles over a Wide Energy Range.

We report on a new measurement of the beam transverse single spin asymmetry in electron-proton elastic scattering, A_{⊥}^{ep}, at five beam energies from 315.1 to 1508.4 MeV and at a scattering angle of 30°<θ<40°. The covered Q^{2} values are 0.032, 0.057, 0.082, 0.218, 0.613 (GeV/c)^{2}. The measurement clearly indicates significant inelastic contributions to the two-photon-exchange (TPE) amplitude in the low-Q^{2} kinematic region. No theoretical calculation is able to reproduce our result. Comparison with a calculation based on unitarity, which only takes into account elastic and πN inelastic intermediate states, suggests that there are other inelastic intermediate states such as ππN, KΛ, and ηN. Covering a wide energy range, our new high-precision data provide a benchmark to study those intermediate states.

[Rheumatoid instability in the cervical spine : Diagnostic and therapeutic strategies]. / Die rheumatische Instabilität der Halswirbelsäule : Diagnostik und therapeutische Strategien.

BACKGROUND: The involvement of the cervical spine in rheumatoid arthritis (RA) continues to be of clinical importance even in this age of biologics. Pathophysiological changes begin with an isolated atlantoaxial subluxation and may progress to a complex craniocervical and subaxial instability. The onset of cervical myelopathy can occur at any time and leads to a deterioration of the prognosis for the patient. THERAPY: Treatment of the rheumatoid cervical spine should be aimed at improvement of the symptoms and prevention of further progress of the disease. In the case of instability, this is only possible by surgical treatment. The increasing usage of biological agents has led to a change in the clinical picture of the cervical involvement in RA patients. There are fewer patients presenting with isolated atlantoaxial instability. In contrast, the number of patients with complex craniocervical and/or subaxial instabilities is increasing. Complex cervical instabilities may require a longer fusion from the occiput to the upper thoracic spine. Modern operative techniques make this complex surgery also possible in severely disabled patients with a high comorbidity.

[Relevance of spinal navigation in reconstructive surgery of the cervical spine]. / Relevanz der spinalen Navigation in der rekonstruktiven Halswirbelsäulenchirurgie.

BACKGROUND: Spinal navigation has made significant advances in the last two decades. After initial experiences with pedicle screws in the thoracic and lumbar spine, technological improvements have resulted in their increased application in the cervical spine. Instrumentation techniques like cervical pedicle screws, lateral mass screws in C1 and transarticular screws C1/C2 have become standard due to the application of image guidance. TECHNIQUE: Different navigation techniques can be distinguished based on the type of imaging. In the cervical spine, the preoperative computer tomography (CT) scan that requires intraoperative matching is still the standard of care due to the high image quality. 3D fluoroscopy navigation techniques are currently widely used in the lumbar spine, but the reduced image quality obviates the application in the more sophisticated cervical anatomy or the cervicothoracic region. The future availability of intraoperative CT scans (iCT) combines the advantages of high image quality with those of intraoperative image acquisition. This will lead to a wider use of image guidance in the cervical spine and will enable the surgeon to apply minimally invasive techniques with higher accuracy. APPLICATION: The successful application of spinal navigation is based on the technical knowledge of navigation systems and its exercise in daily routine. Only the sufficient experience of the clinical staff makes it possible to standardize operational procedures to increase patient safety, reduce radiation dose and shorten operation time.

New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets.

New measurements of the beam normal single spin asymmetry in the electron elastic and quasielastic scattering on the proton and deuteron, respectively, at large backward angles and at ⟨Q^{2}⟩=0.22 (GeV/c)^{2} and ⟨Q^{2}⟩=0.35 ( GeV/c)^{2} are reported. The experimentally observed asymmetries are compared with the theoretical calculation of Pasquini and Vanderhaeghen [Phys. Rev. C 70, 045206 (2004).PRVCAN0556-281310.1103/PhysRevC.70.045206]. The agreement of the measurements with the theoretical calculations shows a dominance of the inelastic intermediate excited states of the nucleon, πN and the Δ resonance. The measurements explore a new, important parameter region of the exchanged virtual photon virtualities.

[Low back pain in rheumatoid arthritis]. / Rückenschmerz bei rheumatoider Arthritis.

Low back pain (LBP) in patients with rheumatoid arthritis (RA) has so far been of little concern in clinical investigations. The main focus of scientific publications on spinal problems in RA was the cervical spine. In a recent study, we could demonstrate that LBP in RA patients leads to a significantly higher degree of disability and depression as well as to a reduction in quality of life compared to RA patients without LBP. If there is a specific reason for the additional symptom of LBP, such as spinal stenosis or segmental instability, surgical treatment may be indicated to improve disability and quality of life. For a successful outcome of spinal surgery it is important to address the specific aspects of RA patients, such as poor bone quality and the immunosuppressive effect of antirheumatic drug treatment. Whenever possible, minimally invasive surgical techniques should be used and the immunosuppressive medication should be stopped before surgery.

Unilateral laminoplasty with lateral mass screw fixation for less invasive decompression of the cervical spine: a biomechanical investigation.

PURPOSE: To compare the stabilization behavior of additional unilateral mass screw fixation with current standard procedures in patients with cervical spondylotic myelopathy (CSM) in a biomechanical study. METHODS: Ten human C2-C7 cervical specimens were tested under various segment conditions: native (NAT), laminoplasty (LP), laminoplasty with unilateral (LPU) or bilateral (LPB) stabilization, laminectomy with bilateral stabilization (LCB), and laminectomy. The instrumented level was from C3 to C6. For each segment condition, in vitro flexibility tests were performed using a spinal simulator and an applied load of ±2.5 Nm. The three-dimensional kinematics of the entire cervical segment in three main loading directions [flexion-extension (FE), lateral bending (LB), and axial rotation (AR)] was measured with an ultrasonic motion analysis system. Analysis of variance followed by a post hoc test was used to determine differences under the specific segment conditions to assess the parameters range of motion (ROM) and neutral zone (NZ). RESULTS: For FE, the total ROM of laminoplasty (-6.3% difference to NAT) and laminectomy (+6.4%) remained at the level of native (p > 0.56), whereas the instrumentations LPU (-37.1%), LPB (-44%), and LCB (-43.2%) lead to significant reductions (p < 0.01) without significant differences in LPU to LPB and LCB (p > 0.38). The same results were found with LB. For AR, the stabilization of all instrumentations was less pronounced, but had the same tendency seen for FE and AR. The results for the NZ showed equivalent values as that for ROM. CONCLUSION: The degree of stabilization was as expected for LC and LCB; namely, no stabilization for LC and maximal stabilization for LCB. LPU exhibited almost the same degree of stabilization as LCB. LPU could be a new treatment option for less invasive decompression for multilevel CSM.

[Complications of surgical interventions on the spinal column]. / Komplikationen bei operativen Eingriffen an der Wirbelsäule.

The number of surgical interventions for spinal diseases has greatly increased due to rapid improvements in surgical techniques. The close anatomical relationship between neural and bony structures and the various anatomical approaches to the spinal column lead to a large variety of possible surgical complications. Therefore, it seems helpful to differentiate the complications with respect to their origin. An incorrect positioning of the patient can result in palsy or even blindness. Surgical access to the spine depends on the pathology and the surgical target. Typical complications can be explained by the anatomical situation, such as the vicinity of the esophagus in the anterior approach to the cervical spine or the great vessels in anterior procedures to the lumbar spine. Complication during the surgical manipulation of the spine can be related to either decompression procedures of neural structures or spinal implants. The correction of spinal deformities can result in very specific complications.

[Incidental durotomy: intraoperative aid in ten steps]. / Iatrogene Duraverletzung: intraoperative Hilfe in zehn Schritten.

OBJECTIVE: Management of the intradural structures safely, closure of the dura according to the tear, and minimizing the epidural dead space. INDICATIONS: Incidental durotomy (ID). CONTRAINDICATIONS: None. SURGICAL TECHNIQUE: 1. Bone removal until whole dural tear is visible (if necessary); 2. intradural inspection; 3. reposition the fibers; 4. perform an inside patch (if ID > 5 mm); 5. dural closure; 6. outside patch; 7. Valsalva maneuver; 8. epidural pedicled muscle flap; 9. multilayer wound closure; 10. lumbar drainage of cerebrospinal fluid (if necessary). POSTOPERATIVE MANAGEMENT: Bed rest up to 48 h; analgesics. RESULTS: The intraspinal part of 4020 surgeries performed with the aid of a microscope were evaluated. The overall prevalence of ID was 4.4%. The prevalence was lowest in virgin microdiscectomies (1.7%) and varied from 3.6% in decompression for spinal canal stenosis up to 14.5% in revision procedures. Of the overall 195 IDs, 127 occurred in primary surgeries and 68 in revision surgeries. In 107 primary surgeries, the individual surgical technique (InT) achieved a single stage closure of the ID in 96 procedures (89.7%). Among 20 virgin surgeries, the ten-step technique (10 ST) was successful in all cases (P = 0.21). Among 42 revision procedures following failed attempts to stop the CSF leakage, the InT achieved single-stage closure in 36 procedures (85.7%), whereas after introduction of the 10 ST, closure was successful in all 26 cases (P = 0.03).

Minimally invasive posterior cervical foraminotomy for treatment of radiculopathy : An effective, time-tested, and cost-efficient motion-preservation technique.

OBJECTIVE: To relieve foraminal root impingement due to lateral soft disc fragments, bony spurs, or other rarer causes. INDICATIONS: Soft disc fragment whose bulk is >2/3 lateral to the lateral border of the thecal sac. Intraforaminal dorsal bony narrowing of the root canal. Intraforaminal synovial cyst, extra/intradural tumor. CONTRAINDICATIONS: Paramedian and median soft/hard disc protrusions. Kyphosis of the index level. SURGICAL TECHNIQUE: Patient prone in reverse Trendelenburg position with the head fixed in a Mayfield clamp. Cervical spine horizontal and approximately 10 cm above the heart. Microscope from skin to skin. Skin incision: 25 mm, about 10 mm off the midline. Microsurgical blunt splitting of the muscle layers along the fiber direction. An expandable tubular retractor or a miniaturized speculum counter retractor, table anchored, is centered on the target lamino-facet junction as confirmed by fluoroscopy. Drilling of the keyhole. The axilla of the root is exposed while preserving most of the facet complex. Epidural exploration until an extruded or subligamentous disc fragment(s) is removed. If needed, removal of the dorsal bone overlying the root exiting in the foramen. The adequacy of decompression is assessed by palpating the root along its course with a small nerve hook. Closure by layers. No drain. POSTOPERATIVE MANAGEMENT: Same day mobilization. No external brace. RESULTS: Minimally invasive posterior cervical foraminotomy (MI-PCF) was used to treat 103 patients for unilateral cervical radiculopathy. Mean follow-up was 32 months. Despite 1 cerebrospinal fluid leak, 1 wound hematoma, and 1 radiculitis during the early postoperative period, no patients required revision surgery. Visual analog scale (VAS) scores for neck/shoulder and arm improved significantly in the early postoperative period (3 months) and were maintained with time (p < 0.001). Neck Disability Index (NDI) improved significantly postoperatively but worsened slightly during follow-up (p < 0.001). Anterior decompression and fusion (ACDF) was required at the index level by 3 patients (mean: 55 months later) and at the adjacent level by 4 patients (mean: 27 months later).

Correction to: Minimally invasive posterior cervical foraminotomy for treatment of radiculopathy : An effective, time-tested, and cost-efficient motion-preservation technique.

Correction to: Oper Orthop Traumatol 2017 https://doi.org/10.1007/s00064-017-0516-6 In this article the following acknowledgement was missing:Acknowledgement: With the kind assistance of Deutsche Arthrose-Hilfe e. ….

Open-door laminoplasty : What can the unilateral approach offer?

OBJECTIVE: Multilevel posterior decompression of subaxial cervical spinal canal stenosis through a less-invasive unilateral approach. INDICATIONS: Degenerative cervical myelopathy due to multilevel subaxial spinal canal stenosis. CONTRAINDICATIONS: Cervical kyphosis or instability, bilateral radiculopathy due to foraminal stenosis, involvement of C2 or C7. SURGICAL TECHNIQUE: Unilateral subaxial approach with detachment of muscles only on one side. The ipsilateral laminae C6 to C3 are cut at the laminofacet junction and opened up. The loss of resistance is usually due to a greenstick fracture in the proximity of the contralateral laminofacet junction. The opened laminae are fixed with Z­shaped thin titanium plates. If necessary, the laminoplasty can be combined with a unilateral fixation and fusion by the same approach. POSTOPERATIVE MANAGEMENT: Early mobilization 4-6 h postoperatively. No orthosis necessary. RESULTS: A total of 131 patients (77 men, mean age 67 years) with a multilevel cervical spondylotic myelopathy (CSM) underwent surgery using a posterior approach. In 52 patients (40%), a unilateral approach was performed (laminoplasty: n = 30; laminoplasty/fusion: n = 22). In this group, the mean operation time was less compared with two other techniques (unilateral approach: 110 min; laminectomy/fusion: 150 min; 360° approach: 210 min). The postoperative European myelopathy score (EMS) improved from 12.8 to 15.2. The overall complication rate was 17% (unilateral approach: 9%; laminectomy/fusion: 18%; 360° approach: 27%).

[The new curriculum for surgery in Hamburg, Germany]. / Integrierte operative Medizin: Die studentische Ausbildung in der Chirurgie in Hamburg.

In October 2004, the medical faculty of Hamburg University started a program to restructure completely clinical teaching according to new state regulations of June 2002. In this new curriculum design, the surgical disciplines were horizontally and vertically interconnected and integrated, with a focus on practical training and problem-based teaching. This study describes the concept of clinical teaching and presents the student evaluation results of the first four blocks with a focus on performance in surgical disciplines. There was high student satisfaction with the new program, compared with results before October 2004 and also with respect to other disciplines within the new curriculum. This was especially true for the practical courses in the newly established skills lab. Future developments in e-learning and practical teaching in the skills lab are necessary to overcome restrictions on medical education due to changes in the German health care system.

[Imaging in rheumatology. Degenerative diseases of the spine]. / Bildgebende Verfahren in der Rheumatologie. Bildgebung bei degenerativen Erkrankungen der Wirbelsäule.

Degeneration of the spine is a common reason for pain in the musculoskeletal system. Radiography is an important tool for diagnosis and differential diagnosis. Cost efficacy and economy of time are advantages in using conventional x-rays. Although narrowing of intervertebral disc spaces, irregular ossification of the vertebral end-plate as well as osteophytes, facet joint osteoarthritis and spondylolisthesis can be observed, early changes in the discs or the subdiscal bone can not be detected by x-rays. Moreover, 3-dimensional imaging is not possible. Computer tomography (CT) and magnetic resonance imaging (MRI) are reliable for identifying disorders of the spine and soft-tissue. Differentiation between inflammation, trauma and tumor is possible. There is still a problem with the relationship between the information obtained by x-rays or MRI and clinical symptoms. Therefore, interpretation of radiological examinations assumes a knowledge of clinical symptoms and the different kinds of diseases which are possible.

Anatomic evaluation of two different techniques for the percutaneous insertion of pedicle screws in the lumbar spine.

STUDY DESIGN: An in vitro study in which a human cadaver model was used to examine the accuracy of two different techniques of percutaneous pedicle screw insertion in the lumbar spine. OBJECTIVES: To investigate the in vitro misplacement rate of pedicle screw insertion for two different percutaneous techniques: 1) the well established Magerl technique, and 2) a new modified technique. SUMMARY OF BACKGROUND DATA: Numerous anatomic and biomechanical studies have been conducted to analyze the in vitro and in vivo characteristics of pedicle screw insertion in the lumbar spine via an open approach, whereas there is a lack of experimental data concerning the more sophisticated percutaneous procedure. METHODS: Thirty human specimens from L1 to S1 were separated into two groups (A and B). In group A, the screws were placed in accordance with the technique described by Magerl; in group B, a new modified technique developed by the authors' research group was used. After screw placement, the specimens were dissected, and pedicle violations were noted with respect to the degree and direction of the screw misplacement. RESULTS: The dissection of the specimens showed that of 360 pedicle screws, 37 were misplaced. This finding translates into an overall misplacement rate of 10%. With the Magerl technique, 23 pedicle violations (misplacement rate, 13%) were found; with the modified technique, only 14 dislocated pedicle screws (misplacement rate, 8%) were detected. This difference was not statistically significant (P = 0.118). In both groups, there were significantly more medical pedicle violations than lateral (32 medial and 5 lateral screw dislocations). The degree of the screw misplacements varied between 1.0 and 5.0 mm. The majority of pedicle violations (30 of 37) were minor, i.e., less than 3.0 mm. CONCLUSIONS: This in vitro study showed that the percutaneous technique of pedicle screw insertion in the lumbar spine is a safe and reliable procedure. Compared with the well-established Magerl technique, the new modified technique did not decrease the misplacement rate significantly, although less pedicle violations were found in the upper lumbar spine.

Multidirectional instability of the thoracic spine due to iatrogenic pedicle injuries during transpedicular fixation. A biomechanical investigation.

STUDY DESIGN: Pedicle fracture was simulated in an in vitro model, and its effect on multidirectional stability provided by pedicle instrumentation was quantified. OBJECTIVES: To quantify the multidirectional flexibility of padicle instrumentation due to different iatrogenic pedicle injuries. SUMMARY OF BACKGROUND DATA: Misplacement of the screw and iatrogenic pedicle fracture are the main complications of pedicle instrumentation. Despite the increasing number of clinical studies dealing with this issue, there is little reliable information concerning the biomechanical effects of an intraoperative pedicle fracture. METHODS: A burst fracture was created in 10 human cadaveric five-vertebrae spine specimens, from the middle and lower thoracic spine regions. The fracture was stabilized with a semirigid pedicle screw fixation device. To simulate an intraoperative pedicle fracture, the pedicles of the instrumented segments were resected in four steps. After each pedicle injury, three-dimensional flexibility in the form of range of motion and neutral zone of the construct was determined and compared with the intact values. RESULTS: Resection of the pedicles had little effect on the multidirectional flexion-extension stability provided by the instrumentation. There were significant increases of axial rotation in the middle thoracic spine when the lateral wall was resected (range of motion, 8.2 degrees vs. 3.6 degrees; neutral zone, 4.2 degrees vs. 1.7 degrees), whereas in the lower thoracic spine, significant increases occurred only when all the pedicles were resected (range of motion, 3.8 degrees vs. 1.4 degrees; neutral zone, 1.1 degrees vs. 0.4 degree). Lateral resection of the pedicle resulted in significant increases of range of motion and neutral zone for lateral bending in both the middle thoracic spine (range of motion, 19.0 degrees vs. 10.0 degrees; neutral zone, 2.4 degrees vs. 1.1 degrees) and the lower thoracic spine (range of motion, 4.3 degrees vs. 2.5 degrees; neutral zone, 0.9 degree vs. 0.3 degree). CONCLUSIONS: Resection of the pedicles results in a significant decrease in axial rotation and lateral bending stability provided by the instrumentation. This effect was higher in the middle than in the lower thoracic spine and may be relevant to pedicle fractures produced by pedicle screws used in these regions.

Growth changes of solidly fused kyphotic bloc after surgery for tuberculosis. Comparison of four procedures.

STUDY DESIGN: A study to analyze the changes of the spinal deformity during the growth period, with regard to different operations for spinal tuberculosis in children. OBJECTIVES: To quantify the changes in the kyphotic angle and the growth ratio of the fusion bloc during spinal growth for different fusion techniques. SUMMARY OF BACKGROUND DATA: Most of the publications dealing with spinal tuberculosis in children focused on the clinical outcome with regard to different conservative and operative treatments. There is little reliable information concerning the growth of the solidly fused kyphotic bone bloc and its influence on the changes of the kyphotic deformity after different operative procedures. METHODS: The study included 117 children operated on for spinal tuberculosis at the age of 2-6 years at the Ruttonjee Sanatorium in Hong Kong during the 1950s and 1960s. Lateral radiographs obtained postoperatively and 5 and 10 years after the operation were analyzed for the growth changes of the solidly fused bone bloc. These results were compared with the different operation techniques (e.g., anterior fusion, posterior fusion, combined anterior and posterior fusion, and anterior debridement without fusion). RESULTS: The patients treated by anterior fusion showed the worst results with respect to the kyphotic angle. This was especially true when the lesion was located in the thoracic spine and several segments were involved. Regarding the growth ratio of the fusion bloc, only the combined fusion and the anterior debridement guaranteed an equal growth of the anterior and posterior height. CONCLUSIONS: Radical anterior surgery for spinal tuberculosis destroys the anterior growth and limits the capacity for spinal remodeling. Therefore, it should be avoided, if it is not absolutely necessary, for the healing of the infection or the primary correction of the tuberculous deformity.

Clinical evaluation and computed tomography scan analysis of screw tracts after percutaneous insertion of pedicle screws in the lumbar spine.

STUDY DESIGN: An examination of the accuracy of percutaneous pedicle screw placement in the lumbar spine. Using computed tomography scan analysis after implant removal, the screw tracts could be analyzed regarding the degree and direction of screw dislocation. OBJECTIVES: To investigate the misplacement rate and related clinical complications of percutaneous pedicle screw insertion in the lumbar spine. SUMMARY OF BACKGROUND DATA: The feasibility of the external fixation test has been investigated in several studies. Although pedicle screw misplacement has been reported as one of the main complications, there are no reliable data on the misplacement rate for this difficult surgical procedure. METHODS: In this study, 51 consecutive patients with suspected segmental instability were investigated after external transpedicular screw insertion for the external fixation test. Computed tomography scans of all instrumented pedicles from L2 to S1 were performed after screw removal. The screw tracts were analyzed, and the direction and degree of the pedicle violations were noted. In addition, the screw and pedicle angles were measured. RESULTS: Of 408 percutaneously inserted pedicle screws, only 27 screws (6.6%) were misplaced. There were 19 medial pedicle violations, 6 lateral cortical defects, and only 1 cranial and 1 caudal displacement. With respect to the spinal level, S1 showed the highest misplacement rate, with 11 screw dislocations (12%). After surgery, found two nerve root injuries were found. Only one of the injuries (L4) was related to the malposition of a screw. CONCLUSIONS: This study has shown that percutaneous insertion of pedicle screws in the lumbar spine is a safe and reliable technique. Despite the low misplacement rate of only 6.6%, it should be kept in mind that the surgical procedure is technically demanding and should be performed only by experienced spine surgeons.

Internal architecture of the thoracic pedicle. An anatomic study.

STUDY DESIGN: In this study, data are presented that provide the surgeon with additional information about the internal structure of the thoracic pedicle, which is especially useful for pedicle screw fixation in the thoracic spine. OBJECTIVES: To quantify the internal structure of the pedicle in the thoracic spine. SUMMARY OF BACKGROUND DATA: There are many studies describing the external dimensions of the thoracic pedicle (i.e., pedicle height, pedicle width, and pedicle axis in the transverse and sagittal planes). However, there is little reliable information concerning the internal structure of the pedicle. METHODS: Eighteen thoracic vertebrae were attached to a thin-sectioning machine and both pedicles were cut in six 1.0-mm thin slices. Slides of contact radiographs were rear-projected to a digitizer and the internal and external borders of the pedicle were digitized. Using special computer software, two external dimensions (i.e., pedicle height and pedicle width) and four internal dimensions (i.e., cortical thicknesses of the superior, inferior, medial, and lateral walls) were calculated. RESULTS: The cancellous core was more than twice as large as the cortical shell, with a range from 65.6% to 78.6% with respect to the pedicle height, and 61.3% to 71.6% with respect to the pedicle width. The medial wall was between two and three times thicker than the lateral wall throughout all the pedicle slices and thoracic levels. These differences were highly significant (P < 0.001). CONCLUSIONS: The thoracic pedicle is a complex three-dimensional structure that is mostly filled with cancellous bone. The medial wall is significantly thicker than the lateral wall, which could explain the fact that most of the pedicle fractures related to pedicle screw insertion occur laterally.

Computer navigation of parapedicular screw fixation in the thoracic spine: a cadaver study.

STUDY DESIGN: An in vitro study to investigate the advantages of computer assistance for the purpose of parapedicular screw fixation in the upper and middle thoracic spine. OBJECTIVES: To evaluate the feasibility and application accuracy of parapedicuar screw insertion with the assistance of an optoelectronic navigation system. SUMMARY OF BACKGROUND DATA: Because of anatomic limitations, thoracic pedicle screw insertion in the upper and middle thoracic spine remains a matter of controversy. The technique of parapedicular screw insertion has been described as an alternative, although the exact screw position is difficult to control. With the assistance of computer navigation for the screw placement, it might become possible to overcome these challenges. METHODS: Four human specimens were harvested for this study; 6-mm screws were inserted from T2 to T8 with the assistance of a CT-based optoelectronic navigation system. During surgery virtual images of the screw position were documented and compared with postoperative contact radiographs to determine the application accuracy. The following measurements were obtained: axial and sagittal screw angles as well as the screw distances to the anterior vertebral cortex and the medial pedicle wall. RESULTS: All 54 screws were inserted in a parapedicular technique without violation of the medial pedicle wall or the anterior or lateral vertebral cortex. The mean +/- standard deviation difference between the virtual images and the radiographs was 1.0 +/- 0.94 mm for the distance to the medial pedicle wall and 1.9 +/- 1.44 mm for the distance to the anterior cortex. The angular measurements showed a difference of 1.6 +/- 1.1 degrees for the transverse screw angle and 2.1 +/- 1.6 degrees for the sagittal screw orientation. CONCLUSION: With the assistance of computer navigation it is possible to achieve a safe and reliable parapedicular screw insertion in the upper and middle thoracic spine in vitro. The application accuracy varies for the linear and angular measurements and is higher in the axial than in the sagittal plane. It is important for the surgeon to understand these limitations when using computer navigation in spinal surgery.

[Mechanical study of potential ceramic implant materials for minimal invasive anterior lumbar interbody fusion]. / Mechanische Untersuchung potentieller keramischer Implantatmaterialien zur minimal-invasiven anterioren lumbalen interkorporellen Fusion.

While autologous bone grafts are highly suitable for use in spinal arthrodesis, their use is also associated with problems (traumatization, complications). Ceramic bone substitute materials provide an attractive alternative for lumbar interbody spinal fusion. The aim of the present study was to investigate the mechanical properties of various types of ceramic using a specific fusion method. Ten specimens each of 7 different types of ceramic were tested using a hydraulic testing machine with two different sample holders: polyurethane foam (mechanical properties similar to cancellous bone) and aluminium. The parameters axial compression and axial torque were investigated. With the polyurethane foam holders, none of the ceramic implants failed under compression, while under axial rotation, two types of ceramic failed. With the aluminium holders, 3 ceramics showed no failure up to 25 kN under compression, while under torsion all the ceramics failed. One type of ceramic showed specific fracture properties with a higher load-bearing capacity after failure in comparison with all the other types studied.