Influence of microsurgical decompression on segmental stability of the lumbar spine - One-year results in a prospective, consecutive case series using upright, kinetic-positional MRI.

BACKGROUND: Standard procedure in patients with lumbar spinal canal stenosis is decompression to relieve the neural structures. Clinical results generally show superiority compared to nonoperative therapy after an observation period of several years. However, there is still a question of postsurgical segmental stability and correlation to clinical findings. Therefore, the aim of this prospective study was to evaluate the clinical outcome in patients who underwent microsurgical decompression in lumbar spine and particularly to analyze intervertebral movement by use of upright, kinetic-positional magnetic resonance imaging (MRI) over a period of 12 months and then to correlate the clinical and imaging data with each other. METHODS: Complete clinical data of 24 consecutive participants with microsurgical decompression of the lumbar spine were obtained by questionnaires including visual analogue scale (VAS) for back and leg, Oswestry Disability Index (ODI), Roland-Morris Disability Questionnaire (RMDQ), Short-Form-36 (SF-36), walking distance and use of analgesics with assessment preoperatively and after 6 weeks and 12 months. At the same points of time all patients underwent upright, kinetic-positional MRI to measure intersegmental motion of the operated levels with determination of intervertebral angles and translation and to correlate the clinical and imaging data with each other. RESULTS: VAS for leg, ODI, RMDQ and physical component scale of SF-36 improved statistically significantly without statistically significant differences regarding intersegmental motion and horizontal displacement 6 weeks and 12 months after operation. Regression analysis did not find any linear dependencies between the clinical scores and imaging parameters. CONCLUSIONS: In awareness of some limitations of the study, our results demonstrate no increase of intersegmental movement or even instability after microsurgical decompression of the lumbar spine over a follow-up period of 12 months, which is equivalent to preservation of intervertebral stability. Furthermore, the magnitude of intervertebral range of motion showed no correlation to the clinical score parameters at all three examination points of time.

In vitro investigation of two connector types for continuous rod construct to extend lumbar spinal instrumentation.

PURPOSE: Instrumentation of the lumbar spine is a common procedure for treating pathologic conditions. Studies have revealed the risks of pathologies in the adjacent segments, with the incidence rate being up to 36.1%. Revision procedures are often required, including extension of the instrumentation by the use of connectors to adjacent levels. The aim of this study was to determine the stiffness of side-to-side and end-to-end connectors for comparison with the use of continuous rods. METHODS: Ten human lumbar spine specimens (L1-S1) were tested about the three axes under pure moment loading of ± 7.5 Nm. Nine conditions were used to investigate the functions of the extensions for different instrumentation lengths (L3-S1 and L2-S1) and different connector levels (L3/4 and L2/3). The intersegmental range of motion (iROM) and intersegmental neutral zone as well as total range of motion (tROM) and total neutral zone (tNZ) were analyzed. RESULTS: The application of the spinal system significantly decreased the tROMs (- 44 to - 83%) and iROMs in levels L2/3 (- 56 to - 94%) and L3/4 (- 68 to - 99%) in all the tested directions, and the tNZ under flexion/extension (- 63 to - 71%) and axial rotation (- 34 to - 72%). These decreases were independent of the employed configuration (p < 0.05). The only significant changes in the iROM were observed under lateral bending between the continuous rod and the side-to-side connector at level L3/4 (p = 0.006). CONCLUSION: From a biomechanical viewpoint, the tested connectors are comparable to continuous rods in terms of ROM and NZ. These slides can be retrieved under Electronic Supplementary Material.

In vitro investigation of a new dynamic cervical implant: comparison to spinal fusion and total disc replacement.

PURPOSE AND METHODS: For the treatment of degenerative disc diseases of the cervical spine, anterior cervical discectomy and fusion (ACDF) still represents the standard procedure. However, long term clinical studies have shown a higher incidence of pathologies in the adjacent segments. As an alternative to spinal fusion, cervical total disc replacement (cTDR) or dynamically implants were increasingly used. This in vitro study analyzed the kinematics and intradiscal pressures in seven multi-segmental human cervical spine using hybrid multidirectional test method. The aim of our study was to compare the intact condition with a single-level dynamic stabilization with DCI(®), with cTDR (activC(®)) and with simulated ACDF (CeSPACE(®) cage and CASPAR plate). RESULTS: No significant changes in the kinematics and pressures were observed in all segments after arthroplasty. The DCI(®) significantly decreased the motion of the treated segment in flexion/extension and lateral bending with some remaining residual mobility. Thereby the motion of the upper segment was increased significantly in flexion/extension. No significant changes of the intradiscal pressures were observed. With simulated fusion the motion of the indexed level was significantly decreased in flexion/extension and axial rotation with the greatest changes in the adjacent levels and the highest pressures. CONCLUSION: Based on our biomechanical study the DCI(®) can pose an alternative to fusion, which has a lesser effect on adjacent levels. This might reduce the risk of long-term degeneration in those levels. In particular, the facet joint arthritis and kyphotic deformity, as a contraindication to the arthroplasty, could be a clinical application of the dynamic implant.

Posterior dynamic stabilization in the lumbar spine - 24 months results of a prospective clinical and radiological study with an interspinous distraction device.

BACKGROUND: Interspinous distraction devices (IDD) are due to maintain or restore intersegmental range of motion (iROM) in a controlled fashion with the aim of stabilization the affected level dynamically. The following study is the first to present clinical and radiological data with the Wallis® spacer during a follow-up of 24 months. METHODS: Ten patients underwent posterior dynamic stabilization (PDS) of the lumbar spine with an IDD (Wallis® spacer) and were controlled clinically and radiologically after 3, 6, 12, and 24 months in a prospective study design. Pain intensity, functional disability and life quality were assessed by use of subjective scores. Motion analyses were performed with the help of lateral functional x-rays to determine the iROM of the operated segments and total ROM (tROM) of the lumbar spine. In addition, roentgen stereophotogrammetric analysis (RSA) was used to measure the iROM of the treated levels. RESULTS: During the postoperative course pain and disability most clinical scores were significantly improved. After 24 months we observed statistically significant reduction in back pain intensity with a mean value of 6.0 on visual analog scale (VAS) before surgery and of 2.7 at the latest evaluation. The leg pain was also decreased without statistical significance from 4.7 preoperatively to 2.1 at final follow-up. The functional disability according to Oswestry Disability Index (ODI) and Roland-Morris Disability Questionnaire (RM) was decreased both with statistical significance at all examination dates with a mean value in ODI of 40.0 % before operation and of 17.3 % after 2 years and an initial mean value in RM of 55.2 and of 23.5 % after latest follow-up. After 24 months, the results of the health related quality of life score also showed much better values with only two exceptions. The iROM of the treated levels was reduced during each follow-up examination with preserved residual mobility. Directly postoperatively and after 3 and 12 months intersegmental mobility was statistically significantly decreased with an average iROM of 6.62° before operation and of 2.69° few days after surgery, of 3.79° and 3.16° 3 and 12 months later. At 6 (4.37°) and 24 (4.01°) months follow-up iROM was also but not statistically significantly reduced. The mean tROM did not change significantly during all postoperative controls. CONCLUSIONS: The radiological findings support the thesis of posterior dynamic stabilization by the used implant. The positive clinical findings should be interpreted with caution because of the limited number of patients and the missing control group.

In vitro-analysis of kinematics and intradiscal pressures in cervical arthroplasty versus fusion--A biomechanical study in a sheep model with two semi-constrained prosthesis.

BACKGROUND: As an alternative technique to arthrodesis of the cervical spine, total disc replacement (TDR) has increasingly been used with the aim of restoration of the physiological function of the treated and adjacent motions segments. The purpose of this experimental study was to analyze the kinematics of the target level as well as of the adjacent segments, and to measure the pressures in the proximal and distal disc after arthrodesis as well as after arthroplasty with two different semi-constrained types of prosthesis. METHODS: Twelve cadaveric ovine cervical spines underwent polysegmental (C2-5) multidirectional flexibility testing with a sensor-guided industrial serial robot. Additionally, pressures were recorded in the proximal and distal disc. The following three conditions were tested: (1) intact specimen, (2) single-level arthrodesis C3/4, (3) single-level TDR C3/4 using the Discover® in the first six specimens and the activ® C in the other six cadavers. Statistical analysis was performed for the total range of motion (ROM), the intervertebral ROM (iROM) and the intradiscal pressures (IDP) to compare both the three different conditions as well as the two disc prosthesis among each other. RESULTS: The relative iROM in the target level was always lowered after fusion in the three directions of motion. In almost all cases, the relative iROM of the adjacent segments was almost always higher compared to the physiologic condition. After arthroplasty, we found increased relative iROM in the treated level in comparison to intact state in almost all cases, with relative iROM in the adjacent segments observed to be lower in almost all situations. The IDP in both adjacent discs always increased in flexion and extension after arthrodesis. In all but five cases, the IDP in each of the adjacent level was decreased below the values of the intact specimens after TDR. Overall, in none of the analyzed parameters were statistically significantly differences between both types of prostheses investigated. CONCLUSION: The results of this biomechanical study indicate that single-level implantation of semi-constrained TDR lead to a certain hypermobility in the treated segments with lowering the ROM in the adjacent levels in almost all situations.

Has overweight any influence on the effectiveness of conservative treatment in patients with low back pain?

PURPOSE: Low back pain and overweight are two relevant disabling health conditions. To date, there is a lack of information about the effectiveness of nonoperative therapy in persons with overweight and low back pain. The aim of our study was to evaluate if overweight has any influence on the effectivity of conservative treatment in patients with low back pain during a mid- to long-term time period. METHODS: 128 patients with low back pain participated in this study. All of them got an inpatient conservative treatment program. The weight status was classified according to the body mass index (BMI) in three weight groups (normal, overweight, obesity). The patients were asked to fill out a standardized questionnaire regarding self-reported pain with the visual analog scale and their disability with the Oswestry Disability Index and the Roland-Morris Disability Questionnaire at four time points (beginning and end of hospital stay and after 5 and 17 months). RESULTS: Concerning the short-term results of the three scores, we always observed an improvement of the patients' condition with statistically significant reduction of pain and disability at discharge. This was true for the total collective as well as for each of the three BMI-groups when considered separately. The pain intensity and disability were still and mostly statistically significantly decreased in the mid- to long-term follow-up. Regarding the three BMI-groups among themselves, the differences of the data in the pain and disability scores showed generally no statistical significance. CONCLUSIONS: We conclude for the first time that a conservative treatment program in patients even with chronic low back pain is effective both in a short-term and a mid- to long-term time period respectively without any significant differences between patients with a normal BMI or with overweight or obesity.

Video Consultations and Their Utilization by Orthopedic and Trauma Surgeons During the COVID-19 Pandemic. A Go-To Technology in the Future or Just a Stopgap? / Die Videosprechstunde: Anwendungsverhalten bei Orthopäden und Unfallchirurgen während der COVID-19-Pandemie. Zukünftiger Dauerbrenner oder nur Eintagsfliege?

BACKGROUND: During the COVID-19 pandemic, the contact restrictions imposed for protection against infection have limited the options for direct medical therapy. Considering this, the present study aimed to evaluate the utility of the rarely used online video consultation as an alternative treatment form for orthopedic and trauma surgeons and analyze its potential for future use. METHODS: During calendar week 24 in the year 2020, 215 specialists in orthopedics and orthopedics and trauma surgery in the city and greater region of Hanover, Germany, were enrolled in a questionnaire-based evaluation of their use of video consultations. The analysis consisted of 125 completed questionnaires, which corresponded to a return rate of 58.1%. The completed questionnaires recorded the number of users, frequency of utilization, and advantages and disadvantages of online treatment, as well as provided an assessment of the future use of telemedicine and video consultations. Furthermore, we considered the necessary requirements for using video consultations and for continuing their use in the future as well as the potential of performing online consultations given that all pertinent conditions are fulfilled. RESULTS: Among the 125 respondents, only 17 (13.6%) had already experienced video consultations, all starting during the COVID-19 pandemic, but with very low frequencies (maximum of one-three times per week). Despite the limitations, the advantages included helping patients receive the required treatments and reducing the need for travel. However, the respondents mentioned that there were several disadvantages due to diagnostic limitations: there was no direct examination, primary consultations were restricted, and possibilities of consultations and explanations were reduced. Of the 108 (86.4%) respondents who had not experienced video consultations, only 9 (8.3%) had specifically planned to conduct online consultation, whereas 57 (52.8%) had no such intention in the foreseeable future and 42 (38.9%) were undecided on this point. They stated diagnostic limitations because of the lack of direct examination (44/77.2%) and the indispensable personal contact with the patient (30/52.6%) as main counter-arguments. According to all the respondents, the main requirements for the implementation of video consultations included establishment of proper technology (81.6%), adequate remuneration (61.6%), legal certainty (58.4%), fast and unbureaucratic support for installation and in case of problems (51.2%), and a manageable bureaucracy during the initial period (44.8%). CONCLUSION: Video consultations and telemedicine in general undoubtedly have advantages, primarily concerning the protection from infection and contact restrictions, which are increasingly requested by patients. However, the collected data indicate that this approach may remain less important than personal consultations in the field of orthopedics and trauma surgery. As suggested by available data, this does not apply to other fields such as psychotherapy or general medicine.

Comparison of molding helmet therapy versus natural course in twins with nonsynostotic head deformation.

This observational study aims to compare the effectiveness of helmet therapy versus natural course in twin siblings suffering from nonsynostotic head deformations. A retrospective analysis of all twin couples treated with helmet therapy between March 2009 and May 2017 at an orthopedic hospital was conducted. Inclusion criteria were me if only one twin received helmet therapy. The other twin acted as control. A classification for different head shapes was used. A total of 61 twin couples was included. Change in outcome parameters of helmet therapy and natural course differed significantly: cranial vault asymmetry (CVA) -0.66 cm vs. -0.04 cm, cranial vault asymmetry index (CVAI) -5.35% vs. -0.51% (both p < 0.001), cephalic index (CI) -3.10% vs. -1.91% (p = 0.006). Helmet therapy showed a success rate (CI < 90% and CVAI ≤7% or better) of 63.6% vs. 21.1% in children with natural course (p = 0.002). Within the limitations of the study it seems that the results of this retrospective, single-center study confirm that helmet therapy to be a reliable treatment for mild to severe positional head deformation.

Reconstruction of the patella with an autogenous iliac graft: clinical and radiologic results in thirteen patients.

PURPOSE: Extension lag, quadriceps weakness and subluxation of the extensor apparatus are known complications of patellectomy. In the case of total knee joint replacement with a nonconstrained system an instability may be encountered. Reconstruction of the patella allows restoration of the moment arm to improve quadriceps leverage. The goal of our study was to analyse the clinical and radiological results after reconstruction of the patella with an autogenous iliac graft. METHODS: 13 previously patellectomized patients had reconstruction of the patella with an autogenous iliac graft and were retrospectively studied by clinical and radiographic examination. For evaluation we used the scores of Feller and the Knee Society. Also, all complications were recorded. RESULTS: After an average follow-up of 40.1 months, nine patients had full strength of the quadriceps, while six had an improved function of the extensor apparatus. The mean Feller score was 21.8 and the Knee Society score was 67.3 for knee and 57.5 for function. Six complications occurred including three infections, two problems with the replaced patella and one fracture of the anterior superior iliac spine. CONCLUSIONS: Reconstruction of the patella with an autogenous iliac graft enables the strength of the extensor apparatus with restoration of the knee joint.

Clinical and radiological outcome of the treatment of osteonecrosis of the femoral head using the osteonecrosis intervention implant.

The aim of this study was to evaluate the clinical and radiological outcome of the treatment of osteonecrosis of the femoral head by implantation of an osteonecrosis intervention rod. In this retrospective study the follow-up of 19 patients with 23 osteonecrotic femoral heads treated with implantation of an osteonecrosis intervention implant was assessed. From 19 patients with 23 necrotic femoral heads, there were 13 cases in which a total hip replacement was necessary. This implies a survival rate of 44% after implantation of an osteonecrosis intervention rod after a mean follow-up of 1.45 years. The outcome after core decompression combined with the insertion of a tantalum osteonecrosis intervention implant did not show superior results compared to core decompression alone. This is in contrast to existing studies. In addition, this study showed that in cases of total hip replacement, no problems appeared during explantation of the tantalum rod.

A customized modular reference array clamp for navigated spine surgery.

INTRODUCTION: The current authors have developed a modular system of reference array fixation which is tailored specifically to the spinal level being operated upon. They believe that this system may further increase the precision and accuracy of pedicle screw placement. MATERIALS AND METHODS: Two formalin-fixed whole body cadavers were used for this study. For cervical spine evaluation of the reference clamp, four odontoid screws (two per cadaver) for C1/C2-fusion and four lateral mass screws (two per cadaver) were implanted. Following navigated screw placement with 2D and 3D fluoroscopic verification, insertion of two lateral mass screws was performed. In the same way, lumbar and thoracic pedicle screws were implanted. Two pedicle screws were placed at two levels of the lumbar and two levels of the thoracic areas giving an overall of 16 screws implanted (8 cervical, 4 thoracic, and 4 lumbar). Postoperative evaluation involved comparison of postoperative 3D scans and preoperative planning images. A simple classification system was used for evaluation of any deviation from the planned trajectory. RESULTS: All pedicle screw placements were performed as planned without any technical problems. The reference array clamps remained in position at all the spinal levels at which they were employed with no loosening or displacement and no secondary damage to any of the spinous processes. Manual manipulation was performed but no displacement or slippage was observed. Image artefacts caused by the reference clamp were not significant as to obscure the area of interest. Both imaging modalities (Iso-C 3D and Vario 3D) generated sufficiently precise 3D images. There was no substantial difference in quality when those two systems were compared. DISCUSSION: Insufficient fixation of the reference clamp can lead to failure and complications. To date, no reference clamp systems have been developed specifically for navigated spine surgery. CONCLUSIONS: Stable reference array fixation is a critical step in navigated surgery. To date, the same reference clamps have been applied to the spinal anatomy as have been developed originally for the appendicular skeleton. The current investigators have developed a novel modular clamp and have demonstrated its efficacy in a cadaveric model.

Total hip arthroplasty and lumbar spine disorders: Plain co-existence or mutual influence?

Lumbar spine disorders (LSD) might influence the outcome after total hip arthroplasty (THA). Despite a known common prevalence of LSD and degenerative hip disorders, this study investigates their mutual influence in case of co-existence with the purpose to advance surgeons planning and patient's prognosis. Patients with and without LSD were compared before and at the one-year postoperative examination. For clinical evaluation the WOMAC was assessed. The radiological analysis focused on cup anteversion and inclination. The total group included 203 consecutive patients. The overall incidence of LSD was 51.0%. Patients with LSD were on average 4.3 years older and had a 1.8 higher BMI than non-LSD patients (P<0.05). The cup positioning and the clinical results were comparable between both groups before and at the last time of follow up (P>0.05). No hip dislocations nor clinical signs of impingement were seen.We can conclude that there is a high degree of co-existence of LSD and hip disorders. However, a strong negative impact of LSD to clinical or radiologic results could not be confirmed in our study.

Conservative treatment of upper cervical spine injuries with the halo vest: an appropriate option for all patients independent of their age?

OBJECT: Most upper cervical spine injuries are able to heal conservatively by halo vest application. The acceptance of the halo is different among patients due to the weight of the apparatus and the limited mobility it causes. Additionally, the fracture healing rate in older patients seems to be inferior to that in younger patients, which would make an operative stabilization procedure more appropriate for the elderly. Furthermore, the risk of complications is assumed to be higher in older people. The purpose of this retrospective study was to find out if there are differences in the clinical and radiological results and in complication rates between 2 patient groups with upper cervical spine injuries and halo vest treatment with special interest of their age group. METHODS: A total of 29 patients with upper cervical spine injuries were treated by halo vest application. The clinical and radiological results and the complication and revision surgery rates were identified. Patients were divided into 2 groups (18 patients were < 65 years and 11 were > 65 years), and the results were evaluated to examine whether there were any differences. RESULTS: The clinical and radiological results and the complication rate were not statistically significantly different between the 2 patient groups; however, there was a tendency for a longer time interval for fracture healing and more complications in the elderly people. CONCLUSIONS: If the conditions for conservative treatment of upper cervical spine injuries with halo fixation are right, the clinical and radiological results are good and almost similar in patients regardless of their age, although there is a tendency for more complications in older people.

Operative management for atlantoaxial instability in case of bilateral high-riding vertebral artery.

INTRODUCTION: In case of atlantoaxial instability dorsal C1-C2 screw fixation is the most appropriate procedure to get immediate and sufficient three-point fixation. However, this method cannot be performed in bilateral high-riding vertebral arteries because of high risk of VA injury. CASE DESCRIPTION: In a 66-year-old woman who presented with neck pain due to atlantoaxial instability bilateral high-riding VAs were detected in CT. To avoid VA injury a dorsal stabilization procedure with a hook-rod system and interspinous autologous iliac crest graft was performed. The intra- and postoperative courses had no complications and the hook-rod construction clinically led to immediate postoperative stability. After 24 months the patient was painfree. CONCLUSIONS: In case of atlantoaxial instability and bilateral high-riding VAs dorsal C1-C2 fixation procedure with a hook-rod system and interspinous bone grafting seems to be an appropriate alternative surgical technique and can get immediate and clinically sufficient stability with no risk of VA injury.

Outcome analysis of molding helmet therapy using a classification for differentiation between plagiocephaly, brachycephaly and combination of both.

PURPOSE: The incidence of positional head deformation has increased during the last decades. Helmet therapy has been proved to be a reliable method for the treatment of nonsynostotic skull deformities. Until today, a simple classification to differentiate between different head shapes has not been established. MATERIALS AND METHODS: We suggest a classification system to group patients with plagiocephaly, brachycephaly, and a combination of both, using two simple values: cranial vault asymmetry (CVA), and cephalic index (CI). We further analyzed a study population of 1050 children treated with molding helmets to identify prognostic variables for better outcome within our proposed classification. RESULTS: In all, 736 patients were male (70.10%) and 314 patients were female (29.90%). Mean improvement of cranial vault asymmetry index (CVAI) ranged from 2.94% to 7.08% (CVA 0.37 cm-0.86 cm) in subgroups of patients defined by classification and severity of deformation. In patients with brachycephaly, CI improved from 4.17% to 8.22%. Duration of therapy differed from 21 weeks to 24 weeks. Children aged 6 months or less showed greater improvement and shorter duration of therapy compared to older patients. In addition to early onset of therapy, classification and severity of deformation were significantly associated with a reduction of the deformation under therapy. There were distinct differences in outcomes between different head shapes. CONCLUSION: Helmet therapy should be initiated early. Our analysis suggests that the proposed classification correctly identifies patients whose deformation is reduced under therapy. LEVEL OF EVIDENCE: III.

Influence of proprioceptive insoles on spinal curvature in patients with slight idiopathic scoliosis.

PURPOSE: Proprioceptive insoles are known to influence the functions of posture and gait by modulations of the sensory structures at the sole of the foot. Literature has shown that they could improve the position of the upper-body in patients with postural complaints of the musculoskeletal system. The aim of this study was to evaluate the influence of proprioceptive insoles on the spinal curvature in patients with slight idiopathic scoliosis. PATIENTS AND METHODS: Eighteen patients were included in this prospective, single-centre, randomized study. All patients needed to have a relevant growth potential and suffered from a slight idiopathic scoliosis. Two groups were used, where group 1 performed physiotherapy twice a week, whereas group 2 was additionally supplied with proprioceptive insoles. Patients underwent three-dimensional rasterstereography for back-shape analysis. Furthermore, a conventional x-ray imaging of the spine was performed at the beginning and 1 year later to document the curvatures. RESULTS: There was no statistical difference in the Cobb angles, and in almost all parameters of the rasterstereography, there was no statistically significant change between and within both groups. CONCLUSION: According to the results of this study, there was no evidence of any statistical significant effect of proprioceptive insoles on spinal curvature in patients with slight idiopathic scoliosis.

Workflow and simulation of image-to-physical registration of holes inside spongy bone.

PURPOSE: Mastoid cells as well as trabecula provide unique bone structures, which can serve as natural landmarks for registration. Preoperative imaging enables sufficient acquisition of these structures, but registration requires an intraoperative counterpart. Since versatile surgical interventions involve drilling into mastoid cells and trabecula, we propose a registration method based on endoscopy inside of these drill holes. METHODS: Recording of the surface of the inner drill hole yields bone-air patterns that provide intraoperative registration features. In this contribution, we discuss an approach that unrolls the drill hole surface into a two-dimensional image. Intraoperative endoscopic recordings are compared to simulated endoscopic views, which originate from preoperative data like computed tomography. Each simulated view corresponds to a different drill pose. The whole registration procedure and workflow is demonstrated, using high-resolution image data to simulate both preoperative and endoscopic image data. RESULTS: As the driving application is minimally invasive cochlear implantation, in which targets are close to the axis of the drill hole, Target Registration Error (TRE) was measured at points near the axis. TRE at increasing depths along the drill trajectory reveals increasing registration accuracy as more bone-air patterns become available as landmarks with the highest accuracy obtained at the center point. At the facial recess and the cochlea, TREs are ([Formula: see text]) mm and ([Formula: see text]) mm, respectively. CONCLUSION: This contribution demonstrates a new method for registration via endoscopic acquisition of small features like trabecula or mastoid cells for image-guided procedures. It has the potential to revolutionize bone registration because it requires only a preoperative dataset and intraoperative endoscopic exploration. Endoscopic recordings of at least 20 mm length and isotropic voxel sizes of 0.2 mm or smaller of the preoperative image data are recommended.

Vertebral artery complications in anterior approaches to the cervical spine: report of two cases and review of literature.

BACKGROUND: Cases of lesions to either the carotid artery or the vertebral artery in anterior approaches to the cervical spine are rarely found in medical literature. Two cases of vertebral artery injury in anterior approaches as well as a review of the pertinent literature are presented. In cases of arterial injury, appropriate management strategies are necessary to avoid or minimize harm to the patient. CASE REPORTS: In the first case, the vertebral artery was injured during decompression of a cervical spinal stenosis while drilling the neuroforamen. Local compression provided sufficient control of hemorrhage. Nevertheless, rebleeding from a pseudoaneurysm occurred 2 days later. After removal of the hematoma, the pseudoaneurysm was treated successfully with coils by an endovascular approach. In the second case, misplacement of one screw in screw-fixation of a type II odontoid fracture caused a pseudoaneurysm of the vertebral artery. This led to a fatal subarachnoid hemorrhage 4 days later. CONCLUSIONS: In ventral approaches to the cervical spine, precise preoperative planning and a detailed knowledge of the surgical anatomy are mandatory. In cases of injury to the vertebral arteries, direct surgical repair is most appropriate to prevent complications arising from fistulas, late-onset hemorrhages, pseudoaneurysms, thrombosis, and emboli. Alternatively, endovascular techniques or even clipping or ligation of the affected artery should be considered.

Risk factors for outcome and complications of dorsal foraminotomy in cervical disc herniation.

BACKGROUND: Dorsal foraminotomy is a standard operative procedure for lateral cervical disc herniation. Factors associated with surgical complications and clinical outcome in dorsal foraminotomy of cervical disc herniation were evaluated in a retrospective cohort study. METHOD: Thirty-nine patients were operated upon for unilateral, monosegmental, mediolateral cervical disc herniation (+/- associated spondylosis) from 1997 to 1999. Preoperative radiologic imaging and surgical reports were analyzed. Motor disfunction, neck irritation, and radicular pain were evaluated. Outcome was ranked according to modified Odom's criteria at 6 weeks and 1 year postoperatively. RESULTS: Six weeks after injury 7 of 39 patients (18%) showed neck irritation. No new neurologic deficit was seen. All patients with preoperative paresis improved; two had early relapses of a medial soft disc prolapse (2/39). Residual radicular pain was seen in 3 of 39 patients (8%) within 30 days postoperatively, necessitating surgical revision. Factors of surgical failure were associated spondylosis (2/3) and residual mediolateral disc protrusion (1/3). In one patient with associated spondylosis, local pain due to a symptomatic fracture of the lateral process of D1 resolved after revision. Duration of preoperative radicular pain was identified as a risk factor for unfavorable outcome. CONCLUSION: In lateral cervical disc herniation, associated spondylosis or medial disc protrusion poses a significant risk of surgical failure and complications of dorsal foraminotomy. Reducing the radicular failure rate by enlarging the bony decompression may lead to local failure. In well-selected patients with a lateral cervical free disc fragment, dorsolateral foraminotomy is successful and safe.

Bioabsorbable interbody magnesium-polymer cage: degradation kinetics, biomechanical stiffness, and histological findings from an ovine cervical spine fusion model.

STUDY DESIGN: An experimental study using a sheep cervical spine interbody fusion model. OBJECTIVE: First, to compare anterior cervical discectomy and fusion of an experimental bioabsorbable cage consisting of a magnesium alloy and a polymer (poly-ε-caprolactone, PCL) with an autologous tricortical iliac crest bone graft. Second, to determine the degradation kinetics of the cage, assess the 2 fusion devices for biomechanical stability, and determine their histological characteristics. SUMMARY OF BACKGROUND DATA: Bioabsorbable cages are not routinely used in spine surgery at present, due to some undesirable effects such as cracks and foreign body reactions. This study involved the manufacture of a bioabsorbable cage from a magnesium alloy and the polymer PCL, which was then used as a device for anterior cervical discectomy and fusion in a sheep cervical spine fusion model. METHODS: Twenty-four sheep had anterior cervical discectomy and fusion of C3-C4 and C5-C6 with an experimental bioabsorbable cage consisting of the magnesium alloy AZ31, which was infiltrated and covered with PCL at 1 level and with an autologous tricortical iliac crest bone graft at a second level. The sheep were divided into 4 groups. After 3, 6, 12, or 24 weeks postimplantation, the animals were killed and the cervical spines were harvested. The intervertebral spaces with the cage were investigated using µ-computed tomographic images to calculate degradation kinetics. Stiffness of all monosegments was determined through biomechanical testing. Histological analysis was performed to evaluate fusion status and to detect any foreign body reactions. The results from both implants were compared. RESULTS: The magnesium-PCL cage showed nonlinear degradation over time. Both implants demonstrated time-dependent increases in stability, with a significantly greater stiffness of the bone graft after 24 weeks in all directions of motion. Histologically, the cage showed no signs of fusion with progressive encapsulation over time. CONCLUSION: In comparison with the bone graft, the bioabsorbable cage showed inferior stiffness and fusion properties. Thus, further component modifications are necessary. LEVEL OF EVIDENCE: N/A.