Ligamentous Augmentation to Prevent Proximal Junctional Kyphosis and Failure: A Biomechanical Cadaveric Study.

STUDY DESIGN: Biomechanical cadaveric study (level V). OBJECTIVE: To evaluate the effectiveness of polyethylene bands looped around the supra-adjacent spinous process (SP) or spinal lamina (SL) in providing strength to the cephalad unfused segment and reducing junctional stress. BACKGROUND: Proximal junctional kyphosis (PJK) is a pathologic kyphotic deformity adjacent to posterior spinal instrumentation after fusion constructs. Recent studies demonstrate a mismatch in stiffness between the instrumented construct and nonfused adjacent levels to be a causative factor in the development of PJK and proximal junction failure. To our knowledge, no biomechanical studies have addressed the effect of different methods of polyethylene band placement at the proximal junction. MATERIALS AND METHODS: Twelve fresh frozen cadavers were divided into 3 groups of 4: pedicle screw-based instrumentation from T10 to L5 ("control"), T10-L5 instrumentation with a polyethylene band to the T9 "SP," T10-L5 instrumentation with 2 polyethylene bands to the T9 "SL." Specimens were tested with an eccentric (10 mm anterior) load at 5 mm/min for 15 mm or until failure occurred. Failure was defined by the inflection point on the load versus deformation curves. Linear regression was utilized to evaluate the effect of augmentation on the load-to-failure. Significance was set at 0.05. RESULTS: Fractures occurred in all specimens tested. The mean peak load to failure was 2148 N (974-3322) for the SP group, and 1248 N (742-1754) for the control group (P > 0.05) and 1390 N (1080-2004) for the SL group. No difference existed between the control group and the SP group in terms of fracture level (P > 0.05). Net kyphotic angulation shows no differences among these 3 groups (P > 0.05). CONCLUSION: Although statistical significance was not achieved, ligament augmentation to the SP increased mean peak load-to-failure in a cadaveric PJK model.

ThermalProGAN: A sequence-based thermally stable protein generator trained using unpaired data.

MOTIVATION: The synthesis of proteins with novel desired properties is challenging but sought after by the industry and academia. The dominating approach is based on trial-and-error inducing point mutations, assisted by structural information or predictive models built with paired data that are difficult to collect. This study proposes a sequence-based unpaired-sample of novel protein inventor (SUNI) to build ThermalProGAN for generating thermally stable proteins based on sequence information. RESULTS: The ThermalProGAN can strongly mutate the input sequence with a median number of 32 residues. A known normal protein, 1RG0, was used to generate a thermally stable form by mutating 51 residues. After superimposing the two structures, high similarity is shown, indicating that the basic function would be conserved. Eighty four molecular dynamics simulation results of 1RG0 and the COVID-19 vaccine candidates with a total simulation time of 840[Formula: see text]ns indicate that the thermal stability increased. CONCLUSION: This proof of concept demonstrated that transfer of a desired protein property from one set of proteins is feasible. Availability and implementation: The source code of ThermalProGAN can be freely accessed at https://github.com/markliou/ThermalProGAN/ with an MIT license. The website is https://thermalprogan.markliou.tw:433. Supplementary information: Supplementary data are available on Github.

Unilateral Biportal Endoscopy for Lumbar Spinal Stenosis and Lumbar Disc Herniation.

Background: Unilateral biportal endoscopy (UBE) is a novel minimally invasive technique for the treatment of lumbar spinal stenosis and lumbar disc herniations. Uniportal endoscopy was utilized prior to the advent of UBE and has been considered the workhorse of endoscopic spine surgery (ESS) for lumbar discectomy and decompressive laminectomy. However, there are theoretical advantages to UBE compared with traditional uniportal endoscopy, including that the procedure utilizes typical spinal equipment that should be readily available, requires less capital cost and optical instrumentation, and provides greater operative flexibility as a result of utilizing both a working and a viewing portal7,8. Description: A 0-degree arthroscope is typically utilized for discectomy and lumbar laminectomies. The use of a radiofrequency ablator is critical to help coagulate osseous and muscle bleeders. For irrigation, gravity or a low-pressure pump, typically <40 mm Hg, can be utilized9,10. Further details regarding irrigation pressure are provided in "Important Tips." The use of a standard powered burr is typical to help osseous decompression, and Kerrison ronguers, pituitaries, osteotomes, and probes utilized in open or tubular cases suffice. Two incisions are made approximately 1 cm lateral to the midline. If working from the left side for a right-handed surgeon, the working portal is typically made at the lower laminar margin of the target level. The camera portal is then made typically 2 to 3 cm cephalad. A lateral radiograph is then utilized to confirm the portal placements. From the right side, the working portal is cephalad and the camera portal is caudal. Because of the switch, the portals may be shifted more distally.The first step is creating a working space because there is no true joint space in the spine. With use of radiofrequency ablation, a working space is created in the interlaminar space. Next, with use of a powered burr or a chiseled osteotomy, the base of the cephalad spinous process is thinned until the insertion of the ligamentum flavum is found. Next, the ipsilateral and contralateral laminae are thinned in a similar fashion. Once the osseous elements are removed, the ligamentum flavum is removed en bloc. The traversing nerve roots are checked under direct high-magnification visualization to ensure that they are decompressed. If a discectomy is necessary, standard nerve-root retractors can be utilized to retract the neural elements. With use of a blunt-tip elevator, the anular defect can be incised and the herniated disc can be removed under direct high-power visualization. In addition, a small curet can be utilized to create a defect in the weakened anulus or membrane covering the extruded disc material in order to help deliver the herniated disc material. Epidural veins are coagulated typically with use of a fine-point bipolar radiofrequency device. Alternatives: Nonoperative treatments include oral anti-inflammatory drugs, physical therapy, and epidural injections; if these fail, alternative surgical treatments include open lumbar laminectomy and/or discectomy, tubular lumbar laminectomy and/or discectomy, and other minimally invasive techniques, such as microendoscopy, uniportal endoscopy, and microscopy-assisted decompression. Rationale: UBE is a minimally invasive surgical procedure that better preserves osseous and muscular structure compared with open and tubular techniques. Conventional lumbar laminectomy involves dissection and retraction of the multifidus muscle from the spinous process to the facet joint. This exposure can damage the delicate posterior dorsal rami. Long retraction time can also lead to pressure-induced muscle atrophy and potentially increased chronic low back pain. Alternatively, smaller incisions and shorter hospital stays are possible with UBE.Similar to UBE, tubular surgery can minimize soft-tissue damage compared with open techniques; however, in a randomized trial assessing techniques for spinal stenosis surgery, Kang et al. found that UBE and tubular surgery had similarly favorable clinical outcomes at 6 months postoperatively but UBE resulted in decreased operative time, drain output, opiate use, and length of hospital stay5.Furthermore, the use of an endoscope in the biportal technique allows ultra-high magnification of the spinal pathology, decreased capital costs, and the ability to use 2 hands with freedom of movement. UBE provides clear visualization of the neural elements while keeping maximal ergonomic efficiency with the surgeon's head looking straight forward, the shoulders relaxed, and the elbows bent to 90°. Continuous irrigation through the endoscope also helps with bleeding and decreasing the risk of infection. Expected Outcomes: Long-term outcomes do not differ substantially between discectomies performed with use of the presently described technique and procedures done with more traditional minimally invasive (i.e., tubular) techniques; however, visual analogue scale scores for back pain may be better in the short term, and there is evidence of a shorter hospital stay with UBE2. Complication rates did not differ from other minimally invasive techniques. When comparing UBE and stenosis, Aygun and Abdulshafi found that UBE was associated with decreased hospital stays, operative time, and blood loss and better clinical outcomes up to 2 years postoperatively compared with tubular laminectomy12. Important Tips: The optimal hydrostatic pressure is 30 to 50 mm Hg. Pressure is determined by the distance between the fluid source and the working space. Because the working space does not change, the height of the bag decides pressure. A simple formula for pressure is calculated by dividing the distance from the working field to the irrigation source by 1.36. A rule of thumb is that if the bag is 50 to 70 cm above the patient's back, the pressure should be adequate. The advantages of using gravity rather than a pressure pump are that excessive fluid solution pressure in the epidural space can cause neurological issues such as nuchal pain, headache, and seizure11. Additionally, if the intertransverse membrane or the lateral margins of the disc are violated, hydroperitoneum can occur unknowingly due to the high-pressure system.Gravity or pump pressure of >40 mm Hg may elevate epidural pressure and mask operative bleeding. When the pump is turned off at the end of the surgical procedure, a postoperative epidural hematoma may occur because the bleeding source may not have been recognized while the pump pressure was on.Excessive pump pressure may lead to an increase in intracranial pressure, causing headache or delayed recovery from general anesthesia with stiff posture and hyperventilation.Make sure fluid is emerging from the working portal and the muscle area is not swelling to prevent soft-tissue fluid extravasation.Epidural veins are coagulated typically with a fine-point bipolar radiofrequency device.Osseous bleeding can be controlled with bone wax or a high-speed burr. Acronyms and Abbreviations: MRI = magnetic resonance imagingRF = radiofrequencyAP = anteroposterior.

Traumatic hyperextension-distraction injuries of the thoracolumbar spine: a technical note on surgical positioning.

PURPOSE: Hyperextension-distraction type injury of the thoracolumbar spine is an unstable fracture pattern that generally necessitates surgical stabilization by posterior instrumentation. Care must be taken when positioning these patients from supine to prone due to the unstable nature of their injury. The study objectives were (1) to describe a novel modification of the Jackson table turn technique, which may be safer and more effective than the conventional log-roll method and traditional Jackson table technique for positioning patients with hyperextension-distraction injuries of the thoracolumbar spine from supine to prone in the operating room and (2) to present two cases in which this technique was successfully performed. METHODS: Two patients were carefully positioned from supine to prone by our modification of the Jackson table turn technique, which utilizes a Wilson frame sandwiched between two flat-top Jackson frames. Case 1: a 65-year-old female presented status-post motor vehicle collision with a T9-T10 extension-distraction injury, requiring T7-T12 posterior spinal instrumented fusion (PSIF). Case 2: a 72-year-old female presented status-post motor vehicle collision with a T9-T10 extension-distraction injury and an unstable L1 burst fracture, requiring T7-L2 PSIF. RESULTS: Both patients remained hemodynamically stable and neurologically intact throughout positioning and postoperatively. CONCLUSIONS: This technique is safe and effective for positioning patients with hyperextension-distraction type injuries of the thoracolumbar spine from supine to prone in the operating room and may be superior to conventional methods. These slides can be retrieved under Electronic Supplementary Material.

Influence of T1 Slope on the Cervical Sagittal Balance in Degenerative Cervical Spine: An Analysis Using Kinematic MRI.

STUDY DESIGN: A retrospective kinematic magnetic resonance imaging (kMRI) study. OBJECTIVE: To evaluate the utility of kMRI in determining the relationship between cervical sagittal balance and TI alignment. SUMMARY OF BACKGROUND DATA: Thoracic inlet parameters play an important role in cervical spine sagittal balance. However, most of the literature is based on lower resolution cervical X-rays or CT scans in the supine position. METHODS: Cervical spine kMRI of 83 patients with degenerative cervical spine conditions (20-68 yr of age) was analyzed for: (1) cervical spine parameters: C2-C7 angle, C2-C7 sagittal vertical axis (SVA), cranial tilt, and cervical tilt; and (2) T1 parameters: thoracic inlet angle (TIA), T1 slope, and neck tilt (NT). Multiple logistic regression analysis and Pearson correlation coefficients were performed. RESULTS: The mean TIA, T1 slope, and NT were 78.0, 33.2, and 44.8°, respectively. The mean C2-7 angle, SVA of C2-C7, cervical tilt, and cranial tilt were -15.4°, 22.0 mm, 18.1°, and 15.1°, respectively. The ratio of cervical:cranial tilt was maintained as 55:45%. A significant correlation was found between the C2-C7 angle and T1 slope (r = 0.731), TIA and C2-C7 angle (r = 0.406), cervical tilt with C2-C7 angle (r = 0.671), T1 slope with TIA (r = 0.429), TIA with neck tilt (r = 0.733), TIA with cervical tilt (r = 0.377), SVA C2-C7 with cervical tilt (r = -0.480), SVA C2-C7 with cranial tilt (r = 0.912), and C2-7 SVA with the ratio of cranial tilt to cervical tilt (r = 0.694). CONCLUSION: An individual with a large T1 slope required large cervical lordosis to preserve physiologic sagittal balance of the cervical spine. Cranial tilt was the cervical parameter most strongly correlated with SVA C2-C7, and thus may be a good parameter to assess decompensation of cervical sagittal balance. LEVEL OF EVIDENCE: 3.

Intraoperative 3-dimensional navigation and ultrasonography during posterior decompression with instrumented fusion for ossification of the posterior longitudinal ligament in the thoracic spine.

STUDY DESIGN: A retrospective clinical study was conducted. OBJECTIVE: The purpose of this study was to describe the clinical outcomes of intraoperative 3D navigation (ITN) and ultrasonography during posterior decompression and instrumented fusion for thoracic myelopathy due to ossification of the posterior longitudinal ligament (OPLL). SUMMARY OF BACKGROUND DATA: The symptoms caused by thoracic-ossification of the posterior longitudinal ligament (T-OPLL) are usually progressive and do not respond to conservative treatment-surgical intervention is the only effective treatment option. Various methods have been described for the treatment of symptomatic T-OPLL, all of which have limitations. METHODS: The study included 18 patients with T-OPLL who underwent posterior decompression with instrumented fusion from 2006 to 2011. A staged operative procedure was used. First, pedicle screws were placed with ITN and a wide laminectomy was performed with resection of ossification of the ligamentum flavum (if present). With insufficient decompression on intraoperative ultrasonography, additional circumferential decompression was performed through a transpedicular approach. ITN-guided OPLL resection was performed using a burr attached to a navigational tracker. In all cases, posterior instrumented fusion was performed in situ. The outcomes were evaluated with the modified Japanese Orthopaedic Association scores and recovery rates. RESULTS: Intraoperative ultrasonography showed that posterior laminectomy was sufficient in 6 patients; the remaining 12 were treated with additional circumferential decompression. The follow-up period ranged from 1 to 6 years (mean period, 2.8 y). Postoperative transient neurological deterioration occurred in 1 patient, and cerebrospinal fluid leakage occurred in 4 patients. All patients showed neurological recovery with a mean Japanese Orthopaedic Association score that improved from 5.5 points preoperatively to 8.5 points at the final follow-up and a mean recovery rate of 54.5%. CONCLUSIONS: Intraoperative ultrasonography and ITN are safe and reliable imaging methods for posterior decompression and instrumented fusion for thoracic myelopathy caused by OPLL.

Occipital-C2 transarticular fixation for occipitocervical instability associated with occipitalization of the atlas in patients with klippel-feil syndrome, using intraoperative 3-dimensional navigation system.

STUDY DESIGN: Retrospective case series. OBJECTIVE: The aim of this study was to describe the clinical outcomes of cervical reduction and occipital-C2 transarticular (OCTA) fixation with an assistance of intraoperative 3-dimensional navigation system (ITNS) during the treatment of reducible occipitocervical instability (OCI) in patients with Klippel-Feil syndrome (KFS) with occipitalization of the atlas and fusion of C2-C3. SUMMARY OF BACKGROUND DATA: Patients with KFS have congenital fusions of at least 2 cervical segments and may gradually develop symptoms at the hypermobile articulations adjacent to the cervical synostosis. This is particularly common in patients with KFS with occipitalization of the atlas and C2-C3 fusion. These patients may be at risk for instability and neurological complications of the occipitocervical junction that require occipitocervical reconstruction and fusion. Numerous treatment techniques are available for this pathological condition. However, there has yet to be a study of reducible OCI, showing successful treatment with intraoperative reduction and posterior OCTA fixation using ITNS. METHODS: From 2006 to 2011, 9 patients with KFS with reducible OCI attributed to occipitalization of the atlas and C2-C3 fusion were surgically treated. After a limited foramen magnum decompression, reduction of the OCI was conducted by intraoperative cervical traction and extension, followed by OCTA fixation using a direct posterior approach and with the assistance of ITNS. The follow-up period ranged from 6 to 60 months (mean, 31 mo). RESULTS: Good decompression and bone fusion were achieved in all the patients. The clinical symptoms had improved for all patients. There were no intraoperative or postoperative complications. CONCLUSION: In patients with KFS with occipitalization of the atlas and C2-C3 fusion, manual cervical traction in tandem with cervical extension, followed by posterior OCTA fixation and fusion provides a safe, effective treatment of OCI and ventral brainstem impingement. IFTN is a feasible tool for monitoring cervical reduction and OCTA screw insertion in patients with KFS with this pathological condition.

[Use sagittal reconstruction CT for making decisions regarding the surgical strategy for cervical ossification of the posterior longitudinal ligament].

OBJECTIVE: Use sagittal reconstruction CT to verify the surgical strategy for cervical ossification of the posterior longitudinal ligament (OPLL). METHODS: A retrospective study of 161 patients (106 males and 55 females) who had undergone surgery for OPLL from July 2007 to November 2010 was performed. The mean age at surgery was 54.5 years (range from 26 to 77 years). The mean follow-up period was 28 months (12 - 54 months). There were 40 patients accept anterior approach surgeries (anterior group) which include 14 cases of anterior cervical corpectomy and fusion and 26 cases of anterior cervical discectomy and fusion. There were 120 patients accept posterior approach surgeries (posterior group) which was spinous process-splitting laminoplasty for cervical myelopathy using coralline hydroxyapatite. One patient accepted combined anterior and posterior approach. According to the sagittal reconstruction CT, the main reason for spinal cord compression was cervical disc herniation in anterior group, and OPLL in posterior group. The level of spinal cord compression was 1 to 2 levels in anterior group, and 1 to 5 levels in posterior group with a major of 2 to 4 levels. As the classification of OPLL, segmental type and circumscribed type were major of segmental type in anterior group and all of the four types were in posterior group, the distribution of each type was average. The patients of posterior group were classified into two groups according to the modified K-line classification, and clinical results were compared between the two groups. The modified K-line was defined as a line that connects the midpoints of the spinal canal at C(2) and C(7) on sagittal CT myelography. Compression to the spinal cord did not exceed the K-line in the modified K-line(+) group and did exceed it in the modified K-line(-) group. Clinical data were compared using t-test or χ(2) test. Correlation analysis was used to determine the relationships of C(2)-C(7) angulation between sagittal reconstruction CT and neutral position X-ray. RESULTS: The patient of anterior group had better recovery rate of the JOA score (72% ± 27%) than the posterior group (59% ± 35%) at the latest follow-up (t = 2.238, P = 0.027). In posterior group, the patients of modified K-line(+) group had better recovery rate of the JOA score (63% ± 37%) than the K-line(-) group (49% ± 30%) at the latest follow up (t = 2.150, P = 0.034). The C(2)-C(7) angulation on sagittal reconstruction CT was 11° ± 9° which has significantly correlated with the C(2)-C(7) angulation on neutral position X-ray which was 10° ± 10° (r = 0.947, P < 0.01). CONCLUSIONS: Considering the selection of surgical approach, it should be combined with the main clinical diagnosis for spinal cord compression, the level of compression, the classification of OPLL and the kyphotic alignment of the cervical spine. The modified K-line is a simple and practical tool for making decisions regarding the surgical strategy for cervical OPLL patients.

Surgical management of symptomatic os odontoideum with posterior screw fixation performed using the magerl and harms techniques with intraoperative 3-dimensional fluoroscopy-based navigation.

STUDY DESIGN: Retrospective case series. OBJECTIVE: To evaluate the accuracy of screw fixation using intraoperative three-dimensional fluoroscopy-based navigation (ITFN) and to assess the clinical outcomes of this treatment regimen. SUMMARY OF BACKGROUND DATA: The surgical management of symptomatic os odontoideum poses considerable difficulties due to the highly variable anatomy of the upper cervical spine and surrounding neurovascular structures. Various methods have been described for the treatment of symptomatic os odontoideum, all of which have limitations. METHODS: Nineteen patients with symptomatic os odontoideum were investigated. Pain scores were assessed using the visual analogue scale. Myelopathy was assessed using the Nurick scale and Odom's criteria. Radiological imaging was carried out in all patients for diagnosis and to assess the atlantodens interval, space available for cord, and presence of intramedullary hyperintensity signals on T2-weighted images at the C1-C2 level. Posterior stabilization was performed for all patients by using ITFN. RESULTS: The mean Nurick score improved from 2.3 before surgery to 0.7 at the time of follow-up. The mean follow-up period was 34.7 months (range, 12-65 mo). According to Odom's criteria, outcomes were as follows: excellent, 47%; good, 37%; fair, 11%; and poor, 5%. All patients with preoperative neck pain had symptom relief or improvement, with all of these patients having more than 83.7% improvement in visual analogue scale scores. The mean preoperative space available for cord value of 9.3 mm improved to 17.7 mm. Solid fusion and reduction of atlantoaxial dislocation were achieved in every patient without screw failure. Sixty screws were placed in 19 patients. Two C2 polyaxial screws in 2 patients and 1 transarticular screw in 1 patient slightly penetrated the transverse foramen with no vascular injury and clinical sequelae. CONCLUSION: ITFN is a safe, accurate, and effective tool for screw placement in patients with symptomatic os odontoideum.

Posterior fixation and fusion of unstable Hangman's fracture by using intraoperative three-dimensional fluoroscopy-based navigation.

PURPOSE: The purpose of this study was to assess the efficacy and accuracy of posterior screw fixation for unstable Hangman's fracture using intraoperative 3D fluoroscopy-based navigation. METHODS: 14 patients with unstable Hangman's fractures (11 males and 3 females), ranging in age from 21 to 59 years, received posterior fixation assisted by an intraoperative 3D fluoroscopy-based navigation system: 11 Levine-Edwards type II and three type IIA cases. The American Spine Injury Association grade was D in 2 and E in 12 cases. RESULTS: Operation time was 110 min (range 90-140 min). Hospital stay was 7.6 days (range 5-12 days). All the patients were observed for an average of 28.8 months (range 15-50 months). No screw-related injury to nerve, or vertebral artery was observed intraoperatively. An average of four screws/patient were inserted. Pedicle screws were placed into C2 and C3, and 5 screws were into the lateral mass of C3. Screw placement accuracy was evaluated using postoperative CT, according to the modified classification of Gertzbein and Robbins; one screw was grade 2 in C2, and three screws were grade 2 in the pedicle of C3. No grade 3 misplacement or clinical deficits were noted. C3 lateral mass screws were successfully inserted. Neck pain was relieved in each case. Neurologic status improved from D to E in 2 cases. Solid fusion was demonstrated in all the cases by static and dynamic films during the final follow-up. CONCLUSIONS: This case series demonstrates that intraoperative 3D fluoroscopy-based navigation is a safe, accurate, and effective tool for screw placement in patients with unstable Hangman's fracture.

Temporal precision in the visual pathway through the interplay of excitation and stimulus-driven suppression.

Visual neurons can respond with extremely precise temporal patterning to visual stimuli that change on much slower time scales. Here, we investigate how the precise timing of cat thalamic spike trains-which can have timing as precise as 1 ms-is related to the stimulus, in the context of both artificial noise and natural visual stimuli. Using a nonlinear modeling framework applied to extracellular data, we demonstrate that the precise timing of thalamic spike trains can be explained by the interplay between an excitatory input and a delayed suppressive input that resembles inhibition, such that neuronal responses only occur in brief windows where excitation exceeds suppression. The resulting description of thalamic computation resembles earlier models of contrast adaptation, suggesting a more general role for mechanisms of contrast adaptation in visual processing. Thus, we describe a more complex computation underlying thalamic responses to artificial and natural stimuli that has implications for understanding how visual information is represented in the early stages of visual processing.

The episodic nature of spike trains in the early visual pathway.

An understanding of the neural code in a given visual area is often confounded by the immense complexity of visual stimuli combined with the number of possible meaningful patterns that comprise the response spike train. In the lateral geniculate nucleus (LGN), visual stimulation generates spike trains comprised of short spiking episodes ("events") separated by relatively long intervals of silence, which establishes a basis for in-depth analysis of the neural code. By studying this event structure in both artificial and natural visual stimulus contexts and at different contrasts, we are able to describe the dependence of event structure on stimulus class and discern which aspects generalize. We find that the event structure on coarse time scales is robust across stimulus and contrast and can be explained by receptive field processing. However, the relationship between the stimulus and fine-time-scale features of events is less straightforward, partially due to a significant amount of trial-to-trial variability. A new measure called "label information" identifies structural elements of events that can contain ≤30% more information in the context of natural movies compared with what is available from the overall event timing. The first interspike interval of an event most robustly conveys additional information about the stimulus and is somewhat more informative than the event spike count and much more informative than the presence of bursts. Nearly every event is preserved across contrast despite changes in their fine-time-scale features, suggesting that--at least on a coarse level--the stimulus selectivity of LGN neurons is contrast invariant. Event-based analysis thus casts previously studied elements of LGN coding such as contrast adaptation and receptive field processing in a new light and leads to broad conclusions about the composition of the LGN neuronal code.

Bipartite atlas with os odontoideum and synovial cyst: case report and review literature.

STUDY DESIGN: Case report and review of the literature. OBJECTIVE: To present an os odontoideum with bipartite atlas and synovial cyst at the C1-C2 junction in a 13-year-old girl and to review the relevant background literature. SUMMARY OF BACKGROUND DATA: Bipartite atlas associated with os odontoideum and synovial cyst at the C1-C2 junction is extremely rare. METHODS: The patient's clinical presentation, evolution of physical findings, and sequential radiologic studies. Surgery of the bipartite atlas with os odontoideum and synovial cyst. Posterior fixation between occipital and C 2 without resection of the mass was performed. RESULTS: The patient had significant improvement and spontaneous regression of the cyst was identified on the follow-up magnetic resonance imaging (MRI) taken 3 months after posterior fixation. To our knowledge, no case of a bipartite atlas with os odontoideum and synovial cyst with complete recovery of an accompanying quadriparesis after reduction has been previously reported in English medical literature. CONCLUSION: We described a rare association of an anterior arch defect, posterior arch aplasia, os odontoideum, and synovial cyst at the C1-C2 junction. This case report supports surgical intervention of synovial cyst with craniovertebral instability using posterior fixation without resection of the cyst.

Functional consequences of neuronal divergence within the retinogeniculate pathway.

The neuronal connections from the retina to the dorsal lateral geniculate nucleus (dLGN) are characterized by a high specificity. Each retinal ganglion cell diverges to connect to a small group of geniculate cells and each geniculate cell receives input from a small number of retinal ganglion cells. Consistent with the high specificity of the connections, geniculate cells sharing input from the same retinal afferent are thought to have very similar receptive fields. However, the magnitude of the receptive-field mismatches, which has not been systematically measured across the different cell types in dLGN, seems to be in contradiction with the functional anatomy of the Y visual pathway: Y retinal afferents in the cat diverge into two geniculate layers (A and C) that have Y geniculate cells (Y(A) and Y(C)) with different receptive-field sizes, response latencies, nonlinearity of spatial summation, and contrast sensitivity. To better understand the functional consequences of retinogeniculate divergence, we recorded from pairs of geniculate cells that shared input from a common retinal afferent across layers and within the same layer in dLGN. We found that nearly all cell pairs that shared retinal input across layers had Y-type receptive fields of the same sign (i.e., both on-center) that overlapped by >70%, but frequently differed in size and response latency. The receptive-field mismatches were relatively small in value (receptive-field size ratio <5; difference in peak response <5 ms), but were robustly correlated with the strength of the synchronous firing generated by the shared retinal connections (R(2) = 0.75). On average, the percentage of geniculate spikes that could be attributed to shared retinal inputs was about 10% for all cell-pair combinations studied. These results are used to provide new estimates of retinogeniculate divergence for different cell classes.

Timing precision in population coding of natural scenes in the early visual system.

The timing of spiking activity across neurons is a fundamental aspect of the neural population code. Individual neurons in the retina, thalamus, and cortex can have very precise and repeatable responses but exhibit degraded temporal precision in response to suboptimal stimuli. To investigate the functional implications for neural populations in natural conditions, we recorded in vivo the simultaneous responses, to movies of natural scenes, of multiple thalamic neurons likely converging to a common neuronal target in primary visual cortex. We show that the response of individual neurons is less precise at lower contrast, but that spike timing precision across neurons is relatively insensitive to global changes in visual contrast. Overall, spike timing precision within and across cells is on the order of 10 ms. Since closely timed spikes are more efficient in inducing a spike in downstream cortical neurons, and since fine temporal precision is necessary to represent the more slowly varying natural environment, we argue that preserving relative spike timing at a approximately 10-ms resolution is a crucial property of the neural code entering cortex.

On and off domains of geniculate afferents in cat primary visual cortex.

On- and off-center geniculate afferents form two major channels of visual processing that are thought to converge in the primary visual cortex. However, humans with severely reduced on responses can have normal visual acuity when tested in a white background, which indicates that off channels can function relatively independently from on channels under certain conditions. Consistent with this functional independence of channels, we demonstrate here that on- and off-center geniculate afferents segregate in different domains of the cat primary visual cortex and that off responses dominate the cortical representation of the area centralis. On average, 70% of the geniculate afferents converging at the same cortical domain had receptive fields of the same contrast polarity. Moreover, off-center afferents dominated the representation of the area centralis in the cortex, but not in the thalamus, indicating that on- and off-center afferents are balanced in number, but not in the amount of cortical territory that they cover.

Temporal precision in the neural code and the timescales of natural vision.

The timing of action potentials relative to sensory stimuli can be precise down to milliseconds in the visual system, even though the relevant timescales of natural vision are much slower. The existence of such precision contributes to a fundamental debate over the basis of the neural code and, specifically, what timescales are important for neural computation. Using recordings in the lateral geniculate nucleus, here we demonstrate that the relevant timescale of neuronal spike trains depends on the frequency content of the visual stimulus, and that 'relative', not absolute, precision is maintained both during spatially uniform white-noise visual stimuli and naturalistic movies. Using information-theoretic techniques, we demonstrate a clear role of relative precision, and show that the experimentally observed temporal structure in the neuronal response is necessary to represent accurately the more slowly changing visual world. By establishing a functional role of precision, we link visual neuron function on slow timescales to temporal structure in the response at faster timescales, and uncover a straightforward purpose of fine-timescale features of neuronal spike trains.

Adaptation to stimulus contrast and correlations during natural visual stimulation.

In this study, we characterize the adaptation of neurons in the cat lateral geniculate nucleus to changes in stimulus contrast and correlations. By comparing responses to high- and low-contrast natural scene movie and white noise stimuli, we show that an increase in contrast or correlations results in receptive fields with faster temporal dynamics and stronger antagonistic surrounds, as well as decreases in gain and selectivity. We also observe contrast- and correlation-induced changes in the reliability and sparseness of neural responses. We find that reliability is determined primarily by processing in the receptive field (the effective contrast of the stimulus), while sparseness is determined by the interactions between several functional properties. These results reveal a number of adaptive phenomena and suggest that adaptation to stimulus contrast and correlations may play an important role in visual coding in a dynamic natural environment.

Dynamic encoding of natural luminance sequences by LGN bursts.

In the lateral geniculate nucleus (LGN) of the thalamus, visual stimulation produces two distinct types of responses known as tonic and burst. Due to the dynamics of the T-type Ca(2+) channels involved in burst generation, the type of response evoked by a particular stimulus depends on the resting membrane potential, which is controlled by a network of modulatory connections from other brain areas. In this study, we use simulated responses to natural scene movies to describe how modulatory and stimulus-driven changes in LGN membrane potential interact to determine the luminance sequences that trigger burst responses. We find that at low resting potentials, when the T channels are de-inactivated and bursts are relatively frequent, an excitatory stimulus transient alone is sufficient to evoke a burst. However, to evoke a burst at high resting potentials, when the T channels are inactivated and bursts are relatively rare, prolonged inhibitory stimulation followed by an excitatory transient is required. We also observe evidence of these effects in vivo, where analysis of experimental recordings demonstrates that the luminance sequences that trigger bursts can vary dramatically with the overall burst percentage of the response. To characterize the functional consequences of the effects of resting potential on burst generation, we simulate LGN responses to different luminance sequences at a range of resting potentials with and without a mechanism for generating bursts. Using analysis based on signal detection theory, we show that bursts enhance detection of specific luminance sequences, ranging from the onset of excitatory sequences at low resting potentials to the offset of inhibitory sequences at high resting potentials. These results suggest a dynamic role for burst responses during visual processing that may change according to behavioral state.

High tibial osteotomy: long term survival analysis and patients' perspective.

High tibial osteotomy has been generally accepted as a useful treatment for unicompartment osteoarthritis of the knee to improve a patient's quality of life. Few studies have examined the outcome from the patient's perspective. A survival analysis of one to twenty-one years was conducted on 67 knees including analysis of the patients' satisfaction level with this procedure. Cumulative survival probability of 89.5% at 5 years, 74.7% at 10 years and 66.9 % for 15 and 20 years was reported. Ninety-one percent of patients had improvement in pain score and would choose to have this surgery again. Average patient satisfaction level was 75.5%. Forty-eight percent of patients were able to perform at a higher level of activity than before surgery, although none was able to perform at the level prior to the onset of knee pathology. It was concluded that this procedure was able to improve a patient's quality of life and achieved high satisfaction among patients. There is an increasing role of high tibial osteotomy as an adjunct to an autologous chondrocyte implantation procedure.