Single-position prone lateral approach: cadaveric feasibility study and early clinical experience.

OBJECTIVE: Lateral lumbar interbody fusion (LLIF) is a useful minimally invasive technique for achieving anterior interbody fusion and preserving or restoring lumbar lordosis. However, achieving circumferential fusion via posterior instrumentation after an LLIF can be challenging, requiring either repositioning the patient or placing pedicle screws in the lateral position. Here, the authors explore an alternative single-position approach: LLIF in the prone lateral (PL) position. METHODS: A cadaveric feasibility study was performed using 2 human cadaveric specimens. A retrospective 2-center early clinical series was performed for patients who had undergone a minimally invasive lateral procedure in the prone position between August 2019 and March 2020. Case duration, retractor time, electrophysiological thresholds, implant size, screw accuracy, and complications were recorded. Early postoperative radiographic outcomes were reported. RESULTS: A PL LLIF was successfully performed in 2 cadavers without causing injury to a vessel or the bowel. No intraoperative subsidence was observed. In the clinical series, 12 patients underwent attempted PL surgery, although 1 case was converted to standard lateral positioning. Thus, 11 patients successfully underwent PL LLIF (89%) across 14 levels: L2-3 (2 of 14 [14%]), L3-4 (6 of 14 [43%]), and L4-5 (6 of 14 [43%]). For the 11 PL patients, the mean (± SD) age was 61 ± 16 years, mean BMI was 25.8 ± 4.8, and mean retractor time per level was 15 ± 6 minutes with the longest retractor time at L2-3 and the shortest at L4-5. No intraoperative subsidence was noted on routine postoperative imaging. CONCLUSIONS: Performing single-position lateral transpsoas interbody fusion with the patient prone is anatomically feasible, and in an early clinical experience, it appeared safe and reproducible. Prone positioning for a lateral approach presents an exciting opportunity for streamlining surgical access to the lumbar spine and facilitating more efficient surgical solutions with potential clinical and economic advantages.

A Portable Shoulder-Mounted Camera System for Surgical Education in Spine Surgery.

The past several years have demonstrated an increased recognition of operative videos as an important adjunct for resident education. Currently lacking, however, are effective methods to record video for the purposes of illustrating the techniques of minimally invasive (MIS) and complex spine surgery. We describe here our experiences developing and using a shoulder-mounted camera system for recording surgical video. Our requirements for an effective camera system included wireless portability to allow for movement around the operating room, camera mount location for comfort and loupes/headlight usage, battery life for long operative days, and sterile control of on/off recording. With this in mind, we created a shoulder-mounted camera system utilizing a GoPro™ HERO3+, its Smart Remote (GoPro, Inc., San Mateo, California), a high-capacity external battery pack, and a commercially available shoulder-mount harness. This shoulder-mounted system was more comfortable to wear for long periods of time in comparison to existing head-mounted and loupe-mounted systems. Without requiring any wired connections, the surgeon was free to move around the room as needed. Over the past several years, we have recorded numerous MIS and complex spine surgeries for the purposes of surgical video creation for resident education. Surgical videos serve as a platform to distribute important operative nuances in rich multimedia. Effective and practical camera system setups are needed to encourage the continued creation of videos to illustrate the surgical maneuvers in minimally invasive and complex spinal surgery. We describe here a novel portable shoulder-mounted camera system setup specifically designed to be worn and used for long periods of time in the operating room.

Sparse coding and high-order correlations in fine-scale cortical networks.

Connectivity in the cortex is organized at multiple scales, suggesting that scale-dependent correlated activity is particularly important for understanding the behaviour of sensory cortices and their function in stimulus encoding. We analysed the scale-dependent structure of cortical interactions by using maximum entropy models to characterize multiple-tetrode recordings from primary visual cortex of anaesthetized macaque monkeys (Macaca mulatta). We compared the properties of firing patterns among local clusters of neurons (<300 microm apart) with those of neurons separated by larger distances (600-2,500 microm). Here we report that local firing patterns are distinctive: whereas multi-neuronal firing patterns at larger distances can be predicted by pairwise interactions, patterns within local clusters often show evidence of high-order correlations. Surprisingly, these local correlations are flexible and rapidly reorganized by visual input. Although they modestly reduce the amount of information that a cluster conveys, they also modify the format of this information, creating sparser codes by increasing the periods of total quiescence, and concentrating information into briefer periods of common activity. These results imply a hierarchical organization of neuronal correlations: simple pairwise correlations link neurons over scales of tens to hundreds of minicolumns, but on the scale of a few minicolumns, ensembles of neurons form complex subnetworks whose moment-to-moment effective connectivity is dynamically reorganized by the stimulus.

Biomechanical Predictors of Sacroiliac Joint Uptake on Single-Photon Emission Computed Tomography/Computed Tomography.

OBJECTIVE: Single-photon emission computed tomography/computed tomography (SPECT/CT) is an emerging imaging modality that identifies sites of heightened bone metabolism in response to increased stresses. The relationship between sacroiliac (SI) joint radiotracer uptake and anatomic biomechanical parameters is poorly understood. METHODS: Adult patients with SPECT/CT scans performed at our institution between 2021 and 2023 for the workup of low back pain were included. Patient charts were reviewed for demographic factors including age, gender, and prior thoracolumbar fusion history. Biomechanical spinopelvic parameters were measured from standing scoliosis radiographs. SPECT/CT scans were reviewed for uptake at the SI joint. Patients were stratified into 2 cohorts; patients with SI uptake greater than iliac crest uptake were designated "hot," whereas those with less or equal uptake were labeled "cold." RESULTS: One-hundred and sixty patients met inclusion criteria. Patients were slightly more male (55%) with average age 55 ± 14.9 years. Sixty-eight patients (43%) had evidence of increased SI activity. Interrater reliability showed substantial agreement (kappa = 0.62). The hot cohort demonstrated greater pelvic incidence (54.8 ± 14.0 degrees vs. 51.0 ± 11.0 degrees, P = 0.031) and pelvic tilt (20.8 ± 9.5 degrees vs. 18.4 ± 8.6 degrees, P =0.047) compared with the cold cohort. Patients were otherwise similar between cohorts (P > 0.05). CONCLUSIONS: Increased pelvic incidence and pelvic tilt angles are associated with SPECT/CT uptake at the SI joint, which may reflect altered biomechanics at the spinopelvic junction. SPECT/CT may be a valuable tool to assess SI degeneration. Future studies are warranted to better characterize the clinical applications of these findings.

Coronal Deformity is Associated With Uptake on Single Photon Emission Computed Tomography in Patients With Low Back Pain.

STUDY DESIGN: Retrospective Cohort Study. OBJECTIVE: Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) is emerging as a valuable imaging test for identifying pain generators within the lumbar spine. The relationship between radiotracer uptake on SPECT/CT and anatomic biomechanical parameters has not been previously studied. METHODS: We performed a retrospective review of all patients seen at our institution between 2021-2023 who obtained SPECT/CT scans for workup of thoracolumbar back pain. Patient data including demographic, clinical symptoms, and surgical history were collected. Radiology reports were reviewed for evidence of pathologic degeneration and increased bone metabolism on SPECT/CT. Biomechanical parameters were measured from standing scoliosis plain radiographs. Patients were stratified into two cohorts by either presence or absence of asymmetric coronal uptake on SPECT/CT. RESULTS: 160 patients met inclusion criteria. Patients were primarily male (55%) with average age 55 ± 15 years. 87 (54%) patients demonstrated asymmetric uptake on SPECT/CT. These patients were older (P < 0.001), but with similar gender, prior fusion history, sacroiliitis, adjacent segment degeneration, and pseudoarthrosis (P > 0.05). This cohort had more disc disease, facet arthropathy, and greater degree of coronal scoliosis and coronal imbalance (P < 0.001). There were significantly more sites of uptake in the asymmetric cohort, and uptake was preferentially observed in the concavity of the lumbar curve (P < 0.001). There were no significant differences in sagittal balance or spinopelvic mismatch between cohorts (P > 0.05). CONCLUSION: Asymmetric uptake on SPECT/CT was associated with coronal deformity in patients with low back pain. Further prospective studies are warranted to assess the effect of coronal deformity on pain generation.

Race and socioeconomic disparities persist in treatment and outcomes of patients with cervical spinal cord injuries: An analysis of the national inpatient sample from 2016 - 2020.

Objective: Previous literature has described race and socioeconomic disparities in both treatment and outcomes following cervical spinal cord injuries (SCI). The goal of this study is to investigate the current state of parity in management and outcomes following SCI. Methods: We surveyed the National Inpatient Sample database (NIS) for patients admitted with primary diagnosis of cervical SCI. 49,320 patients were identified. Univariate and multivariate analyses were performed to evaluate racial and socioeconomic differences in SCI care and outcomes. Results: Compared to white patients, minority race was associated with a longer time from presentation to operative intervention (p < 0.001) and longer length of stay following admission for cervical SCI (16 vs 13 days, p < 0.001). Minority patients were more likely to have an unfavorable discharge (skilled nursing facility, against medical advice, death) status than white patients (p < 0.001). Patients in the bottom quartile of median household income were associated with more unfavorable discharges than the top two quartiles (p < 0.001). Patients with the lowest median household income quartile also had higher total costs than those in the top quartiles ($221,654 vs 191,723, p < 0.001). Black, Hispanic, and Asian/Pacific Islander incurred higher treatment costs than White patients. Conclusion: Minority and lower socioeconomic status are independently associated with unfavorable discharge and LOS in cervical SCI. Furthermore, racial and economically disadvantaged groups have longer wait times from admission to surgical intervention. These disparities persist despite being highlighted by previous publications and increased societal awareness of healthcare inequities, necessitating further work to reach parity.

Maximum-entropy network analysis reveals a role for tumor necrosis factor in peripheral nerve development and function.

Gene regulatory interactions that shape developmental processes can often can be inferred from microarray analysis of gene expression, but most computational methods used require extensive datasets that can be difficult to generate. Here, we show that maximum-entropy network analysis allows extraction of genetic interactions from limited microarray datasets. Maximum-entropy networks indicated that the inflammatory cytokine TNF-alpha plays a pivotal role in Schwann cell-axon interactions, and these data suggested that TNF mediates its effects by orchestrating cytoplasmic movement and axon guidance. In vivo and in vitro experiments confirmed these predictions, showing that Schwann cells in TNF(-/-) peripheral sensory bundles fail to envelop axons efficiently, and that recombinant TNF can partially correct these defects. These data demonstrate the power of maximum-entropy network-based methods for analysis of microarray data, and they indicate that TNF-alpha plays a direct role in Schwann cell-axon communication.

Predictors of subsidence after lateral lumbar interbody fusion.

OBJECTIVE: Lateral lumbar interbody fusion (LLIF) facilitates the restoration of disc height and the indirect decompression of neural elements. However, these benefits are lost when the graft subsides into the adjacent endplates. The factors leading to subsidence after LLIF are poorly understood. This article presents a case series of patients who underwent LLIF and reports factors correlating with subsidence. METHODS: A retrospective review of a consecutive, prospectively collected, single-institution database of patients who underwent LLIF over a 29-month period was performed. The degree of subsidence was measured on the basis of postoperative imaging. The timing of postoperative subsidence was determined, and intraoperative fluoroscopic images were reviewed to determine whether subsidence occurred as a result of endplate violation. The association of subsidence with age, sex, cage size and type, bone density, and posterior instrumentation was investigated. RESULTS: One hundred thirty-one patients underwent LLIF at a total of 204 levels. Subsidence was observed at 23 (11.3%) operated levels. True subsidence, attributable to postoperative cage settling, occurred for 12 (5.9%) of the levels; for the remaining 11 (5.4%) levels, subsidence was associated with intraoperative endplate violation noted on fluoroscopy during cage placement. All subsidence occurred within 12 weeks of surgery. Univariate analysis showed that the prevalence of true subsidence was significantly lower among patients with titanium implants (0 of 55; 0%) than among patients with polyetheretherketone cages (12 of 149; 8.1%) (p = 0.04). In addition, the mean ratio of graft area to inferior endplate area was significantly lower among the subsidence levels (0.34) than among the nonsubsidence levels (0.42) (p < 0.01). Finally, subsidence among levels with posterior fixation (4.4% [6/135]) was not significantly different than among those without posterior fixation (8.7% [6/69]) (p = 0.23). Multivariate analysis results showed that the ratio of cage to inferior endplate area was the only significant predictor of subsidence in this study (p < 0.01); increasing ratios were associated with a decreased likelihood of subsidence. CONCLUSIONS: Overall, the prevalence of subsidence after LLIF was low in this clinical series. Titanium cages were associated with a lower prevalence of observed subsidence on univariate analysis; however, multivariate analysis demonstrated that this effect may be attributable to the increased surface area of these cages relative to the inferior endplate area.

Information-geometric measure of 3-neuron firing patterns characterizes scale-dependence in cortical networks.

To understand the functional connectivity of neural networks, it is important to develop simple and incisive descriptors of multineuronal firing patterns. Analysis at the pairwise level has proven to be a powerful approach in the retina, but it may not suffice to understand complex cortical networks. Here we address the problem of describing interactions among triplets of neurons. We consider two approaches: an information-geometric measure (Amari 2001), which we call the "strain," and the Kullback-Leibler divergence. While both approaches can be used to assess whether firing patterns differ from those predicted by a pairwise maximum-entropy model, the strain provides additional information. Specifically, when the observed firing patterns differ from those predicted by a pairwise model, the strain indicates the nature of this difference--whether there is an excess or a deficit of synchrony--while the Kullback-Leibler divergence only indicates the magnitude of the difference. We show that the strain has technical advantages, including ease of calculation of confidence bounds and bias, and robustness to the kinds of spike-sorting errors associated with tetrode recordings. We demonstrate the biological importance of these points via an analysis of multineuronal firing patterns in primary visual cortex. There is a striking scale-dependent behavior of triplet firing patterns: deviations from the pairwise model are substantial when the neurons are within 300 microns of each other, and negligible when they are at a distance of >600 microns. The strain identifies a consistent pattern to these interactions: when triplet interactions are present, the strain is nearly always negative, indicating that there is less synchrony than would be expected from the pairwise interactions alone.

Single-Position Surgery: Prone Lateral Lumbar Interbody Fusion: 2-Dimensional Operative Video.

Lateral lumbar interbody fusion (LLIF) is a widely used technique for anterior fusion. However, posterior decompression or instrumentation often requires repositioning the patient, which increases operative time. This video describes the prone LLIF as a modification of the standard surgical technique. The prone LLIF facilitates simultaneous decompression and fusion, which avoids the need for repositioning the patient, increasing operative efficiency. Positioning, fluoroscopic considerations, and operative nuances involved in performing the LLIF in the prone position are described, and an illustrative case is presented. The patient provided informed consent for the procedure and videography. LLIF in the prone position can decrease operative time and increase operative efficiency. The prone position is a viable alternative to the conventional lateral decubitus position. Video used with permission from Barrow Neurological Institute, Phoenix, Arizona.

Lateral Interbody Fusion at L4/5: Management of the Transitional Psoas.

OBJECTIVE: Managing retraction of the lumbar plexus is critical to safely perform lateral lumbar interbody fusion (LLIF) via the transpsoas approach. Occasionally, a transitional psoas is encountered at L4/5 and has been postulated to be a contraindication to transpsoas LLIF. A case series of patients with transitional psoas who underwent L4/5 LLIFs is presented. METHODS: This retrospective review assessed 79 consecutive patients who underwent L4/5 LLIF during a 24-month period. Preoperative imaging was reviewed, and patients were classified into 2 groups: normal psoas or transitional psoas. Intraoperative features and outcomes were compared between groups. RESULTS: Seventy-nine patients underwent L4/5 LLIFs, of whom 23 had transitional psoas anatomy and 56 had normal psoas anatomy. Among patients with transitional psoas, the center of the psoas was a mean (range) of 11.2 (5.2-26.6) mm in front of the center of the vertebral body compared with 2.0 (0-4) mm in the normal psoas group. The mean (range) retraction time was similar between groups (10.8 [6.7-14.9] minutes in the transitional psoas group vs. 11.0 [7.8-15.0] minutes in the normal psoas group). No permanent motor injuries occurred in either group, and no differences in length of stay or preoperative or postoperative Oswestry Disability Index scores were found between the groups. The protocol for L4/5 LLIF in patients with transitional psoas anatomy is described. CONCLUSIONS: Transitional psoas anatomy is frequently encountered in surgical candidates for L4/5 LLIF. Through careful identification of the lumbar plexus and judicious retraction, the transpsoas LLIF can safely be performed in these patients.

When Indirect Decompression Fails: A Review of 220 Consecutive Direct Lateral Interbody Fusions and Unplanned Secondary Decompression.

STUDY DESIGN: A consecutive series of patients who underwent minimally invasive spinal surgery by a single surgeon at a high-volume academic medical center were studied. OBJECTIVE: The objective of this study was to identify the prevalence, radiographic features, and clinical characteristics of patients who require unplanned secondary decompressive laminectomy or foraminotomy after lateral lumbar interbody fusion (LLIF). SUMMARY OF BACKGROUND DATA: LLIF indirectly decompresses the spinal canal, lateral recess, and neural foramen when properly performed. However, indirect decompression relies on endplate integrity, reasonable bone quality, and sufficient contralateral release so that ligament distraction can occur. Some patients have insufficient decompression, resulting in persistent axial low back pain or radiculopathy. METHODS: Patients undergoing LLIF for radiculopathy or refractory low back pain were enrolled in a prospective registry. Preoperative and postoperative imaging, clinical presentation, and operative reports were reviewed from this registry. RESULTS: During registry collection, 122 patients were enrolled (220 lumbar levels treated), with nearly even representation between men (64/122, 52.5%) and women (58/122, 47.5%). Overall, right-sided lumbar spinal approaches (74/122, 60.7%) were more common. Ultimately, 4.1% (five of 122) of patients required unplanned direct decompressive laminectomy or foraminotomy because of refractory radiculopathy and persistent radiographic evidence of compression at the index LLIF level. All patients for whom indirect decompression failed were men who underwent stand-alone LLIF and had radiculopathy contralateral to the side of the LLIF approach. Most patients (59.8%, 73/122) had evidence of graft subsidence (grade 0 or 1) or osteoporosis. CONCLUSION: We report a 4.1% rate of return to the operating room for failed indirect decompression after LLIF for refractory radiculopathy. Graft subsidence and osteoporosis were common in these patients. All five patients who required secondary decompressive laminectomy or foraminotomy underwent stand-alone primary LLIF, and the persistent radiculopathy was consistently contralateral to the initial side of the LLIF approach.Level of Evidence: 4.

The DOWN Questionnaire: A Novel Screening Tool for Cervical Spondylotic Myelopathy.

STUDY DESIGN: Case-control study. OBJECTIVES: Cervical spondylotic myelopathy (CSM) is the most common cause of spinal cord injury in adults aged over 55 years. However, since the onset is typically insidious, accurately diagnosing CSM can be challenging, often requiring referral to a subspecialist and advanced imaging. To help identify patients at risk for CSM, this case-control study compared responses to a series of 4 questions (DOWN questionnaire) in myelopathic and non-myelopathic patients. METHODS: Ninety-two patients, 46 with and 46 without myelopathy, were recruited for the study. Each patient answered 4 questions encompassing common symptoms associated with CSM. Responses between patient groups were compared, and Cohen's κ was used to assess for agreement between responses and the diagnosis of myelopathy. RESULTS: We found a sensitivity of 91% and a κ of 0.54 to 3 positive responses and a sensitivity of 72% and a κ of 0.61 to 4 positive responses. CONCLUSIONS: Positive responses to 3 or more DOWN questions has high sensitivity and moderate agreement with the diagnosis of myelopathy based on history, physical exam, and review of advanced imaging by an orthopedic or neurological surgeon. The DOWN questionnaire is a potentially useful screening tool to identify patients at risk for CSM.

Cannabinoid neuromodulation in the adult early visual cortex.

Sensory processing is an active process involving the interaction of ongoing cortical activity with incoming stimulus information. However, the modulators and circuits involved in this interaction are incompletely understood. One potential candidate is the cannabinoid-signaling system, which is known to modulate the dynamics of cortical networks. Here, we show that in the primate primary and secondary visual cortices, the cannabinoid CP55940 modulates not only population dynamics but also influences the dynamics of the stimulus-response relationship of individual neurons. At the population level, CP55940 decreases EEG power, LFP power, and LFP coherence. At the single-neuron level, intrinsic spike train dynamics appear relatively unchanged, but visual receptive fields are altered: CP55940 induced an overall delay and broadening of the temporal component of V1 and V2 spatiotemporal receptive fields. Our findings provide neurophysiologic evidence for a link between cannabinoid-signaling, network dynamics and the function of a canonical cortical circuit.

Subpopulations of neurons in visual area v2 perform differentiation and integration operations in space and time.

The interconnected areas of the visual system work together to find object boundaries in visual scenes. Primary visual cortex (V1) mainly extracts oriented luminance boundaries, while secondary visual cortex (V2) also detects boundaries defined by differences in texture. How the outputs of V1 neurons are combined to allow for the extraction of these more complex boundaries in V2 is as of yet unclear. To address this question, we probed the processing of orientation signals in single neurons in V1 and V2, focusing on response dynamics of neurons to patches of oriented gratings and to combinations of gratings in neighboring patches and sequential time frames. We found two kinds of response dynamics in V2, both of which were different from those of V1 neurons. While V1 neurons in general preferred one orientation, one subpopulation of V2 neurons ("transient") showed a temporally dynamic preference, resulting in a preference for changes in orientation. The second subpopulation of V2 neurons ("sustained") responded similarly to V1 neurons, but with a delay. The dynamics of nonlinear responses to combinations of gratings reinforced these distinctions: the dynamics enhanced the preference of V1 neurons for continuous orientations and the preference of V2 transient neurons for discontinuous ones. We propose that transient neurons in V2 perform a differentiation operation on the V1 input, both spatially and temporally, while the sustained neurons perform an integration operation. We show that a simple feedforward network with delayed inhibition can account for the temporal but not for the spatial differentiation operation.

Speed dependence of tuning to one-dimensional features in V1.

Using drifting compound grating stimuli matched in energy and frequency spectrum, we previously showed that neurons in the primary visual cortex (V1) were tuned to line-like, edge-like, and intermediate one-dimensional features. Because these compound grating stimuli were drifting, allowing for potential interaction between shape and motion, we examine here the dependence of V1 feature tuning on drift speed. We find that the feature selectivity and specificity of individual V1 neurons strongly depend on speed. A simple model explains these observations in terms of an interaction between linear filtering by the receptive field and the static nonlinearity of spike threshold, embedded in a recurrent network. Although the speed-dependent behaviors in single V1 neurons preclude their acting as extractors of one-dimensional features, the population as a whole retains a representation of a full suite of features.