Perioperative Management of Comorbidities in Spine Surgery.

The number of spinal operations performed in the United States has significantly increased in recent years. Along with these rising numbers, there has been a corresponding increase in the number of patient comorbidities. The focus of this article is to review comorbidities in Spine surgery patients and outline strategies to optimize patients and avoid complications.

Initial learning curve after switching to uniportal endoscopic discectomy for lumbar disc herniations.

PURPOSE: The purpose was to investigate the learning curve for elective endoscopic discectomy performed by a single surgeon who made a complete switch to uniportal endoscopic surgery for lumbar disc herniations in an ambulatory surgery center and determine the minimum case number required to safely overcome the initial learning curve. METHODS: Electronic medical records (EMR) of the first 90 patients receiving endoscopic discectomy by the senior author in an ambulatory surgery center were reviewed. Cases were divided by approach, transforaminal (46) versus interlaminar (44). Patient-reported outcome measures (visual-analog-score (VAS) and the Oswestry disability index (ODI)) were recorded preoperatively and at 2-week, 6-week, 3-month, and 6-month appointments. Operative times, complications, time to discharge from PACU, postoperative narcotic use, return to work, and reoperations were compiled. RESULTS: Median operative time decreased approximately 50% for the first 50 patients then plateaued for both approaches (mean: 65 min). No difference in reoperation rate observed during the learning curve. Mean time to reoperation was 10 weeks, with 7(7.8%) reoperations. The interlaminar and transforaminal median operative times were 52 versus 73 min, respectively (p = 0.03). Median time to discharge from PACU was 80 min for interlaminar approaches and 60 min for transforaminal (p < 0.001). Mean VAS and ODI scores 6 weeks and 6 months postoperatively were statistically and clinically improved from preoperatively. The duration of postoperative narcotic use and narcotics need significantly decreased during the learning curve as the senior author realized that narcotics were not needed. No differences were apparent between groups in other metrics. CONCLUSIONS: Endoscopic discectomy was shown to be safe and effective for symptomatic disc herniations in an ambulatory setting. Median operative time decreases by half over the first 50 patients in our learning curve, while reoperation rates remained similar without the need for hospital transfer or conversion to an open procedure in an ambulatory setting. LEVEL OF EVIDENCE: Level III, prospective cohort.

High Rate of Revision Surgery After Limited Decompression of Lumbar Facet Cysts.

INTRODUCTION: The surgical treatment of lumbar facet cysts has long been debated. Some surgeons elect for limited decompression of such cysts while other surgeons elect for primary decompression and fusion over concerns for recurrence and instability. Previous studies have suggested the rate of revision surgery after facet cyst excision to be as low as 1%, whereas others have reported this rate to be markedly higher. In this study, we examined revision surgery rates and patient-reported outcomes and conducted a radiographic analysis to identify predictors of failure after limited decompression of lumbar facet cysts. METHODS: A retrospective review of the electronic medical records of patients treated at our institution using the Current Procedural Terminology code 63267 before January 2018 was conducted. The primary outcome measure was revision surgery at the index level for recurrence or instability or a minimum 2-year follow-up without revision surgery. Secondary outcome measures include radiographic assessments of preoperative and postoperative spondylolisthesis and patient-reported outcome measures. Using preoperative MRI studies, an analysis of facet angles at the surgical level was conducted and the presence, location, and amount of facet fluid were calculated. RESULTS: A total of 162 patients met inclusion criteria. Of these, 93 patients had a minimum 2-year follow-up. Of these, 19 had undergone a revision surgery at the index level for cyst recurrence or instability. The revision rate for this group was 20.4%. The median time to initial revision surgery was 2.2 years. The median time from index operation to last follow-up was 3.8 years. No differences were observed between the groups regarding the presence of preoperative spondylolisthesis, age, sex, body mass index, blood loss, or patient demographics. 60.2% of all procedures were done at the L4-5 level, but this level accounted for 73.7% of primary failures. A radiographic analysis showed facet angle >45° at L4-5 to be associated with risk of failure of primary decompression. The presence and absolute amount of fluid in the facets were not associated with risk of failure at the L4-5 level. DISCUSSION: Our revision rate of 20.4% is higher than what is commonly reported in the literature. The radiographic analysis shows that at the L4-5 level, a facet angle of >45° is associated with failure of primary decompression.

Cauda Equina Syndrome.

Cauda equina syndrome (CES) involves compression of some or all of the lumbar and sacral peripheral nerve roots. However, there is a lack of consensus in the literature regarding the exact diagnosis criteria in this patient population. Much of the pathophysiology has been studied regarding the onset of this condition; however, the long-term effects are not able to be accurately predicted at this time. Recent literature has associated timing to surgical decompression, severity of symptoms at time of onset, and involvement of bladder dysfunction as prognostic indicators of CES.

Preoperative Narcotic Use and Inferior Outcomes After Anatomic Total Shoulder Arthroplasty: A Clinical and Radiographic Analysis.

INTRODUCTION: Our purpose was to determine whether the chronic use of preoperative narcotics adversely affected clinical and/or radiographic outcomes. METHODS: Seventy-three patients (79 shoulders) with primary total shoulder arthroplasty for osteoarthritis were evaluated clinically and radiographically at preoperative visits and postoperatively at a minimum follow-up of 2 years: 26 patients (28 shoulders) taking chronic narcotic pain medication for at least 3 months before surgery and 47 patients (51 shoulders) who were not taking narcotics preoperatively. RESULTS: Postoperatively, significant differences were noted between the narcotic and nonnarcotic groups regarding American Shoulder and Elbow Surgeons scores and visual analog scale scores, as well as forward elevation, external rotation, and all strength measurements (P < 0.01). The nonnarcotic group had markedly higher American Shoulder and Elbow Surgeons scores, better overall range of motion and strength, and markedly lower visual analog scale scores than the narcotic group. CONCLUSION: Chronic preoperative narcotic use seems to be a notable indicator of poor outcomes of anatomic total shoulder arthroplasty for glenohumeral osteoarthritis.

Liposomal bupivacaine mixture has similar pain relief and significantly fewer complications at less cost compared with indwelling interscalene catheter in total elbow arthroplasty.

BACKGROUND: Postoperative pain control, short-term and long-term narcotic consumption, complication rates, and costs of indwelling interscalene catheter (ISC) were compared with a liposomal bupivacaine (LBC) mixture in patients undergoing primary total elbow arthroplasty. METHODS: Forty-four consecutive patients were identified, the first 28 with an ISC and the later 16 with intraoperative LBC injection that also included ketorolac and 0.5% bupivacaine. Medical records were reviewed for visual analog scale scores for pain, oral morphine equivalent (OME) use, complications, and facility charges. RESULTS: Average visual analog scale scores at 24 hours, 2 weeks, 6 weeks, and 12 weeks were not significantly different. Mean OME use was significantly greater in the LBC group at 24 hours but less at 12 weeks, although this difference was not statistically significant. Twelve anesthetic-related complications occurred in the ISC group (1 major and 11 minor); 10 patients (36%) had at least 1 complication. The major complication was respiratory failure requiring emergent tracheostomy. Minor complications included leaking pump/catheters, catheters inadvertently pulled out early, global hand paresthesias, forearm paresthesias, and pain at the catheter site. There were no anesthetic-related complications in the LBC group. The average charge for the LBC mixture was $327.10; charges for ISC, including equipment and anesthesia fees, were $1472.42. CONCLUSIONS: An LBC mixture provides similar pain relief with fewer complications at a lower cost than indwelling ISC after total elbow arthroplasty. Although the OME use in the LBC group was almost double that of the ISC group at 24 hours, there was no difference at later time points.

Diagnosis and Management of Intra-articular Causes of Pain After Total Knee Arthroplasty.

Total knee arthroplasty (TKA) is an effective procedure for decreasing pain, improving functional capability, and increasing the overall quality of life for thousands of people with chronic knee osteoarthritis. Although patient outcomes and satisfaction remain high, a substantial percentage of patients report residual pain after TKA. Sources of postoperative pain include intra- and extra-articular etiologies as well as factors unrelated to the implants themselves. A patient-centered approach to the painful TKA may aid clinicians in diagnosing and treating patients with intra-articular causes of pain after TKA. A thorough understanding of the mechanisms involved may lead to improved preoperative planning and patient selection, ultimately decreasing the number of patients with less than optimal postoperative outcomes.

Spontaneous reduction of a chronic radial head subluxation after open reduction and percutaneous pin fixation of a radial neck fracture: a case report and review of the literature.

BACKGROUND: Fractures of the radial neck in children have shown to account for 5-10% of traumatic elbow injuries in the pediatric population. Chronic dislocation of the radial head with concomitant fracture has been shown to result in progressive deformity and unacceptable loss of motion. METHODS: In this case report, we describe a patient who sustained a type 2 radial neck fracture with 100% displacement. The patient's clinical and surgical management will be discussed and a review of the literature is provided as it relates to this particular case. RESULTS: The patient underwent open reduction and percutaneous pin fixation of her displaced, dislocated left radial neck fracture in the operating room after multiple failed attempts at closed reduction due to interposition of the annular ligament. Three months after her operation radiographs revealed a well-healed radial neck with no signs of avascular necrosis with an anterior dislocation of her radial head, which was a new finding from her previous radiographs. Fourteen months after her initial injury and operation, radiographs taken at this visit revealed a radial neck fracture that was completely remodeled and had spontaneous relocated and was now aligned with the capitellum without any reduction attempt. CONCLUSION: Closed reduction of displaced radial neck fractures may be unsuccessful and open reduction may be warranted. Excess callus formation post-operatively may have resulted in the radial head subluxation; however there was spontaneous reduction with conservative treatment without a reduction attempt, most likely related to remodeling of the excel callus formation.

The effects of prefrontal cortex inactivation on object responses of single neurons in the inferotemporal cortex during visual search.

Inferotemporal cortex (IT) is believed to be directly involved in object processing and necessary for accurate and efficient object recognition. The frontal eye field (FEF) is an area in the primate prefrontal cortex that is involved in visual spatial selection and is thought to guide spatial attention and eye movements. We show that object-selective responses of IT neurons and behavioral performance are affected by changes in frontal eye field activity. This was found in monkeys performing a search classification task by temporarily inactivating subregions of FEF while simultaneously recording the activity from single neurons in IT. The effect on object selectivity and performance was specific, occurring in a predictable spatially dependent manner and was strongest when the IT neuron's preferred target was presented in the presence of distractors. FEF inactivation did not affect IT responses on trials in which the nonpreferred target was presented in the search array.

Paired neuron recordings in the prefrontal and inferotemporal cortices reveal that spatial selection precedes object identification during visual search.

We addressed the question of how we locate and identify objects in complex natural environments by simultaneously recording single neurons from two brain regions that play different roles in this familiar activity--the frontal eye field (FEF), an area in the prefrontal cortex that is involved in visual spatial selection, and the inferotemporal cortex (IT), which is involved in object recognition--in monkeys performing a covert visual search task. Although the monkeys reported object identity, not location, neural activity specifying target location was evident in FEF before neural activity specifying target identity in IT. These two distinct processes were temporally correlated implying a functional linkage between the end stages of "where" and "what" visual processing and indicating that spatial selection is necessary for the formation of complex object representations associated with visual perception.

Cooperation and competition among frontal eye field neurons during visual target selection.

The role of spike rate versus timing codes in visual target selection is unclear. We simultaneously recorded activity from multiple frontal eye field neurons and asked whether they interacted to select targets from distractors during visual search. When both neurons in a pair selected the target and had overlapping receptive fields (RFs), they cooperated more than when one or neither neuron in the pair selected the target, measured by positive spike timing correlations using joint peristimulus time histogram analysis. The amount of cooperation depended on the location of the search target: it was higher when the target was inside both neurons' RFs than when it was inside one RF but not the other, or outside both RFs. Elevated spike timing coincidences occurred at the time of attentional selection of the target as measured by average modulation of discharge rates. We observed competition among neurons with spatially non-overlapping RFs, measured by negative spike timing correlations. Thus, we provide evidence for dynamic and task-dependent cooperation and competition among frontal eye field neurons during visual target selection.

Frontal eye field activity enhances object identification during covert visual search.

We investigated the link between neuronal activity in the frontal eye field (FEF) and the enhancement of visual processing associated with covert spatial attention in the absence of eye movements. We correlated activity recorded in the FEF of monkeys manually reporting the identity of a visual search target to performance accuracy and reaction time. Monkeys were cued to the most probable target location with a cue array containing a popout color singleton. Neurons exhibited spatially selective responses for the popout cue stimulus and for the target of the search array. The magnitude of activity related to the location of the cue prior to the presentation of the search array was correlated with trends in behavioral performance across valid, invalid, and neutral cue trial conditions. However, the speed and accuracy of the behavioral report on individual trials were predicted by the magnitude of spatial selectivity related to the target to be identified, not for the spatial cue. A minimum level of selectivity was necessary for target detection and a higher level for target identification. Muscimol inactivation of FEF produced spatially selective perceptual deficits in the covert search task that were correlated with the effectiveness of the inactivation and were strongest on invalid cue trials that require an endogenous attention shift. These results demonstrate a strong functional link between FEF activity and covert spatial attention and suggest that spatial signals from FEF directly influence visual processing during the time that a stimulus to be identified is being processed by the visual system.

Neural control of visual search by frontal eye field: effects of unexpected target displacement on visual selection and saccade preparation.

The dynamics of visual selection and saccade preparation by the frontal eye field was investigated in macaque monkeys performing a search-step task combining the classic double-step saccade task with visual search. Reward was earned for producing a saccade to a color singleton. On random trials the target and one distractor swapped locations before the saccade and monkeys were rewarded for shifting gaze to the new singleton location. A race model accounts for the probabilities and latencies of saccades to the initial and final singleton locations and provides a measure of the duration of a covert compensation process-target-step reaction time. When the target stepped out of a movement field, noncompensated saccades to the original location were produced when movement-related activity grew rapidly to a threshold. Compensated saccades to the final location were produced when the growth of the original movement-related activity was interrupted within target-step reaction time and was replaced by activation of other neurons producing the compensated saccade. When the target stepped into a receptive field, visual neurons selected the new target location regardless of the monkeys' response. When the target stepped out of a receptive field most visual neurons maintained the representation of the original target location, but a minority of visual neurons showed reduced activity. Chronometric analyses of the neural responses to the target step revealed that the modulation of visually responsive neurons and movement-related neurons occurred early enough to shift attention and saccade preparation from the old to the new target location. These findings indicate that visual activity in the frontal eye field signals the location of targets for orienting, whereas movement-related activity instantiates saccade preparation.

Cognitively directed spatial selection in the frontal eye field in anticipation of visual stimuli to be discriminated.

Single neuron activity was recorded in the frontal eye field (FEF) of monkeys trained to perform a difficult luminance discrimination task. The appearance of a cue stimulus informed the monkeys of the locations of two gray luminance stimuli that would appear within 500-1500ms. The monkeys were rewarded for making a saccade to the brighter of the two luminance stimuli, or if they were the same luminance, for making a saccade to the cue stimulus. Sixty percent (51/85) of FEF neurons exhibited elevated activity when the cue informed the monkeys that one of the luminance stimuli would appear in their response field (RF). This spatially selective anticipatory activity occurred without any visual stimulus appearing in their RF and was not related to saccade choice or latency. The responses of 27 of the anticipatory neurons (32% of the total sample) were also incompatible with the hypothesis that the activity represents saccade probability because they did not exhibit elevated activity for the cue stimulus which was the most probable saccade target. Behaviorally, monkeys exhibited improved perception at locations informed by cue than at unpredictable locations. These results provide physiological evidence that FEF serves an important role in endogenous spatial attention in addition to its well-known role in saccade production.

A perceptual representation in the frontal eye field during covert visual search that is more reliable than the behavioral report.

Neuronal activity in the frontal eye field (FEF) identifies locations of behaviorally important objects for guiding attention and eye movements. We recorded neural activity in the FEF of monkeys trained to manually turn a lever towards the location of a pop-out target of a visual search array without shifting gaze. We examined whether the reliability of the neural representation of the salient target location predicted the monkeys' accuracy of reporting target location. We found that FEF neurons reliably encoded the location of the target stimulus not only on correct trials but also on error trials. The representation of target location in FEF persisted until the manual behavioral report but did not increase in magnitude. This result suggests that, in the absence of an eye movement report, FEF encodes the perceptual information necessary to perform the task but does not accumulate this sensory evidence towards a perceptual decision threshold. These results provide physiological evidence that, under certain circumstances, accurate perceptual representations do not always lead to accurate behavioral reports and that variability in processes outside of perception must be considered to account for the variability in perceptual choice behavior.

The effect of visual search efficiency on response preparation: neurophysiological evidence for discrete flow.

Most models assume that response time (RT) comprises the time required for successive processing stages, but they disagree about whether information is transmitted continuously or discretely between stages. We tested these alternative hypotheses by measuring when movement-related activity began in the frontal eye field (FEF) of macaque monkeys performing visual search. Previous work showed that RT was longer when visual neurons in FEF took longer to select the target, a finding consistent with prolonged perceptual processing during less efficient search. We now report that the buildup of saccadic movement-related activity in FEF is delayed in inefficient visual search. Variability in the delay of movement-related activity accounted for the difference in RT between search conditions and for the variability of RT within conditions. These findings provide neurophysiological support for the hypothesis that information is transmitted discretely between perceptual and response stages of processing during visual search.

Measurements of simultaneously recorded spiking activity and local field potentials suggest that spatial selection emerges in the frontal eye field.

The frontal eye field (FEF) participates in selecting the location of behaviorally relevant stimuli for guiding attention and eye movements. We simultaneously recorded local field potentials (LFPs) and spiking activity in the FEF of monkeys performing memory-guided saccade and covert visual search tasks. We compared visual latencies and the time course of spatially selective responses in LFPs and spiking activity. Consistent with the view that LFPs represent synaptic input, visual responses appeared first in the LFPs followed by visual responses in the spiking activity. However, spatially selective activity identifying the location of the target in the visual search array appeared in the spikes about 30 ms before it appeared in the LFPs. Because LFPs reflect dendritic input and spikes measure neuronal output in a local brain region, this temporal relationship suggests that spatial selection necessary for attention and eye movements is computed locally in FEF from spatially nonselective inputs.

Frontal eye field contributions to rapid corrective saccades.

Visually guided movements can be inaccurate, especially if unexpected events occur while the movement is programmed. Often errors of gaze are corrected before external feedback can be processed. Evidence is presented from macaque monkey frontal eye field (FEF), a cortical area that selects visual targets, allocates attention, and programs saccadic eye movements, for a neural mechanism that can correct saccade errors before visual afferent or performance monitoring signals can register the error. Macaques performed visual search for a color singleton that unpredictably changed position in a circular array as in classic double-step experiments. Consequently, some saccades were directed in error to the original target location. These were followed frequently by unrewarded, corrective saccades to the final target location. We previously showed that visually responsive neurons represent the new target location even if gaze shifted errantly to the original target location. Now we show that the latency of corrective saccades is predicted by the timing of movement-related activity in the FEF. Preceding rapid corrective saccades, the movement-related activity of all neurons began before explicit error signals arise in the medial frontal cortex. The movement-related activity of many neurons began before visual feedback of the error was registered and that of a few neurons began before the error saccade was completed. Thus movement-related activity leading to rapid corrective saccades can be guided by an internal representation of the environment updated with a forward model of the error.

Neuronal basis of covert spatial attention in the frontal eye field.

The influential "premotor theory of attention" proposes that developing oculomotor commands mediate covert visual spatial attention. A likely source of this attentional bias is the frontal eye field (FEF), an area of the frontal cortex involved in converting visual information into saccade commands. We investigated the link between FEF activity and covert spatial attention by recording from FEF visual and saccade-related neurons in monkeys performing covert visual search tasks without eye movements. Here we show that the source of attention signals in the FEF is enhanced activity of visually responsive neurons. At the time attention is allocated to the visual search target, nonvisually responsive saccade-related movement neurons are inhibited. Therefore, in the FEF, spatial attention signals are independent of explicit saccade command signals. We propose that spatially selective activity in FEF visually responsive neurons corresponds to the mental spotlight of attention via modulation of ongoing visual processing.