Fixation Period Research Articles

Management of infected total knee arthroplasty by Ilizarov fixator

Introduction Persistent infection after total knee arthroplasty (TKA) is a very serious complication. Arthrodesis is considered if the prosthesis cannot be retained or revision surgery is obviated. The purpose of this study was to evaluate the radiological and functional results of knee arthrodesis with Ilizarov external fixator to treat infected TKA. Patients and methods This was a retrospective study of 13 patients with infected TKA treated by implant removal, debridement, and fusion by Ilizarov fixator operated from October 2010 to March 2015. The study included nine females and four males with a mean age of patients of 64.08 years. Seven patients were diabetics and two had a past history of deep venous thrombosis. Time, from the primary TKA till knee fusion, ranged from 18 to 37 months. All patients had previous surgical interventions with a mean of 4.62 procedures. Eleven patients had draining sinuses. In addition to clinical and radiographic evaluation, the functional assessment was done by Western Ontario and McMaster Universities Osteoarthritis index questionnaire. Results Patients were followed up for a mean of 28.62 months. The mean external fixator period was 7.77 months. Postoperative hematoma occurred in one patient. Pin track infection occurred in 10 cases. All cases had successful fusion except two patients and infection was controlled in all cases. The mean leg length discrepancy was 3.96 cm. The mean postoperative Western Ontario and McMaster Universities Osteoarthritis index score was 30.08. Conclusion Knee arthrodesis by Ilizarov external fixator for treating persistently infected TKA achieved high fusion and infection control rates and provided a stable limb with pain relief and functional improvement.

Spring technique for correction of multilevel deformity using hexapod external fixator

Context: Osteotomies in several parts of one long bone are recommended for correction of a long, curved, and wide-angled deformity. Hexapod external fixators (HEFs) allow for the single-stage correction of multiplanar deformity, but they are heavy, expensive, and requires continuous management of 12 struts, if at more than one level. Aims: We proposed the use of springs with HEF to support the intermediate ring. Deformity between the proximal and distal rings is corrected using one HEF, and the intermediate fragment is automatically corrected by the tension of the springs. Settings and Design: This was a retrospective descriptive study. Subjects and Methods: We treated seven males and eight females with 17 affected limbs. Four patients with familial hypophosphatemic rickets, five posttraumatic deformities, two osteogenesis imperfectas, three fibrous dysplasias, and one neurofibromatosis were included. The mean preoperative angle between the most proximal and distal fragments was 62.5°. First, small distraction at each level was initiated with one HEF fixed to the most proximal and distal rings, and Ilizarov hinges applied between the proximal and intermediate rings. Then, a set of three springs was applied for each interval between the rings. Gradual correction using HEF was performed, considering only the axes of the proximal and distal bone fragments. Results: Good alignment was achieved in all patients without severe complications. The mean correction period was 5.5 weeks and mean fixation period was 33.8 weeks. Conclusion: Combination of HEF and springs is capable of correcting severe deformity.

Fixed Time and Fixed Angle External Fixation in the Treatment of Gartland Type III Supracondylar Humerous Fractures in Children

Objective: To assess the efficacy of open reduction internal fixation (ORIF) combined with fixed-time and fixed-angle external fixation (FTFAEF) in the treatment of Gartland type III supracondylar humerous fracture (SHF) in children. Methods: Clinical data of 172 children with Gartland type III SHF from March 2012 to December 2017 were prospectively analyzed. All 172 patients were initially treated with ORIF, then 86 underwent FTFAEF for 3 weeks post-surgery (intervention group) while the remaining 86 received conventional plaster external fixation (70°-90°) for 3 weeks post-surgery (control group). The plaster casts were removed from both groups after the 3-week fixation period and functional exercise was initiated. Regular clinical and radiologic follow-ups were conducted on all patients. Range of motion (ROM) measurements and modified Hospital for Special Surgery (HSS) elbow function assessments were performed at 1 and 3 months post-surgery. Results: At 1 month post-surgery, both ROM and modified HSS scores were significantly higher in the intervention group (85.8±6.1° and 65.2±3.6°, respectively) than in the control group (62.3±5.2° and 56.6±2.1°, respectively)(both P<0.05). After 3 months, both ROM and modified HSS scores were still significantly higher in the intervention group (132.0±4.7° and 98.5±1.3°, respectively) than in the control group (107.5±24.4° and 85.0±10.3°, respectively) (both P<0.05). Furthermore, the percentage of patients scoring excellent on the HSS scale was significantly higher in the intervention group (100%) than in the control group (74.42%) (P<0.05). Conclusions: ORIF combined with FTFAEF is an efficacious approach that should be widely promoted for the treatment of Gartland type III SHF in children.

Dynamics of the Formation of Protection for Circulatory Bed in Bone Regenerate

Evaluation of the bone regenerate maturation in 21 patients, aged 27 – 66 years, with closed shoulder fractures was performed in the course of treatment by Ilizarov technique according to the rate of blood supply velocity at functional load and by the value of that load. Examination was performed in 1 and 2 weeks as well as in 1 and 2 months after fixation. Within the first 2 weeks the bone fragments micro mobility at 10 kgF axial load on the extremity made up 194±42 µm. Subsequently as the regenerate became compact the bone fragments micro mobility decreased up to 53±13 µm (p≤0.02). During the fixation period the load tolerance increased from 5 to 15 kgF. The threshold of load tolerance was detected by the occurrence of unpleasant feelings the regenerate zone and increased rate of blood circulation in the vessels. At the end of fixation period the rate of blood circulation was decreased by 2 times and practically did not change at increasing loads confirming the formation of the protection system for circulatory bed in the bone regenerate.

Dynamics of the formation of protection for circulatory bed in bone regenerate

Evaluation of the bone regenerate maturation in 21 patients, aged 27 - 66 years, with closed shoulder fractures was performed in the course of treatment by Ilizarov technique according to the rate of blood supply velocity at functional load and by the value of that load. Examination was performed in 1 and 2 weeks as well as in 1 and 2 months after fixation. Within the first 2 weeks the bone fragments micro mobility at 10 kgF axial load on the extremity made up 194±42 µm. Subsequently as the regenerate became compact the bone fragments micro mobility decreased up to 53±13 µm (p≤0.02). During the fixation period the load tolerance increased from 5 to 15 kgF. The threshold of load tolerance was detected by the occurrence of unpleasant feel- ings the regenerate zone and increased rate of blood circulation in the vessels. At the end of fixation period the rate of blood circulation was decreased by 2 times and practically did not change at increasing loads confirming the formation of the protection system for circulatory bed in the bone regenerate.

Autocorrelation Structure in the Macaque Dorsolateral, But not Orbital or Polar, Prefrontal Cortex Predicts Response-Coding Strength in a Visually Cued Strategy Task.

In previous work, we studied the activity of neurons in the dorsolateral (PFdl), orbital (PFo), and polar (PFp) prefrontal cortex while monkeys performed a strategy task with 2 spatial goals. A cue instructed 1 of 2 strategies in each trial: stay with the previous goal or shift to the alternative goal. Each trial started with a fixation period, followed by a cue. Subsequently, a delay period was followed by a "go" signal that instructed the monkeys to choose one goal. After each choice, feedback was provided. In this study, we focused on the temporal receptive fields of the neurons, as measured by the decay in autocorrelation (time constant) during the fixation period, and examined the relationship with response and strategy coding. The temporal receptive field in PFdl correlated with the response-related but not with the strategy-related modulation in the delay and the feedback periods: neurons with longer time constants in PFdl tended to show stronger and more prolonged response coding. No such correlation was found in PFp or PFo. These findings demonstrate that the temporal specialization of neurons for temporally extended computations is predictive of response coding, and neurons in PFdl, but not PFp or PFo, develop such predictive properties.

Оценка численности хондроцитов в суставном хряще при дистракционном остеосинтезе голени в комбинации с накостной пластиной

Introduction The number of chondrocytes in the articular cartilage of the femoral condyles and talus junction surface in the conditions of distraction osteosynthesis of the tibia with the Ilizarov apparatus combined with plating was estimated. Material and methods Seven dogs underwent tibial lengthening at a daily rate of 1 mm for 4 steps and to 14–16 % of the initial length of the segment with the use of the Ilizarov apparatus and plating. Stages of the study were days 30 and 90 in the fixation phase when only plating was left. Histomorphometry of semi-thin sections of the articular cartilage was carried out with the help of an Opton photomicroscope (Germany), DiaMorf software complex (Russia) and VideoTest-Master morphology program. The proportion of chondrocytes (N ch, %), the proportion of empty lacunae (NN em.lac, %), and isogenic groups (NN is.gr, %) were determined in the total sample volume of 200 lacunae. A control group was articular cartilage of five intact dogs. Results The articular cartilage of both articular surfaces retained the zonal structure. Disorder in the homogeneity of the superficial part of the surface zone and destruction of a part of chondrocytes were noted. In the articular cartilage of the femoral condyles, the Nch value was lower than in the control animals by 5.74 %. NN em.lac was increased 2.3 times while NN is.gr values decreased to 2.06 % in the femoral condyle articular cartilage after 30 days of fixation period with the plate. After 90 days of fixation, the N ch values were lower with respect to the controls by 3.73 %. Low values of NN is.gr (4.3 %) and high values of NN em.lac (27.54 %) were maintained. In the articular cartilage of the talus, N ch was lower than in the control group by 1.98 %; NN em.lac increased 1.5 times and NN is.gr decreased to 4.7 % relative to controls after 30 days of fixation. After 90 days, the value of NN em.lac remained at the same level as in the previous experiment stage. The values of NN is.gr were comparable with the control group. Conclusion The technique of distraction osteosynthesis of the tibia in combination with plating is of low traumatic effect on the adjacent joints. A comparative analysis of quantitative parameters of the articular cartilage revealed that the most vulnerable site was the articular cartilage of the femoral condyles.

Short-term effectiveness of Kirschner wire elastic fixation in treatment of Doyle type Ⅰ and Ⅱ mallet finger

To evaluate the short-term effectiveness of Kirschner wire (K-wire) elastic fixation in the treatment of Doyle type Ⅰ and Ⅱ mallet finger. Between July 2016 and March 2017, 18 patients with Doyle type Ⅰ and Ⅱ mallet finger were treated. There were 12 males and 6 males, with an average age of 45 years (range, 16-61 years). The index finger was involved in 2 cases, the middle finger in 3 cases, the ring finger in 10 cases, and the little finger in 3 cases. The interval from injury to operation ranged from 2 hours to 45 days (median, 5.5 hours). There were 8 patients of closed wound and 10 patients of open wound. Fourteen patients were simply extensor tendon rupture and 4 were extensor tendon rupture complicated with avulsion fracture. The distal interphalangeal joints (DIPJ) of injured fingers were elastically fixed with the K-wire at mild dorsal extend position. The K-wire was removed after 6 weeks, and the functional training started. The operation time was 34-53 minutes (mean, 38.9 minutes). Patients were followed up 3-8 months (mean, 5 months). All incisions healed primarily and no K-wire loosening or infection happened during the period of fixation. All mallet fingers were corrected. The range of motion (ROM) in terms of active flexion of injured DIPJ was (75.83±11.15)° at 6 weeks after operation, showing significant difference when compared with the normal DIPJ of contralateral finger [(85.28±6.06)°] ( t=3.158, P=0.003). The ROM in terms of active flexion was (82.67±6.78)° in 15 patients who were followed up at 8 months after operation, showing no significant difference when compared with the normal DIPJ of contralateral finger [(86.00±5.73)°] ( t=1.454, P=0.157). After the removal of K-wire at 6 weeks, visual analogue scale (VAS) score of active flexion and of passive flexion to maximum angle were 1.78±0.88 and 3.06±1.06, respectively. According to the total active motion criteria, the effectiveness was rated as excellent in 10 cases, good in 5 cases, moderate in 2 cases, and poor in 1 case, and the excellent and good rate was 83.33%. The patients' satisfaction were accessed by Likert scale, which were 3-5 (mean, 4.2). K-wire elastic fixation in the treatment of Doyle typeⅠand Ⅱ mallet finger can repair the extensor effectively, correct the mallet finger deformity, and also be benefit for the flexion-extension function restoration of DIPJ.

The effect of plasma rich in growth factors combined with follicular unit extraction surgery for the treatment of hair loss: A pilot study.

Hair transplant surgery using follicular unit extraction technique (FUE) is a common surgical procedure for the treatment of severe hair loss. Blood-derived autologous growth factors have also proved to promote hair regeneration in patients with different types of alopecia. The aim of this study was to evaluate the safety and clinical efficacy of plasma rich in growth factors (PRGF) technology as an adjuvant therapy for FUE surgery in hair loss affected patients. The biologic potential of PRGF was firstly invitro evaluated over follicular germinal matrix and dermal papilla cells. Afterward, fifteen patients were subjected to routine FUE procedure while 15 patients underwent FUE+PRGF therapy. PRGF group included intradermal injections of growth factors and follicular transfer unit (FTU) preservation in an autologous fibrin clot. Postsurgical patient satisfaction and clinical improvement were evaluated, and PRGF or saline-preserved hair grafts were histomorphometrically analyzed. Follicular cell proliferation and migration was induced after autologous growth factors treatment. PRGF-preserved FTUs presented higher bioactivity signals and improved integrity of perifollicular structures and extracellular matrix proteins such as collagen and elastic fibers. PRGF not only reduced the postsurgical crust healing and hair fixation period, but also decreased the inflammatory pain and itching sensation. This preliminary data demonstrate that PRGF is able to minimize the postsurgical follicle loss and potentiate the performance of grafted hairs. The fibrin clot not only acts as a protective barrier against environmental factors, but also provides a biologically active scaffold that induces resident cell proliferation and maintains an optimal integrity of the grafted hair.

THE NEW METHOD OF LONG BONE MULTILEVEL DEFORMITIES CORRECTION USING THE ORTHOPEDIC HEXAPOD (PRELIMINARY REPORT)

For the treatment of patients with multilevel deformities when there are contraindications for an acute single step correction the external fixation should be applied including orthopedic hexapods. At the same time a separate orthopedic hexapod is used for each level of deformity. This leads to a significant bulkiness of the overall frame assembly. Calculation of deformity correction in the presence of an intermediate fragment (fragments) and practical implementation of correction represent by no means a simple task.Purpose of the study – to perform a clinical approbation of “spring” technique for multilevel correction of long bones deformities and to evaluate the results.Materials and methods. The authors developed an original technique for correcting multilevel deformities using a single orthopedic hexapod. During the procedure the hexapod struts are fixed only to the proximal and distal rings, and the intermediate ring (rings) is fixed to the adjacent supports using the springs – a so-called “spring” technique. The new method has been successfully tested in the treatment of 7 patients with 2 and 3-level deformities of long bones.Results. The reported correction accuracy was 97.6%. The fixation period averaged 47 weeks (from 37 to 54 weeks). In 2 cases the authors observed soft tissues inflammation around of transosseous elements eradicated by the administration of antibiotics. In one patient with post-traumatic deformity a premature consolidation was observed at one of the levels which required re-osteotomy with further correction using two hexapods.Conclusion. Preliminary results demonstrated that the use of simultaneous correction of deformities at several levels applying one orthopedic hexapod Ortho-SUV and springs simplifies correction calculations, provides optimal timing for deformity correction while maintaining the minimal frame dimensions.

Gaze-in-World movement Classification for Unconstrained Head Motion during Natural Tasks.

Accurate classification of eye movements is an integral component of many psychophysical experiments. Most event classifiers are restricted to the analysis of eye-in-head (EIHv) vectors while the head is fixed, and detect two classes of gaze events, namely fixations and saccades. Classification of eye movements as Vestibular Ocular reflex (VOR) or Smooth pursuits (SP) require that we compensate gaze motion with a person's head movements. As the complexity of naturalistic behavioral paradigms increases, so does the need for gaze classification with head-free motion which could detect these complex eye movements. We propose the use of a supervised Machine Learning (ML) classifier for the automated analysis of head free gaze signal. As a preliminary test, we used a SVM classifier to label a 60 Hz test dataset from a virtual reality ball catching task into periods of fixations, saccades and pursuit. This preliminary test resulted in 94% accuracy in a sample to sample comparison with an artificially generated set of gaze movements reflective of measured gaze statistics, and visual inspection shows very high correspondence to subjective analysis of the gaze signal. This promising methodology has since been extended to the analysis of data collected during natural tasks. Five subjects' head and gaze movements were recorded using an IMU and a 120 Hz SMI Wireless ETG2 as they performed four different natural tasks for 10 minutes each. This yielded 120 minutes of angular velocity data of the gaze in world vector (GIWv) during natural tasks. Four experts manually annotated a subset of the data as periods of fixation, saccade, smooth pursuit, and blinks. Inter-labeler reliability was measured to generate a confidence metric and a cost function for misclassifications. We summarize the statistics of natural eye movements and compare various ML based temporal series classification schemes. Meeting abstract presented at VSS 2017

Saccade latencies in an overlap paradigm when manipulating the stimuli timing, energy and transient changes.

Previous studies showed that a temporal overlapping of the fixation-target with the saccade-target onset induces a shift of saccade reaction time distributions towards longer values. Here we present a series of experiments probing how an overlap paradigm, combined with the manipulation of stimuli durations, energy and transient changes might modulate saccadic reaction time distributions. We recorded saccadic reaction time in four participants in six experiments in which a saccade-target appeared at a random amplitude after a fixation period. First we parametrically manipulated the duration of the overlap using a range of intervals (from 0 to 200 ms). In a second experiment we probed the interaction of various foreperiod intervals (i.e. the duration of the fixation period prior to saccade-target onset) and overlap using two overlap intervals (20 or 140 ms). In two additional experiments we manipulated either the stimuli sizes or their contrasts in overlap paradigms (20 or 140 ms). Lastly, we introduced a visual transient during the overlap interval via two manipulations (both with a range of SOA): either a distractor ring appeared around the fixation-target, or dynamic random noise replaced the fixation-target. Results show reliable modifications in the latency distributions depending on the overlap interval as well as idiosyncratic differences. Furthermore, all our additional experimental manipulations also affected the latency distributions revealing strong interacting inhibitory processes. We conclude that the effects of overlap intervals may combine with the influence of other stimuli properties to produce strong effects on decision process.

Incomitance and Eye Dominance in Intermittent Exotropia.

PurposeTo determine if the deviation angle changes in subjects with intermittent exotropia as they alternate fixation between the right and left eye in primary gaze.MethodsIn this prospective observational cohort study, 37 subjects with intermittent exotropia were tested for evidence of incomitance. The position of each eye was recorded with a video tracker during fixation on a small central target. A cover–uncover test was performed by occluding one eye with a shutter that passed infrared light, allowing continuous tracking of both eyes. The deviation angle was measured during periods of right eye and left eye fixation. Incomitance was assessed as a function of eye preference, fixation stability, and exotropia variability.ResultsThe mean exotropia was 18.2° ± 8.1°. A difference between right exotropia and left exotropia was detectable in 16/37 subjects. Allowing for potential tracking error, the incomitance had a mean amplitude of 1.7°. It was not related to a difference in accommodative effort, eye preference, fixation stability, or variability in deviation.ConclusionsComitance is regarded as a feature that distinguishes strabismus from paralytic or restrictive processes. Unexpectedly, eye tracking during the cover–uncover test showed that incomitance is present in approximately 40% of subjects with intermittent exotropia. It averages 10% of the exotropia, and can equal up to 5°. When substantial, it may be worth considering when planning surgical correction.

Salvage of failed ankle arthrodesis after posttraumatic septic arthritis by Ilizarov external fixator: mid-term results

Background: Failed septic ankle arthrodesis is a challenging problem. This study evaluated the results of salvage revision ankle arthrodesis using Ilizarov external fixation to treat nonunited arthrodesis of posttraumatic septic ankle arthritis and to analyze the functional outcome of this method. Methods: This prospective study included 14 patients with a mean age of 48 yr. Patients had already undergone a mean of 4.43 previous surgeries at a mean of 17.14 mo from primary arthrodesis. Five patients had associated deformity. The mean preoperative American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score was 23.93. Meticulous debridement was done and an Ilizarov fixator was applied in compression in a one-stage procedure. Results: The mean follow up period was 41.71 mo with mean external fixation period of 17.29 wk. Successful arthrodesis in perfect alignment was achieved in 13 of 14 patients without additional procedures. One ankle did not go on to union. A chronic discharging sinus persisted in one patient. One infected loose wire was exchanged in two patients. One diabetic patient reported moderate daily diffuse pain. The mean postoperative AOFAS ankle-hindfoot score was 71.57. Patients with successful fusion were satisfied with the procedure. Conclusions: Using an Ilizarov fixator to salvage nonunited septic posttraumatic ankle arthrodesis was effective, with patients reporting a stable ankle and dramatic functional improvement with minimal complications.

Behaviour and performance of suckling gilts and their piglets in single housing with different fixation times

Abstract. The objective was to evaluate suckling performance and behaviour traits of gilts and piglets in two different single-housing farrowing systems under practical conditions. Performance data of 70 crossbred gilts and their 842 piglets were collected. The behavioural observation included 17 gilts and 211 piglets. Gilts of the control group (full-time crating, FTC) were fixed during farrowing and suckling (Pro Dromi® 1), and in the experimental group (short-time crating, STC) gilts were fixed for 6 days postpartum (p.p.) only (Pro Dromi® 1.5). Six farrowing crates were included in each group, and six replications were carried out. Performance data were collected and gilts' and piglets' behaviour was observed with 10 min scan samples and categorized by standing, walking (only in STC), sitting and lying (side and belly). The management and the housing systems were in accordance with the Tierschutz-Nutztierhaltungsverordnung (TierSchNutztV, 2017). No significant (p &gt; 0.05) differences between FTC and STC were found in piglets born alive (13.2 and 13.9, respectively), loss of piglets (1.4 and 1.55, respectively) and weaned piglets including cross-fostering (12.0 and 12.4, respectively). Piglet loss due to crushing was 0.6 (FTC) and 0.64 (STC), with no significant difference (p &gt; 0.05). Overall, 82.5 % of all piglets killed due to crushing were lost from farrowing to day 2 p.p. The daily gain of STC piglets was significantly higher than that of FTC piglets (205 g vs. 199 g, respectively; p &lt; 0.05) during the suckling period (3 weeks). Concerning gilts' behaviour, significant differences (p ≤ 0.05) were found in sitting duration only (FTC 5.8 % and STC 4.0 %, respectively). FTC piglets spent more time lying, sitting and standing (7.4 % vs. 4.4 %, 0.5 % vs. 0.4 %, 9.6 % vs. 8.4 %, respectively; p ≤ 0.05). The reason could be the higher acceptance of the piglet nest in STC. It was possible to conclude that gilts' welfare was improved by STC compared to FTC, and farrowing crates with loose single housing did not lead to higher piglet loss in the suckling period. An earlier end of the fixation period of the gilt at day 2 or 3 p.p. should be tested.

Active Vision: Dynamic Reformatting of Visual Information by the Saccade-Drift Cycle

Visual processing depends on rapid parsing of global features followed by analysis of fine detail. A new study suggests that this transformation is enabled by a cycle of saccades and fixational drifts, which reformat visual input to match the spatiotemporal sensitivity of fast and slow neuronal pathways.

Anatomical reconstruction of the fourth brachymetatarsia with one-stage iliac bone and cartilage cap grafting

We present a one-stage procedure for lengthening the fourth brachymetatarsia with autogenous iliac bone and cartilage cap grafting for the anatomical reconstruction of the metatarsophalangeal (MTP) joint METHODS: During the last 8 years, 56 feet in 41 patients with congenital brachymetatarsia ofthe fourth toe were corrected with a one-stage operation to reposition the articularcartilagecap to the distal part of interpositional iliac bone graft at the metatarsal epiphysis. The length of the harvested iliac bone graft was 22.9mm on average. The mean fixation period was 58.5 days, and the mean gain in length and percentage increase was 20.9mm and 39%, respectively. MRI showed a stable MTP joint over viable cartilage cap in 83.3% of the cases. Mean postoperative American Orthopedic Foot and Ankle Society lesser MTP-interphalangeal score was 82.0. Neither neurovascular impairment nor recurrence of brachymetatarsia occurred in the mean follow-up period of 43.6 months. All patients were satisfied with the postoperative cosmetic results. Thirteen patients (23.2%) complained of limited active dorsiflexion of the fourth toe, and extensor adhesion was released by extensor tenolysis in only one patient. In a single case of nonunion at the bone graft site, additional surgery was not necessary. Anatomical reconstruction of the fourth brachymetatarsia with one-stage interpositional iliac bone and cartilage cap grafting resulted in excellent cosmetic results and a physiologic MTP joint, providing the benefits of one-stage lengthening with a low complication rate. Therapeutic, IV.

Fixation target representation in prefrontal cortex during the antisaccade task.

Neurons that discharge strongly during the time period of fixation of a visual target and cease to discharge before saccade initiation have been described in the brain stem, superior colliculus, and cortical areas. In subcortical structures, fixation neurons play a reciprocal role with saccadic neurons during the generation of eye movements. Their role in the dorsolateral prefrontal cortex is less obvious, and it is not known if they are activated by fixation, inhibit saccade generation, or play a role in more complex functions such as the inhibition of inappropriate responses. We examined the properties of prefrontal fixation neurons in the context of an antisaccade task, which requires an eye movement directed away from a prepotent visual stimulus. We tested monkeys with variants of the task, allowing us to dissociate activity synchronized on the fixation offset, presentation of the visual stimulus, and saccadic onset. Fixation neuron activity latency was most strongly tied to the offset of the fixation point across task variants. It was not well predicted by the appearance of the visual stimulus, which is essential for planning of the correct eye movement and inhibiting inappropriate ones. Activity of fixation neurons was generally negatively correlated with that of saccade neurons; however, critical differences in timing make it unlikely that they provide precisely timed signals for the generation of eye movements. These results demonstrate the role of fixation neurons in the prefrontal cortex during tasks requiring timing of appropriate eye movement and inhibition of inappropriate actions.NEW & NOTEWORTHY Properties of neurons that discharge during eye fixation and go silent before saccade initiation have been described in subcortical structures involved in eye movement generation, but their role in the dorsolateral prefrontal cortex presents a puzzle. Our results demonstrate the role of fixation neurons in the prefrontal cortex during tasks requiring precise timing of appropriate eye movement and inhibition of inappropriate actions.

Alteration of the microsaccadic velocity-amplitude main sequence relationship after visual transients: implications for models of saccade control.

Microsaccades occur during gaze fixation to correct for miniscule foveal motor errors. The mechanisms governing such fine oculomotor control are still not fully understood. In this study, we explored microsaccade control by analyzing the impacts of transient visual stimuli on these movements' kinematics. We found that such kinematics can be altered in systematic ways depending on the timing and spatial geometry of visual transients relative to the movement goals. In two male rhesus macaques, we presented peripheral or foveal visual transients during an otherwise stable period of fixation. Such transients resulted in well-known reductions in microsaccade frequency, and our goal was to investigate whether microsaccade kinematics would additionally be altered. We found that both microsaccade timing and amplitude were modulated by the visual transients, and in predictable manners by these transients' timing and geometry. Interestingly, modulations in the peak velocity of the same movements were not proportional to the observed amplitude modulations, suggesting a violation of the well-known "main sequence" relationship between microsaccade amplitude and peak velocity. We hypothesize that visual stimulation during movement preparation affects not only the saccadic "Go" system driving eye movements but also a "Pause" system inhibiting them. If the Pause system happens to be already turned off despite the new visual input, movement kinematics can be altered by the readout of additional visually evoked spikes in the Go system coding for the flash location. Our results demonstrate precise control over individual microscopic saccades and provide testable hypotheses for mechanisms of saccade control in general.NEW & NOTEWORTHY Microsaccadic eye movements play an important role in several aspects of visual perception and cognition. However, the mechanisms for microsaccade control are still not fully understood. We found that microsaccade kinematics can be altered in a systematic manner by visual transients, revealing a previously unappreciated and exquisite level of control by the oculomotor system of even the smallest saccades. Our results suggest precise temporal interaction between visual, motor, and inhibitory signals in microsaccade control.

Application of a customized 3D printed reduction aid after external fixation of the femur and tibia: Technical note.

To construct a fracture-specific reduction aid by means of virtual reduction technology and 3D printing to reduce malreduced, externally fixed, long bone fractures. Following application of an external fixator to a malreduced long bone fracture, we performed postoperative computed tomography to visualise the fragments and their position relative to Schanz screws. DICOM data were transferred to 3D planning software, and the fracture was then virtually reduced. Subsequently, a reduction aid was designed to cover the Schanz screws in such a way that it would maintain the position of the new fragments. Following 3D printing, the solid reduction aid could be applied onto the Schanz screws. The reduction aid fit only in the reduced position of the fracture, thus maintaining correct bone alignment. Our reduction technique can be applied during the temporary external fixation period on the preexisting external fixator or as a reduction aid during definitive treatment.