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Stephen M. Howell - One of the best experts on this subject based on the ideXlab platform.
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Empirical Relationship Between Lengthening an Anterior Cruciate Ligament Graft and Increases in Knee Anterior Laxity: A Human Cadaveric Study
Journal of biomechanical engineering, 2006Co-Authors: Dustin M. Grover, Maury L. Hull, Dustin M. Thompson, Stephen M. HowellAbstract:Lengthening of an anterior cruciate ligament (ACL) graft construct can occur as a result of lengthening at the sites of tibial and/or Femoral Fixation and manifests as an increase in anterior laxity. Although lengthening at the site of Fixation has been measured for a variety of Fixation Devices, it is difficult to place these results in a clinical context because the mathematical relationship between lengthening of an ACL graft construct and anterior laxity is unknown. The purpose of our study was to determine empirically this relationship. Ten cadaveric knees were reconstructed with a double-looped tendon graft. With the knee in 25 degrees of flexion, the position of the proximal end of the graft inside the Femoral tunnel was adjusted by moving the Femoral Fixation Device until the anterior laxity at an applied anterior force of 134 N matched that of the intact knee. In random order, the graft construct was lengthened 1, 2, 3, 4, and 5 mm by moving the Femoral Fixation Device distally along the Femoral tunnel and anterior laxity was measured. The increase in the length of the graft construct was related to the increase in anterior laxity by a simple linear regression model. Lengthening the graft construct from 1 to 5 mm caused an equal increase in anterior laxity (slope=1.0 mmmm, r(2)=0.800, p
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The EZLoc: A Simple, Rigid Femoral Fixation Device for a Soft Tissue Anterior Cruciate Ligament Graft
Techniques in Orthopaedics, 2005Co-Authors: Akio Matsumoto, Stephen M. HowellAbstract:Summary: The EZLoc is a new Femoral Fixation Device for soft tissue anterior cruciate ligament (ACL) reconstruction that combines superior Fixation properties (1427 N strength, N/mm stiffness, and high resistance to slippage) with a simple surgical technique. The EZLoc is composed of a slotted body through which the ACL graft is looped and a deployable lever arm that rigidly fixes the graft on the anterolateral cortex of the femur. The EZLoc comes in a sterile package with a sharp-tip passing pin that is secured in the slotted body with a suture tied under tension. After the ACL graft is passed into the Femoral tunnel, the suture is cut, the passing pin is removed, and the suture is tensioned, which deploys the lever arm and fixes the EZLoc on cortical bone. The EZLoc can be used with both the one- and 2-tunnel ACL reconstruction techniques, and is available in several length and diameter combinations that are for use in tunnels ranging from 20 to 60 mm in length and ACL grafts ranging from 5 to 10 mm in diameter. Key Words: EZLoc—Anterior cruciate ligament reconstruction— Femoral Fixation Device—Soft tissue graft—Superior Fixation properties—Reliable surgical technique. The EZLoc (Arthrotek, Inc., Warsaw, IN) is a Femoral Fixation Device for soft tissue anterior cruciate ligament (ACL) reconstruction. The EZLoc provides superior Fixation properties that allow aggressive rehabilitation combined with a simple, reliable surgical technique. Both the high-volume and occasional ACL surgeon and surgical team have found the EZLoc easy to use since being approved for use in late 2004.
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In Vivo Calibration of a Femoral Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension: A Study in an Ovine Model
Journal of biomechanical engineering, 2001Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. Howell, Keith W. LawhornAbstract:Toward developing a transducer for measuring in vivo tension in anterior cruciate ligament grafts in humans, the objectives of this study were to determine the following: (1) whether the calibration of a previously reported Femoral Fixation Device transducer (FDT) (Ventura et al., 1998) is affected by the presence of the graft when implanted in the tibial metaphysis of an ovine model, (2) whether the FDT remains calibrated at 4 weeks postoperatively, and (3) whether the biological incorporation of the graft occurs prior to a change in the FDT calibration. The FDT was implanted in the hind limb of five sheep using an extra-articular procedure. Both the proximal common digital extensor tendon (i.e., graft) and a Teflon-coated wire were looped around the FDT inside a tunnel in the tibial metaphysis. The FDT was calibrated on three occasions using the loop of wire: once intraoperatively before graft insertion, once intraoperatively after graft insertion, and once postoperatively after the animals had been sacrificed at 4 weeks. Following sacrifice, the load transmitted to the FDT by the graft was also determined. The FDT exhibited linear calibration intraoperatively both before and after graft insertion with an average error relative to the calibration before insertion of the graft of -4.6 percent of full-scale load (150 N) and this average relative error was not significantly different from zero (p = 0.183). After 4 weeks of implantation, the average relative percent error was -5.0 percent and was not significantly different from zero (p = 0.434) indicating that the FDT remained calibrated in the in vivo environment. Because only 15 percent of the graft tension was transmitted to the FDT after 4 weeks, biological incorporation of the graft preceded the loss of calibration. In light of these findings, the FDT offers the capability of measuring the intra-articular ACL graft tension in vivo in animal models and possibly humans before the biological bond develops and also of monitoring the formation and maturation of the biological bond between a graft and bone tunnel.
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Static and fatigue strength of a Fixation Device transducer for measuring anterior cruciate ligament graft tension.
Journal of biomechanical engineering, 2000Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. HowellAbstract:To determine which exercises do not overload the graft-Fixation complex during intensive rehabilitation from reconstructive surgery of the anterior cruciate ligament (ACL), it would be useful to measure ACL graft loads during rehabilitative activities in vivo in humans. A previous paper by Ventura et al. (1998) reported on the design of an implantable transducer integrated into a Femoral Fixation Device and demonstrated that the transducer could be calibrated to measure graft loads to better than 10 percent full-scale error in cadaveric knees. By measuring both the static and fatigue strengths of the transducer, the purpose of the present study was to determine whether the transducer could be safely implanted in humans without risk of structural failure. Eight Devices were loaded to failure statically. Additionally, seven Devices were tested using the up-and-down method to estimate the median fatigue strength at a life of 225,000 cycles. The average ultimate strength was 1856 +/- 74 N and the median fatigue strength was 441 N at a life of 225,000 cycles. The maximum graft load during normal daily activities is estimated to be 500 N and the 225,000 cycle life corresponds to that of the average healthy individual during a 12-week period. Considering that patients who have had an ACL reconstruction are less ambulatory than normal immediately following surgery and that biologic incorporation of the graft should be well developed by 12 weeks thus decreasing the load transmitted to the Fixation Device, the FDT can be safely implanted in humans without undue risk of structural failure.
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An implantable transducer for measuring tension in an anterior cruciate ligament graft.
Journal of biomechanical engineering, 1998Co-Authors: C. P. Ventura, Maury L. Hull, J. Wolchok, Stephen M. HowellAbstract:The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a Femoral Fixation Device. To devise a practical in vivo calibration protocol for the Fixation Device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the Device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and Femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the Femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the Femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.
Maury L. Hull - One of the best experts on this subject based on the ideXlab platform.
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Empirical Relationship Between Lengthening an Anterior Cruciate Ligament Graft and Increases in Knee Anterior Laxity: A Human Cadaveric Study
Journal of biomechanical engineering, 2006Co-Authors: Dustin M. Grover, Maury L. Hull, Dustin M. Thompson, Stephen M. HowellAbstract:Lengthening of an anterior cruciate ligament (ACL) graft construct can occur as a result of lengthening at the sites of tibial and/or Femoral Fixation and manifests as an increase in anterior laxity. Although lengthening at the site of Fixation has been measured for a variety of Fixation Devices, it is difficult to place these results in a clinical context because the mathematical relationship between lengthening of an ACL graft construct and anterior laxity is unknown. The purpose of our study was to determine empirically this relationship. Ten cadaveric knees were reconstructed with a double-looped tendon graft. With the knee in 25 degrees of flexion, the position of the proximal end of the graft inside the Femoral tunnel was adjusted by moving the Femoral Fixation Device until the anterior laxity at an applied anterior force of 134 N matched that of the intact knee. In random order, the graft construct was lengthened 1, 2, 3, 4, and 5 mm by moving the Femoral Fixation Device distally along the Femoral tunnel and anterior laxity was measured. The increase in the length of the graft construct was related to the increase in anterior laxity by a simple linear regression model. Lengthening the graft construct from 1 to 5 mm caused an equal increase in anterior laxity (slope=1.0 mmmm, r(2)=0.800, p
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In Vivo Calibration of a Femoral Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension: A Study in an Ovine Model
Journal of biomechanical engineering, 2001Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. Howell, Keith W. LawhornAbstract:Toward developing a transducer for measuring in vivo tension in anterior cruciate ligament grafts in humans, the objectives of this study were to determine the following: (1) whether the calibration of a previously reported Femoral Fixation Device transducer (FDT) (Ventura et al., 1998) is affected by the presence of the graft when implanted in the tibial metaphysis of an ovine model, (2) whether the FDT remains calibrated at 4 weeks postoperatively, and (3) whether the biological incorporation of the graft occurs prior to a change in the FDT calibration. The FDT was implanted in the hind limb of five sheep using an extra-articular procedure. Both the proximal common digital extensor tendon (i.e., graft) and a Teflon-coated wire were looped around the FDT inside a tunnel in the tibial metaphysis. The FDT was calibrated on three occasions using the loop of wire: once intraoperatively before graft insertion, once intraoperatively after graft insertion, and once postoperatively after the animals had been sacrificed at 4 weeks. Following sacrifice, the load transmitted to the FDT by the graft was also determined. The FDT exhibited linear calibration intraoperatively both before and after graft insertion with an average error relative to the calibration before insertion of the graft of -4.6 percent of full-scale load (150 N) and this average relative error was not significantly different from zero (p = 0.183). After 4 weeks of implantation, the average relative percent error was -5.0 percent and was not significantly different from zero (p = 0.434) indicating that the FDT remained calibrated in the in vivo environment. Because only 15 percent of the graft tension was transmitted to the FDT after 4 weeks, biological incorporation of the graft preceded the loss of calibration. In light of these findings, the FDT offers the capability of measuring the intra-articular ACL graft tension in vivo in animal models and possibly humans before the biological bond develops and also of monitoring the formation and maturation of the biological bond between a graft and bone tunnel.
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Static and fatigue strength of a Fixation Device transducer for measuring anterior cruciate ligament graft tension.
Journal of biomechanical engineering, 2000Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. HowellAbstract:To determine which exercises do not overload the graft-Fixation complex during intensive rehabilitation from reconstructive surgery of the anterior cruciate ligament (ACL), it would be useful to measure ACL graft loads during rehabilitative activities in vivo in humans. A previous paper by Ventura et al. (1998) reported on the design of an implantable transducer integrated into a Femoral Fixation Device and demonstrated that the transducer could be calibrated to measure graft loads to better than 10 percent full-scale error in cadaveric knees. By measuring both the static and fatigue strengths of the transducer, the purpose of the present study was to determine whether the transducer could be safely implanted in humans without risk of structural failure. Eight Devices were loaded to failure statically. Additionally, seven Devices were tested using the up-and-down method to estimate the median fatigue strength at a life of 225,000 cycles. The average ultimate strength was 1856 +/- 74 N and the median fatigue strength was 441 N at a life of 225,000 cycles. The maximum graft load during normal daily activities is estimated to be 500 N and the 225,000 cycle life corresponds to that of the average healthy individual during a 12-week period. Considering that patients who have had an ACL reconstruction are less ambulatory than normal immediately following surgery and that biologic incorporation of the graft should be well developed by 12 weeks thus decreasing the load transmitted to the Fixation Device, the FDT can be safely implanted in humans without undue risk of structural failure.
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An implantable transducer for measuring tension in an anterior cruciate ligament graft.
Journal of biomechanical engineering, 1998Co-Authors: C. P. Ventura, Maury L. Hull, J. Wolchok, Stephen M. HowellAbstract:The goal of this study was to develop a new implantable transducer for measuring anterior cruciate ligament (ACL) graft tension postoperatively in patients who have undergone ACL reconstructive surgery. A unique approach was taken of integrating the transducer into a Femoral Fixation Device. To devise a practical in vivo calibration protocol for the Fixation Device transducer (FDT), several hypotheses were investigated: (1) The use of a cable versus the actual graft as the means for applying load to the FDT during calibration has no significant effect on the accuracy of the FDT tension measurements; (2) the number of flexion angles at which the Device is calibrated has no significant effect on the accuracy of the FDT measurements; (3) the friction between the graft and Femoral tunnel has no significant effect on measurement accuracy. To provide data for testing these hypotheses, the FDT was first calibrated with both a cable and a graft over the full range of flexion. Then graft tension was measured simultaneously with both the FDT on the Femoral side and load cells, which were connected to the graft on the tibial side, as five cadaver knees were loaded externally. Measurements were made with both standard and overdrilled tunnels. The error in the FDT tension measurements was the difference between the graft tension measured by the FDT and the load cells. Results of the statistical analyses showed that neither the means of applying the calibration load, the number of flexion angles used for calibration, nor the tunnel size had a significant effect on the accuracy of the FDT. Thus a cable may be used instead of the graft to transmit loads to the FDT during calibration, thus simplifying the procedure. Accurate calibration requires data from just three flexion angles of 0, 45, and 90 deg and a curve fit to obtain a calibration curve over a continuous range of flexion within the limits of this angle group. Since friction did not adversely affect the measurement accuracy of the FDT, the Femoral tunnel can be drilled to match the diameter of the graft and does not need to be overdrilled. Following these procedures, the error in measuring graft tension with the FDT averages less than 10 percent relative to a full-scale load of 257 N.
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Telemetry system for monitoring anterior cruciate ligament graft forces in vivo.
Medical & biological engineering & computing, 1998Co-Authors: E. L. Mckee, Derek P. Lindsey, Maury L. Hull, Stephen M. HowellAbstract:Quantifying changes in the tension of an anterior cruciate ligament (ACL) graft in vivo during rehabilitative exercises is useful for developing the optimum rehabilitation for patients who have had reconstructive surgery. The purpose of the work reported is to design, build and test a telemetry system that can measure the in vivo ACL graft tension post-operatively. A commercially available Fixation Device is modified to sense the graft tension, house electronic components, transmit an output signal and pass the power generating signal. A transcutaneous inductive link is used to power the implanted telemetry electronics. The current difference technique is used to measure changes in two resistance strain gauges that monitor shear strain developed on the Femoral Fixation Device by the ACL graft. This current regulates a frequency-modulated output signal that is transmitted using a new technique. Harnessing the ionic and volume conduction properties of the body fluids, the new technique involves injecting current subcutaneously into the tissue and then sensing the potential developed on the skin by surface electrodes. The waveform shape, amount of charge injected, charge density and current density are regulated to avoid tissue damage, pain and unwanted muscular stimulation. A signal conditioning board detects and converts the output to an analogue voltage for collection by a computer data-acquisition system. A performance evaluation demonstrates that the telemetry system either meets or exceeds all of the criteria necessary for the application.
Isaac Zacharias - One of the best experts on this subject based on the ideXlab platform.
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In Vivo Calibration of a Femoral Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension: A Study in an Ovine Model
Journal of biomechanical engineering, 2001Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. Howell, Keith W. LawhornAbstract:Toward developing a transducer for measuring in vivo tension in anterior cruciate ligament grafts in humans, the objectives of this study were to determine the following: (1) whether the calibration of a previously reported Femoral Fixation Device transducer (FDT) (Ventura et al., 1998) is affected by the presence of the graft when implanted in the tibial metaphysis of an ovine model, (2) whether the FDT remains calibrated at 4 weeks postoperatively, and (3) whether the biological incorporation of the graft occurs prior to a change in the FDT calibration. The FDT was implanted in the hind limb of five sheep using an extra-articular procedure. Both the proximal common digital extensor tendon (i.e., graft) and a Teflon-coated wire were looped around the FDT inside a tunnel in the tibial metaphysis. The FDT was calibrated on three occasions using the loop of wire: once intraoperatively before graft insertion, once intraoperatively after graft insertion, and once postoperatively after the animals had been sacrificed at 4 weeks. Following sacrifice, the load transmitted to the FDT by the graft was also determined. The FDT exhibited linear calibration intraoperatively both before and after graft insertion with an average error relative to the calibration before insertion of the graft of -4.6 percent of full-scale load (150 N) and this average relative error was not significantly different from zero (p = 0.183). After 4 weeks of implantation, the average relative percent error was -5.0 percent and was not significantly different from zero (p = 0.434) indicating that the FDT remained calibrated in the in vivo environment. Because only 15 percent of the graft tension was transmitted to the FDT after 4 weeks, biological incorporation of the graft preceded the loss of calibration. In light of these findings, the FDT offers the capability of measuring the intra-articular ACL graft tension in vivo in animal models and possibly humans before the biological bond develops and also of monitoring the formation and maturation of the biological bond between a graft and bone tunnel.
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Static and fatigue strength of a Fixation Device transducer for measuring anterior cruciate ligament graft tension.
Journal of biomechanical engineering, 2000Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. HowellAbstract:To determine which exercises do not overload the graft-Fixation complex during intensive rehabilitation from reconstructive surgery of the anterior cruciate ligament (ACL), it would be useful to measure ACL graft loads during rehabilitative activities in vivo in humans. A previous paper by Ventura et al. (1998) reported on the design of an implantable transducer integrated into a Femoral Fixation Device and demonstrated that the transducer could be calibrated to measure graft loads to better than 10 percent full-scale error in cadaveric knees. By measuring both the static and fatigue strengths of the transducer, the purpose of the present study was to determine whether the transducer could be safely implanted in humans without risk of structural failure. Eight Devices were loaded to failure statically. Additionally, seven Devices were tested using the up-and-down method to estimate the median fatigue strength at a life of 225,000 cycles. The average ultimate strength was 1856 +/- 74 N and the median fatigue strength was 441 N at a life of 225,000 cycles. The maximum graft load during normal daily activities is estimated to be 500 N and the 225,000 cycle life corresponds to that of the average healthy individual during a 12-week period. Considering that patients who have had an ACL reconstruction are less ambulatory than normal immediately following surgery and that biologic incorporation of the graft should be well developed by 12 weeks thus decreasing the load transmitted to the Fixation Device, the FDT can be safely implanted in humans without undue risk of structural failure.
Keith W. Lawhorn - One of the best experts on this subject based on the ideXlab platform.
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In Vivo Calibration of a Femoral Fixation Device Transducer for Measuring Anterior Cruciate Ligament Graft Tension: A Study in an Ovine Model
Journal of biomechanical engineering, 2001Co-Authors: Isaac Zacharias, Maury L. Hull, Stephen M. Howell, Keith W. LawhornAbstract:Toward developing a transducer for measuring in vivo tension in anterior cruciate ligament grafts in humans, the objectives of this study were to determine the following: (1) whether the calibration of a previously reported Femoral Fixation Device transducer (FDT) (Ventura et al., 1998) is affected by the presence of the graft when implanted in the tibial metaphysis of an ovine model, (2) whether the FDT remains calibrated at 4 weeks postoperatively, and (3) whether the biological incorporation of the graft occurs prior to a change in the FDT calibration. The FDT was implanted in the hind limb of five sheep using an extra-articular procedure. Both the proximal common digital extensor tendon (i.e., graft) and a Teflon-coated wire were looped around the FDT inside a tunnel in the tibial metaphysis. The FDT was calibrated on three occasions using the loop of wire: once intraoperatively before graft insertion, once intraoperatively after graft insertion, and once postoperatively after the animals had been sacrificed at 4 weeks. Following sacrifice, the load transmitted to the FDT by the graft was also determined. The FDT exhibited linear calibration intraoperatively both before and after graft insertion with an average error relative to the calibration before insertion of the graft of -4.6 percent of full-scale load (150 N) and this average relative error was not significantly different from zero (p = 0.183). After 4 weeks of implantation, the average relative percent error was -5.0 percent and was not significantly different from zero (p = 0.434) indicating that the FDT remained calibrated in the in vivo environment. Because only 15 percent of the graft tension was transmitted to the FDT after 4 weeks, biological incorporation of the graft preceded the loss of calibration. In light of these findings, the FDT offers the capability of measuring the intra-articular ACL graft tension in vivo in animal models and possibly humans before the biological bond develops and also of monitoring the formation and maturation of the biological bond between a graft and bone tunnel.
Alejandro Espejo-reina - One of the best experts on this subject based on the ideXlab platform.
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Anatomic outside-in anterior cruciate ligament reconstruction using a suspension Device for Femoral Fixation.
Arthroscopy techniques, 2014Co-Authors: Alejandro Espejo-baena, Alejandro Espejo-reinaAbstract:Cortical suspension is one of the most frequently used methods of Femoral Fixation in anterior cruciate ligament reconstruction. We present a simple technique for anterior cruciate ligament reconstruction using a suspension Device for Femoral Fixation. The purposes of this technique are to ensure greater contact between the graft and the tunnel walls—a goal that is achieved by using the Femoral Fixation Device with the shortest possible loop—to avoid the flip step and the need for hyperflexion, and in short, to minimize the risk of complications that can occur when using the anteromedial portal to drill the Femoral tunnel. To this end, both the Femoral and tibial tunnels are created in an outside-in manner and with the same guide. The graft is passed through in a craniocaudal direction, and the suspension Device is fitted inside an expansion piece for a better adaptation to the Femoral cortex.
