Dryver R. Huston

A Sagittal Plane Model of the Knee and Cruciate Ligaments With Application of a Sensitivity Analysis

In this investigation the complex multi-bundle structure of the cruciate ligaments and their interaction with the tibiofemoral joint was modeled analytically by representing the different regions of the cruciates with ligament elements. A sensitivity analysis was then performed to describe the effect that variations of the model input parameters had on the model variables (outputs). The effect that the cruciate ligament bundles had in controlling joint kinematics was dependent on knee flexion angle, and the load applied to the tibiofemoral joint. For passive range of knee motion with the thigh in the horizontal plane (a common rehabilitation activity), all cruciate ligament bundles were strained with the joint positioned between 0 and 10 deg of knee flexion, between 10 and 50 deg only the anterior bundle of the posterior cruciate ligament A-PCL was strained, and from 50 to 90 deg both the anteromedial portion of the anterior cruciate ligament A-ACL and the A-PCL were strained. This finding indicates that a strain distribution about a transverse cross section of the cruciates exists, and demonstrates the importance of differentiating between the strained and unstrained (unloaded) states of these ligaments. The strain value of a cruciate ligament bundle was an indication of how the bundle controls joint kinematics, while the unstrained values describe how much the ligament bundle must deform before it becomes strained and a restraint to tibiofemoral joint motion. In response to anterior and posterior directed loads, applied parallel to the tibial plateau, the respective, ACL and PCL load values were larger in magnitude. The sensitivity of the model outputs to the input parameters was highly dependent on knee flexion angle. The geometrical input parameters of the model (including the ligament insertion site locations and articular surface geometry) had the most pronounced effect on the model output quantities, while the stiffness and initial strain conditions of the ligament bundles had less of an effect on the model outputs. When loaded, the strain values of the ligament bundles were sensitive to the ligament insertion site position. The greatest sensitivity of the model outputs was the femoral insertion of the ACL; supporting clinical impressions and previous experimental findings. Changes in the anterior-posterior dimension of the femoral articular surface did not produce a substantial effect on the model outputs, while changes in the proximal-distal dimension created a large effect; similar results were found for the tibial surface dimensions. These findings indicate that rigid body contact between the articular surfaces may not be a realistic assumption particularly with application to the prediction of tibiofemoral compressive loading and the force/strain values of the cruciate ligament elements. This also has important implications for the design and clinical application of total knee replacements (that function as rigid bodies), particularly those that spare the PCL.

Corrosion detection in reinforced concrete roadways and bridges via embedded fiber optic sensors

The problems associated with the application of chloride-based deicing agents to roadways and specifically bridges include chemical pollution and accelerated corrosion of strength members (especially the rebar) within the structure. In many instances, local ordnances are attempting to force state agencies to reduce, if not eliminate, the use of these chlorides (typically at the cost of increased driving hazards). With respect to the corrosion aspects of chloride application, cracks that occur in the roadway/bridge pavement allow water to seep into the pavement carrying the chloride to the rebar with the resultant increase in corrosion. In tandem with these efforts has been the continuing use of embedded fiber optic sensors for identification of faults or cracks within a highway structure - i.e., structural health monitoring. In this paper, we present multiple-parameter sensing fiber optic sensors which may be embedded into roadway and bridge structures to provide an internal measurement and assessment of its health. Such issues are paramount in determining if remedial or preventative maintenance should be performed on such structures. Laboratory results, comparisons with conventional sensing methods as well as a review of real-world issues in highway sensing are presented.

Performance and health monitoring of the Stafford Medical Building using embedded sensors

The University of Vermont is in the process of constructing a new major facility to house various biotechnology research laboratories and offices. This five-storey, 65000 square foot concrete structure, named the Stafford Building, is being equipped with fiber optic and conventional sensors embedded into the concrete superstructure. These sensors will allow monitoring of stresses incurred during the construction phase and monitoring of concrete curing as well as vibration sensing and internal crack sensing. Longitudinal studies of the buildings in-service performance and overall health will also be carried out. A description of the sensor choices, physical placements, use and review of relevant construction practices are presented in this paper.

GIMA ground penetrating radar system for monitoring concrete bridge decks

Ground Penetrating Radar (GPR) has been investigated as a non-destructive method for evaluating damage in concrete structures. However, the commercially available techniques are limited to detection of gross quantities of deterioration, due to the limited resolution of the system. The objective of this research is to evaluate a ground penetrating radar system with a novel Good Impedance Match Antenna (GIMA) for concrete structural assessment. This system has the capacity to detect concrete cracks as small as 1 mm thick, while being able to reflect from and detect features at depths of up to 360 mm. Laboratory results of testing of the GIMA antenna by using a step-frequency and a high-frequency impulse system are presented. The experimental results reveal that the GIMA antenna is capable for use in frequency ranges, at least as broad as 500 Mhz to 6 GHz for the step-frequency and 1 to 16 GHz for the high-frequency impulse system.

Embedded fiber optic sensors for bridge deck chloride penetration measurement

The use of chloride-based deicing agents to help clear U.S. highways of roadway hazards leads to associated chemical related problems. Fouling of local rivers and streams due to runoff of the waterborne chlorides is significant and has contributed to local ordinances that are attempting to force state agencies to reduce, if not eliminate, the use of these chlorides (typically at the cost of increased driving hazards). With respect to the corrosion aspects of chloride application, cracks that occur in the roadway/bridge pavement allow water to seep into the pavement carrying the chloride to the rebar with the resultant increase in corrosion. The costs of this corrosion are considerable and have led to the widespread use of chloride/water impermeable membranes on roadways and especially within bridges. Fiber optic sensors have repeatedly been shown to provide measurement capabilities of parameters within such reinforced concrete structures. Development of fiber optic chloride sensors capable of being embedded within a roadway or bridge deck is reported.

Development of High-Speed Ultrawideband Ground-Penetrating Radar for Rebar Detection

This paper describes the development of new air-coupled ultrawideband ground-penetrating radar (GPR) for highway pavement and bridge deck inspections that can achieve high spatial resolution and high inspection performance while operating on vehicles driving at regularhighwayspeeds.Themajordesignfeaturesincludedual-frequencybandoperation,8gigasamplespersecondhigh-speedreal-time data acquisition,high-speedlargevolumedatatransmissionandstorage,andcustomizedsignal-processingalgorithmsforGPRimageenhancement and feature extractions. For design validations, steel reinforcing bar detection experiments in various setups are conducted. The measurement results show good agreement with the subsurface feature configurations. DOI: 10.1061/(ASCE)EM.1943-7889.0000458.

A High-Performance Low-Ringing Ultrawideband Monocycle Pulse Generator

In this paper, a performance-enhanced ultrawideband monocycle pulse generator circuit using a step recovery diode is designed and tested. Factors that could cause pulse waveform distortions are analyzed. By applying an attenuator and a simple yet effective pulse-shaping circuit, the impedance matching between the pulse generator and the oscillator source is considerably improved, and a quality monocycle pulse is generated with small ringing and leveraged amplitude. Measured results validate the design.

Pin loosening in a halo-vest orthosis: a biomechanical study.

STUDY DESIGN The cranial pin force history of a halo-vest orthosis was measured using an instrumented halo in a clinical study with three patients. Pin force values at the time of halo-vest application and at subsequent clinical visits during the halo-vest wear period were compared. OBJECTIVES To document the pin force reduction in the cranial pins of a halo-vest orthosis in vivo. SUMMARY OF BACKGROUND DATA The halo-vest is an orthosis commonly used to immobilize and protect the cervical spine. An important problem with halo-vest use is pin loosening. There have been no previous reports of pin force history in vivo. METHODS A custom-built strain-gauged, open-ring halo was used to measure the compressive force and superiorly-inferiorly directed shear forces produced at the tips of the two posterior pins. The instrumented halo was applied to three patients with cervical spine fractures. Pin force measurements were recorded at the time of halo application and at subsequent follow-up visits during the entire treatment period. RESULTS A mean compressive force of 343 +/- 64.6 N was produced at the pin tips during halo application with the patient in a supine position. On average, the compressive forces decreased by 83% (P = 0.002) during the typical halo-vest wear period. The compressive forces were substantially greater than the shear forces, which averaged only -11+/-30.2 N at the time of halo application and which did not change significantly with time. CONCLUSIONS The study confirmed the hypothesized decrease in the compressive pin forces with time. All patients had developed at least some clinical symptoms of pin loosening at the time of halo-vest removal.

Wireless inspection of structures aided by robots

The inspection of structures by humans is often hampered by safety and accessibility concerns. One method of reducing human inspection activities is to use remotely located sensors, such as strain gages and accelerometers. Running cables to power the sensors and transmit data can be expensive and inconvenient. This paper describes a development effort in which a robot is used to power and interrogate remotely placed sensors. The sensors are powered by a noncontact inductive system, which eliminates the need for batteries or interconnecting lead wires. The data are sent by a wireless connection back to a central data logger and processor. The power demands of telemetering data are decreased by close proximity of robot. The system utilizes existing microminiature, multichannel, wireless programmable Addressable Sensing Modules (ASMs) to sample data from a wide variety of sensors. Demonstration style robots are built and tested with ASMs in simple tabletop design, and a more robust task specific I-beam crawler robot for structural application.

Concrete bridge deck condition assessment with automated multisensor techniques

Early and accurate detection, location and assessment of damage in reinforced concrete bridge decks may be beneficial in the scheduling and performance of maintenance and rehabilitation activities. This article presents the results of a multiple sensor study of the condition of the reinforced concrete deck of the Van Buren Road Bridge in Dumfries, VA. The tests compared the following five different methods: (1) visual inspection and photographic recording; (2) half-cell electrochemical potential; (3) impulse type multipoint scanning ground penetrating radar; (4) chain drag and (5) impact echo. The bridge was tested on two separate occasions. The results of the tests were that each instrument nominally performed and collected data as expected, but that the condition assessments did not necessarily agree. The data are registered, overlaid and compared. The potential for developing automated multisensor systems that fuse data for efficient and effective bridge deck measurements is discussed.