Mohamed Samir Hefzy

A two-dimensional dynamic anatomical model of the human knee joint.

The objective of this study is to develop a two-dimensional dynamic model of the knee joint to simulate its response under sudden impact. The knee joint is modeled as two rigid bodies, representing a fixed femur and a moving tibia, connected by 10 nonlinear springs representing the different fibers of the anterior and posterior cruciate ligaments, the medial and lateral collateral ligaments, and the posterior part of the capsule. In the analysis, the joint profiles were represented by polynomials. Model equations include three nonlinear differential equations of motion and three nonlinear algebraic equations representing the geometric constraints. A single point contact was assumed to exist at all times. Numerical solutions were obtained by applying Newmark constant-average-acceleration scheme of differential approximation to transform the motion equations into a set of nonlinear simultaneous algebraic equations. The equations reduced thus to six nonlinear algebraic equations in six unknowns. The Newton-Raphson iteration technique was then used to obtain the solution. Knee response was determined under sudden rectangular pulsing posterior forces applied to the tibia and having different amplitudes and durations. The results indicate that increasing pulse amplitude and/or duration produced a decrease in the magnitude of the tibio-femoral contact force, indicating thus a reduction in the joint stiffness.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of wrist kinematics using a magnetic tracking device

The objective of this work is to present a method to determine the three-dimensional kinematics of the human wrist joint under physiological loading conditions using a magnetic tracking device. Euler angles were used to determine wrist extension-flexion, radial-ulnar deviation and supination-pronation. The screw displacement axis (SDA) method was used to describe the relative motion between carpal bones. Computer graphics were also used to obtain a better visualization of the three-dimensional motions of the carpal bones. This was accomplished by combining motion data and digitization data describing the geometry of the articular surfaces of the carpal bones. Geometric data included the locations of several points located on the articular surfaces forming the radio-scaphoid and radio-lunate joints. The SDA axes describing the motions of the capitate or the lunate or the scaphoid with respect to the radius during flexion-extension were found almost parallel to the medial-lateral direction. Translations along any SDA did not exceed 2 mm. One can thus consider the motion of each carpal bone as a pure rotation about a screw axis. Also, the SDA axis describing the motion of the capitate with respect to the radius was found to pass through the proximal end of the capitate. The graphical display of carpal motions shows that, as the wrist is flexed, the surface of the lunate within the radio-lunate articulation moves from palmar to dorsal. On the other hand, the palmar-dorsal location of the proximal surface of the scaphoid within the radio-scaphoid articulation remains almost unchanged.

Kinematics of the human pelvis following open book injury.

The objective of this study is to determine the three dimensional kinematics of the human pelvis including both sacroiliac joints following a simulated open book injury induced on cadavers by applying anterior-posterior compressive loads to the pelvis. An electromagnetic digitizing and motion tracking system was utilized to measure the morphology of the pelvis and the relative movements of its bones during this simulated open book fracture. The screw displacement axis method was used to describe the relative motion between the sacrum and each hipbone. Morphologically, it was found that the articular surfaces forming the sacroiliac joints could be approximated with planar surfaces directed from proximal and lateral to distal and medial and from posteromedial to anterolateral. The kinematic data obtained from this study indicate that there is a direct correlation between the opening of the symphysis pubis and the opening of the sacroiliac joint (SIJ) during open book injury. This suggests that the extent of injury of the SIJ maybe estimated from the degree of opening of the symphysis pubis as demonstrated on anteroposterior (A-P) x-rays. The results obtained from this study also indicate that the motion of the hipbone with respect to the sacrum on the side of the sacroiliac joint opening is almost a pure rotation, which translates clinically on the A-P x-rays as pure opening of the SIJ without vertical displacement. The average axis of rotation was found to be almost parallel to the SIJ planar articular surface. Furthermore, the pubic bone on the side of SIJ opening was found to displace inferiorly and posteriorly. One can thus conclude that in open book pelvic injuries, the pubic bone on the side of injury displaces inferiorly on the outlet projection x-rays with no vertical displacement of the SIJ. This is important since the initial assessment of the open book injury in the emergency room includes outlet projection x-rays. From this study, the relative vertical positions of the pubic bones on these x-rays can help the surgeon in differentiating open book fracture injury from other pelvic injuries.

Design and Development of a Pressure Relief Seating Apparatus for Individuals with Quadriplegia

Persons with spinal cord injury above C7 lack the ability to extend their elbows and grip with their hands. Consequently, when seated, they are unable to press down to shift their weight to relieve pressure on the ischial tuberosities. This can ultimately cause serious pressure sores to develop on the buttocks. Those with adequate insurance coverage can eliminate this problem with an electric power recliner wheelchair. With the touch of a button, the backrest will fold down to a laying position, thus relieving the pressure on the ischial tuberosity. Unfortunately, not all individuals with quadriplegia possess this type of coverage. Therefore, the problem requires an alternate design that will utilize mechanical rather than electrical power to produce a cost-effective solution. The purpose of this project was thus to design and build an affordable apparatus adaptable to wheelchairs that allows individuals with quadriplegia to shift their weight from one side to the other thus relieving the pressure on the ischial tuberosities. A pneumatic system that utilizes two inflatable air bladders was employed. One cushion is placed under each buttock and inflated separately to tilt the user from one side to the other. The inflated cushion elevates one side of the buttock, which relieves the pressure from the other side. The power required to operate the system is generated using repetitions of elbow flexion. The system was evaluated on an individual with C6 quadriplegia. The subject demonstrated independent pressure relief without intrusion on cosmesis or independence.

State of the art review of knee-ankle-foot orthoses.

Knee–ankle–foot orthoses (KAFOs) are used to assist in ambulation. The purpose of this paper is to review existing KAFO designs which can be grouped into passive KAFOs, stance control (SC) KAFOs, and dynamic KAFOs. The conventional passive KAFOs do not provide any active control for knee motions. SCKAFOs lock the knee joint during the stance phase and allow free rotations during the swing phase. Some SCKAFOs switch between the stance and swing phases using body posture, while others use some kind of a control system to perform this switch. Finally, dynamic KAFOs control the knee joint during both stance and swing phases. Four dynamic systems are identified in the literature that use pneumatics, linear springs, hydraulics, and torsional rods made of superelastic alloys to control the knee joint during the gait cycle. However, only the two systems that use linear springs and torsional rods can reproduce the normal knee stiffness pattern which has two distinct characteristics: a soft stiffness during the swing phase and a hard stiffness during the stance phase. This review indicates that there is a need to conduct research regarding new KAFO designs that duplicate normal knee function during the whole gait cycle.

The Effect of a Liner on the Dispersion of Sacral Interface Pressures During Spinal Immobilization

Sacral pressure ulcers are a significant problem following spinal cord injury and are felt to be in part due to the high interface-pressures generated while strapped to the spine board. The objective of this study was to determine sacral interface-pressure and sensing area in healthy volunteers on a spine board and the effects of a gel pressure dispersion liner. Thirty-seven volunteers were placed on a pressure-sensing mat between the subject and the spine board. Measurements were carried out with and without a gel liner. Pressures and sensing area were recorded every minute for 40 minutes. The highest pressure was generated at the sacral prominence of each subject. Mean interface-pressures were higher on the spine board alone than with the gel liner (p < .0001). Overall, mean sensing area was lower on the spine board than with the gel liner (p < .0001). Standard spinal immobilization causes high sacral interface-pressures. The addition of a gel liner on the spine board decreased overall mean sacral pressures and increased mean sensing area. Generation of sacral pressure ulcers may be related to the initial interface-pressures generated while the patient is strapped to the spine board. The addition of a gel liner may reduce the incidence of sacral pressure ulcers.

Development of a Dynamic Knee Actuator for a KAFO Using Superelastic Alloys

A knee-ankle-foot orthosis (KAFO), which covers the knee, ankle and foot, can mitigate abnormal walking pattern caused by weak quadriceps. Several types of KAFOs are currently available in the market: passive KAFOs, stance-control KAFOs and dynamic KAFOs. In passive KAFOs, the knee joint keeps being locked during standing and walking, and can be unlocked manually to allow free rotation for sitting. Stance-control KAFOs (SCKAFOs) allow free knee motion during swing phase when the braced leg is unloaded. Dynamic KAFOs are able to reproduce normal walking ability throughout whole gait cycle. This research is directed at using superelastic alloys to develop a dynamic knee actuator that can be mounted on a traditional passive KAFO. The actuator stiffness can match that of a normal knee joint during the walking gait cycle. This proposed knee actuator utilizes a storing-releasing energy method to apply functional compensation to the knee joint, controlling the knee joint during both stance and swing phases. Fundamentally, the knee actuator is composed of two distinct parts which are connected with the thigh and shank segments, respectively. There are two superelastic actuators that are housed within these two parts and activated independently. Each actuator is developed by combining a superelastic rod and a rotary spring in series. When neither actuator is engaged, the knee joint is allowed to rotate freely. The stance actuator works only in the stance phase and the swing actuator is active for the swing phase. The conceptual design of the knee actuator is verified using numerical simulation and a prototype is developed through additive manufacturing for confirming the concept.Copyright

A Dynamic Knee-Ankle-Foot Orthosis With Superelastic Actuators

A knee-ankle-foot orthosis (KAFO) spans the knee, ankle and foot, and assists in the walking motion of those who suffer neuromuscular deficiencies. KAFOs can be classified as passive, semi-dynamic and dynamic. Passive KAFOs lock the knee joint during the whole gait cycle. Semi dynamic KAFOs lock the knee joint during the stance phase. Dynamic KAFOs attempt to reproduce normal knee motions during the whole gait cycle. Two types of dynamic KAFOs have been reported in the literature. The first one is activated by using a pneumatic system, and the second one uses a spring mechanism. Both systems are bulky and controlled through complex control systems that limit their application as assistive devices. The purpose of our research is to develop a dynamic KAFO that is actuated easily by employing shape memory materials. Such an actuation system makes the KAFO lightweight and with a great commercialization potential. The purpose of this paper is to present a conceptual design for the knee actuator of a dynamic KAFO. This actuator uses torsional shape memory rods to match the stiffness of the knee joint of the KAFO with that of a normal knee joint during the walking gait cycle. Joint stiffness is measured by the moment around the joint per degree of joint rotation. The proposed actuator includes two parts that work independently during the two phases of the gait cycle. The first part engages only during the stance phase and the other works only during the swing phase. Each part is developed by combining a superelastic (SE) rod and a rotary spring in series. The conceptual design is verified by simulation. The simulation results show that the proposed knee actuator reproduces the stiffness of the normal knee joint during the whole gait cycle. It is thus possible to develop a novel dynamic KAFO that can provide normal knee stiffness characteristics to assist individuals with quadriceps deficiency.Copyright

Design and Evaluation of a Knee Actuator for a Dynamic Knee-Ankle-Foot Orthosis

Dynamic KAFOs are developed to recover the normal walking ability during both stance and swing phases. Three types of dynamic KAFOs have been reported in the literature. Various actuation mechanisms including spring, pneumatic and hydraulic systems have been used. These devices can improve walking disability and compensate lower leg muscle deficiency. However, they are bulky, in some cases need complex control systems and do not recreate the normal gait pattern. These shortcomings have limited the application of dynamic KAFOs in daily life. The purpose of this paper is to develop a novel knee actuator for a dynamic KAFO that is actuated easily by employing shape memory materials. Such an actuation system makes the KAFO lightweight and has a greater potential to restore the normal gait. Torsional superelastic alloys are used in this actuator in order to match the stiffness of the knee joint of the KAFO with that of a normal knee joint during the walking gait cycle. There are two distinct parts in the knee actuator, acting independently to mimic the two phases of the gait cycle. One engages only in the stance phase and the other works in the swing phase. Each part is developed by combining a superelastic rod and a stiff rotary spring, in series. According to numerical simulation, such combination reproduces the varying knee stiffness during the whole walking gait. Also mechanical experiments have been conducted to further verify the conceptual design. The simulation and experimental results show that the actuator is able to reproduce the stiffness of the normal knee joint during the gait cycle.Copyright

Emergency Medical Services Backboard With a Pressure Dispersion Liner

Spinal immobilization is of utmost importance when caring for major trauma victims. Because of the potential for spinal cord injury, trauma victims must be secured to a rigid backboard. Patients are held in position by placing blocks on either side of their head, straps across their forehead, chest, and legs. The goal of using a hard backboard is to reduce the chances of damaging the victim’s neurological functions because of movement of unstable or injured vertebrae. These backboards serve their function of patient immobilization but present another problem for the patient. They have been associated with a skin breakdown condition called decubitus ulcers (bed sores). Bed sores are areas of damaged skin and tissue that develop when sustained pressure causes a restriction of blood circulation to vulnerable parts of the body. Without adequate blood flow, the affected tissue dies. Some patients may be secured to these boards for up to four hours waiting to undergo x-rays. This is more than enough time for ulcers to reach Stage IV which is the deepest and most destructive ulcer. The incidence of pressure ulcers in newly admitted patients has been reported as high as 59% and 50% have been reported at the sacral region [1, 2]. In experimental studies performed on dogs it has been shown that a constant pressure of only 60mmHg for one hour is enough to cause irreversible tissue damage [3]. When the patients are on the backboards it has been shown that there is often a high pressure spike at the sacral prominence where average maximum interface pressure spike of 260mmHg have been noted. When a thin but very heavy gel pad was added to the backboard, the sacral interface pressure was reduced to an average maximum pressure of 188 mmHg [4]. The objective of this project is to develop a backboard with a light pressure dispersion liner to reduce interface pressures on pressure sensitive areas in the supine position.Copyright