Surgery – Magnetic field applied to body for therapy – Electromagnetic coil
Reexamination Certificate
1998-03-02
2001-07-17
Kamm, William E. (Department: 3762)
Surgery
Magnetic field applied to body for therapy
Electromagnetic coil
C600S013000, C607S002000
Reexamination Certificate
active
06261221
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to pulsed electromagnetic field (PEMF) therapy that promotes healing of skeletal bones and other body tissues, and more particularly to a PEMF system having a high-efficiency single-coil transducer for providing PEMF therapeutic stimulation to a target area of a patient's body.
BACKGROUND OF THE INVENTION
Pulsed electromagnetic fields (PEMF) for treating therapeutically resistant problems of the musculoskeletal system are typically low-energy, time-varying magnetic fields. PEMF therapy has been used to treat non-union bone fractures and delayed union bone fractures. Non-union bone fractures are typically defined as injuries which have not satisfactorily healed within nine months or more after the trauma which caused the injury. Delayed union fractures are typically considered injuries which have not satisfactorily healed within nine months or less after the trauma which caused the associated injury. PEMF therapy has also been used for treatment of corresponding types of body soft tissue injuries.
PEMF therapy has been satisfactorily used in treating spinal fusion, failed arthrodeses, osteonecrosis, and chronic refractory tendinitis, decubitus ulcers and ligament, tendon injuries, osteoporosis, and Charcot foot. During PEMF therapy, an electromagnetic transducer coil is generally placed in the vicinity of the musculoskeletal injury (sometimes referred to as the “target area”) such that pulsing the transducer coil will produce an applied or driving field that penetrates to the underlying damaged bone or other body tissue.
Present day PEMF transducers use a substantial amount of energy. In order to account for such energy use, present products may use a rechargeable battery pack, such as either a nickel cadmium or nickel metal hydride battery. Rechargeable battery packs are expensive, heavy, and must be carried by the patient. Many existing PEMF therapy systems must be recharged frequently, which increases the cost and inconvenience of operating such PEMF therapy systems.
The weight of many PEMF bone growth stimulators is generally proportional to the size of the batteries used to power the electrical circuitry as well as by the windings used to generate the output signal. Patient comfort while using such devices is often inversely proportional to the weight. Reducing the battery size and weight will help to reduce the weight and cost of such equipment and improve the patient's comfort.
Recently, ultrasound-based equipment has been used to accelerate healing of body tissue. Ultrasound therapy may also be used for treating non-union and delayed union fractures.
SUMMARY OF THE INVENTION
Various aspects of the invention are directed to a PEMF therapy system having a transducer coil for generating a PEMF signal. The PEMF therapy system includes a drive circuit for recovering flyback energy from the transducer coil and dumping a voltage equal to a predetermined amount, such as four times the battery voltage, for permitting sequencing of the current through the transducer coil in both a first, positive direction and a second, negative direction.
The invention eliminates the need for a secondary coil to recover energy and thereby reduces overall weight and power consumption. The flyback energy of the transducer coil is dumped to an energy recovery capacitance circuit that provides an energy recovery voltage. This voltage is available to supply current during the energize phase of the transducer energize/recover cycle. By having a recovery voltage equal to approximately four times the battery voltage available, current through the transducer coil can be sequenced, in much the same way as is done with a full-bridge or half-bridge circuit, to go in both directions. Therefore, for a given magnetic field strength (PEMF output signal strength), the peak current can be cut in half, resulting in a factor of four reduction in I
2
R (energy) loss. The drive circuit, instead of using a separate voltage boost supply circuit, uses its own flyback pulse to provide the recovery voltage. Energy recovery without a secondary coil is also more efficient because there are no coupling losses that arise with a secondary coil (i.e., there is no leakage inductance). In addition, a transducer coil incorporating teachings of the present invention possesses technical advantages of being simpler and less expensive to manufacture.
For example, the transducer coil used to generate the desired PEMF may have fewer windings. Thus, there are fewer electrical connections. This makes the resulting PEMF device more reliable while also being more energy efficient.
Another advantage of the invention is that the use of a single coil sufficiently reduces the size and weight of the device such that it is practical to locate its drive electronics in a small housing proximate to the coil. No interconnecting cables or connectors are required to connect the drive electronics with the primary coil or winding.
Another advantage is that coil heat losses are minimized, and the wire gauge may be smaller. This further helps to make the resulting PEMF transducer lighter and economical to manufacture. The ultimate result is, therefore, a more comfortable, less expensive PEMF therapy system.
Because the PEMF transducer is more energy efficient, it is possible to use a smaller, lighter, non-rechargeable battery. The present invention may use, for example, a commercially-available nine-volt lithium or alkaline non-rechargeable battery.
A particular embodiment of the invention has a flexible transducer coil, and is especially useful for treating soft tissue. The transducer may be placed in or on a cast or bandage covering the location to be treated. It may remain in place until the cast or bandage is removed from the patient.
An advantage of this flexible transducer embodiment is that the PEMF therapy system may be started by the physician and will continue to operate for a predetermined treatment cycle such as four hours per day until the cast has been removed. As a result, patient intervention is not required to ensure that the desired treatment cycle is applied to the target area.
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PCT International Search Report, Jun. 23, 1999.
Kuo Peter
Tepper John C.
Winstrom William
AMEI Technologies Inc.
Baker & Botts L.L.P.
Kamm William E.
Layno Carl H.
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