Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Reexamination Certificate
1996-08-02
2001-01-16
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
C600S595000
Reexamination Certificate
active
06174294
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a limb load monitoring system, and more particularly to a lower limb load monitoring device for measuring or detecting the amount of force applied to, or weight borne by, a lower limb of the body (either natural or prosthetic) and providing a signal to the user when a predetermined threshold level is exceeded.
2. Description of the Prior Art
Numerous situations exist where it is important to limit the load or force which is applied to or borne by a lower natural or prosthetic limb of the body during standing, walking, stepping, running or jumping activities or during rehabilitation therapy. Situations also exist where it is important that the lower limb be exposed to a certain load or force, particularly during rehabilitation therapy. In both situations it is important to monitor such load or force and to provide a signal to the user when such force is exceeded or met. Examples include post-surgery or injury rehabilitation of hips, knees, ankles or any other portion of the body which is affected by force applied to or borne by at least one of the user's legs or any other situation in which monitoring of the weight on a lower limb during standing, walking, jumping or other activities is desired. Because of the clear economic benefits, including the potential of substituting outpatient care for clinical rehabilitation and the speeding or other enhancement of the rehabilitation process, the health care industry is exhibiting increased interest in improved devices which detect and monitor the force applied to the lower limbs.
Various patents currently exist which reflect the state of the art. One device is illustrated in U.S. Pat. No. 3,702,999 issued to Gradisar. In this device, a force sensitive means is positioned in two predetermined locations in the shoe of the user via a foot pad assembly: one beneath the heel and the other beneath the ball of the user's foot. Each of the force sensing means in this patent comprise a pair of electrical conductors which are spaced by a resilient dielectric member. Each of the force sensing means includes a set screw threadedly received by one of the conductors and extending toward the other. As a compressive force is applied to the pair of conductors, the resilient dielectric compresses causing the set screw to engage the other conductor. This closes the circuit and results in the generation of a signal. If the user desires the amount of force to be varied, the adjustment of the set screw is varied. Although this device conceptually provides a signalling device when a predetermined load is exceeded, the force sensing means themselves require a relatively thick profile since its operation requires vertical movement between two conductive plates with springloads between them. This creates a bulky orthopedic monitor which impedes the patient's normal walking style. Additionally, because of the mechanical nature of the pair of conductors, and the manner in which the set points are achieved, the patient, in some cases, must don and doff the device several times before achieving the correct calibrated set point. Also, variations in performance are inherent due to material wearing and aging. Still further, there is no means to combine the forces or loads of the two sensing means.
A second device is described in U.S. Pat. No. 4,745,930 issued to Confer. This device, however, is not a weight monitoring device, but instead is a force sensing insole used in association with an electro-goniometer for analyzing the gait of a patient. The device includes a multi-layer structure and a plurality of switches which sequentially close and open as the weight of the user is applied to the insole.
A further device described in U.S. Pat. No. 4,647,918 issued to Goforth relates a multi-event notification system for monitoring preselected critical pressure points on the feet of the user. This device discloses a plurality of battery powered pressure transducers in foot sensor pads for measuring the pressure at a number of points as a function of time. The information from such sensors is important for persons who have been diagnosed as having diminished sensation in the feet such as from diabetes mellitus. There is no disclosure in this patent of a device for warning the user of excessive instantaneous application of pressure or weight and accordingly it is not suitable for application as a lower limb load monitor.
Still other devices are described in U.S. Pat. No. 3,791,375 issued to Pfeiffer and U.S. Pat. No. 3,974,491 issued to Sipe. Although both relate generally to devices for signalling when excessive load is being borne by the lower limb, both devices rely on the detection of pressure created in a fluid containing load cell of the like. Thus, both are susceptible to failure from puncture to the fluid bladders. Further, contamination or degradation of the fluid can cause drift of sensor calibration or failure of the sensor in operation. Still further, the mechanical nature of the fluid transfer and the size of the tube required to transfer load information to a monitoring device necessarily requires a relatively bulky structure.
Accordingly, there is a need in the art for a lightweight, compact lower limb load monitor device which utilizes a relatively thin force sensing means for sensing both total load and load distribution.
SUMMARY OF THE INVENTION
In contrast to the prior art, the present invention relates to a lower limb load monitor which is lightweight, which does not suffer from mechanical wear because it has no mechanical or moving parts and in which all of the sensing components are sealed. Further, the force sensing element of the present invention is a “thin film” force sensor preferably on the order of less than 20-30 mils thick. Thus, the device does not significantly alter the walking style of the user. Further, the monitor of the preferred embodiment of the present invention is capable of monitoring total load on the lower limb as well as load distribution between various selected positions.
The force sensing element of the present invention utilizes a force measurement based on a change in electrical properties associated with the sensing element. Although it is contemplated that a variety of electrical properties may be utilized, the force sensor in accordance with the preferred embodiment embodies a pair of flat membranes in which a force variable circuitry is disposed between such membranes and in which the force applied to such membranes is measured as a function of the change in resistance in such circuitry.
The force sensing elements of the present invention may be positioned in an insole or an outsole embodiment and are electrically connected to an electronic control box positioned near the sensing elements. Preferably, the control box is sufficiently compact so that it can be attached to the user's belt or hip area, the shoe or other area surrounding the lower portion of the user's leg or foot. The control box includes source of a voltage or other electrical signal to the force sensing elements, a comparator to compare the resistivity or other electrical property of the force sensing elements to a set point, an alarm generator and an alarm or signalling means for providing a signal to the user when a predetermined force level is met or exceeded. The control box may also be provided with transmitting means for transmitting force information to a remote signalling device for providing a visual, audio, vibratory or some other signal at a remote location.
Accordingly, it is an object of the present invention to provide a lightweight, low cost lower limb load monitor.
Another object of the present invention is to provide a lower limb load monitor having heel and ball sensors and means for differentiating feedback signals from such sensors.
Another object of the present invention is to provide a lower limb load monitor utilizing flexible, thin film force sensing elements.
A further object of the present invention is to pro
Crabb Thomas M.
Kelhcut Anthony J.
Richter Robert C.
O'Connor Cary
Orbital Technologies, Inc.
Wingood Pamela
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