Surgery – Diagnostic testing – Measuring anatomical characteristic or force applied to or...
Reexamination Certificate
1999-08-19
2001-10-16
Hindenburg, Max (Department: 3736)
Surgery
Diagnostic testing
Measuring anatomical characteristic or force applied to or...
Reexamination Certificate
active
06302856
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention concerns a measuring device for determining the drawer displacement of the tibia with respect to the femur in the leg of a patient.
In the articulating or bracing structure of the knee joint the tibia can, in a so-called drawers movement, be slid toward the front or the back in a drawers-like manner with respect to the femur, wherein the femur condyles can perform a sliding movement upon the facing tibia plateau. Such sliding or translational movements occur, besides during a simple rolling motion, also in the active extension/flexion of the knee joint and again mirror the ligamentary condition thereof. For clinical research of the drawers phenomenon the so-called “Lachmann-Test” is known, in which a researcher grasps the thigh and the calf close to the knee of a patient lying on his back and pulls the shinbone towards the front in the sense of a ventral drawer under application of pressure. This test is subjective and provides no quantitative result with respect to the displacement of a drawer. It is particularly not suited for systematic research of the relationship between the drawer freedom and the condition of the ligamentary complex.
SUMMARY OF THE INVENTION
Beginning therewith, it is an object of the invention to make possible the objective measurement of the drawer displacement at the knee joint and in particular also in functional situations, such as during standing, walking and running.
The invention is based upon the idea, of determining both the spatial position or orientation of the femur as well as also the tibia in the knee joint area by the isolated measurements in a common reference system. In order to make this possible, in accordance with the invention an attachable reference frame is provided on the calf of a leg, two distance sensors which are fixedly mounted on the reference frame spaced apart from each other and which can be moved towards the front side of the leg in the area of the proximal tibia and the distal femur, and a measurement device able to receive input signals from the distance sensors for determining the drawer displacement. Therewith it becomes possible to obtain objective, precise measured values of movements generated passively from outside as well also active drawer displacements, without it being necessary to immobilize the leg. Further, considering the parallel determination of the starting signal by both distance sensors, it becomes unnecessary that the reference framework be completely rigidly fixed or connected with the calf, which during an active drawer displacement test in particular is not satisfactorily possible.
It is advantageous when a distance sensor is directed against the front kneecap surface (Facies anterior patellae) as outer or external reference surface for the position of the femur medial condyles and the other distance sensor is directed against the front shinbone tuberosity (Tuberositas tibiae) as reference point for the position of the tibia head.
In order to place the starting signals of the distance sensors in direct perspective or context to the transverse displacement to be measured, the distance sensors are provided with parallel measuring extensions, which run parallel to the tibia plateau in the essentially anterior-posterior direction. Therewith the drawer displacement can be determined in simple manner according to measurement of a differential value of the starting signals of the distance sensors.
For adjustment to a suitable measuring position the distance sensors are preferably limitedly movable in all three spatial directions and are fixable in their displacement direction in fixed position on the reference framework.
The distance sensors can comprise a capacitative, inductive or ohmic resistance based odometer sensor, of which the measurement distance is predetermined with respect to a reference point fixed with respect to the frame. Therewith it becomes possible to determine the instantaneous respective spatial positions of the sensed leg surfaces in a common reference system formed by the reference framework. In a simplified embodiment the distance sensors are formed as linear potentiometers, of which the two free ends of the sliders can be urged against the front side of the leg against a spring bias.
Alternatively the distance sensors can be formed as ultrasonic, infrared or laser sensors for contactless measurement.
It is advantageous when the reference framework is supportable against the front side of the calf via a support padding. The support padding makes possible a substantially painless fitting to the anatomy, wherein foam materials such as polystyrene or polyurethane in particular exhibit satisfactory characteristics. The reference signal is constructed appropriately in a lightweight manner, in order to be carried on the calf, wherein it can be fixed to the calf by means of circular tensionable VELCRO closure straps. In this manner it becomes possible in an advantageous manner to form a secure attachment of the reference framework to the calf, so that relative movements of the reference framework can substantially be avoided.
It is advantageous when external forces can be introduced into the calf via a force transmission device preferably including a band sling, wherein the amount of the force to be imparted can be determined by a force recorder.
In a mobile embodiment it is advantageous, when the measurement device includes a hand-held portable indicator unit, by means of which the sensed values of the distance sensors can be displayed in an LCD-display. Therein it can be sufficient, when the maximal values obtained during a measurement cycle are indicated. For wireless connection of the distance sensors with the evaluation device a telemetric device can be provided.
It is further advantageous, when the evaluation device includes a microcomputer which, via an analog/digital converter, is in communication with the digitalized output signals of the distance sensors and in certain cases the output signals of a force recorder. Thereby the data processing can be carried out in suitable manner for purposes of scientific evaluation.
For supplemental research of muscular activation electromyographic signals can be detected by external electrodes, wherein in particular the M. biceps femoris in the thigh area and the M. gastrocnemius in the calf are suitable as sensory points.
In order to make it possible to detect possibly the rotational movement of the reference framework with respect to the calf, there are preferably provided at least three distance sensors on the reference framework, wherein a first distance sensor is provided in the proximal tibia area and a second distance sensor in the distal femur area against the front side of the leg, and wherein at least a further distance sensor is directed against the calf in a horizontal and/or vertical separation from the second distance sensor.
REFERENCES:
patent: 3782188 (1974-01-01), Korber et al.
patent: 4804000 (1989-02-01), Lamb et al.
patent: 5425775 (1995-06-01), Kovacevic et al.
patent: 5454838 (1995-10-01), Vallana et al.
patent: 0074407 (1983-08-01), None
patent: 0710466 (1996-08-01), None
patent: WO 87/05789 (1987-10-01), None
Hindenburg Max
Pendorf & Cutliff
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