DE3636843A1 - Measuring device for the determination of front and rear drawer signs in the human knee joint in various rotary positions of the lower leg and in various bending positions - Google Patents

Abstract

Measuring device for the determination of front and rear drawer signs in various bending positions and rotary positions of the lower leg in tests of the knee ligaments. The mobility of the knee joint in the sagittal direction at right angles to the lower leg is to be measured as a function of the rotary position of the lower leg and the flexion in the knee joint. For determination of the displaceability, rigid fixators are dispensed with, with the exception of the foot, and supports are only provided on the femoral condyles. Moreover, there is a specially constructed chair which immobilises the patient. The lower leg is loaded with the required force, and the displacement between upper leg and lower leg is measured electromechanically. The references employed for the boney skeleton are, on the one hand, the soft tissues of the upper leg which are not displaced relative to the bone in the given set-up, and, on the other hand, a tripod magnet which rests closely against the head of the tibia and operates a linear potentiometer via a switch. The device is intended for diagnosing and monitoring the progress of instabilities of the knee ligaments.

Description

Field of use:

The device enables an objective examination of the ligament apparatus on the knee joint and is therefore especially for the Orthopedics and traumatology of interest.  

Purpose:

For diagnostics, documentation and follow-up as well for assessing ligament damage to the knee joint an investigator-independent, specific and reproducible Tape loosening required.

State of the art and criticism:

Much of the methods used so far are used X-rays that are expensive, the number of examinations limit due to radiation exposure and when evaluating and archiving problems. Other Electromechanical processes sometimes work with unusual elaborate fixation procedures or switch the Influences of soft tissue shifts are not sufficient. Others too generously do without fixations and use them insufficient measuring points.

DEXEL, M. X-ray diagnosis in lesions of knee ligaments. Injuries of the ligaments and their repair; Hand knee foot Thieme Verlag, 1975

FORSTER, G. The standardized "held recording" for Diagnosis of ligament injuries on the lower extremity. Current surgery 13: 1978, 239-252.

HEJGAARD, N. Prospective stress radiographic study of knee ligament injuries in 62 patients treated by acute repair.

JACOBSEN, K. Demonstration of rotatory instability in injured knees by stress radiography. Acta orthop. scand. 49: 1978, 195-204.

KENNEDY, J.C. Medial and anterior instability of the knee. The Journal of Bone and Joint Surgery. Vol. 53-A, No. 7, 1971, 1257-1270.

MARKOLF, K.L. In vivo knee stability. Journal of Bone and Joint Surgery, Vol 60-A. No. 5, 1978, 664-674.  

NYGA, W. X-ray imaging of cruciate ligament injuries of the knee joint. Journal of Orthopedics 107: 1970, 340-344.

SYLVIN, L.-E. A more exact measurement of the sagittal stability of the knee joint. Acta orthop. scand. 46: 1975, 1008-1011.

Task:

The measurement of ligament stability at the knee should be the one practiced so far correspond to clinical examination and at low Fixation effort without complicated evaluation of direct results deliver and be repeatable any number of times.

Solution:

The subject sits on a chair with a short and recessed seat ( 1 ), which holds the pelvis and prevents shifts in the soft parts of the thighs. This eliminates the need for complex fixation agents. All that is then required is support on the inner and outer femoral condyle towards the front and on the outer outside, and fixation of the foot to fix the rotation of the lower leg. The actual measuring device can now be placed on the front of the thigh without hesitation. To determine the position of the lower leg, a measuring plane is created in the frontal plane, which lies closely against the shinbone head and cannot be shifted with the forces that are used.

Advantages of the device:

- Independence from the examiner.
- The procedure corresponds to the clinical examination.
- Defined positions are created without fixations that are unpleasant for the test subject.
- Can be applied to the same person as often as required.
- Works without radiation exposure.
- Delivers several meaningful measurements directly and quickly via the knee ligament apparatus.

Description of an embodiment:

The following description includes drawings 1 and 2. Is shown in:

Fig. 1 shows the schematic side view, with omission of the base plate and of the linkage for attachment of the different supports and guide rollers,

Fig. 2 shows the view of the tripod magnet from the side.

The subject sits on a chair, the seat ( 1 ) of which is deeply recessed to fix the pelvis and which is very short to largely expose the soft parts of the thigh. The chair is adjustable in height and has armrests.

The foot is fixed on a rotatable footplate ( 6 ), which can be fixed in the desired rotational position of the lower leg by means of pin ( 7 ), by heel cup ( 8 ), Velcro fastener ( 9 ) and toe pin ( 10 ) between the first and second toes.

A support rests on the right and left of the patella with adjustable support plates ( 11 ). This creates a strong abutment when measuring the front drawer. Another support ( 12 ) is applied from the outside. It is only necessary when measuring the rear drawer to compensate for the torque generated by the femoral neck angle.

A support plate ( 13 ) with counterweight ( 14 ) and extension arm ( 15 ) lies loosely on the front of the thigh. The boom carries the linear potentiometer ( 5 ) whose sliding contact measures the displacement of the tibia head via the button ( 4 ).

The button ( 4 ) rests on a magnet ( 2 ), the front of which is covered by a mirror ( 3 ). The magnet is recessed on the mirror side to avoid centralization of the button caused by the field divergence. Two feet ( 2 a ) and an adjusting screw ( 2 b ) allow the magnet to be aligned exactly from the front.

In the middle of the calf, a padded Velcro fastener ( 16 ) is used to apply force to the lower leg. The force is exerted by a weight ( 19 ) via the deflection roller ( 18 ) for the front and additionally via the roller ( 17 ) for the rear drawer.

The measurement of the drawers in other flexion positions in particular for the laughing man test at 20 degrees using a second footplate which is attached to the frame accordingly carried out. Booms, outriggers and pulleys changed in a simple way.

The potentiometer setting is displayed on a Digital voltmeter. One digit corresponds to 1/10 mm.

Claims (4)

1) Measuring device for determining front and rear drawers on the human knee joint, characterized in that the displaceability of the lower leg in the sagittal direction perpendicular to the lower leg in different knee flexion positions and different rotational positions of the lower leg can be measured specifically with a selectable load. 2) Measuring device according to claim 1), characterized in that the device at well defined and easily reproducible Place the leg against or supports. They are the ones Femoral condyles on the left and right of the patella as well as the External femoral condyle and the attachment of the patellar tendon. 3) Measuring device according to claim 1), characterized in that the subject sits on a chair, the seat ( 1 ) is very short and additionally recessed, so that in this way a fixation of the leg and pubis and thus the pelvis in the front and rear Direction comes about. 4) Measuring device according to claim 1), characterized in that a measuring plane is produced as a reference for the lower leg by a tripod, disc-shaped magnet ( 2 ) is pressed by elastic and Velcro closure in close bone contact to the front of the shinbone head and on the front of the magnet a mirror ( 3 ) for checking the alignment of the button ( 4 ) of the measuring potentiometer ( 5 ) and for almost frictionless sideways displacement of the button.