GB2121688A

GB2121688A - Alignment device

Info

Publication number: GB2121688A
Application number: GB08215202A
Authority: GB
Inventors: Dr Marilyn Lord
Original assignee: University College London
Current assignee: University College London
Priority date: 1982-05-25
Filing date: 1982-05-25
Publication date: 1984-01-04
Also published as: GB2121688B

Abstract

The present invention provides a lower limb prosthetic alignment device comprising a footplate (1) on which the patient can stand, the footplate comprising a plurality of force transducers (2); computing means (3) connected to the force transducers (2) for calculating the centre of foot pressure (CFP) from the output of the force transducers; CFP display means (4) to display the position of the CFP; and a substantially vertical indicator (5) which is movable on or adjacent the leg of the patient. <IMAGE>

Description

SPECIFICATION Alignment device The present invention relates to a device for aiding the alignment of lower limb prostheses.

Visual alignment of a lower limb prosthesis on the patient has generally been achieved by the prosthetist simply appraising visually the orientation of the leg of a patient, using a plumbline. In addition, the line of the load through the limb and the proportion of load borne by each leg has generally been estimated visually. In other words, the alignment is simply done "by eye". Obviously, this method leaves some room for human error.

An object of the present invention is to provide an alignment device with which lower limb prostheses can be aligned with greater ease and reliability, and from which loading information is given.

According to the present invention there is provided a lower limb prosthetic alignment device comprising a footplate on which the patient can stand, the footplate comprising a plurality of force transducers; computing means connected to the force transducers for calculating the centre of foot pressure (CFP) from the output of the force transducers; CFP display means to display the position of the CFP; and a substantially vertical indicator which is movable on or adjacent the leg of the patient.

Preferably, the footplate is a double forceplate comprising one forceplate for each foot, each forceplate comprising a plurality of force transducers.

Preferably, the CFP display means are arranged on or adjacent the footplate so that the CFP can be seen in relation to the leg itself.

The movable indicator can be a cursor in the form of a elongate movable rod, or can be vertical beam of light which can be projected against the leg of the patient.

Preferably, the device further comprises a position transducer to record the position of anatomical landmarks in relation to the CFP position.

The position transducer can be incorporated into the movable indicator or can be a separate device. In both cases, the output of the position transducer can be relayed to the computing means.

In an advantageous embodiment of the invention, the device further comprises a visual display unit (VDU), connected to the computing means, on which the distribution of load under each foot is displayed as well as the CFP. In this case, a scale on the VDU and a corresponding scale on the footplate could be used to position the movable indicator.

The device of the invention has the great advantage that it allows the load line of the leg to be accurately visualised against the leg.

Further, accurate measurement of the alignment of prostheses can be achieved and thus prostheses can be positioned with greater reliablity.

An embodiment of the present invention is described in more detail below, by example only, with reference to the accompanying drawings, wherein: Figure 1 is a schematic block diagram showing the construction of the alignment device; Figure 2 is a perspective view of the footplate, CFP display means and movable indicator of the device; and Figure 3 is a sketch of the possible output of the visual display unit.

As shown in Fig. 1, the alignment device comprises a footplate 1 with force transducers 2, a microcomputer 3, CFP 4 and a movable indicator 5. A position transducer 6 and a VDU 7 are optionally connected to the microcomputer 3.

The footplate 1, as shown in Fig. 2, comprises two forceplates 8, one for each foot, mounted in a platform 9. The platform 9 has preferably only a very small height, since patients should not be expected, and may indeed not be able, to climb steps.

The force transducers 2 are standard commercially available transducers, but may also be simply stiff springs the compression of which measured by potentiometric means.

There is generally a minimum of three transducers 2 under each forceplate 8, but there may be any greater number.

More transducers enable the physical dimensions of the base of support to be reduced and enable the CFP be determined with greater accuracy.

The outputs of the transducers 2 are fed into the microcomputer 3. The microcomputer 3 calculates from the information provided by the transducers 2 the position of the CFP beneath each foot.

The position of the CFP is then communicated to the CFP display 4 which in the illustrated embodiment is a row of lights 10 along the edge of the footplate 1.

The movable indicator 5 is illustrated in Fig.

2 as a cursor in the form of a simple vertical rod or scale 11. The rod 11 can be moved horizontally to the displayed position of the CFP and to positions corresponding to the positions of anatomical landmarks.

The position transducer 6 is preferably incorporated into the movable indicator 5 and, utilizing for example a linear potentiometer, detects the position of the indicator 5.

As mentioned above, the alignment device also preferably includes a VDU 7 connected to the microcomputer 3. On the VDU 7 can be displayed the distribution of load beneath each foot and the position of the CFP in plan view; with stylized outlines of the feet, as indicated in Fig. 3. This is advantageous since it allows the prosthetist to see whether the patient is balanced and can stand adequately.

When the alignment device of the invention is in use, a patient simply stands on the footplate 1, with one foot on each forceplate 8, the CFP position is indicated on the row of lights 10 and the rod 11 is first moved to that position. The prosthetist can then simply measure the position of the anatomical landmarks, such as the ankle, knee, hip, posterior aspect of the heel and tip of the forefoot, by moving the rod 11 to align with each of these landmarks in turn. Particular points on a prosthesis can also be measured in the same way.

It is important that the movable indicator 5 is near to the patient's leg since otherwise the above measurements could not be made accurately. The particular points on the limb can often not be identified without direct palpation of the limb, so that measurements taken from a two dimensional representation of the leg and vertical load line would not be satisfactory.

The measurements taken by the prosthetist are, in a preferred embodiment, logged via manual logging console (not shown) into the microcomputer 3. Thus, at each position of the rod 11, a button on the console is pressed and the output of the position transducer 6 is relayed to the microcomputer 3. The measurements could then be displayed on the VDU screen for easy reference. Further, a printed record of the measurements could be obtained if a printer unit was attached to the microcomputer 3.

The position of the CFP on the footplate 1 could be determined from a grid on the screen of the VDU 7 and a corresponding scale on the footplate 1. In this case, the position of the CFP shown on the VDU 7 could simply be read off the VDU screen and identified on the footplate scale. However, it is advantageous to have the CFP indicator 4 along the edge of the footplate 1 since this allows the prosthetist to see easily whether the CFP position is changing, i.e. whether the patient is moving or swaying, while he or she is taking measurements.

The movable indicator 5 need not be in the form of a rod 11. For example, it could be a movable lamp which emits a vertical beam of light. This beam of light could be aligned with the CFP position and could then be clearly seen against the leg of the patient.

Further, the position transducer 6 need not be attached to the indicator 5. It could comprise a retractable string originating from a fixed point on the footplate 1 which string could be pulled out to each landmark. In this separate device, the position of the landmark is determined from the length and orientation of the string, which can be determined by potentiometric means.

Claims

1. A lower limb prosthetic alignment device comprising a footplate on which the patient can stand, the footplate comprising a plurality of force transducers; computing means connected to the force transducers for calculating the centre of foot pressure (CFP) from the output of the force transducers; CFP display means to display the position of the CFP; and a substantially vertical indicator which is movable on or adjacent the leg of the patient.

2. A device according to claim 1, wherein the footplate is a double forceplate comprising one forceplate for each foot, each forceplate comprising a plurality of force transducers.

3. A device according to claim 1 or 2, wherein the CFP display means are arranged on or adjacent the footplate.

4. A device according to any preceding claim, wherein the indicator is an elongate rod.

5. A device according to any of claim's 1 to 3, wherein the indicator is a beam of light.

6. A device according to any preceding claim, further comprising a position transducer to record the position of anatomical landmarks in relation to the CFP position.

7. A device according to claim 6, wherein the position transducer is incorporated into the indicator.

8. A device according to claim 7, wherein the position transducer comprises a linear potentiometer.

9. A device according to any of claims 6 to 8, wherein the position transducer is connected to the computing means.

10. A device according to any preceding claim, further comprising a visual display unit (VDU), connected to the computing means, on which the distribution of load under each foot is displayed as well as the CFP.

11. A device according to any preceding claim, wherein the CFP display means comprises a row of lights.

12. A lower limb prosthetic alignment device, substantially as herein defined with reference to the accompanying drawings.