WO2004008962A1

WO2004008962A1 - Improvements in and relating to the measurement of joint laxity

Info

Publication number: WO2004008962A1
Application number: PCT/GB2003/003154
Authority: WO
Inventors: Dean Gunn
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-07-24
Filing date: 2003-07-24
Publication date: 2004-01-29
Anticipated expiration: 2005-01-24
Also published as: GB0217156D0; AU2003254471A1

Abstract

Apparatus for measuring ankle dorsiflexion in a patient comprising a foot locating station (15) for locating a patient's foot at a predetermined datum position for dorsiflexion of the ankle. The foot locating station is positioned so that the patient can stand upright at the station (15). A measuring means (1, 2, 3, 6, 8, 17) is positioned, dimensioned and arranged relative to the station (15) so as to be contactable my the patient's knee when the patient flexes the ankle. The measuring means comprises a knee contacting member (1) connected (2) to a pointer (6) that slides along a scale (8) when the patient's knee contacts the member (1) during dorsiflexion of the patient's ankle, and thereby indicates the amount of dorsiflexion of the ankle as a measurement along a linear scale (8).

Description

Improvements in and relating to the measurement of joint laxity

This invention relates to the measurement of joint laxity and has particular reference to the measurement of ankle dorsiflexion. One of the most common ligament injuries is ligament injury to the ankle. These injuries usually heal without long-term problems but do not necessarily heal in such a way as to provide biomechanical stability to the joint. This can cause instability of the joint particularly in the case of the ankle, and can lead to pain, re-injury and the degeneration in the joint often accompanied by the onset of arthritis.

In order to diagnose an injury to the ligament of an ankle, a laxity test is performed on the ankle. Usually, this is done by a person holding the patient's foot with one hand and rotating the ankle joint with the other in an anterior- posterior (forward and backward) or inversion-eversion (twisting inward and outward). Load is applied to the foot and the resulting motion is observed; this technique is highly subjective.

A time honoured method used by physiotherapists to measure dorsiflexion is to stand the patient with their foot displaced from a vertical wall surface and then have the patient, while supporting their weight on the ankle, flex the ankle to bring the knee into contact with the wall. This operation is repeated moving the foot a little further away from the wall on each occasion until a point is reached at which the knee just touches the wall at the limit of comfortable flexing of the ankle in a forward-direction. The physiotherapist then measures the distance of the patient's big toe from the wall. This provides a measure of the flexing of the ankle for that patient.

While providing some kind of measure with very little sophistication, it will be appreciated that this is at best a subjective measurement; even though this method has long been recognised to give a wide range of results, it is still widely used despite numerous attempts to overcome the problem and provide accurate measurement of dorsiflexion.

United States Patent Specification No 5,402,800 describes and claims an ankle laxity measurement system for measuring laxity of the ankle joint of a patient that includes a frame secured to the patient's foot. A reference point is established on the patient's ankle, and movement between the foot clamp and a reference point is measured in six degrees of freedom. A handle secured to a frame is used to apply a force which is measured in the anterior-posterior and inversion-evolution directions, and signals corresponding to these forces and the six degrees of freedom movements are supplied to a computer. The computer records and displays the motions and loads. United States patent specification No 5,957,869 provides apparatus and a method for providing force and distance indication readings for an orthopaedic joint laxity measurement using the well established KT 1000 measuring device.

The apparatus of each of these prior art devices is cumbersome and bulky and requires expert interpretation of the results. Furthermore such apparatus is extremely costly to install and operate and requires technical or trained medical staff to interpret the results. In short, such apparatus represents technical overkill of a simple measurement required by physiotherapists particularly when dealing with sportsmen overcoming injuries, typically ankle injuries.

British Patent Specification No 2 363 203A describes the use of an electromagnetic switch to indicate when the patient's heel is raised during measurement of dorsiflexion. This apparatus, however, requires the alignment of the bony landmarks of the ankle with the measuring gauge of the goniometer. Since these bony landmarks differ quite considerably from patient to patient, there is a certain amount of subjectivity in the resulting measurements.

Other methods of determining ankle joint dorsiflexion includes x-ray techniques which suffer from the disadvantage of needing to produce and interpreted the result of x-ray film. Such techniques also have the disadvantage that the apparatus is not readily portable and there is the additional hazard of exposure to X-radiation.

Goniometers have also been used to measure non-weight bearing dorsiflexion in a patient's ankle; while inexpensive, such simple apparatus has the disadvantage of some degree of variability between patients and the way in which medical professionals use them.

It is common practice in orthopaedic and physiotherapy departments for non- weight-bearing range of movement of the ankle to be measured with a goniometer. This measure may often demonstrate a comparable range of dorsiflexion to the uninjured ankle however, when a weight-bearing dorsiflexion measure is taken, significant deficiency of range of motion at the injured ankle compared to the non-injured ankle is frequently apparent.

It is increasingly recognised that to return a patient to optimum function, there is a need to ensure that weight bearing dorsiflexion (both with extended and flexed knee) range of movement is fully restored.

Weight bearing dorsiflexion with a flexed knee forms a necessary component of walking and becomes increasingly vital for activities such as running, changing direction, squatting, ascending and descending stairs, in addition to activities required for optimum high-level physical and sporting performance.

From a biomechanical perspective the requirement for the lower leg to move forward in combination with tibial internal rotation, over the ankle, and thus allow the sub-talar joint to "unlock", post heel contact, for normal gait propulsion differs in large part from the fixed tibia (foot and ankle) movement that constitutes non-weight-bearing dorsiflexion.

From the foregoing, therefore, it will be apparent that there is no readily available and easily portable apparatus for measuring the weight bearing dorsiflexion of ankles.

An object of the present invention is to provide an apparatus for measuring the weight-bearing dorsiflexion of ankles that is readily portable. According to one aspect of the present invention, therefore, there is provided Apparatus for measuring ankle dorsiflexion in a patient comprising a foot locating station (15) for locating a patient's foot at a predetermined datum position for dorsiflexion of the ankle, characterised in that the foot locating station is positioned so that the patient can stand upright at the station (15), and a measuring means (1, 2, 3, 6, 8, 17) is provided comprising a knee contacting plate (1) that is positioned, dimensioned and arranged relative to the station (15) so that in use the member (1) is contacted by the patient's knee when the patient flexes the ankle, said knee contacting member (1) being connected by a rod (2) to a pointer (6) that slides along a scale (8) when the patient's knee contacts the member (1) during dorsiflexion of the patient's ankle, and thereby indicates the amount of dorsiflexion of the ankle as a linear measurement along the scale (8).

Preferably the locating station (15) has a toe board (5) that defines a datum position against which the patient can place a toe. Preferably the station (15) comprises a baseplate (4), and the measuring means (1, 2, 3, 6, 8, 17) comprises a slidable member (2, 6) in spaced parallel relationship with the base plate (4).

The locating station (15) may include securing or clamping means (16, 17) to locate the patient's foot at the datum position for the apparatus.

Preferably the knee contacting member (1) has a contact surface to provide for changes in attitude of the knee and change of contact point of the slidable member (1) with the knee as the knee flexes about an axis of rotation of the ankle.

The measuring means (1, 2, 3, 6, 8, 17) preferably comprises a housing (17) mounted on the base plate (4), and the housing (17) has a top surface in which there is an elongate slot (19) along which the pointer (6) can slide.

In one embodiment the pointer (6) is directly mounted on a rod (2) that slides in a bore in the housing (17) and carries the knee contacting plate (1) at a free end thereof.

In an alternative embodiment the pointer (6) comprises a plate (20) that slides on a top surface of the wall of the housing (17) that has the elongated slot (19), a saddle plate (22) is located in the slot (19) and dimensioned so as to be able to slide along the slot (19), and a carrier plate (23) attached to the saddle plate (22), which slides on an underside of the wall and is mounted on the rod (2).

If desired, a detection means (27) is provided at the locating station (15) that is operable to provide an indication of when a patient's heel is lifted off the base plate during dorsiflexion of the ankle. The indicator means (25) may be in the form of a light, bell or buzzer, to indicate when the heel is lifted.

Preferably the slidable member (2) includes a pointer (6) which is adapted to indicate linear deflection on the scale (8), and the measuring means (6, 8, (17) includes means for "zero-ing" the pointer (6) along the scale (8) scale with the patient's ankle and leg in the reference position.

An advantage of the present invention is that the apparatus is capable of recording an absolute measure of deflection. The linear measurement of the deflection, which in one aspect of the invention is in millimetres, at a given fixed height from the plane of the datum is an effective measurement of the angular deflection in degrees. In another aspect of the apparatus of the invention, provision may be made for the accurate location of the ankle joint by the locating means, in this way the angular deflection at a given distance from the ankle joint will be the same for each patient irrespective of the length of the leg. This has a major advantage over the wall measurement system used by the majority of physiotherapists at the present time because the variables that made obtaining this measurement inconsistent have been removed. The wall measurement system of measurement is peculiar to that patient because it depends upon the size of the foot and the length of the lower leg. While in broad terms there is a relationship between the two, nevertheless, the measurement is still specific to that particular patient. Using the apparatus in accordance with the present invention, however, the linear measurement of the slider is an absolute measurement of the angular movement of the ankle, and will enable comparisons between different patients.

The apparatus of the present invention permits the comparison of the readings for different patients, a comparison of the subsequent readings of the same patient in a rehabilitation situation, a comparison of the good and the injured ankle of a subject, and the use of comparative data in a sporting situation during pre and post warm-up exercises.

In one aspect of the invention the apparatus may be formed as a plastic moulded article and be capable of being folded for ease of portability. Thus, in view of the relative simplicity of the apparatus and the ease of transport, it can be made readily available to training facilities and gymnasia so that athletes and sportsmen can measure dorsiflexion readily and easily without qualified professional help. Thus, for example, in a "warm up" session, and an athlete can measure dorsiflexion at regular intervals to determine when he or she has "warmed up". Following is a description, by way of example only and with reference to the accompanying drawings, of one embodiment in accordance with the present invention. In the drawings:

Figure 1 is a perspective view of dorsiflexion measuring apparatus in accordance with the present invention.

Figure 2 is a side view of the apparatus in use.

Figure 3 is a side view of the apparatus illustrating the point of maximum deflection.

Figure 4 is a plan view of the apparatus of Figure 1.

Figure 5 shows a modified pointer assembly for the apparatus of Figure 1, and

Figure 6 shows the apparatus of Figure 1 fitted with a heel movement detector.

The dorsiflexion measuring device in accordance with the present invention comprises a base plate 4 having towards one end of thereof, a foot locating station 15 having a toe board 5 and a pair of laterally spaced longitudinally extending guide bars 16 between which the patient's foot is located. One of said guide bars is provided with a strap 7 and a patient stands with their foot located in the apparatus with the big toe abutting board 5 and with the strap 7 secured to maintain the base of the foot firmly on the upper surface of base plate 4. The base plate 4 has four legs 9 attached to it to support a measuring means 3 which comprises a longitudinally extending housing 17 having a central bore 18 adapted to accommodate a longitudinal rod 2. The longitudinal rod 2 is adapted to slide within housing 17 and is provided at its distal end with a limb contacting plate 1. The plate 1 and rod 2 is positioned, dimensioned and arranged relative to the station 15 so that the plate is positioned at a height above the base plate 4 so that the plate (1) can be contacted by the patient's knee when the patient flexes the ankle. The plate 1 is appropriately dimensioned, so as to accommodate a wide range of knee heights. The arrangement is such that the rod 2 is capable of sliding movement within housing 17. Rod 2 carries intermediate along its length a pointer 6 which projects through a longitudinal slot 19 in the upper portion of housing 3 for movement with rod 2. The pointer 6 provides a reading on a scale 8 to provide a measure of movement of plate to and from a datum position. The scale (8) has a zero point and positive or negative values each side of the zero point. The scale (8) is calibrated so that the zero point is set when the plate (1) is aligned with the toe board (5) (thus defining a reference plane containing the plate (1) and the board (5)).

In use as shown in Figure 2, the patient stands on the base plate with their foot secured into the device as indicated above by means of strap 7 with their big toe against the toe board and their lower leg defining substantially a right angle with the base plate 4. The contact plate 1 is moved into touching contact with the patient's knee in the rest or datum position. The position of the pointer 6 is then read off the scale 8 and recorded as the initial position. (This may be a negative or positive value depending upon the position of the knee relative to the datum plane). Having set the rest or datum in this way, the patient is then asked to flex his ankle in a forward direction whilst keeping their heel on the base plate 4, and the extremity of flexing in the forward position is measured on scale 8. As the patient flexes the ankle to move his knee forward, the limb contact plate 1 pushes the rod 2 into the housing 3 until an extremity of angular flexing is reached. The position of the pointer 6 along the scale 8 is then read again to provide a measure of the dorsiflexion.

It will be appreciated that this is a piece of apparatus that can be moulded in plastic components, and the legs 9 can be arranged to hinge about pivotal connections (not shown) where the legs 9 are joined to the base plate 4 and the measuring means 3 so that the apparatus can be folded flat for transport.

Referring to Figure 5 there is shown a modification of the pointer 6 shown in Figure 3, at least the top surface of the housing 17 is made of a thin plastics material and has an elongate slot 19 extending along its length. The pointer 6 comprises a transparent rectangular plate 20 of plastics material with an arrow marked on the plate 20. The plate 20 slides on the top surface of the housing 17. A filler piece 21 which is of the same colour as the background of the scale 8 (preferably white) is located under the plate 20 so that when one looks down on the pointer one does not look into a dark space. Located underneath the filler piece 21 is a saddle plate 22 which is approximately the same thickness as, or slightly thicker than, the thickness of the wall of housing 17. The saddle plate 22 has a recess 23 extending across its width and the plate 22 is located in the slot 19 and is dimensioned so as to be free to slide along the slot 19 without jamming. A carrier plate 24 is located beneath the saddle plate 22 and fits into the recess 22. The carrier plate 24 overlaps the edges of the slot 19 so as to slide on the underside surface of the top wall of the housing 17. The plate 20, filler piece 21, saddle plate 22 and carrier plate 24 are fixed together by two screws 25 to provide a pointer assembly 6 that can slide along the slot 19. The carrier plate 24 is mounted on the rod 2 by means of single pin 26 so that the pointer assembly 6 moves with the rod 2 when the rod 2 slides in the housing 17. The pointer assembly 6 restricts rotation of the rod 2 about its longitudinal axis.

In the embodiment described above, the patient's foot is strapped into place on the base plate. If desired, and as an alternative, the patient's foot need not be strapped in position provided that a detector means 27 is provided to detect when the patient's heel lifts off the base plate when flexing the ankle. Referring to Figure 6 there is shown a heel movement detection device 27 for placement in the foot locating station 15 at the region where the heel of the patient's foot rests. The detector is mounted on a plank 28 that can slide in a direction along its length so that the detector can be moved to a position under the heel of the patient when standing with their big toe against the toe board 5. All the electrical circuits and buzzers are located out of sight on the end of the plank 28 within the housing 17. The detector 27 provides an indication in the form of a light 29, bell, or buzzer when the patient's heel is lifted off of the base plate 4 during flexure of the ankle. The detection device could be a pressure sensitive pad or a micro switch that operates the light, bell or buzzer.

Claims

CLAIMS:

1. Apparatus for measuring ankle dorsiflexion in a patient comprising a foot locating station (15) for locating a patient's foot at a predetermined datum position for dorsiflexion of the ankle, characterised in that the foot locating station is positioned so that in use, the patient can stand upright at the station (15), and a measuring means (1, 2, 3, 6, 8, 17) is provided comprising a knee contacting member (1) that is positioned, dimensioned and arranged relative to the station (15) so that the member (1) is contacted by the patient's knee when the patient flexes the ankle, said knee contacting member (1) being connected by a rod (2) to a pointer (6) that slides along a scale (8) when the patient's knee contacts the member (1) during dorsiflexion of the patient's ankle, and thereby indicates the amount of dorsiflexion of the ankle as a linear measurement along the scale (8).

2. Apparatus according to claim 1 in which the locating station (15) comprises a baseplate (4) and the measuring means (1, 2, 3, 6, 8, 17) comprises a slidable member (2, 6) in spaced parallel relationship with the base plate (4).

3. Apparatus according to claim 1 or claim 2 wherein the locating station has a toe board (5) that defines a datum position against which the patient can place a toe.

4. Apparatus according to claim 1 or claim 2 wherein the locating station (15) includes securing or clamping means (16, 17) to locate the patient's foot at the datum position for the apparatus.

5. Apparatus according to any one of the preceding claims in which the member (1) has a contact surface to provide for the changes in attitude of the knee and change of contact point of the slidable member (1) with the knee as the knee flexes about an axis of rotation of the ankle.

6. Apparatus according to any one of the preceding claims wherein the measuring means (1, 2, 3, 6, 8, 17) comprises a housing (17) mounted on a base plate (4).

7. Apparatus according to claim 6 wherein the housing (17) has a wall in which there is an elongate slot (19) along which the pointer (6) can slide.

8. Apparatus according to claim 6 or claim 7 wherein the pointer (6) is mounted on a rod (2) that slides in a bore in the housing (17) and carries the knee contacting plate (1) at a free end thereof.

9. Apparatus according to any one of claims 6 to 8 wherein the pointer (6) comprises a plate (20) that slides on a top surface of the wall of the housing (17) that has the elongated slot (19), a saddle plate (22) located in the slot (19) and dimensioned so as to be able to slide along the slot, and a carrier plate 3 attached to the saddle plate 22, which slides on an underside of the wall of the housing 17 and is mounted on the rod (2).

10. Apparatus according to any one of the preceding claims wherein a detection means (27) is provided at the locating station (15) that is operable to provide an indication of when a patient's heel is lifted off the base plate (4) during dorsiflexion of the ankle.

11. Apparatus according to claim 10 wherein an indicator means (29) in the form of a light, bell or buzzer is provided to indicate when the heel is lifted.

12. Apparatus according to any one of the preceding claims in which the slidable member (2) includes a pointer (6), which is adapted to indicate linear deflection on the scale (8).

13. Apparatus according to claim 12 in which the pointer (6) is set at zero along the scale (8) with the knee contacting member (1) aligned with the toe board 5.

14. Apparatus according to claim 12 or claim 13 wherein the spacing between the sliding member (2) and the locating station (15) is chosen so that a linear measurement of the deflection in millimetres is an effective measurement of the angular deflection in degrees.

15. Apparatus according to any one of the preceding claims wherein a detection means (27) is provided at the location station (15) that is operable to provide an indication of when a patient's heel is lifted off the base plate (4) during dorsiflexion of the ankle.

16. Apparatus according to claim 15 wherein the detector (27) is movable relative to a toe board (5) to accommodate different heel positions.

17. Apparatus according to any one of the preceding claims wherein the apparatus is formed as a plastic moulded article and is capable of being folded for ease of portability.