GB2363203A - Apparatus for measuring ankle dorsiflexion - Google Patents

Abstract

The apparatus comprises a knee brace for maintaining the leg of the measured ankle in an extended position and a base unit or platform incorporating heel cups or pads, a goniometer and first and second electromechanical switches for indicating the position of heel lift. The goniometer has a leg lever (3, Fig.4) which is attached to the shin by an elastic strap (1, Fig.4), an axis indicator (6, Fig.4), dial (5, Fig.4) and an indicator needle (4, Fig.4). The platform carries markings to assist in the taking of repeated measurements and the whole apparatus is light and portable.

Description

Page 1 2363203

The description

Title: An apparatus to measure ankle dorsiflexion This invention relates to the construction of an ankle dorsiflexion (moving the top of the foot towards the leg) measurement apparatus using a weight bearing system that reflects functional forces. The apparatus unjjs light and portable and can be use easily used within a clinical setting.

Reliable accurate measurements of in vivo small joint range of motion (ROM), direction of motion (DOM) and symmetry of motion (SOM) is notoriously difficult to accomplish (Low 1976). Ankle joint dorsiflexion assessment has been found to be particularly unreliable with different study methods yielding inconsistent results (Rome 1996). Explanations for measurement errors are mumerous. Bohannon et al (1989) noted discrepancies in the positioning of surface markings due to inconsistent conditions when identifying the subcutaneous bony landmarks, therefore epidermal designation will inaccurately reflect the underlying osseous structures. Mosely and Adams (1991) describe force application as being unquantified when applied to the foot (the lever) at an unknown distance and direction from the ankle (the fulcrum). This causes intra and intertester inconsistent torque and consequently varying dorsiflexion DOM and ROM displacement. Additional errors will occur as a result of uncontrolled tractograph parallax alignment with epidermal markings and variable optical recording angles giving inconsistent recording positions, which will affect measurement reliability.

Weight-bearing static measurements are obtained when the talocrural becomes loaded by the superior body mass locating the foot against the floor, by frictional forces, causing ankle torque by leg leverage (Segal 1980). Banks and DiNapoli (1993) have acknowledged the theory and practise of the weight-bearing measurement method as reflecting more accurately the functional capacities of ankle joint dorsiflexion. Alignment of the foot and ankle differ during non-weight-bearing and weight-bearing conditions illustrated by Kitoaka et al (1995) concluding that this indicates foot and ankle quantitative alignment appraisal be performed while weight-bearing.

Page 2 Merriman and Tollafield (1995) describe a weight-bearing measurement method, which displays consistent results, by a contralateral stride and anterior knee flexion causing dorsiflexion at the posterior ankle. The tractograph is aligned with the floor and fibular bisection landmarks of the posterior leg and measurement noted. Barton and Gregg (1993) compared non-weight-bearing to weight-bearing procedures noting non-weight-bearing assessment displayed a poor correlation when compared to weight-bearing assessment, which displayed consistently higher dorsiflexion ROM measurements.

The increased reliability of weight-bearing assessment may be due to reducing the variables by aligning the tractograph with the floor and loading the foot with body weight. However, this necessitates end point dorsiflexion identified by heel lift, which is open to various interpretations. Neither Barton and Young (1993) nor Astrom and Arvidson (1995) accurately describe the precise moment heel lift occurs when describing weight-bearing measurement methods. Recent research has questioned the reliability and validity of commonly used measurement approaches in podiatric biomechanics (Menz 1998). It is evident from the literature that a reliable and quantifiable dorsiflexion measurement system needs to be developed. Strategies for decreasing measurement errors are discussed by Wevers et al (1982) and Rome (1996) suggesting the use of a jig apparatus. Standardising limb positions allowing utilisation of similar equipment enabling replicating of the measurement technique.

The object of this apparatus is to produce a suitable test that will eliminate and inhibit the known sources of errors associated with ankle joint dorsiflexion measurements. This will increase the repeatability and precision of recorded values offering a reliable intra and intertester system of quantitative measurement. The apparatus composes of a knee brace, base platform, which incorporates foot alignment indicators, stride target, electromechanical switch assembly to identify heel raise and a goniometer with calibration dial and attachable leg lever indicator.

Page 3 The subject steps onto the apparatus and stands on the pads positioning their heels against the heel stops (6, fig 1). The popliteal skin crease was marked then the knee brace positioned and fastened with the straps (4, fig 2) while aligning and viewing the marked skin crease via the brace window markers (5,6, fig 2). Tensioning of the straps was done by manual manipulation being tight enough to hold the brace in position without expressed discomfort by the subject. Positioning of the foot was accomplished by aligning the second web space with the platform's centre line (2, fig 1) and heel stop bisection line (4, fig 3). The goniometer axis indicator (6, fig 4) was positioned visually inline with lateral malleolus landmark by unlocking the gonionieter slide rod (9, fig 4) requiring anticlockwise rotation of the locking handle (10, fig 4). This allows anteriorlpostenor and proximalldistal movement of the goniometer, which was locked in position by manual clockwise rotation of the locking handle (10, fig 4) once the desired position is obtained. The leg lever (3, fig 4) is rotated posteriorly until it meets the anterior aspect of the leg (shinbone) and is held in place by attaching the Velcro elastic leg strap (1, fig 4). Calibration of the goniometer was done by rotating the dial (5, fig 4) until 00 is aligned with the red indicator needle (4, fig 4), this must be done while the subject is looking strait ahead standing erect with ipsilateral arm relaxation, allowing for a repeated centre of gravity position.

The control box (1, fig 5) was switched on (4, fig 5) and the subject asked to step beyond the red line (stride marker) (3, fig 1) or further if possible. The subject can then place their hands on the wall, they are facing at shoulder high, assisting balance if required while slowly flexing the anterior knee. Prior to this the subject is requested to relax the right leg during flexion of the left knee allowing passive dorsiflexion against ground reaction forces. When complete dorsiflexion was achieved heel raise will occur resulting in activation of the 1st switch (1, fig 7) illuminating the green light (2, fig 5). A reading from the goniometer needle indicator and dial should be taken and noted 4, 5, fig 4). If further knee flexion occurs heel raise continues activating the 2 nd switch (2, fig 7) shown as a red light (3, fig 5) and the subject is requested to extend (straighten) the knee lowering the heel extinguishing the red light. A dorsiflexion measurement is noted only when the green light is on. After the Page 4 measurement is recorded the subject is requested to step back and the apparatus is unstrapped.

Page 5 References Astrom, M. Arvidson, T. (1995) 'Alignment and Joint Motion in the Normal Foot' Journal of Oithopaedid and Sports Physical Therapy. Vol 22. No 5: pp216-222.

Banks, A.S. DiNapoli, R. D., (1993) 'Ankle Dorsiflexion' Joumal of the American Podiatfic Medical Association. September. Vol 83. No 9: pp541543.

Bohannon, R. W. Tiberio, D. T. Michael, Z. (1989) 'Selected Measures of Ankle Dorsiflexion Range of Motion Differences and Intercorrelations'. Foot and Ankle. Vol 10. No 2: pp 99-103.

Kitaoka, H.B. Lunberg. A. Luo, Z.P. An, K-N., (1995) 'Kinematics of the Normal Arch of the Foot and Ankle Under Physiologic loading' Foot and Ankle International. August. Vol 16. No 8: pp492-499.

Low, L.L., (1976) 'The Reliability of Joint measurement'. Pysiolyherapy. July. Vol 62. No 7: pp 227-229.

Merriman, L.M. Tollafleld, D.R. (1995) 'Assessment of the locomotor system'. Assessment of the Lower Limb. First edition. Edited by Merriman, L.M. Tollafield, D.R. Published by Churchill Liviston. Edinburgh: ppl39189.

Menz, H.B. (1998) 'Alternative Techniques for the Clinical Assessment of the Foot'. Joumal of American Podiatric Medical Association. March. Vol 88. No 3: ppl 19-129.

Moseley, A. Adams, R., 'Measurement of passive ankle dorsiflexion: Procedure and reliability'. Australian Physiotherapy. Vol 27. No 3: ppl75181.

Rome, K., (1996)'Ankle Joint Dorsiflexion Measurement Studies A Review of Literature'. Journal of American Podiatric Medical Association. May. Vol 86. No 5: pp205-21 1.

Page 6 Segal, D., (1980) 'Ankle Function: Measurement and Functional Bracing of the Fractured Ankle'. Foot and Ankle. First edition. Edited by Bateman, E. Trott, A.W. Published by Thieme and Stratton. New York: p20.

Wevers, H.W. Siu, D.W. Cooke, T.D. (1982) 'A quantitative method of assessing malalignment and joint space loss of the human knee'. Joumal Biomedical Engineering. October. Vol 4. No 4:pp 319-24 Figure 1 Key 1Base unit 1m x 0.360m x 0.018m. 2- Centre line indicators. 3- Stride target 4mm wide positioned 0.5m from rear edge of heel pad. 4- Goniometer. 5- Electromechanical switch lever. 6- Heel pads. 7- Cable. 8- Control box.

Figure 2 Key 1 - Knee brace 34cm x 13cm. 2- Interior surface covered with 6mm thermoplastic. 3- Self-locking spring buckles. 4- Equally spaced nylon strapping 15mm x 72cm. 5- Popliteal fossa skin crease alignment window 40mm x 25mm centred 21cm from the top edge. 6- popliteal skin crease alignment indicator. 7- strapping reinforcement bar 20mm wide. 8- No. 10 x 6mm self tapping screws.

Figure 3 Key 1 - Plan elevation 9cm in diameter. 2- Rear elevation 9cm Acm. 3- Heel cup window 2.5cm square. 4- Heel stop bisection line.

Figure 4 Key 1- 50cm x 4cm elastic goniometer leg strap with Velcro attachments. 2- Leg lever strap Velcro attachment. 3- 20cm x 5mm brass leg lever with central 900 bend 1 Ocm from axis. 4- 1 mm needle indicator 2mm from dial face. 550cm radius gauge dial. 6- Axis alignment indicator. 72mm lock nut with nylon washers. 8- 2mm x 50mm screw. 9- 1 Ocm x 4cm slide rod. 10- 8mm locking handle. 11- 8cm goniometer fixing bracket. 12- 4mm bracket fixing holes.

Figure 5 key 1- 15cm x 6cm x 5cm plastic control box. 2- Green light. 3Red light. 4- On off switch. Cable to electromechanical switches.

The apparatus comprises of a knee brace (fig 1) and measurement platform (1, fig 2) that incorporates foot alignment indicators (2, fig 2), a stride target (3, fig 2), electromechanical switch lever assembly (5, fig 2), goniometer (4, fig 2), heel cups (6, fig 2) and control box (8, fig2). Figure 1 I I I [n 1 1 1. 7 1 - ---)) 7 - - I&--- + ) 8<-, I 11 - II: I L-4) J i \-i Figure 2 4 8 0 00 4 0 0 0 8 \I 2 q

Claims (4)

Claims

1. The apparatus is light and portable and employs a weight-bearing system of measurement that reflects functional forces. The apparatus includes a knee brace to maintain the leg, of the measured ankle, in an extended position. The apparatus will eliminate the need for manual parallax alignment of the goniometer with bony landmarks. The apparatus will allow a repeatable foot position, in relation to the apparatus, with a calibrated starting position off 00. The apparatus will incorporate an electromechanical switch that will identify the measurement recording position during heel raise.

2. An apparatus as in Claim 1 that includes a knee brace, the arrangement of an electromechanical switch lever assembly with control box, goniometer leg lever assembly and associated plafform markings.

3. An apparatus as claimed in any preceding claim, which is made from metal, plastic material or wood, or from a combination of these materials.

4. An apparatus substantially as here in described and illustrated in the accompanying drawings.