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BIOMECHANICS OF ORTHOSES

Jean Christophe AriasOccupational therapist, OrthotistRegular Member of GEMMSOR

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WHAT YOU NEED BEFORE MOULDING YOUR ORTHOSIS

- Choose the right position of the hand.

- Take into account the arches of the hand.

- Take into account the creases of the hands.

- Respect the pressure points.

- Know the biomechanical peculiarities of the hand.

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HAND POSITIONS

First:

- Never let the patient in supination.

- Avoid the radial slope (Rheumatoid Polyarthritis, De Quervain tendonitis, Root arthrosis, Scaphoid fracture, Hemiplegia).

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REST POSITION

The therapeutic objective is the analgesia

- Rheumatic pathologies: wearing protocol of the orthosis during the night

- Tendonitis: wearing protocol during the day, 3 or 4 weeks (Then, never forget the prevention).

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Dorsiflexion of the wrist between 0 and 20°

Curling of MCP, PIP and DIP joints, with more flexion on the

5th one than on the 2nd one.

Thumb in extension and abduction, outside the

motion path of the other (long) fingers

In polyrheumaticconditions, the MCP joints are extended

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FUNCTIONAL POSITIONEnhance grasp (day wearing protocol)

Dorsiflexion of the wrist between 30 et 45° max.

The long fingers are lined up at the same level.

Rotation of the thumb on its base.

Thumb in opposition or grasp position.

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INTRINSIC POSITION (Prevention from shortening)

- Healing : wearing protocol day and night, most of the time during 6 weeks.

- Central and peripheral paralysis: wearing protocol only the night (Day is dedicated for stimulation and rehabilitation).

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Position extrinsic or intrinsic minus: obtained with muscular contraction of the forearm.

The hand is stiffened, with a shortening of the muscles, capsules, ligaments and tendons.

Intrinsic or intrinsic plus position: obtained with the muscular contraction of

the hand.

This is the position we are looking for prevention from shortening and shrinkage: dorsiflexion of the

wrist between 20 et 30°, MCP joints flexion 70°, PIP and DIP straightness, thumb in opposition.

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CHOOSE THE FORM OF THE ORTHOSIS

- volar

- Dorsal

- Lever system

- Circular

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- With two contact points to obtain the flexion.

- three points, toto obtain the extension.

- More (circular immobilization).

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PALMAR OR VOLAR

Basically used for the resting orthoses, and additionally for the

intrinsic position.

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Wrist orthosis: tendonitis, arthrosis, carpal tunnel (extension 0°): night wearing protocol.

Orthosis for poly-arthritis: have a look on the rings on the Velcros which facilitate the

donning and doffing.

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Intrinsic orthosis for healing. Permanent wearing protocol,most of the time sixweeks (except for

scaphoid fractures, twelve weeks).

Also used in case of paralysis (night

wearing protocol).

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DORSALUsed most of the time for the correcting

orthoses, it’s

indeed better to pull than to push.

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Push: the strength is maximal in the middle and in more, we note the

friction in the extremities which

prevents from opening the joint.

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Pull: avoid the friction, and divides the strength by 2. It is necessary to take 2 precautions: pull perpendicularly to the

Max pressure: 50g/cm2

segment, and mould perfectly the orthosis.

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In case of ulnar deviation, this small functional orthosis protects the joints, and helps the patient

to make the movements of the everyday life.

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LEVER SYSTEM

This system offers more power to correct thedeformations, or to

stabilize the joints if we wish to make a

functional orthosis.

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The big part of the lever system is 3 times as long asthe little one; then, with 100 grams of

pressure in the proximal extremity, we obtain 300 grams of strength to raise

the hand.

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CIRCULAR

With the elastic products, the distribution of the pressures isperfect: it is the best solution to immobilize, when we look

for a healing.