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Hand and Finger Prosthetics - from Form to Function

AWARE07/11/2019
Food for Thought Winter '19

Even when we take every precaution to ensure our workers are safe when doing their job and receive all the correct training and follow the right procedures, life-changing accidents can still happen. A slip or trip with a sharp knife, a distraction whilst slicing meat, or carelessness in the food packaging line could all lead to irreparable damage or loss of digits. 

The hand is often taken for granted, but when we look closely at the intricacies of finger movements, fine motor control and how everything works in unison, it is easy to appreciate just how complex hand and finger movements are.

A 40% impairment of the thumb equates to 16% impairment of the hand. This equates to 14% impairment of the upper extremity which is 8% of the whole person - all from just a 40% disability to the thumb.

More digit injuries increase the level of disability to the hand, the upper extremity and the person as a whole. 

Claims for such injuries tend to arise from industrial accidents where individuals rely on their hands to complete most, if not all, tasks at work. Taking that away from someone has a profound psychological effect and cosmetic prosthetics just aren’t good enough to return any function. 

In recent years there has been a small explosion in devices, both active and passive. Passive devices are useful, but not where you want to be able to find practical solutions to problems and return individuals to a state where their bilateral hand dexterity is functional at work and in daily life.

There are a number of designs in the market place at the moment, all of which will have pros and cons for a particular user:

A new product to the UK comes in the form of bespoke made, active prosthetics from Naked Prosthetics. The devices can be exclusively obtained in the UK via PACE Rehabilitation. All of the devices are custom made. There is a fixed ratio of movements on the prosthetic between what is left of the finger(s)/thumb and what is in the prosthetic. It is developed for strength where it is needed for functionality and to create digits that move naturally through a wide range of movement. It’s best considered as a functional tool rather than a cosmetic device. The appearance will not be for everyone, but experience has shown that attitudes towards appearance have changed. Function is being preferred by some, over cosmetic appearance.

The range of movement does not extend from a completely open palm to a completely closed fist. This would weaken the structural integrity of the device and so the device extends from being able to make a large “C” with the hand to being able to hold tightly around the width of a hammer’s handle. The shorter that range of movement, the greater the strength and rigidity there is in the product. On a day to day basis, most of us do not need a completely open palm, or a completely closed fist, unless of course you want to slap or punch someone!

There are three products to the NP range and the choice depends on where the amputation is.

PIP driver

This is used where the patient is amputated above the PIP joint (the second knuckle down on each finger). It is essentially a finger-tip extension. Think of it as a more dextrous and natural thimble on the end of a stump, as it were. It is comfortable, lightweight, very natural to use and intuitive. The ratio of movement is bespoke to the individual, with the length being such that it would match where the tip of the original finger would be. The product itself has a three year life cycle. It is resistant to all chemicals and water and it can be cleaned without any specialist equipment. It is heat resistant and can realistically be used in any environment.

MCP Driver

This is where the amputation is just above the MCP joint (the knuckle nearest the hand), where there is some residual stump remaining. The movement is amplified through the mechanics of the prosthetic finger and once again the ratio of movement is measured and bespoke to the individual. It is a full length finger prosthetic which is attached over the stump, almost like fitting into a glove, and is connected to a support across the back of the hand. The support plate is secured in place with a simple Velcro design. Weight through the digits is distributed across the back of the hand evenly. Generally speaking, it’s about one third weaker than a normal hand but is still more than strong enough and functional enough for most activities of daily living.

This product comes with a five year life cycle. All items, including components and individual fingers, are modular by design. Should any part break, it can easily be replaced by the patient themselves. Maintenance is very straightforward; the joint component is kept tight with a small Allen key and cleaned in the usual way. Failures are rare, but replacement parts can be shipped quickly.

Thumb driver

This works in a very similar way to the MCP, but drives off two joints. There is a function to allow bend and rotation to give a much more natural feel to the prosthetic. It can follow the multi-axial movement of the thumb and it can create opposition to the fingers, to help with increasing grip strength.

There is even the ability to tighten or loosen a small screw at the fingertip to fine tune the tip of the thumb, to grip at different dexterities. PACE are currently the only provider of these devices in the UK. Should a patient be referred, full assessment of functional impairment is measured by specialist prosthetists and occupational therapists, looking at grasp/grip patterns and what can and cannot be done without a device. If the digits are viable, then they look at what function can be gained by adding the “dummy” prosthetic. If they can proceed, they will cost up, take measurements and a cast, and send that off to the US for the device to be produced.

It is a bespoke device and is usually turned around in about eight weeks. Replacement parts, should they be needed, can then be created from that original cast, to save repeat casts being taken. 

Outcome measures are critical in analysing what prosthetic intervention is available. The prosthetist/occupational therapist will look at what stumps are left and what movement/function remains. What can the patient do and what might they be able to do with a suitable prosthetic. The specialists will need to look at the appropriate goals to enable the patient to optimise their own outcome?

Costs

Single PIP with one year warranty

£5,500

4 MCP fingers and a thumb driver with 5 year warranty is around

£31,000

Continual maintenance costs are likely to be approximately £300 per year for each device, for items such as fingertip pads, replacement screws, Velcro straps etc. Of course, we will get a better feel for this with time.

Naked Prosthetics are establishing a formal UK distributor, which is likely to be announced shortly. The UK company are an established distributor of prosthetics in the UK. This will add support within the UK, allowing for technical assistance, after sales support and availability of replacement items at the time of continual maintenance.

At the time of going to print, the first UK fitting/supply of a Naked Prosthetics device had just happened at the PACE facility in Bredbury, Stockport. We understand it was a very successful and emotional fitting!