Hip Protector Standards

Background

Hip fractures are an extremely unpleasant injury that can cause considerable pain and often lead to permanent disability. Sometimes they prove fatal. Usually the result of a fall, often at home, they are most common amongst older people. Osteoporosis, which weakens the bones, can make this type of fracture much more likely. 1 in 3 women and 1 in 12 men in the UK will have some degree of osteoporosis over the age of 50. So it is not surprising that around 310,000 fractures connected with osteoporosis will occur each year in the UK. That is one every three minutes or so. And of those, 70,000 will be hip fractures. Around 14,000 people will die each year as a direct result of the hip fractures, with another 28,000 loosing the ability to live independently. With an increasing population, these numbers can only increase.

There are several ways that the likelihood of hip fractures can be reduced. For example, drug therapy and calcium-vitamin D supplements can over time improve bone strength. Even simple things, like removing trailing electric leads and loose carpets in people’s homes can be very effective at reducing the number of falls. A method of providing immediate protection against hip fractures is to use hip protectors. Hip protectors can be very useful for healthcare professionals treating people at risk of hip fractures. They provide protection whilst other methods of fracture prevention are put in place and allow time for them to become effective.

The term hip fracture is in some ways a misnomer. It is actually a fracture of the neck of the femur – the top part of the main leg bone close to the hip joint. And it is to the top of the femur and the hip joint that hip protectors should aim to provide protection. Hip protectors generally take the form of specially-designed underwear garments that include protective shells. They provide impact protection that reduces the impact of a fall on the hip joint.

The idea of using hip protectors has been around for a very long time – but it was not until 1992 that one was designed which was actually shown to work. People had previously thought that placing a metal plate or protective pad over the hip joint would protect against fractures – but unfortunately the physics of the situation was against them. The situation changed in 1993 when Professor Lauritzen published an article in The Lancet. He had worked out the physics and had designed a hip protecting shell that shunted the impact of a fall away from the hip joint – thus avoiding a fracture. Clinical trials showed that they really worked if they were worn.

But all ‘hip protectors’ are not equal and there are many designs of hip protector – but unfortunately only a few have been proven to work by clinical trials. Several designs could, at best, be considered as unproven. Other designs simply could not work, and thus provide a false expectation of protection. The different designs claim to work by very different mechanisms – and clinical evidence generated for one design of hip protector cannot normally be applied to another design. Poorly designed ‘hip protectors’ would not only give people false security, they would also give hip protectors a poor reputation – thus dissuading people from wearing them.

But, unfortunately, there is currently a lack of proven standards and test methods concerning hip protectors. A test method would show if a particular hip protector could provide protection to the hip joint during a fall (although it will not take away the need for clinical trials to prove that a particular hip protector design actually works in practice). It will provide additional assurance that a particular hip protector is likely to be safe and effective. Most of all, it will help ensure that poor and ineffective hip protector designs do not become available on the market – and help ensure that people who wear hip protectors have real protection.

Developing a Standard

Hip fractures, or to be more precise, fractures at or about the neck of the femur, occur most frequently as a result of a sideways fall when the victim lands on their hip. There are a number of factors that will influence the outcome of such a fall. The most significant ones are as follows.

  1. The force of the impact.
  2. The angle of impact.
  3. The nature of the surface on which the victim lands.
  4. Tissue thickness.
  5. Tissue density.
  6. Bone density (brittleness).
  7. Flexibility of the skeletal form.

Of these, the force of the impact is by far the most likely to influence the outcome. Points 2 and 3 are in the hands of fate and outside anyone's influence. Points 4, 5, 6 and 7 will vary from person to person and it has been argued that whilst the flexibility of the skeletal form may influence the extent on the injury once it has occurred, it may not play a great part in causing or preventing the initial injury. Hence of these seven factors, the only one that can be subjected to outside influence is the impact force.

Look for a moment at the two extremes of the other three 'human factors'. A person with a thick layer of dense tissue over a strong bone structure is unlikely to suffer more than severe bruising from a sideways fall. At the other extreme, a person with a thin layer of soft tissue covering brittle bones is likely to suffer a fracture regardless of any external intervention. However, for the vast majority of people who lie between these two extremes, the force of the impact generated as a result of a fall is the most significant factor in determining if they suffer a fracture. Hence it should not take a great leap of faith to believe that anything that can reduce the level of the force that is transmitted to the femur must surely reduce the risk of the person suffering a fracture even though in some cases this reduction may not be sufficient.

This then introduces the role of the hip protector. From the individual's point of view it matters not how the protector achieves the force reduction, only that it reduces it sufficiently to avoid serious injury. This is the approach a test method for hip protectors must take. To analyse not how a product works but how effective it is in reducing impact force and that alone. Whilst the physiological factors will obviously play a part in determining the final clinical outcome of the incident, to allow for them in a basic 'impact reduction' measurement test of a hip protector would only serve to confuse the results.

If a basic test method can be established it may subsequently be possible to use it as a research tool to investigate how these physiological factors, with and without a hip protector, influence residual impact force. This in turn may lead to a more informed selection of product most appropriate to individual patient needs. However, this can only happen if a basic test method can be widely agreed and used. Otherwise researchers will continue to devise their own test methods which may produce interesting results but it will be difficult if not impossible to relate one set to another.

In the early days of such a standard test method it will be risky to establish a pass / fail figure even though this is what manufacturers and users would most wish for. However, it will be obvious that a product that shows a high reduction of force is likely to have a high success rate, Similarly, a product that shows little or no reduction is unlikely to offer any protection at all. If this can be achieved it would be a major step forward and is long overdue.