What is a prosthetic reconstruction?
When a part of the body is lost due to injury or disease, it is sometimes possible to reconstruct the missing parts. Whenever possible, plastic surgeons try to use to use the patient’s own tissues for any reconstruction. This is called an autologous reconstruction. But, if the missing parts are too large (e.g. a whole leg or arm) or too complex (e.g. a missing eye), then one alternative is to use an artificial (prosthetic) device to replace the missing parts. This is called prosthetic reconstruction. Almost any part of the body can be replaced with an artificial alternative although the ability of the prosthesis to mimic the function and appearance of the missing part can vary enormously.
How is it performed?
After the patient’s tissues have healed (e.g. amputation stump) the patient is usually referred to a prosthetic center for fitting of an appropriate prosthesis. A conventional prosthesis can be attached to the body in a number of different ways depending on the particular needs of the patient. This includes:
- glue – for smaller prosthetics such as parts of the face, ears, noses and eyes
- spectacles – for parts of the face, eyes and noses
- sockets and straps – for limbs
- osseointegrated bone-anchor – for all types of prosthetics
Each of the different ways of attaching a prosthesis has different advantages and disadvantages. However, using an osseointegrated bone-anchor to attach a prosthesis to the human body is a relatively new method.
What is osseointegration?
Osseointegration is a description for the way in which certain materials are accepted by the bone as part of itself rather than as a foreign body. When this happens, bone will grow right up to or onto the surface of the implant without the formation of an intervening layer of scar or soft-tissue (Figure 1). Once integrated, the implant will not easily loosen and can then be used as a permanent anchorage point fixed in the bone (i.e. a bone-anchor).
Only titanium or titanium containing alloys are known to exhibit this property. It is thought that the bony tissues are actually reacting/fusing with the titanium oxide layer which forms on the surface of the metal implants. A similar effect can be obtained when a metal implant is coated with a bioactive layer such as hydroxyapatite (which mimics bone). Strictly speaking, the surrounding bone fuses with the hydroxyapatite resulting in bio-integration rather than osseointegration but fixation of the implant in the bone will be just as secure.
How can an osseointegrated bone-anchor be used to secure a prosthesis?
Achieving osseointegration or bio-integration of a metal implant in the bone is now a very well understood and reliable process. However, to allow an osseointegrated implant to be useful as a bone-anchor for an external prosthesis, part of the implant must protrude through the overlying skin so that a prosthesis can be secured to it (Figure 2). This is where things become difficult.
Human skin has evolved over many millions of years as a barrier between the external and the internal environment. Whenever that barrier is breached, there is a potential risk for infection. Having a piece of metal protruding permanently through the skin clearly breaches the skin barrier exposing the patient to that increased risk.
Research has been carried out (and still continues) into the best method for reducing the risk of infection with bone-anchored implants. The aim has always been to create a tight seal between the external and internal environments at the junction between the implant and the skin. Currently, there are two ways in which this can be done. The first approach is to thin the soft-tissues so that the skin can become adherent directly to the periosteum of the underlying bone. Alternatively, a skin graft is applied directly to the periosteum of the bone immediately adjacent to the implant. This is the method recommended for use with the Branemark and Southern Implant systems. The second approach is to thin the soft-tissues and then encourage the skin to become adherent to the surface of the implant. This is the method recommended for use with the ITAP system. Both approaches appear to work, but success appears to be partly dependent on the setting (i.e. part of the body). Mr Kang will be able to advise you on the relative merits of each approach and will use whichever method is necessary for the type of implant system which is most suitable for your particular needs.
Which parts of the body can be reconstructed using a bone-anchored implant?
Bone-anchored implants have been used for attaching prostheses to nearly every part of the human body. They have been used in the mouth, the nose, the eye, the ear, the hand, the forearm, the arm and the thigh. They have not been used in the leg, but work is being carried out to see if there are any advantages to bone-anchored implants for below knee amputees. On the other hand, you only need to see how well Oscar Pistorius (the “Blade-Runner”) did in the recent London Olympics to know that a conventional, socket-fitted prosthesis can function amazingly well (for below-knee amputees) without the need for a bone-anchored implant.
When bone-anchors are used for attaching an artificial limb both above elbow or above knee, the advantages appear to be even greater than when used for attaching a static prosthesis (e.g. eye or ear). With a conventional, socket-fitted prosthesis, patients often experience problems with chaffing or ulceration of the skin within the socket or under the straps used to hold the prosthesis in place. The socket is also cumbersome and may even result in a significant restriction in the range of movement. As a result, many conventional upper limb prosthetic users (approximately 80%) stop using their prosthesis within 2 years of being issued with one since the prosthesis often fails to improve function. A similar story can be told for above knee amputees.
Using a bone-anchored prosthesis avoids many of the problems associated with conventional methods of attachment. Direct skeletal attachment of the prosthesis feels much more “natural” for the patient and allows for greater range of movement at the residual joints resulting in greater function. It is also much easier/convenient for patients to attach a prosthesis using a bone-anchor and patients often report being able to “sense” the prosthesis in a way that they are unable to do with a conventional prosthesis. This is referred to as osseoperception.
At the Royal Free, we have experience of inserting bone-anchored implants in the head and neck region and the upper limb. However, we also work with colleagues who have experience of using bone-anchored implants in the lower limb (above knee).
What disadvantages are there with bone-anchored implants?
One problem with all types of bone-anchor is the need to undergo further surgery after the initial surgery to remove the diseased part (e.g. after amputation of a limb). This means having to go through the discomfort of two or three additional procedures before the implant can be used as a bone-anchor.
In addition, there is the ever-present risk of infection at the skin-implant interface. In most cases, patients only experience minor and superficial infections which can be easily treated with oral antibiotics. However, in a few cases, the infections can become more persistent and severe – this may require removal of the implant.
Patients must also put up with a change in appearance of the treated part. There will be a piece of metal protruding from the skin – permanently. Some patients find it difficult to adjust to this change in appearance but most accept it as the price they must pay to achieve their reconstructive goals.
What has been the experience with bone-anchored implants so far?
Every year, many thousands of patients are treated with bone-anchored implants which are used to secure new teeth. Similarly, there are many hundreds of patients who have bone-anchored implants inserted in the head and neck region (but outside the mouth) with excellent results using all the types of bone-anchor which are currently available.
There has been much less experience with the use of bone-anchored implants in the upper limb because there is less demand for this type of surgery. Most of the data on bone-anchored implants in the hand suggest that a two-stage approach is most successful. Worldwide, there have only been a handful of patients who have been treated with bone-anchored implants for forearm and above-elbow amputations. However, the experience with these patients has been almost uniformly positive.
Is surgery to insert osseointegrated implants available on the NHS?
Yes, although approval for funding the procedure may need to be obtained from your local health authority first. Most of the cost of the procedure is associated with the external prosthesis and the annual maintenance needed to ensure that it functions correctly. We also welcome enquiries from patients overseas. However, these patients will need to be self-funding for both their implants and their prostheses.
How can I find out whether I am suitable for this procedure?
If you are interested and would like to be considered for this type of surgery, please ask your GP to send a referral letter to Mr Norbert Kang FRCS(Plast), Department of Plastic Surgery, Royal Free Hospital Pond Street, Hampstead, London NW3 2QG. An out-patient appointment will then be sent to you.