Direct skeletal fixation of limb prostheses using an intraosseous transcutaneous implant

Limb amputation is traumatic and affects quality of life. Lower-limb amputation (above or below the knee) is the most common reason for a person to use a prosthetic limb (customised prosthesis). The most common reason for lower-limb amputation is peripheral vascular disease. Other causes include trauma, infection, diabetes and cancer. Upper-limb amputations are less common and are mainly a result of trauma. A small proportion of people need prosthetic limbs because of congenital limb loss or deformities.

The customised prosthesis is fitted to replace the function of the missing limb and provide cosmesis for major amputations. The type of prosthesis depends on what part of the limb is missing. Conventionally, the prosthesis is attached to the residual stump by belts and cuffs, suction, or by a suspension system. The conventional prosthesis usually has a socket, which is custom made from a plaster cast of the stump. Every effort is made to ensure people have sockets that fit well and are comfortable. One of the main problems with this type of prosthesis is rubbing between the stump and the socket. This can cause pain, ulceration and improper distribution of body weight that can affect balance and lead to falls. This may mean the user has limited use of the prosthesis or may have to abandon it for a period because of poor fit. For most people a conventional prosthesis is appropriate and well tolerated. But, when a conventional socket prosthesis is unsuitable or causes problems, direct skeletal fixation of limb prostheses using an osseointegrated implant may be an option for some people.

The procedure aims to surgically insert an osseointegrated implant, producing a secure connection between the remaining bone and the implant for prosthetic attachment. The implant may be in 1 piece or modular with a separate small, metal extension (abutment).

The advantages of direct skeletal fixation of an osseointegrated implant are:

• proper transfer of load from the prosthesis to the person's body

• better function and mobility (such as walking)

• improved comfort while sitting

• better balance

• fewer stump problems

• increased prosthesis use, and

• improved quality of life.
  
  The potential problems are:

• soft-tissue infection where the skin and the prosthesis meet

• deep infection

• fracture or loosening around the implant, and

• implant failure.

Direct skeletal fixation of limb prostheses using an osseointegrated implant is done under general or regional anaesthesia (depending on the level of amputation). The procedure can be done all in 1 stage or in 2 stages separated by a period of time. In the first stage, a metallic implant (with either an outer surface threaded like a screw or a press-fit design) is inserted into the medullary cavity of the residual bone. Then healing components are attached to the implant to secure the bone graft during healing. The second stage of the procedure is usually done about 2 to 6 months later, after the implant has integrated into the bone (osseointegration) and the stump wound is completely closed and healed. It involves surgically removing the healing components and re-exposing the distal end of the implant. It is then attached to an abutment with an abutment screw or bridge component. The wound is closed with the abutment penetrating the skin. The external limb prosthesis can then be attached to the osseointegrated implant using various components, depending on the level of amputation.

A period of extensive physiotherapy and rehabilitation follows the procedures, and the load on the prosthesis is gradually increased until full weight-bearing is allowed a few weeks later.