Professor Branemark and his team from Sweden are credited for the discovery and first successful limb osseointegration on May 15, 1990. Osseointegration is a surgical procedure that is carried out as an alternative means of connecting a prosthetic arm to the amputee’s residual limb. The procedure is especially beneficial for the amputees who face issues in using a prosthesis with a socket as it eliminates the need for a socket for suspending the prosthesis. The procedure consists of surgically inserting a metal implant (titanium fixture) to function as an anchor, into the bone of the residual limb that penetrates and enters through the skin. A transcutaneous connector is attached to the implant that has a metallic extension, also known as an abutment through which the prosthetic arm is directly attached to the residual limb.
Such a prosthesis is also referred to as a bone-anchored prosthesis that successfully eliminates all the problems associated with the use of a socket, such as sweating, pinching, displacement of the prosthesis, nerve pain, heat entrapment, and skin irritation. Sockets often restrict the ROM and many amputees are uncomfortable due to the harness systems used with conventional socket prosthesis. Therefore, in such situations, bone-anchored prosthesis attached via osseointegration is a viable and effective option as they allow natural shoulder and arm motions, without a harness system. The osseointegrated implants can also be used in conjunction with bionic arms that utilize EMG signals from the residual limb to control and operate prosthetic components. Often, targeted muscle reinnervation (TMR) is also done to enhance the strength of the EMG signals.
Bone anchored prostheses are commonly indicated for amputees with appropriate bone quality and strength, facing difficulties in fitment and use of conventional prosthesis with no reported disabilities or ongoing treatment processes such as chemotherapy or immunosuppressive therapies. Other contraindications include patients with diabetes mellitus, peripheral vascular diseases, geriatric patients over the age of 70, pregnant women, skeletally immature patients and patients with compliance problems due to physical or psychological limitations.
Advantages of osseointegration and bone-anchored prosthetic arms -
Osseoperception – The major benefit of osseointegration is osseoperception, whereby the prosthesis feels like it is a part of the amputee’s body. This is believed to be due to the stimulation of mechanoreceptors in the residual limb that sends feedback to the central nervous system, allowing the patient to passively perceive the position and functioning of the prosthetic arm. Some researchers believe that this sensory feedback may also be due to the reinnervation of the residual bone.
Amputees using conventional type prostheses with sockets often have weak bones due to disuse osteoporosis because of inactive muscles and absence of loading on the residual bone. Studies have reported that the following osseointegration, the residual limb bone regain their strength due to muscle reactivation and restoration of loads on the bone.
Osseoperception further improves the amputee’s quality of life and helps the amputee to regularly use their prosthesis with ease, which may not have been possible with socket prostheses.
Bone anchored prostheses also prevent fluctuations in residual limb volume, the formation of neuromas, and phantom limb sensations that are often noted in patients using sockets. To resolve these issues, bone-anchored prostheses can be used along with different procedures like osseointegration, TMR, and RPNI (regenerative peripheral nerve interfacing).
The direct attachment of the prosthetic arm to the residual limb also offers various other advantages for the user such as prosthetic stability, easy donning doffing, increased use of the prosthesis, improved sensations, and control, and a greater range of motion.
Drawbacks associated with osseointegration and bone-anchored prosthetic arms -
Osseointegration increases the risk of infections of the skin and deep tissue structures.
There is an associated risk of peri-prosthetic fractures due to osseointegration that may further necessitate proximal amputations.
The area of skin penetration needs to be cleaned with water and soap daily to prevent infections.
The recovery period following the surgery is long with associated muscular pain for at least a year.
Increased risk of bending or breaking of the abutment.
Osseointegration and Upper Extremity Prosthetics
With respect to the upper limb, osseointegration has successfully been carried out for amputations at the transhumeral, transradial levels as well as for thumb amputations. There are specially designed systems and components available for different amputation levels. For instance, the attachment devices for transhumeral and transradial levels are available in 2 different sizes and consist of a lightweight, quick-locking-unlocking mechanism whereas for thumb amputations, only 1 size is available. Where required, a shock absorber is also used to prevent impact on the osseointegration system. When the systems are used with bionic arms, they incorporate flexible bars that hold the electrodes in place. For protecting the abutment when the prosthetic arm is off, a distal cap is incorporated to cover the exposed components.
