Functional Prostheses can be divided into two categories: (1) Body-powered prostheses Body-powered prostheses (cables) usually are of moderate cost and weight. They are the most durable prostheses and have higher sensory feedback. However, body-powered prostheses are less cosmetically pleasing than a myoelectric unit, and they require more gross limb movement. A body-powered prosthesis, sometimes called a conventional prosthesis, is powered and controlled by gross body movements. These movements, usually of the shoulder, upper arm, or chest are captured by a harness system which is attached to a cable that is connected to a terminal device (hook or hand). For some levels of amputation or deficiency an elbow system can be added to provide the patient additional function. REQUIREMENTS: For a patient to be able to control a body-powered prosthesis he or she must possess at least one or more of the following gross body movements: Glenohumeral flexion Scapular abduction or adduction Shoulder depression and elevation Chest expansion Also necessary are: Sufficient residual limb length Sufficient musculature Sufficient range of motion ADVANTAGES: Due to it’s simple design, this type of prosthesis is highly durable and can be used for tasks that involve water and dust and in other potentially damaging environments. Many patients who wear a body-powered prosthesis comment that they have increased control due to proprioception. Proprioception gives the wearer feedback as to the position of the terminal device. A wearer will know, for example, if the hook is open or closed by how much pressure the harness is exerting on his or her shoulder area without having to look at the terminal device. There is also a reduced maintenance cost for a body-powered prosthesis as most repairs are related to broken control cables, replacement harnesses, and realignment of terminal devices. These types of repairs are all fairly economical when compared to other prosthetic options such as electrically-powered prostheses. DISADVANTAGES: The most common complaint that wearers of this type of prosthesis note is the uncomfortable and restrictive control harness. Although new materials aid in reducing discomfort, the harness must be tight in order to capture the movement of the shoulder and suspend the prosthesis. The tight harness can also restrict range of motion and the functional envelope (the area in space where the patient can control his or her prosthesis). For many, the functional envelope, when wearing a body-powered prosthesis, is limited to directly in front of them from waist level to mouth level . Significant control reduction occurs when attempting to operate the prosthesis out to the side, down by the feet, and above the head. Other patients dislike the look of the hook and control cables and request a prosthesis that is more "lifelike". Myoelectric prostheses Prostheses operated by myoelectricity may give more proximal function and increased cosmesis, but they can be heavy and expensive. They have less sensory feedback and require more maintenance. Myoelectric control uses the electrical signals generated by muscle contraction as the control input for a prosthesis controller. (2) They function by transmitting electrical activity that the surface electrodes on the residual limb muscles detect to the electric motor. Two types of myoelectric units exist. The 2-site/2-function device has separate electrodes for flexion and extension. The 1-site/2-function device has one electrode for both flexion and extension. The patient uses muscle contractions of different strengths to differentiate between flexion and extension. For example, a strong contraction opens the device, and a weak contraction closes it. (UTAH ARM) HOW ARE THE PROSTHESES ATTACHED? CINEPLASTY (body powered, myoelectric) Cineplasty is the surgical isolation of a loop of muscle of chest or arm, covering it with skin, and attaching to it a prosthetic device to be operated by contraction of the muscle in the loop. (3) Tunnel cineplasty is a variation of this surgical technique, which attaches muscle in the residual limb to the prosthesis. While no longer popular, newer cineplasty methods have the potential to provide excellent sensory feedback and control for the prosthesis wearer. It is similar to osseointegrated fixtures in that the body is working on direct attachments. How was it developed? Tunnel cineplasty was developed initially by German surgeon Ernst Ferdinand Sauerbruch, before World War I, based on earlier work in Italy. With the use of a team approach to rehabilitation--surgeon, physiologist, and technician working together--tunnels were constructed in the muscles of the residual limb and lined with skin grafts. Connecting pins inserted into the skin-lined tunnels allowed the force of the muscles to travel directly to the prosthesis. There were several stages in the evolution of this method, including the biceps tunnel cineplasty developed by surgeon M. Lebsche, a student of Sauerbruch. This procedure was performed on many veterans after World War II. With a biceps tunnel, when the muscle is relaxed, the hand is open. When the muscle is contracted, the hand is closed and the force in the fingers is proportional to the force in the muscle. This method allows for sensory feedback, a useful property. Although tunnel cineplasty fell out of favor by the 1970s, partly because of several cases in which the procedure failed to transfer sufficient muscle power to the prosthesis, more recent versions of the procedure have addressed this issue. The technique developed by Dr. Robert Beasely, called "tendon exteriorization," enables muscles and tendons to be hooked up to external controllers that basically multiply the power to the prosthesis, while still preserving the same degree of control. Today, development of high forces in the muscle and forearm is not necessary, since low forces can suffice; a control system can be used to transduce low forces into high forces. Current application: The use of external power sources for the prosthesis has enabled smaller cineplasties to be performed. This, in turn, creates the possibility of multiple cineplasties in a group of muscles, e.g., the forearm, to create a greater degree of control in the fingers of an artificial hand. (4) Attaching the externalized muscle to a prosthetic component through a controller that embodies the concept of extended physiological proprioception (EPP) allows the position, speed, and force of the controlling muscle to be directly correlated (in a one-to-one manner) to the position, speed, and force of the prosthetic component. The physiological sensory feedback inherent in the skin and muscle of the cineplasty informs the user of the state of the prosthesis in a somewhat subconscious and natural manner. Using the cineplastized muscle as a control input to an EPP controller provides a method of physically linking a skeletal muscle to an externally powered device. In the case of an electrically powered prosthetic device, the cineplasty is only required to produce a control signal; the power needed to drive the prosthesis itself comes from the batteries. In addition, the controller is flexible enough to be adjusted to accept, as its control input, the range of force and excursion available from the amputee's cineplastized muscle. In essence, this idea of extended physiological proprioception (EPP) control of a prosthesis can be compared to power steering for a car. This means that even small muscles of the forearm or hand could be used effectively for prosthesis control. (5) COOL VIDEO: http://www.hbi.dmr.or.ir/movies/movie/cineplasty.mpeg What the future in cineplasty may hold: With the creation of control interfaces surgical revisions beyond the initial amputation surgery will need to be made. Preservation of residual muscle tone, length, and excursion will be of utmost importance if future revisions are to be successful at creating novel physical, muscle-prosthesis interfaces. Weir et al. suggest the use of Myoplasty and/or myodesis at the time of initial amputation surgery to aid the retention of residual musculature to easily develop tension and reduce associated muscle atrophy. In myoplasty, agonist-antagonist residual muscle pairs are tied off against each other. In myodesis, the residual muscle is stitched to the bone. Myoplasty could be performed on the superficial residual muscles while myodesis could be used on the deep residual muscles. [Weir et al.] OSSEOINTEGRATION (future of cosmetic prostheses) Osseointegration is the permanent incorporation of a non-biological component to carry unlimited functional load in endoprosthetic and exoprosthetic replacement of structure and function. (6) In this procedure, a direct skeletal attachment is made to the prosthetic limb. (7) Through series of tempering processes the titanium is machined to have threads much like a screw. Over time the bone tissue will grow in between the threads forming a strong, tight bond that doesn’t allow for any movement. (8) By connecting the prosthesis directly to the bone, the need for weight bearing through prosthetic sockets is eliminated. (9) Should this concept prove successful over the long-term, it could eliminate many of the inherent difficulties of wearing a socket to connect prosthesis to residual limb possible outcome. (10) Why is it applied? Often the contact between the soft tissue on the limb and the prosthetic attachment can cause problems such as blisters, cyst, edema, and other skin irritations. Another common problem is that the weight load on prosthetic limb can be painful and restrict blood flow limiting the use or time the patient can be mobile. To a lesser extent the straps and belts that hold the prosthetic limb on can be uncomfortable and a hassle. (11) How it works: During the original amputation or during a revision to prepare the patient for osseointegration, a surgeon exposes the ulna, and installs a titanium implant, which is like a bolt that's inserted into the cavity of the bone. After six months, during which time the living bone cells attach themselves firmly to the surface of the titanium, the second stage of the surgery exposes the end of the ulna and the head of the implant and connects that to another titanium component, called an abutment, which then comes through the skin and through the end of the patient's stump. The limb can then be attached to the abutment with a wrench. Since the titanium abutment permanently pierces the skin, the danger of infection is always present. In fact, infection seems to be the chief complication, although the literature reports that most can be effectively treated with antibiotics. It is safe to assume that the osseointegrated patient must make an effort to keep that area clean. There is no feeling of increased weight, no lack of positive prosthesis control, no increase in energy consumption to operate the prosthesis, no need to bear weight on other parts of the body, no fitting problems due to weight gain or loss, no socket induced skin irritation, and no problems donning and doffing the prosthesis. Currently, osseointegration is not performed in the US. Where it is performed, generally only younger unilateral amputees who can't be successfully fitted by conventional means are considered. Moreover they must have a sound bone in the residual limb, not have systemic diseases, such as diabetes or peripheral vascular disease, and not be smokers. This technique is still considered experimental and the amputees who are accepted for osseointegration are considered experimental subjects. (13) References: (1) http://www.utaharm.com/ (2) http://www-cdr.stanford.edu/Touch/workshop/private/drafts/weir.html (3) http://www.egrmc.com/glossary/index.php?letter=c (4) http://www.vard.org/jour/02/39/3/sup/Childress.htm (5) http://www.vard.org/jour/01/38/4/weir384.htm (6) http://www.ele.uri.edu/Courses/ele382/F02/DanK1.pdf (7) http://www.orthopedictechreview.com/issues/janfeb02/pg36.htm (8) http://www.ele.uri.edu/Courses/ele382/F02/DanK1.pdf (9) http://www.orthopedictechreview.com/issues/janfeb02/pg36.htm (10) http://www.llop.com/images/LeTourneau.pdf (11) http://www.ele.uri.edu/Courses/ele382/F02/DanK1.pdf (12) http://www.amputee-coalition.org/communicator/vol2no3pg4.html (13) http://www.amputee-coalition.org/communicator/vol2no3pg4.html