Anatomically contoured socket design involves far more than simply matching the volume and surface shapes of the residual limb. Volume and surface shape are indeed important considerations in this amputation level because of the large tissue to bone ratio. However, merely containing the tissue is insufficient to create a really useful foundation for a prosthesis. One must make every attempt to grab the boney structures to achieve the greatest amount of stability and control. Since this is achieved through the soft tissue envelope, contouring must be smooth and transition gradually.
Direct skeletal attachment for the upper limb has not yet been perfected. Subsequently, the practitioner must work to create dynamic stability of prosthesis by using the remaining anatomy. This is the science and the art of prosthetics.
Many of the socket designs discussed herein are not new. Variations of these have been taught over the years in schools of prosthetics. Each has had many different incarnations across literally generations of practitioners. The human body has not changed. Materials, components, technology, surgical techniques, and understanding of anatomy and physiology have advanced greatly.
Many of the techniques used in modern prosthetics have been innovated and successively modified by practitioners over the years, in response to particular problems exhibited by their patients. Necessity is indeed the mother of invention. Prosthetists are necessarily inventors, often conceiving unique ideas that can make an individual's life better.
The human body is a dynamic organic system. When an extremity of that body is amputated, a cascade of events takes place that impacts the already changeable system. Muscles may be moved and repositioned. Nerves are cut and may become entrapped in scar tissues or grow neuromas in troublesome spots. Bones are exposed, cut, and can continue to be induced to grow because of pressures and other forces acting upon them within the prosthetic socket.
Although the amputation site has a certain volume and shape to begin with, changes occur as the body heals and reaches a kind of stability. Amputation of the upper limb at the level of the elbow or higher, leaves an unstable mass of soft tissue that must be contained, supported comfortably, and yet must still somehow be used as a foundation for the suspension, stability, and dynamics of the prosthesis that is attached.
PARAMETERS OF TRANSHUMERAL AND ELBOW DISARTICULATION SOCKET DESIGN
From a socket design perspective, practitioners consider comfort, suspension, rotational control, stability, prosthesis activation, length, and aesthetics. This article discusses several anatomically contoured socket designs that make aggressive use of the remnant anatomy to achieve stability, function, comfort, and suspension.
Amputation at the level of elbow disarticulation is performed for a variety of reasons. The primary rationale being that this can be a less disruptive procedure since the surgery is through a joint and therefore creates less disruption of the bone and tissue. However, there are significant mechanical and cosmetic problems with fitting a prosthesis to this level of amputation.
This level of amputation provides a very long lever arm for excellent cable control as well as the possibility of capturing humeral rotation. The oval shape at the end of the limb, when it can be captured, provides excellent rotational control and a lower proximal trim line. This is particularly important for accurate placement of the terminal device especially in the position of shoulder abduction. An added benefit is the extra length and rotational control limits the natural momentum of the laterally moving forearm as the humerus positions the prosthesis.
Elbow disarticulation requires either the use of outside locking hinges or placement of the prosthetic elbow distal to the normal anatomical placement of the elbow. Either option may lead to significant functional and cosmetic problems since the natural proportions of the arm are disturbed.
A disadvantage in the use of outside locking hinges is that greater width is created at the elbow, which may not be cosmetically acceptable. Furthermore, the locks used with these hinges are not as durable as standard prosthetic elbows and they make adding a lift assist difficult. The choices are limited at this level of amputation requiring the selection between less desirable alternatives. The case studies below illustrate these problems and offer some unique solutions. These include ways to provide forearm lift assist or eliminate the outside joints altogether.
SUSPENSION SYSTEMS—SUPRACONDYLAR SUSPENSION
When present, the width and length of fully formed condyles must be accommodated in the socket. The shape and pressure tolerance of the epicondyles will determine the optimal design for the elbow disarticulation level of amputation. Several test sockets may be required to optimize the design.
The elbow disarticulation socket can provide suspension from the flair at the distal end of the limb. The use of the epicondyles for suspension requires that they are nontender and well shaped. The widest portion of the epicondyles must pass into the socket and then somehow be “locked” in place.
Common designs used to provide suspension and comfort include
- The windowed socket: A removable door or window in the socket can be used to allow the epicondyles to pass down into the lower part of the socket. A window, without the addition of a door, will lose any suspension possibilities. Closing the window with a door achieves suspension but adds bulk, making it less cosmetic (Figure 1).
- The screw-in socket: A spiral opening or channel can allow the epicondyles to lock into, or screw into, the distal end with less bulk than the window with a door but is much more difficult to design for comfort (Figure 2).
- Flexible wall socket types: Flexible wall sockets can often be used to provide entry and suspension at this level.
- Inserts and soft liners: By using a soft insert with accommodations for the epicondyles, a comfortable fit can be obtained. This design provides good protection of the skin over boney areas but has the disadvantage of requiring a large cylindrical socket that can be uncosmetic.
Typically, the elbow disarticulation prosthesis requires a harness to provide body-powered control and often auxiliary suspension. Two of the following cases illustrate methods that possibly eliminate or minimize the need for a harness. An interesting lift assist is also illustrated.
ELBOW DISARTICULATION: CASE 1—VS
There are length problems associated with the elbow disarticulation or long transhumeral level amputation when complicated by excessive distal redundant tissue. This case study illustrates how ongoing surgical follow-up can improve function.
VS, at the start of care, was a 24-year-old male laborer, who was injured in a conveyer belt accident on the job. He sustained a crushing injury to his left arm that resulted in an elbow disarticulation length amputation.
His limb was surgically closed but had significant distal redundant tissue and scarring from the skin trauma. Because of the excess tissue his muscle stabilization was not ideal with significant pain upon muscle contraction. He had good glenohumeral and scapular range of motion (ROM) with good shoulder strength (Figure 3A).
The humeral length on his residual limb was nearly equal to the contralateral limb. However, the soft tissue length measured 2.5 cm (1 inch) longer than his sound-side length, due to the redundant tissue.
He was seen for prosthetic care 8 weeks postamputation and was not yet completely healed because of skin trauma. He was provided with an elastic shrinker to facilitate limb shaping and support for the distal tissues, which were painful when unsupported.
Because of insurance delays, his fitting could not begin until 10 weeks after his amputation. He was well healed at that time but still had moderate pain complaints.
Because of the excessive residual limb length, the prosthesis was constructed using outside locking hinges, a total contact laminated socket, figure of eight harness, a voluntary opening hand, and interchangeable voluntary opening aluminum split hook (Figure 3B).
After therapy, he was able to use the prosthesis but pain in his residual limb from neuromas and scar tissue made the prosthesis uncomfortable. He elected to undergo revision surgery to reduce the excessive distal tissue, stabilize the muscles, remove the scar tissue, and remove the painful neuromas. The surgeon removed 7.5 cm (3 inches) of excess soft tissue and bone from the distal end of his limb and performed a myoplasty to stabilize the muscles.
He received a new prosthesis 2 months later, with a conventional locking elbow and a chest strap harness to reduce pressure on the sound side axilla from the harness (Figure 3C). This prosthesis included a roll-on suspension liner to further reduce the harness forces. Eleven months postinjury, a new prescription was written for a new prosthesis to eliminate the ongoing irritation from the harness and to provide greater terminal device grip than available using the body-powered device. The myoplasty resulted in better comfort when using the residual limb muscles. He received a myoelectrically controlled prosthesis with powered elbow, hand, and hook. Unfortunately, this patient moved out of the country and was lost to follow-up (Figure 3D).
ELBOW DISARTICULATION: CASE 2—THE PURPLE ARM
A 10-year-old boy with acquired elbow disarticulation amputation of left arm as a result of a lawn mower accident at 3 years of age. This young man has been fit in the past with a conventional socket and mechanical componentry including figure 8 harness, outside locking hinges, voluntary-opening hook and fair-lead control cable.
The patient lists his dislikes as:
- Dislikes harness—too tight.
- Dislikes hook—looks funny and will not grip the way he wants it to.
- Dislikes cable—takes too much thinking and effort to pull on it.
- Dislikes the way the elbow locks—requires coordination using harness and cables.
Although nearly every amputee at this level or higher might express similar feelings, in this individual's case the total dislikes added up to not finding the prosthesis useful.
A prosthesis was created that addressed each of the issues with which the patient had expressed concern. The device included a Variety Ability Systems Incorporated electric hand that was myoelectrically controlled via a single electrode. This eliminated the need for a cable and cable control harness to control the terminal device. Next, an Otto Bock ball-and-socket, friction wrist provided a large ROM for positioning the hand (Figure 4A). Custom installation of an Otto Bock Automatic Forearm Balance (AFB) automatically lifted the forearm and eliminated the need for a control cable and control harness to position the forearm (Figure 4B). Otto Bock Ratchet Joints instead of outside locking hinges allowed the elbow to lock against extension automatically via the combination of the AFB and Ratchet joints. This eliminated the need for a cable and harness to achieve elbow locking. This joint selection provided a more streamlined installation than would standard outside joints with a cable actuated locking mechanism.
Finally, suspension was achieved via a custom laminated silicone liner with integral Velcro lanyard. The lanyard was fished out through a hole in the bottom front of the socket and fastened to a Velcro strip running vertically along the front of the socket providing sufficient suspension to eliminate the need for a harness.
This design achieved a completely self-suspended prosthesis that eliminated his complaints. The prosthesis was myoelectrically controlled, eliminating need for control cable and control harness. The “Ballistic” control of elbow flexion, and the outside ratchet locks eliminate the need for lock/unlock control cable and harness with the additional benefit of less bulk.
This strategy has been utilized on several more occasions for adults with long transhumeral or elbow disarticulation level amputations who also prefer to minimize control cables and harnesses (Figure 4C).
ELBOW DISARTICULATION: CASE 3—EB
This case illustrates a method for anatomical control of an elbow disarticulation in which the oval distal end is too hypersensitive to use for suspension and rotational control.
EB is a 58-year-old professional woman who suffered quadramembral amputation as a result of systemic infection secondary to a bout of pneumonia. The infection left her with right transradial, left elbow disarticulation, right transtibial, and left knee disarticulation amputations.
She is small in stature such that the amount of excursion available for cable control for both upper limbs was insufficient. As a county-elected official, aesthetics were of great importance to her, although function was paramount. By using a self-suspending (Sauter ¾ socket1), myoelectrically controlled prosthesis on the right side, it was possible to eliminate the need for a control harness and cable.
After successfully fitting both lower limbs and her right transradial extremity, several approaches were investigated for the left elbow disarticulation. Hypersensitivity of the lateral epicondyle and the distal humeral structure precluded the use of the boney anatomy for suspension and, to a large extent, rotational control. Attempts to do so resulted in considerable discomfort and dissatisfaction.
A great deal of creativity was involved in designing a socket and control system for the left elbow disarticulation to achieve suspension and dynamic control whilst eliminating or minimizing the need for a harness.
The initial prosthesis utilized a frame style socket. Suspension was provided with a silicone suction socket and distal ratchet locking mechanism. Because of the sensitivity of the distal bony structures the distal contours could not be utilized to adequately provide rotational stability of the prosthesis.
Initially, no elbow was installed; instead, a ball-and-socket wrist was positioned 45° to the axis of the humerus and internally rotated about 45° (at about a 2 o'clock position as viewed from patient perspective). The electric hand could then be positioned in a 45° cone (Figure 5A).
A new socket was designed that incorporated rotational control via a compressed anterior/posterior dimension about the shoulder, as described by Andrew.2 The humerus was stabilized by flattening the anterior and posterior walls of the socket from mid-humerus to just superior to the hypersensitive distal end. The result enhanced flexion and extension control of the prosthesis (Figure 5B).
A custom silicone liner was used to cushion the sensitive distal end and lateral epicondyle. With incorporated buttons that snap into the frame when donned, the liner afforded suspension (Figure 5C).
The final prosthesis integrates outside ratchet joints, an AFB, and electric hand with ball-and-socket wrist as described above in case 2.
THE TRANSHUMERAL AMPUTEE—SOCKET SHAPES
Although the true elbow disarticulation may have a flattened, “screwdriver” shape with which to control rotation and epicondyles to provide suspension, the transhumeral level does not have this advantage. In addition, as discussed in case 1 above, there can be a greater soft tissue envelope surrounding the transected humerus, making both rotation and translational control of the prosthesis challenging.
MODIFICATIONS TO ANATOMICAL STRUCTURES
Over the years, there have been attempts made through surgical means to achieve these ends. Marquardt3, Witso4 and others, have performed surgical techniques to enhance the boney structure or change the contour and shape of the remnant arm with implants to gain additional control of the prosthetic socket. These techniques, while successful in many instances carry the inherent risks of surgery, including a longer recuperation time. This can further delay prosthetic fitting.
Branemark et al.5 has had success with osseointegration of a threaded implant, screwed into the medullary cavity of the bone. After about 6 months, the implant has integrated to the bone and an abutment, or pin, is inserted into the implant through the skin at the distal end of the residual limb. The prosthesis attaches to the mechanism by clamping onto this pin. This technique has been used primarily on transfemoral amputees. Such a direct skeletal attachment in the transhumeral level amputee has been clinically demonstrated, although further development is necessary before this will be a viable alternative for this type of amputation.
Without surgical intervention to provide either rotational control or direct skeletal fixation, the socket and prosthesis must be stabilized in another way. Before the early 1980s, a harness and stump socks were commonly used for suspension and rotational control. The negative aspects of a harness can include discomfort, frustration or difficulty in donning, restriction in ROM, and contralateral brachial plexus pressure potentially leading to neuropathy in the sound hand. A self-suspending socket eliminates or reduces the pressure applied by the harness.
McLaurin and Sauter6, reported on fabrication procedures for the open-shoulder above-elbow socket. They describe a socket design for transhumeral level amputations in which unnecessary parts of the socket were eliminated; specifically, the acromial cap. The advantages stated included reduced bulk, less plastic in contact with the skin, and superior stability and mobility (Figure 6A).
The key features presented were an “axillary yoke” for stabilization of the proximal end, and the “distal ring” for stabilization of the distal end of the residual limb. The rest of the socket was needed for structural integrity only. A harness design was recommended for this socket design as well (Figure 6B). Pentland and Wasilief7 endorsed a similar proximal brim design in a paper relating to their experience with total suction, trans-humeral socket suspension.
Dynamic stability related to transhumeral amputation is an important concept discussed by Andrew and coworkers8 after developing the fitting techniques appropriate for use with the Utah Artificial Arm and other myoelectrically controlled elbows. Control of an electric elbow using electrodes integrated into the prosthetic socket requires intimate contact with the skin. Typical sockets for body-powered prostheses used stump socks and harnessing to maintain fit and stability. Providing a close coupling of the residual limb (humeral motion) and the prosthesis is a fundamental goal and has been taught in prosthetics schools for decades. In fact, this is critical to the function of a body-powered prosthesis where any lost motion significantly limits the function of the prosthesis due to loss of potential cable excursion. In an externally powered prosthesis, without the socks, more aggressive anatomical contouring of the socket is needed to provide stability and control.
The authors define dynamic stability as the response of the prosthesis to the subtle movements of the residual limb as it acts upon it from within the confines of the socket. The goal of dynamic stability is to link the prosthesis to the user so that humeral motions cause prosthesis motion, with minimal lost motion, and external moments are counteracted in a similar way through socket stability features. If achieved, along with effective suspension, the amputee may feel that the prosthesis is more a part of his body.
The “Utah Dynamic Socket technique” for transhumeral design as an outgrowth of the previously cited work by Pentland.7 The efforts of McLaurin and Sauter6 also precede this anatomically directed socket design.
The critical features of the “Utah Dynamic Socket technique” include:
- An abbreviated lateral trim line;
- A firmly compressed anterior-posterior (AP) dimension for rotational control along the humeral axis. This is achieved by gripping the boney and muscular anatomy of the shoulder over the scapula and molding smoothly into the delto-pectoral area, excluding the humeral head and coracoid process.
- A compressed medial-lateral (ML) dimension at the level of the axilla for control of the humerus in abduction. Proper shape of the medial and lateral walls combined with firm compression in this dimension prevents socket instability, such as cantilevering on the distal end of the humerus, proximal lateral trim line gapping, and proximal medial pressure. A socket with an appropriately compressed ML will allow the weight of the prosthesis to be borne along the entire shaft of the humerus when in abduction.
- By compressing the ML dimension, the soft tissue envelope is displaced forward and backward in the mid and distal AP dimension. In the case of a firm residual limb, the tension on this tissue may be sufficient to create enough humeral support to provide stability for prosthesis motion and/or cable control as the shoulder is flexed. Such control with a “wide” AP dimension is usually only effective with “firm” and some “medium” tissue types (Figure 7).
The most difficult fitting is often with a soft remnant limb or one that has experienced considerable atrophy. There is often anterior and posterior motion of the humerus within the tissue envelope despite the compression described above. Clinical success has been achieved using a design variant that Andrew refers to as a “humeral AP clasp.” The humeral AP clasp, as described here, is a more aggressive attempt to control the humerus. It can be envisioned as a wedge shaped cross-section in the midsection of the socket. The humeral shaft lies in the angle of the wedge. Flattening lateral aspect of the anterior and posterior socket walls creates the sides of the wedge. More aggressively, the walls can be concave. The benefit of this modification is that the humerus is exposed to the inner surface of the socket with a minimum of soft tissue covering. In this manner, motion of the bone is almost immediately transmitted to the socket enhancing position control of the prosthesis during glenohumeral flexion and abduction (Figure 8A). It is particularly achievable when the residual limb has experienced sufficient atrophy that the shaft of the humerus can be intimately gripped (Figure 8B). Case 2 below is an excellent example of this contoured shape.
A third benefit from a compressed ML dimension occurs in the case of a remnant limb with some soft tissue but with a poorly padded distal end. The compressed tissue, besides being compressed to the anterior and posterior as described above, also gets pushed distally. Two and a half decades of clinical experience has demonstrated that potential distal end problems that might occur due to a boney distal end can be cushioned in this manner.
The Utah Dynamic Socket technique has been clinically shown to be effective for both body-powered and externally powered implementations as well as suction suspension techniques, with and without liners.
Socket materials and fabrication have changed over the years from leather and wood, to rigid polyester laminates, to flexible thermoplastics, and composite reinforced frames. Innovations in silicone techniques are available to create a complete socket. This provides a gradual transition from rigid to flexible. This flexibility gradient may be more compatible with the living skin and tissues and can provide suspension as well (Uellendahl et al9).
Harnesses are still necessary, particularly in the case of body-powered systems that require control of forearm and terminal device. Anatomically contoured sockets can assist with suspension as well as control.
Transhumeral sockets suspended via passive, pull-in suction continue to be a useful suspension technique as long as patient volume is stable.2,7
Currently, elevated vacuum suspension techniques, originally designed for lower limb applications, are finding their way into the upper limb armamentarium. In one method, a vacuum chamber can be incorporated into the socket and evacuated with a hand pump. As vacuum pump technology becomes more miniaturized, another possibility is to employ an electric pump.
Roll-on suction liner suspension is becoming mainstream in the transhumeral level of amputation. Although miniaturization of lock hardware requires further development by manufacturers, roll-on suction liners can be mechanically linked to the prosthetic socket/frame via Velcro or string lanyards. In a more limited application a pin lock can be utilized. The pin lock works best if the residuum is quite firm or boney. A soft residuum may not provide sufficient tension on the pin to prevent it from being pushed backwards into the tissue of the limb rather than down into the receiver. Alternatively, a drawdown shuttle can be used.
Daly10 described a technique for use of roll-on suction sleeves with myoelectrically controlled transhumeral prostheses. Improvements are still needed in electrical communication through the liner from skin surface to preamplifier. Although snap electrodes allow easy roll-on of the liner, wires must still be exposed and dealt with after being snapped into place when the socket is donned. Ideally, a conductive pathway through the silicone or wireless transmission of the signal would be available. A prototype conductive pathway, produced by Liberating Technologies, Inc., is currently undergoing limited clinical trials.
TRANSHUMERAL CASE EXAMPLES
CASE 1—PATIENT DK
DK is a 35-year-old rancher who suffered a left transhumeral amputation as the result of a systemic infection. He was fit initially with a “hybrid” preparatory prosthesis consisting of a Utah Dynamic Socket, flexible inner socket with rigid outer frame, suction suspension, Utah “Happy-V” harness, Otto Bock Ergo elbow, a myoelectrically controlled wrist and terminal devices. Follow up was approximately every 3 weeks, because of the distance from his home. Each visit was arranged around doctor visits and occupational therapy sessions.
After using this hybrid prosthesis for about 60 days in his own environment, he was very discouraged. His main complaint was that despite the rotational control of the Utah Dynamic Socket, the length of the forearm amplified the momentum of any movement such that he was unable to accurately position the terminal device. This was exceedingly frustrating for him.
After discussing his concerns, an elbow-less prosthesis in which the electric TD is positioned very close to the end of the residual limb was created (Figure 9A). A short module carrying the electric wrist rotator was attached to a locking, flexion wrist unit embedded in the distal end of the socket. The standard Otto Bock wrist coupling system was incorporated into the other end of this module, creating a mini-forearm that had about 30 degrees of flexion. Suspension was via a silicone suction suspension sleeve connected to the prosthesis via a Velcro lanyard (Figure 9B).
With the new socket design, most of the mass was kept proximal. Accurate placement of the terminal device was greatly improved. Patient satisfaction was significantly increased. DK stated, “This is fantastic!” Although the final prosthesis was only somewhat lighter than the original, it was much more controllable. As can be seen in Figure 9C, the patient has amazing ROM and dexterity without the need for a suspension harness.
CASE 2—PATIENT JN
JN is a 52-year-old miner, blaster, and rancher. Following a work-related injury in which his left arm was caught in a steam-powered drill, JN suffered a left transhumeral amputation with a residual length of approximately 4 inches (as measured from the axilla). The right leg was also severely damaged and was subsequently amputated about 1 year later.
Before the injury, he was a very active individual and his passion was horses and team roping. JN stated that the loss of an arm and a leg was only tragic if he were unable to ever rope or ride again. In addition to the typical demands of any prosthetic device, JN insisted that the prostheses must assist him to continue to rope and ride (Figure 10A–C).
His first prosthesis was a body-powered device incorporating a Utah Dynamic transhumeral socket, a silicone suction liner with pin lock suspension, Otto Bock Ergo Elbow, two flexion wrist units and a Model 6 locking Farmer's hook. The two flexion wrists are a little unusual. In this case, a Sierra Flexion unit is screwed into the flexion wrist embedded in the forearm. It flexes in a plane perpendicular to the other allowing additional ROM for all his activities of daily living. JN is an amazingly active individual and the added adjustability is essential for his activities on the ranch. The injection-molded forearm of the Ergo elbow became damaged within the first month and was subsequently reinforced with a carbon composite lamination.
A second, hybrid prosthesis was designed similarly using the Otto Bock Ergo Elbow but incorporating an externally powered Otto Bock SensorHand Speed and Utah “ETD ” electric hook. Advantages of this prosthesis included increased controllability and size of grip needed for to handle the explosive packages used in the mine as well as improved aesthetic appearance for church and social activities.
Two preparatory sockets were required to sustain a functional prosthesis while his limb was undergoing normal atrophy. Because he lives a great distance from the clinician's office, silicone suspension liners and pin locks were used in order to keep up with the shrinkage.
JN developed sensitivity to the silicone liners. Once the limb volume had stabilized, a prescription change was recommended to eliminate the silicone suction liner suspension and instead incorporate a pull-in type of suction suspension. Presently, definitive sockets for both arms are being fabricated.
This case is an excellent example of the utility of the Humeral AP Clasp (Figure 10D–F).
Because JN′s residuum had atrophied considerably, it was possible to push most of the soft tissue surrounding the distal half of the humerus medially, allowing the humerus to be “gripped”, achieving a firm clasp on the bone in the AP direction. The firmness of the grip on the humerus that can be achieved by this socket modification very much depends on the quality, character, and pressure tolerance of the individual patient's limb. It requires a balance. On one hand, the more aggressive compression will provide greater stability. In conjunction with, the pressure created must be tolerable to the physiology. This additional design feature imparts remarkable control especially in flexion and abduction. It is especially beneficial when it comes to controlling the cables on the body-powered prosthesis. It also provides stability when holding his prosthesis almost horizontal in flexion or abduction. According to JN, “These prostheses have become critical parts of my everyday routine, as essential as breathing.”
Multiple parameters have been discussed with respect to the planning and implementation of anatomically contoured sockets for transhumeral and elbow disarticulation amputation levels. Each of these design attributes impact the other and therefore must be considered synergistically to achieve an optimal outcome.
Comfort is often the most important. When there is pain, discomfort, or when the prosthesis is too complex to don or wear, it will not be used consistently by the patient. It is also imperative to consider the dynamic factors of rotation, stability, and suspension that help create a more anatomical connection from the prosthesis to the person. No matter how sophisticated the hardware and technical capabilities of the device, if the patient cannot position or control the placement of the terminal device, the result will be rejection of the prosthesis.
The dynamics of the socket determine the efficiency and effectiveness of the chosen control method as well. Contouring the socket to the boney anatomy is able to provide more efficient operation of the prosthesis. This provides placement of the TD in space no matter which control system is used. In the case of body-powered control, performance of the cable systems is directly related to the stability of the socket. With myoelectrically controlled systems, a stable socket maintains reliable electrode contact throughout the entire working envelope.
Several socket features have been presented in this article. In general, these are socket features that are rooted in sound prosthetic principles as practiced and taught in the prosthetics schools for decades. Since most sockets are typically made from a cast and then a modified model shaped to achieve these principles, the term “anatomically contoured” may generally apply to any socket design that follows these conventions. Using these socket designs yields a more successful prosthesis than when they are ignored.
There is strong clinical evidence to support the advantages of aggressive anatomically contoured transhumeral sockets, when sufficient anatomy is available. By gripping the proximal shoulder AP, the practitioner can create significant rotational control of the prosthesis with minimal harnessing. In the authors' experience, a mid-shaft humeral clasp can significantly stabilize humeral motion, in the AP dimension, within the soft tissue envelope. The patient has more control of placement and terminal device positioning with the prosthesis. This is true no matter what control or suspension system is used. There is increased comfort and greater ROM. Also the need for socks and a harness to achieve stability is eliminated. In summary, a prosthesis is a machine in search of a person. The aggressive anatomically contoured socket is a superior way to connect this machine to the individual.