20 Ideas that Upper Extremity Specialists Use
Gerald Stark, MSEM, CPO/L, FAAOP
Prosthetists that specialize in upper extremity often employ a variety of techniques in external and body power control systems that optimize prosthetic use.
These techniques, individual to the patient and prosthetist, often arise from personal experience and empirical results. Often it is difficult to develop this clinical knowledge since upper extremity prosthetics constitutes roughly 10.13% of the total amputee population.1 For a locally based prosthetist, upper extremity amputees are relatively few in number and require individual solutions based on limb length, ROM, and a variety of other factors. Often increased creativity, people skills, or mechanical acumen are sited as the resource that specialists use, but in reality it is the ability to draw upon a large number of solutions a number of individual fittings and adapt them to an individual case. This situational recall and adaptability aptitude allows these prosthetists to create solutions for external or body power prostheses.
As Jack Uellendahl, CPO notes, "Body power solutions can often be considered more challenging with regard to control application and optimization. Often they become more problematic if the basic function is not understood".2Admittedly these solutions are non-evidence based and drawn from successful applications where the specialist has seen, heard, and performed techniques with other colleagues and patients. Typically a "fitting logic" is developed among these specialists to optimize fit and performance and limit fitting variables. Although there are a multitude of individual solutions, below are more than 20 of these solutions that have been helpful in a number of special cases.
The 4-Function is named for the four functions of the wrist that it control Pronation/Supination, Flexion/Extension (Fig 1 ). These movements are critical especially for shorter limb length or bilaterally involved patients. The classic device was created from various components, but primarily used separate rotation and flexion wrists. These wrists were spring-loaded using a wound cable housing for the rotating wrist and a rubber band for flexion.
When released the springs acted to pull the hook into pronation and flexion. The control cable pulled the hook into the correct angle of pro/supination and that mode was locked with a proximal "bump or brush" latch. The flexion angle was then adjusted by again pulling on the control cable and a distal latch on the wrist flexion device was then activated. This fairly simplistic device was able to add two more modes of active positioning with the control cable. The disadvantage was that many of these components were adapted individually by Jim Caywood, CP and others and remain fairly singular.
Off-the-shelf versions have been created, but the mode latches still need to be created or adapted from much larger "nudge" controls for elbow control.2, 3, 4
A less obtrusive nudge or bump latch can be made for the 4-function wrist above or other components requiring modal controls such as elbow or wrist locking with standard components (Fig 2 ). A cable hanger may be silver soldered to both the cable and the cable housing, then attached to a D-ring which is anchored to the external lamination by an anchor plate. It is important to attach the hanger, cable and cable housing all to each other so the cable housing can act as a return spring. The D-ring swivels and angles the hanger proximally as it is pushed. The housing also acts as the return spring and helps to pull the hanger back distally since it is affixed to the hanger and cable. Other designs employed a larger "paddle" design with a piece of plastic, 70mm long, mounted on two D-rings that swivels in the same fashion to activate the lock. While functionally equivalent it is much larger and requires more cable hardware then the aforementioned simplified design.4
Harnessing the transhumeral patient can be challenging because of the increased excursion demands and the limited power requirements. The average patient requires approximately 62mm to lift the forearm fully and 50 mm to open the terminal device; adding to 112mm to fully use the prosthesis.5, 6 This can be quite challenging for the medium to short transhumeral amputee. To preserve excursion and maintain an inferior position of the harness many prosthetists employ an elastic cross-back strap (Fig 3 ). The strap must be elastic to make donning the harness possible. Although this preserves some excursion it may not fully capture all of the motion available. A Z-strap is a cross back strap variation that is more rigid in nature. The control attachment strap passes through the control cable hanger and passes across the back to the adjustable 4-bar buckle on the axillary pad or strap. This variation still allows easy donning but not sacrifice excursion demands. As the patient activates the control cable, the hanger will swivel into position and "find" the optimal position based on prosthetic orientation.
For the transradial amputee self-suspension interface design two methods have predominated. The Otto Bock-Muenster, first developed by Otto Fruzinsky, CPO is ideally suited for medium to short limb lengths placing particular emphasis on A-P cubital to triceps bar loading as well as supracondylar M-L modifications to allow full ROM. This design maximizes the loading of the limb by pulling the cubital tissue inside the interface. The Northwestern Design developed by John Billock also employs M-L supracondylar loading, but drops the trimline to within 50mm of the distal end.7 The A-P tension with the triceps bar is created with slight loading along the anterior trimline. This allows the Northwestern design to offer push-in donning. The prosthetist can utilize both designs depending on limb length and hybridize them at the medium limb length by increasing the cubital loading for shorter limbs and increasing M-L pressure and dropping the anterior trimline for longer limb lengths (Fig 4 ).7
The St. Anthony Circuit, also known as the cookie crusher is often used for a simplified onesit control for juveniles, but it can also provide simplified control for high level upper extremity prostheses such as shoulder disarticulation or interscapular thoracic level. Muscular contraction usually provides the signal for opening and relaxation returns the device to a gripping position.
The disadvantage is that the maximum gripping force is applied everytime so the grip force of the hand needs to be decreased to 6-9 lbs instead of the normal 24 lb. force. This control can also be incorporated into a three position pull to provide multiple modes for elbow flexion, extension, and hand function.
Sometimes the small nuances of upper extremity design are a great aid for the patient. During unilateral donning, it is fairly difficult to hold the prosthesis on while the anterior chest strap is fished through a D-ring. A backpack buckle is also difficult for unilateral amputees since both sides of the buckle must be positioned, inserted, then squeezed closed with one hand. A sliding D-ring and clip, often used for anterior closures in orthotic devices, as an aid for unilateral donning. The sliding D-ring can be easily placed in the clip attached to the prosthesis and sinched tight or removed (Fig 5 ). It may be necessary to open the clip slightly to allow easier insertion.
Tom Andrew, CPO first developed this transhumeral interface to design to create a tighter interface that could index electrode placement and to help off load the increased weight of external power control systems.8 Using a splinting technique he separated the distal volumetric containment with the proximal loading of the deltopectoral groove and infraspinous scapular region.8 The distal interface was created with loading on the M-L of the humeral shaft and A-P loading of the shoulder. The proximo-lateral trimline could then be lowered to the axillary level (Fig 6 ). Although the anterior trimline reduced the amount of glenohumeral flexion, it created a tighter fit with less lost motion in the interface and increased abduction range of motion. The same A-P pressure was also used with shoulder disarticulation designs to off load the shoulder for external control systems.3
A mechanical elbow and electric arm hybrid is advantageous with transhumeral fittings for a variety of reasons. The most obvious is the decreased cost associated with the elbow. The expense is focused on the terminal device component that is used the more often and has the benefit of increased pinch force. If the harnessed correctly, the body power elbow is usually faster when compared to externally controlled elbows. The hybrid also has the advantage of separate simultaneous control of the elbow and terminal device.9 Using body power to lift the elbow, the patient has increased proprioception of the gross movement which directly links body motion to elbow postition.9 External control of the hand remains fully functional during flexion, rather than waiting for the arm to be locked into position, making manipulation of objects faster. Although a standard mechanical elbow can be configured to use external controls, more options have been developed specifically for hybrid control.
When reconfiguring a standard mechanical system the wiring for the electronic controls needs to be made longer, should be routed posterior to the elbow axis, and enclosed in automotive flexible cable covers.9 Usually an internal battery system is used and it is preferred that it is in the humeral section if it is cosmetically acceptable to decrease live lift load and wiring issues. Hybrid control can also be applied to elbow disarticulation where there are few external elbow control options.2, 3
Along with hybridization of body and external control systems, different external control systems may be mated together. When matching different components, there are a variety of factor to consider. The first is the control output to the device and second is the control voltage. The components that are the easiest to hybridize usually have no controller internally. One hybrid option that can be used for a transhumeral prosthesis is to use a transradial control system that can operate the hand and the wrist control can be used for a simple two-wire elbow device. This allows a much less expensive transhumeral prosthesis to be created, but may require a modal switch to switch between hand to elbow control.
The use of low friction donning sheaths may not seem like a large technologic advancement, but it makes the use of tighter fitting interfaces and vacuum suction for external control much more practical. This is extremely important to prevent the development of painful tissue rolls in the medial humeral axilla area as well as the cubital fold. Anecdotally there seems to be less tissue distraction that may contribute to myosite migration in the definitive prosthesis.
The fitting of partial hand amputations can be challenging due to the lack of distal space for the attachment and wrist components. One characteristic among upper extremity components is that the majority are 1/2-20 screw thread regardless if it is an adult or even infant size. An infant size wrist is small and compact so it can be used with an adult terminal device to utilize for a partial hand prosthesis. The wrist is small enough to be mounted in the palmar aspect of the hand. The infant wrist may also be used for other attachments hat use a 1/2-20 thread including a shoulder or elbow rotation.
Harnessing alternatives are needed to provided stability and comfort with as few straps and attachments as possible. Cross point harnesses are frequently used to optimize excursion responsiveness, but often cause discomfort or even permanent nerve compression issues in the axilla. More elastic designs can be used to increase comfort at the expense of excursion and function. Chest strap and shoulder pad harnesses can be used to transfer the weight away from the axilla to the thoracic area of the chest. However, these harnesses are more encumbering and involved strapping configurations. When using external power, a simple three strap harness may be used to lessen the overall harnessing. A three strap harness involves a simple cross-back strap, chest strap and a superior back strap that attaches just anterior to the apex of the deltoid to provide suspension (Fig 7 ). Normally a chest strap is not utilized for the female anatomy, but the axilla pad may be constructed to have the attachment more superior so the chest strap traces across the sternal notch.
In the past, it was fairly difficult to combine the superior suspension of gel liner sleeves with myoelectric sensors. Previously, holes were cut in the sleeves to allow access to the myo sites, but the soft tissues would migrate to the area and insulate the myoelectric signals. Wayne Daley, CPO utilized modified remote myosites, originally used by therapists to test muscle activity, to create a "snap-on" electrode (Fig 8 ).13 These smaller diameter electrodes could rolled on with the liner attached through the gel layer to a series of external snaps. The elastic tension of the gel liner maintained intimate skin contact, with perspiration contact, in all functional positions with little gapping.13 The disadvantage is that holes need to be cut in to the frame to accommodate the higher profile attachment and the myosites were snapped into everytime the devices was donned. This increase in donning time led Karl Fillauer, CPO to created stud electrodes which were broad plates that make contact with the inner set of liner electrodes.
Leather straps and pads have the advantage of providing multidirectional strength, body conformance, and pliable comfort. Unfortunately it is an organic porous material that readily absorbs odors especially in the axilla area. Spenco can also be used as an alternative to leather for its conformability, but does exhibit long-term strength, is still somewhat porous, and cannot be riveted. TPE materials are not as elastic, but can readily conform to body shape and are easily formed at low temperature. Their non-porous nature resists the absorption of odor for shoulder saddles and axial pads (Fig 9 ). It has greater stiffness for rivets, but will still cold flow with localized force.
Titanium terminal devices and wrists were not offered previously because of difficulty forging and shaping the metal. Titanium provides the same strength as 17-4 PH Stainless Steel, but at 60% of the weight. For moderate use, Aluminum devices are strong enough although contact points cold flow and can fatigue long term. Titanium devices are lighter, but also have a higher spring constant that resist deformation, but also make them harder to machine and make.
Although well known in Europe, the triple control harness provides a number of alternatives to figure of 8 harnesses commonly used in the US. It provides simultaneous control since the medial cable is used to lift the elbow and the lateral cable operates the terminal device. An elastic strap, used for elbow locking is seated at the base of the neck and all straps tie into the anterior axilla attachment. The cross point was also allowed to migrate as the prosthesis is used in different positions. The only main disadvantage is the elbow cable excursion loss due to the medial placement of the cable.
Bill Sauter, CPO of Toronto Canada separated the transradial interface into four separate quadrants, proximal-distal, anterior-posterior. He advocated the removal of the proximal posteror quadrant to increase comfort by creating a window over olecranon (Fig 10 ). The patient has sensation when holding the limb on a table, but this necessitates relief over the ulnar shaft. Also the relief should not exceed the M-L at the epicondyles or the elbow may migrate through the window at full flexion. Anecdotally the supracondylar M-L tension may need to be increased with the window to maintain suspension at 90 degrees.
The triceps bar, proximal to the olecranon remains as a counterforce to the anteriorly directed cubital or anterior trimline.12 Dick Plettenburg, Ph.D. with the WILMER research group from the University of Delft has also shown a transradial design with detachable triceps bar of padded metal that can provide a more open interface design.
The trend for Shoulder Disarticulation and Interscapular Thoracic interface design is to decrease the interface coverage area to the most functional structural components. By utilizing A-P pressure in the deltopectoral area and the sub-spinous area of the scapula, contact above the shoulder is greatly decreased or obviated and can be opened. Utilizing thin and strong composites, Randy Alley, CP and John Miguelez, CP advocated a Micro-Frame or X-frame construction.11 The upper X is the deltopectoral and scapular area (Fig 11 ). The lower X forms the base support of the anterior and posterior costal margin. Both advocate corrugations to increase stiffness. This interface design allows a more open proximal margin will maintaining the compression of the lower costal region for stability. The harness is formed with elastic or Spenco straps wrapping on the contralateral thoracic area.
Along with the interface the design the shoulder component can be altered to increase function of the shoulder disarticulation prosthesis. The attachment for a friction shoulder joint can be inverted to fit with the X-frame Micro construction. The metal attachments can also be replaced with thermoformable carbon material to make the layer even thinner. Also, one of the attachment bolts can be removed as a conduit for the electrode wires that originate from the interface design.
While many prosthetists adjust, the elbow flexion attachment in body power to allow easier lifting for the forearm many do not take the time to optimize the base plate placement. This is crucial for the cabling of short limb lengths that must optimize excursion responsiveness. The baseplate should be placed 10mm proximal to the cut end of the humerus in the posterior lateral corner. As an aid it can be soldered to a padded adjustable ring strap to adjust its placement. The baseplate should be placed more anterior and proximal to increase lifting power at the expense of increased excursion need. A more distal posterior position decreases excursion, but increases the power requirement to flex the elbow. Often two retainers are required to maintain excursion with a distal attachment, but keep the most proximal attachment proximal to the cut end of the bone so the arm does not rotate laterally (Fig 12 ).
The reader has been promised 20 ideas, but two more act as a baker's dozen and, it is hoped, insure approval.
A double cross point ring is frequently applied for body power users with broad backs. As they use a typical figure of 8 harness the cross point may have a tendency to ride up the back. A double ring harness, attached by a short 35mm strap, insures that the cable attachment remains inferior as the patient uses the harness and that it will not ride on the neck (Fig 13 ). Bob Radocy from TRS has presented a one-piece plastic version that is an elongated cross point.
Microprocessor control now allows for multiple inputs for terminal device, wrist, elbow, and shoulder control. Now it is possible to achieve simultaneous function for many controls without relying on modal switches between function. This speeds the switching of control and allows the amputee. Also the interpretation of the controls has a greater impact in control switching. For example a myo signal with a quick rate may have a wrist function, where a slightly slower rate As a result there are many combinations of controls.
Of course there are many more concepts that are utilized by upper extremity specialists. The preceding list is a synopsis of the ideas that have been more commonly used. Without question the list is incomplete, but hopefully introduce and stimulate interest for those wishing to develop their upper extremity prosthetic ability.
The Fillauer Companies, Inc. Chattanooga, Tennessee
- Dillingham, T., Limb Amputation and Limb Deficiency: Epidemiology and Recent Trends in the United States., Southern Medical Journal, Vol. 95., No. 8, August 1, 2002.
- Uellendahl, J., Upper Extremity Control Methods Workshop, Hanger Upper Extremity Education Fare, Reno, Nevada, February, 2008.
- Heckathorne, C., The Four-Function Forearm Setup, Northwestern University Rehabilitation Engineering Program, Northwestern University, Chicago, Illinois.
- Caywood, J., The Four Function Wrist, Hanger Orthopedic, American Canyon, California, 2004.
- Karolewski, T., Upper Extremity Prosthetic Manual, Northwestern University Prosthetic-Orthotic Center, Northwestern University, Chicago, Illinois, 2007.
- Edwards, M., Upper Extremity Prosthetic Manual, Northwestern University Prosthetic-Orthotic Center, Northwestern University, Chicago, Illinois, 2007.
- Billock, J., The Northwestern University Supracondylar Suspension Technique for Below-Elbow Amputation., Selected Readings: A review of Orthotics and Prosthetics, pp. 229-235. American Orthotic and Prosthetic Association, Washington, D.C. 1980.
- Andrew, T., Elbow Disarticulation and Transhumeral Amputation: Prosthetic Principles, Chapter 9B: Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles. Smith DG, Michael, JW, Bowker JH, eds., American Academy of Orthopedic Surgeons, edition 2, 1992, Rosemont, IL.
- Childress, D., Elbow Disarticulation and Transhumeral Amputation: Prosthetic Principles, Chapter 6D: Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles. Smith DG, Michael, JW, Bowker JH, eds., American Academy of Orthopedic Surgeons, edition 2, 1992, Rosemont, IL.
- Bertels, T.H., Functions of the Body Harness for Upper Extremity Prostheses, Bertels, T.H., Otto Bock Healthcare, 2001.
- Miguelez JM, Miguelez MD, Alley RD. Amputations about the shoulder: prosthetic management. In: Smith DG, Michael, JW, Bowker JH, eds. 3rd ed. Altas of Amputations and Limb Deficiencies—Surgical, Prosthetic, and Rehabilitation Principles. Rosemont, IL: American Academy or Orthopaedic Surgeons; 2004:263-273.
- Sauter WF, Naumann S, Milner M. A threequarter type below elbow socket for myoelectric prostheses. Prosthet Orthot Int 1986;10:79-82.
- Daly W. Clinical application of roll-on sleeves for myoelectrically controlled transradial and transhumeral prostheses. J Prosthet Orthot 2000;12:88-91.