Chapter 9B - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles
Elbow Disarticulation and Transhumeral Amputation: Prosthetic Principles
J. Thomas Andrew, C.P.
There are several factors that are crucial when designing and optimizing transhumeral and elbow disarticulation prostheses, including the following:
- Length of the bony lever arm
- Quality and nature of soft-tissue coverage
- Shape and muscle tone of the residual limb
- Flexibility, range of motion, and stability of the proximal joints
While severe trauma does not always leave the surgeon many options, optimization of these factors will significantly aid the amputee by facilitating his prosthetic rehabilitation and minimizing the need for revision surgery. Consideration should be given to what prosthetic components might be utilized so that elective amputation can be done at a level that will enhance the prosthetic result. In the transhumeral case, if the adult humerus is transected 10 cm (4 in.) above the olecranon tip, all available elbow options can be utilized successfully, including external power.
Elbow disarticulation, on the other hand, will require the use of outside locking joints located on either side of the humeral epicondyles external to the socket. Although this level may add active rotary control and the possibility of a self-suspending socket, both component durability and cosmesis are reduced. The functional advantages of disarticulation make it especially valuable to the bilateral upper-limb amputee, who must use the residual limb for self-care. It is also preferred over the transhumeral level in children since the epiphysis is preserved and bony overgrowth is prevented.
There should be sufficient tissue to cover and cushion the distal portion of the bone without being redundant or creating a bulbous distal contour (Fig 9B-1.). Length due to redundant tissue is functionally useless and serves only to complicate the prosthetic fitting. Myoplasty helps to firm the residual limb, helps prevent redundancy, and provides improved electromyographic (EMG) potential for use in myoelectrically controlled prostheses. Scar lines, drains, and skin grafts should be placed away from cut bones and away from the axilla whenever possible. In these prostheses the anterior, lateral, and axillary surfaces of the residual limb are pressureand force-bearing areas. Any painful or severely scarred tissue in these areas will complicate prosthetic fitting.
In this author's experience, muscle transfers have proved beneficial both as soft-tissue replacement and for providing a potential replacement EMG source for a myoelectric prosthesis when the natural muscle has been lost or denervated. Latissimus transfers seem to be the most common. Innervated pectoralis-to-biceps transfer has also resulted in a very functional bicepslike EMG control site for use with a myoelectric prosthesis (Fig 9B-2.). Sural nerve graft following brachial plexus injury has also resulted in sufficient muscle strength to prevent shoulder subluxation while allowing fitting with a myoelectric device (Fig 9B-3.).
The author has successfully fitted some individuals whose very short humeral stumps were lengthened by utilizing a vascularized fibular graft inserted into the remnant humerus. Another somewhat successful alternative has been the use of progressive distraction and callus formation via an external fixator (the Ilizarov technique). While such techniques are certainly not the answer for every short transhumeral stump, the potential benefits are significant. One of our patients, after lengthening via a fibular graft, now has a long, strong transhumeral residual limb capable of operating both an externally powered Utah Arm and a fully functional cable-powered prosthesis (Fig 9B-4.).
Much has been written on the subject of immediate and early postsurgical prosthetic fitting. Advantages include control of edema and postamputation pain by containing the remnant limb in a snug dressing. Circulation seems to be improved by the lack of edema, thereby promoting quicker healing of the limb. The patient has an improved outlook since he has a usable replacement immediately following amputation and can maintain two-handed grasp patterns. It has been suggested that EMG signals seem to be improved when a limb is contained in a rigid dressing. Despite these potential benefits, however, upper-limb immediate fittings have never enjoyed widespread popularity. This may be simply due to the infrequency of this level of amputation.
Biofeedback training or muscle re-education using functional electrical stimulation has been shown to be an effective technique to enhance myoelectric control. Other important preprosthetic considerations include exercise to maintain strength and range of motion and careful determination of the amputee's vocational and avocational goals.
Several authors have discussed the "golden period" from 30 to 90 days postamputation when prosthetic fitting is most successful. When prosthetic rehabilitation is delayed for many months, it appears that the amputee becomes more and more adept at one-handed work patterns. Once this occurs, learning to use a prosthesis can become a much more frustrating and difficult experience. If immediate fitting has not been possible, early fitting within a few weeks of amputation is strongly recommended.
Prosthetic socket design is largely determined by the physical characteristics of the residual limb. In the case of elbow disarticulation, intimate fitting at and above the condyles provides rotational control and suspension. Socket design alternatives are analogous to those for the knee disarticulation or Syme ankle disarticulation level and include the following:
- Soft insert with an integral supracondylar wedge
- Fenestration with a cover plate (Fig 9B-5.)
- Flexible bladder variants for the less bulbous remnants
- "Screw-in"type sockets (Fig 9B-6.)
Marquardt has described a clever approach for providing rotary control via humeral osteotomy. See Chapter 36A for more information on this technique, which is generally reserved for cases with bilateral upper-limb congenital absences. He has also successfully fit patients with elbow disarticulation and very short transradial remnants with a unique "socketless" design. This technique utilizes an open mediolateral framework, supracondylar pads, and circumferential straps placed superior and inferior to the biceps. While the supracondylar pads provide suspension, the combination of pads and straps allows humeral rotation control of the prosthesis. The fact that there is no encompassing socket results in a lighter, cooler prosthetic interface as well as excellent tactile sense(Fig 9B-7.).
Flexible inner sockets with a rigid outer structural frame originally developed for transfemoral amputees have become increasingly common for upper-limb amputees as well and offer similar advantages. Amputees report that the thin, flexible socket is cooler than conventional rigid alternatives. The pliability of the inner socket also allows for contour and volume changes that occur with normal muscle expansion, thereby increasing comfort and proprioception (Fig 9B-8.).
INFLUENCE OF HUMERAL LENGTH
Leverage for prosthetic control varies directly with the length of the humerus. Amputation through the distal third of the humerus provides functional control very similar to the elbow disarticulation except for the loss of humeral rotary control and condylar suspension. In the transhumeral prosthesis, these last two functions must be provided by the socket design and harnessing. Dynamic load bearing is also a function of socket design. The goal is to provide uniform and comfortable pressure along the humerus throughout the range of abduction and flexion of the prosthesis. Primary control of the prosthesis is by the humerus with additional control offered by scapular motion.
As humeral length diminishes, both leverage and power decrease significantly. Soft-tissue coverage also affects prosthetic function since painful, adherent scarring may limit the force that the amputee can comfortably generate. Conversely, too much tissue makes donning the prosthesis more difficult and often compromises prosthetic humeral length and cosmesis. Guillotine amputations are difficult to fit either conventionally or myoelectrically due to the instability in the soft tissue from a lack of distal attachment.
Amputation in the proximal third of the humerus (proximal to the deltoid insertion) is particularly challenging prosthetically. Primary control is by scapular motion with assistance from the humerus. Due to the obvious reduction in strength and leverage at this level, conventional cable-powered prosthetic control is severely limited. Body-powered systems require up to 5 in. of total excursion to open the terminal device with the elbow in the fully flexed position. Since the average adult transhumeral amputee can achieve no more than 2½ to 3 in. of excursion when using biscapular abduction, externally powered components are usually necessary for full function.
Numerous combinations of body-powered and externally powered components have proved successful. Common examples include using an electric elbow with a body-powered terminal device (Fig 9B-9.). This preserves the inherent proprioceptive feedback of the force generated to use the terminal device and is particularly useful for the amputee who chooses to wear a hook. It is also quite possible to use body power for elbow flexion in combination with an electric terminal device (Fig 9B-10.). Since myoelectric control can provide a very precise yet powerful grip, this hybrid approach is particularly useful for hand users. If suitable sites for myoelectric hand control exist, they can often be adapted for myoelectric elbow control as well (Fig 9B-11.). The precise component configurations must be individualized for each amputee and the relative importance of function, reliability, cosmesis, weight, and cost weighed for each alternative.
UTAH DYNAMIC SOCKET
Over the past decade, experience in fitting significant numbers of externally powered transhumeral prostheses has led to refinements in socket design and harnessing techniques. The author has previously described the "Utah Dynamic Socket technique" for transhumeral socket design, which is an outgrowth of the previous work of Pentland and Wasilieff. Mediolateral stability is enhanced by casting the remnant limb in a special fashion (Fig 9B-12.). Careful shaping of the shoulder region adds rotational stability (Fig 9B-13.). The properly fitted dynamic socket does not require socks for comfort or stability, although they may be worn if desired. This socket design is suitable for either myoelec-trically controlled or body-powered prostheses or for a hybrid prosthesis combining both options (Fig 9B-14.,A-C).
This technique can also be adapted to provide suction suspension. With myoelectrically controlled transhumeral fittings, suction suspension allows minimal harnessing, decreases loading in the contralateral axilla (which may reduce deleterious effects on the sound-side brachial plexus), enhances proprioception, and improves EMG consistency. In selected fully myoelectric prostheses, the harness may be totally eliminated. Contraindications to suction socket transhumeral fittings are analogous to those for transfemoral cases and include remnant limbs with excessively bulbous distal ends, painfully adherent distal scarring, and fresh skin grafts. (Grafted amputations may eventually accept suction once they are well healed and mature.) Although it is sometimes possible for the bilateral amputee to pull himself into the socket with an appropriately designed pull sock, the difficulty of donning a suction socket should be carefully considered (Fig 9B-15.).
While a thorough discussion of harnessing is included in Chapter 6B, one variant works particularly well with the dynamic socket described above. The Utah inverted V harness (Fig 9B-16.) is a modification of the standard Northwestern figure-of-8 ring type. Since the socket design enhances rotary stability, both the lateral suspensor and the anterior suspensor straps are eliminated. The elastic "V" provides improved suspension by functioning as a shoulder saddle while also providing elastic recovery for the body-powered elbow locking cable.
Follow-up could be considered to be the most important aspect of prosthetic rehabilitation and yet may be the most often neglected. Three important tasks must occur during the period following prosthetic fitting:
- Maintenance of socket fit, suspension, and comfort despite limb volume changes
- Monitoring to ensure that the patient fully understands and masters the functions of his prosthesis in his home and work environment
- Re-evaluation of socket style, harness design, and component selection based on amputee experience
There are many aspects to upper-limb prosthetic rehabilitation that cannot be addressed until the patient has had reasonable time to assimilate the many new features of his life. There are continuing questions to be answered and new skills to be mastered. The fit, comfort, and function of the prosthesis must be maintained and optimized over time as the amputee alters and refines his initial goals and aspirations.
Successful long-term use of an upper-limb prosthesis depends primarily on its comfort and its perceived value to the amputee. Innovative design and careful custom adaptation of socket and harness principles, careful attention to follow-up adjustments, and prescription revisions based on the amputee's changing needs are the essential factors for successful prosthetic rehabilitation.
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Chapter 9B - Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles