The Myo-Prosthetic Management of the Very Short Trans-Radial Amputee
Heidi Bauer-Hume, CP © Sol Wierzba, RTP © Sol Wierzba, RTP ©
The very short trans-radial amputee presents a fitting dilemma for the prosthetist. Should the client be fitted with an above-elbow type of device or a below-elbow device? Fitting with an above-elbow prosthesis assures adequate suspension, weight distribution, rotational control and availability of myoelectric sites. However, the resulting prosthesis is heavy and cumbersome and restricts shoulder motion. Fitting as a below-elbow requires more precise socket fitting but does enable the child to wear the lightest, least restrictive and obtrusive powered device pos- sible. We chose to fit our clients with modified below-elbow devices. The fitting of two clients will be discussed.
Keana is a 15 month old girl with a unilateral congenital forearm deficiency (Picture 1. ). The X-ray of her arm reveals only a small bony fragment distal to the humerus (Picture 2. ). Despite such a short forearm segment, she has some elbow motion.
Keana had worn a passive crawling prosthesis since she was 6 months old. It was a below-elbow type of device fabricated completely out of silicone-impregnated stockinette with a small crawling hand attached. The trim lines were extended to the mid-humeral level and donning and doffing were facilitated by an anterior flap with a velcro closure. Flexibilty and comfort were the primary concerns in the design of Keana's first prosthesis.
When Keana became old enough to receive a myoelectric device, a different design approach was required. The prosthesis needed to provide a higher degree of suspension , weight distribution and rotational control, as well as a solid area for electrode mounting . We decided to keep the entire socket rigid in order to met all of the fitting criteria. (We had experienced rotational control problems with another client when we used a socket which incorporated a proximal silicone portion.) In Keana's hard socket, the medial, lateral and posterior walls were extended proximally by 1/2" and the anterior wall was extended to the elbow crease (Picture 3. ).
A single site voluntary opening system was used and the electrode was placed medially. A suitable site could not be located on the lateral side. Keana received a 0-3 Vasi hand and a Vasi Omni wrist (Picture 4. ). The Omni wrist provides 30 degrees of passive wrist motion in all directions. In order to increase functional range even more, we preflexed the forearm 30 degrees. This gave Keana the ability to perform most activities.
Denise is an 18 year old young woman with a unilateral traumatic trans-radial amputation (Picture 5. ). She has significant scarring over her entire residuum and virtually no flexion or extension at the elbow. Denise's X-ray reveals a stabilizing rod and a small segment of the ulna (Picture 6. ).
Denise suffered her amputation at 2 years of age and has had many types of devices since then, including an above-elbow prosthesis. The latest device was an elbow disarticulation prosthesis which incorporated a polyethylene liner. The major problem with this device was doffing. The scar tissue adhered to the liner making doffing very difficult. To address this issue, we fitted Denise with a much lower profile below-elbow prosthesis (Picture 7. ).
Our greatest challenge was locating two viable muscle sites. During the site selection, the usual mediolateral electrode positioning showed no useable muscle activity. We then tried anterior-posterior placement which showed sufficient activity to enable Denise to isolate the signals and achieve consistent opening and closing of the myoelectric hand (Picture 8. and Picture 9. ). This was an option because Denise has no elbow motion which would have normally interfered with myoelectric control.
The socket design is similar to Keana's socket in which the medial, lateral and posterior walls were extended. In order to increase function, we split the socket and forearm and connected them with one Vasi friction elbow hinge (Picture 10. ). This gave her full passive flexion of the forearm. On the opposite side we used a threaded washer, screw combination to keep the device as slim as possible.
Denise has a 71/4 Otto Bock stud hand with a Vasi Omni wrist. Suspension is very good and she is pleased with the cosmesis and comfort of the de- vice. This design solved the doffing problem.
In summary, then, it is feasible to fit children and young adults with below-elbow myoelectric prostheses even when they present with very short forearm deficiencies. We were able to fit these clients comfortably and effectively by using a rigid supra-condylar socket with extended walls. To enhance functional range, we pre-flexed the forearm, used a flexible, passive wrist and in the case of the older child, we split the socket and forearm and connected them with an external friction elbow hinge.
This type of below-elbow fitting enables the child to wear the lightest, least restrictive powered device possible.
Please direct all correspondence to:
Heidi Bauer-Hume C.P. (c)
Bloorview MacMillan Center,Toronto.