How the prosthesis for Transtibial amputees with short stumps might be improved?
By Nur Rachmat
Short stump of Transtibial amputee is one of the difficulties of the Prosthetic management. Many complications such as short lever arm abducted and hyper extended stump which might be accompanied with mediolateral instability challenging Prosthetist to improve the Prosthetic treatment, to achieve better result for the patient. Several Factors such as pressure distribution, socket design, suspension, and Alignment of the Transtibial Prosthesis are to be considered.
Transtibial stump which less the 12 cm in length is considered as short stump, or the amputation which is done on proximal 1/3rd of tibia. Short stump having many characteristics, such as:
Abducted Stump. The stump is abducted which due to the strong iliotibial band which stretch the stump in abduction. Iliotibial band is inserted to the lateral condyle of tibia.
Hyper extended Stump. The reason is due to the strong knee extensor muscle (Quadriceps muscle), which unopposed by the knee flexor muscle. The Gastrocnemius which serve as a flexor of knee joint had been cut during amputation. Due to lost of this muscle power, the knee tends to be hyper extended.
Mediolateral instability of knee joint. Short stump may have mild mediolateral instability which possibly due to laxity or rupture of collateral ligaments. Short stump will have to bear more force which comes from body weight; it is due to less area of pressure distribution. More force coming to knee joint which leads to ligament fatigue, then laxity or ruptured of these ligaments may occur and medial lateral stability of knee joint will be disturbed.
Short lever Arm. Due to the length of the Tibia which is too short, the lever arm for the stump to bring about movement of the prosthesis is also less. Less lever arm will have to bear more force coming from body weight during stance, need more energy or muscle activity to raise the prosthesis during swing phase.
Less area for Pressure Distribution. Normally, in socket, more pressures are to be bear by Pressure tolerance area, and less forces are to be born by Pressure sensitive area. Less area on short stump limiting for pressure distribution, as more Pressure tolerance area, that is bulk of muscle on medial and lateral Tibial flare have been cut. Bony areas which are pressure sensitive area left in residual limb, which leads in difficulty in pressure distribution.
Figure No.1. Show bilateral Transtibial amputee. Note that both of the stumps are very short. Left stump is more abducted. Figure adopted from http://www.dinf.ne.jp/doc/english/intl/z15/z15001p1/z15001g/z1500104g01.jpg
Improvement in Transtibial Prosthesis
Several ways can be done to improve Transtibial prosthesis for short stump. The idea is to understand the characteristic of the short stump, and to accommodate those characteristic in the prosthesis. The deviation present in the stump can not be corrected in the prosthesis, which means, prosthesis should follow the stump shape. The improvement on the prosthesis can be done by means of alignment, socket design, suspension, and selection of prosthetic component
Prosthesis Alignment. Short stump usually abducted and hyper extended. In frontal view, Socket is to be aligned in abduction to follow the stump deviation. But the shank should be vertical. By this alignment, amputee will stand comfortably on static alignment, with the shank and foot located symmetrically as the sound leg. It is also prevent from medial or lateral trust gait deviation. In sagital view, the socket is to be aligned in more flexion, that is up to 150 flexion. Increase flexion will prevent the knee hyperextension.
Suspension. Selection of suspension is also critical important. Supra-Condylar Suspension is preferable if the patient having good mediolateral stability. Good suspension because of the contour of femoral condyle as well as easy donning and doffing makes this suspension preferable. Pressure above the Patella is needed to prevent hyperextension. If mediolateral instability present, thigh corset can be use for suspension, as mechanical knee joint will be used to stabilize the knee.
Socket Design. Supra-condylar Supra-Patella (SCSP) design is best for short stump when mediolateral instability absent. SCSP trim lines are above femoral condyle for suspension and above patella for supra patella pressure, thus prevent hyperextension.
Figure No. 2. show PTB SC-SP Socket design.
Note the high trim lines above femoral condyle and patella. Figure adopted from: http://books.google.com.pk/books?id=FuuNnSsK8-4C&pg=PA87&lpg=PA87&dq=SCSP+socket&source=web&ots=1fY4Nm_bDO&sig=RdeOrgj3k52_k95BpJL14d17NSA&hl=en&sa=X&oi=book_result&resnum=4&ct=result#PPA87,M1
Prosthetic Component. Weight of the prosthesis is also in critical important. Short stump will not able to carry more weight. There for selection of light in weight but strong component is important. Component made form titanium, which is prefabricated by ottobock, ossur, endolite, proteor can be an option.
Transtibial short stump having characteristic of abducted and hyper extended, improvement on the prosthesis can be done by means of alignment, socket design, suspension, and selection of prosthetic component. Accommodate the shape of the stump what ever it is. Align the socket in same abduction angle in the stump and 150 flexion if hyperextension present in the stump. If flexion contracture present, accommodate that angle in the socket. PTB-SCSP and light in weight but strong material is preferable.
1.Gonzalez E, Corcoran P, Reyes R. Energy expenditure in below knee amputation: correlation with stump length. Arch Phys Med Rehabil. 1974;55:111-119.
2.Murphy EE, Wilson AB Jr. Anatomical and psychological considerations in BK prosthesis. Artificial Limbs. 1962;6:4-15.