|
Year |
2002 |
|---|---|
|
Question Number |
240. |
|
Category |
Rehabilitation |
Question
A 27 yr old man with traumatic transtibial amputation reports buckling of his knee in the stance phase. What is the most likely cause of his symptoms?
1. Ineffective suspension
2. prosthetic foot too soft
3. prosthetic foot placed too far forward
4. prosthetic foot placed too far back
5. excessive prosthetic length
Figures
Answer (click for answer)
Preferred Answer: 4
A transtibial amputation, or BKA, is preferred to be 12-15 cm below the tibial tuberosity. The mechanical axis of the tibia is from the center of the tibial plateau to the center of the ankle.
Normally, during the stance phase the knee remains in extension until toe off. At heel strike the leg is extended. The only way for this patient to experience "buckling" (knee flexion) would be for the foot to be behind the center of rotation of the knee. If the foot was too far forward, the knee would stay in extension longer and the patient would have difficulty during toe off, at the end of the stance phase, and beginning of the swing phase.
The three most common types of suspension systems for BKA prosthetics are: a supracondylar cuff suspension strap, a wedge suspension, and a silicone suction socket. If the problem is with the suspension, there would be instability throughout all phases of walking.
Too long of a prosthesis would also increase knee extension during the stance phase as the foot would need to be placed even farther forward due to extended length. Too soft of a prosthetic foot would cause loss of force at toe off.
Reference: OKU 6 pp139-149.