Physical Therapy Assistant Practice Exam

What is a possible cause for early knee flexion from midstance through preswing in a patient with a transtibial amputation?

1. The socket is aligned in excessive flexion

2. The prosthetic foot is too dorsiflexed

3. The patient is lacking hip extension strength

4. The knee mechanism is locked

The correct answer is: The socket is aligned in excessive flexion

The alignment of the socket in excessive flexion can lead to early knee flexion from midstance through preswing in a patient with a transtibial amputation. This is due to the anatomical position of the residual limb in relation to the prosthetic alignment. When the socket is set too far forward or flexed, it affects the biomechanics during walking, resulting in the knee bending prematurely instead of allowing the individual to achieve a stable midstance phase. In this situation, the residual limb does not properly extend during the gait cycle, which allows for early loading and consequently causes the knee to flex earlier than normal. This mechanical position can hinder stability and balance, making it difficult for the patient to progress through their gait effectively. Other options, while they may also influence gait mechanics, do not directly contribute to early knee flexion in the same manner. For example, excessive dorsiflexion of the prosthetic foot might impact foot clearance or provide a different gait pattern, and lacking hip extension strength typically leads to compensatory movements elsewhere rather than a direct cause of knee flexion issues during these phases of gait. Similarly, if the knee mechanism is locked, it would prevent flexion from occurring at all, which would contradict the question’s scenario of observing early