During initial contact in transtibial prostheses, what can cause the knee to remain fully extended?

During the initial contact phase in gait, a fully extended knee in a transtibial prosthesis can be attributed to the suspension system's effectiveness in securing the prosthesis to the residual limb. If there is faulty suspension, the prosthesis may not maintain proper alignment or stability, leading to inadequate control during the loading of the heel. As the prosthetic foot makes contact with the ground, the absence of sufficient suspension forces can prevent the knee from flexing appropriately, thus allowing it to remain fully extended.

The knee needs a certain amount of flexion during initial contact to facilitate shock absorption and proper weight-bearing as the gait cycle progresses. When the suspension system fails, it compromises the positioning and control of the knee joint, leading to the undesired position of full extension.

In contrast, excessive knee preflexion may actually promote flexion at initial contact, and improper foot alignment can lead to misaligned forces transmitted through the prosthesis, which might not necessarily result in full extension at the knee. Weak musculature can affect overall gait, but doesn't directly cause the knee joint to remain extended in this specific context. Thus, the faulty suspension is the primary factor in maintaining a fully extended position during initial contact.