Why is it not advised to choose a SACH foot with a firm heel durometer for a TT patient with poor knee stability?

Choosing a SACH foot with a firm heel durometer for a transtibial (TT) patient with poor knee stability is not advised because a firm heel can negatively impact stability. The SACH foot, which stands for Solid Ankle Cushion Heel, is designed to provide some shock absorption and assist with the loading response during gait. However, a firm heel can be less forgiving upon heel strike, leading to an increased risk of buckling at the knee for patients who already have compromised stability.

In patients with poor knee stability, it is crucial to have a foot that can help control the moment during the initial loading phase of the gait cycle. A softer heel may allow for a smoother transition into the mid-stance phase, aiding in the overall control, stability, and smoother weight transfer. This is particularly important for patients who might rely more heavily on the prosthesis to provide support and prevent falls.

A firm heel may lead to jarring or abrupt forces, which can exacerbate instability and increase the risk of falls. Therefore, selecting a more compliant heel would be more beneficial in promoting stability and a safer walking pattern for these patients.