solid ankle, cushion heel or SACH refers to a compressible heel wedge that provides “pseudo-plantar flexion” after heel strike. The rigid wooden keel provides midstance stability but little lateral movement. The SACH is inexpensive, light, durable, and available in various heel heights so people can wear different shoes.
The SACH foot was developed at the university of California at Berkeley in 1955 and was based on a Canadian prototype for Syme prosthesis.
In SACH prosthesis, ankle and foot are combined into one component consisting of rigid wooden keel with a compressible heel firmly attached to the shank of the leg so as to eliminate constant loosening and resultant torsion.