According to the LL Theorem, the edges of a rectangular triangle establish congruence with the edges of a second rectangular triangle. This means that both rectangular triangles are congruent. When the edges of two rectangular triangles are congruent, the SAS (or SSS) postulates determine that these rectangular triangles are equal.
The LL theorem refers to the congruence of these rectangular triangles, so we can say that the LL theorem is a special case of the SAS Postulate or SSS Postulate.