This is a variation of the cretan stitch. It shows a technique where knots can be added on the elbows to give it a decorative look. The thicker the thread, the bigger the knot that will be formed. It can look similar to a zig zaged coral stitch.

I will work between four parallel stitch lines. You need to know the cretan stitch to be able to continue with this tutorial.

knotted_cretan_stitch_1        knotted_cretan_stitch_2
Fig 1: Start by taking the needle out through B, then in through D and C, as you would for the cretan stitch.   Fig 2: Now, take the needle in through the stitch. Keep the thread below the needle as shown and pull the needle out to form a knot at the ‘elbow’. Then, move to making the next stitch.
knotted_cretan_stitch_3   Fig 3: A finished structure of knotted cretan stitch would look like this.