The legs of Arich Anpin sustained the broken vessels; the folding of the legs repaired and elevated them.
A"A's legs sustained the broken vessels during the breaking. The folding of the legs is the first cosmic ascent — the broken vessels rerooted from Netzach, Hod, Yesod (NHY) to also Chesed, Gevurah, Tiferet (CGT).
Op. 67 names a cosmogonic-anatomical detail of the repair process. After the breaking, the broken vessels were sustained — kept from total collapse — by A"A's legs. The folding of the legs is a structural rearrangement that elevates the broken vessels and reroots them at a higher anatomical level.
In the cosmic-anatomical picture, A"A (Arich Anpin) has a structural body with head, body, legs. The legs (Netzach, Hod, Yesod — the lower three Sefirot of A"A) are A"A's lower-anatomy. When the breaking happened in Nekudim, the broken vessels fell to the level of A"A's legs — that is, they came to rest at A"A's lower anatomy.
The folding of A"A's legs is the cosmic operation that elevates them. When A"A folds his legs (raises them up to the level of CGT — Chesed, Gevurah, Tiferet, the body's middle-anatomy), the broken vessels that were resting on the legs are elevated with them. Now the broken vessels are also rooted in CGT, not just NHY. The rerooting elevates the broken vessels to a higher operational anatomy.
This is the cosmic-operational seed of aliyah — the doctrine of ascent above the intrinsic level (Op. 132). The folding-of-legs is the first cosmic ascent; the closing chapters will treat ascent as a regular operational rhythm.
Op. 132 (aliyah vs. hagdalah — distinguishing ascent from growth) generalises the Op. 67 framework. Op. 133 (Zeir Anpin (Z"A)'s ascent after the Second Maturity) is a specific operational instance.