Leaves may have fallen off, but the leafnodes are still there. While the flower clusters are in bloom, deadhead faded individual blossoms as they fade and brown, then when entire cluster is finished, prune down to just above next flower cluster stem.
Once all flowers are finished blooming, then prune just above a healthy plump leafnode/bud (bump on the stem that is not a thorn) that is outward facing -- pointing in the direction that you would want to have grow.
Treat the bare stems for fungal infection -- that's how the leaves fell off prematurely. Probably a good idea to rake up the infected fallen leaves on the ground if any.
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