Injection Sites for Botulinum Toxin Treatment of Bunny Lines
For treating bunny lines (nasolabial wrinkles), inject botulinum toxin type A into the borders of the nasalis, procerus, orbicularis oculi, and levator labii superioris alaeque nasi muscles—NOT directly into the wrinkle itself, as this targets non-muscular connective tissue and produces suboptimal results. 1
Anatomical Understanding
The area beneath bunny lines contains a non-muscular triangular zone (termed the "bunny triangle") bordered by four key muscles 1:
- Procerus muscle (medially)
- Nasalis muscle (inferiorly)
- Orbicularis oculi muscle (laterally)
- Levator labii superioris alaeque nasi (LLSAN) muscle (inferolaterally)
The wrinkles themselves form over thin skin and connective tissue between these muscle borders, not over muscle bellies. This explains why conventional injection directly into visible wrinkles often fails—you're injecting into non-contractile tissue rather than the muscles causing the dynamic lines. 1
Optimal Injection Technique
Target the muscle borders surrounding the bunny triangle rather than the wrinkle center 1, 2:
- Nasalis muscle: Inject along the lateral nasal wall where the transverse portion of the nasalis creates diagonal wrinkles 2
- Procerus muscle: Consider injections at the superior border if wrinkles extend toward the glabella 2
- Orbicularis oculi (medial fibers): Target the medial canthal region where OOc contributes to lateral bunny line formation 1
- LLSAN muscle: Inject along the inferolateral border where this muscle contributes to lower bunny line wrinkles 1, 2
Critical Technical Points
Dosing and depth: Use small doses (1-3 units per injection point) placed intramuscularly at the identified muscle borders, not subcutaneously into the wrinkle itself 2, 3
Avoid central injection: The bunny triangle's non-muscular composition means central wrinkle injection wastes product and increases risk of toxin migration to unintended structures 1
Individual variation: The size and shape of the bunny triangle varies based on procerus and nasalis muscle width—wider muscles create smaller non-muscular zones 1. Palpate muscle borders during animation (have patient wrinkle their nose) to identify optimal injection sites.
Common Pitfalls
Ptosis risk: Injecting too close to the levator palpebrae superioris (which lies deep to the medial orbicularis oculi) can cause eyelid ptosis 4, 5. Stay lateral and superficial when targeting the medial OOc contribution to bunny lines.
Inadequate effect: Injecting only into visible wrinkles without targeting the surrounding muscle borders produces minimal improvement because you're not addressing the contractile forces creating the lines 1
Lip asymmetry: Excessive LLSAN weakening can affect upper lip elevation—use conservative doses (1-2 units) at this border 2, 5