Indications

“Bunny lines” are wrinkles that radiate from the medial canthal region and run inferomedially on each side of the nose. Bunny lines are not found on every patient and are not universally disliked but can be unacceptable for some patients. Occasionally these rhytids can become stronger over time when all the other upper facial muscles have been treated with BoNTA and these are the only muscles left that the patient can move. They also contribute to deep horizontal glabellar rhytids. In those cases, BoNTA injections can be used to soften this region.

Anatomic Considerations

The superior portion of the nasalis muscle (pars transversa) originates over each incisor foramen and inserts into an aponeurosis on the nasal dorsum. At this aponeurosis, the fibers meet those of the opposite nasalis muscle and the midline procerus muscle. When contracted, these muscles create wrinkles or lines on the nose as well as pull the center of the forehead down and contribute to horizontal glabellar creases.

Injection Technique

Topical anesthesia may be used and ice may be applied, though neither is necessary in most cases. These patients are usually asked to wrinkle their nose up “like a bunny,” or “like they smell something bad.” This movement will indicate where the muscle is located and the strength of the nasalis fibers.

A single injection point can be placed into the muscle on each side using 2 to 3 BU. Assessing muscle location and activity during contraction is essential in determining the proper placement of BoNTA in this area. The muscle is not deep, so the injection need only be placed in the subdermal subcutaneous tissue.

Another technique is to insert the needle across the belly of the muscle and then inject retrograde. The injection occurs at or perpendicular to the direction of the actual bunny lines seen during muscle contraction. Alternately, for larger muscles and extensive lines, more injections can be placed, with care being taken not to extend too far laterally.