Overview
The marginal mandibular branch of the facial nerve is at risk in operations on the neck, the salivary glands and the lower face. The authors review six decades of studies on where the nerve runs as it crosses the facial artery and vein, relative to the lower border of the jaw, along with branching, injury and recovery.
Findings
- The nerve usually crosses the facial vessels on their surface; deep passage and looping have been reported.
- Behind the facial artery, one or more branches run below the lower jaw border in about 19-39% of cases.
- In front of the artery, the nerve is almost always above the jaw border.
- A meta-analysis of 1861 hemifaces reported a pooled 39% prevalence of at least one branch below the jaw border.
- Reported injury rates from surgery range from 16% to 47%, largely temporary.
- Recovery varies, which the authors link to a richer network of nerve connections than once assumed.
- The point where the facial artery crosses the jaw border is a practical guide to finding the nerve.
- The 2 cm rule does not reliably protect the nerve, which may lie lower, especially behind the vessels and when the neck is extended.
- Safer access combines bone and vessel reference points, dissection beneath the platysma, and attention to branching variation.
What it means for a patient
- The nerve branch along the jawline can sit lower than surgeons once assumed, so neck and lower face surgery puts it at risk.
- Limits: a review of past studies. The abstract does not give injury rates for face lift or neck lift on their own.
Why this paper matters
It gathers six decades of studies on this nerve branch. It states that the 2 cm rule is not a reliable safe zone and points to the facial artery crossing at the jaw border as a guide to the nerve.
Terms
- Marginal mandibular branch: the facial nerve branch that runs along the jawline to the muscles of the lower lip.
- Inferior mandibular border: the lower edge of the jawbone.
- Hemiface: one side of the face.
- 2 cm rule: the teaching that the nerve stays within 2 cm below the jaw border.
- Subplatysmal dissection: surgery beneath the platysma, the thin muscle sheet of the neck.