咬筋ボツリヌス毒素注入前の下顔面構造の超音波による包括的評価法

A Comprehensive Ultrasound Evaluation Approach of Lower Facial Structure Before Masseter Muscle Botulinum Toxin Injection.

抄録

背景:

ボツリヌス神経毒A（BoNT-A）注射による咬筋縮小術は、東アジアで人気のある治療法です。不適切な注入は様々な合併症を引き起こす可能性がある。

BACKGROUND: Masseter reduction by botulinum neurotoxin A (BoNT-A) injection is a popular procedure in East Asia. Inappropriate injection could result in various complications.

目的:

下顎角の形状、咬筋の厚み、皮下脂肪の厚みに基づき、下顔面構造を総合的に評価するアプローチを提案した。この方法を超音波検査により検証し、BoNT-A注入を容易にした。

OBJECTIVES: An approach for comprehensively evaluating the lower facial structure was proposed based on the shape of the mandible angle, the thickness of the masseter and the thickness of subcutaneous fat. This approach was validated by ultrasound examination to facilitate BoNT-A injection.

方法:

咬筋のBoNT-A注射を希望する患者から臨床プロファイルと標準的な超音波画像を収集した。下顎骨、咬筋、皮下脂肪と皮膚の3つの側面から下顔面構造を評価した。下顎角はその程度により外向型、直線型、内向型に分類した。咬筋の中間部の起始点を記録した．咬筋表層部の深下腿腱，表層腹，深層腹の厚さ，およびそれらの収縮力を測定した．全体の厚み、皮下脂肪と皮膚の厚みも測定した。

METHODS: Clinical profiles and standard ultrasound images were collected from patients seeking masseter BoNT-A injections. Lower facial structures were evaluated based on three aspects: mandible, masseter, and subcutaneous fat and skin. The mandibular angle was classified as extroverted, straight or introverted based on the degree. The starting point of the middle part of the masseter was recorded. The thickness of the deep inferior tendon, the superficial and deep belly of the superficial part of the masseter, and their contractility were measured. Overall thickness and the thickness of subcutaneous fat and skin were also measured.

結果:

42名の患者の84個の咬筋が含まれた．下顎直角が最も多く（48.81％），次いで内向型（26.19％），外向型（25.00％）であった．咬筋の中間部は下顎骨縁上2.33±0.36cmから始まっており，通常の注入点より上であった．静止状態、食いしばり状態ともに表層腹は深層腹より厚く（P=0.048, P=0.001）、収縮力が大きかった。全体の平均厚さは1.87±0.29cmであった。

RESULTS: Eighty-four masseters from 42 patients were included. Straight mandibular angles were the most common type of angle (48.81%), followed by introverted (26.19%) and extroverted angles (25.00%). The middle part of the masseter starts from 2.33 ± 0.36 cm above the mandible edge, which is above the usual injection points. The superficial belly was thicker than the deep belly in both static and clenching states (P = 0.048, P = 0.001) and had greater contractility. The average overall thickness was 1.87 ± 0.29 cm.

結論:

超音波検査に基づく下顔面の輪郭と構造の包括的な評価は、信頼性が高く再現性のある評価方法となりうる。

CONCLUSIONS: Comprehensive evaluation of lower facial contour and structure based on ultrasound examination could be a reliable and replicable assessment approach.