Angular back - Kakujo Totsuhai

...the 13th daughter (Jusan no Kimi) of the Shin Sarugaku-ki, which is said to have been written by Fujiwara no Akihira, is thought to be an example of this ("Kuguse, hato mune"). Quasimodo in V. Hugo's Notre Dame de Paris has a congenital deformity and a rickets-related deformity. Other examples of hunchback include senile kyphosis, in which the thoracic and lumbar vertebrae are bowed with age, and kyphosis angulata, in which one or two vertebrae are destroyed by tuberculosis or fracture, forming a wedge shape, with the spinous process of the vertebrae protruding backwards like a horn. According to the Chinese Song Dynasty medical book "Law of Infants" (edited by Zheng Huiqing), a hunchback in which the body is bent above the waist and the neck is short, making the baby look like a turtle, is often caused by hunchback ("hunchback" means "disease caused by hunchback worms"), but it also urges caution in child-rearing methods, stating that the condition can also develop if the baby's back is cooled or if the baby is made to sit up too early.

*Some of the terminology explanations that refer to "angular back" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…藤原明衡の作とされる《新猿楽記》の13番目の娘(十三の君)はこの例と考えられ(〈偊僂（くぐせ）にして鴒胸（はとむね）なり〉)，V.ユゴーの《ノートル･ダム･ド･パリ》のカジモドQuasimodoは先天性奇形にくる病性変形が加わっている。せむしにはこのほかに加齢とともに胸椎と腰椎が弓状に曲がる老人性円背，結核や骨折により1～2個の脊椎骨椎体が破壊されてくさび状となり，その部の脊椎棘突起（きよくとつき）が角状に後方へ突出する角状突背も含まれる。中国，宋代の医書《嬰幼（えいよう）論》(鄭恵卿編)によれば，腰より上が屈して頸が短く，亀のようになる亀背は多くは疳（かん）の虫が病因(〈せむし〉は〈背虫による病〉の意)であるが，また乳児期に背を冷やしたり早期に座らせたりしても発症するとして，育児法に注意を促している。…

※「角状突背」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報