Frequency and size of ossifications in the caudal attachements of the ligamentum flavum of the thoracic spine. Role of rotatory strains in their development

Summary

Ossifications in the caudal attachments of the ligamentum flavum were studied on 121 dried thoracic spines. Most of them were aged. Frequence increased in a caudal direction. At T12, frequence depended on the orientation of the zygapophyseal joints of T11–12 which determined the range of rotation. When they were of thoracic orientation, allowing large range of rotation, ossifications were present in 83% of cases. If orientation was lumbar, allowing poor range of rotation, ossifications became much less frequent:33%. The size of ossifications was also studied. The smaller were in T1 and T2. In T11 and T12, size also depended on the orientation of the zygapophyseal joints of T11–12. If it allowed important range of rotation, ossifications were large sized. In the opposite case, they were small sized. Ossifications of caudal attachements of ligamentum flavum appear to be a normal feature of the aged lower thoracic spine. Their frequence in a given motion segment seems to be influenced by rotational strains

Résumé

Les ossifications de l'insertion caudale du ligament jaune ont été étudiées sur 121 rachis thoraciques dont la plupart étaient âgés. Leur fréquence croissait en direction caudale. Sur T12, elles dépendaient de l'orientation des articulations zygapophysaires caudales qui fixe les possibilités rotatoires de ce segment. En cas d'orientation de type thoracique, coronale, autorisant une importante rotation, les ossifications étaient fréquentes (83% des cas). En cas d'orientation lombaire, n'autorisant qu'une faible rotation, elles devenaient plus rares : 33%. Leur taille fut étudiée. Les plus petites étaient en T1 et T2. Sur T11 et T12, elle dépendait aussi de l'orientation des articulations zygapophysaires de l'étage T11–12. Si cette orientation autorisait une importante rotation, les ossifications étaient de forte taille. Dans le cas contraire, elles étaient de petite taille. Ces ossifications appartiennent à l'anatomie normale des dernières vertèbres thoraciques du sujet âgé. A chaque étage, leur fréquence semble être influencée par les contraintes rotatoires.