3D Characterisation of the Skull Base Deformation in Congenital Muscular Torticollis

Description

The congenital muscular torticollis (CMT) is defined by an abnormal posture of the head and the neck compared to shoulders' level of the newborn. The mainly affected muscle is the sternocleidomastoid muscle (SCM) causing a lateral inclination of the head on the side affected by the CMT and a rotation on the opposite side. It is the third cause of neonatal deformation and affect nearly one newborn out of six, most of the time transiently.

Three types of CMT exist : CMT secondary to a tonus disorder (postural torticollis), CMT presenting a tumor on the SCM and CMT caused by a retraction and fibrosis of the SCM.

The exact aetiology of CMT is not well known. However, per partum intrauterine restrictive stress is very much involved in the genesis of CMT.Treatment is mainly based on physiotherapy, it needs to be started early and associated with parental education. In the event of a failure of the physical therapy, a surgical treatment can be considered. CMT is a risk factor for delayed psychomotor development and can lead to long term sequelae in motor coordination.

CMT comes with asymmetrical deformation of the skull or plagiocephaly. Skull deformation in plagiocephaly is a 3D deformation affecting the calvaria, the skull base and the face. The skull base asymmetry can be found at the mastoid process of the petrous bone, insertion of the SCM on the base of the skull. The facial asymmetry in CMT can have an aesthetic impact on the face or a functional impact on the long term occlusion. CMT also come with abnormalities of the junction between the skull and the vertebrae, they impact the cervical mobility and foster premature arthrosis. The CMT care will modify the seriousness of the skull and face deformation, severity is major in neglected or not treated CMT.

Plagiocephly, facial asymmetry, skull and cranio-vertebral deformation in CMT are the results of a complex mechanism of biomechanical stresses upon a developing skull. These stresses appear in a context of intrauterine postural distortions and/or during postnatal distorting sequences. The SCM responsible for CMT is inserted on the mastoid process of the petrous bone for its base of the skull insertion, the petrous bone is a fundamental component in the biomechanics of the base of the skull.

The hypothesis of a traction force on the base of the skull from the SCM could explain most of all the 3D asymmetrical deformation encountered in CMT. It would be associated to a compression force at the occipital level particularly linked to a sleep position of the infants on their back, position that is now recommended.

The traction force is different depending on the CMT with no or little force in postural torticollis and strong and constant forces in torticollis with fibrosis.

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