Biomechanics of the Spine

Abstract

The spine is a multiarticular structure composed of motion segments whose correct function has stability as prerequisite.

Spinal stability is a fundamental property for the protection of nervous elements, the active generation of forces in the body trunk and the transfer of them between the upper and lower limbs, the prevention of the early biomechanical deterioration of its own components and the reduction of energy expenditure during muscle action.

The stabilization of the spine is guaranteed by a stabilization system consisting of three closely related subsystems: (1) the spinal bones and joints or passive subsystem; (2) the muscles forming the active subsystem; (3) a central control unit, the CNS.

Spine instability is a frequent and often misdiagnosed cause of neck and back pain and disability. In particular degenerative instability is considered a common cause of acute and chronic spinal pain and disability as well as a frequent indication for surgery.

During the instability phase, several MR signs can be found including endplate oedema, peduncle and isthmus oedema, traction spurs, discal vacuum associated with disc space narrowing, joint effusion, synovial cysts, anterolisthesis and retrolisthesis.

Open MR systems allow positional-dynamic studies in either standing or seated positions to detect increased and abnormal intersegmental movements which can worsen or uncover a central canal, lateral recesses and/or foraminal stenosis, disc protrusion or disc extrusion.