The spine includes lumbar vertebra, thoracic vertebrae and cervical vertebrae, protects the spinal cord and nerve root, supports the body and relieves the external impact. The spine of the human body has a structure formed by stacking multiple vertebrae. The intervertebral disc is located between the vertebrae and evenly distributes the load and impact to the entire spine.
However, recently, spinal diseases continue to increase due to the lack of exercise and incorrect postures. The treatment of diseases related to the spine generally includes an indirect treatment using physical therapy and a direct treatment for correcting and fixing the spine by attaching a separate fixing device to the injured vertebrae.
There are various causes of spine injury. Among the causes, the bio-mechanic cause is known as the most likely cause. Therefore, for the purpose of the physical chiropractic of the injured spine, a spinal fixing device such as a pedicle screw is generally operated.
A general spinal fixing operation using the pedicle screw, that is, the above-mentioned direct treatment, is performed by inserting (at least two) pedicle screws into the vertebrae respectively and then by fixing and coupling the housing coupled with the each pedicle screw to the spine rod disposed approximately parallel with the longitudinal direction of the spine.
Meanwhile, the pedicle screw is divided into a mono type where the screw and the housing are integrally formed with each other and a polyaxial type where the screw and the housing are separately made such that a predetermined rotation is allowed between the screw and the housing, and then are coupled to each other.
The shape of the vertebra (into which the pedicle screw is inserted) is not constant according to patients and operation position. Therefore, at the time of the operation, the polyaxial type pedicle screw is widely used in order that a doctor is allowed to insert the pedicle screw more easily to a part into which the mono type pedicle screw cannot be inserted.