A polyaxial screw is used for connecting

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

to rods in

spinal surgery Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty concerned with the surgical treatment of disorders which affect any portion of the nervous system including the brain, spinal cord and peri ...

, particularly spinal fusion procedures. It is a type of screw whose spherical head is enclosed in a housing, which allows the screw a range of motion along several different axes relative to the housing. The

ball joint In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles, and are used on virtually every automobile made. They bionically resemble the ball-and-socket joints found in most tetrapod animals. ...

allows the surgeon some flexibility in placing the screws. The screws are typically placed into the pedicle of the

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

. It has also been hypothesized that polyaxial screws add a safety benefit by failing in the housing/screw interface before breaking in the shaft of the bone screw or in the orthopaedic rod. Unlike standard lateral mass plate and screw systems, the new cervical polyaxial screw and rod system easily accommodates severe degenerative

cervical spondylosis Spondylosis is the degeneration of the vertebral column from any cause. In the more narrow sense it refers to spinal osteoarthritis, the age-related wear and tear of the spinal column, which is the most common cause of spondylosis. The degenera ...

and curvatures. This instrumentation system allows for polyaxial screw placement with subsequent multiplanar rod contouring and offset attachment.

External links

* "Anterior spinal polyaxial locking screw plate assembly", 1996

References

Orthopedic screws {{Surgery-stub