Many of the procedures performed on the spine involve fusion of bony segments to prevent motion, avoid further neurologic injury, resolve pain from motion, and prevent future deformity. The fusion of bony spinal segments does not necessarily require instrumentation (use of metallic implants). Fusion procedures can also be attempted without the use of these implants. However, fusion rates are not as good without instrumentation. Through basic science research we now know that immobilization enhances the chance of fusion. Many years ago, the use of metallic implants was a revolutionary idea, and so surgeons used external immobilization such as casting and bracing to enhance fusion. However, their use is not well tolerated amongst patients since they can be big, uncomfortable, and cosmetically objectionable. Since their introduction, the use of these implants have increased substantially and also improved to provide more reliable and increased rigidity. The technique for their use has also become easier as well as versatile. They are currently used in almost all areas of the spine and are routinely used in the neck, chest, and lower back. This page provides graphical examples of common uses of surgical implants in the spine.
Much research has been performed regarding spinal implants regarding their biomechanical and biological properties. Previous implants were made of stainless steel, but since Titanium implants do not interfere with MRI and CT scanning, the use of Titanium implants has increased. The biomechanical properties of Titanium are different than stainless steal in that it is more rigid, as well as more brittle. Still, it provides for a rigid construct, enhancing chances of fusion.
Several generations of implants have been developed and they are still evolving every year to increase rigidity, reliability, and ease of use. New techniques have also been developed like the pedicle screw. Their use is increasing and their application is becoming more universal. Over the past 15 years, their use has become standard of care in the lower back (lumbar spine) and becoming more common in the mid back (thoracic spine). With the introduction of the pedicle screw, the used of other types of implants have decreased. The pedicle screw provides better control of correction and its maintenance.
Even though spinal implants are very commonly used with many advantages, their use is not without risk. They increase operative time, chance for neural injury, chance of infection, and may even cause more serious infections when they do occur. Furthermore, they may cause pain and prominence in special situations. In most situations, once they are placed as a spinal implant they are not removed, but at times, they may require removal which leads to a second surgical procedure.
In the cervical spine (neck) implants can be used to increase fusion rates when used from the front or the back. The X-ray on the left is an example of lateral mass plating in the posterior neck (back of neck). Screws are placed in very specific areas of bone with high degree of accuracy through a metallic plate. This provides a very rigid construct until fusion does occur. (The pictures in this page can be enlarged by clicking the cursor on the images). The screws must be directed to precise locations to avoid injury to nerves and vessels in the area. The fusion in the pictures was performed to avoid late deformity after a decompression procedure over the spinal cord.
Fusion of the cervical spine from a front approach (anterior cervical fusion) is much more common than fusion from the back (posterior fusion). The use of anterior plates is also common to enhance fusion rates while avoiding post-operative bracing. The picture to the right is an example of such plate placed after placement of bone graft in front of the spinal cord between the segments to be fused. The picture to the right is depicting the plate used prior to implantation. There are many different companies that manufacture these implants, but the basic concepts of the plates are all very similar.
The lumbar spine (low back) is the site that many instrumentation (implant) devices are used. In recent years (approximatley15 years) the pedicle screw was introduced to spine surgeons. The pedicle screw is placed from the back and enters the bone to a front direction. It has many advantages since it provides rigid immobilization and allows control of the applied force. However, its placement requires training and experience and has unique complications for its application. Applied properly and without complications it is considered by some spine surgeons as state of the art spinal implant. The picture to the left is just one example of a pedicle screw system available to the spine surgeon. The picture to the right depicts the placement of the screws in the spine.
Pedicle screws can also be placed in other areas of the spine like the thoracic area (chest area). The placement of such screws in that area is much more difficult due to the precise nature of direction and depth of the required screw. In recent years, there has been a higher trend in placement of these screws in the thoracic spine. Still, there may be other options in the thoracic spine like hooks and wires. Each of these implants may have their own complications and benefits. The decision for the use of these implants is made by the surgeon since each surgeon may have different preference and training. To the left is one example of placement of thoracic pedicle screw.
Some disease processes may require fusion of the spine from front and back approach. This increases fusion rates and some surgeons prefer this approach. For that reason implant devices were developed to be applied to the front of the spine. Cages, and bone spacers are available for implants to use in front of the spine. The X-ray to the left is an example of cages placed from the front of the spine.
The picture to the left is an example of a metallic implant prior to its placement. In recent years some of these implants have also been constructed from cadaveric bones. The theory in favor of the use for cadaveric bone is that our body resorbs the bone and forms new bone in its place over time.
To the left is an example of front and back fusion of the lumbar spine. There any many different disease processes that require such procedures. The application of instrumentation from the front and back of the spine ensures higher likelihood of fusion. Even though fusion rates are higher, the patient and the surgeon must consider the higher operative risk with larger scale surgery. As in any surgery, risks, benefits, and alternatives should be reviewed and considered prior to the final decision regarding treatment.
Cases which require correction of deformity usually require more extensive placement of implants. These surgical procedures are lengthy and complicated and have higher risk of complications. The picture to the left is an example of such procedure with extensive use of metallic implants.
In summary, the use of spinal implants is very common in advanced spine surgery. When properly used, they can provide solid fixation to help and enhance fusion rates. The final decision for the use of implants should be reviewed with your surgeon. Risks, benefits, and alternatives should be reviewed in advance to achieve the best possible outcome.
