A fusion of the vertebrae, which is also known as an arthrodesis procedure, is a procedure performed to cause a part of two or more vertebrae to “fuse” together over time. The procedure involves placing bone graft between the parts of the vertebrae the physician wants to fuse together. The goal of the procedure is to prevent movement of vertebrae which are causing the patient pain and also helps to stabilize the spine when it has been compromised by disease. Some common diseases that impact the spine include but are not limited to degenerative disk disease, spondylosis, and spondylolisthesis.
Fusions are first classified as either anterior fusions where the surgeon makes an incision from the front of the body and works his way down to the spine or as posterior where the surgeon makes an incision from the back of the body and works his way down to the spine that way. For posterior fusions, we then have some more options – the fusion can be posterior/posterolateral only, interbody, or combined. When an operative report directly tells us what type of fusion is performed, it can be straightforward to line up the term posterior, interbody, or combined fusion to the code descriptions in the CPT manual. But what happens when the surgeon doesn’t use one of these terms? Are we unable to code the procedure without getting additional information from the physician? Fortunately for us coders, there are some keys we can look for to help us determine the type of fusion performed.
Let’s start with an interbody fusion and break down the word “interbody.” Inter means “between” and body refers to the “vertebral body” so this word literally means “between the vertebral bodies.” The vertebral body is the large part of the vertebra positioned in front of the spinal cord towards the front of the body. This part of the vertebra will have an intervertebral disk above and below it to cushion the bone and prevent it from hitting against other vertebrae. Here is a great picture with the large vertebral body labeled so you can visualize what this part of the vertebra looks like: Vertebral Body Picture. If a surgeon is performing an “interbody fusion” he is removing part or all of that intervertebral disk that is between the vertebral bodies and replacing that disk with bone graft placed between the vertebral bodies which eventually causes those vertebral bodies to fuse together. Surgeons place this bone graft material in one of two ways. After removing part or all of the intervertebral disk, they place something known as a structural bone graft where the disk used to be and the presence of this bone graft eventually causes the vertebral bodies to fuse together. Alternatively, they may place a device known as a cage which provides structural support to prevent the vertebrae from collapsing into one another if a lot of the disk had to be removed, and they pack that cage with bone graft chips. The presence of the bone graft inside of the cage has the same effect of eventually causing the vertebral bodies to fuse together over time. With an interbody fusion, you are looking for keys in the note which indicate that the physician removed part of the intervertebral disk and that he has replaced that disk with a structural bone graft or a cage packed with bone graft. If he’s placing bone graft into that interbody location only, that makes the procedure an interbody fusion.
A posterior or posterolateral fusion involves placing bone graft material between one or more of the structures on the back (aka the posterior) part of the vertebrae. The bone graft in this type of fusion if often placed between the transverse processes but may also be placed between the facet joints, lamina, or the lateral masses. Here’s another great picture with some of the structures on the back of the vertebrae labeled so you can picture where the bone graft would be placed in this type of procedure: Posterior Elements of Vertebra. The operative report will often read that the transverse processes (or whatever structure is being fused on the back of the spine) were decorticated and then bone graft material was laid over the top of these bones. When bone graft is placed between two structures on the back of the vertebrae only, this is known a posterior or posterolateral fusion (regardless of which term is used this type of fusion is coded the same way).
Finally, a combined fusion as the name implies is a combination of the interbody fusion and the posterior/posterolateral fusion when performed at the same level of the spine. In this type of fusion, you will see the surgeon remove part of the intervertebral disk and place a structural bone graft or a cage packed with bone graft chips in the interbody location and then also place bone graft between elements on the back of the vertebra at that same level (e.g., L4-L5). When the surgeon does the work of an interbody and a posterior/posterolateral fusion “combined” at the same level of the spine, you know you are looking at a combined fusion.
So let’s test this out. What type of fusion is documented for each of the examples below?
Example #1: After sterile prep and drape, a midline incision was made centered over the C4 vertebrae. The incision was extended down to C7. After decompressing the exiting nerve roots at all levels (coded separately in addition to fusion), we decorticated the lateral masses from C4-C7 and place a mixture of autologous bone graft harvested during decompression and morselized allograft over the surfaces. What type of fusion was performed?
Answer Example #1: This is a posterolateral fusion. After opening the patient, the surgeon “decorticates” or roughs up the lateral masses which are the large pillars of bone on the sides of the back of the vertebrae. He then places bone graft harvested from the patient’s own body and synthetic bone graft (morselized allograft) over these bone surfaces which were just decorticated. Because the bone graft is placed over the lateral masses, this is a posterolateral fusion.
Example #2: After sterile prep and drape, a midline incision was made overlying the spinous processes from L1-L3. Part of the spinous process and lamina on the right were removed. The disk space was entered and part of the disk on the right was removed. Then a PEEK cage packed with DBM was placed into the disk space. What type of fusion was performed?
Answer Example #2: This is an interbody fusion. The spinous process and lamina which are on the back of the vertebra are removed to gain access to the disk space. Then part of the disk is removed and a cage (in this case a PEEK cage) is packed with DBM (which is a type of synthetic bone graft material) and placed into that disk space. Because bone graft is placed into the disk space (aka the “interbody location”), this is an interbody fusion.
Example #3: After sterile prep and drape, a midline incision was made overlying the spinous processes from L2-L5. Part of the lamina and facet joint were removed to gain access to the disk space at L2-L3. Herniated and degenerative disk material was removed on the left. Then the disk space was sized and an 8 mm structural allograft spacer was inserted. To provide additional support, the transverse processes at L2-L3 were decorticated and an onlay graft of autologous bone was placed over the transverse processes. What type of fusion was performed?
Answer Example #3: This is a combined fusion. The lamina and the facet joint which are on the back of the vertebra are removed to gain access to the disk space. After removing part of the disk, a structural bone graft (the 8 mm allograft spacer) is inserted into the disk space (aka the interbody location) to fuse this area. This part of the procedure is an interbody fusion at L2-L3. Then after the interbody fusion is completed, at the same level, the transverse processes which are small bones that protrude from the side of the back of the vertebra are decorticated or roughed up. An onlay graft (which is a graft made of small bone fragments placed between two bones intended to be fused) is then placed between the transverse processes. This is a posterolateral fusion. Since both the interbody and posterolateral fusion are performed at the same level of the spine (L2-L3), this is a combined fusion.
