At this point in our discussion of lumbar pathology we come to one very important topic: spondylolisthesis of the lumbar spine. First described in the mid-1800s, spondylolisthesis literally means slipping bones. In this painful condition there is forward slippage of one vertebral body over the body below. If you want to get academic about it, the severity of this slippage is classified according to the Meyerding Scale:
- Grade I: <25% slip
- Grade II: 25-50% slip
- Grade III: 50-75% slip
- Grade IV: 75-100% slip
- Grade V: >100% slip (the vertebral body above is floating freely in front of the body below.)
Some patients obsess about grading schemes like these but they’re really not that important for a typical patient with spondylolisthesis. Grade I is by far the most common grade and if you’ve been told you have a spondylolisthesis this is probably what you have. I will occasionally operate on a grade II and I can count on one hand the number of times I’ve operated on a grade III. The higher grades really aren’t seen in adult patients. They usually require a congenital defect in the bony anatomy of the spine and thus usually are already symptomatic in childhood (which is why, since I’m not a pediatric neurosurgeon, I don’t see these cases.) A patient with spondylolisthesis may first present with only non-specific back pain. As the patient ages and their spine degenerates the spondylolisthesis may become unstable and start to progress. The slip eventually becomes severe enough that the patient develops back and leg pain and they come to see me. This is the condition for which I most commonly book lumbar fusion procedures. See figure 1.
Figure 1: Sagittal MRI showing the forward slip of L4 on L5 in a typical spondylolisthesis. The image on the right is a schematic of the same process (source: SpinePro III for iPad)
Spondylolisthesis is commonly asymptomatic (radiographic studies on normal volunteers tell us that nearly 10% of us are walking around with this condition yet have no pain.) In my clinic, though, patients with spondylolisthesis have progressed to the point where they now have pain. Patients with spondylolisthesis typically present with a combination of two types of pain: mechanical back pain from stress on the facet joints as well leg pain from compression of nerves. As one vertebral body slips forward over the one below, this puts a tremendous amount of stress on the facet joints at the back of the spine (imagine how your knee would feel if was repeatedly bent outside of its normal range of motion.) As they struggle to maintain the structural integrity of the spine they get stressed, become inflamed and arthritic and thus cause the back pain associated with spondylolisthesis. Also, as the vertebral body slips forward, the nerves within are guillotined causing severe pain, numbness, tingling and even weakness. The condition is especially debilitating because both nerves at the level of the slip can be compressed and injured. First, there is compression of the exiting nerve because of foraminal stenosis caused by the slip and resultant foraminal height loss. The traversing nerve (the nerve still within the spinal canal that will exit at the foramen below) also gets crushed in the lateral recess underneath the severely degenerated facet joint as one part of the joint slides forward in relation to the other (see figure 2). For example a slip at L4/5 can cause compression of both the exiting L4 nerve and the traversing L5 nerve. Both the back pain and leg pain associated with spondylolisthesis get worse as the patient stands up for even a short period of time. When the patient is upright this loads the spine, aggravates the slippage and thus causes worsening pain.
Figure 2: On the left is a sagittal MRI showing severe foraminal stenosis associated with a spondylolisthesis at L4/5 (red arrow); contrast this with a normal foramen at the level above (green arrow). On the right is an axial MRI of the same patient. Note the severe lateral recess stenosis crushing the traversing nerve below the facet joint (red arrow). Also seen is severe facet arthropathy (blue arrow) as indicated by a displaced joint and fluid within the joint.
There are several types of spondylolisthesis described in the textbooks. The two most common types by far are degenerative spondylolisthesis (DS) and isthmic spondylolisthesis (IS). DS, the most common form, occurs, as the name would suggest, as the spine degenerates over time. As the intervertebral disc degenerates it no longer can properly absorb motion. The facet joint tries to take up the slack but eventually, after enough time as a defacto shock absorber, becomes arthritic and incompetent (the same thing my wife says is happening to me.) This incompetent facet joint can no longer maintain the structural integrity of the spine and the spine becomes unstable, allowing slippage to occur. For reasons that aren’t entirely understood, most people with normal, age-related wear and tear of their spine do NOT develop DS. A small number of unlucky folks are predisposed to this condition, however, perhaps because of the morphology of their facet joints or a genetic predisposition to accelerated disc and facet degeneration (degenerative conditions like this do run in families.) DS more commonly occurs in older patients at the L4/5 level.
IS, a.k.a. lytic spondylolisthesis, occurs as a result of a fracture of the pars interarticularis, a small bridge of bone connecting the facet joint at one level to that of the level above (see figure 3). This condition, also referred to as spondyloLYSIS, is thought to begin as an innocuous stress fracture in young athletes. Only a small percentage of patients with a pars fracture will ever develop pain and an even smaller number will ever develop a slip. Again, there seems to be a subset of patients who are predisposed to developing a slip in the setting of a pars fracture. One theory is that patients with a high pelvic incidence (PI) are more likely to progress, mainly because of the force of gravity pulling the spine forward (PI is a measure of the morphology of one’s pelvis usually associated with a steep downward sloping sacrum. More on this in a later post.) IS more commonly occurs in younger patients at the L5/S1 level (secondary to pars fractures at L5, see figure 4). Again, as a patient, don’t get too bogged down in the details of different types of spondylolisthesis here. If you have a spondylolisthesis it’s probably a degenerative one although it may be an isthmic one. In the end, though, it doesn’t matter as the treatment is the same.
Figure 3: Left, posterior view of lumbar spine at L4/5 level (red line indicates location of a fracture across the pars of L5.) Image on right shows schematic of slip at L4/5 that has developed as a result of a pars fracture at L4 (yellow arrows.)
Figure 4: Lateral standing Xray showing spondylolisthesis at L5/S1 associated with pars fracture at L5 (thin red lines). This patient also has a high pelvic incidence with a steeply sloping sacrum (the top of which is indicated by blue line). You can imagine how the force of gravity is contributing to the development of the slip in this patient by pulling L5 forward and downward (red arrow.)
Even today there continues to be a great deal of controversy over the treatment of spondylolisthesis. As I mentioned previously, spondylolisthesis and spondylolysis are commonly asymptomatic. Interestingly, several large population studies have failed to show a strong correlation between the presence of spondyolysis/spondylolisthesis and pain, even when the slip progresses. Patients can have this condition, a structural deformity of their spine, and be just fine. IT raises the question: should these patients even be treated at all? Ultimately, though, once a spondylolisthesis progresses to the point where it’s now an unstable deformity of the spine, patients usually begin to seek treatment.
When I first see a patient with a spondylolisthesis I’ll begin by offering conservative treatments such as physical therapy (PT) and epidural steroid injections. PT will relieve pain in patients with spondylolisthesis, even when the slip is unstable and associated with stenosis. I’ve been amazed at how some patients, with horrible looking MRIs, will do just fine with regular PT. If nothing else, even if the patients do progress to surgery, I prefer that the patient has completed a course of PT because it strengthens them for recovery after surgery. Only when PT and injections fail to provide lasting relief of pain do we consider surgical intervention.
As mentioned in a previous post, instability is one of the clearest indications for spinal fusion. Indeed, patients with back pain and radiculopathy from an unstable spondylisthesis almost uniformly have excellent outcomes with the proper surgical intervention. There is some controversy on the best surgical approach to address spondylolisthesis. In my opinion, though, the best intervention is that which, using minimally-invasive approaches, best restores the structural alignment of the diseased level. This intervention provides stability to relieve back pain and also, through indirect decompression, relieves nerve root compression and thus relieves leg pain. More on the surgical treatment of spondylolisthesis in upcoming posts…
Thanks for reading!
J. Alex Thomas, M.D.