INTRODUCTION:  Degenerative spondylosis (DS) is frequently accompanied by capsular facet cysts that can protrude into the canal and lead to painful radiculopathy.  While it has been known to occur in DS, it's actual frequency has not yet been described.  Previous authors have either retrospectively reviewed surgical patients with  synovial cysts (Tillich, 2001) or groups with cysts to determine the frequency of spondylolisthesis.

METHODS:  We analyzed MR (sagittal and axial T2 ) images presenting to our clinic and coded (738.4) for DS, for the presence of cyst formation, size (3 mm), position within the canal.  We also measured the maximum facet gap at the listhetic level, the mid disc height, degree slip, and the degree of motion on flexion extension films. Demographics of age, gender, race and presence of lumbar scoliosis were also noted.

We excluded  those with prior instrumented surgery at the listhetic level, trauma, tumor, infection , isthmus spondylolistheis at the index level, patients without proper MRIs and those without a demonstrable slip.  

For continuous variables, both parametric (mean, (95%CI) and standard deviation)  and non parametric (median interquartile range, range) descriptive statistics were used. To determine whether patient-level demographics deferred between those with and without cysts, chi squared and Fisher's exacts tests were used.

RESULTS:  We accessed 593 charts.  69 were ithmic spondylolisthesis; 92 had no slip; 22 had no or poor MRIs and 42 had prior surgery.  This left 368 MRI's.

95% complained of back and or leg pain.  IT was 75% female although those with a cysts were only 58% female.  Mean age was 68.  it was 79% caucasian, 15% Asian, 10% Hispanic and 5% Black.  16% had more than one level of slip (P= 0.005).  There were no other differences in age sex or race between those with and those without a cyst.

The most common level was L4-5 (725( and the most common slip grade was 1 (83%). 91 of 368 (25%) were found to have a cyst. There was a trend towards more cysts in Grade 1 (28%) versus grade 2 (13%) ( p=0.071). Cysts were more common at L4-5 vs. L5-S1 (31% v. 7%) (P=0.002)  The anatomic location of the cyst was almost equally divided between antero-medial within the canal (45%) , and posterior to the facet without any canal impingement (47%). 5% were within the foramen and 3% were lateral.  They were equally divided between right and left and the average cyst size was 4.9mm. There was no association between flexion extension motion or the presence of scoliosis, and the likelihood of a cyst.

DISCUSSION: In studying, for the first time, a large population of patients with DS, we have identified an incidence of 25% of whom have degenerated facet cysts.  The majority are either within the canal with impingement of neural structures (11%); or posterior to the facet into the surrounding muscle (12%).  This number is important for treating physicians who care for faffected patients, in not only making the diagnosis but managing the appropriate treatment, whether operative or non-operative.