A study examining the relationship between facet joint angulation, joint tropism, and Degenerative Spondylolisthesis (DS) found a clinically significant link between DS and facet tropism, as well as observing facet tropism in non-DS disc levels of the study subjects. This supports the theory that tropism may pre-exist and contribute to the development of DS, rather than being a by-product of the condition.
What’s at Stake?
DS is a common condition affecting middle-aged and the elderly population—especially women. Frequently occurring at the L4-L5 spinal level, the condition has been associated with a number of potential causes, including facet joint orientation. Patients with DS may have more sagittal-oriented facet joints, which allows anterior gliding of their superior vertebra. When a patient’s left and right facet joints are asymmetrical by a minimum of 8 degrees, the condition is considered to be tropism. The authors of this study compared patients with DS with a control group of patients who had no DS to determine how facet joint angulation and/or the presence of facet tropism might play a role in the development of DS.
A retrospective radiographic study of 45 patients with single-level DS, presenting with lower back pain (LBP), leg pain with or without neurological effects, and neurogenic claudication compared the images of the subjects in Group A with a control group (B) of 45 non-DS patients surgically treated for disc prolapse or stenosis, matched in sex and age. Patients with previous spinal surgery or trauma, tumors, vertebrae or congenital anomalies, degenerative lumbar scoliosis, and isthmic spondylolisthesis, as well as those with flawed imaging, were excluded from the group.
MRI axial images of various disc levels were processed and analyzed with PACS software in order to calculate the facet joint angles. A difference of 8 degrees of angulation was termed facet tropism. An independent and case-blinded observer assessed the images of both groups, and an analysis was conducted as to the orientation of the facet joints at three levels in both groups.
Group A was comprised of 15 male subjects and 30 female subjects between 38 and 79 years of age, with a mean age of 62.2. Of the 45 Group A patients, 8.8 percent (4/45) presented with DS, two of which (50%) had facet tropism at index level. All four of these subjects also presented with facet tropism at an adjacent distal level. A total of 37 patients (82.2 percent) showed DS in the L4-5 level, and of those patients, 14 (37.8 percent) also had facet tropism at index level. Eleven patients (29.7 percent) presented with tropism at adjacent proximal level, and 29.7 percent (11) showed the condition at adjacent distal level. Four subjects had DS at L5-S1 level, and all of thse patients had facet propism at index level. A single patient also had tropism at adjacent L4-5 level, as well.
Twenty of the 45 Group A patients (44.4 percent) demonstrated facet tropism at the level of DS. IN addition, 12 of the patients (26.6 percent) had it at a proximal level to DS level, and 15 (33.3 percent) at level distal to the DS level. Nineteen of the subjects (42.2 percent) had it at a single level, 9 showed tropism at two levels, and 4 (8.8 percent) had it at all three of the levels examined. In all, 71.1 percent of the patients in Group A had facet tropism at one or more levels.
The numbers in Group B were considerably lower, with 2 patients showing facet tropism at L3-4, 5 at L4-5, and 2 at L5-S1. Five of the subjects had single-level tropism, and 2 had it at two levels. None of the Group B patients had tropism at all three levels. In all, only 15.5 percent of the Group B subjects had facet tropism.
The study confirms the association between facet joint tropism and DS. More notably, the observation of higher numbers of facet joint tropism at adjacent non-DS levels in the DS group suggests that facet tropism could contribute to the development of DS, rather than being a secondary symptom of the condition. Patients presenting with single level DS should be followed up closely to monitor adjacent spinal segments that could become symptomatic in the future.