Charles F. Xeller, M.D., Mark Sanders, M.D., Mohammed Athari, M.D. and Ralph Gibson, M.D


It was the purpose of this study to demonstrate any relationship of facet asymmetry, spina bifida occulta and transitional vertebrae to the possible causation of low back pain. Now, these specific vertebral anatomical anomalies are frequently identified on plain x-ray films. In the past, there have been several studies that have analyzed the possible relationship of these anatomical variations to backache, and the results have provided a wide range of differing conclusions. It was speculated that perhaps the difference in conclusions could possibly have resulted because different physicians diagnosed these anatomical variations with different rates of accuracy. In this study, 1,000 lumbar spine AP view x-rays were interpreted by 3 separate physicians and their conclusions in diagnosing the conditions of facet asymmetry, spina bifida occulta and transitional vertebrae were recorded. The 1000 patient x-rays were selected from 1000 consecutive emergency room visits. Five hundred fifty-three (553) patients were seen for diagnoses of mechanical low back pain. Four hundred forty-seven (447) were seen for diagnoses other than mechanical low back pain, but had x-rays of the LS spine. All physicians read the x-rays in isolation from the other two doctors. The physicians were also “blinded” as to whether the patient had back pain or not.

Materials and Methods

One thousand consecutive patients were recorded who presented to the emergency room and had an AP x-ray demonstrating the lumbar spine. The records and subsequent files were reviewed to establish whether the patient had a presentation of significant low back pain, or a different medical problem identified (such as a urinary tract infection). For this study, significant back pain was defined as pain that prevented the performance of manual labor or resulted in a prescription for analgesic medications. The x-rays were interpreted separately by 3 physicians for the presence of facet asymmetry, spina bifida occulta and transitional vertebrae. The doctors were not aware of the diagnosis for each particular case. All results were tabulated and then a statistical analysis was performed.

Of the initial 11000 cases, 914 were included in this study. There was a drop out of 86 cases due to loss of records/x-rays, patient migration, or the lack of a diagnosis.

Results and Statistical Analysis

Of the 914 patients studied, 514 had a spina problem that manifested as backache, and 400 had another condition, the majority of which were identified as either prostate or kidney problems. The results of x-rays interpreted for facet asymmetry, spina bifida occulta and transitional vertebrae are presented in tables 1, 2, and 3, respectively.

Table 1. Identification of Facet Asymmetry

  Dr. A Dr. B Dr. C
Backache 227/514 253/514 138/514
Other 180/400 180/400 87/400
Backache 44.1% 49.2% 26.8%
Other 45.0% 46.0% 21.8%

Analysis of the above table shows that doctors A and B found no significant difference between the patients with backache and the other diagnoses. However, Dr. C showed a 5% greater rate of facet asymmetry in those patients with backache.

Table 2. Identification of Spina Bifida Occulta

  Dr. A Dr. B Dr. C
Backache 96/514 100/514 62/514
Other 55/400 49/400 52/400
Backache 18.6% 19.5% 12.0%
Other 13.8% 12.3% 13.0%

Table 2 information shows a significant correlation in the presence of spina bifida occulta to the group of individuals with mechanical low back pain for the data of Dr. A and Dr. B. However, Dr. C showed a higher rate of detection of spina bifida occulta in the group without backache.

Table 3. Identification of Transitional Vertebrae

  Dr. A Dr. B Dr. C
Backache 106/514 152/514 112/514
Other 75/400 113/400 88/400
Backache 20.6% 29.6% 21.7%
Other 18.7% 28.3% 22.0%

With respect to transitional changes, all physicians demonstrated less than a 2% difference in the rate of detection between groups with backache vs. the other set of patients.

The following statements can be made:

1. There was considerable variance among the 3 doctors in diagnosis of the spinal anomalies of facet asymmetry, spina bifida occulta and transitional vertebrae.

2. There was no clear cut evidence for the anomalies to be associated with low back pain.


A review of the orthopaedic medical literature does not enable one to establish a definite conclusion as to the relationship of the anatomical variations of facet asymmetry, spina bifida occulta, or transitional vertebrae to the prevalence of low backache in the adult population.

Lumbosacral Facet Asymmetry:

Vertebral facet asymmetry (tropism) is defined as the condition in which the facet joint surfaces of adjacent vertebrae are oriented in different spatial planes when comparing the right vs. the left facets. With spinal motions a vertebral motion segment with facet asymmetry will demonstrate a different torque strength as well as a displacement of the instant center of rotation when compared to a motion segment with parallel facets(1). With facet tropism, there is a decreased ability of that vertebral joint to resist rotational stresses. It is postulated that due to this variance in biomechanical property of that particular motion segment, that accelerated annular degeneration will ensue, and therefore an increased incidence of back pain(2).

Farfan and Sullivan, in a clinical study involving 78 patients, demonstrated a high correlation between facet tropism and low back pain with associated sciatica(2). Together, they analyzed at surgery, the relationship of facet asymmetry to annular degeneration.

In another study, authored by Fischer, Friedman and Van DeMark, x-rays of 200 soldiers with low back pain was compared to a control group of 100 individuals who were asymptomatic. The results of this study demonstrated a higher incidence of facet asymmetry in the control group(3).

In a third study, by LaRocca and Macnab, two groups of individuals who were employed in a heavy manual labor type of position were examined. Each group consisted of 150 individuals. One group was under disability due to lumbar pain and the other group was asymptomatic. All radiographs were reviewed by one doctor. There was no correlation of facet asymmetry to backache that was

Splithoff also examined patients to establish a possible correlation with facet tropism to backache. He studied 100 patients with chronic lumbar pain vs. 100 patients with no history of backache. In this study, there was no relationship of the condition of facet asymmetry to low back pain(5).

In the present study, the level of agreement in diagnosing facet asymmetry between the 3 independent physicians was quite poor. This is understandable. First, it is quite hard to make a specific diagnosis of facet asymmetry on AP plain x- rays. (This diagnosis is best made on CT scan.) Second, one needs to establish just how much difference in facet orientation one would accept before one establishes a diagnosis of tropism. Perhaps the controversy in the literature is due to the variance in observers diagnosing the condition. For a more accurate study, there should be a more rigid definition of facet asymmetry (e.g. exactly what degree difference in orientation of the facets would constitute a recognition of the condition). Perhaps, one could perform CT scans of the facet joints and make direct degree measurements and then judge the possible contribution of facet tropism to low back pain.

Spina Bifida Occulta:

Spina Bifida occulta denotes a developmental anomaly of the posterior elements of the vertebrae in which there is a defective closure of the bony encasement of the spinal cord without any associated protrusion of the spinal cord or the meninges. The neural arch cleft is composed of nonossifying fibrous tissue in the midline between the neural arch defect. It has been postulated that this defect in the posterior neural protective bony arch should produce a slight increase loss of mechanical stability. Due to this loss of mechanical stability there should be an associated increased rate of disc deterioration and an increase in backache in this population(6).

Hodges and Peck studied a group of 447 patients with low back pain and sciatica, and they compared their interpretations to a control group of 538 individuals. In this study there was found to be an increased rate of spina bifida occulta in patients with back pain and sciatica(6).

Several other studies, however, have demonstrated that there is no increased rate of occurrence of backache in patients with spina bifida occulta vs. a control group(7,8,9). In the study of Hodges and Peck, it is noted that there is a variance in the reporting of spina bifida occulta. It is their explanation for this discrepancy in the rate of reporting of the condition as due to individuals employing different diagnostic criteria(6).

In the present study, the doctors demonstrated considerable variance in the rate of detection of the spinal anomalies when compared to each other. However, for the diagnosis of spina bifida occulta the doctors demonstrate fairly good agreement. Of the 3 anatomical variants reported in this study, this was the only category that did show some slight statistical correlation with backache. Spina bifida occulta is probably the easiest of these variants to detect on plain x-rays of the lumbar spine. This could possibly explain the result of the various doctors detecting this condition at about the same rate.

Transitional Vertebrae:

A transitional vertebrae is either a sacralized lumbar vertebrae or a lumbarized sacral vertebrae. In the present study, a transitional vertebrae is defined as a vertebrae that presents with a distinctive enlargement of the transverse processes with or without fusion of the processes to the sacrum. Vertebrae that were bilaterally sacralized or lumbarized were not considered a transitional vertebrae. The reported prevalence of transitional type of vertebrae at the lumbosacral junc- tion has varied from 0.6 to 25% of persons (10,11).

Sacralization, and the presence of lumbosacral transitional vertebrae are anomalies in which an increased incidence of backache have been established in some reports, while other studies have revealed no apparent association.

Those who report a correlation between transitional vertebrae and backache feel that the etiology of the production of pain is due to the alteration in the symmetrical supportive bony architecture of the spinal vertebral column. With an asymmetrical condition the center of spinal rotation moves from the midline and is located nearer to the side of sacral articulation/fusion. The facet articulations and related structures on the side with a free transverse process will move through a greater arc of motion and be subjected to a greater amount of torsional stresses. This greater degree of stress predisposes to facet degeneration, disc deterioration, and possible disc protrusions(10,11).

Tiley, in a study of 7,236 pre-employment radiographs demonstrated 1,103 (14%) with sacralization of the fifth lumbar vertebrae. He noted a significant relationship between unilateral sacralization and variation in the articulating mechanism of the facets. Individuals with sacralization showed a greater occurrence of low back pain and more time lost from work than those workers without the condition(12).

Paillas, Winniger and Louis studies 1,000 individuals with lumbar pain and sciatica and 500 with proven disc protrusions, and they demonstrated a strong association between transitional vertebrae and back pain. The occurrence of pain and sciatica was nearly twice that of patients without transitional vertebrae (15.5% vs. 7.78%). They also demonstrated that the average age of patients with lumbar pain and congenital anomalies was 10 years younger than for individuals with a normal lumbar spine(13).

Hodges and Peck studies 447 individuals with back pain and 538 controls (as was previously mentioned). With respect to transitional vertebrae, the study showed a significant association with back pain(6).

Transitional vertebrae have been linked by some doctors to a clinical entity consisting of low back pain, with or with-out sciatica, which is associated with a disc herniation at the vertebral level craniad to the sacral articulation (Bertolotti’s syndrome). This syndrome may be another cause of pain associated with the condition of a transitional vertebrae. Keim, has presented a series of 12 patients with this clinical presentation(14).

There are also several studies that did not establish any association between transitional vertebrae and the presence of back pain. It is postulated that a transitional vertebrae, by virtue of its enlarged process, is more stable and better protected from stresses, than a “free” vertebrae.” The large transverse process is believed to add to the rotational stability of the vertebral column. LaRocca and Macnab, in their study of 150 men with back pain vs. a control group of 150 men, did not demonstrate a difference due to the presence of a transitional vertebrae(4). These findings were duplicated in the reports of Fischer, Friedman, and Van Demark(3), as well as in the study of Splithoff(5).

In the present study, no correlation was established for the occurrence of a transitional vertebrae and the presence of back pain. Also, just as for facet asymmetry, the rate of agreement between the three physicians in diagnosing transitional vertebrae was poor.


In considering the presence of facet asymmetry, spina bifida occulta and transitional vertebrae in relation to low backache, in this study, only spina bifida occulta showed any statistical association with low back pain. Even for this anomaly, the statistical correlation was slight. This was also the only condition in which the doctors showed a similar rate of diagnosis (agreement in the diagnosis of the condition). In analyzing various combinations of the anomalies and the predisposition to back pain, the presence of all three anomalies showed some association, however, the agreement of the physicians in delineating such individuals was quite poor. As stated in this report, a review of the medical literature reveals considerable variances in relating congenital anomalies of the lumbar spine to backache/pain. As demonstrated in this study, this could be due to the considerable rate of difference among observers in diagnosing an anomaly as present. If one were to attempt to remedy this problem, perhaps an application of more stringent criteria in defining these conditions could help to provide more answers as the etiology of low back pain.


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