The Use of CT Scanning for the Study of Posterior Lumbar Intervertebral Articulations N. Hermanus 1, D. de Becker 2, D. Baleriaux 2 and J. P. HauzeuP Departments of Radiology, IBrugmann University Hospital and 2Bordet Institute, 3Department of Rheumatology, Brugmann University Hospital, Bruxelles, Belgium
Summary. The spine is composed of three articular axes: one discal, two facetal. The slightest alteration in one of these axes affects the others. CT is particularly effective in demonstrating biochemical alternations due to architectural pathologies of the column. A judicious therapeutic approach is suggested. Key words: CT - Spine - Interve~Lebral facets
At the beginning of the century, posterior vertebral articulations were thought of as being the only cause of low back pain. This theory was discarded in favour of the intervertebral disc and the narrow lumbar canal (NLC). The aim of this article is to underline the importance of the articular facets in relation to low back pain and sciatica. CT is an excellent method of studying both the facets and the entire vertebra with the surrounding organs [6, 8-10]. The causes of lumbalgia are multiple and each cause must be thoroughly investigated. The treatment may not be successful if one of these factors is ignored.
~ ~ 10 20 30 40 Age
Fig. 1. (See text)
50 60 70
Material and Methods
Fifty patients with chronic low back pain were examined with a third generation scanner (Somatom
SF). The levels of the slices and the orientation of the incident ray were determined on a toposcan. The slices, which were 2mm thick and taken every 4mm, passed through at least three levels of the vertebral facets. In many cases, only the levels indicated by the clinical examination were investigated; in only 15 cases was the whole lumbar column examined (L1 to SI). The findings were characterized according to the criteria suggested by Carrera et al. [2-4]: reduction of the interfacetal space, thickening of subchondral bone, osteophytes, capsular and ligamentous calcifications (Fig. 3). Firstly we correlated the age and sex with the pathologies most frequently found (Fig. 1 and Table 1). Secondly we measured the angles formed by the axis of the articular facets and the axis of symmetry of each vertebra (Tables 2 and 3, Fig. 2). Results
Discal herniation (as the only cause of lumbalgia) as well as the early signs of articular disturbance appeared around the age of 30 (Table 1). Narrowing of the articular facets and subchondral condensation often appeared together. The first signs of degeneration seldom affected the whole lumbar column but often one or two isolated levels according to local stress. Beyond the age of 50, lumbalgia was seen principally in women. This phenomenon is chiefly attribuated, to a sudden variation of the hormonal balance. Moreover, tumors and metastases are most frequently encountered at this period. The angles formed by the facetal axes and the axis of vertebral symmetry widened in the cranio0028-3940/83/0024/0159/$01.00
160 Table 1. Correlation between mean age and pathologies Disc herniation Narrow lumbar canal (NLC) Hemisacralisation Spina bifida Spondylolysis Reduced interfacetal space Asymmetry of articular facets Ligamentous calcifications Arthrodal deformations Tumor and metastasis
Table 2. Angle between facetal joints and sagittal axis
caudal direction (Table 2), varying from 25 ° to 35 ° at L1 L2 and reaching 45 ° to 55 ° at L5 S1. The widest angles were found in two obese patients (70°); the degenerative signs were also significant in these two cases. The narrowest angles occurred in a context o f articular asymmetry, hemisacralisation or narrow lumbar canal.
Widening of the angles and arthrosis tend to increase the articular area under sl:rain, sagittalisation of facetal angles appears more in the dysplastic column. We have often noticed an asymmetry of the facetal angle in this same context (Table 3). In certain cases of lumbalgia, asymmetry with articular narrowing was found. The frequency of asymmetry increased when we approach the lumbosacral hinge with a maximum incidence in the region of L4 L5 and L5 $1 . This asymmetry was not necessarily linked to a malrotation of the pedicles or the', lamina supporting the articular process.
Degenerative pathology is the most frequent cause of low back pain (38 cases/50) and affects even the young adult and becomes more serious later (Table 4). To recapitulate, the degenerative pathology is the accelerated attrition of the articular cartilage (causing articular narrowing) and results from mechanical overloading of the articulation. This is followed by a thickening of subchondral bone, lacunae and an anarchic proliferation of the bone (osteophytes) (Fig. 3). This achieves an increase in the strength of support of the column. In this context, one must not forget that vertebral stress passes along three axes (disc and two posterior articular masses). Any change in the distribution of the load may be responsible for a degenerative process [1, 5]. This explains how any deterioration of the disc affects in turn the facetal joints and vice-versa. We have correlated the symptomatology and the proposed CT diagnoses (Table 4) and have found distinct neurological signs in each case of disc herniation. The opposite is not the case. In one particular case with abnormal signs on neurological examination we found only a marked al~ficular asymmetry. Degenerative processes of varying severity at one or more levels were found in each c,ase and could explain in some the persistence of pain after surgery for disc herniation (Table 5). Other pathology affecting bones, cartilages and ligaments most often causes vague chronic pains at varying locations and sometimes far away from the lesion revealed by the CT scan (two cases). This may be explained by the complex inne,rvation [3, 4, 7] of the capsule and the ligaments from a subdivision of the posterior branch of the spinal nerve; filaments may cross the midline and may innervate levels adjacent to that of their origin.
CT scan is peculiarly effective in the study of architectural pathologies of the column; it appears that a number of etiological factors of low back pain are involved and they are often related. Indeed, disc herniation, for instance, is frequently associated with facetal asymmetry, the first signs of arthroses and ligamentous calcification, providing explanations of pain recurrence after treatment. The three vertebral axes must be evaluated, one discal and two facetal, the slightest defect in one of which can affect the two others. Moreover, in view of the complexity of the innervation, the entire lumbar column from L1 to L5 S1 must be investigated: it is not uncommonly that low sciatica is caused by a more cranial lumbar pathology. This systematic study promotes better understanding of the etiology of low back pain and suggests a judicious therapeutic attitude.
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Received: 18 December 1981
Dr. N. Hermanus Service de Radiologie H6pital Universitaire Brugmann 4, place A. van Gehuchten B-1020 Bruxelles Belgium