INTRODUCTION
Low back pain is a common complaint among middle aged and elderly person. There are many causes but one of it could be sacralisation of the fifth lumbar vertebra on sacrum. The incorporation of the fifth lumbar vertebra with the sacrum may be unilateral or bilateral producing partial or complete sacralisation. Sacralisation is commonly regarded as a cause of altered patterns of degenerative spine changes. This review will focus on whether sacralisation of the fifth lumbar vertebra is a radiological entity or a clinical entity.
REVIEW OF LITERATURE
Mario Bertolotti (1917) described unilateral or bilateral enlargement of the transverse process of the fifth lumbar vertebra (L5), which may produce an articulation or get fused with the sacrum or ilium.[1] When L5 gets fused with S1(unilateral or bilateral), L5-S1 behaves as one unit (like a block vertebra). The L5-S1 disc does not take part in sharing load any more during movement. As a result, L4-L5 disc has to take more load and therefore subjected to more stress and disc degeneration sets in early. Loss of disc height results in increased facet pressure and the setting in of facet arthropathy. Thus, with the onset of degenerative disc disease, a degenerative cascade starts.
Castellvi et al.[23] classified lumbo-sacral transitional vertebra (LSTV) in 1984 [Figure 1]. The prevalence of sacralisation varies widely in the spine literature from 3.9% to 35.6%. Matson et al. found the percentage of subgroups as follows—Type 1: 41.72%, Type II: 41.4%, Type III: 11.5%, Type IV: 5.2%.[4]
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Figure 1: Classification of lumbo-sacral transitional vertebra (LSTV), proposed by Castellvi et al. in tabular form (A) and pictorial form (B)
Khashoggi et al.[5] studied the prevalence among a total of 2078 patients who underwent kidney and urinary bladder (KUB) examinations and found sacralisation was present in 158 patients, while lumbarisation was present in 5 patients (3.2%). Among those, incomplete was 136 (86.3%) and complete was17 (10.7%).
Uçar et al.[6] studied 1843 female and 1764 male subjects and found 623 subjects as positive for sacralisation. The prevalence found was 17.2%, 276 (44.5%) women and 344 (55.5%) men.
A significant reduction of total muscle volume of paraspinal and trunk muscles was also seen in subjects with sacralisation. The reduction of bulk rectus abdominis, external oblique, and paraspinal muscles was studied with increased muscle degeneration.[7]
Pelvic incidence (PI) was significantly decreased in subjects with four lumbar vertebrae compared with those with normal spines (PI measured 38.5 in specimens with four lumbar vertebrae, and 46.7 and 47.1 in specimens with five and six lumbar vertebrae).[8] A PI critical value of 42 or lower was found to have a fourfold increase in the development of degenerative disc disease.[9] Surgical errors occur when magnetic resonance imaging (MRI) of the lumbar spine is reported without accompanying conventional radiographs or cervicothoracic MR localisers.[10] This error is most frequently observed in lumbosacral spine. Anatomical variations of the lumbosacral spine are a major risk factor.[11]
Two distinct clinical entities were described in literature in sacralisation of the fifth lumbar vertebra—(i) Bertolotti syndrome and (ii) degenerative spondylolisthesis. Bertolotti’s syndrome has been described as a group of clinical presentations as a consequence of sacralisation of the fifth lumbar vertebra. It has been considered a possible cause of low back pain.[12] The following changes had been described in literature: disk, spinal canal, and posterior element pathology at the level above a transition; degeneration of the anomalous articulation between an LSTV and the sacrum; facet joint arthrosis contralateral to a unilateral fused or articulating LSTV; extraforaminal stenosis secondary to the presence of a broadened transverse process.[101314] The presence of LSTV was associated with an increased prevalence of low back pain (LBP).[15] The disc below the transitional vertebra was protected from degeneration among the middle-aged men, whereas the disc above the transitional vertebra showed signs of degeneration among the young asymptomatic men.[16]
The sacralisation of L5 is thought to cause stress concentration on L4-L5, which can accentuate development of degenerative spondylolisthesis and promote degenerative changes. The incidence of L5 sacralisation was higher (54/78 = 69%) in patients with degenerative spondylolisthesis at L4-L5.[17] Abbas J et al.[18] found that among 95 individuals with spinal stenosis, 57.6% have sacralisation (unilateral and bilateral together) compared with 26.1% in the control group. Pseudoarticulation between the transverse process and the sacrum creates a “false joint” susceptible to arthritic changes and osteophyte formation potentially leading to nerve root entrapment.[19] Reports were published of double crush of L5 spinal nerve root due to L4-L5 lateral recess stenosis and bony spur formation of lumbosacral transitional vertebra pseudoarticulation.[20] There was a definite causal relationship between the transitional vertebra and the degeneration of the disc immediately cephalad to it.[21]
CONCLUSION
With this review, we conclude that sacralisation of the fifth lumbar is not a radiological entity but a clinical entity.
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Conflicts of interest
There are no conflicts of interest.
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