European Journal of Cardiovascular Medicine

The lumbar spine, formed by five vertebrae (L1–L5), is the principal weight-bearing segment of the axial skeleton and the region most frequently affected by degenerative disease, disc herniation and canal stenosis.1 Its vertebral bodies are the largest and strongest of the pre-sacral column, and their dimensions, together with those of the bony spinal canal they enclose, determine both the mechanical competence of the segment and the space available to the neural elements.2 Morphometry — the quantitative analysis of the size and shape of anatomical structures — therefore provides the anatomical foundation on which the radiological diagnosis of stenosis and the design of spinal implants rest.3

The vertebral body increases in size from L1 to L5 in response to the progressively greater axial load transmitted to the lower spine, while the anterior body height comes to exceed the posterior height at the lowest levels, producing the wedging that generates the physiological lumbar lordosis.4 The bony canal, triangular in the lower lumbar region, is defined antero-posteriorly by the mid-sagittal diameter (MSD) and transversely by the interpedicular distance (IPD); the ratio of the MSD to the antero-posterior body diameter (APD) expresses the sagittal reserve of the canal relative to the body it accompanies.5 A reduced mid-sagittal diameter is the anatomical substrate of developmental canal stenosis, and knowledge of its normal level-wise value is a prerequisite for distinguishing normal variation from pathological narrowing.6

A recurring conclusion of the literature is that these dimensions vary appreciably between ethnic and geographic groups, so that reference values derived in one population cannot be transferred uncritically to another.7 Comparative osteometric work has shown that the mean diameters of both the canal and the body differ significantly between populations, and that no single set of values is valid for all.8 Much of the classic reference data derives from Caucasian cadaveric and osteometric series,9,10 and although Indian studies have accumulated, level-wise normative data for the vertebral body and canal from many regions of the subcontinent remain sparse.11,12 Tertiary care teaching centres, which combine diverse patient populations with anatomical and radiological expertise, are well placed to generate such data.

Accurate body and canal morphometry has direct clinical value. Body dimensions guide the sizing of interbody devices and the interpretation of vertebral height loss, while canal dimensions underpin the diagnosis of stenosis and the assessment of patients presenting with low back pain and neurogenic claudication.13 Because the lumbar canal is narrowest in its sagittal plane in the mid-to-lower lumbar region, this is the commonest site at which developmental and degenerative stenosis becomes clinically manifest, and population-appropriate critical thresholds are essential for its correct identification.6,14

The present study was therefore undertaken to measure the principal morphometric parameters of the vertebral body and bony spinal canal across all five lumbar levels in an adult population, to examine their variation with sex and age, and to compare the resulting reference values with published series. The aim was to provide locally derived, level-wise data to support the radiological diagnosis of stenosis and the planning of lumbar instrumentation.

Study design and setting. This observational, cross-sectional osteometric study was carried out in the Department of Anatomy of a tertiary care teaching centre over a period of one year. The institution's combination of teaching, clinical care and research, together with access to a large osteological collection and to trained anatomists, made it a suitable setting for morphometric work.

Specimens and sampling. Adult dry human lumbar vertebrae (L1–L5) from the departmental collection formed the study material. All undamaged lumbar vertebrae without visible pathological change were included. Vertebrae showing anatomical distortion arising from evident damage, disease or incomplete ossification that would impair measurement were excluded. The sample size was calculated from the formula n = 4pq/d², where p is the expected prevalence, q = (100 − p) and d the precision (10%); taking p = 30% gave n = (4 × 30 × 70)/10² = 217. Accordingly, 217 vertebral specimens fulfilling the inclusion criteria were examined.

Parameters and measurement. Each specimen was placed in the axial plane and measured in millimetres with a digital caliper (least count 0.01 mm). Six parameters relating to the vertebral body and bony canal were recorded: (1) antero-posterior body diameter (APD) — the maximum antero-posterior distance of the vertebral body; (2) transverse body width — the maximum mediolateral distance across the body; (3) anterior body height — the vertical height at the anterior margin of the body; (4) posterior body height — the vertical height at the posterior margin of the body; (5) interpedicular distance (IPD) — the minimum distance between the medial surfaces of the two pedicles, recorded as the transverse diameter of the vertebral canal; and (6) mid-sagittal canal diameter (MSD) — the maximum antero-posterior distance of the vertebral canal in the midline. The ratio of the mid-sagittal diameter to the antero-posterior body diameter (MSD/APD) was derived for each level.

To minimise inter-observer error, every dimension was measured independently by three members of the team and the mean of the readings was used for analysis; measurements were repeated on the right and left sides where applicable and averaged. Standardised anatomical landmarks were used throughout, and the calipers were checked against a reference scale before each session.

Data handling and statistical analysis. Readings were entered in Microsoft Excel and analysed in SPSS version 29. Continuous variables are expressed as mean ± standard deviation (SD) with range. Level-wise trends from L1 to L5 were described for each parameter. The Student's t-test was used to compare male and female values, and Pearson's correlation coefficient to test the association between each parameter and the subject's age. A probability value of p < 0.05 was taken as statistically significant.

Ethical considerations. The study used dry osteological specimens from the departmental teaching collection and did not involve living participants or identifiable human material; institutional norms for the respectful use of such specimens were observed.

A total of 217 adult lumbar vertebral specimens (L1–L5) fulfilling the inclusion criteria were examined. Each parameter was measured independently by three observers and the mean of the readings used for analysis. Continuous variables are expressed as mean ± SD.

Table 1 — Distribution of the study sample by sex and age group (n = 217).

The sample comprised 123 males (56.7%) and 94 females (43.3%), with a mean age of 42.6 ± 12.8 years. Subjects were fairly evenly spread across the third to sixth decades, providing an adequate adult age range over which age-related associations could be tested.

Table 2 — Mean ± SD of vertebral body dimensions from L1 to L5.

The vertebral body enlarged progressively from L1 to L5. Both the antero-posterior diameter and, more markedly, the transverse width increased in a cranio-caudal direction, consistent with the greater axial load borne by the lower lumbar bodies. Anterior body height exceeded posterior height at L4 and L5, the difference widening at L5 (26.5 mm vs 22.8 mm); this anterior wedging is the osseous basis of the normal lumbosacral lordosis.

Table 3 — Canal transverse (interpedicular) and antero-posterior (mid-sagittal) dimensions with the MSD/APD ratio.

The interpedicular distance widened steadily and most sharply between L4 and L5 (25.4 mm to 28.7 mm), giving the lower canal its characteristic triangular cross-section. In contrast, the mid-sagittal (antero-posterior) canal diameter was smallest in the mid-lumbar region around L3 (16.5 mm) and slightly larger at L1 and L5. The MSD/APD ratio fell from 0.61 at L1 to about 0.53 at L3–L4; a low ratio at this level marks the canal as relatively narrow in the sagittal plane and is the region where developmental canal stenosis most often becomes clinically manifest.

Table 4 — Gender comparison of key L5 body and canal parameters (Student's t-test). * = statistically significant (p < 0.05).

Males had significantly larger values than females for every body and canal dimension examined. The male–female gap was proportionally largest for the vertebral body dimensions and the interpedicular distance (all p < 0.001), whereas the canal mid-sagittal diameter differed by a smaller margin (p = 0.006). This suggests that body size scales more strongly with sex than the bony canal itself, and confirms that sex should be accounted for when deriving reference values.

Table 5 — Pearson correlation of body and canal parameters with age.

None of the parameters showed a statistically significant correlation with age (all p > 0.05). The mid-sagittal canal diameter showed only a weak negative trend (r = −0.11, p = 0.09) that did not reach significance, in keeping with the osseous dimensions of the vertebra being established at skeletal maturity and changing little across adult life.

Detailed morphometry of the lumbar vertebral body and spinal canal underpins both the radiological diagnosis of stenosis and the safe sizing of interbody and pedicle instrumentation, and a central theme of the literature is that these dimensions vary between populations, so that locally derived reference values are needed.7,8

In the present series the antero-posterior and transverse dimensions of the body increased steadily from L1 to L5, and anterior height exceeded posterior height at the lower levels, producing the wedging that underlies lordosis. This cranio-caudal enlargement is among the most consistent findings in the field: cadaveric and CT series report the body width rising from about 40 mm at L1 to 49 mm at L5 and the anterior height rising while the posterior height falls toward L5, a pattern almost identical to that observed here.4,8 The APD values recorded (≈28–32 mm) fall within the 30–33 mm range documented in osteometric and CT control series, supporting the internal validity of the measurements.15

The interpedicular distance widened progressively, most sharply across L4–L5, the anatomical basis of the triangular lower canal. The same caudal widening and the same abrupt L4–L5 step are reported in essentially every series; absolute values differ by a few millimetres — CT-based series tending to read higher than dry-bone series — but the trend is uniform, differences being attributed to measurement modality and ethnicity.16,17

The behaviour of the mid-sagittal diameter is the one area in which the literature genuinely diverges, and the present data sit within that debate. Here the diameter was smallest in the mid-lumbar region around L3 and slightly larger at L1 and L5, giving the lowest MSD/APD ratio at L3–L4. Dry-bone canal–body series show exactly this mid-lumbar minimum, whereas MRI studies measured at the disc level report a smooth decrease to a minimum at L4–L5.5,18 The discrepancy is largely methodological — measurements at the pedicle level show the mid-lumbar trough, while those at the disc level capture lower-level soft-tissue narrowing. Whichever pattern applies, the clinically important point is preserved: the mid-to-lower lumbar canal has the least sagittal reserve and is the commonest site of stenosis, with critical thresholds of about 11–12 mm quoted in Indian MRI series.6,19

Everybody and canal dimension was significantly larger in males, in keeping with the well-documented male predominance of lumbar dimensions in Turkish, Pakistani and North Indian series.17,20 The canal mid-sagittal diameter differed by a smaller margin than the body dimensions, suggesting that body size scales more strongly with sex than the bony canal itself. No parameter correlated significantly with age, consistent with the principle that the osseous dimensions of the vertebra are fixed at skeletal maturity; any age-related canal narrowing seen clinically is predominantly a soft-tissue phenomenon (ligamentum flavum hypertrophy, disc bulging, facet arthropathy) rather than a change in the bony canal itself.3,13 These findings confirm that sex-specific, locally derived reference values are the most reliable basis for stenosis assessment and implant selection in the study population.

Limitations. The specimens came from a single centre and geographic region, which may limit generalisability; measurement of dry bone, while precise, cannot capture the soft-tissue contribution to canal narrowing that imaging would show; and the sample was not stratified equally by sex. Larger, multi-centre and imaging-based extensions are the natural next step.

The adult lumbar vertebral body enlarges progressively from L1 to L5 with anterior wedging at the lower levels, while the bony canal widens transversely toward L5 but reaches its least sagittal reserve in the mid-to-lower lumbar region. All body and canal dimensions are significantly larger in males and independent of age. These orderly, level-wise reference values — derived locally, and confirming the established caution against transferring absolute dimensions between populations — provide a sound anatomical basis for the radiological diagnosis of canal stenosis and for the sizing of lumbar implants, and are best applied alongside the individual patient's imaging.

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