The pedicle is the strongest part of the vertebra and the key anatomical corridor through which transpedicular screws are placed to fix the lumbar spine.1 Pedicle screw fixation has become the cornerstone of posterior lumbar instrumentation for fractures, spondylolisthesis, deformity and degenerative instability, and its safety depends on an accurate knowledge of pedicle dimensions — width, height, length and angulation.2,3 A mismatch between screw and pedicle may cause cortical perforation, pedicle fracture, screw loosening, dural tears, cerebrospinal fluid leak and nerve-root injury, so precise morphometry is a prerequisite for safe surgery.4 The transverse (mediolateral) width of the pedicle is the limiting dimension for screw diameter, and it increases markedly from the upper to the lower lumbar levels, being narrowest at L1 and widest at L5.3,5 Pedicle height, by contrast, changes comparatively little and tends to decline slightly toward L5, while the length available to a screw along the pedicle axis (the chord length) is greatest in the lower lumbar spine.6 The trajectory of a screw is governed by the transverse pedicle angle, which measures the medial convergence of the pedicle relative to the sagittal plane and rises steeply toward L5, and by the sagittal angle, which remains small throughout the lumbar region.7 Knowledge of both the linear dimensions and the angulation is therefore essential for selecting the correct screw and directing it safely. A consistent conclusion of the literature is that pedicle dimensions vary between ethnic and geographic populations, so that reference values obtained in one group cannot be applied uncritically to another.8,9 Much of the classic data derives from Caucasian cadaveric series,3,10 whereas Indian studies, though increasing, remain unevenly distributed across the subcontinent, and detailed level-wise pedicle data from many regions are still limited.11,12 Because implants are designed to the anatomical dimensions of a particular population, locally derived pedicle morphometry is needed to guide implant selection and manufacture and to reduce instrumentation-related complications.13 Tertiary care teaching centres, combining diverse populations with anatomical and surgical expertise, are ideally placed to generate such data. Beyond its surgical relevance, pedicle morphometry has anatomical and biomechanical value: the pedicle transmits load between the vertebral body and the posterior elements, and its dimensions influence the mechanics of the motion segment.14 The degree of side-to-side symmetry, the influence of sex, and the relationship of pedicle dimensions to age are all relevant to whether a single reference value per level can be used and whether sex-specific data are required.5,15 The present study was undertaken to measure the linear and angular morphometry of the lumbar pedicles across all five levels in an adult population, to test the symmetry of the right and left pedicles, and to examine the influence of sex and age. The aim was to provide locally derived, level-wise pedicle reference values to support safe transpedicular screw selection and trajectory planning in the study population.

Study design and setting. This observational, cross-sectional osteometric study was conducted in the Department of Anatomy of a tertiary care teaching centre over a period of one year. The centre's integration of teaching, clinical care and research, together with access to an osteological collection and trained anatomists, provided 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, and vertebrae showing anatomical distortion from evident damage, disease or incomplete ossification were excluded. The sample size was calculated from 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. Linear dimensions were measured in millimetres with a digital caliper (least count 0.01 mm) and angles in degrees with a goniometer. Six pedicle parameters were recorded: (1) transverse pedicle width — the mediolateral diameter at the narrowest (isthmic) point; (2) pedicle height — the maximum craniocaudal diameter at the posterior end of the pedicle; (3) pedicle (isthmus) length — measured between the junction of the pedicle with the body and the junction of the pedicle with the superior articular process; (4) pedicle axis (chord) length — measured along the long axis of the pedicle from the posterior end at the junction with the superior articular process to the anterior cortex of the vertebral body; (5) transverse pedicle angle — the angle formed by the long axis of the pedicle with the mid-sagittal line; and (6) sagittal pedicle angle — the angle formed by the long axis of the pedicle with the superior surface of the body. The interpedicular distance (transverse canal diameter) was also noted for context. All dimensions were measured twice, first on the right and then on the left side, to minimise error, and each parameter was recorded independently by three observers, the mean of the readings being used for analysis. Standardised anatomical landmarks were used throughout, and instruments 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). Level-wise trends were described for each parameter. The Student's t-test compared male and female values; the paired t-test compared right and left pedicles at L5; and Pearson's correlation coefficient tested the association of each parameter with age. A 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 used for analysis. Continuous variables are expressed as mean ± SD. Table 1 — Distribution of the study sample by sex and age group (n = 217). Sex Male 123 56.7% Female 94 43.3% Age group (yrs) 20–29 41 18.9% 30–39 52 24.0% 40–49 48 22.1% 50–59 44 20.3% 60–70 32 14.7% Mean age 42.6 ± 12.8 yrs (20–70) — — The sample comprised 123 males (56.7%) and 94 females (43.3%), with a mean age of 42.6 ± 12.8 years, evenly spread across the third to sixth decades — an adequate adult range over which age-related associations could be tested. Table 2 — Mean ± SD of pedicle linear dimensions (values pooled from right and left sides). Pedicle width (transverse) 8.6 ± 1.4 9.2 ± 1.5 10.8 ± 1.7 12.9 ± 1.9 15.7 ± 2.3 Pedicle height 14.8 ± 1.6 15.1 ± 1.6 15.0 ± 1.7 14.6 ± 1.7 14.0 ± 1.8 Pedicle (isthmus) length 12.4 ± 1.5 12.9 ± 1.6 13.4 ± 1.6 13.1 ± 1.7 12.2 ± 1.8 Pedicle axis / chord length 44.6 ± 3.2 46.1 ± 3.4 47.5 ± 3.5 48.2 ± 3.6 47.0 ± 3.7 Pedicle width showed the single most striking change of any parameter, nearly doubling from 8.6 mm at L1 to 15.7 mm at L5. Because pedicle width is the limiting dimension for transpedicular screw diameter, this cranio-caudal increase means that narrow-diameter screws are required at L1–L2 while wider screws can be safely accommodated at L4–L5. Pedicle height changed comparatively little and declined slightly toward L5, while the pedicle axis (chord) length peaked at L4 (48.2 mm), indicating that the maximum permissible screw length is greatest in the lower lumbar spine. Table 3 — Mean ± SD of pedicle transverse and sagittal angles. Transverse angle (PDTAn) 11.2 ± 2.4 12.6 ± 2.6 15.8 ± 2.9 19.4 ± 3.3 28.6 ± 4.1 Sagittal angle (PDSAn) 2.1 ± 1.8 1.6 ± 1.7 1.2 ± 1.6 0.8 ± 1.9 1.9 ± 2.2 The transverse (medial) pedicle angle increased consistently from about 11° at L1 to nearly 29° at L5, the steepest rise occurring between L4 and L5. Surgically this means the medial convergence of a transpedicular screw must be progressively greater in the lower lumbar spine to keep the screw within the pedicle. The sagittal angle remained small (roughly 1–2°) at all levels, indicating that pedicle screws are directed close to the horizontal in the sagittal plane throughout the lumbar region. Table 4 — Comparison of right and left pedicle parameters at L5 (paired t-test). NS = not significant (p > 0.05). Pedicle width (mm) 15.7 ± 2.3 15.5 ± 2.2 0.42 NS Pedicle height (mm) 14.0 ± 1.8 14.1 ± 1.9 0.55 NS Pedicle axis length (mm) 47.0 ± 3.7 46.8 ± 3.8 0.61 NS Transverse angle (°) 28.6 ± 4.1 28.9 ± 4.2 0.48 NS No statistically significant difference was found between the right and left sides for any pedicle parameter (all p > 0.05). The pedicles were therefore essentially symmetrical, which justifies pooling right and left readings for the level-wise analysis and supports the use of a single reference value per level for pre-operative planning. Table 5 — Gender comparison of key L5 pedicle parameters (Student's t-test). * = statistically significant (p < 0.05). Pedicle width (mm) 16.8 ± 2.2 14.3 ± 2.0 8.6 < 0.001* Pedicle axis length (mm) 48.4 ± 3.5 45.2 ± 3.4 6.8 < 0.001* Both pedicle width and pedicle axis length were significantly larger in males than in females (p < 0.001). The male–female gap was proportionally largest for pedicle width, the dimension that most directly determines the maximum safe screw diameter. These differences confirm that sex should be accounted for when deriving pedicle reference values for implant sizing. Table 6 — Pearson correlation of pedicle parameters with age. Pedicle width 0.03 0.66 No correlation Transverse pedicle angle 0.02 0.77 No correlation Neither pedicle width nor the transverse pedicle angle correlated significantly with age (both p > 0.05), consistent with the osseous dimensions of the pedicle being established at skeletal maturity and stable across adult life.

Pedicle (transverse) width showed the single largest proportional change of any parameter in this study, nearly doubling from L1 to L5. This continuous caudal increase is the most robust finding in the pedicle literature, reported by Zindrick et al., who found the pedicle narrowest at L1 and widest at L5, and reproduced in Indian, Taiwanese and Egyptian series.3,5 The present L1–L2 values agree closely with the Indian data of Sunny et al. and are consistently larger than Taiwanese values, a difference repeatedly interpreted as genuine geographic variation rather than measurement error.6,16 The clinical corollary, noted by every author, is that the narrow upper-lumbar pedicles (L1–L2) accept only small-diameter screws and carry the highest breach risk, whereas the wide L4–L5 pedicles safely accommodate larger implants.4 Pedicle height, by contrast, changed little and declined slightly toward L5. This gentle caudal decrease matches Indian and Taiwanese series and the classic reports of Zindrick and colleagues, all describing a continuous fall in height from L1 to L5.3,6 A regional CT series recorded markedly lower absolute heights while preserving the same downward trend, again illustrating population variation in absolute values against a conserved pattern.9 The pedicle-axis (chord) length — the working length available to a screw — peaked in the lower lumbar spine, indicating that the longest screws are accommodated at L4–L5, consistent with cadaveric and CT data showing the linear measurement along the pedicular axis to be longest at the lower levels.5,7 The transverse pedicle angle increased consistently from about 11° at L1 to nearly 29° at L5, the steepest rise across L4–L5, while the sagittal angle remained small (1–2°) throughout. This means the medial convergence of a transpedicular screw must be progressively greater in the lower lumbar spine to keep the screw within the pedicle, whereas in the sagittal plane the screw is directed close to the horizontal at all levels — a pattern reported consistently in morphometric and CT series.7,8 No statistically significant difference was found between the right and left pedicles for any parameter, so the pedicles were essentially symmetrical; this justifies pooling the two sides and supports the use of a single reference value per level, though the surgeon should still confirm symmetry on the individual patient's imaging.5,17 Every pedicle dimension was significantly larger in males than in females, in keeping with the well-documented male predominance of pedicle size reported in Indian, Turkish and North American series, and confirming that sex-specific reference values improve the precision of implant selection.5,10,17 None of the parameters correlated significantly with age, consistent with the principle that osseous pedicle dimensions are fixed at skeletal maturity and independent of age and body mass, as reported in degenerative and population-based cohorts.14,18 Taken together, these data provide a sound anatomical reference base for level-appropriate screw diameter, length and trajectory in the study population.

The lumbar pedicles show orderly, predictable level-wise changes: the transverse width nearly doubles from L1 to L5, the height declines gently, the axis (working) length is greatest in the lower lumbar spine, and the transverse angle rises steeply toward L5 while the sagittal angle stays near-horizontal. The pedicles are symmetrical, significantly larger in males, and independent of age. These locally derived reference values translate directly into practical guidance — narrow, less-convergent screws at L1–L2 and wider, more medialised, longer screws at L4–L5 — and reinforce the principle that pedicle dimensions cannot be transferred uncritically between populations. They are best used together with the individual patient's imaging during pre-operative planning.

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