Morphometric study of the lumbar vertebrae in dried anatomical collections

Introduction

In Latin language, ‘lumbus’ means ‘lion’, hence lumbar vertebrae are compared to a lion. They are very flexible and offer stability to the vertebral column. There are few studies available, which offer the morphometric data of the lumbar vertebrae, however there are not many studies available about the dimensions of pars inter-articularis in the anatomical collections. Pars interarticularis is located between the superior and inferior articular facets of the zygapophyseal joints of each vertebra. In the radiographs of the lumbar vertebrae, the pars inter-articularis resembles the neck of a Scottish dog. Since the surgical techniques of the vertebral column involve the utilization of bony anatomical landmarks, the morphometric data of the various parts of the vertebrae are essential. The accurate anatomical dimensional knowledge is important to understand the etiopathogenesis of the lower backache. The bony landmarks like the pars inter-articularis, transverse process, superior and inferior articular facets are particularly important during the internal fixation of the lumbar spine. The pars interarticularis are important parts of lumbar vertebrae, which help during the surgical instrumentation.¹ The anatomical studies help in understanding the detail complex morphometry of the vertebral column.^2,3 There is an assumption that the morphometry of the vertebrae play a role in degenerative diseases of the vertebral column.⁴ The measurements are essential while choosing a suitable implant and this may avoid the intervertebral space exceeding and subsequent injury of the blood vessels.⁵ In this context, the objective of this anatomical study was to perform the morphometry of dried lumbar vertebrae of the human cadavers in sample Indian population.

Methods

This descriptive anatomical study included 200 adult cadaveric dry lumbar vertebrae. The sample size was calculated by referring the article by Singh et al.⁶

The formula applied was

Z_1-α/2=Z value at ‘α’ level of significance

Z_1-β=Z value at (1-β) % power

σ=anticipated population standard deviation of the outcome variable (or) common assumed standard deviation between the two groups

d=clinically significant difference

The protocol of this present research is available online at https://www.protocols.io/view/morphometric-study-of-the-lumbar-vertebrae-in-drie-cjqhumt6. The study duration was 6 months from 17.02.2022 to 17.08.2022. The age and sex of the specimens was not taken into consideration. The present study did not segregate the vertebrae into typical or atypical, because of the random collections of the dried vertebrae. We could not number the vertebrae with respect to the lumbar region. Congenitally deformed lumbar vertebrae were excluded from the present study. Measurements of this study are performed by the digital Vernier calipers. All the measurements were performed by one among the authors of this manuscript. The same author performed the measurements to prevent the inter-observer error. Three measurements were performed and the average of it was taken to prevent the intra-observer error.

The data are expressed in millimeters and tabulated as mean±standard deviation. The details of the measurements performed in this investigation are represented in Figure 1 and Table 1. The SPSS software (version 26) was utilized to perform the statistical analysis. The paired ‘t’ test was applied to compare the parameters between the right and left sides.

Figure 1. Morphometric parameters of the lumbar vertebrae performed in this study (n=200).

The dimensions given here in this table, are to be correlated with Figure 1.

The ethics committee of our institution has approved this research (Institutional Ethics Committee, Kasturba Medical College, Mangalore, IEC KMC MLR: 02/2022/60, dated 17.02.2022). Since this is a study from the cadaveric dried bones, the consent from the participants is not applicable. This was waived by our institutional ethics committee. This present research is following the guidelines of the international ethical standards. Since this is a cross sectional study from the dried lumbar vertebrae of the donated cadavers and did not reveal the identity of the body donor, the written informed consent was not taken from the body donor’s family for the use and publication of this research.

Results

The anatomical data obtained in this study are given in Tables 2 and 3. The vertebral body anteroposterior dimension was more at its lower border than at the upper (p<0.01). The length of lamina was higher over the right side (p < 0.001). The height of lamina, width of inferior articular facet, diameter of lateral recess and thickness of pars inter-articularis were greater for the left side (p<0.01). The remaining parameters, which were compared on the right and left sides did not reveal the difference with respect to the statistical significance (p>0.05).

Discussion

If the significant part of vertebral body is involved in a disease, there will be neurological deficits and instability of the back. Internal fixation of vertebral column is the best management available for the traumatic spine injury, lumbar canal stenosis, spondylolisthesis and malignant tumors. The internal fixation offers better stabilization and decreases the duration of the morbidity. The spinal surgery is also performed in prolapsed intervertebral disc and conditions like scoliosis. It was reported that, this is among the hardest surgeries to perform as it is prone for the postoperative complications.⁷ Krag et al.⁸ performed the morphometry of the vertebrae in cadavers, both manually and radiologically. Characterizing the morphology of the spine among populations, would allow personalizing the conditions under which each individual should be exposed. The morphometric data of the vertebrae are not only useful in the field of neurosurgery, but are also essential to the specialties like neurology and orthopedics. Dimensions of the cervical and thoracic spine were already determined in our collections, few years ago.⁹ This present study was the continuation of this and here we determined the parameters in the lumbar vertebrae. The morphometrical data of various parts of lumbar vertebrae, procured from this study can be considered as the reference data for our study population.

There are not many studies being performed about the morphometry of pars inter-articularis. It offers structural support to the vertebral column and considered as the main support. Pars inter-articularis is a dense cortical bone and is exposed in the posterior approaches. There are morphometrical studies, which are performed by using the radiological methods like utilizing the radiographs and computed tomogram scans.¹⁰ The vertebral column robusticity increased significantly over the time affecting the dimensions of the vertebral body as well.¹⁰ According to Kapoor et al.,¹¹ the inter-pedicular distance was 18.5 mm at the first lumbar vertebra, 21.5 mm at the lower lumbar vertebrae. Aly and Amin¹² reported that the interpedicular distance in the lumbar vertebrae varies from 17 to 43.4 mm and this increases towards inferior region. Nayak et al.¹³ opined that the dimensions of vertebral foramen are higher in the atypical lumbar vertebrae than in the typical. The height of body of vertebrae was 171 cm in males and 158.2 cm in females.¹⁰

During the neurosurgical procedures like pedicle screw insertion, improper design of the implant, the depth of insertion, morphometry, density of bone and iatrogenic mistakes can lead to complications like injury to the meninges, CSF leakage and injury to the neurovascular structures.¹⁴ Best knowledge of human anatomy about the morphometry and angulations of the pedicles in relation to the clinically oriented anatomical landmarks can prevent these complications.¹⁴ A South African research studied the ethnic variation in the osseous morphology of the dried lumbar vertebrae.¹⁵ In this present study, the ethnic variations were not studied and also the comparison with the previously published data was not possible as there were differences in the method of measurements performed.

In the present study, we could not segregate the vertebrae with respect to their number, age and sex. The segregation of the lumbar vertebrae into typical and atypical groups might have added more clarity and specificity. This can be considered as a limitation of this anatomical research. In this study, repeatability of the measurements by asking a secondary observer was not performed. It would have been better if a subset of the sample was measured by a secondary observer and intraclass correlation was applied statistically. If the measurements are consistently taken by one observer incorrectly and then averaged to one value it still might not be representative of the ‘true’ dimensions of the vertebrae. Statistically confirming the agreement between these measurements would strengthen the quality of the research. If the intra-observer error is high, it might suggest the requirement for better measurement definitions or suggest using different tools for them in the field of vertebral morphometry in general.

Since it was just a cross sectional anatomical investigation from the dried vertebrae, the specimens from the same cadaver could not be determined as these are random collections. More studies with larger cohort and validated methods of accurate geometric measurements will be helpful in studying this complex anatomy. However, this study offers data about the pars interarticularis of the lumbar vertebrae, which are scarcely reported in the scientific literature. This makes this study interesting as this is novel in the anatomical literature and different from the previous publications.

Conclusion

We report the measurements of parts of the vertebrae of the lumbar region in sample Indian population. It is believed that, these data will help the operating neurosurgeons and spine surgeons during the surgeries like laminectomy and decompression. They are also essential in planning the accurate sizes of the plates and screws in the internal fixation. The implants have to be manufactured depending on the anatomical dimensions of that particular sample population.