Relationship of sacral articular surfaces and gender with occurrence of lumbosacral transitional vertebrae

Abstract

Background context

Research on lumbosacral transitional vertebra (LSTV) has yielded important information on the structural alterations of the sacrum associated with LSTV. Nevertheless, very little data are available on the relationship of a given type of LSTV with either a typical pattern of sacral morphology or its gender distribution in the population.

Purpose

To investigate the probable relationship between different variants of LSTVs with sacral morphology at the articular surfaces of the bone and the gender distribution of the anomalies in the population.

Study design

Cross-sectional descriptive study involving dried human sacral bones and meta-analysis of data available related to LSTVs.

Methods

Three hundred twenty sacra were screened for the presence of LSTV, the type of auricular surface, and facet joints in them. Samples were grouped against their sexes, type of the auricular surfaces present in them, the nature of facet joints, and the variety of LSTV (if present). Data on LSTV from reliable Internet databases were collected to account for the prevalence of LSTV in the population in terms of the types of the anomaly and their gender distribution.

Results

The detection rates of LSTV in the present study were similar to those observed in available literature. Accessory L5–S1 articulations and lumbarization of S1 were more commonly observed in the women. Sacralization was seen to be predominantly distributed in men. Higher auricular surfaces were associated with accessory articulations; lower auricular surfaces were present with partially separated S1 segment and in L5–S1 specimens. Morphology of the facets significantly altered in LSTV with accessory articulations.

Conclusions

Different lumbosacral transitions share a stronger, definite, and specific patterns of relationship with certain sacral morphologies and gender. It is important to recognize the nuances of these connections so as to understand low back pain conditions in the setting of a typical sacral articular morphology or the sex of the individual.

Introduction

Lumbosacral transitional vertebrae (LSTVs) are commonly reported in clinical practice [1], [2], [3], [4], [5], [6]. The association of LSTV and low back pain has been long documented. This allusion has often been debated when seen in light of a cause and effect relationship [7], [8], [9], [10], [11], [12]. These anomalies at the lumbosacral interface have also been associated with altered morphology of the sacrum in comparison to non-LSTV or normal sacral bone samples [13], [14], [15], [16], [17], [18]. These alterations range from a shift in the position of the sacral auricular surfaces, changes in the relative dimensions and angular orientations of the sacrum, and changes related to the morphology and orientation of articular facets in the sacra associated with LSTV [19], [20], [21], [22]. These morphological alterations related to LSTV are reciprocally associated with altered patterns of load bearing at these regions [13], [15], [20], [23].

Morphological variations in sacra are commonly encountered even in samples obtained randomly across normal population [24], [25]. Sexual dimorphisms in sacrum are often the fundamental characteristics that determine the sex of both the skeletal remains of an individual in general and pelvis in particular [24], [26], [27], [28]. In comparison to the male counterparts, the female sacrum is a smaller bone with a more triangular dimension. Load transmissions in these sacra are predominantly concentrated in the upper segments of the sacral corpus. The male sacra, on the other hand, possess broader lower segments and have larger overall dimensions than that of women; of course, they also sustain greater amount of loads above them in comparison to women. The anatomical differences between the sacra in the two sexes are well documented but not yet analyzed in terms of differential load bearing in them.

The significance of LSTV in a population with low back ailments has been conjectured for a long time [4]. The polymorphisms in the sacral dimensions in context of gender have also been well understood and defined. In addition to the sexual dimorphisms exhibited in human sacra, it has been demonstrated that depending on their positions as normal, high, and low, the auricular surfaces of a sacrum may be one of the three Types I, II and III, respectively [13], [14], [16], [18]. Although studies point to the concurrence of LSTV with certain specific alterations in the sacral morphology (auricular surface position and facet morphology), very little has been documented on the probable correlation between a specific sacral morphology and the gender of the sacrum, with their predilection for LSTV. Occurrence of LSTV has been linked to developmental defects that result during improper segmentation of the embryo, and several genes have been implicated in the formation of LSTV in humans [29], [30]. Anomalous embryological segmentation at the lumbosacral region etches out not only the different varieties of LSTVs at the L5–S1 junction but possibly also results in certain distinct morphological alterations in the sacrum below. This study is an effort to investigate the presence of any particular anatomical feature in the human sacra that links or predisposes them to occurrence of LSTV. The study also investigates the probability of any form-function relationship between specific morphology in sacrum and a given transitional anomaly.