Variable positions of the sacral auricular surface: classification and importance

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Although the area at the auricular surface defines the magnitude of weight transmission to the hip bones, this study proposes that the position of the auricular surfaces may also significantly influence load bearing patterns at the sacrum. This study attempts to investigate and classify variable positions of the auricular surfaces that may cause vertical shifts in weight-bearing patterns between the L-5 and S-1 segments, altering weight distribution at the lumbosacral and sacroiliac regions.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Three hundred human sacra were studied to determine the position and extent of their auricular surfaces in relation to the sacral segments. Specimens were grouped as “normal,” “high-up,” and “low-down” auricular surface-bearing sacra. All bones were also scrutinized for the presence of accessory articulating facets on the ala of the sacrum and sacralization of the L-5 segment or lumbarization of the S-1 segment. Seven dimensions and 5 articular areas were measured in all sacra. Nine indices were calculated to show proportional representation of dimensions and areas in the bones. Obtained data were analyzed for differences in groups of sacra bearing different auricular surface positions.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Thirty-nine of the sacra (13%) showed auricular surfaces that occupied a high-up position (from upper S-1 to low S-2 segments). Forty-four of the sacra (15%) exhibited a low-down auricular surface (from the low S-1 to low S-3 sacral segments). The remaining bones demonstrated a normal position of the surface (from the S-1 to the middle of the S-3 segments). Twenty of the high-up sacra demonstrated unilateral or bilateral accessory articulating facets on the alae that articulated with extended transverse processes of the L-5 vertebrae. The low-down sacra transmitted load predominantly via lower (S2–3) segments and exhibited stouter, broader, and efficient weight-bearing lower sacral elements, and a prominent gap between the S-1 segment and the rest of the sacrum. The high-up sacra: 1) were shorter and broader in comparison with the normal sacra; 2) at times presented accessory articular facets on their alae; 3) had a smaller body span and a wider ala; 4) were found to have the plane of the facet joints nearer to the posterior aspect of the S-1 body; and 5) had the smallest of the facet areas. The low-down sacra were longer than they were broad, had a substantially broad body span at S-1, possessed the smallest interauricular distance, and showed considerable depth of the plane of the facet joints.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The position of the auricular surface varies in human sacra. These variations are associated with differential load bearing at the sacral joints. Only the high-up sacra demonstrated the presence of accessory articulating facets between L-5 and S-1. The position of the auricular surface can explain or possibly predict low-back pain situations.</jats:p></jats:sec>

Partial lumbosacral transitional vertebrae: 2 cases of unilateral sacralization

“…In each case, the skeletal anomaly limited ipsilateral flexion and coincided with ipsilateral muscular symptomatology. These findings seem to echo the arguments of Mahato, [22][23][24][25][26][27] who suggested that the biomechanical alterations brought on by the skeletal anomaly could contribute to the symptomatology. Conservative treatment directed at the involved muscle group in these cases resulted in decreases in symptom frequency and intensity, although it did not result in complete resolution in either case.…”

“…Some have argued that altered biomechanics of weight transmission across the L5-S1 articulation result because LSTV are associated with altered morphology at the joint. [22][23][24][25][26][27] These altered biomechanics are hypothesized to cause biomechanical compensations, which may partially explain the ipsilateral muscle hypertonicity noted in the current cases and by Brenner. 21 Other investigators 8 have suggested that LSTV increase the severity of the clinical picture, regardless of the causal relationship between LSTV and low back pain.…”

“…In case 1, improvements in pain levels and mobility were noted following a course of manual treatment. If, as Mahato [22][23][24][25][26][27] suggests, the decreased mobility at the L5/S1 junction resulted in biomechanical changes and altered weight distribution at this level, it is possible that these biomechanical changes increased the stress on the muscles in the region of the sacroiliac and lumbosacral junctions on the affected side, which resulted in the observed presentation. If that is the case, there is a possible role for conservative care in patients with this type of anomaly, not to relieve pressure on an impinged nerve but instead to address muscular alterations in the lumbopelvic musculature.…”

Lumbosacral transitional vertebrae: variations in low back structure, biomechanics, and stress patterns

“…The side bearing the additional L5/S1 relationship (unilateral pseudoarticulation, sacralization, or lumbarization) would transmit larger proportion of load on that side. 4,5 This would possibly result in, as Muir has observed in both of his cases, (a) lateral tipping of the iliac crest(s) to the same side and (b) the convexity of a scoliotic curve (if at all subjectively present) directed towards the side of the unilateral transition. This author has observed discrete side-related variations (in area and of vertical positioning) of the sacral auricular surfaces in context of LSTV.…”

“…In cases of unilateral sacralizations, it is interesting to note that fusion of the ends of L5 transverse process to the sacral ala augments the auricular area on that side only. 5 Muir has reported an additional, small sacroiliac (SI) articulation in his case 2. Unilateral increase in the auricular area most probably results in (a) increased loading of that joint, (b) greater wear and subsequently irritation of the joint, (c) greater fixation on examination, and possibly (d) increased one-sided muscle activity.…”