Auricular surface morphology and surface area does not influence subchondral bone density distribution in the dysfunctional sacroiliac joint

Abstract

Background: The subchondral lamella of the sacroiliac joint (SIJ) auricular surface is morphologically inconsistent, varying inter-individually and side-dependently. These variations have been well documented, however, the morpho-mechanical relationship to sacroiliac joint dysfunction (SIJD) remains unstudied to date. Here, the bone mineralisation density of the iliac and sacral auricular surface subchondral endplate is compared between morphological subtypes, as well as in large and small surfaces, in a cohort comprising SIJD joints and controls.Methods: Computed tomography (CT) datasets from 29 patients with bilateral or unilateral SIJD were subjected to CT osteoabsorptiometry. Sacral and iliac surface areas and posterior angles were calculated and surfaces were classi ed into small (<15 cm 3 ) and large (≥15 cm 3 ) joints and morphological types 1 (>160°), 2 (130-160°) and 3 (<130°), respectively. Mineralisation patterns were classi ed into four patterns, two marginal (M1 and M2) and two non-marginal (N1 and N2). Each sacral and iliac surface was subsequently classi ed into one of these mineralisation groups.Results: The surface area of all joints in the cohort averaged 15.0±2.4 cm 2 (males 16.2±2.5 cm 2 , females 13.7±1.6 cm 2 ). No age correlations with surface area were found nor differences in mean HU values when comparing sizes, sexes or morphology type when looking at painful joints (unilateral or bilateral) and contralateral non-painful joints. Comparisons of controls with the SIJD cohort revealed signi cant differences in female sacra (p=0.02) and small sacra (p=0.03). There was low conformity in marginal and non-marginal patterns, 26% for contralateral non-painful joints, and 46% conformity in painful joints.The majority of dysfunctional joints was of type 2 morphology (59%), equally distributed between small (49%) and large joints (51%). Larger joints had the highest frequency of painful joints (72%). Regarding the prominence of sub-patterns, M1C was more prominent in painful joints.Conclusions: Load distribution related to difference in auricular surface morphology seems to have little impact on pain-related subchondral bone adaptation in cases of SIJD. Larger joints may be predisposed to the onset of pain due to the weakening of the extracapsular structures. Pain-affected joints re ect common conformity patterns of sacral apex mineralisation with corresponding superior corner iliac mineralisation.

Influence of size and shape of the auricular surfaces on subchondral bone density distribution in the sacroiliac joint

“…Datasets for patients CT‐OAM were acquired by means of a conventional clinical CT (SOMATOM as64 open, Siemens) according to previous studies (Poilliot et al, 2022 ; Poilliot, Tannock, et al, 2020 ). The slice thickness averaged 1.25 mm (0.98 resolution) for the patient datasets and 0.75 mm (average of 0.6 resolution) for the cadaveric specimens.…”

“…Regarding the role of the auricular surface in joint mobility and bipedal force transmission, some studies have looked into the influence of the morphological differences and placement of the auricular surfaces in relation to the bony anatomy (Brunner et al, 1991 ; Rana et al, 2015 ; Waldrop et al, 1993 ). However, few studies have looked into whether the general shape and size of the SIJ auricular is associated with SIJ pain and what differences there may be between sexes (Jesse et al, 2017 ; Nishi et al, 2020 ; Ou‐Yang et al, 2017 ; Poilliot et al, 2022 ). Furthermore, no study has yet looked into the influence of different morphologies, including shape and size of a joint, on the overall long‐term force transmission within the ‘healthy’ pelvis and what that might imply for the development of subsequent dysfunction or for the general function of the SIJ.…”

“…A previous paper assessed the subchondral bone density distribution between the three morphology types in control SIJs and in joints with sacroiliac joint dysfunction (Poilliot et al, 2022 ) and found variable mineralization patterns in the patients with dysfunction than the ‘healthy’ controls. Applying the same methods for the creation of subchondral bone densitograms on the sacral and iliac sides, this study aims to visualize and compare the mineralization patterns between the three morphological types in the painless/healthy state of the joint.…”

The Sacroiliac Joint

“…The SIJ, a large, irregularly shaped diarthroidal joint with cartilage surfaces, is the largest surface area joint in the body. Poilliot et al measured the surface area in patients with SIJ dysfunction and reported the dysfunctional cohort area averaged 15.0 ± 2.4 cm 29 . They concluded that larger joints are predisposed to develop pain, which may be due to the dysfunction of extracapsular joint structures, which take active part in pelvic load distribution.…”

“…The joint is also composed of bony anatomy and ligamentous components. The ilium and the sacrum articulate with a typically c-shaped surface 9-12 . There is variation in the number of segments, with there reliably being at least 2 segments.…”