Quantification of fat in the posterior sacroiliac joint region applying a semi-automated segmentation method

A literature review of biomechanical studies on physiological and pathological sacroiliac joints: Articular surface structure, joint motion, dysfunction and treatments

BACKGROUND

Sacroiliac joints are affected by mechanical environments; the joints are formed under mechanical stimulation, receive impact of walking between the upper and lower parts of the bodies and can be a cause of pain due to non-physiological loads. However, there are so far very few studies that reviewed biomechanics of physiological and pathological sacroiliac joints. This review article aims to describe the current sacroiliac joint biomechanics.

METHODS

Previous original papers have been summarized based on three categories: articular surface structure, sacroiliac joint motion and sacroiliac joint dysfunction and treatments.

FINDINGS

Although the articular surface morphologies vary greatly from individual to individual, many researchers have tried to classify the joints into several types. It has been suggested that the surface morphologies may not change regardless of joint dysfunction, however, the relationship between the joint structure and pain are still unclear. The range of sacroiliac joint motion is demonstrated to be less than 1 mm and there is no difference between physiological and pathological joints. The sacroiliac joint absorbs shock within the pelvis by the joint structures of pelvic morphology, ligaments and fat tissues. The morphology and motion of the sacroiliac joints may be optimized for upright bipedal walking.

INTERPRETATION

There is no doubt that pelvic mechanical environments affect pain induction and treatment; however, no one has yet provided a concrete explanation. Future research could help develop treatments based on sacroiliac joint biomechanics to support joint function.

Fat quantification in the sacroiliac joint syndesmosis: a new semi-automatic volumetric approach

Fat is physiologically embedded within the interosseous ligaments in the posterior part of the sacroiliac joint (PSIJ). This composite of fat and ligaments is hypothesized to serve a shock-absorbing, stabilizing function for the sacroiliac joint and the lumbopelvic transition region. Using a novel Python-based software (VolSEQ), total PSIJ volume and fat volume were computed semi-automatically. Differences within the cohort and the viability of the program for the quantification of fat in routine computed tomography (CT) scans were assessed. In 37 CT scans of heathy individuals, the PSIJ were first manually segmented as a region of interest in OSIRIX. Within VolSEQ, 'fat' Hounsfield units (- 150 to - 50 HU) are selected and the DICOM file of the patient scan and associated region of interest file from OSIRIX were imported and the pixel sub volumes were then automatically computed. Volume comparisons were made between sexes, sides and ages (≤ 30, 31-64 and > 65 years). PSIJ volumes in both software (VolSeq vs. OSIRIX) were non-different (both 9.7 ± 2.8cm3; p = 0.9). Total PSIJ volume (p = 0.3) and fat volume (p = 0.7) between sexes were non-different. A significant difference in total PSIJ volume between sexes (p < 0.01) but not in fat volume (p = 0.3) was found only in the ≥ 65 years cohort. Fat volume within the PSIJ remains unchanged throughout life. PSIJ volume is sex-dependent after 65 years. VolSEQ is a viable and user-friendly method for sub-volume quantification of tissues in CT.

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

The subchondral lamella of the sacroiliac auricular surface is morphologically inconsistent. Its morpho-mechanical relationship with dysfunction (SIJD) remains unstudied. Here, the iliac and sacral subchondral bone mineralization is compared between morphological subtypes and in large and small surfaces, in SIJD joints and controls. CT datasets from 29 patients with bilateral or unilateral SIJD were subjected to CT-osteoabsorptiometry. Surface areas and posterior angles were calculated and surfaces were classified by size: small (<15 cm³ ) and large (≥15 cm³ ), and morphological types: 1 (>160°), 2 (130°-160°), and 3 (<130°). Mineralization patterns were identified: two marginal (M1 and M2) and two non-marginal (N1 and N2). Each sacral and iliac surface was subsequently classified. Dysfunctional cohort area averaged 15.0 ± 2.4 cm² (males 16.2 ± 2.5 cm² , females 13.7 ± 1.6 cm² ). No age correlations with surface area were found nor mean Hounsfield Unit differences when comparing sizes, sexes or morphology-type. Controls and dysfunctional cohort comparison revealed 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-dysfunctional joints, and 46% for dysfunctional joints. The majority of painful joints was of type 2 morphology (59%), equally distributed between small (49%) and large joints (51%). Larger joints had the highest frequency of dysfunctional joints (72%). Auricular surface morphology seems to have little impact on pain-related subchondral lamella adaptation in SIJD. Larger joints may be predisposed to the onset of pain due to the weakening of the extracapsular structures. Dysfunctional joints reflect common conformity patterns of sacral-apex mineralization with corresponding superior corner iliac mineralization.

Three-Dimensional Magnetic Resonance Arthrography of Post-Arthroscopy Hip Instability Demonstrates Increased Effective Intracapsular Volume and Anterosuperior Capsular Changes

Purpose

To quantify the magnetic resonance arthrography (MRA) capsular morphologic findings associated with postarthroscopy hip instability.

Methods

Among patients with clinically significant iatrogenic hip instability at a single center, patients with preindex and postindex surgery MRAs were identified. These MRAs were compared regarding effective intracapsular volume calculated by semi-automated 3-dimensional pixel intensity region segmentation, 2-dimensional anterior proximal intracapsular area in the femoral neck axial plane reconstruction, maximal anterior fluid pocket depth, capsule retraction distance, and capsular instability grade. Morphological measurements were conducted using Horos image processing software. Paired t-test, paired Wilcoxon signed rank test, and the McNemar test were used for identifying statistical significance.

Results

In 42 patients, mean effective intracapsular volume was significantly greater in the postindex surgery MRAs (19.44 cm³ vs 17.26 cm³; P = .006). Proximal anterosuperior (12-3 o'clock) intracapsular area was also significantly greater after index surgery (2.84 cm² vs 1.43 cm²; P < .001. Proximal anteroinferior (3-6 o'clock) intracapsular area (1.34 cm² vs 0.97 cm²; P = .002), capsule deficiency grade (P < .001), anterior capsule retraction distance (4.83 mm vs 0.34 mm; P < .001), and maximum anterior fluid depth (8.33 mm vs 4.90 mm; P <.001) were also significantly increased after index surgery.

Conclusion

In comparison to the preoperative state, iatrogenic hip instability is associated with MRA findings that include increases in total effective intracapsular volume, proximal anterosuperior and anteroinferior intracapsular cross-sectional area, maximum proximal anterosuperior fluid depth, and capsule retraction distance.

Level of Evidence

Level IV, diagnostic case series.

Subchondral bone strength of the sacroiliac joint-a combined approach using computed tomography osteoabsorptiometry (CT-OAM) imaging and biomechanical validation

Bone mineral density distribution patterns at the sacroiliac joint (SIJ) may reflect long-term adaptation patterns to the loading the joint endures. This study aims to display bone mineralisation patterns of the articular SIJ subchondral lamella using computed tomography (CT) osteoabsorptiometry and mechanical indenting, to determine whether a relationship exists between mineralisation and mechanical strength. Twenty hemipelves were CT-scanned before osteoabsorptiometry densitograms were derived. Each articular side of eleven SIJs was mechanically indented following a 10-mm grid scheme. The sacral surface displayed lower Hounsfield unit (HU) values (≤ 700 HU) than the iliac side (> 700 HU). The apex, superior corner and borders yielded the highest HU scores (> 700 HU). Penetration strength was significantly higher on the iliac side (p < 0.04). Mineral density correlated positively with penetration strength of the subchondral bone layer (p < 0.05). No correlations were found between the HU values, nor between penetration strength of corresponding sides of the same SIJ in the majority of cases (p > 0.05). The iliac subchondral lamella is mechanically denser than the sacral aspect. The non-correlation between density and bone strength of articulating sides indicates biomechanical non-conformity. Loading throughout the SIJ may follow a complex distribution pattern involving the surrounding soft tissues, suspending the sacrum between the ilia.