Subchondral Bone Changes Following Sacroiliac Joint
Arthrodesis – A Morpho-mechanical Assessment of
Surgical Treatment of the Painful Joint
Authors: Poilliot Amelie 
Published: May 2021

Background: Sacroiliac joint arthrodesis is an ultima ratio treatment option for sacroiliac joint
dysfunction. Fusion drastically reduces sacroiliac joint movement providing long-lasting pain-relief
associated with tension-relief to the innervated sacroiliac joint structures involved in force closure.
Objectives: To display the bone mineralization distribution patterns of the subchondral bone plate
in 3 distinct regions (superior, anterior, and inferior) of the sacral and iliac counterparts of the sacroiliac
joint pre- and post-sacroiliac joint arthrodesis and compare patterns of sacroiliac joint dysfunction postsacroiliac
joint fusion with sacroiliac joint dysfunction pre- arthrodesis patterns and those from healthy
controls.
Study Design: An observational study.
Setting: The research took place at the University of Basel, Switzerland, where the specific image
analysis program (Analyze, v7.4, Biomedical Imaging Resources, Mayo Foundation, Rochester, NY, USA)
was made available.
Methods: Mineralization densitograms of 18 sacroiliac joint dysfunction patients pre- and post-sacroiliac
joint arthrodesis (≥ 6, ≥ 12, and ≥ 24 months post-surgery) were obtained using computed tomography
osteoabsorptiometry. For each patient, pre- vs. post-surgery statistical comparisons were undertaken,
using the Hounsfield unit values derived from the subchondral mineralization of superior, anterior, and
inferior regions on the iliac and sacral auricular surfaces. Post-operative values were also compared to
those from a healthy control cohort (n = 39).
Results: In the pre-operative cohort at all 3 follow-up times, the superior iliac region showed significantly
higher Hounsfield unit values than the corresponding sacral region (P < 0.01). Mineralization comparisons
were similar for the sacrum and ilium in the anterior and inferior regions at all follow-up points (P > 0.5)
with no surgery-related changes. Sacral density increased significantly in the post-operative state; not
observed on the ilium. Post-operative sacroiliac joints showed a significantly increased mineralization in
the superior sacrum after ≥ 6 months (P < 0.05), not replicated after ≥ 12 nor ≥ 24 months. Further
comparison of post-operative scans versus healthy controls revealed significantly increased mineralization
in the superior sacral region at (≥) 6, 12, and 24 months (P < 0.01), likely related to bone grafting, and in
the anterior and inferior regions in post-operative scans at ≥ 12 and ≥ 24 months follow-up (P < 0.05).
Limitations: The given study is limited in sample size. Post-operative computed tomography scans
had screws which may have left artifacts or partial volume effects on the surfaces. Healthy controls were
different patients to the sacroiliac joint dysfunction and post-operative cohorts. Both cohorts were agematched
but this comparison did not take into account potential population differences. Size differences
in the regions may have also been an influencing factor of the results as the regions were based on the
size and shape of the articular surface.
Conclusions: Sacroiliac joint arthrodesis results in an increased morpho-mechanical conformity in the
anterior and inferior sacrum and reflects variable morpho-mechanical density patterns compared to the
healthy state due to permanent alterations in the kinematics of the posterior pelvis.
Key words: Bone mineral density, bone mineralization, computed tomography, Hounsfield units,
osteoabsorptiometry, sacroiliac, sacroiliac joint arthrodesis, sacroiliac joint fusion, sacroiliac joint
dysfunction, subchondral bone plate