Article
Spontaneous ossification of the sacroiliac joint – prevalence and risk factors
Spontane Verknöcherung des Iliosakralgelenks – Prävalenz und Risikofaktoren
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Published: | June 4, 2021 |
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Objective: Sacroiliac joint (SIJ) degeneration is common in middle aged and elderly patients. In some cases, spontaneous intraarticular ossification can occur, even in the absence of prior spinal fusion surgery or any symptoms. Why some patients exhibit spontaneous SIJ ossification while others do not, remains unclear. We aimed to assess the prevalence of spontaneous SIJ ossification and to describe different ossification patterns. We also examined factors associated with spontaneous SIJ ossification.
Methods: Using pelvic CT imaging, we examined ossification patterns across the SIJ in 200 subjects: 100 subjects after transforaminal lumbar interbody fusion (TLIF) and 100 control subjects, which underwent CT as part of tumor staging diagnostics unrelated to the SIJ or the spine. Cases were categorized according to the following patterns of spontaneous SIJ ossification: anterior, entheseal or posterior (Figure 1 [Fig. 1]). Patient characteristics were derived from the electronic medical records.
Results: Pelvic CT examinations of 116 men and 84 women between 2019 and 2020 were evaluated. Subjects in the control group were significantly older (mean 70.4y, SD 11.3) compared to those after TLIF (mean 65.2y, SD 14.3; p=0.006). The overall prevalence of spontaneous SIJ ossification was 64.0%, 62% in the control group and 66% in the TLIF group. We observed a trend towards a predominance of the anterior type SIJ ossification in both groups (control group: 28/62 [45.2%] vs. TLIF group: 43/66 [65.2%]) followed by posterior type (20/62 [32.3%] vs. 11/66 [16.6%]) and entheseal (14/62 [22.5%] vs. 12/66 [18.2%]). Factors associated with the occurrence of spontaneous SIJ ossification were age (OR 1.03; 95% CI: 1.01-1.06; p=0.005) and previous spinal fusion surgery (OR 0.46, 95% CI (0.25-0.85); p=0.013).
Conclusion: Our findings highlight that spontaneous SIJ ossification is a frequent phenomenon, both in non-spine patients and in patients with previous spinal fusion surgery. The fact that most commonly the anterior SIJ section displayed ossification may reflect higher load bearing in this location. Since patients in the control group were at higher risk of displaying SIJ ossification, previous spinal fusion surgery may be less of a deciding factor in SIJ degeneration than frequently assumed.