Osteitis condensans ilii masquerading as sacroiliitis: a case report of an underdiagnosed condition

Abstract

Introduction and Importance:

Osteitis condensans ilii (OCI) is a benign, non-inflammatory condition characterized by triangular sclerosis of the iliac bone adjacent to the sacroiliac joint, typically with preserved joint space and normal inflammatory markers. It can mimic inflammatory sacroiliac disorders, leading to misdiagnosis.

Case Presentation:

We report the case of a 38-year-old multiparous woman with chronic low back pain that began during pregnancy and persisted for 2.5 years. The pain was mild, intermittent, and aggravated by activity. She had initially been treated for spondyloarthritis without improvement. Examination revealed normal spinal mobility and localized tenderness over the sacroiliac region. Laboratory tests, including inflammatory and autoimmune markers, were normal. The radiographs demonstrated bilateral triangular iliac sclerosis without erosions. MRI confirmed sclerosis with preserved sacroiliac joint space, consistent with OCI.

Clinical Discussion:

OCI is often underrecognized and may be mistaken for axial spondyloarthritis. Mechanical stress, particularly during pregnancy, is implicated; however, cases in men and nulliparous women suggest a multifactorial etiology. Imaging is crucial for diagnosis, as plain radiographs may be insufficient.

Conclusion:

OCI should be considered in patients with chronic low back pain to prevent unnecessary immunosuppressive therapy. Conservative management with physiotherapy, non-steroidal anti-inflammatory drugs (NSAIDs), and short-term muscle relaxants can provide significant symptomatic improvement, though complete resolution may require longer follow-up and adherence to rehabilitation measures. The overall prognosis is favorable.

Introduction

Osteitis condensans ilii (OCI), also known as osteopathia condensans ilii or hyperostosis triangularis ilii, is marked by a benign, triangular area of sclerosis in the ilium adjacent to the sacroiliac joint[1]. It is a condition that can lead to low back pain and is often regarded as an orthopedic enigma. It is typically discovered incidentally on radiographs, which reveal sclerosis of the iliac bone next to the sacroiliac joint. Although many articles have been published since OCI was first described, its pathogenesis remains poorly understood. Mechanical stress on the sacroiliac joints has been suggested as a possible contributing factor, especially since OCI is more commonly observed in women during or after pregnancy. However, it can also affect men and nulliparous women^[2,3].

HIGHLIGHTS

• This case report describes osteitis condensans ilii (OCI), a benign, non-inflammatory condition, in a 38-year-old multiparous woman. The patient developed mild, intermittent lower back pain, exacerbated by physical activity and prolonged standing, beginning in the second trimester of her pregnancy.

• She was initially misdiagnosed with sacroiliitis and treated with methotrexate, sulfasalazine, and tofacitinib without improvement, highlighting the diagnostic challenges.

• Imaging, particularly X-ray and MRI, is crucial for differentiating OCI – which shows localized anterior iliac sclerosis and minor asymmetric bone marrow oedema (BME) – from sacroiliitis, which presents with diffuse BME and structural lesions.

• Highlights conservative management with physiotherapy, NSAIDs, and short-term muscle relaxants, resulting in significant symptomatic improvement.

• Stresses the importance of recognizing OCI to prevent unnecessary immunosuppressive therapy and ensure appropriate, patient-centered care.

Distinctive radiographic features of OCI include the preservation of the sacroiliac joint space without evidence of erosions or ankylosis. Additionally, patients typically present with normal inflammatory markers and negative human leukocyte antigen (HLA)-B27, and the condition generally carries a favorable prognosis[4]. Despite being a known entity, OCI continues to be underrecognized and frequently misdiagnosed as axial spondyloarthritis, leading to unnecessary investigations and potentially harmful immunosuppressive therapy. This case underscores the diagnostic challenges of OCI, highlights the need for careful imaging interpretation, and addresses the limited literature on its clinical presentation, particularly in multiparous women with chronic low back pain. Here, we present the case of a 38-year-old woman with back pain initially managed as sacroiliitis, later diagnosed as OCI following MRI of the sacroiliac joint.

This case report was drafted in accordance with the CARE Case Report Guidelines (2013) and the TITAN guidelines (TITAN 2025)^[5,6].

Case presentation

A 38-year-old multiparous woman (G2P2L2) presented to the rheumatology outpatient department with a chief complaint of lower back pain that had persisted for the past 2.5 years. The pain was insidious in onset, intermittent, dull aching in nature, non-radiating, aggravated by physical activity and prolonged standing, and mild in intensity. Notably, the pain improved slightly with the use of analgesics. Her back pain had started during the sixth month of her second trimester of pregnancy.

There was a history of early morning stiffness lasting less than half an hour; however, there was no limitation of back or neck movements or involvement of other joints. There was no history of dactylitis, enthesitis, psoriasis, urethritis, uveitis, or inflammatory bowel disease. There was no significant family history of back pain, nor any preceding history of trauma. She denied bowel or bladder incontinence, saddle anesthesia, lower extremity weakness, fever, night sweats, or recent changes in appetite or weight.

Prior to this presentation, she had visited multiple health care centers, where she was diagnosed and treated for spondyloarthritis; however, her back pain persisted despite therapy. Her treatment included sulfasalazine, methotrexate, and subsequently Tofacitinib, a Janus kinase (JAK) inhibitor, yet no clinical improvement was achieved.

Clinical examination revealed a normal erect posture with increased lumbar lordosis, without any limitation in spinal mobility. Mild tenderness was elicited over the bilateral sacroiliac joints and at the L4 and L5 levels of the lumbar spine. The modified Schober’s test measured 6 cm (normal >5 cm), and chest expansion was within the normal range at 7.5 cm (normal >5 cm). Lateral lumbar flexion resulted in a finger-to-floor distance of 7 cm (normal <10 cm), and the tragus-to-wall distance was 7.5 cm (normal <10 cm). There were no clinical signs of peripheral arthritis. Both the Straight Leg Raise Test and the Flexion, Abduction, and External Rotation test were negative. Neurological examination demonstrated intact sensory and motor function in the lower limbs, with preserved deep tendon reflexes bilaterally; no neurological deficits were noted.

Based on the clinical findings, the differential diagnosis included conditions affecting the sacroiliac region, such as mechanical causes of low back pain, axial spondyloarthritis, infectious sacroiliitis, OCI, Paget’s disease, and metastases.

Laboratory investigations, including complete blood count, erythrocyte sedimentation rate, C-reactive protein, and vitamin D levels, were performed and found to be within normal physiological limits. Similarly, screening for autoimmune markers – including antinuclear antibody by the indirect fluorescent antibody method, rheumatoid factor by nephelometry, HLA-B27 by polymerase chain reaction, and extractable nuclear antigen profile by immunoblot – also yielded normal results.

Radiographic examination (X-ray) demonstrated triangular sclerosis of the iliac side of the bilateral sacroiliac joints (Fig. 1). An MRI performed at an outside centre was reported as sacroiliitis, and treatment was initiated accordingly; however, her symptoms did not improve. Subsequently, she presented to our center, where an MRI of the sacroiliac joints was reviewed and demonstrated iliac sclerosis, with minimal bone marrow oedema (BME) adjacent to the area of sclerosis without evidence of erosions or joint space narrowing, supporting an alternative diagnosis of osteitis condensans ilii (Fig. 2).

Figure 1.

X-ray of sacroiliac joints showing bilateral SI joints with sclerosis of joints without any bony erosion or joint space narrowing.

Figure 2.

MRI scan showing sclerosis of the iliac bones adjacent to the sacroiliac joints, with preservation of the joint space and no evidence of erosions.

The patient was counseled regarding the benign nature and favorable prognosis of OCI. A detailed timeline of the patient’s symptoms, treatment attempts, presentation at our center, and follow-up is provided in Table 1. She was advised to follow a structured physiotherapy program aimed at improving pelvic stability and reducing sacroiliac joint stress. The regimen included core stabilization exercises to strengthen the abdominal and lower back muscles, pelvic floor exercises to enhance pelvic support, postural correction techniques to optimize daily alignment, and stretching of the hip flexors, hamstrings, and gluteal muscles to alleviate muscular tension. Pharmacological management included anti-inflammatory medication (ibuprofen 400 mg three times daily for 2 weeks, then as needed) along with a short course of muscle relaxant (cyclobenzaprine 5 mg three times daily for 5 days, then as needed) to relieve pain. At 2-month follow-up, the patient remained largely asymptomatic in the sacroiliac region but report occasional midline lower back pain. Symptomatic improvement was achieved with short-term muscle relaxants and continued physiotherapy, indicating that conservative management can provide significant pain relief, though complete resolution of symptoms may require longer-term follow-up.

Table 1.

Timeline of the patient’s clinical course, treatments, and follow-up

Timeline	Event	Treatment	Outcome
Symptom onset	2.5 years; began in 6th month of second pregnancy	Analgesics as needed	Mild improvement
Prior to presentation	Diagnosed as spondyloarthritis at another centre	Sulfasalazine → Methotrexate → Tofacitinib	No clinical improvement
Presentation at our center	Detailed evaluation	MRI reviewed	Correct diagnosis: OCI
Post-diagnosis	Conservative management	Anti-inflammatory drug,Physiotherapy,muscle relaxants	Significant improvement at 2-month follow-up. Occasional mild lower back pain

Discussion

OCI is a non-inflammatory condition of uncertain etiology characterized by sclerotic lesions predominantly affecting the iliac side of the sacroiliac joints. In many patients, it is detected as an incidental imaging finding; however, it can be associated with lower back pain and may clinically mimic inflammatory rheumatic conditions such as axial spondyloarthritis[4]. In our case, the patient presented with lower back pain mimicking sacroiliitis and was initially managed at another center; however, subsequent evaluation at our center led to the correct diagnosis of OCI.

The pathophysiological mechanisms of pain in OCI and the development of triangular sclerosis remain incompletely understood, with no definitive explanations established thus far[4]. Mechanical strain across the pelvis and sacroiliac joints, particularly during pregnancy when vascularity and ligamentous laxity increase, is thought to contribute to subchondral sclerosis, especially on the iliac side. However, this does not fully account for cases in nulliparous women and men, suggesting additional factors, such as hip anatomical variations (e.g., protrusio acetabuli and coxa profunda). Histopathological findings revealed normal articular cartilage and ligaments, increased concentric lamellar bone deposition, narrowed Haversian canals, and occasional marrow fibrosis, notably without inflammatory infiltrates, synovitis, erosions, or ossification. Collectively, these findings support the view that OCI is a non-inflammatory, mechanically mediated condition, leading some authors to propose the term idiopathic pelvic sclerosis as a more accurate descriptor^[7–9]. The prevalence of OCI during pregnancy has been reported to range from 27% to 73%, with the highest incidence occurring around 3 months postpartum and gradually declining to 12–41% by 12 months[4]. However, in our case, it occurred during the second trimester, at 6 months of pregnancy.

OCI is often overlooked and requires a high index of clinical suspicion for diagnosis. It is usually diagnosed through radiological evaluation, and careful distinction from spondyloarthropathies, inflammatory arthritis, and malignancy is essential. Radiographic sclerosis on the iliac side of the sacroiliac joints may not always be apparent on plain radiographs; therefore, advanced imaging modalities, such as MRI or CT, may be necessary for clearer delineation. MRI findings characteristic of OCI include localized subchondral sclerosis of the anterior sacroiliac joint, predominantly on the iliac side, occasionally associated with bony irregularities and minor BME. The BME is typically continuous, ventrally located, and often bilateral but asymmetric, sometimes extending more than 10 mm in depth[4]. Although BME in OCI is typically minor and confined to areas adjacent to anterior sclerosis, it can occasionally be extensive, thereby mimicking the imaging features of active inflammatory sacroiliitis[10]. In contrast, sacroiliitis shows more diffuse BME involving both sacral and iliac sides, often extending posteriorly, with structural lesions such as erosions, subchondral cysts, fat metaplasia, and progressive joint space narrowing, sclerosis, or ankylosis^[10,11]. In our case, the presence of BME and sclerosis along with early morning stiffness and pain aggravated by prolonged standing could have suggested a diagnosis of sacroiliitis; however, the hallmark structural changes of sacroiliitis were absent, highlighting the potential for misdiagnosis due to overlapping clinical and imaging features. Moreover, OCI is considered a non-inflammatory condition as it is typically not associated with elevated inflammatory markers[12].

There are no specific treatment regimens for OCI and no randomized controlled trials have evaluated their efficacy. The primary goal of management is to alleviate pain, stiffness, and limited mobility, thereby enhancing the patients’ quality of life. The initial steps include educating and reassuring patients about the benign nature and nonprogressive course of the disease. Conservative approaches, such as physical therapy, muscle relaxants and NSAIDs, are generally effective, whereas image-guided corticosteroid injections can be considered in patients unresponsive to conservative measures. Rarely, when pain persists, invasive procedures such as percutaneous iliac drilling or surgical resection of the sclerotic bone have been used, although evidence is limited due to the small number of patients^[13–15] .A study by Biswas et al reported notable improvement with physiotherapy and anti-inflammatory treatment at 3 months; however, Bashyal et al reported limited efficacy of physical therapy. In our patient, similar interventions achieved significant symptomatic improvement, though complete resolution was not achieved^[2,12]. The optimal management of refractory cases remains uncertain[2].

In resource-limited settings like ours, advanced diagnostic modalities such as MRI, CT, or PET scans may not be feasible for all patients with low back pain. However, considering OCI as a potential differential diagnosis can facilitate timely and accurate identification, while avoiding unnecessary or inappropriate treatments.

Conclusions

OCI is a benign, noninflammatory condition that can mimic sacroiliitis, leading to misdiagnosis and prolonged symptoms. An accurate diagnosis requires a high index of suspicion, thorough clinical evaluation, and appropriate imaging, as plain radiographs may be insufficient. OCI typically presents with sclerosis of the iliac side of the sacroiliac joints without erosions or joint space narrowing, and lacks systemic inflammatory markers. Management focuses on patient education, physiotherapy, and symptomatic relief using anti-inflammatory medications. This case highlights the importance of considering OCI in the differential diagnosis to avoid unnecessary treatment and ensure appropriate management of chronic low back pain.

Ethical approval

Ethical approval is not required for a case report.

Consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Sources of funding

Not applicable.

Author contributions

R.R.B.: Conceptualization, Investigation, Project administration, Supervision, validation, visualization, Writing – original draft, writing-review and editing. P.K.:Conceptualization, Investigation, Project administration, Supervision, validation, visualization, Writing – original draft, writing-review and editing. A.S.: Conceptualization, Project administration, Writing – original draft, writing review and editing. S.P.: conceptualization, Writing – original draft, writing-review and editing. S.G.: conceptualization, Writing – original draft, writing-review and editing. N.S.: conceptualization, Writing – original draft, writing-review and editing. R.R.:conceptualization, Writing – original draft, writing-review and editing.

Conflicts of interest disclosure

None.

Research registration unique identifying number (UIN)

Not applicable.

Guarantor

Rishi Ram Banjade, Prabin Khatri, Aabishkar Subedi.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Data availability statement

Not applicable.