CASE 15130 Published on 03.11.2017

Otto pelvis

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Tosha Desai1 Nandini Bahri2Shilpa Chudasama3 Dipak Parmar4 Shailesh Bhuriya5

Shri GGG HOSPTAL, M.P Shah medical college; P.N Marg 361008 Jamnagar, India; Email:toshajdesai@gmail.com

1 Tutor, Department of Radiodiagnosis
2 Professor, Department of Radiodiagnosis
3 Associate Professor, Department of Radiodiagnosis
4 Associate Professor, Department of Orthopedics
5 Resident, Department of Radiodiagnosis
Patient

35 years, female

Categories
Area of Interest Bones, Musculoskeletal bone, Pelvis, Musculoskeletal joint ; Imaging Technique MR
Clinical History
A 35-year-old female patient came with complaints of gradually increasing bilateral hip pain and restriction of motion since 7 years. No past history of trauma or steroid intake. Blood counts were normal.
Imaging Findings
On X-ray PBH AP view, the distance between medially located acetabular line and laterally located ischio-femoral line was 7 mm on the right side and 3 mm on the left side. The centre edge angle of Wiberg was 70 degrees on the right side and 58 degrees on the left side, suggestive of right moderate and left mild protrusio acetabuli. (Figure 1)
There was severe symmetrical reduction in the joint space with medial migration of femoral heads, femoral head articular surface deformity in the form of mild collapse, flattening and irregularity, subchondral sclerosis and femoro-acetabular osteophytes (grade IV osteoarthritis). (Figure 2)
On MRI with T1WI, PDfatsat, STIR and T2WI, the above findings were confirmed. Additional findings noted were near complete denudation of articular cartilage, subchondral cysts, thin curvilinear hypo-intense subchondral lines in weight bearing portion of femoral epiphyses (possible subchondral fractures), patchy hyper-intensities (on STIR) involving bilateral femoral heads and juxta-articular acetabulum with minimal bilateral joint effusion.(Figures 3 and 4)
Discussion
Otto pelvis or arthrokatadysis is an unusual form of primary osteoarthritis with primary protrusio acetabuli, described first by German pathologist Otto in 1824 [1], frequently affecting young women. Familial factors like failure of ossification or remodelling of weak acetabulum are implicated in its aetiology. In one-third of patients it is bilateral [2].
Usually osteoarthritis is associated with supero-lateral subluxation of the femoral head. However, in the 20% of individuals who present with primary acetabular protrusion, there is concentric joint space loss and medial intra-pelvic displacement of the medial wall of the acetabulum and the femoral head with degenerative changes established at an early age [3]. Patients may be asymptomatic or may present with hip (or rarely knee) pain, restriction of movements and joint stiffness [4].
Plain AP radiographs of bilateral hip joints are adequate in diagnosis. MR arthrograms with radial sequences may be required pre-operatively for assessing cartilage injury, marrow changes and any associated features of pincer femoro-acetabular impingement [5].
Normally, on an AP radiograph, the medial wall of the acetabulum lies 2 mm lateral to the ilio-ischial line (Kohler’s line) in males and 1 mm medial to this line in females. If the medial wall of acetabulum protrudes medial to the ilio-ischial line by 3 mm in males or 6 mm in females, it favors the diagnosis of protrusion. Protrusion is graded as mild (1 to 5 mm), moderate (5 to 10 mm) and severe (10 to 15 mm) with reference to the ilio-ischial line. Center Edge angle of Wiberg is an angle formed by a line drawn from the centre of the femoral head to the outer edge of the femoral roof and a vertical line drawn through the centre of the femoral head. Protrusion is present if the CE angle is greater than 35 degrees. Normally, the CE angle is around 25 degrees while an angle less than 20 degrees suggests dysplasia [5].
In cases without cartilage degeneration, open surgical dislocation with osteochondroplasty of the acetabular rim and the femoral neck is recommended. Valgus inter-trochanteric osteotomy may be indicated in cases with inadequate femoroacetabular clearance. In cases with early cartilage degeneration on MRA, osteochondroplasty is not sufficient and osteotomy of the pelvis, femur, or both depends on the individual morphology. In adult patients with advanced degenerative changes, total hip arthroplasty is the treatment of choice [6].
Differential Diagnosis List
Otto pelvis
Rheumatoid arthritis
Ankylosing spondylitis
Idiopathic chondrolysis
Osteomalacia
Final Diagnosis
Otto pelvis
Case information
URL: https://www.eurorad.org/case/15130
DOI: 10.1594/EURORAD/CASE.15130
ISSN: 1563-4086
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