Type:
Educational Exhibit
Keywords:
Education and training, Education, MR, CT, Conventional radiography, Musculoskeletal bone, Bones, Anatomy
Authors:
A. N. Pérez Pérez1, A. P. Marrero González2, J. R. Ortiz-Cruz1, J. Lugo-Rosado2, E. Trullenque1, J. Vidal1; 1San Juan, PR/US, 2San Juan, Puerto Rico/US
DOI:
10.1594/ecr2018/C-2377
Findings and procedure details
HIP AND KNEE
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Diagrammatic overview
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Fig. 1 and Fig. 2
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Pictorial review
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Os acetabuli
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Prevalence: 3%[1]
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Location: Adjacent to the acetabular rim
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Overview: Or os acetabulare,
an unfused secondary ossification center at the acetabular rim.
Also thought to represent a rim fracture fragment secondary to a cam type femoroacetabular impingement (FAI).
[2,3] Studies have proposed that “true” os acetabuli have cartilagenous growth plates more parallel to the joint surface,
whereas FAI acetabular rim fragments growth plates are more perpendicular to the joint surface.
[2,4] May be misdiagnosed as a fractured osteophyte,
acetabular chondro-ossification or prior acetabular fractures.[1]
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Radiographic characteristics: Usually rounded with a concave lateral border and convex medial border.
May be bilateral and/or fused to the acetabulum.
AP pelvis,
false profile and Dunn views of the hip are recommended to fully characterize the femoral and acetabular anatomy.[5]
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*See Fig. 1 for diagram and Fig. 3 for case
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Os fabella
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Prevalence: 10-30%; 63-85% bilateral; [6] higher rates in Asian population (66-87%).[7]
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Location: Lateral head of the gastrocnemius (rarely in the medial head) articulating with the lateral or medial femoral condyle.
[6,8]
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Overview: Bilateral,
bipartite,
tripartite or double.
May cause posterolateral femoral pain exacerbated by direct pressure,
known as fabella syndrome, due to friction between the fabella and the posterolateral femoral condyle.
[1,2] Has been shown to present with common fibular nerve palsy.
[7] May be misdiagnosed as a loose body.
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Radiographic characteristics: Elliptical or circular in shape and may vary in size,
from 3.5-13.5 mm in length,
2-9 mm in width and 1.5-10 mm in depth.[6] Best visualized in lateral radiographs of the knee.
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*See Fig. 2 for diagram and Fig. 4 for case
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Cyamella
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Prevalence: Extremely infrequent in humans
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Location: Within the popliteus tendon,
at the popliteus myotendinous junction.[1,9]
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Overview: Also known as the popliteal fabella,
or fabella distalis.
Articulates with the posterior surface of the lateral femoral condyle.[6] Considered to be a sesamoid bone,
as it lies within the popliteus tendon.[2,6] Seen in approximately 84% of dogs,
100% of cats and decreases in prevalence in higher primates and humans.[10] Rarely shown to cause symptoms,
with one case report citing sesamoiditis with pseudo-locking and clicking.
May be misdiagnosed as an intra-articular loose body,
a fabella,
or heterotopic ossification.[2,9]
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Radiographic characteristics: Best seen on AP radiographs of the knee,
most commonly found within the lateral femoral groove.
[3] On T1,
T2 and T2*-weighted MR images,
the cyamella appears as an ossicle with low signal intensity along its borders.
[9]
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*See Fig. 2 for diagram and Fig. 5 and Fig. 6 for case
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Meniscal ossicle
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Prevalence: 0.15%.[3]
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Location: Posterior horn,
within medial meniscus[6]
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Overview: Three theories as to its origin: it is an anatomical variant,
it is a post-traumatic result of heterotopic ossification,
or it is the product of mucoid degeneration.[2] Composed of mature lamellar and cancellous bone,
surrounded by hyaline cartilage.[6] Usually incidental and asymptomatic,
but may produce diffuse pain and a locking sensation,
mimicking a torn meniscus or an intra-articular loose body.[3] Should not be confused with an avulsion of the PCL.
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Radiographic characteristics: Best seen on AP radiographs.
Lateral views have shown that the ossicle moves with the tibia during knee rotation.[6] MR imaging is useful in differentiating it from common misdiagnoses, exhibiting marrow intensity on all sequences,
with a surrounding peripheral rim of low signal intensity,
corresponding to its cortex.[2,3]
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*See Fig. 2 for diagram and Fig. 7 for case
FOOT
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Diagrammatic overview
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Fig. 8
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Pictorial Review
***See Table 1 and Table 2 for complete poster summary***