|Year : 2016 | Volume
| Issue : 2 | Page : 156-157
Femoroacetabular impingement mimicking avascular osteonecrosis on bone scintigraphy
Juan Pablo Suarez1, María Luz Domínguez1, Zulema Nogareda1, María Asunción Gómez1, Jose Muñoz2
1 Department of Nuclear Medicine, Caceres Hospital, Cáceres, Spain
2 Department of Nuclear Medicine, University Medical Center, Orense, Spain
|Date of Web Publication||9-Mar-2016|
Juan Pablo Suarez
Department of Nuclear Medicine, "San Pedro de Alcántara" Hospital, Cáceres, Ave. Pablo Naranjo S/N 10003, Cáceres
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Femoroacetabular impingement (FAI) is a structural abnormality of proximal femur and/or acetabulum. It has been recently described, and there are limited reports in nuclear medicine literature because bone scintigraphy is not listed in its diagnostic protocol, but it should be included on differential diagnosis when evaluating patients, with hip-related symptoms because it may be misinterpreted as degenerative changes or avascular necrosis, and its early treatment avoid progression to osteoarthritis. We describe the case of a male who suffered from hip pain. Bone planar scintigraphic appearance mimicked avascular necrosis, but single photon emission computed tomography (CT) imaging and CT examination confirmed the diagnosis of FAI.
Keywords: Avascular osteonecrosis, bone scintigraphy, femoroacetabular impingement, hip
|How to cite this article:|
Suarez JP, Domínguez ML, Nogareda Z, Gómez MA, Muñoz J. Femoroacetabular impingement mimicking avascular osteonecrosis on bone scintigraphy. Indian J Nucl Med 2016;31:156-7
|How to cite this URL:|
Suarez JP, Domínguez ML, Nogareda Z, Gómez MA, Muñoz J. Femoroacetabular impingement mimicking avascular osteonecrosis on bone scintigraphy. Indian J Nucl Med [serial online] 2016 [cited 2019 Nov 15];31:156-7. Available from: http://www.ijnm.in/text.asp?2016/31/2/156/178337
A 42-year-old man presented with one year history of progressive left hip pain resulting in restricted mobility in flexion and internal rotation. There was no history of trauma, and a radiograph of the left hip demonstrated a cortical bump in the femoral neck and a slight narrowing of the joint space. Tc-99m hydroxymethylenediphosphonate bone scan [Figure 1] anterior and posterior planar images (a) demonstrated an incomplete "donut" of increased activity surrounding a relatively "cold" left femoral head suggesting the presence of avascular necrosis. Single photon emission computed tomography (SPECT) of the pelvis was performed to further evaluate this area (b). Correlation between scintigraphic uptakes and radiological findings on pelvic CT scan is shown at selected coronal slices of CT (c) and SPECT study (d) and radiograph (e) of left hip. The increased tracer uptakes were located at the lateral bump on the left head-neck junction (thick arrows), in the superolateral and inferointernal aspect of the acetabulum related to degeneration (thin arrows) and in an osteophyte in the inferior aspect of the femoral head (heads of arrows). CT axial slices of left femoral head (f) did not show typical findings of avascular necrosis (low-density areas or clumping and distortion of trabeculae), so all findings suggested the diagnosis of femoroacetabular impingement (FAI) of the cam type.
FAI is characterized by a pathologic contact during hip joint motion between skeletal prominences of the acetabulum and the femur.  Two types of impingement are distinguished [Figure 2]a: Cam, which is associated with reduced femoral head-neck offset (more common in young men) and pincer, present with acetabular retroversion (more common in middle-aged women), with the majority of the patients having both (mixed type). 
|Figure 1: Anterior and posterior (a) planar images with Tc-99m hydroxymethylene diphosphonate (HMDP) demonstrated abnormal uptake in the left femoral head. Axial, coronal and sagittal slices of SPECT of the pelvis (b) allowed a better anatomical location. Correlation between scintigraphic uptakes and radiological findings is shown at selected coronal slices of CT (c) and SPECT study (d), and radiograph (e) of left hip. CT axial slices of left femoral head (f) did not suggest the presence of avascular necrosis|
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|Figure 2: (a) Graphical illustration of the types of femoro-acetabular impingement. The shaded areas indicate the sites of abnormality. (b) Volumetric imaging of pelvis showing pathological uptake around left head-neck junction (arrows)|
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Although bone scintigraphy is not included in the diagnostic protocol of FAI,  it should be included on the differential diagnosis when evaluating patients with hip-related symptoms. The scintigraphic features reflect the pattern of remodeling that occurs at the sites of impingement  (increased focal uptake involving the anterosuperior aspect of the acetabulum and/or increased tracer uptake along the anterosuperior aspect of the femoral neck), with normal blood flow images. , Positive bone scintigraphy can be an early indicator of intraarticular cartilage damage that may present before the onset of symptoms.  These findings can be misdiagnosed as degenerative changes  to avascular necrosis,  so it is very important to add tomographic images, preferably with SPECT-CT for anatomic information because early surgical correction can reduce the progression of osteoarthritis.  Surgery eliminates the pathomechanics of structural deformities: Cam impingement can be treated with anterolateral osteoplasty, often arthroscopically whereas pincer-type impingement can be treated with periacetabularosteotomy, so these treatments will ultimately reduce the necessity of hip replacements. 
We would like to remark that volumetric imaging of our case [Figure 2]b showed pathological uptake around left head-neck junction (arrows). This finding could suggest that real structure of FAI anatomic abnormality is not restricted to a focal defect, but reach the whole femoral head-neck junction although this finding has not been described in the literature to date.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]