- Email: [email protected]
Imaging Features of Osteonecrosis of the Femoral Head
Imaging Features of Osteonecrosis of the Femoral Head Alan Laorr, MD*,† Imaging studies are paramount in the diagnosis and treatment planning of femoral head osteonecrosis. Radiography, computed tomography, and magnetic resonance imaging are all valuable diagnostic tools. The imaging characteristics allow for proper staging of ONFH, and certain findings are useful prognostic predictors. It is also important to distinguish ONFH from other entities which may have some overlapping MRI features. Semin Arthro 18:192-197 © 2007 Elsevier Inc. All rights reserved. KEYWORDS osteonecrosis, femoral head, hip, imaging
Radiography
A
lthough lacking in sensitivity for early disease, radiography remains an important diagnostic tool. Conventional radiographs are often the initial imaging test performed in the evaluation of patients for osteonecrosis of the femoral head. Both anterior–posterior (AP) and frog leg lateral views should be performed. With advancing disease, the radiographic findings progress as follows: normal, cystic or sclerotic changes, subchondral radiolucency or crescent sign (subchondral fracture), femoral head flattening (collapse), joint space narrowing, and advanced degenerative changes1 (Fig. 1). Advanced secondary osteoarthritic changes would include osteophytosis, prominent joint space narrowing, superolateral subluxation of the femoral head, subchondral cystic lesions and sclerosis on both sides of the joint, and loose bodies (Fig. 2).
Scintigraphy In the past, nuclear medicine scans have been used extensively in the diagnosis of hip osteonecrosis. Single photon emission computed tomography (SPECT) has increased sensitivity compared with planar bone scintigraphy. However, poor specificity and lack of anatomic detail limit this imaging modality. The emergence of computed tomography (CT) and magnetic resonance imaging (MRI) has replaced scintigraphy to the point that bone scans are no longer widely performed
*Department of Radiology, University of Minnesota Medical Center, Minneapolis, MN. †Suburban Radiologic Consultants, Minneapolis, MN. Address reprint requests to Alan Laorr, MD, Department of Radiology, University of Minnesota Medical Center, Fairview, 2450 Riverside Avenue, Minneapolis, MN 55454. E-mail: [email protected]
192
1045-4527/07/$-see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2007.06.010
in the evaluation of osteonecrosis of the femoral head (ONFH).
Computed Tomography Computed tomography has proven to be a valuable diagnostic tool in the evaluation of ONFH. The development of multislice helical CT scanners allows for rapid scan times, highresolution images, and thin-cut multiplanar reconstructed images. Slice thickness should be 3 mm or less. CT has higher sensitivity than radiography for ONFH and shows the radiographic findings in greater detail. CT is excellent in the depiction of cortical and trabecular bone. In particular, CT is the imaging modality of choice for diagnosing subchondral fractures of the femoral head. CT is more sensitive than plain radiographs in demonstrating subchondral fractures,2 especially when minimally or not displaced (Fig. 3). Subchondral fracture is the most prognostically important predictor of progression to osteoarthritis, and therefore its presence is crucial for staging and treatment planning of osteonecrosis. It appears as a subchondral radiolucent line, with or without extension to the articular surface (Fig. 4). In patients for whom MRI is contraindicated (pacemaker, aneurysm clip, etc), CT could be used as the primary modality in the diagnosis and follow-up of ONFH. Otherwise, CT is best used as an important adjunct in the staging of established osteonecrosis, not only for the detection of subchondral fractures, but also articular collapse and secondary osteoarthritic changes2 (Fig. 5).
Magnetic Resonance Imaging Magnetic resonance imaging is the most accurate modality in the detection of early osteonecrosis of the femoral head, with
Imaging features of ONFH
193
Figure 1 (A) AP pelvic radiograph demonstrates areas of sclerosis and radiolucency within the left femoral head, typical of osteonecrosis. There is subtle evidence of subchondral collapse superiorly. (B) Frog leg lateral view more clearly demonstrates a subchondral fracture with collapse at the articular surface.
monly appear as crescentic, serpiginous, ring-like, oval, or wedge-shaped3 (Fig. 8). In the setting of ONFH, the presence of bone marrow edema has been shown to have a strong association with the clinical presentation of pain. Bone marrow edema is also reported to be a significant risk factor for clinical worsening of hip pain and subsequent femoral head collapse.7,8 It has low signal on T1-weighted images and corresponding bright signal on T2-weighted and STIR sequences. In contrast to the typically distinct border of osteonecrosis, edema typically is seen as ill-defined abnormal signal. It extends into the femoral neck and often into the intertrochanteric region (Figs. 9 and 10). Subchondral fractures appear as a crescentic, curvilinear, or irregular low signal lines on T1-weighted sequences. There is usually corresponding high signal intensity on T2weighted and STIR images due to the presence of thin fluid accumulation within the fracture.2 The fracture may be obscured on T1-weighted images due to surrounding necrotic marrow, fibrosis, sclerosis, cellular debris, granulation tissue, and edema—all of which have low signal with T1-weighting.2,7 If there is fluid within the fracture, it may be obscured on T2-weighted and STIR sequences due to adjacent edema or granulation tissue. Occasionally the fracture may have low signal with T2-weighting due to the absence of fluid or the presence of gas within the fracture. In these instances, the fracture may not be appreciated due to low signal from surrounding fibrosis and sclerosis.2,7 These factors contribute to the decreased fracture detection rate of MRI relative to CT (Fig. 11).
Differential Diagnoses specificity.3
a sensitivity approaching 100%, and high MRI will depict disease involvement before abnormalities are appreciated on radiographs, bone scan, or CT. The examination typically includes the pelvis and both hips, with the use of a body coil and large field of view. This allows for detection of potential asymptomatic osteonecrosis in the contralateral hip as well as other possible sources of hip pain, such as pubic or sacral insufficiency fractures and metastatic disease.4 A routine protocol would include imaging in the coronal and axial planes; many centers also add sagittal images through the femoral heads. T1-weighted sequences are performed, as well as short tau inversion recovery (STIR) and/or fat-suppressed T2-weighted series. T2-weighted imaging should be performed with fat-suppression (FS) due to significantly improved detection of edema compared with conventional T2weighting. Recent studies have shown that the initial MRI appearance of ONFH on T1-weighted images is a subchondral low signal band-like or linear area, which forms at the border between necrotic and reparative bone (Fig. 6). This corresponds to fibrovascular tissue and reactive sclerosis.5 With T2-weighting, the outer rim of sclerotic bone remains low signal, but the inner rim of vascularized granulation tissue becomes high signal, resulting in the classic “double line sign”3,6 (Fig. 7). On T1-weighted sequences, the low signal foci also com-
Usually the MRI findings are pathognomonic for ONFH. However, there are other conditions in which the MRI features overlap with those of ONFH. In these cases, correlation with the clinical circumstances, and sometimes additional imaging exams, should enable differentiation from osteone-
Figure 2 AP radiograph of the pelvis shows advanced left hip osteonecrosis with secondary osteoarthritis. These changes include femoral head flattening, joint space narrowing, superolateral subluxation of the femoral head, and osteophytosis.
194
A. Laorr
Figure 3 CT imaging is more sensitive than plain radiography in the identification of subchondral fractures. AP (A) and lateral (B) radiographs show osteonecrosis of the femoral head with no evident subchondral fracture. Axial (C) CT with sagittal (D) and coronal (E) reconstructions of the same femoral head demonstrate a nondisplaced subchondral fracture.
Imaging features of ONFH
Figure 4 Axial CT image of the left hip reveals changes of osteonecrosis, including a subchondral fracture extending to the articular surface with associated collapse (arrows).
crosis. These entities include bone marrow edema syndrome, previously known as transient osteoporosis of the hip, hematopoietic marrow persistence or reconversion, subchondral cystic change, osteochondral lesion, and insufficiency fracture. Bone marrow edema syndrome (BMES) is an insidious process typically seen in middle-aged and young adults, who present with nontraumatic debilitating pain (see related paper by Koo and coworkers in this Seminars in Arthroplasty issue). The condition is usually self-limited, with symptoms resolving 2 to 6 months after conservative therapy. The imaging features also eventually return to normal. If similar findings later appear in the contralateral hip or another joint, the term regional migratory osteoporosis has been applied.4,9 On MRI, there is diffuse bone marrow edema from the femoral head to the intertrochanteric region, without the hall-
Figure 5 Axial CT image demonstrates advanced bilateral hip osteonecrosis with secondary osteoarthritic changes.
195
Figure 6 Coronal T1-weighted image shows early osteonecrosis of the right femoral head, with a subchondral band of low signal.
mark abnormal subchondral changes of osteonecrosis. Another helpful distinguishing imaging feature for BMES, if present, is focal osteopenia radiographically, although positive MRI findings may precede abnormal radiographs by 1 to 2 months.9 If the diagnosis remains in question, follow-up radiography and MRI could be performed to confirm resolution of the abnormal findings. When present within the femoral head, hematopoietic (red) marrow can be misinterpreted as osteonecrosis on MR imaging. Adults typically have fatty marrow within the femoral heads, which appears as bright signal with T1-weighting, and low signal on fat-suppressed T2-weighted and STIR sequences. However, occasionally residual foci of red marrow
Figure 7 Coronal fat-suppressed T2-weighted image depicts the classic “double line sign” of osteonecrosis, within the left femoral head (arrows).
A. Laorr
196 may persist within the femoral head.4 Red marrow reconversion may also occur, such as with anemia or chemotherapy. Red marrow has low to intermediate signal intensity on T1weighted images and intermediate to high signal intensity on T2 FS and STIR sequences, and therefore can be confused with osteonecrosis. Nevertheless, comparing the signal to adjacent skeletal muscle should allow the distinction to be made. Specifically, on T1-weighted images, red marrow appears isointense or slightly hyperintense in relation to muscle, whereas osteonecrosis is hypointense compared with muscle.4 In addition, red marrow would not have any associated linear signal abnormality. Subchondral cystic change in association with degenerative joint disease can be confused with osteonecrosis. One helpful differentiating feature is that cysts usually demonstrate homogeneously bright signal, similar to joint fluid, on T2 and STIR images. Cyst margins also tend to be more rounded and smooth when compared with osteonecrosis. Finally, if no subchondral collapse is seen, the presence of additional osteoarthritic changes such as osteophytosis, joint space narrowing, and acetabular reactive subchondral change would favor subchondral cyst formation.4 Osteochondral lesions of the femoral head are typically seen in higher-level athletes with a history of trauma. These lesions tend to occur within the medial portion of the femoral head, with extension to the overlying cartilage. In contradistinction, osteonecrosis often originates at the anterosuperior aspect of the femoral head. Correlating the imaging findings with a detailed clinical history should enable the proper diagnosis to be made.4 Subchondral insufficiency fractures have been reported to occur in the femoral head. Although the imaging findings
Figure 9 (A) Coronal T1-weighted image reveals bilateral femoral head osteonecrosis with adjacent ill-defined low signal, representing bone marrow edema. (B) The edema extends into the intertrochanteric regions and has high signal intensity on the corresponding fat-suppressed T2-weighted sequence. Small bilateral hip joint effusions are also noted.
may be very similar to osteonecrosis, the patient profile is different. The described insufficiency fracture patients have tended to be elderly and osteoporotic, and without predisposing risk factors for osteonecrosis, who present with severe pain. The fracture may coexist with an adjacent acetabular insufficiency fracture. If there is suspicion for an insufficiency fracture, correlation with a bone densitometry scan (dualenergy x-ray absorptiometry) would be recommended in confirming the presence of osteoporosis.4,7,10,11
References
Figure 8 (A and B) Coronal T1-weighted images show serpiginous areas of low signal within the right femoral head, diagnostic of osteonecrosis.
1. Steinberg ME, Hayken GD, Steinberg DR: A quantitative system for staging avascular necrosis. J Bone Joint Surg Br 77B:34-41, 1995 2. Stevens K, Tao C, Lee SU, et al: Subchondral fractures in osteonecrosis of the femoral head: Comparison of radiography, CT, and MR imaging. Am J Roentgenol 180:363-368, 2003 3. Saini A, Saifuddin A: MRI of osteonecrosis. Clin Radiol 59:1079-1093, 2004 4. Jackson SM, Major NM: Pathologic conditions mimicking osteonecrosis. Orthop Clin North Am 35:315-320, 2004 5. Kim YM, Oh HC, Kim HJ: The pattern of bone marrow oedema on MRI
Imaging features of ONFH
197
Figure 10 Coronal (A) T1-weighted and (B) STIR images show left femoral head osteonecrosis with collapse and prominent secondary degenerative joint disease. Note the prominent associated bone marrow edema on both sides of the joint. Joint effusion is also present.
6.
7.
8.
9.
in osteonecrosis of the femoral head. J Bone Joint Surg Br 82:837-841, 2000 Mitchell DG, Kressel HY, Rao VM, et al: The unique MRI appearance of the reactive interface in avascular necrosis: The double-line sign. Magn Reson Imaging 5:41, 1987 (suppl 1) Huang GS, Chan WP, Chang YC, et al: MR imaging of bone marrow edema and joint effusion in patients with osteonecrosis of the femoral head: Relationship to pain. Am J Roentgenol 181:545-549, 2003 Ito H, Matsuno T, Minami A: Relationship between bone marrow edema and development of symptoms in patients with osteonecrosis of the femoral head. Am J Roentgenol 186:1761-1770, 2006 Gil HC, Levine SM, Zoga AC: MRI findings in the subchondral bone marrow: A discussion of conditions including transient osteoporosis, transient bone marrow edema syndrome, SONK, and shifting bone
Figure 11 Axial (A) T1-weighted and (B) fat-suppressed T2weighted images demonstrate osteonecrosis of the right femoral head. No definite associated subchondral fracture is seen. (C) CT image at the same axial level clearly depicts a subchondral fracture line (arrow).
marrow edema of the knee Semin Musculoskelet. Radiol 10:177-186, 2006 10. Rafii M, Mitnick H, Klug J, et al: Insufficiency fracture of the femoral head: MR imaging in three patients. Am J Roentgenol 168:159-163, 1997 11. Buttaro M, Della Valle AG, Morandi A, et al: Insufficiency subchondral fracture of the femoral head: Report of 4 cases and review of the literature. J Arthroplasty 18:377-382, 2003
Radiography
A
lthough lacking in sensitivity for early disease, radiography remains an important diagnostic tool. Conventional radiographs are often the initial imaging test performed in the evaluation of patients for osteonecrosis of the femoral head. Both anterior–posterior (AP) and frog leg lateral views should be performed. With advancing disease, the radiographic findings progress as follows: normal, cystic or sclerotic changes, subchondral radiolucency or crescent sign (subchondral fracture), femoral head flattening (collapse), joint space narrowing, and advanced degenerative changes1 (Fig. 1). Advanced secondary osteoarthritic changes would include osteophytosis, prominent joint space narrowing, superolateral subluxation of the femoral head, subchondral cystic lesions and sclerosis on both sides of the joint, and loose bodies (Fig. 2).
Scintigraphy In the past, nuclear medicine scans have been used extensively in the diagnosis of hip osteonecrosis. Single photon emission computed tomography (SPECT) has increased sensitivity compared with planar bone scintigraphy. However, poor specificity and lack of anatomic detail limit this imaging modality. The emergence of computed tomography (CT) and magnetic resonance imaging (MRI) has replaced scintigraphy to the point that bone scans are no longer widely performed
*Department of Radiology, University of Minnesota Medical Center, Minneapolis, MN. †Suburban Radiologic Consultants, Minneapolis, MN. Address reprint requests to Alan Laorr, MD, Department of Radiology, University of Minnesota Medical Center, Fairview, 2450 Riverside Avenue, Minneapolis, MN 55454. E-mail: [email protected]
192
1045-4527/07/$-see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1053/j.sart.2007.06.010
in the evaluation of osteonecrosis of the femoral head (ONFH).
Computed Tomography Computed tomography has proven to be a valuable diagnostic tool in the evaluation of ONFH. The development of multislice helical CT scanners allows for rapid scan times, highresolution images, and thin-cut multiplanar reconstructed images. Slice thickness should be 3 mm or less. CT has higher sensitivity than radiography for ONFH and shows the radiographic findings in greater detail. CT is excellent in the depiction of cortical and trabecular bone. In particular, CT is the imaging modality of choice for diagnosing subchondral fractures of the femoral head. CT is more sensitive than plain radiographs in demonstrating subchondral fractures,2 especially when minimally or not displaced (Fig. 3). Subchondral fracture is the most prognostically important predictor of progression to osteoarthritis, and therefore its presence is crucial for staging and treatment planning of osteonecrosis. It appears as a subchondral radiolucent line, with or without extension to the articular surface (Fig. 4). In patients for whom MRI is contraindicated (pacemaker, aneurysm clip, etc), CT could be used as the primary modality in the diagnosis and follow-up of ONFH. Otherwise, CT is best used as an important adjunct in the staging of established osteonecrosis, not only for the detection of subchondral fractures, but also articular collapse and secondary osteoarthritic changes2 (Fig. 5).
Magnetic Resonance Imaging Magnetic resonance imaging is the most accurate modality in the detection of early osteonecrosis of the femoral head, with
Imaging features of ONFH
193
Figure 1 (A) AP pelvic radiograph demonstrates areas of sclerosis and radiolucency within the left femoral head, typical of osteonecrosis. There is subtle evidence of subchondral collapse superiorly. (B) Frog leg lateral view more clearly demonstrates a subchondral fracture with collapse at the articular surface.
monly appear as crescentic, serpiginous, ring-like, oval, or wedge-shaped3 (Fig. 8). In the setting of ONFH, the presence of bone marrow edema has been shown to have a strong association with the clinical presentation of pain. Bone marrow edema is also reported to be a significant risk factor for clinical worsening of hip pain and subsequent femoral head collapse.7,8 It has low signal on T1-weighted images and corresponding bright signal on T2-weighted and STIR sequences. In contrast to the typically distinct border of osteonecrosis, edema typically is seen as ill-defined abnormal signal. It extends into the femoral neck and often into the intertrochanteric region (Figs. 9 and 10). Subchondral fractures appear as a crescentic, curvilinear, or irregular low signal lines on T1-weighted sequences. There is usually corresponding high signal intensity on T2weighted and STIR images due to the presence of thin fluid accumulation within the fracture.2 The fracture may be obscured on T1-weighted images due to surrounding necrotic marrow, fibrosis, sclerosis, cellular debris, granulation tissue, and edema—all of which have low signal with T1-weighting.2,7 If there is fluid within the fracture, it may be obscured on T2-weighted and STIR sequences due to adjacent edema or granulation tissue. Occasionally the fracture may have low signal with T2-weighting due to the absence of fluid or the presence of gas within the fracture. In these instances, the fracture may not be appreciated due to low signal from surrounding fibrosis and sclerosis.2,7 These factors contribute to the decreased fracture detection rate of MRI relative to CT (Fig. 11).
Differential Diagnoses specificity.3
a sensitivity approaching 100%, and high MRI will depict disease involvement before abnormalities are appreciated on radiographs, bone scan, or CT. The examination typically includes the pelvis and both hips, with the use of a body coil and large field of view. This allows for detection of potential asymptomatic osteonecrosis in the contralateral hip as well as other possible sources of hip pain, such as pubic or sacral insufficiency fractures and metastatic disease.4 A routine protocol would include imaging in the coronal and axial planes; many centers also add sagittal images through the femoral heads. T1-weighted sequences are performed, as well as short tau inversion recovery (STIR) and/or fat-suppressed T2-weighted series. T2-weighted imaging should be performed with fat-suppression (FS) due to significantly improved detection of edema compared with conventional T2weighting. Recent studies have shown that the initial MRI appearance of ONFH on T1-weighted images is a subchondral low signal band-like or linear area, which forms at the border between necrotic and reparative bone (Fig. 6). This corresponds to fibrovascular tissue and reactive sclerosis.5 With T2-weighting, the outer rim of sclerotic bone remains low signal, but the inner rim of vascularized granulation tissue becomes high signal, resulting in the classic “double line sign”3,6 (Fig. 7). On T1-weighted sequences, the low signal foci also com-
Usually the MRI findings are pathognomonic for ONFH. However, there are other conditions in which the MRI features overlap with those of ONFH. In these cases, correlation with the clinical circumstances, and sometimes additional imaging exams, should enable differentiation from osteone-
Figure 2 AP radiograph of the pelvis shows advanced left hip osteonecrosis with secondary osteoarthritis. These changes include femoral head flattening, joint space narrowing, superolateral subluxation of the femoral head, and osteophytosis.
194
A. Laorr
Figure 3 CT imaging is more sensitive than plain radiography in the identification of subchondral fractures. AP (A) and lateral (B) radiographs show osteonecrosis of the femoral head with no evident subchondral fracture. Axial (C) CT with sagittal (D) and coronal (E) reconstructions of the same femoral head demonstrate a nondisplaced subchondral fracture.
Imaging features of ONFH
Figure 4 Axial CT image of the left hip reveals changes of osteonecrosis, including a subchondral fracture extending to the articular surface with associated collapse (arrows).
crosis. These entities include bone marrow edema syndrome, previously known as transient osteoporosis of the hip, hematopoietic marrow persistence or reconversion, subchondral cystic change, osteochondral lesion, and insufficiency fracture. Bone marrow edema syndrome (BMES) is an insidious process typically seen in middle-aged and young adults, who present with nontraumatic debilitating pain (see related paper by Koo and coworkers in this Seminars in Arthroplasty issue). The condition is usually self-limited, with symptoms resolving 2 to 6 months after conservative therapy. The imaging features also eventually return to normal. If similar findings later appear in the contralateral hip or another joint, the term regional migratory osteoporosis has been applied.4,9 On MRI, there is diffuse bone marrow edema from the femoral head to the intertrochanteric region, without the hall-
Figure 5 Axial CT image demonstrates advanced bilateral hip osteonecrosis with secondary osteoarthritic changes.
195
Figure 6 Coronal T1-weighted image shows early osteonecrosis of the right femoral head, with a subchondral band of low signal.
mark abnormal subchondral changes of osteonecrosis. Another helpful distinguishing imaging feature for BMES, if present, is focal osteopenia radiographically, although positive MRI findings may precede abnormal radiographs by 1 to 2 months.9 If the diagnosis remains in question, follow-up radiography and MRI could be performed to confirm resolution of the abnormal findings. When present within the femoral head, hematopoietic (red) marrow can be misinterpreted as osteonecrosis on MR imaging. Adults typically have fatty marrow within the femoral heads, which appears as bright signal with T1-weighting, and low signal on fat-suppressed T2-weighted and STIR sequences. However, occasionally residual foci of red marrow
Figure 7 Coronal fat-suppressed T2-weighted image depicts the classic “double line sign” of osteonecrosis, within the left femoral head (arrows).
A. Laorr
196 may persist within the femoral head.4 Red marrow reconversion may also occur, such as with anemia or chemotherapy. Red marrow has low to intermediate signal intensity on T1weighted images and intermediate to high signal intensity on T2 FS and STIR sequences, and therefore can be confused with osteonecrosis. Nevertheless, comparing the signal to adjacent skeletal muscle should allow the distinction to be made. Specifically, on T1-weighted images, red marrow appears isointense or slightly hyperintense in relation to muscle, whereas osteonecrosis is hypointense compared with muscle.4 In addition, red marrow would not have any associated linear signal abnormality. Subchondral cystic change in association with degenerative joint disease can be confused with osteonecrosis. One helpful differentiating feature is that cysts usually demonstrate homogeneously bright signal, similar to joint fluid, on T2 and STIR images. Cyst margins also tend to be more rounded and smooth when compared with osteonecrosis. Finally, if no subchondral collapse is seen, the presence of additional osteoarthritic changes such as osteophytosis, joint space narrowing, and acetabular reactive subchondral change would favor subchondral cyst formation.4 Osteochondral lesions of the femoral head are typically seen in higher-level athletes with a history of trauma. These lesions tend to occur within the medial portion of the femoral head, with extension to the overlying cartilage. In contradistinction, osteonecrosis often originates at the anterosuperior aspect of the femoral head. Correlating the imaging findings with a detailed clinical history should enable the proper diagnosis to be made.4 Subchondral insufficiency fractures have been reported to occur in the femoral head. Although the imaging findings
Figure 9 (A) Coronal T1-weighted image reveals bilateral femoral head osteonecrosis with adjacent ill-defined low signal, representing bone marrow edema. (B) The edema extends into the intertrochanteric regions and has high signal intensity on the corresponding fat-suppressed T2-weighted sequence. Small bilateral hip joint effusions are also noted.
may be very similar to osteonecrosis, the patient profile is different. The described insufficiency fracture patients have tended to be elderly and osteoporotic, and without predisposing risk factors for osteonecrosis, who present with severe pain. The fracture may coexist with an adjacent acetabular insufficiency fracture. If there is suspicion for an insufficiency fracture, correlation with a bone densitometry scan (dualenergy x-ray absorptiometry) would be recommended in confirming the presence of osteoporosis.4,7,10,11
References
Figure 8 (A and B) Coronal T1-weighted images show serpiginous areas of low signal within the right femoral head, diagnostic of osteonecrosis.
1. Steinberg ME, Hayken GD, Steinberg DR: A quantitative system for staging avascular necrosis. J Bone Joint Surg Br 77B:34-41, 1995 2. Stevens K, Tao C, Lee SU, et al: Subchondral fractures in osteonecrosis of the femoral head: Comparison of radiography, CT, and MR imaging. Am J Roentgenol 180:363-368, 2003 3. Saini A, Saifuddin A: MRI of osteonecrosis. Clin Radiol 59:1079-1093, 2004 4. Jackson SM, Major NM: Pathologic conditions mimicking osteonecrosis. Orthop Clin North Am 35:315-320, 2004 5. Kim YM, Oh HC, Kim HJ: The pattern of bone marrow oedema on MRI
Imaging features of ONFH
197
Figure 10 Coronal (A) T1-weighted and (B) STIR images show left femoral head osteonecrosis with collapse and prominent secondary degenerative joint disease. Note the prominent associated bone marrow edema on both sides of the joint. Joint effusion is also present.
6.
7.
8.
9.
in osteonecrosis of the femoral head. J Bone Joint Surg Br 82:837-841, 2000 Mitchell DG, Kressel HY, Rao VM, et al: The unique MRI appearance of the reactive interface in avascular necrosis: The double-line sign. Magn Reson Imaging 5:41, 1987 (suppl 1) Huang GS, Chan WP, Chang YC, et al: MR imaging of bone marrow edema and joint effusion in patients with osteonecrosis of the femoral head: Relationship to pain. Am J Roentgenol 181:545-549, 2003 Ito H, Matsuno T, Minami A: Relationship between bone marrow edema and development of symptoms in patients with osteonecrosis of the femoral head. Am J Roentgenol 186:1761-1770, 2006 Gil HC, Levine SM, Zoga AC: MRI findings in the subchondral bone marrow: A discussion of conditions including transient osteoporosis, transient bone marrow edema syndrome, SONK, and shifting bone
Figure 11 Axial (A) T1-weighted and (B) fat-suppressed T2weighted images demonstrate osteonecrosis of the right femoral head. No definite associated subchondral fracture is seen. (C) CT image at the same axial level clearly depicts a subchondral fracture line (arrow).
marrow edema of the knee Semin Musculoskelet. Radiol 10:177-186, 2006 10. Rafii M, Mitnick H, Klug J, et al: Insufficiency fracture of the femoral head: MR imaging in three patients. Am J Roentgenol 168:159-163, 1997 11. Buttaro M, Della Valle AG, Morandi A, et al: Insufficiency subchondral fracture of the femoral head: Report of 4 cases and review of the literature. J Arthroplasty 18:377-382, 2003