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Pathological fracture of the femoral neck as the first manifestation of osteonecrosis of the femoral head
J Orthop Sci (2000) 5:605–609
Case reports Pathological fracture of the femoral neck as the first manifestation of osteonecrosis of the femoral head Young-Min Kim and Hee Joong Kim Department of Orthopaedic Surgery, Seoul National University College of Medicine, 28 Yongondong, Chongnogu, Seoul 110-744, Korea
Abstract We describe two cases of pathological fracture of the femoral neck occurring as the first manifestation of osteonecrosis of the femoral head (ONFH). No abnormal findings suggestive of ONFH were identified on the radiographs for either of the patients, and the fractures occurred like spontaneous fractures without any trauma or unusually increased activity. The patients’ medical history, age, and good bone quality suggested ONFH as a possible underlying cause of the fractures. If we had not suspected ONFH as a predisposing condition, these minimally displaced fractures might have been fixed internally with multiple pins, and this would have led to nonunion or collapse of the femoral head. To avoid inappropriate treatment, ONFH should be considered as a predisposing factor in pathological fractures of the femoral neck.
spontaneous fracture, which occurred as the first manifestation of osteonecrosis of the femoral head (ONFH). No abnormal findings indicative of ONFH were identified in the femoral heads on radiographs in either of these patients. The entire femoral head was found to be necrotic, and the fracture had occurred subcapitally at or near the junction of the necrotic and regenerative bone. We discuss the importance of ONFH as a predisposing factor involved in pathological fracture of the femoral neck.
Key words Fracture · Femoral neck · Osteonecrosis · Femoral head
A 58-year-old man was seen because of a 3-month history of progressive pain in the left hip. The onset of pain had been sudden, and the pain had occurred for no apparent reason while he was walking on a level street. Initially, he neglected the symptom because he had tolerable pain only on weight-bearing. About 2 months after its onset, he consulted a general physician, and radiographs (which we later reviewed) were obtained (Fig. 1a). Unfortunately, this physician did not recognize the abnormal radiographic findings of linear sclerotic change at the junction of the left femoral head and neck, and the posterior tilting of the femoral head, and treated the patient conservatively, being under the impression that he had muscular strain. When the patient visited our clinic, he was using crutches. On radiographs taken on presentation, an additional abnormal finding, of cortical breakage, was observed at the inferior aspect of the left femoral headneck junction (Fig. 1b). However, no abnormality was identified in the femoral head itself. The nature of the onset of the symptom and the radiographic findings were quite similar to those in spontaneous fracture of the femoral neck due to osteoporosis. However, the patient was relatively young to have a spontaneous frac-
Introduction In contrast to fatigue stress fracture, spontaneous stress fracture of the femoral neck, a form of insufficiency fracture, occurs without an associated history of recent or unusually increased activity. The conditions predisposing to insufficiency fractures include osteoporosis, osteogenesis imperfecta, Paget’s disease, hyperparathyroidism, osteomalacia, scurvy, rheumatoid arthritis, status postirradiation, fibrous dysplasia, and osteopetrosis.4,6 In this report, we describe two cases of pathological fracture of the femoral neck, resembling
Offprint requests to: H.J. Kim Received: November 20, 1999 / Accepted: July 22, 2000
Case reports Case 1
606
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
ture of the femoral neck, and radiographs revealed no remarkable decrease in bone density. The patient was a heavy drinker, consuming more than 100 g of alcohol every day. We thus suspected ONFH as a predisposing condition, and performed bone scintigrams and magnetic resonance (MR) imaging.
The bone scintigram showed markedly increased radionuclide uptake in the neck of the left femur, as well as decreased uptake in both femoral heads (Fig. 1b). On T1-weighted MR images, the fracture site was identified as a vertical low-signal intensity band. A moderately low-intensity area was demonstrated distal to
a
b
c
d
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
607
this band.3,8,10 Because this area appeared on T2weighted images as slightly high signal intensity, it was interpreted as an area of edema. In the lower medial part of the femoral head, another low-signal intensity band was identified. This band was interpreted as the outer margin of the original necrotic area. MR images also demonstrated typical findings of ONFH in the right femoral head, a low-signal intensity band on T1weighted images and the double-line sign on T2weighted images9 (Fig. 1c). The fracture was treated with bipolar hemiarthroplasty, and the resected femoral head was observed both grossly and microscopically. Almost the entire femoral head was necrotic, and adjacent living trabeculae were thickened by appositional new bone. Between the dead and regenerative bone there was a thin, Vshaped band of granulation tissue. The fracture appeared to have occurred through the vertical portion of
the V-shaped band and propagated into the medial part of the neck distal to the horizontal portion of the Vshaped band (Fig. 1d). These findings were compatible with the MR findings. Case 2 A 60-year-old man presented with a 1-month history of right hip pain. The pain had developed abruptly while he was sitting down in a car, and it gradually became worse. Prior to the onset of the pain, he had been undergoing steroid therapy for aplastic anemia for 7 months. Radiographs taken on presentation demonstrated the typical findings of stress fracture of the right femoral neck: irregular sclerosis at the femoral head-neck junction and minor cortical breakage at the superior aspect of the femoral neck (Fig. 2a). No abnormalities were
b
a
b
Fig. 1a–d. Case 1. a Radiographs taken 2 months after the onset of left hip pain. Irregular linear sclerotic change is seen at the junction of the left femoral head and neck, and partly in the femoral head. The femoral head is slightly tilted medially and posteriorly. b Radiographs at first presentation and, inset, bone scintigram. There is a minor cortical breakage at the inferior aspect of the head-neck junction of the left femur. The bone scintigram shows markedly increased radionuclide uptake in the left femoral neck, and definitely decreased uptake in both femoral heads. c Magnetic resonance (MR) images. T1-weighted images demonstrate a very low-signal intensity band at the fracture site of the left femur (arrows). A moderately low-signal intensity area is shown distal to the fracture line. At the infero-medial aspect of the left femoral head, there is a curved thin low-signal band representing the outer margin of the original necrotic lesion (open arrowheads). Solid arrowheads indicate medial cortex bone. There is an irregular low-signal intensity band in the right femoral head.
Fig. 2a,b. Case 2. a Radiographs at presentation and, inset, bone scintigram. Irregular linear sclerotic change is seen at the head-neck junction of the right femur, with minor cortical breakage in the superior aspect. The bone scintigram shows markedly increased radionuclide uptake in the right femoral neck and markedly decreased uptake in the right femoral head. b MR images. T1-weighted MR images show a broad low-signal intensity band at the head-neck junction of the right (rt.) femur. In the left (lt.) femoral head, there is an area of irregular signal intensity surrounded by a low-signal intensity band
On T2-weighted images, the signal intensity of the area distal to the fracture line is slightly increased. A typical double-line sign is seen in the right femoral head. d Photographs of the midcoronal plane of the resected femoral head and neck, and the whole mounted histological specimen. There is a Vshaped reactive zone in the femoral head-neck junction (open arrowheads). The fracture line runs through the vertical portion of the reactive zone into the medial aspect of the femoral neck, distal to the horizontal portion of the reactive zone (arrows, sites of cortical breakage). Microscopically, the reactive zone is composed of an inner vascularized fibrous tissue band and outer trabeculae thickened by appositional new bone formation. The trabecular bone and marrow in the femoral head are necrotic. The cortical fragment at the inferior aspect of the head and neck (solid arrowheads) seems displaced toward the horizontal portion of the V-shaped reactive zone. The displacement seems to account for the line of the reactive zone being unclear on MR images
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Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
observed in either femoral head. Because of his previous medical history, bone scintigrams and MR imaging were performed, a week later. Bone scintigrams of the right hip showed increased radionuclide uptake in the femoral neck and decreased uptake in the femoral head (Fig. 2a). However, no abnormal findings were seen in the left hip. T1-weighted MR images demonstrated a broad, irregular low-signal intensity band at the fracture site in the right femoral head. A typical finding of ONFH, an area of irregular signal intensity surrounded by a low signal band, was identified in the left femoral head (Fig. 2b). The right hip was treated with bipolar hemiarthroplasty. Histological examination confirmed that the excised femoral head was necrotic. Four years later, the left femoral head collapsed and total hip arthroplasty was performed on the left hip.
These findings suggested the presence of an underlying condition. Fortunately, because both patients had some risk factors for ONFH, it was apparent that ONFH could be a possible predisposing factor. Although numerous diseases or conditions are known to be implicated in the etiology of ONFH, a large proportion of ONFH cases are idiopathic, without a clearly identifiable etiologic factor. When fractures of the femoral neck occur in idiopathic ONFH, it may not be readily apparent that ONFH could be an underlying condition. In both of our patients, the fracture was treated by replacement arthroplasty, because the patients were not young. If fracture of the femoral neck occurs in young patients with ONFH, the fracture could be fixed with pins, along with a salvage operation for ONFH, such as core decompression and vascularized bone grafting. ONFH can occur as a complication of femoral neck fractures, but undisplaced or minimally displaced stress fractures of the neck are complicated by ONFH only on extremely rare occasions.1,7 In the patients we have described, their past histories, the necrosis of the entire femoral head, and the condition of the contralateral femoral head suggested that the fractures had occurred after the onset of ONFH. In conclusion, ONFH should be considered as a predisposing condition in pathological fracture of the femoral neck, and a high index of suspicion is necessary in order to avoid unsuccessful treatment, such as simple internal fixation. When the fracture occurs in a patient whose bone quality is not poor enough for a spontaneous fracture to occur, MR imaging or bone scintigram is necessary to determine the condition of the affected femoral head.
Discussion Femoral neck fracture rarely occurs during the course of ONFH, but when it does, it is almost always without significant trauma, and usually at the junction of the necrotic and regenerative bone.2,11 Most of these patients have typical radiological findings of ONFH in the femoral head.11 Thus, it is usually evident that femoral neck fracture is associated with ONFH. In contrast to these findings, the radiographs in our patients showed minimal displacement of the femoral head, without any typical findings of ONFH. If the patients’ previous histories had not suggested ONHF, these minimally displaced fractures might have been fixed internally with multiple pins, and this would have led to nonunion or collapse of the femoral head. According to the hypothesis proposed by Glimcher and Kenzora,5 the structural breakage of the femoral head in ONFH is initiated by the focal resorption of the subchondral bone plate during the repair process. The breakage can propagate in two different directions. One is via a subchondral fracture through the necrotic area and the other is via a fracture through the junction of the dead bone and the zone of bone repair. They observed that the fracture tended to occur through the bone repair zone when the necrotic lesion was large. In both the patients we have described, osteonecrosis involved almost the entire femoral head, and a large part of the fracture occurred through the bone repair zone at the femoral head-neck junction. It seems that extensive necrosis is a prerequisite for pathological fracture of the femoral neck in ONFH. Our patients were 58 and 60 years old, respectively, and their bone quality was not poor enough for a spontaneous fracture of the femoral neck to occur.
References 1. Blickenstaff LD, Morris JM. Fatigue fracture of the femoral neck. J Bone Joint Surg Am 1966;48:1031–47. 2. Debeyre J, Kenesi C, Boucker C. Trois observations de fractures cervico-capitales spontanees, complications de la necrose primitive de la tete femorale. Rev Rheum Mal Osteoartic 1969;36:23–6 (in French). 3. Deutsch AL, Mink JH, Waxman AD. Occult fractures of the proximal femur: MR imaging. Radiology 1989;170:113– 6. 4. Dorne HL, Lander PH. Spontaneous stress fractures of the femoral neck. Am J Roentgenol 1985;144:343–7. 5. Glimcher MJ, Kenzora JE. The biology of osteonecrosis of the human femoral head and its clinical implications. Clin Orthop 1979;140:273–312. 6. Jeffery CC. Spontaneous fractures of the femoral neck. Orthop Clin North Am 1974;5:713–27. 7. Johansson C, Ekenman I, Tornkvist H, et al. Stress fractures of the femoral neck in athletes. The consequence of a delay in diagnosis. Am J Sports Med 1990;18:524–8.
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
609
8. Lee JK, Yao L. Stress fractures: MR imaging. Radiology 1988;169: 217–20. 9. Mitchell DG, Rao VM, Dalinka MK, et al. Femoral head avascular necrosis: correlation of MR imaging, radiographic staging, radionuclide imaging, and clinical findings. Radiology 1987;162: 709–15.
10. Stafford SA, Rosenthal DI, Gebhardt MC, et al. MRI in stress fracture. Am J Roentgenol 1986;147:553–6. 11. Usui M, Inoue H, Yukihiro S, et al. Femoral neck fracture following avascular necrosis of the femoral head. Acta Med Okayama 1996;50:111–7.
Case reports Pathological fracture of the femoral neck as the first manifestation of osteonecrosis of the femoral head Young-Min Kim and Hee Joong Kim Department of Orthopaedic Surgery, Seoul National University College of Medicine, 28 Yongondong, Chongnogu, Seoul 110-744, Korea
Abstract We describe two cases of pathological fracture of the femoral neck occurring as the first manifestation of osteonecrosis of the femoral head (ONFH). No abnormal findings suggestive of ONFH were identified on the radiographs for either of the patients, and the fractures occurred like spontaneous fractures without any trauma or unusually increased activity. The patients’ medical history, age, and good bone quality suggested ONFH as a possible underlying cause of the fractures. If we had not suspected ONFH as a predisposing condition, these minimally displaced fractures might have been fixed internally with multiple pins, and this would have led to nonunion or collapse of the femoral head. To avoid inappropriate treatment, ONFH should be considered as a predisposing factor in pathological fractures of the femoral neck.
spontaneous fracture, which occurred as the first manifestation of osteonecrosis of the femoral head (ONFH). No abnormal findings indicative of ONFH were identified in the femoral heads on radiographs in either of these patients. The entire femoral head was found to be necrotic, and the fracture had occurred subcapitally at or near the junction of the necrotic and regenerative bone. We discuss the importance of ONFH as a predisposing factor involved in pathological fracture of the femoral neck.
Key words Fracture · Femoral neck · Osteonecrosis · Femoral head
A 58-year-old man was seen because of a 3-month history of progressive pain in the left hip. The onset of pain had been sudden, and the pain had occurred for no apparent reason while he was walking on a level street. Initially, he neglected the symptom because he had tolerable pain only on weight-bearing. About 2 months after its onset, he consulted a general physician, and radiographs (which we later reviewed) were obtained (Fig. 1a). Unfortunately, this physician did not recognize the abnormal radiographic findings of linear sclerotic change at the junction of the left femoral head and neck, and the posterior tilting of the femoral head, and treated the patient conservatively, being under the impression that he had muscular strain. When the patient visited our clinic, he was using crutches. On radiographs taken on presentation, an additional abnormal finding, of cortical breakage, was observed at the inferior aspect of the left femoral headneck junction (Fig. 1b). However, no abnormality was identified in the femoral head itself. The nature of the onset of the symptom and the radiographic findings were quite similar to those in spontaneous fracture of the femoral neck due to osteoporosis. However, the patient was relatively young to have a spontaneous frac-
Introduction In contrast to fatigue stress fracture, spontaneous stress fracture of the femoral neck, a form of insufficiency fracture, occurs without an associated history of recent or unusually increased activity. The conditions predisposing to insufficiency fractures include osteoporosis, osteogenesis imperfecta, Paget’s disease, hyperparathyroidism, osteomalacia, scurvy, rheumatoid arthritis, status postirradiation, fibrous dysplasia, and osteopetrosis.4,6 In this report, we describe two cases of pathological fracture of the femoral neck, resembling
Offprint requests to: H.J. Kim Received: November 20, 1999 / Accepted: July 22, 2000
Case reports Case 1
606
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
ture of the femoral neck, and radiographs revealed no remarkable decrease in bone density. The patient was a heavy drinker, consuming more than 100 g of alcohol every day. We thus suspected ONFH as a predisposing condition, and performed bone scintigrams and magnetic resonance (MR) imaging.
The bone scintigram showed markedly increased radionuclide uptake in the neck of the left femur, as well as decreased uptake in both femoral heads (Fig. 1b). On T1-weighted MR images, the fracture site was identified as a vertical low-signal intensity band. A moderately low-intensity area was demonstrated distal to
a
b
c
d
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
607
this band.3,8,10 Because this area appeared on T2weighted images as slightly high signal intensity, it was interpreted as an area of edema. In the lower medial part of the femoral head, another low-signal intensity band was identified. This band was interpreted as the outer margin of the original necrotic area. MR images also demonstrated typical findings of ONFH in the right femoral head, a low-signal intensity band on T1weighted images and the double-line sign on T2weighted images9 (Fig. 1c). The fracture was treated with bipolar hemiarthroplasty, and the resected femoral head was observed both grossly and microscopically. Almost the entire femoral head was necrotic, and adjacent living trabeculae were thickened by appositional new bone. Between the dead and regenerative bone there was a thin, Vshaped band of granulation tissue. The fracture appeared to have occurred through the vertical portion of
the V-shaped band and propagated into the medial part of the neck distal to the horizontal portion of the Vshaped band (Fig. 1d). These findings were compatible with the MR findings. Case 2 A 60-year-old man presented with a 1-month history of right hip pain. The pain had developed abruptly while he was sitting down in a car, and it gradually became worse. Prior to the onset of the pain, he had been undergoing steroid therapy for aplastic anemia for 7 months. Radiographs taken on presentation demonstrated the typical findings of stress fracture of the right femoral neck: irregular sclerosis at the femoral head-neck junction and minor cortical breakage at the superior aspect of the femoral neck (Fig. 2a). No abnormalities were
b
a
b
Fig. 1a–d. Case 1. a Radiographs taken 2 months after the onset of left hip pain. Irregular linear sclerotic change is seen at the junction of the left femoral head and neck, and partly in the femoral head. The femoral head is slightly tilted medially and posteriorly. b Radiographs at first presentation and, inset, bone scintigram. There is a minor cortical breakage at the inferior aspect of the head-neck junction of the left femur. The bone scintigram shows markedly increased radionuclide uptake in the left femoral neck, and definitely decreased uptake in both femoral heads. c Magnetic resonance (MR) images. T1-weighted images demonstrate a very low-signal intensity band at the fracture site of the left femur (arrows). A moderately low-signal intensity area is shown distal to the fracture line. At the infero-medial aspect of the left femoral head, there is a curved thin low-signal band representing the outer margin of the original necrotic lesion (open arrowheads). Solid arrowheads indicate medial cortex bone. There is an irregular low-signal intensity band in the right femoral head.
Fig. 2a,b. Case 2. a Radiographs at presentation and, inset, bone scintigram. Irregular linear sclerotic change is seen at the head-neck junction of the right femur, with minor cortical breakage in the superior aspect. The bone scintigram shows markedly increased radionuclide uptake in the right femoral neck and markedly decreased uptake in the right femoral head. b MR images. T1-weighted MR images show a broad low-signal intensity band at the head-neck junction of the right (rt.) femur. In the left (lt.) femoral head, there is an area of irregular signal intensity surrounded by a low-signal intensity band
On T2-weighted images, the signal intensity of the area distal to the fracture line is slightly increased. A typical double-line sign is seen in the right femoral head. d Photographs of the midcoronal plane of the resected femoral head and neck, and the whole mounted histological specimen. There is a Vshaped reactive zone in the femoral head-neck junction (open arrowheads). The fracture line runs through the vertical portion of the reactive zone into the medial aspect of the femoral neck, distal to the horizontal portion of the reactive zone (arrows, sites of cortical breakage). Microscopically, the reactive zone is composed of an inner vascularized fibrous tissue band and outer trabeculae thickened by appositional new bone formation. The trabecular bone and marrow in the femoral head are necrotic. The cortical fragment at the inferior aspect of the head and neck (solid arrowheads) seems displaced toward the horizontal portion of the V-shaped reactive zone. The displacement seems to account for the line of the reactive zone being unclear on MR images
608
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
observed in either femoral head. Because of his previous medical history, bone scintigrams and MR imaging were performed, a week later. Bone scintigrams of the right hip showed increased radionuclide uptake in the femoral neck and decreased uptake in the femoral head (Fig. 2a). However, no abnormal findings were seen in the left hip. T1-weighted MR images demonstrated a broad, irregular low-signal intensity band at the fracture site in the right femoral head. A typical finding of ONFH, an area of irregular signal intensity surrounded by a low signal band, was identified in the left femoral head (Fig. 2b). The right hip was treated with bipolar hemiarthroplasty. Histological examination confirmed that the excised femoral head was necrotic. Four years later, the left femoral head collapsed and total hip arthroplasty was performed on the left hip.
These findings suggested the presence of an underlying condition. Fortunately, because both patients had some risk factors for ONFH, it was apparent that ONFH could be a possible predisposing factor. Although numerous diseases or conditions are known to be implicated in the etiology of ONFH, a large proportion of ONFH cases are idiopathic, without a clearly identifiable etiologic factor. When fractures of the femoral neck occur in idiopathic ONFH, it may not be readily apparent that ONFH could be an underlying condition. In both of our patients, the fracture was treated by replacement arthroplasty, because the patients were not young. If fracture of the femoral neck occurs in young patients with ONFH, the fracture could be fixed with pins, along with a salvage operation for ONFH, such as core decompression and vascularized bone grafting. ONFH can occur as a complication of femoral neck fractures, but undisplaced or minimally displaced stress fractures of the neck are complicated by ONFH only on extremely rare occasions.1,7 In the patients we have described, their past histories, the necrosis of the entire femoral head, and the condition of the contralateral femoral head suggested that the fractures had occurred after the onset of ONFH. In conclusion, ONFH should be considered as a predisposing condition in pathological fracture of the femoral neck, and a high index of suspicion is necessary in order to avoid unsuccessful treatment, such as simple internal fixation. When the fracture occurs in a patient whose bone quality is not poor enough for a spontaneous fracture to occur, MR imaging or bone scintigram is necessary to determine the condition of the affected femoral head.
Discussion Femoral neck fracture rarely occurs during the course of ONFH, but when it does, it is almost always without significant trauma, and usually at the junction of the necrotic and regenerative bone.2,11 Most of these patients have typical radiological findings of ONFH in the femoral head.11 Thus, it is usually evident that femoral neck fracture is associated with ONFH. In contrast to these findings, the radiographs in our patients showed minimal displacement of the femoral head, without any typical findings of ONFH. If the patients’ previous histories had not suggested ONHF, these minimally displaced fractures might have been fixed internally with multiple pins, and this would have led to nonunion or collapse of the femoral head. According to the hypothesis proposed by Glimcher and Kenzora,5 the structural breakage of the femoral head in ONFH is initiated by the focal resorption of the subchondral bone plate during the repair process. The breakage can propagate in two different directions. One is via a subchondral fracture through the necrotic area and the other is via a fracture through the junction of the dead bone and the zone of bone repair. They observed that the fracture tended to occur through the bone repair zone when the necrotic lesion was large. In both the patients we have described, osteonecrosis involved almost the entire femoral head, and a large part of the fracture occurred through the bone repair zone at the femoral head-neck junction. It seems that extensive necrosis is a prerequisite for pathological fracture of the femoral neck in ONFH. Our patients were 58 and 60 years old, respectively, and their bone quality was not poor enough for a spontaneous fracture of the femoral neck to occur.
References 1. Blickenstaff LD, Morris JM. Fatigue fracture of the femoral neck. J Bone Joint Surg Am 1966;48:1031–47. 2. Debeyre J, Kenesi C, Boucker C. Trois observations de fractures cervico-capitales spontanees, complications de la necrose primitive de la tete femorale. Rev Rheum Mal Osteoartic 1969;36:23–6 (in French). 3. Deutsch AL, Mink JH, Waxman AD. Occult fractures of the proximal femur: MR imaging. Radiology 1989;170:113– 6. 4. Dorne HL, Lander PH. Spontaneous stress fractures of the femoral neck. Am J Roentgenol 1985;144:343–7. 5. Glimcher MJ, Kenzora JE. The biology of osteonecrosis of the human femoral head and its clinical implications. Clin Orthop 1979;140:273–312. 6. Jeffery CC. Spontaneous fractures of the femoral neck. Orthop Clin North Am 1974;5:713–27. 7. Johansson C, Ekenman I, Tornkvist H, et al. Stress fractures of the femoral neck in athletes. The consequence of a delay in diagnosis. Am J Sports Med 1990;18:524–8.
Y.-M. Kim and H.J. Kim: Fracture of femoral neck in ONFH
609
8. Lee JK, Yao L. Stress fractures: MR imaging. Radiology 1988;169: 217–20. 9. Mitchell DG, Rao VM, Dalinka MK, et al. Femoral head avascular necrosis: correlation of MR imaging, radiographic staging, radionuclide imaging, and clinical findings. Radiology 1987;162: 709–15.
10. Stafford SA, Rosenthal DI, Gebhardt MC, et al. MRI in stress fracture. Am J Roentgenol 1986;147:553–6. 11. Usui M, Inoue H, Yukihiro S, et al. Femoral neck fracture following avascular necrosis of the femoral head. Acta Med Okayama 1996;50:111–7.