Approach Considerations
Determining cause of bony defect
In a limited number of patients, bony defects are found serendipitously during radiographic evaluation of the affected part for other reasons. In these instances, the orthopedist is asked to determine if the discovered bony defect is a benign event requiring no further management or one that needs further investigation. The following are examples of defects that may be found:
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A stippled, calcific, benign-appearing enchondroma found in the proximal humerus during an evaluation of a patient for a rotator cuff tear
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Bony physiologic changes in the intertrochanteric area of the proximal femur, which may be found on plain anteroposterior (AP) pelvic radiographs during evaluation of the pelvis for other reasons
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An area of fibrous dysplasia, which may be observed on radiographs that have been taken of a patient involved in some traumatic event
It is often difficult to determine whether a bony defect found during a bone survey for metastatic disease is the result of that disease or of some other condition. For instance, a benign bone island, an area of osteopoikilosis or fibrous dysplasia, can produce a similar radiographic appearance. A bone biopsy is often required to determine the actual diagnosis of such a defect. If the patient has already been diagnosed as having a primary tumor, the management of the recently discovered bony defect is relatively uncomplicated.
When the diagnosis of the bony defect must be proved for therapeutic reasons, biopsy is appropriate. For example, the radiotherapist or oncologist may need confirmation that the recently discovered bony defect is the same as the primary tumor or that the bony site results from another condition. Bone biopsies can be accomplished in a number of ways, but for the diagnosis of bony metastases, the most appropriate and least invasive method is needle biopsy.
Predicting probability of fracture
If the biopsy confirms that the bony defect has been caused by metastatic disease, the orthopedist must then decide if the defect fits the criteria for an impending fracture. The definition of an impending fracture is the presence of a bony defect that is likely to result in a pathologic fracture with physiologic loading (eg, with activities of daily living). In this case, the orthopedist should determine the probability of fracture by examining plain radiographic findings and by conducting an interview with the patient.
Quantitating the risk of fracture on the basis of plain radiography alone is highly subjective. The broad guidelines in the literature are based on small numbers of patients and therefore are of limited value; using them can result in errors of judgment more than 50% of the time.
According to a report by Hipp et al, useful criteria are as follows [24] :
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Defect geometry affecting load-bearing capacity
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Histologic cell causing the defect - Blastic, lytic, or mixed
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Anatomic site - Femoral neck vs greater trochanter
For instance, according to the study, the factor of risk for fracture of a normal proximal femur is approximately 0.4. The thinnest part of a cortical wall is the critical factor for predicting loss of strength. Central lesions with a 50% symmetrical loss of bone produce a 60% loss of bending strength. In patients who have eccentric bone loss, a 50% bone mass reduction results in a 90% reduction of bending strength. Therefore, a lesion located in areas that increase the risk factors to the bone must be considered.
Length of a bony lesion has been reported as critical only in torsional loads. The load-bearing capacity of bone apparently depends on the following:
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Location of the defect with respect to the applied load
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Type of applied load
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Amount of bone loss
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Condition of the remaining bone
The anatomic location of a bony lesion also is important. As the literature has shown, a drill hole that has been placed inappropriately in the lateral femoral shaft (at or below the level of the lesser trochanter) for fixation of a nonneoplastic femoral neck fracture results in a high risk of bone fracture with weightbearing through the lateral femoral cortical drill hold defect. Therefore, a similarly sized metastatic lesion in this area can be expected to create a similarly high fracture risk.
Laboratory Studies
Laboratory tests that can be used in the diagnosis of metastatic bone disease include the following:
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Serum alkaline phosphatase (ALP) - Indirect reflection of bone destruction because it is a reflection of osteoblastic response; may not be elevated in purely lytic tumors, such as plasma cell myelomas; nonspecific because it can also be elevated in Paget disease, benign insufficiency fractures, endocrine disease, and others
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Serum protein electrophoresis (SPEP)
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Urinalysis, urine protein electrophoresis (UPEP)
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N-telopeptide (NTx) of type II collagen - Marker of bone resorption, but not widely used
Radiography
Radiography can be used for the basic assessment of the extent of a tumor and the degree of cortical erosion. It can also be used for a skeletal survey in patients with multiple myeloma. (See the images below.)
Lateral view of the femur of a 70-year-old man with metastatic prostate carcinoma, the most common cause of osteoblastic metastases in men.
Radiograph of a patient with severe rest- and activity-related pain at the time of presentation.
Pathologic fracture. Radiograph shows a displaced fracture through an osteolytic lesion in the distal femur of a 53-year-old woman with lung carcinoma.
Radiograph shows osteolytic metastasis in the distal femur of a 51-year-old woman with breast carcinoma.
Computed Tomography
Computed tomography (CT) is the most sensitive imaging modality for detecting bone destruction, providing the best assessment of the extent of cortical destruction. However, it is not always indicated if radiography and the clinical picture are informative and the surgical plan is clear. [25] (See the images below.)
Axial computed tomography scan shows 2 rounded, mixed osteolytic-sclerotic lesions in the thoracic vertebral body of a 44-year-old woman with lung carcinoma.
Axial computed tomography scan shows a destructive osteolytic lesion in the left acetabulum of a woman with vulval carcinoma. Soft-tissue extension into the pelvic cavity is present.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is the most sensitive study for assessing the anatomic (intramedullary and extraosseous) extent of a lesion. (See the images below.)
Sagittal spin-echo T2-weighted magnetic resonance image shows hypointense lesions in the T10 and L3 vertebrae in a 66-year-old man with lung carcinoma. The tumor involves the T10 pedicle. See also the next image.
Sagittal short-tau inversion recovery magnetic resonance (MRI) from a 66-year-old man with lung carcinoma. This MRI shows hyperintense lesions in the T10 and L3 vertebrae, with T10 pedicular involvement.
Sagittal short-tau inversion recovery (STIR) magnetic resonance image (MRI) in a 68-year-old man with thyroid carcinoma. This MRI shows severe compression of the L1 vertebra with retropulsion. Affected T11-L2 vertebrae show signal hyperintensity, posterior vertebral body marginal bulging, and spinal canal narrowing. See also the next image.
Sagittal gadolinium-enhanced spin-echo T1-weighted magnetic resonance image from a 68-year-old man with thyroid carcinoma. This image shows heterogeneous enhancement of the T11-L2 vertebrae, with prominent epidural component enhancement and spinal canal compromise. See also the next image.
Axial spin-echo T1-weighted magnetic resonance image (MRI) in a 68-year-old man with thyroid carcinoma. This MRI shows tumor extension from the L1 vertebral body and left pedicle into the left psoas muscle and epidural space, with resultant spinal cord compression. See also the next image.
Axial gadolinium-enhanced spin-echo T1-weighted magnetic resonance image from a 68-year-old man with thyroid carcinoma. This image shows heterogeneous enhancement of the soft tissue component of the L1 vertebral metastatic tumor.
Bone Scanning
Technetium-99m (99mTc) bone scanning is a very sensitive study for the detection of occult lesions and the assessment of the biologic activity of lesions. However, it is not useful by itself for multiple myeloma. This modality is part of the workup for an unknown primary site to identify other lesions and to determine which lesion will be easiest to biopsy.
99mTc bone scanning also provides an indirect measure of destruction, because it reflects the activity of osteoblasts. In addition, it can be used to demonstrate increased activity, because a lesion consolidates in response to radiotherapy. (See the image below.)
Typical scintigraphic pattern of bone metastases in a 60-year-old man with nasopharyngeal carcinoma. This posterior technetium-99m bone scintiscan shows multiple randomly distributed focal lesions scattered throughout the skeleton, particularly the spine, ribs, and pelvis.
Angiography
Angiography has essentially has been supplanted by MRI. It is still useful, however, for the preoperative embolization of vascular lesions, such as renal cell carcinomas, thyroid metastases, and (occasionally) myelomas.
Biopsy
Any isolated (solitary) presumed metastasis should be treated as a resectable primary tumor until there is proof to the contrary.
A biopsy should be obtained from any soft-tissue mass that is present. If no soft-tissue mass is present, a biopsy should be obtained from the most accessible bone; preferably, the biopsy should be performed in a mechanically safe area (eg, metaphysis vs diaphysis, acetabulum vs subtrochanteric femur).
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Lateral view of the femur of a 70-year-old man with metastatic prostate carcinoma, the most common cause of osteoblastic metastases in men.
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Radiograph of a patient with severe rest- and activity-related pain at the time of presentation.
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Pathologic fracture. Radiograph shows a displaced fracture through an osteolytic lesion in the distal femur of a 53-year-old woman with lung carcinoma.
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Radiograph shows osteolytic metastasis in the distal femur of a 51-year-old woman with breast carcinoma.
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Lateral radiograph shows sclerotic metastasis of the L2 vertebra in a 54-year-old man with prostatic carcinoma.
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Axial computed tomography scan shows 2 rounded, mixed osteolytic-sclerotic lesions in the thoracic vertebral body of a 44-year-old woman with lung carcinoma.
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Axial computed tomography scan shows a destructive osteolytic lesion in the left acetabulum of a woman with vulval carcinoma. Soft-tissue extension into the pelvic cavity is present.
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Sagittal spin-echo T2-weighted magnetic resonance image shows hypointense lesions in the T10 and L3 vertebrae in a 66-year-old man with lung carcinoma. The tumor involves the T10 pedicle. See also the next image.
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Sagittal short-tau inversion recovery magnetic resonance (MRI) from a 66-year-old man with lung carcinoma. This MRI shows hyperintense lesions in the T10 and L3 vertebrae, with T10 pedicular involvement.
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Sagittal short-tau inversion recovery (STIR) magnetic resonance image (MRI) in a 68-year-old man with thyroid carcinoma. This MRI shows severe compression of the L1 vertebra with retropulsion. Affected T11-L2 vertebrae show signal hyperintensity, posterior vertebral body marginal bulging, and spinal canal narrowing. See also the next image.
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Sagittal gadolinium-enhanced spin-echo T1-weighted magnetic resonance image from a 68-year-old man with thyroid carcinoma. This image shows heterogeneous enhancement of the T11-L2 vertebrae, with prominent epidural component enhancement and spinal canal compromise. See also the next image.
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Axial spin-echo T1-weighted magnetic resonance image (MRI) in a 68-year-old man with thyroid carcinoma. This MRI shows tumor extension from the L1 vertebral body and left pedicle into the left psoas muscle and epidural space, with resultant spinal cord compression. See also the next image.
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Axial gadolinium-enhanced spin-echo T1-weighted magnetic resonance image from a 68-year-old man with thyroid carcinoma. This image shows heterogeneous enhancement of the soft tissue component of the L1 vertebral metastatic tumor.
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Typical scintigraphic pattern of bone metastases in a 60-year-old man with nasopharyngeal carcinoma. This posterior technetium-99m bone scintiscan shows multiple randomly distributed focal lesions scattered throughout the skeleton, particularly the spine, ribs, and pelvis.
