Surgical Intervention of Nonvertebral Osseous Metastasis
Surgical Intervention of Nonvertebral Osseous Metastasis
Evaluation of osseous stability is challenging even for the experienced surgeon. Plain radiographs provide the most insight into the structural integrity of bone. CT scans will define cortical architecture in more detail. Magnetic resonance imaging (MRI) scans will show the intramedullary extent of tumor and any softtissue extension. However, CT and MRI scans will magnify the extent of osseous disease seen on plain radiographs and will exaggerate the risk of fracture. Most of the studies that have provided classic guidelines for predicting impending pathological fractures and the indications for prophylactic fixation have relied on plain radiographs. Orthopedic surgeons therefore place most weight on plain films when evaluating the mechanical stability of bone.
Although no absolute guidelines exist, a number of studies have provided criteria to support clinical judgment and radiographic interpretation. In 1973, Fidler suggested that a long bone lesion with more than 50% cortical destruction should be prophylactically stabilized. In 1982, Harrington reviewed the literature and summarized the trends at that time of indications considered for prophylactic stabilization of the femur, which included (1) a lesion ≥ 2.5 cm, (2) a lesion with > 50% cortical destruction, and (3) a lesion causing persistent pain after a trial of radiation therapy.
In 1989, Mirels developed a scoring system to predict the risk of impending fracture in long bones. Results were based on a retrospective analysis of plain films, primarily in patients with metastatic breast carcinoma. Four criteria were analyzed, with a maximum of 12 points, based on lesion site, size, degree of sclerosis/lysis, and pain. Though these are not categorical or absolute criteria, subsequent studies have validated this system as having high sensitivity but low specificity. In other words, at the very least, this scoring system provides a relative framework whereby orthopedic surgeons can support clinical decisions based on plain film interpretation.
Current and future projects involve the use of more advanced imaging to predict fracture risk based on quantitative structural analysis. For example, CT-based structural rigidity analysis has been investigated to quantify mechanical stability in children with benign bone tumors. Axial images of an osseous lesion can be compared to normal contralateral bone and then used to calculate the axial, bending, and torsional rigidity of an osseous lesion. This potentially can provide the clinician with a quantifiable risk for fracture.
Hong et al similarly applied these algorithms to quantitative CT, MRI, and dual-energy x-ray absorptiometry in order to estimate the relative fracture risk of trabecular defects in vertebral bodies. Keyak et al employed CT-based finite element modeling to quantify the strength and stability of femoral shafts with and without metastatic lesions as a means to predict the risk of pathological fracture. However, practical application of these noninvasive advanced imaging techniques has not yet been established, and they have not yet replaced clinical judgment and plain film interpretation.
Evaluation of Mechanical Stability
Evaluation of osseous stability is challenging even for the experienced surgeon. Plain radiographs provide the most insight into the structural integrity of bone. CT scans will define cortical architecture in more detail. Magnetic resonance imaging (MRI) scans will show the intramedullary extent of tumor and any softtissue extension. However, CT and MRI scans will magnify the extent of osseous disease seen on plain radiographs and will exaggerate the risk of fracture. Most of the studies that have provided classic guidelines for predicting impending pathological fractures and the indications for prophylactic fixation have relied on plain radiographs. Orthopedic surgeons therefore place most weight on plain films when evaluating the mechanical stability of bone.
Although no absolute guidelines exist, a number of studies have provided criteria to support clinical judgment and radiographic interpretation. In 1973, Fidler suggested that a long bone lesion with more than 50% cortical destruction should be prophylactically stabilized. In 1982, Harrington reviewed the literature and summarized the trends at that time of indications considered for prophylactic stabilization of the femur, which included (1) a lesion ≥ 2.5 cm, (2) a lesion with > 50% cortical destruction, and (3) a lesion causing persistent pain after a trial of radiation therapy.
In 1989, Mirels developed a scoring system to predict the risk of impending fracture in long bones. Results were based on a retrospective analysis of plain films, primarily in patients with metastatic breast carcinoma. Four criteria were analyzed, with a maximum of 12 points, based on lesion site, size, degree of sclerosis/lysis, and pain. Though these are not categorical or absolute criteria, subsequent studies have validated this system as having high sensitivity but low specificity. In other words, at the very least, this scoring system provides a relative framework whereby orthopedic surgeons can support clinical decisions based on plain film interpretation.
Current and future projects involve the use of more advanced imaging to predict fracture risk based on quantitative structural analysis. For example, CT-based structural rigidity analysis has been investigated to quantify mechanical stability in children with benign bone tumors. Axial images of an osseous lesion can be compared to normal contralateral bone and then used to calculate the axial, bending, and torsional rigidity of an osseous lesion. This potentially can provide the clinician with a quantifiable risk for fracture.
Hong et al similarly applied these algorithms to quantitative CT, MRI, and dual-energy x-ray absorptiometry in order to estimate the relative fracture risk of trabecular defects in vertebral bodies. Keyak et al employed CT-based finite element modeling to quantify the strength and stability of femoral shafts with and without metastatic lesions as a means to predict the risk of pathological fracture. However, practical application of these noninvasive advanced imaging techniques has not yet been established, and they have not yet replaced clinical judgment and plain film interpretation.