Metastases to bone are the most frequent cause of destructive lesions to the skeleton in adults. The most common primary malignancies that metastasize to bone are breast, lung, kidney, and prostate carcinoma. The typical distribution of metastatic lesions is to the spine, ribs, pelvis, and proximal limb girdles.1 However, almost any primary malignancy may metastasize to bone, and any bone in the body may be involved. In the upper extremity, the most common location is the humerus, usually the proximal third or the diaphysis. Lesions in the distal third of the humerus are less common and typically occur in patients with myeloma or lung or renal carcinomas. Diagnosis of metastatic humeral bone lesions and alternatives for treatment vary depending on whether the patient has a large impending lesion or complete fracture, which region of the bone is affected, the extent of overall disease, the histologic diagnosis, and the nature of prior treatment.
Presentation and Evaluation
Several distinct presentations of upper extremity metastatic disease can occur. Patients with known metastatic disease may have either an asymptomatic or a painful and disabling lesion. A small percentage without a known history of cancer may present with a destructive bone lesion secondary to an occult primary tumor. Complete fractures secondary to metastatic lesions often occur after very minor trauma, such as rolling over the arm in bed, a minor fall, opening a jar, or other simple activities. The presence of substantial arm or shoulder pain in the patient with a history of cancer indicates the possibility of bone metastases. Common characteristics include pain at rest, night pain, and pain unresponsive to anti-inflammatory medications and narcotics.
During evaluation, the clinician must determine whether the pain is secondary to bone metastases or to nononcologic sources, such as glenohumeral arthritis or rotator cuff tendinosis, which also manifest as diffuse discomfort, night pain, difficulty with sleeping on the affected side, and limited use of the upper extremity secondary to pain. Plain radiographs are the first step in evaluation. An anteroposterior view of the shoulder and humerus is done to assess the proximal half of the humerus and scapula, and a scapular axillary view is made to evaluate the glenoid and coracoid process. If the discomfort exhibits a radicular pattern or if the shoulder pain extends proximally into the neck, radiographs of the cervical spine should be obtained. If plain radiographs do not show a destructive lesion and bone metastases are suspected, technetium Tc 99m (99mTc) bone scanning or magnetic resonance imaging (MRI) may be done. 99mTc bone scanning is an excellent modality for screening the cervical spine and shoulder girdle, especially when previous scans are available for comparison. MRI of the shoulder can differentiate pain secondary to rotator cuff tendinosis from that of metastatic disease and can identify bone marrow infiltration by tumor cells and rotator cuff inflammation. Short tau inversion recovery (STIR) or a T2-weighted fast spin-echo fat-saturated sequence is the optimal method for assessing tumor presence. Although computed tomography (CT) is sensitive in detecting cortical bone destruction in the scapula and humerus, its use is limited because it cannot detect marrow invasion in the absence of bone destruction. However, CT is more accurate than other diagnostic tools in determining structural compromise.
Criteria for Impending Fracture
Determining the risk for pathologic fracture is subjective and depends on many factors, including the pattern of bone destruction, location in the bone, response of the host bone, and anticipated loading conditions. Most classification systems2-6 used to predict areas at risk of fracture are based on the amount of cortical bone destruction measured on anteroposterior and lateral radiographs. Bone destruction of 25% of the cortical diameter has a low risk of fracture (Fig. 1, A); bone destruction of 75% of the cortical diameter is associated with a high risk of fracture.2-4 When bone destruction is between these extremes, the risk of fracture is more difficult to predict. Most surgeons consider that ≥50% bone destruction indicates impending fracture (Fig. 1, B).
Mirels4 developed a 12-point scoring system based on the location, type, and amount of bone destruction and the presence or absence of activity-related pain. Combined scores of 9, 8, and 7 respectively had a 33%, 15%, and 4% risk of fracture. There was a low risk of fracture in patients with <50% cortical bone destruction. Although this is an objective scoring method, many surgeons do not use the Mirels system because of the subjectivity of the variables and the substantial overlap between the fracture and nonfracture groups, which underscores the difficulty in predicting risk of fracture.
Mirels4 showed that purely lytic bone metastases have a much higher risk of fracture than do purely blastic metastases (often seen in patients with metastatic breast and prostate carcinoma). However, many patients have a combination of lytic and blastic metastases. Lesions in the proximal humeral metaphysis are less prone to fracture than are those in the diaphysis or in the transition zone between the metaphysis and diaphysis (in the region of the insertion of the pectoralis major muscle).
The anticipated loading of the upper extremity is also an important consideration. A patient with an isolated metastasis in the humerus can easily protect against overloading the upper extremity during the course of irradiation and/or chemotherapy. In contrast, a patient with substantial concomitant lower-extremity disease requiring protected weight bearing with crutches or a walker may subject the upper extremity to increased loading. In such a situation, internal fixation may be necessary to prevent fracture.
Most humeral metastases that have not fractured can be managed with external beam irradiation without surgery. The decision may be dependent on the histology of the tumor. Patients are counseled to avoid provocative activities that may lead to fracture while the lesion heals. Patients generally undergo 1 week to 2 weeks of external beam irradiation (usually 3,000 cGy in 10 fractions).7,8 If the isolated lesion occurs in a patient with an excellent prognosis, a longer course of treatment may be recommended in an effort to provide more durable local control. Treatment of humeral metastases with a single dose of 800 cGy can be successful in reducing pain in patients with terminal disease and short life expectancies; 9-12 this is especially useful when patient transport to the radiation therapy facility is difficult. Although tumor progression generally halts after the completion of irradiation, activity should be modified for 2 to 3 months. Patients can continue activities of daily living such as eating, cleaning, bathing, and changing clothes, but exertions such as tennis, changing a tire, opening tight jars, overhead throwing, and swinging an ax are discouraged.
Patients with complete fractures are poor candidates for nonsurgical treatment. Fracture braces and casts are not effective in controlling discomfort, and patients avoid using their extremities because of pain. In contrast with nonpathologic humeral fractures, which heal quickly, complete fractures secondary to metastatic bone disease heal very slowly if it all. Flemming and Beals13 and Douglass et al14 reported poor results with nonsurgical management of pathologic humeral fractures and later characterized the results of closed management as “unsatisfactory, producing limited use, incomplete pain relief, and unpredictable healing.”13
The general medical condition of the patient must be assessed before surgery. Terminally ill patients (anticipated survival, <2 to 3 weeks) are poor candidates, unlikely to benefit from the surgery. Although there are no absolute criteria to predict survival of the patient with metastatic bone disease, poor prognostic factors include hypercalcemia, substantial cytopenia from bone marrow failure, cachexia, and poor performance status.
Careful preoperative planning is essential. The cervical spine should be carefully assessed for destructive lesions so that injury can be avoided while anesthetizing or positioning the patient, and plain radiographs or a recent 99mTc bone scan should be reviewed. The entire humerus should be viewed with plain radiography in two orthogonal planes to determine if there are multiple lesions. Positioning the end of the fixation device at a site of diseased bone must be avoided so that fracture does not occur in this transition zone when the patient begins using the extremity. CT and MRI scans generally are not needed for preoperative planning. However, if plain radiographs are equivocal as to the presence of cortical destruction in regions designated to receive the fixation device, MRI can be used to confirm the presence of disease.
Because patients with metastatic bone disease may survive only 3 to 12 months, the goal of surgery is to attain rigid and durable internal fixation and, accordingly, immediate postoperative use of the upper extremity. Rigid fixation can be achieved with a variety of internal fixation or prosthetic devices. These devices can be used with or without methylmethacrylate. Fracture healing should not be necessary to achieve functional stability.
The selection of the reconstruction device, such as an intramedullary nail, plate, or prosthesis, depends on the area of humeral involvement and the degree of bone destruction. When selecting a fixation method, it is convenient to divide the humerus into three regions: (1) proximal metaphyseal, (2) metadiaphyseal and diaphyseal, and (3) distal metadiaphyseal and metaphyseal (supracondylar) (Fig. 2).
Proximal Metaphyseal Region
Complete or impending fractures of the proximal humerus usually are managed with a humeral endoprosthesis. Intramedullary nails are difficult to use in the proximal metaphysis because rigid proximal fixation cannot be achieved. Plate fixation is likewise ineffective for solid fixation because of the thin and compromised cortical bone.
The surgical procedure is similar to that for a nonpathologic fracture, in which a deltopectoral approach is used to osteotomize the humeral head. For a pathologic fracture, the proximal fragments are excised. The proximal humeral metaphysis is carefully curetted to remove all of the gross tumor but not the cortical shell or periosteal tissues. The humerus is prepared through the entire diaphysis to receive a long-stem prosthesis. The prosthesis is carefully cemented in place so that the cement does not enter the soft tissues; extravasation through humeral defects might result in neurologic or vascular injury. A long-stem prosthesis spanning the diaphysis to the supracondylar region is generally used to maximize protection of the entire humeral shaft.
Metadiaphyseal and Diaphyseal Region
Metadiaphyseal and diaphyseal lesions can be managed with either intramedullary nail or plate fixation. Both methods are effective, and the choice of implant rests with the individual surgeon. Each technique has specific advantages and disadvantages.
Intramedullary Nail Fixation Intramedullary nailing, the most popular method used for humeral shaft lesions, can be done either closed or open through an anterograde or retrograde approach. The major advantage of intramedullary nail fixation is that it can protect a long segment of the humerus. When augmented with methylmethacrylate, it also can provide rigid fixation of a long segment of diseased bone. Other advantages include a low risk of implant failure and the fact that the nail can be placed in a closed manner. The major disadvantage of anterograde intramedullary nailing is the mandatory incision and repair of the rotator cuff. Many patients experience residual rotator cuff tendinitis and weakness. Prominent hardware (proximal interlocking screws or the tip of the nail) can cause persistent symptoms.
Intramedullary nail fixation can be used for destructive bony lesions from 2 to 3 cm below the level of the greater tuberosity (proximal one sixth of the humerus) to approximately 5 cm above the olecranon fossa.15 Anterograde or retrograde nailing may be used; care must be taken to protect areas of bone destruction.16 To achieve rigid fixation, there must be at least 4 to 5 cm of intramedullary nail on either side of the lesion with intact cortices surrounding its proximal and distal ends. An intramedullary nail can be used for more proximal or distal lesions if the fixation can be made rigid with an interlocking screw or methylmethacrylate. If the bone destruction occurs in the supracondylar region of the distal humerus, plate fixation or crossed flexible nails can be used.
The amount and location of the bone destruction must be carefully assessed. Closed nailing is an excellent technique for both impending and complete fractures. Proximal and distal locking is recommended to ensure rigid fixation for complete fractures. Patients with intact cortices after nailing may be treated with proximal interlocking alone or with proximal and distal interlocking (Fig. 3). With the closed technique, augmentation with methylmethacrylate generally is not necessary. However, for severe bone destruction with no remaining cortices over a length of 3 to 6 cm, open nailing with curettage of the tumor and methylmethacrylate can be considered to supplement the fixation.
Open nailing is done with a technique similar to closed nailing. The fracture site can be approached through an anterolateral or posterior incision or, if the entire humerus needs to be exposed, through a deltopectoral approach proximally and the anterolateral approach distally. A portion of the deltoid insertion is elevated off the humerus, and the brachialis muscle is split to expose the humeral shaft. After either exposure, a cortical window is made through the area of bone destruction, and all of the gross tumor is removed with curettes. The humerus is prepared to receive the nail, as in the closed technique. The open fixation can be supplemented with methylmethacrylate (Fig. 4).
After the nail is inserted over a guide wire, the entire humerus is imaged to verify satisfactory length and fracture reduction. The nail is then withdrawn into the proximal fragment to a level just above the point where the cement augmentation is to end. The cement is mixed, placed in the cement gun, and injected through a small insertion tube first into the distal fragment, then the proximal fragment. The guide wire is generally left in the proximal and distal fragments. The fracture is reduced and the nail advanced into the distal fragment. Interlocking screws then can be placed if necessary. If sufficient cement has been injected into the distal fragment to secure the nail, an interlocking screw can be placed proximally to augment stability in the proximal fragment.
Plate Fixation Plate fixation is also an acceptable technique for impending and complete fractures of the proximal metadiaphyseal and diaphyseal region (Fig. 5). A major advantage of plate fixation is that the rotator cuff is not disturbed as it is with anterograde intramedullary nailing. Disadvantages of plate fixation include more blood loss than with closed nailing, the potential for radial nerve injury, and inability to protect as much humeral length as with intramedullary nailing.16 When considering plate fixation, the radiographs must be studied carefully to determine that at least three screws can be placed in normal cortical bone on either side of the fracture. When there is diffuse involvement of the humerus, intramedullary nailing is a better choice because a plate may not provide solid fixation.
The exposure for plate fixation can be done through an anterolateral or posterior approach. A cortical window is created large enough to curette the gross tumor. Care must be taken not to remove an excessive amount of normal bone; otherwise, it will be difficult to achieve rigid fixation in the remaining cortical bone. The cement can be applied before or after the internal fixation, but it is easier to reduce the fracture and place the internal fixation device first. To obtain good apposition of bone ends, irregular fracture ends can be shortened if necessary. Once the plate is applied, the screws that span the defect are removed, and cement is placed by hand into the defect. The screws can be replaced while the cement is curing or by drilling and tapping once the cement hardens.
Distal Metadiaphyseal and Metaphyseal Region
Lesions within 2 to 4 cm of the olecranon fossa are best managed with plate fixation. Neither anterograde nor retrograde nails can provide rigid fixation in these distal lesions. Plating through a posterior triceps muscle-splitting approach is very effective when the distal fragment is large enough to receive three 4.5-mm screws. Distal lesions that involve the supracondylar area are difficult to manage. Fixation can be achieved with medial and lateral plates, flexible nails inserted from the epicondyles, or prosthetic arthroplasty.
After prophylactic fixation or surgical treatment of a pathologic fracture, radiation therapy to the site of the lesion and the implanted device is recommended to decrease the risk of continued bone destruction (which could lead to increased pain), loosening of the fixation, and the need for additional surgery.17 In a study of 64 procedures in 60 patients, Townsend et al17 found that the addition of external beam irradiation to surgery significantly (P = 0.02) improved functional outcome. There was also a significantly (P = 0.035) higher risk of the need for a second surgical procedure in patients who did not receive postoperative radiation. The dose of radiation is similar to that used when treating patients nonsurgically (3,000 cGy in 10 fractions over 1 week to 2 weeks). Treatment is generally delayed to 10 days after surgery so that the skin incision can heal.
Patients may begin range of motion movement of the elbow and shoulder during the first postoperative week. If the patient has not previously undergone radiation therapy, the sutures or staples are removed 2 weeks after surgery. If the patient has previously received radiation, the sutures are left in place for approximately 4 weeks.
Alternative Surgical Techniques
Rush rods can be used for very proximal (within 3 cm of the humeral head) fractures at the surgical neck.18 There is too little proximal bone in this region for intramedullary nail fixation. The proximal hook of the Rush rod is anchored in the rotator cuff, and the fixation is supplemented with methylmethacrylate. If the hook protrudes, it can cause symptoms with overhead activity; if it is driven through the proximal cortical bone, there will be less purchase in the proximal fragment. Flexible nails also have been used for diaphyseal and proximal metadiaphyseal lesions.19
Custom proximal humeral prostheses can be used selectively when large segments of bone need to be resected.20 Resection is usually reserved for patients with progressive disease after external beam irradiation or in patients with failed internal fixation and poor bone stock. Some custom modular devices allow the restoration of length of the humerus with immediate rigid fixation after resection of variable lengths of the proximal humerus (Fig. 6). Other devices have been designed to permit resection and reconstruction of the diaphysis in the presence of an intact proximal humeral segment.21 These designs, with medullary stems cemented into the proximal and distal intramedullary canals, are still in development and are associated with complication rates as high as 25%.22
Pain relief can be reliably obtained in >90% of patients treated with rigid fixation.21-23 Redmond et al15 described good to excellent pain relief in 12 of 13 patients treated with intramedullary nail fixation for humeral pathologic fractures. In 10 patients with documented postoperative range of motion, there was a mean of 101° of abduction (range, 55° to 180°) and a mean of 98° of forward flexion (range, 45° to 170°). Of the 13 patients, 11 recovered use of the arm for activities of daily living.15 Dijkstra et al16 retrospectively compared nail and plate fixation in 37 patients with 38 pathologic humeral fractures. There was good to excellent subjective pain relief in approximately 90% of the patients treated with either method. The authors also reported early fixation failure secondary to angular deformity and rotational instability in patients treated with intramedullary nails without proximal and distal locking.16 Most treatment failures are secondary to disease progression or early loss of fixation.17 Patients with renal cell carcinoma are especially prone to disease progression and often are treated with higher initial doses of radiation (4,500 cGy) to reduce the risk of early failure.
Metastatic disease of the humerus is common, and effective management can improve the quality of life for cancer patients. Nonsurgical treatment with external beam irradiation is used for symptomatic lesions with <50% cortical bone destruction. With ≥50% cortical bone destruction, intramedullary nailing is the most common method of both prophylactic and fracture fixation. Locked intramedullary nails can provide rigid fixation with early pain relief. Methylmethacrylate can be used to aid in the reconstruction of defects caused by the surgical treatment of large lesions and to improve fixation. Plate fixation also can be used for diaphyseal and distal lesions. Immediate rigid fixation is necessary to achieve consistently good pain relief.
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