Metastatic bone disease (MBD) is cancer that spreads to bone from other organs such as the lungs, breast, or prostate. Metastatic bone disease weakens and damages the bones causing bone fractures and pain.
Surgery for MBD is performed to remove the tumor and fix the broken or weakened bone in place using instrumentation such as wires, plates, rods, pins, nails, or screws. In many cases, the defect caused by the tumor is filled with bone cement to provide additional strength.
Bone metastases in the upper extremity
- Humeral shaft: Humeral shaft tumors are found along the length of the upper arm bone and are also addressed with various treatment techniques. In cases with large defects and failed previous surgery, segmental spacers are used after the removal of the tumor. Segmental spacers involve removal of the middle part of the bone and substituting it with metal.
- Mid-arm (near the elbow): Bone metastases to the mid-arm can be treated with the use of flexible nails. These flexible nails cover the entire humerus, preserve the natural elbow joint, and provide excellent functional recovery. In some cases, if the tumor involves the joint, elbow replacement may be needed.
- Forearm/Hand: These tumors are located below the elbow and may have spread from the lungs, breast, or kidneys. They can be treated with flexible rods, plates and screws, or bracing.
Upper humerus: Bone metastases to the humerus, the upper arm bone that connects the shoulder to the elbow, can be treated with various techniques depending on the extent of involvement. Normally, only the arm side of the shoulder joint is replaced without involving the socket side of the joint.
Bone metastases in the lower extremity (leg)
- Pelvis and acetabulum (hip): Surgical treatment is usually performed when conservative treatment has failed and there are impending fractures and significant involvement of the acetabulum (hip joint cup) or other portions of the pelvis. The most common long bone involved in bone metastases is the femur or the thighbone.
- Femoral head and neck: For femoral head and neck tumors, joint replacement is indicated.
- Lower hip (Peritrochanteric): Bone metastases to the lower hip are usually treated with metal rod placement down the central canal of the femur in tandem with screw and side plate implants. In severe cases, a special hip replacement may be needed.
- Below the hip (Subtrochanteric): For bone metastases below the hip, screw and side plate implants are used. In severe cases, upper femoral replacement may be needed. Metallic nails are used where a break has not yet occurred but is likely to occur anytime.
- Femoral shaft: Femoral shaft tumors are treated using plates, bone cement, or metal rods.
- Distal femoral (Supracondylar): Lower end femoral tumors are usually treated with metallic implants. But when the bone is severely damaged knee replacement may be considered as a treatment option.
- Shinbone (Tibia): Metastasis to the shinbone (tibia) is rare and is treated with cement, plates, and screws. But, if the bone is severely damaged, then replacement of the upper end of the tibia and the knee joint may be required.
- Foot: Bone metastasis to the foot occurs very rarely.
- Spine: Bone metastases to the spine are common and usually do not require surgery except in advanced cases.
Metastatic bone disease causes pain in the location of the metastasis and anemia (decreased production of oxygen-carrying red blood cells). It can also weaken the bones causing them to fracture.
Bone metastases most commonly spread to the spine, pelvis, ribs, skull, upper arm and long bones of the leg. When cancer spreads to the bone, the bone will have been entirely destroyed in a specific area. This is known as osteolytic bone destruction. As a result of cancer spread, new bone (osteoblasts) will grow in an abnormal manner making the other bones weak and deformed. Patients may also present with pathologic fractures (broken bones) or sometimes impending pathologic fractures where the bone is not broken but is so weak that a break can occur anytime. Patients with these conditions require prolonged bed rest which is likely to cause chemical imbalance in the blood. In some cases, if cancer has spread to the spinal bones, the patient can experience paralysis of the affected bone area.
To diagnose metastatic bone disease, your doctor will take a medical history and perform a physical examination of the affected area.
X-rays are obtained to evaluate the involvement of the bone. Sometimes if the spine or pelvis is involved, other diagnostic imaging techniques such as CT scan or MRI are used. A bone scan may be helpful to know if other bones of the body are also affected. A biopsy of the affected bone (removal of a piece of the tissue) may be performed especially in the case of primary tumors.
Complex deformities require surgical correction that is performed one of two ways, namely, open reduction and closed reduction, and depends on the complexity of the condition. In open reduction, the surgeon makes an incision on the skin directly over the affected area and inserts internal fixators. In closed reduction, external fixators are used without making any incision.
- External fixation: In this method, the surgeon places external fixators such as pins or screws into the fractured bone. These pins are then connected to clamps or rods outside the skin which will form an external frame that will bring about stability and allow the bone to heal.
- Internal fixation: In this method, your surgeon makes an incision over the injured area and inserts internal fixators such as wires, screws, pins, or plates. These are fixed either in front of the pelvis or at the back and help to prevent further injury such as arthritis and prevent displacement of the bone. Your doctor may apply casts or suggest you use crutches and avoid weight-bearing activities or physical work for a few weeks to allow the bones to join.
- Ilizarov method: The Ilizarov method is a minimally invasive procedure where correction of deformities is done using a circular ring fixator. During surgery, a small incision is made to gain access to that part of the bone which is to be cut. A hospital stay of 1-3 days may be required after which rehabilitation with the application of splints may be recommended.
Bone lengthening begins a few days or weeks after surgery. With the use of external fixators the patient or family member attending to them is asked to perform small twists to apply pressure on the leg. As the bones are pulled apart, new bone gradually starts to grow between the bone ends. The rate of growth is usually 1mm per day. X-rays are taken once every 2 to 3 weeks to check for new bone growth, nerve and muscle function, and also to watch for any complications.
After achieving the required bone length, no further adjustments are made to the device. The newly formed bone is weak and will tend to break if it is not supported by external or internal devices. Lengthening over nails (LON) is used as an external device. This device remains in the bone until the distraction phase. After the removal of LON, a rod is placed internally at the end of the bone for support. The rod hardens the newly formed bone. The function of the internal device automatically ceases once the bone attains the desired length. Bone healing is evaluated with X-rays that are taken once a month. The X-ray shows the amount of calcium present in the bone. After the bone is healed, the rods are removed.
The removal of the external fixator device is done under general anaesthesia at which time the patient is unconscious. After the removal, a cast made of plaster of paris (POP) is placed for a month for protection. No such cast is placed for patients with an internal fixator device as the support protects the bone internally.
Bone implantation: During this procedure, healthy bone is removed from another part of the body and implanted onto a bone which cannot be joined. It is performed when fragmented bones cannot be joined by other surgical methods.
The patient should always follow the post operative instructions provided by the doctor to ensure a successful outcome. Never put weight on the treated leg until your doctor permits. Use crutches or a walker to move around as ordered. If an external device is fixed, you need to perform the manual turns as instructed by your doctor. Follow your doctor’s instructions on cleaning around the pins and wires of the external device to prevent infection. Take your pain medications as prescribed. Perform stretching exercises to help in strengthening leg muscles. Follow-up visits are scheduled every 2-3 weeks during which X-rays are taken to evaluate bone growth. It is important to maintain a healthy diet and eat nutritious foods rich in calcium.
Risks and Complications
Bone complications include:
- Delayed union or non-union: Bone healing is delayed due to damage of bone tissues at the time of bone cutting.
- Premature consolidation: This occurs when the bone growth is too abundant or healing is too fast.
- Axial deviation: This can occur due to unbalanced forces that bend the bone during the lengthening process.
Soft tissue complications include:
- Muscle contractures: These occur when the soft tissue cannot adapt to the changes in the bone length. Passive stretching and soft tissue mobilization can help. Pain medications should be taken 30 minutes before therapy to minimize discomfort.
- Muscle weakness: This is caused by lack of movement resulting from inability to walk normally. Nerve Injury: This occurs when certain nerves do not stretch in coordination with the bone lengthening.
Complex joint reconstruction surgery is performed to restore joint stability, improve lost functionality, and relieve pain in patients with metastatic bone disease with the goal of improving the patient's quality of life.