Courtesy: Manoj Veetil FRCS Tr and Orth, Birmingham, UK

Metastatic Bone Disease: Practical Principles and Management Pathways

Overview of Metastatic Bone Disease

• Metastatic bone disease is one of the most symptomatic and disabling manifestations of advanced cancer.
• Bone metastases typically occur in a predictable distribution, most commonly involving the spine, pelvis, ribs, and proximal limb girdles.
• Involvement beyond the knee or elbow is uncommon and should raise suspicion for alternative diagnoses.
• Common primary sources include breast, prostate, lung, renal, and thyroid cancers.
• Improved systemic therapies have increased survival in recent years, requiring durable orthopedic management strategies.

Mechanism and Pathophysiology

• Metastatic lesions weaken bone through osteoclastic activation and local bone destruction.
• Chemical mediators such as transforming growth factor beta stimulate tumor activity and osteoclastic bone resorption.
• Most pathological fractures occur with minimal trauma and are preceded by weeks of prodromal pain.

Clinical Presentation

• Pain is the most common presenting symptom and is typically worse at night.
• Patients may present with pathological fractures following minimal trauma.
• Some patients present with unexplained chronic musculoskeletal pain.
• Occasionally metastatic bone disease may be diagnosed before the primary tumor is identified.

Diagnostic Approach

• A complete history and clinical examination should be followed by targeted investigations.
• Baseline laboratory testing includes routine blood tests, bone profile, liver function tests, tumor markers, and myeloma screening.
• Imaging includes plain radiographs, magnetic resonance imaging of the affected bone, computed tomography of chest, abdomen, and pelvis, and bone scintigraphy.
• Biopsy is required if the diagnosis is uncertain or the primary tumor is unknown.

Differential Diagnosis

• Lesions must be differentiated from primary bone tumors and infection, as treatment differs significantly.
• A solitary lesion should be treated as a primary tumor until proven otherwise.

Risk of Pathological Fracture

• Prophylactic fixation reduces complications compared with treating established fractures.
• Scoring systems such as Mirels score help assess fracture risk but should be interpreted with clinical findings.
• Cortical destruction greater than half of bone diameter suggests high fracture risk.
• Functional pain during daily activities is a strong indication for prophylactic fixation.

Non Surgical Management

• Radiotherapy may relieve pain and promote sclerosis in radiosensitive tumors.
• It is particularly effective in lymphomas, myeloma, breast, and prostate cancers.
• Chemotherapy and endocrine therapy are used depending on tumor type.
• Bisphosphonates and denosumab reduce osteoclastic activity and skeletal complications.
• Other treatments include percutaneous ablation techniques for selected lesions.

Principles of Surgical Management

• Surgical treatment aims to relieve pain, restore mobility, and provide durable stabilization.
• Reconstruction should allow immediate weight bearing and outlast the patient’s life expectancy.
• Bone grafting is generally ineffective in metastatic disease.
• Cement augmentation is frequently used to improve implant stability.

Preoperative Considerations

• Patients require medical optimization including nutritional and anesthetic assessment.
• Bone marrow suppression and coagulation abnormalities are common.
• Hypercalcemia must be corrected before surgery.
• Some tumors such as renal and thyroid metastases are highly vascular and may require preoperative embolization.
• Venous thromboembolism prophylaxis and adequate analgesia are essential.

Site Specific Management

• Proximal femur is commonly affected; options include cemented arthroplasty or endoprosthetic replacement.
• Subtrochanteric lesions often require endoprosthetic reconstruction for durability.
• Diaphyseal lesions are often treated with intramedullary nailing and postoperative radiotherapy.
• Distal femur and proximal tibia lesions may be treated with locking plates and cement augmentation.
• Upper limb lesions are often managed with plating or nailing; joint involvement may require prosthetic replacement.

Pelvic and Acetabular Metastases

• Pelvic disease significantly impacts mobility and quality of life.
• Small acetabular lesions may be managed with cementoplasty.
• Larger lesions require reconstruction techniques to restore weight bearing function.
• Management often involves tumor debulking and structural reconstruction.

Spinal Metastases

• The spine is the most commonly affected site.
• Patients may present with back pain, neurological compromise, or paralysis.
• Magnetic resonance imaging is the investigation of choice.
• Surgery is indicated for instability, neurological compression, radioresistant tumors, and intractable pain.
• Radiotherapy is useful for radiosensitive lesions and selected cases of spinal cord compression.

Treatment Algorithms

• Patients with known malignancy and compatible lesions may proceed directly to treatment after staging.
• Patients without known malignancy require full workup including imaging and biopsy.
• Younger patients require careful evaluation for primary bone tumors.
• Restaging is required in previously treated cancer patients presenting with new lesions.

Key Principles and Outcomes

• Orthopedic management should be integrated into multidisciplinary care.
• Early intervention improves mobility and quality of life.
• Implants must outlast patient survival to avoid revision surgery.
• Failure to intervene appropriately or use durable reconstruction results in poor outcomes.

Discussion Highlights

• Intramedullary nailing remains appropriate for many diaphyseal lesions with reasonable prognosis.
• Endoprosthetic reconstruction is preferred for metaphyseal destruction.
• Positron emission tomography scans are not routinely required but may be useful in selected cases.