Cancer can occur in the knee, with the area around the joint being one of the most common sites for primary bone tumors to develop. This region includes the distal end of the femur (thigh bone) and the proximal end of the tibia (shin bone). Primary cancers originate directly in the bone or surrounding soft tissues, though they account for less than one percent of all cancer diagnoses. Cancers that spread to the knee from other organs, known as secondary or metastatic tumors, are possible but less common in the knee bones compared to the spine or pelvis.
Types of Malignancies Affecting the Knee
Malignancies affecting the knee are broadly categorized into those arising from bone and those from soft tissues. Osteosarcoma is the most common primary bone cancer, frequently targeting the long bones around the knee (distal femur and proximal tibia). This aggressive tumor typically affects children, adolescents, and young adults during periods of rapid bone growth. Another primary bone tumor found here is Ewing Sarcoma, which tends to occur in the long bones of the legs and is characterized by a distinctive genetic translocation involving the EWSR1 gene.
Cancers that develop in the surrounding muscles, fat, ligaments, and tendons are known as soft tissue sarcomas (STSs). The knee is a common site for these tumors, particularly Synovial Sarcoma, which is a soft tissue cancer that often appears near large joints despite its name. Synovial sarcoma is a high-grade tumor that can be slow-growing and may not be immediately painful, sometimes reaching a significant size before detection.
Recognizing Potential Symptoms
A malignancy in the knee often presents with symptoms that differ subtly from more common conditions like arthritis or sports injuries. The most frequent initial complaint is persistent pain in the area, which tends to worsen over time and does not respond well to typical pain relievers or rest. A characteristic sign is pain that is particularly bothersome at night, sometimes severe enough to awaken a person from sleep.
The presence of an unexplained swelling, lump, or mass in or around the joint is another significant warning sign. This swelling may be noticeable only after the pain has begun. Other symptoms can include limited range of motion in the joint, a noticeable limp, or systemic issues such as unexplained fever, fatigue, or unintended weight loss. Any persistent knee pain, especially when accompanied by a mass or nocturnal pain, warrants a thorough medical evaluation.
Navigating the Diagnostic Process
The diagnostic pathway begins with a thorough physical examination and detailed medical history, focusing on the nature and duration of the pain. Imaging tests are the next step, typically starting with standard X-rays of the knee, which can reveal characteristic signs of a bone tumor. These signs can include a destructive bone pattern, a “sunburst” appearance, or a Codman’s triangle, which are suggestive of aggressive bone growth.
Following the initial X-ray, advanced imaging is necessary to fully stage the tumor and plan treatment. Magnetic Resonance Imaging (MRI) is the preferred technique, providing detailed images of the tumor’s extent within the bone marrow and soft tissues. The MRI also maps the tumor’s proximity to neurovascular structures, which is crucial for surgical planning to maximize the chance of saving the limb.
A definitive diagnosis requires a biopsy, which involves surgically removing a small sample of the suspicious tissue for microscopic analysis by a pathologist. The biopsy must be meticulously planned and performed by a specialized orthopedic oncologist, as an improperly placed biopsy track can contaminate surrounding tissue and compromise the success of later limb salvage surgery. Tissue analysis confirms the exact type of malignancy, its grade (aggressiveness), and genetic markers, all of which are essential for determining the most effective treatment plan.
Treatment Approaches for Knee Cancers
Treatment for knee-area sarcomas is highly specialized and involves a multidisciplinary team of surgeons, oncologists, and radiation specialists. Modern care prioritizes limb salvage surgery (LSS), which aims to remove the entire tumor with a margin of healthy tissue while preserving the function of the limb. For bone tumors like osteosarcoma, the cancerous section of the bone is resected and replaced with a custom-made metal prosthesis or a bone graft.
Chemotherapy plays a significant role, often administered before surgery in a strategy called neoadjuvant chemotherapy. This pre-operative treatment shrinks the tumor, making surgical removal easier and more effective, and kills any microscopic cancer cells that may have already spread. After surgery, adjuvant chemotherapy is often given to eliminate any remaining cancer cells in the body and reduce the risk of recurrence.
Radiation therapy may be used in combination with surgery, particularly for soft tissue sarcomas or for tumors that are difficult to remove completely due to their location near vital structures. While amputation may be necessary in complex cases where the cancer has extensively invaded nerves and blood vessels, advancements in surgical techniques and chemotherapy have made limb salvage the standard approach for most patients. The overall treatment regimen is personalized based on the tumor type, size, grade, and the patient’s overall health.