What are the early signs and symptoms of knee cancer?

Early Signs and Symptoms of Knee Cancer

The earliest and most critical symptom of knee cancer is pain that begins insidiously, becomes constant, occurs at rest or during the night, and is non-mechanical in nature—this "night pain" is a red flag requiring immediate investigation. 1, 2

Cardinal Presenting Symptoms

Pain Characteristics (The Primary Warning Sign)

• Pain is the first symptom in 100% of cases, typically beginning insidiously and gradually becoming constant over weeks to months 1, 3
• Night pain and rest pain are the most distinguishing features that separate malignant bone tumors from benign musculoskeletal conditions 1, 2
• Pain intensity may vary initially but becomes progressively severe, with neoplastic knee pain characterized as constant and rapidly progressive 4
• The pain is non-mechanical in nature, meaning it does NOT improve with rest (unlike typical sports injuries or arthritis) 1
• Pain lasting less than 4 months with severe intensity carries significantly higher risk for malignancy (OR 7.6 and OR 5.7 respectively) 4

Swelling and Physical Changes (Later Findings)

• Localized swelling appears as a later finding, typically noticed an average of 7 weeks after pain onset 1, 3
• Swelling only becomes evident once the tumor has progressed through the cortex and distended the periosteum 1
• A palpable mass may develop, often associated with the pain and swelling 5
• Limitation of joint movement occurs as the disease progresses 1

Additional Clinical Features

• A limp may develop in approximately 67% of patients, and notably, this can occur even without pain on weight bearing 3
• The average duration of symptoms before patients seek medical attention is 3 months, though many present later 2, 3
• A history of recent minor trauma is present in approximately 53% of cases—this does NOT exclude cancer and must not delay appropriate workup 2, 3

Critical Age-Specific Context

The knee is the most common location for bone cancer, with 75% of all osteosarcomas arising around the knee joint 1

For Patients Under 40 Years

• Primary bone sarcoma (osteosarcoma or Ewing sarcoma) is more likely 2
• Osteosarcoma most commonly affects adolescents and young adults, with median age of 15-20 years 1
• The distal femur and proximal tibia (around the knee) are the most frequent sites 1, 2

For Patients Over 40 Years

• Metastatic carcinoma or myeloma becomes the most common diagnosis and should be investigated first 2
• Secondary osteosarcoma related to Paget's disease or prior radiation may occur 1

Common Diagnostic Pitfalls to Avoid

The presence of trauma history or intermittent pain does NOT rule out malignancy—physicians often mistake early osteosarcoma symptoms for "growing pains" or sports injuries, leading to dangerous delays 2, 3

• The mean total delay from symptom onset to definitive diagnosis averages 17 weeks (range 4-55 weeks), with significant delays occurring even after swelling becomes noticeable 3
• In some patients, the interval from presentation to radiography exceeded 3 weeks despite noticeable swelling 3
• Any adolescent or young adult with persistent knee pain, especially with night pain, requires urgent plain radiographs in two planes 2, 6

Immediate Action Required

If X-ray shows bone destruction, new bone formation, periosteal swelling, or soft tissue swelling, urgent referral to a bone sarcoma center is mandatory BEFORE any biopsy is performed 2, 6

• Inappropriate biopsy techniques performed outside specialized centers can irrevocably compromise chances for limb salvage or cure 1, 6
• All suspected cases should be discussed at a multidisciplinary team meeting before definitive treatment 1