The appearance of a lump on the knee can respond to different causes, including synovial diseases such as bursitis or Baker’s or vascular cysts. The recommendation before the appearance of a lump in the knee would be to go to an orthopedic surgeon.
The knee is a joint exposed to multiple injuries, especially if a sport is practiced since it is the joint that supports most of the body’s weight when we are standing.
The knee is formed by the distal portion of the femur and the proximal portion of the tibia (femoral-tibial joint) with two fibrocartilaginous discs between them that are the menisci. In the anterior and inferior portion of the femur is the patella forming the femoro-patellar joint. The bony surfaces are covered with cartilage.
The knee performs mainly flexion and extension movements through muscles that are attached by tendons to the knee bones. The ligaments give it stability and prevent it from dislocating, the most important being the external lateral ligament, the internal lateral ligament, the anterior cruciate ligament (ACL), and the posterior cruciate ligament. The knee is surrounded by a joint capsule; the inner layer of this capsule is the synovial membrane that produces the synovial fluid that acts as a lubricant.
The most common knee injuries are those that affect the ligaments and tendons. These injuries can cause swelling of the knee. Thus, for example, it is typical of an ACL tear to notice a clicking noise with subsequent swelling of the knee with the presence of joint effusion (the presence of fluid in the knee that, if it is blood, is known as hemarthrosis). Other causes of the lump in the knee would be arthritis (due to autoimmune rheumatological diseases such as rheumatoid arthritis, infectious diseases, or storage diseases such as gout). or osteoarthritis (degeneration of articular cartilage due to “aging”). In these cases, the swelling is usually accompanied by pain and functional impotence and by a hot and red knee in the case of arthritis.
Another reason for consultation would be localized “lumps” on the knee, which are palpated by the patient or appear on a radiological examination. The main recommendation would be to go to an orthopedic surgeon who will perform a physical examination of the knee and will indicate whether any additional examination (ultrasound, radiography, CT, or MRI) is necessary to reach a diagnosis and be able to indicate the appropriate treatment.
Magnetic resonance imaging is of great help to study bone and soft tissue lesions that can be located in the joints or periarticular tissues and establish a differential diagnosis between benign and malignant tumors and non-neoplastic lesions. Most knee “bumps” are benign entities; if the suspicion is a tumor, the diagnosis is made with a biopsy or surgical removal.
Causes Of Knee bursitis
- Bursitis: bursas or bags are periarticular cavities that when inflamed, generally due to trauma or overload, present thickening and increased synovial fluid and cause pain. Knee bursitis most often occurs above the kneecap or on the inside of the knee below the joint.
- Baker’s cyst or popliteal cyst: It is a soft, synovial fluid-filled lump that forms at the back of the knee that develops due to some damage done to the knee. A differential diagnosis must be made with a popliteal aneurysm that presents as a pulsatile mass.
- Meniscal cyst: a collection of synovial fluid located within or adjacent to a meniscus (para meniscal) of traumatic or degenerative origin. They are usually associated with a tear of the meniscus. They can present as a “bulge” in the joint line.
- Arborescent lipoma: the lipomatous proliferation of the synovium, usually associated with arthritic or traumatic joint processes.
- Synovial osteochondromatosis: it is a cartilaginous metaplasia of the synovial membrane with the formation of free osteocartilaginous bodies.
- Pigmented villonodular synovitis: benign synovial proliferation. It usually presents with pain, inflammation, limited movement and recurrent hemarthrosis. Treatment is usually surgery.
- Focal nodular synovitis: benign intra-articular proliferation of a synovial area.
- Synovial hemangioma: is a rare, benign tumor originating in the vessels of the joint capsule and/or the synovial membrane.
- Vascular malformations: they are benign non-tumor lesions: Doppler ultrasound and antiresonance can be useful for diagnosis.
- Hemangioma: a benign vascular tumor that can appear as a red mass or take on a bluish hue.
- Storage diseases.
- Gouty arthritis: Gout is caused by an increase in uric acid. Focal deposits of monosodium urate are called tophi and are located in periarticular soft tissues.
The most common benign solid masses are lipomatous (formed by fat cells), neurogenic, or myxoid in origin and affect periarticular soft tissues.
- PECOMA is a perivascular epithelial cell mesenchymal tumor with uncertain malignant potential.
- The distal femur or proximal tibia enchondroma is a benign tumor that is usually asymptomatic. Surgery is only performed in case of pain, enlargement, or suspicion of malignancy.
Malignant Tumors (Sarcoma Type, Bone Lymphoma…)
Persistent, non-mechanical, predominantly nocturnal pain and a growing mass should be considered alarm symptoms.
- Cyclops lesion: localized arthrofibrosis seen in a small percentage of patients with anterior cruciate ligament surgery.
- Intra and periarticular cystic lesions(subchondral and synovial cysts and ganglions).
What you should know…
- The recommendation before the appearance of a lump in the knee would be to go to an orthopedic surgeon who will perform a physical examination of the knee and indicate if any additional examination is necessary (ultrasound, radiography, CT or MRI) to reach a diagnosis and be able to indicate the proper treatment.
- The appearance of a lump on the knee can respond to different causes, including synovial diseases such as bursitis or Baker’s or vascular cysts.
- Benign and also malignant tumors can present with a lump. In the latter case, if it is a mass that is growing and is accompanied by persistent, non-mechanical pain that is predominantly nocturnal, it should alert us and take us to a consultation.