What's going on with a protruding lump on the knee?

The knee is a joint that connects the thigh and calf. It is very important to the human body. Walking, running, jumping, squatting and other movements require bending of the knee. Since people do not pay enough attention to the care of their knees, some knee diseases may occur. For example, a protrusion on the knee is a common situation. So what is the cause of a protrusion on the knee?

A protrusion on the knee is most likely caused by tibial tubercle epiphysisitis.

How does tibial tubercle epiphysisitis occur?

The tibial tuberosity epiphysis appears at around 11 to 13 years of age and fuses with the proximal femoral epiphysis at around 17 to 18 years of age. The epiphysis is located in the front and upper part of the femur, extending downward in a tongue-like shape, covering the anterior part of the proximal epiphysis of the tibia, and is the attachment site of the quadriceps tendon under the patella. Repeated minor trauma and strong traction of the infrapatellar quadriceps tendon are the main causes of this disease. It is more common in male adolescents.

The proximal tibial epiphysis of children is cartilage, and the front edge extends downward in a tongue-like shape. At around 11 years old, the ossification center of the tibial convexity appears. At around 16 years old, the proximal tibial epiphysis and the ossification center of the tibial convexity combine to form the tibial tuberosity. Before fusion, blood circulation to this area comes from the patellar ligament. During strenuous exercise or trauma, the patellar ligament may excessively pull the bone protrusion in some cases, causing partial avulsion, thereby affecting blood circulation and causing epiphyseal ischemia. Due to the differentiation of fibroblasts and the activity of osteoblasts, heterotopic ossification may occur in the patellar ligament and its surrounding soft tissues, and new ossicles may appear in the anterior and superior part of the tibial tuberosity. The histological appearance of these new bones is exactly the same as that observed in myositis ossificans. Due to the traction of the patellar ligament, the osteoblasts at the tibial tuberosity become active, resulting in bone hyperplasia, which enlarges the tibial tuberosity and protrudes forward significantly. The proximal tibial epiphysis may fuse early, causing complications of high patella and knee recurvature after the epiphysis matures.

In which populations does tibial tubercle epiphysisitis commonly occur?

This disease is more common in adolescents aged 12 to 18 years old, more common in boys than in girls. It is mostly unilateral, but can also be bilateral (about 30%). It is more common in middle school students who like strenuous sports (such as running, jumping, ball games, etc.) and has a slow onset.

What are the symptoms of tibial tubercle epiphysisitis?

Pain, mild swelling and tenderness at the tibial tuberosity, worse with exertion. Some children have a history of strenuous exercise or trauma before the onset of the disease. The pain worsens when the knee is extended, because the affected epiphysis is tightened by the recruited quadriceps femoris; it is also painful during passive knee flexion, because the quadriceps femoris pulls on the epiphysis.

1. The tibial tuberosity of the affected limb gradually swells and becomes painful. Climbing stairs and brisk walking can make the pain worse. In severe cases, lameness may occur. Weakness in extending the knee.

2. The tibial tuberosity of the affected limb is raised, with obvious local tenderness, but the skin is not red or hot. When the knee is extended under resistance, the local pain is aggravated.

What auxiliary tests can be done to help with the diagnosis?

X-ray findings: Lateral views of the knee, especially those with slight internal rotation, are most helpful for diagnosis. Because the tibial tuberosity is located slightly to the outside of the middle part of the tibia. In the early stages of the disease, local soft tissue swelling, thickening of the patellar tendon, and disappearance of the inferior angle of the infrapatellar fat pad can be seen. Later, one or several free new bone fragments can be seen in front of the tibial tubercle. In the later stage, the new bone films are more obvious, and there is bone hyperplasia in the adjacent tibial tuberosity.