Where is the patella located

The human body is a very sophisticated mechanism. Every muscle, every bone, and every organ performs its functions and plays an irreplaceable role. The human body has a total of 206 bones, including the skull, trunk and limbs. The skull protects the important organs of the brain in the head. The trunk bones serve as support. The limb bones are mainly used for daily activities. In the lower limbs, the patella plays a very important role.

The patella is also known as the kneecap, kneecap, and kneecap. Anatomical eponymous bone. The knee joint is formed by ligaments together with the lower end of the femur and the upper end of the tibia. It can be felt on the surface of the body and is the largest sesamoid bone in the human body. Located in the front of the lower end of the femur, inside the quadriceps tendon, it is wide at the top and pointed at the bottom, rough at the front and has an articular surface at the back, and is articulated with the femoral patella.

What diseases of the patella occur?

1 Patellar malformation

Patellar chondromalacia is a degenerative change caused by damage to the patellar cartilage, which includes a series of symptoms such as swelling, fragmentation, shedding and corrosion of the cartilage. Finally, the corresponding articular surfaces of the femur and patella also undergo the same changes, gradually forming reactive hyperplasia of the patellofemoral joint, which will later lead to osteoarthritis.

The symptoms of patellar chondrosis mainly occur in a half-squatting position, and the pain is more severe when walking up and down stairs, especially when going downstairs. As the disease progresses, when the cartilage becomes fibrotic and the synovium becomes inflamed, the uneven surface of the patella may cause the knee joint to suddenly become unable to flex or extend (i.e., locking symptom). If inflammatory reactions such as joint effusion occur, the knee joint will become swollen and painful. In the later stages of the disease, osteoarthritis will develop.

2 Patellar instability

Patellar instability is a common cause of anterior knee pain and one of the important causes of patellofemoral joint degeneration, patellar cartilage softening or patellofemoral osteoarthritis. It includes patellar displacement, patellar tilt, patellar subluxation, patellar high position or patellar dislocation.

1. Factors affecting patellar stability

The factors that cause patellofemoral joint instability can be summarized into four categories:

(1) Abnormalities of the quadriceps femoris and its expansion part: including atrophy or hypoplasia of the vastus medialis muscle, relaxation, rupture or tear of the medial supporting ligament, tension of the lateral supporting ligament and high patella.

(ii) Abnormal knee joint force alignment: including increased Q angle and knee inward. Valgus and recurvature of the knee.

(iii) Abnormal patella shape: such as split patella (patella bipartite) and heteromorphic patella (types III and IV).

(iv) Hypoplasia, secondary deformation of the femoral condyle, or abnormal shape of the lateral femoral condyle.

The common feature of the above changes is that the normal relationship between the patellar joint is lost, resulting in abnormal movement trajectory of the patella and placing the patella in an unstable state.

2. Clinical manifestations and diagnosis

The clinical manifestations of patellar instability lack characteristic features. Many subjective symptoms are very similar to other knee diseases, while there are few unique objective signs. Therefore, the diagnosis requires a comprehensive analysis of the medical history and physical examination, and relies on imaging and auxiliary examinations to make a judgment.

1. Symptoms

1. Pain: It is the most common symptom, and its location is mostly on the anterior medial side of the knee. The pain may be aggravated by excessive activity, especially when going up and down stairs, climbing high, or doing flexion and extension activities for a long time.

2. "Soft legs": When walking with weight, the knee joints feel momentarily weak and unstable. This is often due to weakness of the quadriceps muscles or due to a subluxated patella sliding out of the intercondylar groove.

3 Pseudo-incarceration is a momentary, involuntary restriction of the knee during extension. Clinically, it is often necessary to distinguish it from true incarceration caused by locking or loose bodies due to meniscus tear or displacement.

2. Physical signs

1 Quadriceps atrophy: It is a common sign of knee joint diseases. It is more obvious when there is dysfunction of the knee extensor mechanism, especially the vastus medialis muscle.

2 Swelling: In severe cases of patellar instability, quadriceps muscle weakness leads to synovitis, joint swelling and a positive floating patella test.

3 Patella "strabismus, genu valgum or high patella, increased femoral anteversion, tibial external rotation and other knee deformities, inward tilt of the patella caused by incorrect force line are common causes of patellar instability.

4 Trajectory test: The patient sits on the bedside with both legs hanging down and the knees flexed 90 degrees. The knee joint is slowly straightened and the trajectory of the patella is observed to see if it is a straight line. If there is outward sliding, it is positive and is a specific sign of patellar instability.

5. Tenderness: mostly distributed at the inner edge of the patella and the medial retinaculum. When the examiner presses the patient's patella with the palm and performs flexion and extension tests, pain under the patella can be induced. Clinically, the tender point is sometimes inconsistent with the patient's chief complaint of pain.

6 Crunching sound: With the knee extended, compress the patella and move it up, down, left and right. You can feel or hear a crushing sound behind the patella, accompanied by soreness. There may be a feeling of friction or a crushing sound during active flexion and extension activities.

7 Fear sign: When the knee is slightly flexed, the examiner pushes the patella outward to induce subluxation or dislocation, which causes fear, anxiety and pain in the patient, and the pain is aggravated when the knee is flexed. Fear signs are also specific signs of patellar instability.

8 Joint laxity is divided into three degrees according to the degree of lateral movement of the patella. I: The center of the patella is on the inside or axis of the lower limb; II: The center of the patella is on the outside of the axis; III: The inner edge of the patella crosses the axis of the lower limb.

9 Abnormal Q angle: The Q angle is an indicator to measure the patellar force line. Femoral internal rotation and tibial external rotation can increase the Q angle. Causes the patella to tilt.