Symptoms of knee instability

The knee joint is an important joint in the human body. Because people use the knee joints in daily life, the degree of strain on the knee joints is also very large. When this strain accumulates to a certain extent, it will cause diseases such as knee arthritis. The manifestations of these diseases are usually knee instability. So if you suffer from knee instability, what are its specific symptoms? Let me introduce it to you today.

1. Symptoms of patellar instability

(1) Pain: It is the most common symptom. Its nature is usually not constant, but its location is always in the anterior knee area, especially 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 places, or doing flexion and extension activities for a long time.

(2) Giving way: Giving way refers to the momentary weakness and instability of the knee joint when walking with weight, and sometimes the patient may even fall. This phenomenon is often caused by weakness of the quadriceps muscles or by the subluxated patella sliding out of the intercondylar groove.

(3) Pseudolocking: Pseudolocking refers to a momentary involuntary restriction that occurs when the knee is extended. This phenomenon often occurs when the weight-bearing knee joint moves from flexion to extension and the subluxated patella slides into the trochlear groove. Clinically, it is often necessary to distinguish it from true incarceration caused by locking or loose bodies due to meniscus tear or displacement.

2. Signs of patellar instability

(1) Quadriceps atrophy: Quadriceps atrophy is a common symptom 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) Squinting knee: When there are knee deformities and misaligned force lines, such as genu valgum, high patella, increased femoral anteversion, and excessive tibial external rotation, the patella tilts inward in order to maintain a normal gait. This is a common factor of patellar instability.

(4) Track test: The patient sits on the bedside with both legs hanging down and the knees flexed 90°. The knees are then slowly straightened to observe whether the track of the patella 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 of his hand and performs flexion and extension tests, subpatellar pain can be induced. Clinically, the tender point is sometimes inconsistent with the pain site complained by the patient.

(6) Crunching sound : When the knee joint is in extended position, compress the patella and move it up, down, left, or right. You may feel or hear a crunching sound (retropatellar crepitation) under the patella, accompanied by soreness. A crunching sound may also be felt or heard during active flexion and extension of the knee joint.

(7) Fear sign: The patient’s knee joint is in a slightly flexed position. When the examiner pushes the patella outward to induce subluxation or dislocation, the patient will feel fear, anxiety and pain, causing the knee joint to flex, which intensifies the pain (Figure 2). The apprehension sign is also a specific sign of patellar instability.

(8) Increased lateral displacement of the patella or joint laxity: In a normal person, the passive lateral displacement of the patella does not exceed 1/2 of its own width when the knee is in the extended position, and the lateral displacement of the patella is even smaller when the knee is flexed 30°. If the joint is loose, it is divided into 3 degrees according to the degree to which the patella can move outward:

Grade I: The center of the patella is on the medial side or axis of the lower limb.

Grade II: The center of the patella is located outside the axis.

Grade III: The medial edge of the patella crosses the axis of the lower limb (Figure 3).

(9) Abnormal Q angle: The Q angle is an important indicator for measuring the patellar force line. Femoral internal rotation and tibial external rotation can increase the Q angle and cause patellar tilt.

The clinical diagnosis can be established based on medical history, clinical manifestations, x-ray examinations and x-ray measurements, especially arthroscopy, CT and MRI examinations.