What Is Knee Instability?

Patella instability is more common in young women. It is a common cause of forearm knee pain. It is a common disease of patellofemoral joints. Advances in biomechanics and imaging technology, as well as the diversification of clinical detection methods, have gradually led to the realization that the degenerative changes of the patellofemoral joint are mostly caused by the instability of the patellar joint caused by the poor fit of the patellofemoral joint or the improper line of the patella. Metatarsal displacement, metatarsal tilt, metatarsal elevation, metatarsal dislocation, etc.

Basic Information

Visiting department: orthopedics
Multiple groups: Young women

Common causes: Infection by droplets, atrophy or dysplasia of medial femoral muscle, knee flexion, valgus and knee flexion, etc.
Common symptoms: Pain, "soft leg, pseudo incarceration"

Causes of Patella Instability

At present, the patella instability is divided into three types: patella subluxation, patella tilt, and a combination of the two. The causes of patella instability actually include abnormalities in every structure of the anterior knee area, and are divided into four categories:

1. Abnormality of the quadriceps and its expansion

These include atrophy or dysplasia of the medial femoral muscle, relaxation, rupture, or tear of the medial support ligament, tension of the lateral support ligament, and high patella.

2. Knee joint line of force is abnormal

These include increased Q angles, and knee flexion, eversion, and knee flexion.

3. Patella shape abnormal

Such as split sacrum, shaped sacrum (type III, IV).

4. Congenital factors

Mainly refers to femoral condyle dysplasia, secondary deformation or abnormal femoral condyle shape.

The common feature of all these changes is that the patellofemoral joint loses its normal structure, resulting in abnormal valgus stress acting on the patella, or abnormal trajectory of the patella, leaving the patella in an unstable state.

Clinical manifestations of patellar instability

Symptoms

(1) Pain is the most common main symptom, usually its nature is not constant, but its location is in the anterior knee area, more common in the anterior medial area of the knee, showing persistent dull pain. Pain can be aggravated by too much activity, especially when going up and down, ascending or prolonged flexion and extension.

(2) Playing "soft legs" means that when walking with a load, the knee joint appears weak and unstable, and sometimes the patient may fall. This phenomenon is usually caused by weakness of the quadriceps muscle, or by the subluxated metatarsal slipping out of the intercondylar fossa.

(3) Pseudo-incarceration refers to the transient non-autonomous restriction disorder that occurs when the knee is stretched. This phenomenon often occurs when the weighted knee joint is flexed to extension, and the subluxated metatarsal slips into the trochlear groove. Clinically, it is often necessary to have true incarceration caused by a twist or free body caused by a torn or displaced meniscus. Phase identification.

2. Signs

(1) Quadriceps atrophy is a common sign of knee joint disorders. It is more obvious when the extensor device has dysfunction, and the medial femoral muscle is the most important.

(2) Swelling In severe cases of patella instability, weakness of the quadriceps femoris leads to synovitis, swelling of the joints, and a positive floater test.

(3) Metatarsal "strabismus" includes knee valgus, high metatarsal height, increased femoral anteversion angle, excessive tibial external rotation, and knee deformities and improper lines of force. In order to maintain normal gait, the metatarsal tilts inward. Is a common cause of patella instability.

(4) Trajectory test The patient sits beside the bed, his lower legs are sagging, and the knee joint is flexed 90 °, so that the knee joint is slowly straightened, and whether the patella motion trajectory is straight. If it slides outward, it is positive, which is a specific sign of metatarsal instability.

(5) Tenderness is mostly distributed at the inner edge of the sacrum and the medial support band. When the examiner's palm compresses the patient's metatarsal bone and conducts extension and flexion tests, sub-condylar pain can be induced, and the clinical tenderness point is sometimes inconsistent with the pain site complained by the patient.

(6) Rolling sound When the knee joint is in an upright position, press the sacrum and move it up, down, left, and right. You can feel or hear a rolling sound under the sacrum, accompanied by soreness. The rolling sound can also be felt or heard when the knee joint is actively stretched and flexed.

(7) Phobia When the knee joint is flexed at 30 °, the examiner moves his patella outward to induce subluxation or dislocation, and the patient develops fear and pain, which causes knee flexion and aggravates pain. Phobia is also a specific sign of patellar instability.

(8) Increased metatarsal displacement or joint relaxation Normal human knees have a range of passive metatarsal movements that do not exceed 1/2 of their own width in the extended position, and a smaller metatarsal metastasis when knees are bent at 30 °. If the joint is loose, it can be divided into 3 degrees according to the extent to which the sacrum can move laterally: The center of the sacrum is inside or on the axis of the lower limb; The center of the sacrum is outside the axis; The inner edge of the sacrum crosses the axis of the lower limb.

(9) Abnormal Q angle Q angle is an important index to measure the zygomatic line of force. Internal rotation of the femur and external rotation of the tibia can increase the Q angle and cause the patella to tilt. Normal values are 8 ° 10 ° for men and 10 ° 20 ° for women, and dislocation tends to be greater than this range.

Patella instability test

1. X-ray inspection

It is a commonly used method for diagnosing patella instability, which usually includes the knee, orthopedic, lateral, and patellofemoral axis images. The knee joint orthotopic radiograph is of little value in judging whether the patellofemoral joint arrangement is normal. The lateral radiograph is the best photograph to evaluate the vertical position of the patella. It is used to judge the high patella. The patella axial radiograph is considered to evaluate the patellofemoral joint arrangement effect. With the highest price-to-price method, tilting and subluxation of the patella can be observed. Using the metatarsal displacement indexing method on the metatarsal axial film can not only reflect the metatarsal displacement, but also accurately determine the extent of the metatarsal displacement. It can also be used as the basis for diagnosis and treatment of metatarsal displacement.

2. Arthroscopy

The positional relationship between the patella and the femur, the trajectory of the patella, and the extent, extent, and location of cartilage damage to the patella and femoral joint can be directly observed under the microscope. At the same time, the release of the lateral sacral support band can also help to choose an appropriate surgical method. It is important to determine whether there are other intra-articular disorders such as synovitis, exfoliative chondritis, and free body, etc., and the corresponding treatment can be done while clarifying the lesion. Jackson classified articular cartilage into three types based on the degree of arthroscopic changes:

(1) Type I patellar cartilage surface has localized softening.

(2) Type II metatarsal cartilage surface is cracked and invaded, while femoral condyle articular surface is normal.

(3) Type III In addition to type II changes, the cartilage surface of the femoral and iliac joints also changed.

3.CT or magnetic resonance (MRI) examination

CT or MRI technology is used to straighten the knee joint to relax the quadriceps. A cross-sectional scan of the middle part of the sacrum joint is provided. The image is clear, repeatable, and easy to measure and calculate. It is a powerful diagnostic method for sacral instability.

4. Ultrasound inspection

Ultrasonography measures the cartilage femoral groove angle of the femoral condyle. In the morbid state, the angle is 154 ° ~ 195 °, exceeding the normal 135 ° ~ 153 °. This is a morphological basis for the easy lateral dislocation of the patella. Measurement of this angle can clearly determine the presence of patella instability.

Diagnosis of Patella Instability

Based on medical history and clinical manifestations, X-ray examination and X-ray measurement, especially arthroscopy, CT and MRI examinations can establish a clinical diagnosis.

Patella instability complications

Dislocation of the patella is the most common complication of patella instability.

Treatment of Patella Instability

Non-surgical treatment

(1) Restricting activities Restricting certain activities in patients' daily lives, such as climbing up and climbing, can reduce the load of the patellofemoral joint and reduce the wear of the patellofemoral joint, especially when it is understood that an activity has a significant relationship with the worsening of symptoms At the same time, by limiting this activity, the purpose of improving symptoms can be achieved.

(2) Quadriceps exercises Subacute or chronic cases are often accompanied by significant quadriceps atrophy and weakened muscle strength, especially the weakening of the medial femoral muscle of the oblique head muscles, which can further aggravate the knee joint instability and make the The joints are swollen and the symptoms are aggravated, so quadriceps exercises should be strengthened to improve the muscle strength ratio of the quadriceps to the hamstrings.

(3) Braces treatment The sacrum branch has the effect of limiting and stabilizing the sacrum. It is used in acute patients or when participating in a certain sport or activity. Long-term wearing can make patients feel local discomfort and easily cause quadriceps atrophy.

(4) Drug treatment Non-steroidal anti-inflammatory drugs can reduce osteoarthritis symptoms of patellofemoral joints.

2. Surgical treatment

After appropriate non-surgical treatment for at least six months, the pain in the anterior iliac region and the symptoms of beating the soft leg repeatedly occur. Multiple examinations have shown that its symptoms are related to abnormal patellofemoral joint structure or malaric line of force, and surgery can be considered. There are several surgical methods: loosen the abnormal lateral restraint tissue; provide a balanced medial media tissue; change the quadriceps-patella-tibia force line; a combination of the above three. Among them, the loosening of lateral tissue is the most commonly used method, and it is also the basic step of other methods. Different methods should be used individually or in combination according to different ages, instability levels, and different pathological factors. The core purpose of the operation is to improve the patella force line, restore the normal fit of the patellofemoral joint, and reconstruct the knee extension device.