On the front surface of the knee joint, between the condyles of the femur, there is the patella (“kneecap”). From the inside, the patella is covered with a thick layer of cartilage, which is needed to glide along with the cartilage of the condyles of the femur. Patella improves muscle traction by working as a block. Also, patella acts as a shield covering the joint from injury.
One of the most common injuries of the ligamentous apparatus of the knee joint is dislocation of the patella. Most common is external dislocation of patella. At the same time, it is displaced outwards and snugged against the external condyle of the femur. Most often, patients with this trauma are athletes and people who lead an active lifestyle. Often they have habitual dislocation or, in other words, the usual instability of patella. Other predisposing factors may include congenital malformations of the knee joint.
The most common cause of an external dislocation of the patella is a direct mechanism: internal rotation of the thigh with moderate flexion of the knee joint and fixed foot. Less commonly, dislocation can occur as a result of a direct blow. In this case, rupture of the ligaments holding patella, joint capsule and damage to the cartilage of the knee joint occurs. If the dislocation occurs for the first time, it is called acute or primary. If the patella is constantly dislocated, it is a habitual dislocation.
Patients have the following characteristic symptoms:
– sharp pain in the knee;
– pronounced irregular shape of the knee, its enlargement resulting from the displacement of the patella;
– palpation determines the apparent displacement of the patella, which is sometimes noticeable even with visual inspection;
– complete or partial lack of ability to make any active movements with the affected leg, and any attempts to make movements cause sharp painful sensations;
– swelling of the knee and instability that may occur as a result of spontaneous reduction with incomplete dislocations.
After preliminary examination and palpation, an X-ray examination is often prescribed, as well as diagnostic methods such as magnetic resonance imaging or computed tomography.
X-ray (left) and MRI of the knee joint (right). Patellar dislocation, cartilage damage, and rupture of the internal supportive ligament of the patella are determined.
In recent years, there has been a requirement to perform arthroscopy in each case of a primary external dislocation, even if MRI does not reveal damage to the patella stabilisers, and osteochondral fractures are not visible. Arthroscopy is the most accurate method for diagnosing intraarticular damage to the KJ. Arthroscopic examination allows to accurately diagnose the presence and localisation of osteochondral fractures, the number and size of osteochondral fragments, to determine the presence and nature of ruptures of the medial soft tissue stabilizers of the patella, to verify the degree of subluxation, etc.
Untimely treatment of this injury in most cases can lead to the development of various diseases, such as, for example, arthritis of the knee joint.
Also, incorrectly reduced primary dislocations can cause habitual dislocations, which result in constant pain in the knee joint. Another unpleasant consequence of habitual dislocation is a gradual destruction of the cartilage and ligamentous apparatus of the knee joint, muscle weakness and limited motor function.
Professional treatment for knee injury usually gives excellent results. In this case, patients are returned full mobility of the injured knee joint and disability.
If the dislocation occurred for the first time, the initial conservative treatment is recommended most often, which consists of reducing the dislocation (if this did not happen spontaneously), then fixing knee joint with an orthosis (for up to 4-6 weeks), relieving pain, limiting axial loads. With a relapse of dislocation, identification of a free body inside the joint, a complete rupture of the internal ligaments holding patella, surgical treatment is indicated. There are many methods for stabilising patella (arthroscopic suturing of the medial ligament of the patella by Yamamoto, transposition of the distal attachment of the patellar ligament, open plastic surgery of the medial ligament of the patella, or arthroscopic plastic operation MPFL (medial patellofemoral ligament reconstruction).
Suturing of the medial patellofemoral ligament
Plastic reconstruction of the medial patellofemoral ligament
The choice of the method of operation is selected by the doctor individually after examination, taking into account all the characteristics of a patient, including assessment of dysplasia of the femoral-patellar joint. In acute dislocation of patella, it is preferable to perform arthroscopy of the knee joint with subsequent seaming of damaged internal patellar ligaments. In case of a habitual dislocation, this intervention is futile.
After surgery, the patient is recommended to undergo rehabilitation treatment to develop movements in the knee joint.