Why does the patella dislocate laterally

The trochlear groove and patella may have abnormal morphology that predisposes to patellar dislocation. The knee is a complex synovial joint that can be affected by a range of pathologies:.

Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys. Updating… Please wait. Unable to process the form. Check for errors and try again. Thank you for updating your details. Log In. Sign Up. Become a Gold Supporter and see no ads. Log in Sign up. Articles Cases Courses Quiz. About Recent Edits Go ad-free. Edit article. Treatment is nonoperative with bracing for first time dislocation without bony avulsion or presence of articular loose bodies.

Operative management is indicated for chronic and recurrent patellar instability. Risk factors. Passive stability. Dynamic stability. Can be classified into the following. Patellar instability classification. Acute traumatic. Chronic patholaxity. Physical exam. J sign. AP views. Blumensaat's line should extend to inferior pole of the patella at 30 degrees of knee flexion. Insall-Salvati method. Blackburne-Peel method.

Caton Deschamps method. Plateau-patella angle. Almost all dislocations are lateral in nature and are most easily reduced by simple extension of the knee, with medial pressure on the patella - analgesia may be required. Some patients will present with spontaneous reduction having occurred pre-hospital. They may relate a history of resolved knee deformity following a twisting injury. Examination findings may be of knee effusion with tenderness medial to the patella.

Examination of the other knee may show a mobile patella or hypermobility. The same investigation and follow up advice applies to these patients. When the patella dislocates it may damage the articular cartilage resulting in chondral scuffing or an osteochondral fracture from either the lateral femoral condyle or patella itself. Patients who sustain a traumatic dislocation are at risk of developing recurrent patellar instability and therefore require knee rehabilitation which includes proprioceptive exercises and VMO strengthening 2.

How are they classified Acute first time dislocation a. With unstable osteochondral fracture b. Without unstable osteochondral fracture Recurrent dislocation a. With identifiable anatomical abnormality b. Without identifiable anatomical abnormality 3. How common are they and how do they occur? It is the second most common cause of a knee haemarthrosis second only to ACL injury The patella usually dislocates laterally when the knee is subjected to a valgus force with the foot firmly planted and the femur internally rotates.

What do they look like - clinically? What radiological investigations should be ordered? It is best to ensure that the patellar is reduced before taking radiographs as the films are not so much for checking the patellar position but for identifying osteochondral fragments With appropriate analgesia AP, lateral, and skyline images should be obtained.

What do they look like on X-ray? Figure 6: Large osteochondral fragment anterior aspect of knee on MRI 7. When is operative treatment required? So far the signs are incredible. After a dislocated kneecap, the medial patellofemoral ligament may become torn.

This is the ligament that secures the kneecap to the inside medial of the knee. Once it is torn it may not heal with the same level of tension as before. This can lead to recurrent dislocation of the kneecap.

You should never try and relocate a dislocated kneecap by yourself as you may cause further damage. A dislocated kneecap can sometimes correct itself. However you should always seek urgent medical help even if it has gone back into position as a dislocation can cause damage to surrounding ligaments and tendons.

If you are unable to walk you should call an ambulance. You will be treated as a medical emergency. Your consultant will manipulate your kneecap back into place normally under anaesthetic. Once the kneecap is back in position you may be given an X-ray to check that the bones are correctly aligned and to rule out further damage. This may need to be performed under local or general anaesthetic. Once the kneecap has been put back into place, you will need to rest the knee and use ice, compression and elevation to control swelling.

You will normally need crutches or a knee brace while your knee is healing. Patients are generally offered physiotherapy to help them to strengthen the muscles and regain movement in the knee.

If you experience recurrent kneecap dislocation, you may be offered surgery to tighten the muscles or reconstruct the inside ligaments. In rare circumstances you may need to have the bone cut and repositioned.