What is kneecap dislocation?
Kneecap dislocation, also known as patellar dislocation, occurs when the kneecap (patella) moves out of its original position. In the process, the connective tissues that hold the patella bone in place may also stretch and tear. We will focus on acquired patella dislocations that happen due to injuries. Some patients may also be born with patella dislocations (congenital).
How does the injury occur?
Most cases of acquired patella dislocations are caused by injury, such as,
- Twisting injury to the knee during sport – indirect injury
- Direct force pushing the patella out of position – such as during a fall
Patella dislocations often occur in dancers and athletes. It is more common in ladies than in men, and there might be underlying anatomical factors that may predispose a person to get dislocated patellas.
- Miserable malalignment syndrome
- Occurs when the femur and/or tibia rotate and develop in such a way that the tibia or femur is rotated relative to the other bone. This can predispose to dislocations of the patella.
- Trochlear or patella hypoplasia (abnormal shape)
- The trochlea is a groove on the end of the femur, where the kneecap sits
- When a person has a flat or dome-shaped trochlea, this causes the kneecap to be unstable, and thus it can be easily dislocated when the knee is bent
- Trochlea hypoplasia is often accompanied by patella hypoplasia.
Symptoms of a dislocated kneecap include,
- A sudden painful popping sound in the knee accompanies the knee injury
- Pain, usually at the front of the knee
- Stiffness or swelling of the knee
- Locking sensation in the knee – inability to straighten or bend the knee
What are the complications of kneecap dislocation?
Kneecap dislocations may pop back into place by itself. However, there are some complications that can arise from a dislocated kneecap,
Patellar instability and recurrent dislocations – in certain patients, especially those with predisposing factors, patella dislocations can happen again. These patients frequently have developed chronic patella instability, where the patella is unstable and comes out with the slightest provocation.
- Osteochondral fractures may occur during the initial dislocation or during subsequent re-dislocations. An osteochondral fracture refers to an injury to the cartilage of the joint, where a piece of the cartilage, with its underlying bone, is broken off. These injuries frequently require surgical treatment and can lead to knee osteoarthritis if left untreated.
- Knee osteoarthritis refers to the chronic loss of joint cartilage over the joint surfaces in the knee. It can arise due to patella instability damage, especially after recurrent dislocations.
How is kneecap dislocation diagnosed?
Your doctor will conduct a medical interview and examination of the knee. Based on the findings, he or she may recommend further imaging tests, which usually includes plain radiographs (X-rays) of the knee. MRI scans and CT scans may also be requested, especially if the injury is recurrent or chronic.
How are kneecap dislocations treated?
- Non-surgical treatment is the mainstay of most patients with single dislocations. This includes initial placement in a plaster half-cast or cast, which is removed after 2 to 3 weeks. This is followed by a course of knee physiotherapy.
- Recovery in this case is usually supported with the use of medications for pain relief
- Patients may also be required to wear a knee brace for up to 2 months following the injury
- Surgical treatment is reserved for patients with a high risk of redislocation, or who have already had multiple episodes of dislocations.
- Depending on the chronicity (how long) of the injury, surgery can range from repair of the restraining patella ligaments, to reconstruction and reshaping options for the trochlea.
- Similarly, most patients after surgery may be placed on a half-cast or cast for a few weeks, and may then be transitioned to a knee brace
- Most patients undergoing surgery will also be required to undergo a course of rehabilitation designed to hasten recovery and improve knee function.
What is the rehabilitation and recovery process like?
Most patients will make a full recovery if the dislocation or surgery were uncomplicated, in 6 weeks. Return to full sporting activities may sometimes take up to 3 or 4 months.
For assessment of your condition, please book an appointment with Dr. Yong Ren.