The patella, commonly known as the kneecap, is a small bone positioned at the front of the knee joint. As you bend and straighten your leg, the patella glides smoothly within a groove on your thigh bone (femur). Sometimes, the patella can shift out of its normal track. When this occurs, it leads to a condition known as patellar instability. This instability can manifest in two ways: a dislocation or a subluxation. Here’s what you should know about both conditions.
By Arete Orthopaedic Centre
Medically Reviewed by Dr Wang Lushun
A patellar dislocation occurs when the kneecap completely moves out of its normal position, most often shifting to the outside of the knee. The force of this displacement frequently damages the soft tissues that stabilise the kneecap. A common associated injury is a tear of the medial patellofemoral ligament (MPFL), an important ligament that prevents the kneecap from shifting outwards.
This significant trauma often results in several immediate and noticeable symptoms:
Patellar subluxation is a partial dislocation where the kneecap temporarily slides out of its groove before spontaneously returning to its normal position. This condition is often linked to issues like ligament laxity, muscle imbalances, or anatomical differences in the shape of the kneecap's groove.
Key symptoms of a patellar subluxation include:
While both patellar dislocation and subluxation involve the kneecap shifting out of its normal position, there are differences to be aware of:
Displacement
A dislocation is a complete displacement of the kneecap, where it fully moves out of its groove. A subluxation, however, is a partial displacement where the kneecap only temporarily slips out before returning to its place.
Cause
Dislocations are often the result of a single, high-impact traumatic event, such as a direct blow or a severe twisting motion. Subluxations are more frequently caused by chronic instability, muscle imbalances, or anatomical factors that make the knee prone to giving way.
Pain and Symptoms
A dislocation typically causes severe pain and often results in a visible deformity of the knee. In contrast, a subluxation is characterised by milder, temporary pain and a sensation of the kneecap "slipping" or the knee "giving way."
Treatment and Recovery
Dislocations may require a medical professional to manually reposition the kneecap, and recovery often involves a longer period of immobilisation. Subluxations, on the other hand, often resolve on their own, but they require a physiotherapy regimen to address the underlying instability and prevent recurrence.
Treatment depends on the severity and frequency of the dislocation. Non-surgical options such as bracing, physiotherapy and muscle strengthening are often effective in restoring stability and function. However, for patients with recurrent or severe dislocations, minimally invasive surgery performed by an orthopaedic surgeon may be recommended to realign and secure the kneecap.
With the right treatment plan, most patients are able to regain confidence in their knee and return to daily activities or sports safely. For more information, please do not hesitate to contact our team.
MBBS (S’pore), MRCS (Edin), MMed (Ortho), FRCS (Ortho) (Edin)
With over 18 years of experience, Dr Wang Lushun is an orthopaedic surgeon who specialises in treating a wide range of sports injuries and musculoskeletal conditions. He has in-depth experience in minimally invasive surgery and advanced robotic surgery. Dr Wang provides orthopaedic care to athletes and everyday individuals throughout their journey to recovery.
