Knee Dislocation

Deformation of the knee joint

What is knee dislocation?

Knee dislocation is a potentially dangerous injury that happens when the bones of the knee are wrenched out of their natural position. This occurs when a significant force is exerted on the knee. The bones that make up the knee joint, including the femur (thigh bone) and tibia (shin bone) can become entirely separated from one another during a knee dislocation.

This can severely harm the ligaments, tendons, and other soft structures that support the knee joint. Knee dislocations are relatively rare but can potentially be very serious and have long-lasting effects on the knee joint that are detrimental, if not treated promptly and properly. 

knee dislocation
The femur and tibia can completely detach from each other.

A knee dislocation is not the same as an acute patellar dislocation, dislocated kneecap, or an unstable kneecap/subluxing patella. Knee dislocation can be a devastating injury by comparison and would require immediate medical intervention. 

Knee dislocations are categorised into different levels based on the degree of displacement of the bones and the severity of the related soft tissue injuries. 

There are several classification systems, but one commonly used method is the Schenck classification:

  • Grade I: partial dislocation with no damage to the ligaments or other soft tissues supporting the knee joint.
  • Grade II: partial dislocation with damage to one or more ligaments or soft tissues, but without complete disruption of the joint.
  • Grade III: complete dislocation with damage to multiple ligaments and soft tissues, but without any significant bone fractures or vascular injuries.
  • Grade IV: complete dislocation with damage to multiple ligaments and soft tissues, as well as associated bone fractures or vascular injuries.

Additionally, knee dislocations can also be classified based on the direction of the dislocation (anterior, posterior, lateral, or medial) and the presence of associated injuries, such as nerve or blood vessel damage. The severity of the dislocation will determine the course of treatment, with more severe cases often requiring surgery and a longer recovery time.

What causes knee dislocation?

Knee dislocations are often caused by a significant force or trauma that causes an excessive amount of strain on the knee joint. 

The following are some of the most prevalent causes of knee dislocations:

  • High-energy traumatic injuries such as falls from significant heights and traffic collisions
  • Direct impact or trauma to the knee, stemming from sports-related activities
  • Existing knee injuries such as subluxated patella
  • Low-energy mechanisms such as obesity
knee dislocation obese
Individuals with obesity can suffer from knee dislocation due to excessive stress on their joints.

What are the symptoms of knee dislocation?

Symptoms of knee dislocations can differ depending on the severity of the injury, but may include:

  • Acute pain in the knee
  • Swelling and bruising
  • Deformity or misalignment of the knee joint
  • Inability to bear weight on the affected leg
  • Stiffness or limited range of motion
  • Numbness or tingling in the foot or lower leg
  • Weakness or muscle spasms in the affected leg
  • Visible injuries which may include open wounds and exposed bone
deformed knee
Deformation of the knee joint is one of the most obvious symptoms of knee dislocation.
If you notice any of the symptoms, make an appointment with an orthopaedic specialist to get an accurate diagnosis and treatment.

Dr Puah KL is our Senior Consultant Orthopaedic Surgeon at Artisan Sports & Orthopaedic Surgery. He used to serve the sports service of Singapore General Hospital - the highest volume trauma centre for orthopaedics in Singapore.

Is knee dislocation painful?

Yes, knee dislocation is a very painful injury.

The force necessary to dislocate the knee joint can cause collateral damage to the surrounding ligaments, muscles, and other soft tissues of the knee, resulting in considerable pain and suffering. Furthermore, joint displacement can put pressure on nearby nerves, which can contribute to further pain or numbness.

Who is at risk of knee dislocation in Singapore?

Knee dislocations are generally uncommon and can happen to anybody, but there are several factors that may enhance the likelihood of this sort of injury. 

These risk factors include:

  • Gender: women are more prone to unstable kneecaps potentially attributed to their wider hips and increased Q angle (the angle between the thigh bone and the kneecap).
  • Age: knee dislocation is common among 10-17 year olds, the likelihood attributed to rough-and-tumble play. 
  • Athletes: unstable kneecap injuries may occur among athletes of contact sports such as football and basketball.  
  • Medical history: individuals with pre-existing knee conditions such as previous patellar subluxation or hypermobility, have a higher risk of being susceptible to knee dislocation. Additionally, patients with obesity too, are more prone to knee dislocations.
Q angle
Women are more prone to knee dislocation due to a wider Q angle, the angle between the thigh bone and the kneecap.

How is knee dislocation diagnosed?

Upon the incidence of knee dislocation, you would usually be directed to the emergency department to have your knee manually repositioned. 

Following that procedure, the tests below would be required to further access the injuries that have occurred: 

  • Physical examination and medical history: inform your orthopaedist of the potential activities that may have led to an injury such as trauma, exercise, or sports. Physically the area of injury will be examined and several motion tests will be conducted to review the injury.
  • Imaging tests: magnetic resonance imaging (MRI) would be required to provide a detailed view of the soft tissues in the knee and can help identify any tears or other damage. An x-ray and computed tomography scan (CT-scan) would be conducted to help identify any fractures or bone damage in the knee joint. 
  • Diagnostic arthroscopy: Arthroscopy involves inserting a small camera into the knee joint to visualise the knee’s structure as well as assess the extent of the injury. This is usually done within 2 weeks of surgery.

What are the treatment options for a knee dislocation in Singapore?

Depending on the severity a knee dislocation can be treated by:

  • Immobilisation: the affected knee would be immobilised in a cast or brace to protect it from damage and enable the ligaments to heal.
  • Medications: non-steroidal anti-inflammatory drugs (NSAIDs) and painkillers are commonly prescribed as the first course of treatment to reduce inflammation and manage pain.
  • Crutches: to limit placing weight on the affected knee.
  • Physiotherapy: upon discontinuation of the use of the cast or brace, an active range of motion exercise would be administered via physiotherapy to regain mobility.
  • Arthroscopic surgery: necessary to repair ligament, cartilage, and meniscus damages. In certain cases, blood clot removal would also be required. Additionally, arterial injuries would call for the need for surgical repair. 
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