Sudden Knee Pain: 10 Possible Causes

Knee pain is a common ailment that affects people of all ages.[1] It can result from a traumatic injury, such as torn cartilage or ligament damage, degenerative conditions, such as osteoarthritis and gout, or an overuse injury.

What are the Symptoms of Sudden Knee Pain?

The symptoms of sudden knee pain vary, depending on the cause of the pain. The knee often becomes painful, swollen, red, and warm to the touch due to inflammation in the joint. It can also become stiff or difficult to straighten. Weakness or instability and popping or clicking noises may also be present.

Causes of Sudden Knee Pain

There are numerous causes of knee pain, including meniscus tears, fractures, knee bursitis, tendonitis, gout, and arthritis.[2] Anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) injuries and dislocated knee caps are common causes of sudden knee pain.

1. Meniscus tears

The meniscus is the tough cartilage that acts as the knee's shock absorber. It lines the inside of the joint - between the shinbone and the thigh bone. Meniscus tears often arise when the knee is forcibly twisted, such as playing squash. A meniscus injury will result in immediate sharp pain, followed by swelling. It may also cause locking of the knee.

2. Anterior Cruciate Ligament (ACL) injuries

The ACL connects the shin bone to the thigh bone and prevents the shinbone from moving too far forward in the joint. ACL injuries occur with sports that require quick, sudden changes of direction or twisting movements.[3] An audible “pop” may be heard with an ACL tear.

3. Posterior Cruciate Ligament (PCL) injuries

Like the ACL, the PCL is located deep in the knee joint. However, the PCL prevents the shinbone from moving backward on the thighbone. PCL injuries result from a direct blow to the shinbone, which could occur during a rugby tackle or a car accident.

4. Collateral ligament injuries

The collateral ligaments also attach the shinbone to the thigh bone but are located on the outside of the knee joint. As with PCL and ACL ligament injuries, quick, forceful twisting movements or blows to the inside or outside of the knee may damage the ligaments. Tears of the collateral ligaments cause swelling and severe pain.

5. Fractures

Fractures are breaks in the bones, including the shin bone, thigh bone, or knee cap. A tibial plateau fracture is a fracture of the top of the larger shinbone that extends into the joint itself, while distal femur fractures are breaks of the thighbone. Fractures of the knee cap are also common. Fractures often occur due to a fall or traumatic injury and cause severe pain, swelling, and an inability to bear weight on the joint.

6. Tendonitis

Tendons connect the muscles to the bones of the knee joint. Tendonitis is the irritation or inflammation of the tendons and occurs with repetitive movements such as running, cycling, or walking. Patellar tendonitis is the most common tendonitis of the knee. The patellar tendon connects the patella (knee cap) to the shinbone and is an extension of the thigh muscles. Patella tendonitis causes pain at the front of the knee that worsens with bending, squatting, and stair-climbing.

7. Knee Bursitis

Bursae are the fluid-filled sacks that cushion the joint, preventing the tendons from rubbing on the underlying bones. Knee bursitis occurs with repetitive movements such as running, cycling or walking, causing the bursae to become irritated, resulting in pain, swelling, and irritation.

8. Dislocations

Injuries or structural problems can cause a dislocation of the knee. Dislocations occur when the position of the thighbone shifts relative to the shinbone. It can occur with sudden twisting movements when the foot is planted on the ground or due to a direct blow to the knee. Knee dislocations cause severe, intense pain and are a medical emergency.

9. Osteoarthritis

Osteoarthritis (OA) is a degenerative disorder that often affects both knees. It is the wearing down of the cartilage that lines the joints, exposing the underlying bones. When this happens, the bones rub together, causing stiffness, pain, clicking sounds, swelling, and sometimes the development of bone spurs.

10. Gout

Gout is a type of inflammatory arthritis caused by the buildup of uric acid in the body. Gout usually affects the big toe but can also affect the knee. The symptoms of gout include pain, swelling, stiffness, and redness around the joint.

How is Sudden Knee Pain Diagnosed?

Unless there is a severe sudden injury, such as a fracture, dislocation, or torn ligament, most people wait a few days or weeks before visiting a doctor or physiotherapist to see if symptoms subside.

Your doctor or physiotherapist will ask you questions about your medical history and what symptoms you may be experiencing. A detailed physical examination will also be performed. The assessment consists of inspecting the knee for swelling and inflammation. The examiner may also move your knee in different directions to stress the ligaments, tendons, and cartilage to evaluate their integrity.

Further investigation may also be necessary. You may be referred for X-rays, CT scans, ultrasound scans, Magnetic Resonance Imaging (MRI), and even blood tests. The nature of the injury and accompanying symptoms will determine which test will be required.

How is Sudden Knee Pain Treated?

The treatment for sudden knee pain depends on the structure that is damaged. Treatment often involves the use of medications such as non-steroidal anti-inflammatories (NSAIDs) or injections to alleviate the pain and swelling, physiotherapy, and in more severe cases, surgery:

• Fractures are medical emergencies that must be assessed by a healthcare provider. Often a cast or splint will be required to stabilise the fracture. Sometimes surgery may be necessary to relocate the bones, followed by a cast and physiotherapy.

• ACL, PCL, collateral ligament, cartilage tears, and dislocations require immediate medical care. Your doctor may refer you for X-rays, CT scans, or an MRI to assess the extent of the injury. Surgery may be required to repair the structures, and a splint or brace will be used to keep the knee from moving. After that, physiotherapy will be necessary to rehabilitate the joint.

• For conditions such as patellar tendonitis, bursitis, or gout, the key is reducing inflammation and swelling. Treatment involves resting from activities, the application of ice, and the use of non-steroidal anti-inflammatories. Physiotherapy will also help to strengthen the joint and provide pain relief.

• Arthritis is a chronic condition that cannot be cured but can be managed. Treatment involves the use of NSAIDs and physiotherapy. Corticosteroid injections are also effective for reducing pain. A joint replacement may be necessary in severe cases where the cartilage is completely worn down.

Outlook

Many factors can cause sudden knee pain, including overuse, degenerative conditions, and traumatic injuries.

Traumatic injuries such as fractures, cartilage, and ligament tears require immediate medical care. Sometimes surgery may be necessary to repair the damaged structure, followed by physiotherapy for rehabilitation of the joint.

Degenerative conditions such as gout and arthritis respond best to conservative treatment such as rest, ice, non-steroidal anti-inflammatories, and physiotherapy.

Overuse injuries such as patella tendinitis and bursitis require resting from activities, icing the joint, and physiotherapy for pain management and rehabilitation.

Overall, if you experience sudden knee pain that won’t subside or your knee locks up, visit your doctor or physiotherapist, who will examine your knee and determine the best course of treatment.