An anterior cruciate ligament injury is the over-stretching or tearing of the anterior cruciate ligament (ACL) in the knee, which is a ligament in the centre of the knee that prevents the shin bone (tibia) from moving forward on the thigh bone (femur). A tear may be partial or complete. Some symptoms may include severe pain and inability to continue activity, rapid swelling, loss of range of motion, a loud ‘pop’ or popping sensation in the knee, or a feeling of instability.

The posterior cruciate ligament (PCL) in the back of the knee helps control posterior movement of the tibia under the femur. PCL tears occur when this stabilizing ligament is stretched beyond its limits, usually due to a high-energy force on the front of the bent knee. As a rule of thumb, it is usually not as disabling as ACL injuries. Symptoms may include pain that worsens over time, swelling and inflammation, a feeling of instability in the knee, stiffness, and difficulty walking.

The medial collateral ligament (MCL) on the inner side of the knee helps stabilize the joint and limit excessive motion. MCL tears occur when this ligament is overstretched or torn, usually due to a blow or sudden twist to the outer knee.

The meniscus is a shock-absorbing cartilage in the middle of your knee. There are two menisci – one on the inside (“medial”) and another on the outside of the knee (“lateral”). The meniscus can be torn in two main ways - traumatic tear or degenerative tear. Symptoms of a meniscus tear includes pain, stiffness, swelling, sensation of your knee giving way, or limited range of motion of the knee.

A patella dislocation occurs when the knee cap pops sideways out of its vertical groove at the knee joint. It's usually caused by force, from a collision, a fall or a bad step. A dislocated patella is painful and will prevent you from walking. Symptoms may include an audible pop, buckling of the knee, intense pain, sudden swelling, kneecap visually out of place, locking and bruising, or more.

A quadriceps tendon tear or strain is an injury to the quadriceps tendon (the tendon that works with the muscles in the front of the leg to straighten the leg). Although quadriceps tears or strains are not common, this injury can make it difficult to participate in day-to-day activities. Symptoms include a noticeable indentation at the top of your kneecap, bruising, tenderness, cramping, bruising, and difficulty walking.

Loose bodies (also known as rice bodies and knee joint mice) are fragments of cartilage or bone that float freely within the synovial fluid component of the knee joint. Loose bodies often cause symptoms such as intermittent locking of the joints, limitation motion of your joints, trouble walking, knee pain, swelling or inflammation, or even feeling like something is moving in your knee.

Jumper's knee, also known as patellar tendonitis, is a condition characterized by inflammation of your patellar tendon. This connects your kneecap (patella) to your shin bone (tibia). Jumper's knee weakens your tendon, and, if untreated, can lead to tears in your tendon. Symptoms of patellar tendinitis includes pain or tenderness around the patellar tendon, swelling, pain when jumping, running, walking, or more.

Pes anserine bursitis is a clinical entity associated with pain at the medial knee and the proximal medial tibial region. A more generic term, pes anserine pain syndrome, has been applied to refer to medial knee pain, which may or may not include inflammation of the bursal sac. Symptoms includes pain slowly developing on the inside of your knee and/or in the center of the shinbone, pain increasing with exercise or climbing stairs, puffiness or tenderness to the touch in this area.

Osteochondritis dissecans (OCD) is a condition that develops in joints, most often in children and adolescents. It occurs when a small segment of bone begins to separate from its surrounding region due to a lack of blood supply. Symptoms include pain and swelling in the affected joint, pain that worsens with motion or activity, locking and “catching” of the affected joint, feeling like your knee is giving way, and changes in the range of motion in the joint.