Common
Arthritis
Osteo (wear and tear), inflammatory (such as rheumatoid) or post-traumatic. Cartilage wear is progressive but can respond to a variety of treatment options.
Meniscal tear
Cartilage tears are usually the result of a twisting or deep bending injury. If there are symptoms for longer than 3 months an arthroscopy (keyhole surgery) may be needed.
Acute
Fractures
After significant trauma, may require surgical fixation.
Dislocations
Most commonly involving the patella (knee cap).
Ligament sprains or ruptures
Partial and total tears can lead to knee instability.
Meniscal tear
In younger people often an acute onset after twisting or deep bending injury.
Tendon ruptures
Major quadriceps or patella tendon ruptures require surgical repair.
Acute knee swelling
Acute inflammation can be caused by a variety of conditions.
Bursitis
Acute inflammation or infection of bursa between joint and skin.
Other
Tendinopathy
Chronic tendon condition requiring specific exercises to improve.
Patello-femoral overload syndrome
Often related to abnormal tracking of the knee cap with several possible causes.
Impingement
Hoffa's fat pad impingement causing pain near the front of the knee.
Plica syndrome
A plica is a normal fold of the inner knee lining but can get thickened causing painful rubbing over the thigh bone.
Ilio-tibial band friction syndrome
Overuse condition causing pain on the outside of the knee.
Baker's or popliteal cyst
A Baker's cyst is a swelling at the back of the knee related to arthritis. A politeal cyst occurs roughly in the same area but is related to tendons.
Osgood-Schlatter disease
Causes a painful lump in adolescents related to bone growth. Pain can persist into adulthood.