What physical condition causes Gregory House's chronic leg pain in House M.D.?

Gregory House's chronic leg pain is caused by a quadriceps infarction in House M.D.

House suffers an infarction in the quadriceps muscle of his right leg, meaning that blood flow to muscle tissue was blocked and part of the muscle died. The injury leaves him with lasting pain, an altered gait, and a dependence on a cane. It is a key part of his character rather than a minor background detail.

House initially has the leg treated with a bypass procedure, but he rejects the recommended amputation. After the infarction, he undergoes a medically induced coma and receives treatment that preserves the leg while leaving permanent damage. The resulting pain helps explain his use of Vicodin and his difficult relationship with pain management.

The condition is often loosely described by viewers as a leg injury or a blood clot. Those descriptions miss the specific diagnosis established in the series: the damaged tissue is the quadriceps muscle, not the bone or Achilles tendon.