A 32 year old man presents to the emergency department with anterior knee pain. He was playing 5 a side football the previous evening and went to kick the ball. As he did this he felt a sudden pain in his anterior knee and was unable to continue the game.

He is previously fit and well.

He can weight bear and just about walk, but with difficulty. He localises pain to the anterior knee below the patella.

On examination he has no knee effusion. There is no bony tenderness and there is a full range of passive movement. His collateral and cruciate ligaments are intact and there is no meniscal tenderness.

However, he is unable to straight leg raise against gravity, but can if gravity is excluded. He is limited in this by severe pain over the patella tendon.

Plain X-ray is normal.