A Boutonniere deformity is caused by a change in the balance of muscles/tendons in the finger, often from an original trauma that has not been appropriately treated in the past.
Often a trauma causing the tendon along the back of the finger to tear then causes the middle joint to be unable to straighten. Without treatment, this stretching over the middle joint causes the tendons at the end joint to over-work, causing the tip of the finger to hyperextend. Depending on the original injury and time since injury, treatment can differ.
If you are experiencing any of these symptoms, book an appointment.