Finger spines are used to help protect your fingers whilst wearing goalkeeper gloves, especially when stopping shots.
The power that some shots are fired at goalkeepers makes finger spines a necessity for the safety of the keeper's hand - if the shot strikes the hand wrong it could cause serious injury, even with the glove on, which could endanger the keeper's career.
Finger spines slot into the finger, usually in special pouches that are built into the glove to keep them in place and prevent them from moving around or causing irritation when the glove is being worn. These are normally easy to remove and re-insert so you can regularly inspect the finger spines to ensure they are still in good condition.
Finger spines are usually made from durable composite plastic which will provide rigidity to support the fingers but also be flexible enough to allow for the movement of the hand when catching and throwing the ball. Usually they only flex one way, to allow for a fist to be formed - but they won't allow for hyperextension of the finger joints.
Each finger spine is sized to fit an appropriate finger and thumb and each one should be used to fit the correct finger for optimal performance. Whilst many gloves come with finger spines in them, these are an ideal replacement if your finger spines break during a game or as a result of an incident, or they just wear down or become brittle over time.