The interphalangeal joints are all hinge joints, or joints that involve the articulation of only two bones and that only move in a single plane. The interphalangeal joints, like other hinge joints in the body, are synovial, which means they are connected by cartilage and an inner synovial membrane.
The interphalangeal joints are the joints that move the fingers. They are represented on the surface of the body by the knuckles. They are small-scale versions of the synovial hinge joints of the elbows and knees. All these joints contain synovial fluid and are reinforced by ligaments and caps of fibrous tissue over each bone.