close-packed position

The close-packed position in anatomy refers to a specific joint configuration where the articulating surfaces of bones fit together perfectly, maximizing contact. In this position, the joint is functionally converted from a synovial joint (diarthrosis) to a synchondrosis, meaning it becomes more stable and less mobile. This occurs due to the combined action of ligaments and the shape of the articular surfaces, effectively locking the bones together. While this position enhances stability, it also makes the joint more vulnerable to injury from sudden torsional stresses, as seen in sprains. Examples include the wrist when fully dorsiflexed.12