An “open wrist” describes a condition in children and adolescents where the bones of the wrist and forearm have not completed their growth. This open state refers to the presence of active growth plates, medically known as physes, in the long bones near the wrist joint. Physes are specialized areas of cartilage that enable the radius and ulna to increase in length. An open wrist is a normal finding in a skeletally immature individual, indicating the child is still growing.
Anatomy and Function of the Physis
The physis, or growth plate, is a layer of hyaline cartilage positioned between the end (epiphysis) and the shaft (metaphysis) of a long bone. This structure is responsible for all longitudinal bone growth. In the wrist, the physes are located at the distal ends of the radius and the ulna.
The growth plate is highly organized into distinct zones of cartilage cells. Cells in the resting zone supply the proliferative zone, where they multiply rapidly and arrange into columns. This multiplication pushes the epiphysis away from the metaphysis, physically lengthening the bone.
Following the proliferative zone is the hypertrophic zone, where cartilage cells enlarge and the surrounding matrix begins to calcify. This region, particularly the zone of provisional calcification, is the weakest part of the structure and is most susceptible to injury. Finally, the calcified cartilage is replaced by bone tissue through endochondral ossification, adding permanent length to the bone shaft.
The Timeline of Growth Plate Closure
The process by which an “open wrist” becomes a “closed wrist” is called skeletal maturity or physeal fusion. During this stage, the production of new cartilage cells stops, and the growth plate is replaced by solid bone tissue. On an X-ray, the distinct dark line of the physis disappears, leaving only a faint physeal scar.
This closure is primarily signaled by hormonal changes during puberty. The timing of fusion is not the same across all bones, but the wrist is frequently examined to estimate a person’s overall skeletal age. The growth plates in the wrist typically close near the end of adolescence, leading to the cessation of longitudinal growth.
In the forearm, the distal ulna physis closes slightly earlier than the distal radius physis. For females, the growth plates in the forearm fuse around 16 to 16.5 years, while for males, this happens around 17 to 17.5 years. This difference reflects the earlier onset of puberty and skeletal maturation in females. Once the physes have fused, the length of the forearm bones can no longer increase.
Clinical Significance in Injury and Treatment
The presence of an open wrist has significant implications for injury because the physis is biomechanically weaker than the surrounding ligaments and mature bone. In a child, a force that might cause a ligament sprain in an adult is more likely to result in a physeal fracture. These fractures account for a substantial percentage of all childhood bone injuries.
Physeal fractures are categorized using the Salter-Harris classification system, which describes the pattern of the fracture line through the growth plate and adjacent bone sections. Type II fractures, involving a break through the physis and into the metaphysis, are the most common type of growth plate injury in children. The higher the number in this classification system, the greater the potential for complications.
The primary concern with a growth plate fracture is the risk of growth arrest, where the injured physis prematurely stops growing. To minimize this risk, treatment strategies for an open wrist are distinct from those for an adult fracture. For diagnosis, healthcare providers may order a comparison X-ray of the uninjured wrist to assess the extent of the damage.
Treatment prioritizes gentle manipulation to realign bone fragments without further damaging the growth cells. If surgery is required, orthopedic surgeons must avoid placing internal hardware, such as screws or plates, across the physis to prevent permanent growth disturbance. Long-term follow-up with X-rays is necessary for up to a year after the injury to monitor for signs of premature closure or abnormal growth.