Epiphysis

A long bone consists of a long central shaft (diaphysis), rounded, broad epiphyses at both ends, and metaphyses between them. The epiphysis is at the very end, where the joint forms.

• Joint surface — The end of the epiphysis is covered with smooth articular cartilage, allowing it to glide smoothly against the neighboring bone.
• Broad surface — It is wider than the shaft, distributing body weight and forces over a broad surface.
• Internal structure — The inside is filled with spongy bone containing many small spaces, surrounded by a thin, hard outer layer of bone. This structure is lightweight yet absorbs impact well.
• Attachment sites for tendons and ligaments — Because this area is near a joint, tendons and ligaments attach nearby to stabilize the joint.

At the knee, the lower epiphysis of the femur and the upper epiphysis of the tibia meet to form the joint. The shoulder, elbow, hip, wrist, and ankle are also places where epiphyses meet.

A child's epiphysis initially consists of cartilage, which gradually turns into bone from the center outward as the child grows. The point within the epiphysis where bone formation begins is called the secondary ossification center. Unlike the primary ossification center, which develops first in the shaft, secondary ossification centers generally appear in sequence after birth. You can read more about this process in Ossification center.

Between the epiphysis and the metaphysis is a layer of cartilage called the growth plate (epiphyseal plate). Height increases as new bone is continually formed at this growth plate. As growth nears completion, the growth plate also turns into bone, joining the epiphysis and the shaft into one continuous structure. The faint line that remains in an adult bone is a remnant of the growth plate.

The timing of the appearance and closure of secondary ossification centers differs from bone to bone. Their appearance on X-rays of the hand and knee can therefore be used to estimate skeletal maturity, or bone age. This is discussed in Bone age.

The epiphysis is especially important in children and adolescents. The area around the epiphysis, where the growth plate is located, is actively growing. Along with tendon attachment sites, it can be a site of discomfort characteristic of the growing years. Related examples include Osgood-Schlatter disease, in which adolescents who do a lot of running or jumping report a painful bump below the knee, and growing pains, in which growing children complain of leg pain.

The growth plate is a relatively weak part of the bone, so when a strong force is applied during the growing years, this area may be injured before the shaft. For this reason, incorporating a variety of movements into exercise during the growing years is said to be better than repeatedly practicing only one sport. You can read more in Overuse injuries in youth sports and Finger growth plate stress injury in adolescent climbers.

• If a child keeps complaining of pain specifically near a joint after exercise, let them rest rather than having them push through it or brushing it aside. Joint pain during the growing years is not viewed in the same way as joint pain in adults.
• During the growing years, allow plenty of rest and a variety of movement. Repeatedly practicing only one sport for long periods places cumulative strain on the same area.
• Nutrition and sleep also support bone growth. Growth hormone is known to be released in large amounts during sleep.
• By adulthood, the growth plates have closed, so the epiphyses no longer grow separately. Instead, maintaining the condition of the articular cartilage and the underlying bone becomes important.