The end of a bone is called the epiphysis. Every long bone in your body, from your thighbone to the small bones in your fingers, has two epiphyses: one at each end. The epiphysis is wider and rounder than the rest of the bone, forming the knobby shape you can sometimes feel at your knees, elbows, and knuckles.
Parts of a Long Bone
A long bone has three main regions. The long, tubular middle section is the diaphysis, or shaft. The wider section at each end is the epiphysis. Between them sits the metaphysis, a narrow transition zone that plays a critical role during childhood growth.
Each end of the bone is labeled based on its position. The epiphysis closest to the center of your body is the proximal epiphysis, while the one farther away is the distal epiphysis. Your thighbone, for example, has a proximal epiphysis at the hip and a distal epiphysis at the knee.
What’s Inside the Epiphysis
The inside of the epiphysis is filled with spongy bone, also called cancellous bone. Unlike the dense, hard bone that makes up the shaft, spongy bone is lighter and has a lattice-like structure of thin plates and bars called trabeculae. The small, irregular spaces between these plates contain red bone marrow, the tissue responsible for producing red blood cells, white blood cells, and platelets. This is one reason bone ends are so important: they’re active sites of blood cell production throughout your life.
Articular Cartilage at the Surface
Where the epiphysis meets another bone at a joint, its surface is coated with a thin layer of hyaline cartilage called articular cartilage. This cartilage is slippery and smooth, allowing bones to glide past each other without grinding together. It reduces friction and absorbs some of the shock that comes with movement, protecting the joint from wear and tear over time.
Articular cartilage doesn’t have its own blood supply, which is why it heals slowly when damaged. Injuries to this cartilage, common in knees and shoulders, can lead to joint pain and eventually arthritis if the protective layer wears thin enough that bone starts contacting bone.
The Growth Plate Connection
In children and teenagers, the metaphysis (the zone between the shaft and the epiphysis) contains the epiphyseal plate, better known as the growth plate. This is a layer of cartilage where new bone tissue is continuously produced, making bones longer as a child grows. The growth plate is the reason kids gain height during childhood and especially during puberty.
Growth plates usually close near the end of puberty. For girls, this typically happens between ages 13 and 15; for boys, between 15 and 17. Once the cartilage fully hardens into solid bone, it becomes a thin line called the epiphyseal line, and no further lengthening is possible. This is why fractures involving the growth plate in children are taken seriously. If the growth plate is damaged before it closes, the bone may not grow to its full length or may grow unevenly.
Epiphysis vs. Apophysis
Not every bony bump at the end of a bone is an epiphysis. Some bones also have projections called apophyses. An apophysis adds to the overall contour and shape of a bone but doesn’t contribute to its lengthening. Instead, apophyses serve mainly as attachment points for muscles and tendons. The bumps you can feel on the outside of your hip or at the back of your heel are examples. In growing children, apophyses have their own cartilage zones that can be injured during sports, often causing pain that mimics a pulled muscle.
Why Bone Ends Are Vulnerable
Because the epiphysis is made of spongy bone rather than the dense compact bone of the shaft, it can be more susceptible to certain types of fractures, particularly compression injuries at joints. In children, fractures at the epiphysis often involve the growth plate. About 75% of growth plate fractures follow a pattern where the break runs horizontally through the plate and exits through the metaphysis, producing a triangular bone fragment visible on X-ray. More severe patterns involve a crack extending through the epiphysis itself and into the joint surface, which requires careful treatment to preserve both growth and joint alignment.
In adults, the epiphysis is a common site for stress fractures in weight-bearing bones and is the region most affected by osteoarthritis as articular cartilage gradually breaks down with age and use.