The ulna is one of two long bones in your forearm, running from the elbow to the wrist along the inner (pinky) side of your arm. It’s the bone you feel when you rest your forearm on a table, and it plays a central role in bending your elbow, stabilizing your wrist, and allowing your hand to rotate.
Where the Ulna Sits in Your Arm
Your forearm contains two bones that run side by side: the ulna and the radius. The ulna sits on the medial side, which is the inner edge closest to your body when your palms face forward. The radius runs parallel on the outer (thumb) side. Of the two, the ulna is larger at the elbow end and tapers as it reaches the wrist, while the radius does the opposite, flaring wider near the wrist.
The easiest way to locate your ulna is to feel the bony point at the back of your elbow. That prominent bump is the olecranon, the very top of the ulna. From there, you can trace a ridge along the back of your forearm all the way down to a small knob near your pinky-side wrist. That knob is the ulnar styloid process, a cone-shaped projection at the bottom of the bone. The styloid process is smaller than the matching one on the radius, which is part of why you can tilt your wrist further toward the pinky side than toward the thumb side.
How the Ulna Connects to Other Bones
The ulna forms joints at both the elbow and the wrist, but its connections at each end are quite different.
At the elbow, the ulna has a deep, C-shaped notch (the trochlear notch) that wraps around a spool-shaped surface on the upper arm bone (humerus). This hinge joint is what lets you bend and straighten your elbow. Just below that notch, a smaller concavity called the radial notch cradles the top of the radius, allowing the radius to spin against the ulna when you rotate your forearm.
At the wrist, something surprising happens: the ulna doesn’t actually touch the small carpal bones of your wrist. Instead, a disc of fibrocartilage sits between the ulna’s head and the carpal bones, acting as a cushion and stabilizer. The ulna connects to the radius at this end through the distal radioulnar joint, held together by ligaments that attach to the styloid process. A shallow groove next to the styloid process houses a tendon that helps extend your wrist.
The Ulna’s Role in Forearm Rotation
When you turn a doorknob or flip your palm up and down, the radius and your hand rotate as a single unit around the ulna. Think of the ulna as a fixed post: the radius swings over and across it, carrying your hand along. Three radioulnar joints (one near the elbow, one along the shaft, and one at the wrist) make this rotation possible.
That said, the ulna isn’t always perfectly still. During everyday movements, your shoulder and upper arm shift, which means the ulna can move too. So the classic textbook description of the radius spinning around a stationary ulna is slightly simplified. In real life, both bones contribute to hand rotation, but the ulna’s main job is to provide a stable axis.
The Ulnar Nerve and “Funny Bone” Sensation
The ulnar nerve, named for the bone it travels alongside, is responsible for the tingling jolt you feel when you hit your “funny bone.” The nerve runs behind the bony bump on the inner side of your elbow (the medial epicondyle) and passes through a narrow space called the cubital tunnel. The tunnel’s floor is formed by ligaments and the elbow joint capsule, while the walls are the medial epicondyle on one side and the olecranon of the ulna on the other.
Because the nerve sits so close to the surface at this spot, with little padding, even a light knock can send electric-like tingling into your ring finger and pinky. Repeated pressure on this area, or prolonged elbow bending, can irritate the nerve over time, a condition known as cubital tunnel syndrome.
Common Ulna Fractures
The ulna can break in several characteristic ways, depending on the force and direction of impact.
A nightstick fracture is an isolated break in the ulna’s shaft, typically caused by a direct blow to the forearm, the kind of impact that happens if you raise your arm to block a strike. It gets its name from the original association with being hit by a baton. Because only the ulna breaks while the radius and joints stay intact, these fractures are often simpler to treat.
A Monteggia fracture is more complex. It involves a break in the upper part of the ulna combined with a dislocation of the radial head at the elbow. These injuries are classified into four types based on which direction the radial head displaces: forward, backward, sideways, or with an additional break in the radius shaft. Monteggia fractures require careful imaging because a subtle radial head dislocation can be easy to miss on initial X-rays. A reliable check involves drawing an imaginary line through the center of the radius on an X-ray. If that line doesn’t pass through the middle of the rounded knob at the bottom of the humerus, dislocation is likely.
Symptoms of any ulna fracture generally include pain at the injury site, visible swelling or deformity, and difficulty moving the forearm. Doctors evaluate the skin, soft tissue, and nerve function around the fracture before ordering X-rays from multiple angles to identify the break and check for associated injuries at the wrist or elbow.
How the Ulna Grows and Matures
Like most long bones, the ulna starts as cartilage in a developing fetus and gradually hardens through ossification. Growth plates near the ends of the bone allow it to lengthen throughout childhood and adolescence. The growth plate at the wrist end of the ulna begins fusing around age 14 to 15 in males and 13 to 14 in females. Full fusion, meaning the growth plate has completely hardened into solid bone, is typically complete by age 18 to 19 in males and 17 to 18 in females.
These timelines matter in two practical ways. First, fractures near a growth plate in children and teens need special attention because damage can disrupt normal bone growth. Second, doctors and forensic specialists sometimes use wrist X-rays to estimate a young person’s skeletal age, since the timing of growth plate fusion follows a predictable pattern.