The radial notch is a shallow, concave depression on the outer side of the ulna, one of the two bones in your forearm. It sits just below the elbow and cradles the edge of the radial head, forming the proximal radioulnar joint, the pivot that lets you rotate your palm face-up and face-down. Despite being only a couple of millimeters deep, this small articular surface plays an outsized role in forearm stability, and damage to it or the structures around it can significantly limit everyday movements like turning a doorknob or using a screwdriver.
Where the Radial Notch Sits and What It Looks Like
If you run a finger along the outside of your elbow, the bony prominence you feel on the pinky side belongs to the ulna. Just below the tip of the elbow, the ulna flares into a region called the coronoid process. The radial notch is carved into the lateral face of that coronoid process, forming a smooth, cartilage-lined pocket that faces outward and slightly forward. The radial head, the disc-shaped top of the radius bone, nestles into this pocket and spins within it every time you rotate your forearm.
A CT-based study of nearly one hundred cadaveric arms measured the notch at roughly 12 mm from top to bottom and about 18 mm from front to back, with a depth at its deepest point of just over 2 mm. Its radius of curvature averaged around 15 mm, making it considerably flatter than a ball-and-socket joint. The notch is also tilted outward by about 33 degrees relative to the transverse plane of the ulna, which helps guide the radial head along a consistent arc during rotation.1PubMed. Computed Tomography Analysis of the Radial Notch of the Ulna
In the neutral position, with the forearm neither fully pronated nor supinated, the radial head sits perpendicular to the notch at its widest diameter. The notch itself is angled about 60 degrees relative to the flexion-extension axis of the elbow, an orientation that lets the joint accommodate both bending and rotating movements without the two bones jamming against each other.2Journal of Shoulder and Elbow Surgery. The anatomy of the proximal radioulnar joint
How the Radial Notch Enables Forearm Rotation
Forearm rotation, the movement doctors call pronation (palm down) and supination (palm up), depends on the radius spinning around the ulna at two points: the proximal radioulnar joint at the elbow and the distal radioulnar joint at the wrist. The radial notch is the ulna’s contribution to the proximal pivot. Because the notch is shallow and smoothly curved, the radial head can glide through a wide rotational arc, typically around 150 to 180 degrees of total forearm rotation in healthy adults.
Kinematic studies using helical axis analysis have confirmed that the forearm’s axis of rotation runs from the radial head at the proximal radioulnar joint down to the ulnar head at the wrist, though the exact path varies somewhat from person to person.3PubMed Central. In-vivo kinematic analysis of forearm rotation using helical axis analysis That variability partly reflects individual differences in the shape and tilt of the radial notch. If the notch is slightly deeper, shallower, or angled differently than average, the axis of rotation shifts accordingly, which usually causes no symptoms but can become clinically relevant after a fracture or when designing an implant.
The Annular Ligament and Joint Stability
The radial notch alone cannot hold the radial head in place. A strong band of fibrous tissue called the annular ligament wraps around the radial head like a collar and attaches to the anterior and posterior edges of the notch, forming a ring that keeps the radius from slipping out of its seat. The front attachment is typically a single solid band, while the rear attachment can be fenestrated, meaning it has small openings or windows in the tissue, a normal variant seen in some individuals.4AJR Am J Roentgenol. Annular ligament of the elbow: MR arthrography appearance with anatomic and histologic correlation
Together, the concavity of the notch and the constraint of the annular ligament create a stable but mobile joint. Lose either component and the radial head can sublux or dislocate. In children, a common injury nicknamed “nursemaid’s elbow” occurs when a sudden pull on the arm causes the annular ligament to slip over the radial head. In adults, annular ligament tears typically accompany fractures of the radial head or the coronoid process, creating a more complex instability pattern that often requires surgical repair.
Injuries That Involve or Affect the Radial Notch
The radial notch is rarely fractured in isolation, but it sits at the crossroads of several important elbow and forearm injury patterns. Understanding its role in each helps explain why seemingly different injuries share overlapping symptoms like restricted rotation and chronic forearm pain.
Monteggia Fractures
A Monteggia fracture combines a break in the proximal ulna with a dislocation of the radial head out of the radial notch. Because the radial head has left its seat, the proximal radioulnar joint is disrupted. Neglected Monteggia fractures, those missed at the time of injury and left untreated, can lead to chronic radial head dislocation, progressive loss of rotation, and secondary arthritis in the elbow.5PubMed Central. Neglected Monteggia fracture: a review In children especially, these injuries are sometimes mistaken for simple forearm fractures, and the radial head dislocation is only discovered years later when the child loses range of motion.
Essex-Lopresti Injuries
An Essex-Lopresti injury is a more devastating pattern. It involves a fracture of the radial head, a tear of the interosseous membrane that connects the radius and ulna along most of their length, and a dislocation at the distal radioulnar joint near the wrist. The result is longitudinal instability of the entire forearm: the radius can migrate upward relative to the ulna because the structures tethering it at both ends and along the middle have all failed.6PubMed Central. Management of the Essex-Lopresti Injury Even though the radial notch itself may be intact, the loss of radial head contact within it destabilizes the proximal joint. Surgeons treating Essex-Lopresti injuries prioritize restoring or replacing the radial head to re-establish that contact, because without it, the mechanical chain of the forearm collapses.
Coronoid and Radial Notch Fractures
Fractures of the coronoid process can extend into the radial notch, especially in complex elbow dislocations sometimes called the “terrible triad” (elbow dislocation plus radial head fracture plus coronoid fracture). A morphometric study found that the radial notch height averaged about 16 mm, similar to the coronoid process height, and showed substantial person-to-person variation, ranging from 11 to 25 mm.7PubMed Central. Morphometrics of the coronoid process and the radial notch of the ulna: implications for fracture assessment That variability matters to surgeons trying to classify coronoid fractures and decide how much bone needs to be fixed versus how much is still intact and supporting the radial head.
Osteoarthritis at the Proximal Radioulnar Joint
When people think of elbow arthritis, they usually picture the hinge between the humerus and ulna. But the proximal radioulnar joint, where the radial notch and radial head meet, develops its own form of wear-and-tear arthritis, and it is more common than many clinicians historically recognized. A CT-based study of patients with elbow osteoarthritis found that osteophytes, bony spurs that build up around a degenerating joint, appeared in the radial notch in about 80 percent of affected elbows. Roughly half showed joint space narrowing at the proximal radioulnar joint, and about a quarter had loose bodies or subchondral cysts. The presence of osteophytes in the radial notch restricted both the flexion-extension arc and the pronation-supination arc of the elbow.8PubMed Central. Osteoarthritis of Proximal Radioulnar Joint: Computed Tomography–Based Assessment and Associations with Clinical Findings
Cartilage wear in the radial notch tends to concentrate in a predictable zone. An anatomical study of cadaveric joints found that cartilage damage clustered in the distal region of the notch, corresponding to the contact area when the elbow is fully extended and the forearm pronated. In that position, the elbow is at its most unstable, and the lateral stabilizing structures can be repeatedly pinched between the radial head and the humerus, a mechanism that over time appears to drive localized cartilage breakdown.9Journal of St. Marianna University. Anatomical Study of the Contact Area and Degenerative Change of the Proximal Radioulnar Joint During Forearm Rotation For anyone whose work or sport involves repeated full-extension, palm-down forearm loading, think of a manual laborer hammering or a tennis player hitting backhands, this wear pattern is worth knowing about.
Congenital Radioulnar Synostosis
In rare cases, the radial notch never fully forms because the radius and ulna fail to separate during fetal development, a condition called congenital radioulnar synostosis. Instead of two distinct bones meeting at a smooth joint, the proximal radius and ulna are fused by a bridge of bone, locking the forearm in a fixed position and eliminating all rotation. Some children are born with the forearm stuck in pronation, others in a neutral or mildly supinated position. A related finding is that posterior dislocation of the radial head and complete radioulnar fusion can occur in the same patient, suggesting these are different expressions of the same developmental glitch in radioulnar differentiation. The same genetic diagnosis has been associated with both presentations in different members of the same family.10PubMed Central. Congenital Radioulnar Synostosis Review: Recommendations and Treatment Outcomes
Children with mild synostosis who are locked near neutral often adapt well and go undiagnosed until a screening X-ray catches the fusion incidentally. Children locked in extreme pronation have more functional difficulty because they cannot supinate at all, making tasks like carrying a bowl of soup or catching a ball genuinely challenging. Surgical treatment typically involves a rotational osteotomy, where the fused bone is cut and the forearm is repositioned at a more functional angle, rather than trying to recreate a joint that never existed.
The Radial Notch in Surgery and Implant Design
Surgeons operating near the proximal radioulnar joint face a practical problem: metal plates or screws placed on the radial head to fix a fracture can impinge against the radial notch when the forearm rotates. This limits both the patient’s recovery and the surgeon’s options for hardware placement. The concept of a “safe zone” describes the arc of the radial head circumference where hardware can sit without entering the notch during pronation or supination. One study of five different plate designs found the average safe zone was about 133 degrees of the radial head’s circumference. Only plates with a specific radial neck design could extend the safe zone by allowing the plate’s edge to pass beyond the lesser sigmoid notch of the ulna during maximum pronation without blocking rotation.11PubMed Central. Is an extension of the safe zone possible without jeopardizing the proximal radioulnar joint when performing a radial head plate osteosynthesis?
This constraint influences implant design more than most people realize. Radial head replacement prostheses, used when the native radial head is too shattered to repair, must match the curvature of the radial notch closely enough to restore smooth rotation but loosely enough to avoid grinding against the notch’s cartilage. If the prosthesis is too large, it overloads the notch and accelerates arthritis there. If it is too small, the forearm becomes unstable. The CT measurements of notch curvature and depth discussed earlier are the kind of data implant engineers rely on to size these devices, and patient-to-patient variability is large enough that a one-size-fits-all approach performs poorly.
Variation Across Individuals
One theme running through the research is just how much the radial notch varies from person to person. The CT study of 98 cadaveric arms reported notch depths ranging from 1.5 mm to 2.7 mm and anteroposterior dimensions spanning 12 mm to 24 mm, meaning the widest notch was double the size of the narrowest.12PubMed. Computed Tomography Analysis of the Radial Notch of the Ulna Similarly, radial notch height ranged from 11 to 25 mm across individuals.13PubMed Central. Morphometrics of the coronoid process and the radial notch of the ulna: implications for fracture assessment
These differences are not just academic trivia. A person with a naturally shallower notch may have slightly less inherent bony constraint on the radial head, making the annular ligament and surrounding soft tissues relatively more important for stability. A person with a deeper notch gets more bony containment but may be more prone to notch-specific osteophyte formation if arthritis develops. When surgeons evaluate imaging after an elbow injury, they have to account for the fact that the opposite, uninjured elbow may look quite different from textbook illustrations, so comparing side to side is more reliable than comparing to a standard template.
Why the Radial Notch Is Easy to Overlook
On standard elbow X-rays, the radial notch is difficult to see clearly because it overlaps with the coronoid process and the radial head in most views. CT scans with three-dimensional reconstruction are far better at revealing its contour, depth, and any fracture lines extending into it. MRI can show cartilage quality and annular ligament integrity but does not image the bony architecture as crisply. This imaging limitation has historically contributed to underdiagnosis of radial notch fractures and proximal radioulnar joint arthritis. As CT scanning has become more routine for complex elbow injuries, clinicians are finding these problems more often, which may partly explain why research attention to this small joint has increased substantially over the past decade.
For patients dealing with unexplained loss of forearm rotation or lateral elbow pain that does not respond to standard treatments for conditions like lateral epicondylitis (tennis elbow), asking about imaging of the proximal radioulnar joint is reasonable. The radial notch and its articulation with the radial head are not always part of the initial diagnostic checklist, but they may be exactly where the problem lives.