An epicondyle is a small bony bump that sits on or just above a condyle, which is the rounded knob at the end of a long bone. Unlike the smooth condyle beneath it, which forms a joint surface with an adjacent bone, the epicondyle’s job is to anchor muscles and ligaments. You have epicondyles at your elbows and your knees, and although they are easy to overlook on an anatomy chart, they play an outsized role in how your limbs generate force and stay stable.
How an Epicondyle Differs From a Condyle
Both condyles and epicondyles live at the ends of long bones, so it is easy to mix them up. A condyle is the larger, smooth, rounded surface that actually forms part of a joint. It is designed to glide against another bone’s surface with minimal friction. An epicondyle, by contrast, is a rougher, smaller projection that sits on or beside the condyle. Its surface is textured because tendons and ligaments attach there; the roughness gives those soft tissues better grip on the bone. In short, the condyle is for articulation with another bone, and the epicondyle is for connecting muscles and ligaments to bone.1ResearchGate. Difference Between Condyle and Epicondyle
You can feel the difference yourself at your elbow. The rounded surface that lets your forearm hinge smoothly is the condyle. The pointy bumps on either side of the elbow that are tender when you press them are the epicondyles. One faces inward (medial epicondyle), one faces outward (lateral epicondyle), and each serves a different group of forearm muscles.
Where Epicondyles Are Found
The most clinically relevant epicondyles are at the elbow and the knee. At the elbow, the bottom end of the humerus (upper arm bone) flares out into two prominent epicondyles. The medial epicondyle is the bump on the inner side of your elbow, and it is the larger and more prominent of the two. If you have ever banged your “funny bone,” you hit this spot: the ulnar nerve runs in a shallow groove right behind it. The lateral epicondyle sits on the outer side. It is smaller and less prominent but no less important functionally.
At the knee, the bottom end of the femur (thigh bone) has its own pair of epicondyles. The medial and lateral femoral epicondyles are bony landmarks on either side of the knee that serve as attachment points for the collateral ligaments that stabilize the joint from side to side. These epicondyles are also critical reference points in orthopedic surgery, a topic we will return to below.
It is worth noting that the word “epicondyle” has been used inconsistently across medicine. An anatomist may describe the femoral epicondyle as a broader region projecting from the condyle, while an orthopedic surgeon typically treats it as a precise bony point used for surgical alignment. A review tracing the term’s history found genuine discrepancies in how surgeons and anatomists define it, with the surgical literature often narrowing the definition to a small prominence rather than a broader area.2PubMed Central / Wiley Online Library (Clin Anat). Evolution of the term “epicondyle of the femur”: Revisiting the anatomical and surgical literature
What Muscles Attach at the Elbow Epicondyles
The lateral epicondyle of the humerus is the origin point for most of the muscles that extend your wrist and fingers. A detailed cadaver study using MRI found that several extensors share a common origin at the top of the lateral epicondyle, while the extensor carpi ulnaris arises from its back-and-lower surface.3PubMed. Detailed MRI-anatomic study of the lateral epicondyle of the elbow and its tendinous and ligamentous attachments in cadavers This cluster of tendons fanning out from one small bump is part of why the region is vulnerable to overuse: many muscles are pulling on a very small piece of bone.
The medial epicondyle anchors the muscles that flex your wrist and rotate your forearm inward (pronation). These include the pronator teres and the flexor carpi radialis, among others. Like their counterparts on the lateral side, these muscles share a common tendon origin, sometimes called the common flexor tendon. The medial epicondyle also serves as an attachment point for the ulnar collateral ligament, which resists the outward-bending (valgus) forces that act on the elbow during throwing.
The anatomy at the lateral epicondyle is not as standardized as textbooks suggest. A literature review found that the muscles originating there can show anatomical variations in anywhere from less than one percent to about a third of people, and researchers have even documented four muscles not described in classical anatomy that can appear in this region.4Perspectives on Health: Knowledge for Life. MUSCULATURE ORIGINATING FROM THE LATERAL EPICONDYLE OF THE HUMERUS BIBLIOGRAPHICAL REVIEW This variability helps explain why two people with apparently the same elbow problem can respond differently to treatment.
Tennis Elbow and Golfer’s Elbow
The two most common conditions involving epicondyles are lateral epicondylitis (“tennis elbow”) and medial epicondylitis (“golfer’s elbow”). The names are a bit misleading in two ways. First, you do not need to play tennis or golf to develop them; any repetitive gripping, twisting, or lifting motion can trigger the problem. Second, the “-itis” suffix implies inflammation, but tissue studies consistently show that the underlying problem is not inflammatory. Instead, the affected tendon undergoes a degenerative process characterized by disorganized collagen and poor blood supply.5Revista Brasileira de Ortopedia (English Edition). Lateral Epicondylitis of the Elbow The more accurate term used in research is “tendinosis” or “tendinopathy” rather than “tendinitis.”
In lateral epicondylitis, the tendon most commonly affected is the extensor carpi radialis brevis, one of the muscles anchored at the lateral epicondyle. Research has proposed that this particular muscle is vulnerable because of how its fibers are stretched during normal forearm use: the elongated position lengthens internal muscle structures, which impairs tiny blood vessels within the tissue. Poor blood flow triggers a cascade in which the body lays down weaker collagen, the tendon loses its load-bearing ability, and abnormal new blood vessels grow into the damaged area, accelerating degeneration rather than healing.6PubMed. A potential factor in the pathophysiology of lateral epicondylitis: The long sarcomere length of the extensor carpi radialis brevis muscle and implications for physiotherapy
Medial epicondylitis follows a similar pattern but on the inside of the elbow. It involves the common flexor tendon and is often associated with repetitive wrist flexion or forearm rotation. Occupational risk factors include repetitive hand movements, exposure to vibrating tools, and sustained gripping of heavy loads.7JURNAL BORNEO AKCAYA. FACTORS THAT RELATED TO INCIDENT MEDIAL EPICONDYLITIS (GOLFER ELBOW) ON WORKERS SPRINGBAD FURNITURE MAKER When conservative treatments fail, surgical management can involve resecting and repairing the degenerated portion of the common tendon at the medial epicondyle.8PubMed Central. Surgical management for refractory medial epicondylitis based on the anatomical characteristics of flexor pronator origin: surgical results of 8 cases and review of the literature
For lateral epicondylitis specifically, a meta-analysis found that adding eccentric exercises (controlled lowering movements that load the tendon while it lengthens) to other treatments significantly improved pain scores and muscle strength compared with other therapy alone.9PubMed Central. The Beneficial Effects of Eccentric Exercise in the Management of Lateral Elbow Tendinopathy: A Systematic Review and Meta-Analysis When imaging is needed before surgery, MRI or ultrasound can map the extent of tendon damage, identify associated problems, and help surgeons plan their approach.10PubMed. Epicondylitis: pathogenesis, imaging, and treatment
Why the Medial Epicondyle Is a Weak Link in Young Throwers
In children and adolescents, the medial epicondyle has a growth plate (apophysis) that does not fully fuse to the rest of the humerus until the mid-to-late teenage years. This makes it the weakest link in the chain when a young arm generates high valgus stress during overhead throwing. Repetitive stress can cause the growth plate to become inflamed, fragmented, or enlarged, a condition commonly called “Little League elbow.”11Orthopaedic Journal of Sports Medicine. The Prevalence and Clinical Characteristics of Medial Epicondyle Apophysitis in Juvenile Baseball Player – Ultrasonographic Assessment of 2,926 Cases
In more severe cases, the growth plate can fracture outright during a single throw. A study of over 300 young patients diagnosed with medial epicondyle overuse injuries found that about 16 percent sustained an actual fracture. The median age was about 13 years, and nearly all were male baseball pitchers. A striking finding was that most of these fracture patients (roughly 84 percent of those with documentation) reported pre-existing elbow pain before the throw that caused the break, suggesting the acute fracture was the endpoint of accumulated damage rather than a sudden event out of nowhere.12PubMed Central. Medial Epicondyle Apophyseal Avulsion Fractures in Youth Throwers: A Severe Variant of Little League Elbow The fracture patients also had higher body mass index compared with those who had only inflammation, which hints that body weight may add mechanical stress to an already vulnerable growth plate.13PubMed Central. Medial Epicondylar Apophyseal Avulsion Fractures in Youth Throwers: A Severe Variant of Little League Elbow
For parents and coaches, the practical takeaway is that elbow pain in a young thrower should never be dismissed as “just soreness.” Persistent inner-elbow pain is a warning sign that the medial epicondyle’s growth plate is under too much stress, and continuing to throw through it raises the risk of a fracture that may require surgery.
The Ulnar Nerve and the Medial Epicondyle
The ulnar nerve, which supplies sensation to your ring and little fingers and powers many of the small muscles of the hand, passes through a tight channel directly behind the medial epicondyle called the cubital tunnel. This is why bumping your “funny bone” sends an electric shock down your forearm: you are compressing the nerve against the bone.
In cubital tunnel syndrome, the ulnar nerve becomes chronically irritated or compressed at this spot. Ultrasound studies show that the nerve swells measurably at the medial epicondyle in affected patients. One study found the nerve’s cross-sectional area was roughly 50 percent larger at the epicondyle than just above or below it, and this enlargement correlated with slower nerve conduction speed.14PubMed Central. Ulnar Nerve Enlargement at the Medial Epicondyle Negatively Correlates With Nerve Conduction Velocity in Cubital Tunnel Syndrome A separate ultrasound study found that a ligament spanning from the medial epicondyle to the olecranon (the bony tip of the elbow) was thickened in patients with cubital tunnel syndrome, physically squeezing the nerve and causing it to swell upstream of the compression point.15PubMed Central. Morphological Changes of Medial Epicondyle-Olecranon Ligament and Ulnar Nerve in the Cubital Tunnel Syndrome: An Ultrasonic Study
The medial epicondyle’s shape and the depth of the groove behind it vary from person to person. People with a shallower groove are more prone to the nerve slipping out of place (subluxation) when the elbow bends, which can contribute to chronic irritation. This is one reason why some people develop cubital tunnel syndrome while others with the same daily habits never do.
Epicondyles as Surgical Landmarks in Knee Replacement
The femoral epicondyles serve a very different purpose in orthopedics: they are used as alignment landmarks during total knee replacement. Surgeons need to position the artificial femoral component at the correct rotation so the kneecap tracks properly and the ligaments stay balanced. The line connecting the medial and lateral femoral epicondyles, known as the transepicondylar axis, is one of the main references used to achieve that rotation.16PubMed. Low reproducibility of the intra-operative measurement of the transepicondylar axis during total knee replacement
Studies comparing different rotational references have found the transepicondylar axis to be more reliable than an alternative reference called the posterior condylar axis, especially in knees that are significantly bowed inward or outward.17PubMed. Femoral Component Rotation in Total Knee Arthroplasty: A Comparison Between Transepicondylar Axis and Posterior Condylar Line Referencing Research on a newer approach called functionally aligned total knee arthroplasty found that the resulting component rotation closely matched the transepicondylar axis and was associated with a low rate of revision surgeries, suggesting it does not lead to significant kneecap-tracking problems.18PubMed. Femoral component rotation in functionally aligned total knee arthroplasty closely aligns with the transepicondylar axis and demonstrates excellent early survivorship
The challenge is that finding the epicondyles during surgery is harder than it sounds. Soft tissue covers the bone, and surgeons have to palpate the bumps by feel. One study found low reproducibility when different surgeons tried to identify the transepicondylar axis intraoperatively.16PubMed. Low reproducibility of the intra-operative measurement of the transepicondylar axis during total knee replacement This is partly why computer-assisted and robotic knee surgery have gained traction: they can map the epicondyles more precisely using preoperative imaging rather than relying solely on the surgeon’s fingertip.
Epicondyles in Evolutionary History
The region around the epicondyle has a surprisingly deep evolutionary backstory. In the earliest vertebrates that transitioned from water to land during the Devonian period, the median nerve and brachial artery needed a route from the upper arm into the forearm. Early tetrapods developed a bony tunnel near the inner (medial) epicondyle called the entepicondylar foramen to house these structures. The channel provided protection to the nerve and artery while accommodating the increasingly complex limb mechanics required for walking on land.19PubMed Central. An arch worth revisiting: a study on the feline humeral supracondylar foramen and its evolutionary significance
As limbs evolved further, most mammals lost this bony tunnel. The nerve and artery gradually shifted course, and the foramen closed over evolutionary time. However, some modern animals still have it. Cats, for example, retain a related structure called the supracondylar foramen near the lower humerus, considered a remnant of a vestigial muscle attachment. In rare cases, humans are born with a bony spur called a supracondylar process near the medial epicondyle, with a ligament bridging from it to the epicondyle. This can form a partial tunnel that compresses the median nerve, a condition known as supracondylar process syndrome. It is essentially a throwback to that ancient bony channel, and the link between epicondylar anatomy and nerve passage has been conserved, in one form or another, for over 350 million years.20Mètode Science Studies Journal. Vestiges of our first steps: An evolutionary view of the supracondylar syndrome
Feeling Your Own Epicondyles
If you want to locate your epicondyles, the elbow is the easiest place to start. Straighten your arm and feel the bony prominences on either side of the elbow joint. The bump on the inside (closest to your body) is the medial epicondyle; it is usually the larger one and tender if you press hard. Now flex your wrist and fingers while pressing that spot and you may feel the muscles pulling on it. The bump on the outside is the lateral epicondyle. Make a fist and extend your wrist upward; the muscles tightening under your fingers on the outer forearm originate right there.
At the knee, the epicondyles are harder to feel because they sit under thicker layers of muscle and fat. With your knee slightly bent, you can sometimes palpate a bony ridge on either side of the kneecap, slightly above the joint line. These are the femoral epicondyles, and they mark where the medial and lateral collateral ligaments attach to the thigh bone. Physical therapists and surgeons routinely locate them during examinations and procedures, but for everyday purposes, the elbow epicondyles are the ones most people encounter, usually when they experience pain there or bang the medial side against a hard surface.