What Is the Lateral Malleolus? Anatomy, Function & Injury

The lateral malleolus is the bony bump on the outside of your ankle, formed by the lower end of the fibula. It is not just a cosmetic landmark you can feel through your skin; it acts as a structural buttress that keeps the ankle joint stable every time you walk, run, or change direction. Because it sits in such an exposed position and bears rotational forces during common movements like rolling an ankle, the lateral malleolus is one of the most frequently fractured bones in the body. Understanding what it does, how it breaks, and what recovery looks like can help you make sense of an injury that affects millions of people each year.

Where It Sits and What It Looks Like

Your lower leg has two bones: the tibia (the thick shin bone on the inner side) and the fibula (the thinner bone running along the outer side). The lateral malleolus is the very bottom of the fibula, the part that extends below the ankle joint line and forms that prominent knob you can grab on the outside of your ankle. The corresponding bump on the inside is the medial malleolus, which is the bottom of the tibia. Together, these two projections create a bony pocket, sometimes called the ankle mortise, that cradles the talus bone of the foot and allows the hinge-like motion of pointing your toes and pulling them up.

CT-based studies show the fibula averages roughly 370 mm in length, with the distal malleolar angle averaging about 164 degrees, though individual variation is significant.¹ The internal canal of the fibula narrows dramatically near the tip. At about 6 cm above the tip, the canal reaches its smallest diameter, and in roughly one in six people it measures 3.5 mm or narrower, which matters for surgeons considering intramedullary fixation.² There is also a shallow groove on the back of the lateral malleolus called the malleolar fossa, which researchers have classified into three shapes based on cross-sectional imaging. The most common is a C-shaped fossa (about 43%), followed by a V-shape (about 32%) and a flat type (about 25%).³ These variations matter mainly for surgical hardware placement, not for how your ankle feels day to day.

The Ligaments That Anchor It

The lateral malleolus serves as an attachment point for several ligaments that keep your ankle from rolling too far in any direction. Three ligaments on the outer side of the ankle connect the lateral malleolus to the foot bones below it:

Anterior talofibular ligament (ATFL): runs from the front of the lateral malleolus to the talus. This is the ligament torn most often in a classic ankle sprain.
Calcaneofibular ligament (CFL): runs downward from the lateral malleolus to the calcaneus (heel bone), providing stability when the foot is flexed.
Posterior talofibular ligament (PTFL): runs from the back of the lateral malleolus to the talus, the strongest of the three and the least commonly injured.

These ligaments have more anatomical variety than textbooks suggest. Cadaver studies have found the ATFL exists as a single band in about half of ankles and as a double band in the other half. The CFL appears as a single band most often (about 73% of cases), though Y-shaped and V-shaped variants also occur. The fibers of these ligaments frequently interconnect with each other and with the joint capsule, creating a web of support rather than isolated straps.⁴ Another cadaver study found that the ATFL attaches about 4 mm from the articular tip of the fibula, while the CFL attaches about 14 mm above the inferior tip, confirming that these are distinct, independent fiber bundles with their own anchor points.⁵

Above the lateral malleolus, the syndesmosis ligaments bind the fibula to the tibia. These ligaments hold the two leg bones tightly together just above the ankle joint and are critical for keeping the mortise at the correct width. When the syndesmosis is torn alongside a lateral malleolus fracture, the injury is more serious and recovery is longer.

What the Lateral Malleolus Actually Does

You can think of the lateral malleolus as a guardrail for the ankle joint. The talus sits in the mortise formed by the tibia above and the two malleoli on either side. The lateral malleolus prevents the talus from shifting or tilting outward, which would destabilize the entire joint. Computer simulations of what happens when a lateral malleolus fracture heals in a bad position show that even small offsets change how forces distribute across the ankle. An outward shift of the malleolus had a larger effect than a backward shift, and the consequences grew worse at greater angles of ankle motion.⁶ In severe cases, an outward offset can cause the fibula to essentially lose its stabilizing function. This is why surgeons care so much about restoring the exact anatomical position of the lateral malleolus after a fracture.

Humans are the only primates that walk exclusively on two legs, and the foot and ankle are under intense evolutionary pressure to handle both balance and propulsion.⁷ The lateral malleolus is part of that story. In quadrupedal animals, the fibula often bears more of the body’s weight; in humans, the tibia handles the overwhelming majority of load, and the lateral malleolus has been refined into a stabilizer and lever arm for the ligaments and tendons that control side-to-side motion.

How Lateral Malleolus Fractures Happen

Most lateral malleolus fractures happen when the ankle is forced into a position it cannot handle, usually some combination of rolling and twisting. The classic scenario involves the foot being slightly inverted (turned inward) while an external rotational force acts on the leg, like planting your foot and then having your body twist over it. Falls, sports collisions, stepping off a curb, and icy sidewalks are all common culprits.

A finite element model simulating this type of injury found that the anterior syndesmosis ligament bears the greatest stress first. As the twisting force continues, the stress shifts to the lateral malleolus itself, causing a fracture. The pressure on the back part of the ankle nearly triples as the injury progresses from the ligament-damage stage to the fracture stage.⁸ This helps explain why lateral malleolus fractures sometimes come with injuries to structures on the opposite side of the ankle, including the deltoid ligament on the inner side or the syndesmosis ligaments above.

Fracture Classification and Stability

Doctors classify lateral malleolus fractures mainly by where the break sits relative to the syndesmosis, the joint between the tibia and fibula just above the ankle. The two systems used most often map onto each other. A Weber type A fracture (below the syndesmosis) corresponds to a supination-adduction mechanism. A Weber type B fracture (at the level of the syndesmosis) corresponds to a supination-external rotation pattern and is the most common type. A Weber type C fracture (above the syndesmosis) corresponds to a pronation-external rotation pattern and implies more ligament damage.⁹

The key clinical question is stability. Fractures involving two or three malleoli, or high fibular fractures with deltoid ligament damage, are generally considered unstable and typically need surgery. The tricky cases are isolated Weber type B fractures, where the fibula is broken at the syndesmosis level but everything else looks intact on initial imaging. Whether these are truly stable remains a matter of some debate among surgeons.¹⁰ A large registry study found that about 70% of these fractures were treated without surgery, and only about 1% of those patients later needed their treatment changed to an operation, suggesting that most genuinely stable fractures can be identified reliably.¹¹

Getting Assessed After an Ankle Injury

Not every twisted ankle needs an X-ray. The Ottawa Ankle Rules are a screening tool used in emergency departments worldwide to decide whether imaging is necessary. They focus on whether you can bear weight for four steps and whether there is tenderness over specific bony landmarks, including the back edge of the lateral malleolus. The rules have close to 100% sensitivity for detecting fractures, meaning they almost never miss one. However, their specificity is modest, around 45%, so many people who pass the tenderness test still get imaged as a precaution.¹² One hospital-based study found that applying the rules consistently could have reduced ankle X-rays by about 31%, though a small number of fractures (about 3%) would have been missed.¹³

When X-rays are taken, they sometimes underestimate the full picture. A study comparing standard X-rays with CT scans found that about 40% of associated pathologies were missed on plain films, regardless of how experienced the evaluator was.¹⁴ Adding a CT scan changed the surgical plan in many cases, leading to more accurate approaches, additional fixation of the posterior malleolus, and more syndesmosis repairs.¹⁵ This does not mean everyone with a broken ankle needs a CT, but surgeons increasingly rely on one for fractures that appear complex or where the stability is unclear.¹⁶

When You Do Not Need Surgery

Stable lateral malleolus fractures, where the ankle mortise remains properly aligned and the ligaments on the inner side are intact, can heal well without an operation. Treatment typically involves immobilization in a cast or walking boot, followed by gradual weight bearing and rehabilitation. One long-term study found that a treatment algorithm prioritizing non-surgical management cut the reoperation rate from about 7% down to about 2.4%, with no loss in outcomes.¹⁷

The trade-off is muscle weakness during recovery. When a cast comes off, the muscles that point your foot down can show nearly 45% less strength compared to the uninjured side, and the muscles that pull your foot up are about 25% weaker. The good news is that rehabilitation closes this gap surprisingly well. After three months of rehab, the strength deficit drops to single digits, and by six months the injured ankle often matches or even slightly exceeds the healthy one in strength testing.¹⁸ Endurance follows a similar pattern: a 54% deficit in pushing-off endurance at cast removal shrinks to about 14% after three months and disappears entirely by six months.

When Surgery Is Needed

Unstable fractures, where the talus can shift within the mortise, almost always require surgical fixation. The standard approach is open reduction and internal fixation (ORIF), where the surgeon realigns the bone fragments and holds them in place with metal plates and screws. A metal plate placed along the side of the fibula is the most traditional option and provides excellent alignment. However, an intramedullary screw placed through the inside of the bone’s canal is a less invasive alternative that produces fewer wound complications and less hardware irritation, making it especially attractive for older adults or people with diabetes or poor circulation.¹⁹ A meta-analysis comparing locking plates (which grip the bone with threaded screw holes) to standard nonlocking plates found no clear benefit to the more expensive locking design for routine lateral malleolus fractures.²⁰

After the bone heals, the hardware sometimes becomes a nuisance. A study of patients who chose to have their plates or screws removed found that pain scores dropped from an average of about 3.4 out of 10 to about 1.3, roughly three-quarters experienced less ankle stiffness, and about 80% felt more comfortable walking on uneven ground afterward.²¹ Hardware removal is not routine, but it is an option for people who have persistent discomfort over the plate, which is common at the lateral malleolus because there is so little soft tissue between the skin and the bone.

Syndesmosis Injuries Alongside a Lateral Malleolus Fracture

When the ligaments holding the tibia and fibula together above the ankle (the syndesmosis) are torn along with a lateral malleolus fracture, the injury is more complex and the ankle is definitionally unstable. Surgeons must repair the syndesmosis to keep the mortise from widening. The two main fixation methods are a traditional metal screw placed across both bones and a flexible suture button device.

Multiple meta-analyses have compared the two. A pooled analysis of randomized trials found that the suture button produced fewer complications (roughly 60% lower complication rate), fewer unplanned reoperations, and better functional scores.²² A separate meta-analysis confirmed that the suture button improved functional outcomes, reduced implant removal and failure rates, and decreased irritation without increasing other complications, though postoperative imaging measurements were similar between the two methods.²³ A more recent study of patients with isolated lateral malleolus fractures and syndesmosis injuries found that the suture button group had significantly higher functional scores and better range of motion at final follow-up, though when screw breakage was excluded from the complication count, the overall complication rates between the two methods were similar.²⁴ The trend in practice has been moving toward suture buttons, particularly for active patients who want to avoid a second surgery to remove a screw.

Sprains, Avulsion Fractures, and the Confusing In-Between

Not every lateral malleolus injury involves a full fracture through the bone. Ankle sprains (ligament injuries without a break) are far more common, and sometimes the ligament pulls a small chip of bone off the lateral malleolus rather than tearing cleanly, creating what is called an avulsion fracture. In children, this distinction gets especially tricky because small bony fragments near the tip of the fibula can be either avulsion fractures or subfibular ossicles, which are normal anatomic variants that look like loose bone chips on imaging.

Dynamic ultrasound can help tell the two apart. Ossicles stay in a fixed position when the ankle is stressed, while avulsion fragments shift because they are not firmly attached. Ossicles are harmless and do not cause symptoms, while avulsion fractures, though they usually heal well with conservative treatment, can occasionally lead to chronic ankle instability in a small number of patients.²⁵

Children and the Growth Plate Problem

In children and adolescents, the lateral malleolus has an open growth plate (physis) near its tip. A fracture in this area can involve the growth plate itself, which adds a layer of concern. The growth plate of the distal fibula is one of the last to close, typically between ages 14 and 17, meaning teenagers are vulnerable for years. Treatment goals in pediatric ankle fractures center on restoring limb alignment and physeal anatomy while preserving joint congruency. For fractures that involve the growth plate, monitoring for growth disturbance may continue until the child reaches skeletal maturity.²⁶ Most growth plate injuries of the distal fibula heal without long-term problems, but fractures that crush or compress the physis carry a higher risk of premature closure, which could result in a leg-length difference or angular deformity.

Osteoporosis and Elderly Patients

At the other end of the age spectrum, osteoporotic bone creates its own challenges. The lateral malleolus is mostly cortical bone (the hard outer shell), but when that cortex thins with age and the internal bone quality deteriorates, standard screws and plates may not grip well. Fixation failure, where the hardware loosens or pulls out of weak bone, is a recognized problem in elderly patients with ankle fractures.²⁷ Surgeons sometimes augment fixation with bone cement, use specialized locking plates, or opt for the less invasive intramedullary screw technique to reduce the chance of wound problems in fragile skin. The goal is to get these patients walking again quickly, because prolonged immobility after an ankle fracture in an older adult carries risks of blood clots, muscle wasting, and loss of independence that can outweigh the risks of the fracture itself.

Peroneal Tendon Problems That Mimic or Accompany Lateral Malleolus Injuries

The peroneal tendons run right behind the lateral malleolus, tucked into a groove on its back surface. These tendons are the primary muscles that evert the foot (turn the sole outward) and help stabilize the ankle from the side. After a lateral malleolus fracture or chronic ankle sprains, the peroneal tendons can become inflamed, partially torn, or even dislocate out of their groove. This type of pathology is an under-appreciated source of persistent outer ankle pain and can be difficult to distinguish from ongoing ligament problems.²⁸ If you have had a lateral malleolus fracture and your outer ankle continues to ache or feel unstable well past the expected healing window, peroneal tendon injury is worth investigating. An MRI or ultrasound can usually clarify whether the tendons are intact and properly positioned in the groove behind the malleolus.