How a Segond Fracture Occurs and Its Link to ACL Tears

A Segond fracture is a small sliver of bone pulled off the outer rim of the tibia, just below the knee joint. Though the fragment itself is tiny and easy to overlook, it functions as a powerful diagnostic clue: seeing one on an X-ray strongly suggests the anterior cruciate ligament (ACL) is torn and that other structures inside the knee are damaged too. Among patients undergoing ACL reconstruction, about 7% show an acute Segond fracture on imaging, and when healed fractures are counted, roughly 15% have evidence of one at some point.¹ The fracture itself rarely needs its own treatment, but recognizing it changes what surgeons look for and how aggressively they examine the rest of the knee.

How a Segond Fracture Happens

The injury occurs when the lower leg twists inward while the knee is also pushed into a varus position, meaning the joint bends so the lower leg angles inward relative to the thigh. Picture a planted foot with the body rotating over it, or a sudden direction change in sport where the knee buckles sideways. That combination of forced internal rotation and inward angulation stretches the structures on the outer side of the knee hard enough to yank a chip of bone off the tibia rather than simply tearing the soft tissue alone.² The fragment is usually small, sometimes only a centimeter or so, and it sits just below and to the outside of the joint line on a standard knee X-ray. Because the forces involved are violent enough to avulse bone, the ACL and other internal structures are almost always damaged in the same event.

Why It Matters for ACL and Meniscus Injuries

The Segond fracture has long been called “pathognomonic” for an ACL tear, a term that in medicine means the finding is so strongly linked to the diagnosis that seeing it essentially confirms it. That label is slightly generous in practice, but the association is striking. In a study of 55 pediatric and adolescent patients with Segond fractures, about 71% had ACL tears, with almost all the rest having tibial spine fractures or other significant intra-articular damage.³ Overall, roughly 87% of those patients needed surgery for the injuries found alongside the Segond fracture. In adults, the association with ACL tears is even more consistent.

The damage extends beyond the ACL. Meniscal tears are common companions. One study found that 76% of patients with a Segond fracture had meniscal pathology, with a total of 49 meniscal injuries identified in 50 patients. Cartilage injuries were also present in about a quarter of cases.⁴ The lateral meniscus appears to take a particular beating. Research comparing ACL-injured knees with and without a Segond fracture found that the rate of lateral meniscus injury was 72% in the Segond group versus 49% when no Segond fracture was present, with patients roughly two and a half times more likely to have a lateral meniscus tear if the fracture was there.⁵ A separate analysis found a similar pattern, with the Segond fracture nearly doubling the odds of a lateral meniscus tear after adjusting for other factors.⁶

The practical takeaway for a patient or clinician is straightforward: a Segond fracture on an X-ray is not just a small bone chip to be brushed off. It signals that the knee has sustained a high-energy rotational injury, and the surgeon should look carefully for ACL, meniscal, and cartilage damage, because the chances of finding them are high.

What Structure Actually Pulls the Bone Off

This question has produced genuine disagreement among researchers, and it matters more than it might sound. The outer side of the knee has a complex web of ligaments, capsular tissue, and a thick band called the iliotibial tract (ITB). For years, surgeons debated which of these structures is responsible for avulsing the bone fragment in a Segond fracture. The answer shapes how people think about surgical repair and whether additional procedures beyond standard ACL reconstruction might help.

A structure called the anterolateral ligament (ALL) became the leading suspect. Cadaver dissections confirmed that the ALL inserts on the proximal tibia in exactly the region where Segond fragments consistently break off, and biomechanical testing showed that overloading the ALL can produce the fracture. In one study, six out of fifteen specimens failed by bony avulsion at the tibial attachment, reproducing a Segond fracture pattern.⁷ Separate anatomical work concluded that the Segond fracture is, in effect, a bony avulsion of the ALL.⁸

But MRI studies of living patients complicated that tidy narrative. When researchers looked at what soft tissue was actually attached to the fracture fragment on MRI, they could not identify a distinct ALL in most cases. Instead, 94% of the time, the attachments were the posterior fibers of the ITB and the lateral capsule.⁹ That study concluded the fracture is better described as an avulsion of the “anterolateral complex” as a whole, a group of overlapping structures, rather than a single clean ligament. The distinction is not just academic. Surgeons deciding whether to add a lateral extra-articular procedure during ACL reconstruction are essentially asking how much the anterolateral structures contribute to knee stability, and the answer depends partly on what the Segond fracture is telling us about which structures failed.

How Much Extra Instability Does It Create

Beyond signaling that the ACL is torn, the Segond fracture adds its own mechanical problem. Cadaver biomechanics testing has shown that once the ACL is cut, the knee already translates and rotates more than normal. But creating a Segond fracture on top of that pushes rotational instability significantly further. In one experiment, the average internal rotation of the tibia at 30 degrees of knee flexion was about 21 degrees with everything intact, rose to about 27 degrees after cutting the ACL, and jumped to about 31 degrees after adding the Segond lesion.¹⁰ During a simulated pivot-shift test, which is the clinical maneuver used to check for rotatory instability, the rotation increased from about 12 degrees in the ACL-deficient knee to about 19 degrees once the Segond fracture was added. That additional rotational laxity is what makes some surgeons worry about addressing the lateral structures during reconstruction, rather than focusing on the ACL alone.

MRI findings support the idea that the injury involves more force than a garden-variety ACL tear. Patients with Segond fractures show more extensive bone bruising throughout the knee, affecting both the lateral and medial compartments, compared with patients who tear their ACL without a Segond fracture.¹¹ Greater bone bruising reflects a harder impact on the joint surfaces and may partly explain the higher rates of meniscal and cartilage damage described earlier.

The Reverse Segond Fracture

If a classic Segond fracture is a chip off the outer (lateral) side of the tibia, a reverse Segond fracture is the mirror image: a small avulsion off the inner (medial) side. It occurs through a different mechanism, typically when the knee is forced into valgus (knocked inward) with external rotation while flexed.¹² The fragment comes from the attachment of the deep portion of the medial collateral ligament on the tibia.

When first described, the reverse Segond fracture was linked to posterior cruciate ligament (PCL) tears and medial meniscus injuries, and radiologists were told to look for those specific associated injuries.¹³ That remains a useful starting point, but a review of published cases found the injury pattern is broader than originally thought. Among 14 reported cases, about 64% also had ACL injuries, and about 71% had medial collateral ligament damage.¹⁴ So while the classic Segond fracture says “look for an ACL tear,” the reverse version says “look for multi-ligament damage,” often involving the PCL but frequently the ACL and MCL as well. It is considerably rarer than the standard Segond fracture, but recognizing the small medial-sided fragment carries the same practical lesson: something much worse is hiding inside the joint.

Segond Fractures in Young Patients

In adults, a Segond fracture and an ACL tear are so tightly linked that the fracture is treated almost reflexively as confirmation of the ligament injury. In children and adolescents, the picture is a bit different. Growing bone behaves differently under stress: the growth plates are weaker than the ligaments around them, so the same forces that tear an adult’s ACL may instead fracture the growth plate or avulse the tibial spine where the ACL attaches.

One case report described a 16-year-old with a Segond fracture who did not have an ACL tear at all. Instead, the patient had a growth-plate fracture of the tibial plateau.¹⁵ A larger study of 53 pediatric and adolescent patients found that while ACL tears were still the most common associated injury at about 74%, tibial spine fractures accounted for 17% of cases.¹⁶ Younger patients, averaging around 14 years, were more likely to present with tibial spine fractures, while older adolescents averaging closer to 16 years were more likely to have standard ACL tears. Meniscal injuries were found in about 70% of these young patients, and the vast majority required some form of surgery.

The practical point for younger patients and their families is that a Segond fracture still demands a thorough workup even if the initial concern is not the ACL. The associated injuries in this age group can be different from what adults experience, but they are just as serious and just as likely to require surgical intervention.

Treatment of the Fracture Itself

Most of the time, the Segond fracture fragment is not specifically repaired. The bone chip is small, and the focus of surgery is on reconstructing the ACL and addressing any meniscal or cartilage damage. However, some surgeons do fix the fragment, particularly if it is large enough to anchor with hardware or if they want to restore tension to the lateral structures it came from.

Techniques for direct repair depend on the size of the fragment. Small pieces, under about two square centimeters, can be sutured back or secured with a small anchor. Larger fragments may be fixed with a cannulated screw. In cases where the surrounding capsule has been stretched out, surgeons may also plicate (tighten) the capsule with absorbable suture.¹⁷ One published rehabilitation protocol after combined ACL reconstruction and Segond repair involves a hinged brace for six weeks, with the knee locked in full extension for the first week and then gradually allowed to bend. Weight bearing with crutches starts on the first day after surgery. Full range of motion is typically achieved by six weeks, a supervised strengthening program begins after the brace comes off, and return to sports is allowed around six months.¹⁸

Whether fixing the Segond fragment improves outcomes beyond standard ACL reconstruction alone is still debated. The growing interest in lateral extra-articular procedures alongside ACL reconstruction has renewed attention to the question, since repairing the Segond fragment is one way to address the damaged anterolateral structures. But most current evidence suggests the fragment does not need its own repair to get a good result from surgery.

Outcomes After ACL Reconstruction

Given the extra rotational instability and the higher burden of meniscal and cartilage injuries in patients with Segond fractures, you might expect worse outcomes after ACL reconstruction. The evidence so far does not bear that out. A systematic review pooling data from multiple studies found that graft failure and revision surgery rates were actually numerically lower in the Segond group, about 3.8% compared with 6.9%, though the difference did not reach statistical significance.¹⁹ Functional scores measuring knee stability, pain, and return to activity were also similar between patients who had a Segond fracture and those who did not. No clinically meaningful difference showed up on any of the standard outcome measures.

That finding is reassuring but also a little puzzling, given the biomechanical data showing worse rotational instability. One possible explanation is that the Segond fracture heals on its own once the knee is stabilized by ACL reconstruction, and the lateral structures scar down enough to restore functional stability. Another is that the additional injuries (meniscal tears, cartilage damage) are being addressed surgically at the time of reconstruction, which may level the playing field. Either way, the current evidence does not support the idea that a concomitant Segond fracture, left unrepaired, leads to worse results after ACL surgery.

Spotting It on Imaging

On a plain X-ray, the Segond fracture appears as a small, thin fragment of bone sitting just lateral to the tibial plateau, usually separated from the tibia by a few millimeters of space. It can be subtle, especially if the fragment is tiny or if the X-ray is not perfectly positioned. Clinicians who are not specifically looking for it can miss it, which is why radiologists and orthopedic surgeons are trained to look at the lateral tibial margin carefully in any knee injury involving a twisting mechanism.

MRI provides far more detail and picks up the associated soft-tissue injuries the fragment implies, including ACL tears, meniscal damage, bone bruising, and capsular disruption. The bone bruise patterns seen on MRI in patients with Segond fractures are often more widespread than in ACL tears without the fracture, extending across both the lateral and medial compartments of the knee.²⁰ This broader bruising pattern on MRI can itself be a clue that the rotational forces were severe and that additional internal damage should be expected.

One area where imaging falls short is in clearly delineating the ALL as a distinct structure. As mentioned earlier, MRI struggles to distinguish the ALL from the surrounding lateral capsule and ITB fibers in most patients, which has fueled the debate over what the Segond fracture is actually an avulsion of. For practical diagnosis, this limitation does not matter much: whatever the fragment is attached to, its presence on imaging means the same thing. But for surgeons planning a lateral procedure, the inability to reliably image the ALL on a standard MRI means they often have to assess the anterolateral structures directly during arthroscopy or through an open incision.