Segond Lesion

For Medical Students

Structure and Location

The Segond lesion is a small fragment of bone pulled off the anterolateral tibia, just below the joint line.

Its position is specific. Conventional teaching places it about 5 to 10 mm below the lateral tibial plateau, between Gerdy's tubercle in front and the fibular head behind.

That position is the tibial attachment of the anterolateral ligament and of the anterolateral capsule, which 2.11.3 covers.

The fragment is small, often only a few millimetres, and it is usually vertical and thin rather than block shaped.

This page is about the anatomy the fragment comes from. The fracture itself and its management are 6.100.

Relations

Above it: the lateral tibial plateau and the lateral meniscus.

In front: Gerdy's tubercle and the iliotibial band's attachment.

Behind: the fibular head and the lateral collateral ligament's attachment.

Attached to it: the anterolateral capsule and the anterolateral ligament's tibial end.

Function

The fragment itself has no function. What matters is that it marks where a structure was attached.

A bone fragment pulled off means the attachment held and the bone gave way, so the soft tissue is often intact and attached to the flake.

Because the attachment restrains internal rotation, the lesion is associated with the rotational injury that also tears the anterior cruciate ligament.

Clinical Relevance

It is almost always accompanied by an anterior cruciate ligament tear. The two share a mechanism.

A small flake at that exact position on a plain radiograph is therefore a reason to examine the cruciate, which is why the sign has outlived every argument about its anatomy.

It is easy to miss, because it is small and it sits at the edge of the film.

6.100 covers the fracture and what is done about it. This page covers what the position means.

MRCS Level

Structure and Location

Describe the fragment by what it carries rather than by its size. Dissection and imaging studies find the anterolateral capsule, the anterolateral ligament's tibial attachment, and sometimes fibres of the iliotibial band on it.

Conventional teaching gives the fragment a vertical height of a few millimetres and a thickness of about 2 mm, with the long axis vertical.

The donor site is a small area of cortex with little cancellous bone behind it, which is why the flake comes off rather than a wedge.

Segond produced the lesion experimentally by forced internal rotation, and described the band attached to it before anyone had a name for that band.

Relations

The lateral inferior genicular artery runs close to the donor site.

The lateral meniscus lies just above, and a meniscal injury often accompanies the lesion because the two share a mechanism rather than an attachment.

The iliotibial band's attachment at Gerdy's tubercle is anterior to the donor site and is not usually involved.

The lateral collateral ligament attaches to the fibula, not the tibia, so it is not part of this lesion.

Blood Supply and Innervation

The fragment's blood supply is periosteal and from the attached soft tissue, which is why it usually unites rather than becoming a loose body.

The donor site is supplied by the lateral inferior genicular artery through the periosteum.

Nerve supply to the region is from the lateral articular branches, which is why the lesion is tender at a point rather than diffusely.

Function

An avulsion fragment is evidence that the attachment was stronger than the bone at the moment of injury. That is a statement about relative strength, not about the quality of either tissue.

Because the attachment restrains internal rotation, the lesion is a marker of a rotational mechanism. 3.11.6 covers the mechanics.

The association with cruciate rupture is mechanical rather than anatomical: the same movement loads both structures.

Clinical Relevance

Examine the anterior cruciate ligament whenever the fragment is seen. The association is strong enough that the radiograph is a cruciate finding.

Look for it specifically on the anteroposterior view at the lateral tibial margin, because its size and position make it easy to miss. 5.3.3 covers fracture imaging.

Expect intact soft tissue attached to the fragment, which is relevant if the anterolateral structures are being considered.

Leave management to 6.100. This page is the anatomy the fragment came from.

FRCS Level

Relations

The fragment is the one direct observation of the anterolateral attachment available in a living patient. Every other account of that attachment comes from a cadaver.

Its donor site is where an anterolateral reconstruction would place its tibial fixation, so the lesion and the operation occupy the same bone.

Thin cortex at the donor site is a fixation consideration if the fragment is to be addressed rather than ignored.

Function

Treat the lesion as a rotational injury marker rather than as a fracture. The fragment is small, usually unites, and rarely requires anything; what it says about the knee is the useful part.

Its presence has been associated with higher grade rotatory laxity, which is consistent with the attachment it represents. 3.11.6 carries that.

Where an anterolateral procedure is being considered, a Segond lesion is evidence that the structure exists in that patient and where it attached.

Clinical Relevance

Assess rotational laxity specifically in a knee with this fragment, because the finding predicts it.

Consider the fragment when planning tibial fixation for an anterolateral construct, since the two occupy the same cortex.

Document the fragment in the operative record even when nothing is done to it. It is evidence about that knee's anatomy that no later investigation can recover.

Avoid treating it as an isolated fracture. 6.100 holds the management and the anatomy says it rarely needs any.