LCL

For Medical Students

Structure and Location

The lateral collateral ligament, also called the fibular collateral ligament, is a round cord rather than a flat band. Conventional teaching gives its length as about 70 mm.

Its femoral attachment is in a small depression close to the lateral epicondyle, slightly above it and slightly behind it. Conventional teaching places the centre about 1 mm proximal and 3 mm posterior to the epicondyle.

Its distal attachment is to the lateral side of the fibular head, in a bony depression. Conventional teaching places the centre about 8 mm behind the front edge of the head and about 28 mm below the tip of the styloid process.

It is extracapsular along its whole length. The capsule, the popliteus tendon and a layer of fat lie between it and the joint.

That separation is the single difference from the medial side worth memorising. The medial collateral ligament attaches to its meniscus; this one attaches to nothing inside the joint.

Relations

Superficial to it: the iliotibial band in front and the biceps femoris tendon behind, with the biceps tendon wrapping around the ligament at the fibular head.

Deep to it: the popliteus tendon crossing underneath on its way to the femur, then the capsule and the lateral meniscus.

Behind it: the popliteofibular ligament and, further back and more superficial, the common peroneal nerve.

A bursa sits between the ligament and the biceps tendon at the fibular head, which is what lets the two slide on each other.

Function

The ligament is the primary restraint to varus force. That is its main job and a varus stress test examines it.

It is tightest in extension and slackens as the knee flexes, which is the reverse of the medial collateral ligament. It is tested at 0 and at 30 degrees for that reason.

It contributes to resisting external rotation, as a secondary structure. 3.10.3 covers its contribution through range.

Clinical Relevance

It can be felt. With the ankle of the injured leg resting on the opposite knee, the figure of four position, the ligament stands out as a cord and can be followed from femur to fibula.

Because the lateral meniscus has no collateral attachment, it is far more mobile than the medial meniscus. That is an anatomical fact with consequences in 2.6 and in Section 6.

An injury here is often not isolated. The posterolateral corner structures lie immediately behind it and 2.10.4 covers them.

The common peroneal nerve lies close behind, so a lateral injury that produces foot drop is a nerve injury alongside a ligament one.

MRCS Level

Structure and Location

Describe the femoral attachment by the depression rather than by the epicondyle, as on the medial side. Conventional teaching gives the footprint an area of the order of 50 square millimetres, which is small enough that a few millimetres of error moves the whole attachment.

The fibular attachment is larger and lies in a depression on the lateral head, with the biceps tendon inserting around it rather than into it.

The ligament runs downwards and backwards, so it is oblique in two planes. A drawing that shows it vertical is wrong in both.

It is the first of three structures that make up the primary posterolateral restraint, with the popliteus tendon and the popliteofibular ligament. 2.10.4 treats the three together.

Relations

The lateral side has three layers in the scheme usually credited to Seebacher. Layer one is the iliotibial band and the superficial part of biceps; layer two is the patellar retinaculum and the patellofemoral ligaments; layer three is the capsule, split into a superficial and a deep lamina.

This ligament lies in the superficial lamina of layer three. The popliteus tendon and the coronary ligament lie in the deep lamina, which is why the two can be separated at operation.

The inferior lateral genicular artery runs between the two laminae, deep to the ligament and superficial to the meniscus.

The common peroneal nerve lies posterior to the biceps tendon, which is posterior to this ligament. The order from front to back at the fibular head is ligament, tendon, nerve, and 2.10.6 holds the detail.

Blood Supply and Innervation

Supply is from the lateral superior and lateral inferior genicular arteries, reaching the ligament through the surrounding fat rather than along a sheath.

The vascularity is adequate but not comparable with the medial side, which is part of why acute lateral repair gives less reliable results than acute medial repair.

Nerve supply is from the lateral articular branches, with contributions from the recurrent articular branch of the common peroneal nerve.

Function

It provides the large majority of varus restraint through the first 30 degrees of flexion and less beyond that, as the capsule and the cruciates take more.

Its contribution to external rotation restraint is real but secondary. The popliteofibular ligament and the popliteus tendon carry more of that, which 2.10.3 covers.

Sectioning studies put varus opening with this ligament alone divided at a few millimetres, and much more when the other two primary structures go with it. 3.10.1 carries the numbers.

Clinical Relevance

Test varus at 0 and at 30 degrees. Opening at 30 degrees alone suggests this ligament; opening at 0 degrees as well suggests the corner and the cruciates. 4.13 covers the examination.

Palpate in the figure of four position before deciding a lateral structure is intact. The ligament is superficial and a gap is felt as well as seen.

Expect a lateral injury to involve more than this ligament. The lateral side is three primary structures within two centimetres of each other.

Document peroneal nerve function at the first assessment of any lateral injury, because a later deficit cannot then be attributed to treatment.

FRCS Level

Relations

The lamina split in layer three is the usable surgical plane on the lateral side. The ligament can be separated from the popliteus tendon because they lie in different laminae, and that is what makes an anatomical reconstruction of both possible.

The femoral attachments of this ligament and the popliteus tendon lie close together on the lateral condyle. Conventional teaching separates their centres by about 18 mm, which is the constraint on any two tunnel construct. 2.10.7 carries the landmarks.

The biceps tendon's wrap around the fibular attachment means a fibular tunnel passes through a field that a tendon occupies, and the nerve lies behind that tendon.

Function

Treat varus restraint as primarily this ligament and rotational restraint as primarily the other two. A reconstruction that restores only this ligament restores the plane it controls and not the rotation.

Its reciprocal relationship with the medial collateral ligament across the range is weaker than the medial side's internal reciprocity: this one is tight in extension and the medial one in slight flexion, so the two sides are not mirror images.

Loss of this ligament alongside a cruciate changes the load on the graft, because varus thrust applies a moment the graft was not tensioned against. 3.10.9 carries it.

Clinical Relevance

Assess all three primary lateral structures before planning. The anatomy puts them within two centimetres and the examination separates them poorly.

Plan the femoral points for this ligament and the popliteus tendon together, because 18 mm of bone has to hold two tunnels that must not converge.

Consider reconstruction rather than repair for a chronic lateral injury, since the vascularity that supports medial healing is not matched here.

Identify the peroneal nerve before any fibular work. The nerve is the one structure on this side whose injury is permanent, and 2.10.6 covers it.