Anterolateral Ligament

For Medical Students

Structure and Location

The anterolateral ligament is a thickening of the anterolateral capsule running from the lateral femur to the anterolateral tibia.

Its femoral attachment is close to the lateral epicondyle, usually described as just behind and above it, near the attachment of the lateral collateral ligament.

Its tibial attachment is between Gerdy's tubercle and the head of the fibula, about 5 to 10 mm below the joint line.

On the way it attaches to the lateral meniscus, which is the feature that distinguishes it from the capsule around it.

It was described by Segond in 1879 as a pearly resistant band, named and renamed many times since, and described again in 2013 in the paper that brought it back into use.

Relations

Superficial to it: the iliotibial band and its deep layers, which 2.11.1 covers.

Deep to it: the lateral meniscus and the joint.

Behind and below: the lateral collateral ligament, which is a separate structure running to the fibula rather than to the tibia.

Its tibial attachment lies in the gap between Gerdy's tubercle in front and the fibular head behind.

Function

It restrains internal rotation of the tibia, particularly in flexion.

It contributes to the control of the pivot shift, which is the movement a torn anterior cruciate ligament allows.

Its meniscal attachment means it also tethers the lateral meniscus anteriorly.

Clinical Relevance

Its tibial attachment is the site of the Segond fracture, which 2.11.4 covers.

Whether it is a distinct ligament or a thickening of capsule is still argued. What is not argued is that something at the anterolateral knee restrains rotation.

Finding it depends on how it is looked for. A dissection from the surface divides it with the capsule; a dissection from the deep surface finds it.

MRCS Level

Structure and Location

Describe the femoral attachment carefully, because this is where descriptions differ most. Reports place it anterior to, posterior to, or coincident with the lateral collateral ligament's attachment, and the disagreement is real rather than careless.

The tibial attachment is more consistent. Conventional teaching places its centre about mid way between Gerdy's tubercle and the fibular head, about 7 mm below the joint line.

Conventional teaching gives the ligament a length of the order of 35 mm and a thickness of a few millimetres, which makes it thin relative to its length.

Identification rates in dissection studies range from about half to essentially all, and the range tracks the dissection method rather than the population.

Relations

It sits in the anterolateral capsule, which is layer three anteriorly in the scheme 2.10.4 uses.

The lateral inferior genicular artery runs close to its tibial attachment.

The capsulo-osseous layer of the iliotibial band lies superficial and slightly posterior, and the two are close enough that a dissection can take them as one. 2.11.1 covers the layer.

Its meniscal attachment is to the body of the lateral meniscus, in the region the popliteal hiatus leaves otherwise untethered.

Blood Supply and Innervation

Supply is from the lateral inferior genicular artery and from capsular vessels, which is to say it shares the supply of the capsule it sits in.

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

Neither supply distinguishes it from the capsule, which is one of the arguments used against calling it a separate ligament.

Function

It restrains internal rotation, with its contribution rising between about 30 and 90 degrees of flexion.

Sectioning it in a cruciate deficient knee increases the pivot shift. Sectioning it in an intact knee changes little, which tells you it is a secondary restraint whose role appears when the primary one has gone. 3.11.3 carries the figures.

Its meniscal attachment makes it a tether for the lateral meniscus in the segment where the hiatus removes the coronary attachment.

Clinical Relevance

Read the Segond fragment as evidence of this attachment rather than as a fracture in its own right, and 2.11.4 covers it.

Expect the pivot shift to be the clinical consequence. The ligament's contribution appears when the cruciate has failed, and 3.11.4 covers the test.

Treat variable identification as a method problem rather than a population problem. How a dissection approaches the capsule decides what it finds.

Avoid arguing about the name at the expense of the function. Something restrains rotation there, and 2.11.5 is where that argument is held.

FRCS Level

Relations

Its proximity to the capsulo-osseous layer of the iliotibial band is the practical problem. Two structures within a few millimetres, both restraining internal rotation, and a dissection plane that can include either or both.

Its tibial attachment is the only part that is reliably reproducible between studies, which is why reconstructions are described from the tibia outwards.

The meniscal attachment means a graft routed along its path does not reproduce it. No graft attaches to a meniscus.

Function

Treat it as a secondary restraint that matters in a cruciate deficient knee. That is the finding every sectioning study agrees on, whatever it calls the structure.

Its contribution and the Kaplan fibres' contribution cannot be separated clinically, which is why 2.11.5 treats the complex as the unit and 3.11.8 carries the combined reconstruction evidence.

The femoral attachment's variability means a reconstruction cannot be anatomical in the sense a cruciate reconstruction can. The target is a function rather than a footprint.

Clinical Relevance

Consider an anterolateral procedure in a knee with a high grade pivot shift, a revision cruciate reconstruction, or generalised laxity, and 3.11.8 carries the indications.

Plan from the tibial attachment, which is consistent, rather than from the femoral one, which is not.

Accept that the construct reproduces a function and not a structure, and say so, because the language of anatomical reconstruction does not apply here.

Avoid over-tensioning in extension. Over-constraint of rotation is the complication this anatomy makes available.

Fellowship Level

Clinical Relevance

The argument is about naming, not about function. Three structures at the anterolateral knee restrain internal rotation: the Kaplan fibres, the capsulo-osseous layer of the iliotibial band, and this. Studies that find a discrete ligament and studies that find a capsular thickening are often describing the same tissue approached differently, and a position on the nomenclature changes no operation.

Reconstruction targets a function. Because the femoral attachment is not reproducible between studies, a construct is positioned by what it should restrain and at what flexion angle, rather than by a footprint. That is a different kind of planning from a cruciate reconstruction and it is worth saying out loud.

Over-constraint is the complication the anatomy makes available. A short, thin structure replaced by a stiffer graft tensioned in extension produces a knee that rotates less than normal, and the patient notices that in a way they do not notice a slightly positive pivot shift.

Indication is the live question rather than technique. 3.11.8 and 3.11.9 carry the evidence and the controversies; the anatomy here says only that there is something to reconstruct and roughly where it runs.

The Segond fragment is the one piece of direct evidence a surgeon ever sees. A patient with one has a demonstrated attachment at that point, which is more than most knees offer, and 2.11.4 covers what the fragment contains.