Deep MCL

For Medical Students

Structure and Location

The deep medial collateral ligament is not a separate ligament in the way the superficial one is. It is the central part of the capsule, layer three, thickened where it crosses the joint line.

It attaches to the edge of the medial meniscus on its way past, and that attachment divides it into two named parts. Above the meniscus is the meniscofemoral portion. Below it is the meniscotibial portion, also called the coronary ligament.

The meniscofemoral portion is the longer and thinner of the two. The meniscotibial portion is short and stout, and it attaches to the tibia just below the articular margin.

A bursa separates it from the superficial ligament, so the two are free to move on each other despite lying one on the other.

Relations

Superficial to it: the bursa, then the superficial medial collateral ligament.

Deep to it: the joint itself. This is a capsular structure, so the synovium is the next layer in.

Attached to it: the medial meniscus, along the whole of its medial border.

Behind it: the posteromedial capsule and the posterior oblique ligament, with which it merges rather than ending.

Function

It is a secondary restraint to valgus. The superficial ligament carries most of that load and this one carries the remainder.

Its larger job is to anchor the medial meniscus. The meniscus is held along its whole medial border, which is why it moves far less than the lateral meniscus does.

Because it crosses the joint line, it is loaded by rotation as well as by valgus.

Clinical Relevance

The anchoring explains the pattern of meniscal tears on the medial side. A structure held at its rim and loaded in rotation tears rather than displaces.

An injury to the meniscotibial portion detaches the meniscus from the tibia while the meniscus itself stays intact, which is an anatomical separation rather than a tear. 6.14 to 6.20 cover what follows from it.

Because it is capsular, swelling from a deep injury enters the joint. A superficial ligament injury need not produce an effusion and a deep one usually does.

MRCS Level

Structure and Location

Conventional teaching gives the meniscofemoral portion a length of the order of 20 mm and the meniscotibial portion of the order of 5 mm. The disparity is the point: one tethers and the other suspends.

The meniscotibial attachment lies within a few millimetres of the articular surface, so there is little bone between the attachment and the joint.

The thickening is greatest in the middle third of the medial side and fades anteriorly and posteriorly, where the capsule becomes thin in front and merges with the posterior oblique ligament behind.

It carries no attachment to the superficial ligament. The two are separated along their whole shared length by the bursa.

Relations

The medial meniscus is attached along its border, not at points. Compare the lateral side, where the popliteus tendon interrupts the attachment and the meniscus is free over that segment. 2.6.2 covers that.

The medial inferior genicular artery runs between this ligament and the superficial one close to the joint line.

Posteriorly it is continuous with the posteromedial capsule and the structures 2.9.4 describes, so the border between a deep ligament injury and a corner injury is anatomical rather than sharp.

Blood Supply and Innervation

Supply is from the medial genicular arteries, reaching it through the capsule rather than along a separate route.

Because it is capsular and peripheral, it lies in the vascular zone of the meniscus. That is the anatomical basis for repairing a peripheral detachment rather than removing tissue.

Nerve supply is from the medial articular branches, with free nerve endings in the capsule accounting for the pain of a deep injury.

Function

Its contribution to valgus restraint rises when the superficial ligament is injured, which is why a combined injury opens more than a simple sum would predict.

It controls the position of the posterior horn of the medial meniscus through the arc of flexion. A meniscus tethered along its rim moves little, and the little it moves is governed here.

It restrains external rotation as a secondary structure. 3.9.4 carries the quantitative picture.

Clinical Relevance

Expect an effusion with a deep injury and not necessarily with a superficial one. The capsule is the boundary and this ligament is part of it.

Read a meniscotibial detachment as a separation rather than a tear, because the treatment follows the anatomy: peripheral tissue in a vascular zone reattaches.

Look for a combined pattern when valgus laxity exceeds what a superficial injury explains. The deep ligament is the next structure in the sequence.

Preserve the meniscal attachment where an approach crosses it. Detaching it to see the joint removes the anchor this page describes.

FRCS Level

Relations

The anatomical sequence from skin to joint on the medial side is fascia, superficial ligament, bursa, this ligament, synovium. An approach that reaches the joint has crossed all five, and each one is a structure rather than a plane to be opened without thought.

The meniscal attachment is the only continuous ligamentous attachment either meniscus has, and it is the reason the medial compartment tolerates less rotation than the lateral.

Posteriorly the ligament has no edge. It becomes the posteromedial capsule, so an injury described as deep ligament and an injury described as posteromedial corner can be the same injury seen from different sides.

Function

Treat it as the structure that converts a meniscus from a free spacer into a loaded wedge. A meniscus that cannot move cannot escape load, which is the mechanical cost of the anchoring this ligament provides.

Its share of valgus restraint is small in an intact knee and material in an injured one, so sequential sectioning figures overstate its role less than they understate it. 3.9.4 carries that.

Loss of the meniscotibial portion changes the posterior horn's position under load, which alters contact area without altering the meniscus itself.

Clinical Relevance

Assess the meniscal attachment when planning any medial opening. Releasing it gives exposure and takes the anchor with it.

Consider reattachment rather than excision for peripheral detachment, because the tissue is vascular and the anatomy supports healing.

Document whether an injury is deep, superficial or both, since the three behave differently and the examination can separate them.

Avoid treating the posteromedial border as a dividing line between this ligament and the corner. The anatomy is continuous and so is the injury.