Surgical Anatomy

For Medical Students

Structure and Location

The medial meniscus is reached arthroscopically through two portals in front of the knee, one either side of the patellar tendon, with the camera usually in one and the instrument in the other.

The anterolateral portal is made first and is the usual viewing portal. The anteromedial portal is made under direct vision, which is why it can be placed to suit the lesion.

From the front, the anterior horn and body are seen directly. The posterior horn is seen by looking across the joint from the opposite portal, and the far posterior part of the horn is the hardest thing in the compartment to see.

Relations

In front of the joint the portals pass close to the patellar tendon medially and laterally, the fat pad behind it, and the infrapatellar branch of the saphenous nerve on the medial side.

The medial compartment is bounded above by the femoral condyle, below by the plateau, and medially by the capsule with the collateral ligament outside it.

Outside the posteromedial capsule, and therefore immediately behind a needle or suture passed from inside, lie the saphenous nerve and the long saphenous vein.

Function

Access to the medial compartment is limited by how far the joint can be opened. The medial side is the tight one, because the collateral ligament is short and the meniscus is tethered.

Flexion angle and valgus stress change what is reachable. The posterior horn is best seen in slight flexion with valgus; the anterior horn needs more extension.

Clinical Relevance

A tight medial compartment is the commonest reason a medial meniscal procedure is difficult, and it is anatomical rather than a matter of skill.

The saphenous nerve behind the posteromedial capsule is the structure at risk in posterior horn repair, and it is why an accessory posteromedial portal is made with care.

Operative technique belongs to 7.8 onwards. This page is what is where.

MRCS Level

Structure and Location

Portal anatomy. The anterolateral portal sits lateral to the patellar tendon, above the joint line and below the patella. The anteromedial portal sits medial to the tendon at a level chosen for the lesion, made with a needle first so its trajectory is checked before the skin is cut.

An accessory posteromedial portal is made for posterior horn work, behind the medial collateral ligament and above the joint line, with the saphenous structures the reason it is localised with a needle under vision.

The diagnostic sequence through the medial compartment runs anterior horn, body, posterior horn, then the posteromedial recess, and the posterior horn is seen last because it needs the most manipulation.

Relations

Instrument trajectory matters more than portal position. A portal too far from the tendon reaches the compartment at a shallow angle; too close and the tendon limits movement.

The posteromedial capsule separates the joint from the saphenous nerve and vein. Any needle, suture passer or anchor directed posteromedially from inside the joint is aimed at them.

The medial collateral ligament is outside the capsule and limits how far the compartment opens. Pie crusting it is a described manoeuvre and is a decision to trade stability for access, owned by Section 7.

The fat pad obstructs the view anteriorly and is often partly resected, with the consequences noted on 2.4.5.

Blood Supply and Innervation

The structures at risk are sensory rather than vascular on this side. The infrapatellar branch of the saphenous nerve crosses the anteromedial portal site and the saphenous nerve itself lies posteromedially.

The vascular structure that matters is the perimeniscal plexus, which a repair suture passes through deliberately. Preserving the capsular tissue preserves the plexus.

The popliteal vessels are a relation of the posterior compartment rather than the medial one, but a suture passed from the medial compartment in a posterolateral direction can reach them.

Function

Visualisation and access are separate problems. The posterior horn can often be seen and not reached from the same portal, which is why instruments and camera are swapped.

The compartment opens with valgus stress and with flexion, and the two are adjusted together. A knee that will not open is a knee in which a repair cannot be placed accurately.

Accurate suture placement depends on reaching the tear perpendicular to its plane, so portal position is chosen from the tear rather than from habit.

Clinical Relevance

Localise an accessory posteromedial portal with a needle under vision every time. The saphenous structures are the reason and there is no substitute for seeing where the needle enters.

In a tight medial compartment, forcing instruments risks iatrogenic cartilage damage, which is the commonest avoidable complication of medial meniscal arthroscopy.

Repair sutures should pass through the capsular tissue carrying the perimeniscal plexus, because that tissue is the healing source.

Portal placement should follow the imaging. A posterior horn tear and an anterior horn tear are reached from different anteromedial positions.

FRCS Level

Relations

The anatomical constraint that cannot be worked around is the medial collateral ligament's length. Everything else about access is adjustable; that is not, except by releasing it.

In a stiff or previously operated knee, capsular scarring reduces the compartment further and the posteromedial recess may be obliterated, so the usual route to the posterior horn may not exist.

Function

Access determines what operation is possible, which means it determines the operation. A repairable tear that cannot be reached accurately will be resected, and that outcome is decided by anatomy and planning rather than by intent.

Pie crusting the collateral trades a small amount of medial stability for access. Whether that trade is right depends on what the access buys, and Section 7 owns it.

Clinical Relevance

Plan portals and the need for an accessory portal before starting, from the imaging. Converting mid procedure is harder than planning for it.

Where the compartment will not open enough for accurate repair, the honest options are to release, to accept resection, or to stop and refer. Forcing is not one of them.

In revision meniscal surgery assume the posteromedial recess is scarred and plan a route accordingly.

No measurement of portal position appears on this page. Published portal descriptions are given in distances from the tendon and the joint line, and those are values this page cannot verify.

Fellowship Level

Clinical Relevance

Three situations where medial compartment access is the operation rather than a step in it.

The tight compartment with a repairable posterior horn tear in a young patient. The decision is whether to release the medial collateral to gain access. Releasing it is a deliberate, small, reversible injury that buys the ability to save a meniscus; not releasing it usually means resecting the meniscus. Stated that way the trade is clearer than it looks at the time.

The ramp lesion at the meniscocapsular junction. It sits in the posteromedial recess, it is missed from the standard anterior view, and finding it needs either a transnotch view or a posteromedial portal. The anatomy is the whole problem: the lesion is in the one place the routine examination does not look.

The previously operated posteromedial corner. Scar replaces the recess, the saphenous structures may be tethered to the capsule, and needle localisation becomes more important rather than less.

In all three the compartment itself is unchanged from the medical student page. What changes is that the access is the limiting factor rather than the pathology.