Surgical Anatomy

For Medical Students

Structure and Location

Medial knee surgery is organised around three bony prominences on the femur: the medial epicondyle, the adductor tubercle and the gastrocnemius tubercle.

The medial epicondyle is the most prominent and the easiest to feel. The superficial collateral ligament attaches in the hollow just above and behind it.

The adductor tubercle sits above and slightly behind the epicondyle, and the adductor magnus tendon attaches to it.

The gastrocnemius tubercle sits below and behind the adductor tubercle, and the medial head of gastrocnemius arises there. The posterior oblique ligament attaches just below and in front of it.

On the tibia there are two reference points: the posteromedial tubercle for the direct arm of semimembranosus, and the distal attachment of the collateral ligament about 6 cm below the joint line.

Relations

The saphenous nerve and its infrapatellar branch cross the medial side. The infrapatellar branch runs transversely across the field of most medial incisions.

The pes anserinus tendons lie superficial to the collateral ligament's distal attachment, with a bursa between.

The medial inferior genicular artery runs under the collateral ligament close to the joint line.

The three femoral prominences lie within a few centimetres of each other, so a landmark identified wrongly puts a structure in the wrong place.

Function

Finding the structures means finding the bone first. Soft tissue after injury does not look like soft tissue in a textbook, and the prominences do not change.

Each prominence names a structure: epicondyle for the collateral ligament, adductor tubercle for adductor magnus, gastrocnemius tubercle for the medial head and the posterior oblique ligament.

Operative technique belongs to Section 7, chapters 7.38 to 7.44. This page covers what is where.

Clinical Relevance

The infrapatellar branch of the saphenous nerve is the structure most often injured in medial knee surgery, and numbness below and outside the incision is the result.

An attachment described as on the medial epicondyle is usually drawn too far forward. The collateral ligament attaches behind and above it.

Because the three prominences are close together, they are identified in relation to each other rather than one at a time.

MRCS Level

Structure and Location

Learn the prominences as a set of offsets. Conventional teaching places the adductor tubercle about 12 mm proximal and 3 mm posterior to the medial epicondyle, and the gastrocnemius tubercle about 10 mm distal and 5 mm posterior to the adductor tubercle.

From those, the attachments follow. The collateral ligament sits about 3 mm proximal and 5 mm posterior to the epicondyle. The posterior oblique ligament sits about 8 mm distal and 3 mm anterior to the gastrocnemius tubercle.

On the tibia the semimembranosus tubercle is about 10 mm below the joint line posteromedially, and the collateral ligament's distal attachment about 6 cm below it anteromedially.

The three femoral points sit within a field roughly 25 mm across, which is why they are described by offset rather than by palpation alone.

Relations

The approach is layered, and the layers are the ones 2.9.1 names. Through skin and fascia is layer one and the pes. Beneath that is the collateral ligament, layer two. Beneath that is the capsule, layer three.

The interval between the collateral ligament and the posterior oblique ligament is the working plane for the corner, and it is a plane proximally and not distally.

The saphenous nerve emerges between sartorius and gracilis. Its infrapatellar branch crosses the field transversely and its sartorial branch runs on down the leg.

The medial head of gastrocnemius covers the corner's femoral attachments from behind and is retracted rather than divided.

Blood Supply and Innervation

The medial superior and medial inferior genicular arteries supply the field. The inferior runs close to the joint line under the collateral ligament and is the one most often met.

The descending genicular artery and its saphenous branch accompany the nerve, so the bleeding and the numbness tend to arrive together.

Preserving the vascularity of a ligament being repaired matters here more than on the cruciate side, because the medial structures heal and that is what the repair relies on.

Function

Exposure is planned from the bone outwards. Identify the epicondyle, work to the adductor tubercle, then to the gastrocnemius tubercle, and the attachments are then located rather than hunted.

The distance between structures is small enough that a fixation point for one can compromise another, which is a constraint on any construct that reproduces two medial structures.

7.38 and 7.39 carry repair and reconstruction. This page carries the field they work in.

Clinical Relevance

Find the infrapatellar branch rather than avoid its area. The branch crosses where the incision runs and avoiding the territory is not possible.

Identify all three prominences before placing anything. One identified alone is frequently the wrong one.

Use the semimembranosus tubercle as the posteromedial tibial reference, because it is bone and the joint line is an estimate.

Retract rather than divide the medial head of gastrocnemius where the approach allows it, since its origin shares bone with the posterior oblique ligament.

FRCS Level

Relations

The constraint on the medial femur is crowding rather than hazard. Nothing there will kill a patient, and three attachments compete for a field 25 mm across, so a point placed for one structure can take the bone another needs.

The nerve is the hazard, and it is a hazard to the result rather than to the limb. A numb patch over the anterior shin is the commonest complication of medial knee surgery and it is anatomical rather than technical.

The plane between the collateral ligament and the corner is the only true interval on the medial side, and it is available for the proximal half of the field.

Function

Plan fixation points together rather than in sequence. Two medial structures reconstructed independently will contest the same bone, and the order of placement decides which one gets the correct point.

The offsets are the plan. Palpation identifies the epicondyle reliably and the other two prominences less so, which is why the measurements exist.

Tension is set in a position, and which position depends on which structure. The collateral ligament is tensioned in flexion and the posterior oblique ligament in extension, as 2.9.1 and 2.9.3 describe, so one construct cannot be set at one angle.

Clinical Relevance

Identify the three prominences and mark them before any fixation, because the field is too small to correct an error by eye.

Plan the graft positions for both structures before placing either, since they compete for bone.

Set tension at the angle each structure is tight, not at a single angle for the construct.

Warn about the saphenous branch before operating. It is the commonest complication here and it is predictable from the anatomy.

Preserve vascularity in tissue intended to heal. On this side of the knee repair is a real option, and it depends on the blood supply the approach either keeps or takes.

Fellowship Level

Clinical Relevance

Approach anatomy divides by what is being addressed rather than by preference. A collateral ligament alone is reached through an anteromedial incision over the epicondyle; a corner needs the incision carried posteriorly and the interval opened proximally, where it exists.

In a knee already operated on, the prominences remain and the intervals do not. Scar obliterates the plane between the collateral ligament and the corner, so a revision is planned from bone and not from tissue.

Tunnel convergence is the medial side's version of the tibial crowding problem. A femoral tunnel for a medial reconstruction, one for an anterior cruciate graft and the origin of the medial head of gastrocnemius occupy adjacent bone, and the convergence is in three dimensions rather than on the surface a surgeon can see. 7.39 carries the technique.

In a multiligament knee the medial side is often repairable when the lateral is not, because the vascularity differs. That asymmetry decides sequence as much as any protocol does.

Consider the chronic medial knee as a length problem rather than a continuity problem. The tissue is usually present and usually long, and an operation that reattaches without shortening restores an anatomy that was already failing.

Where the dynamic component is absent, say so in the plan. A static reconstruction in a limb with a wasted medial hamstring restores a limit that will be reached more often than the construct was designed for.