Surgical Anatomy

For Medical Students

Structure and Location

Lateral knee surgery is organised around four landmarks: the lateral epicondyle, Gerdy's tubercle, the fibular head with its styloid process, and the biceps femoris tendon.

The lateral epicondyle is the femoral reference. The collateral ligament attaches just above and behind it and the popliteus tendon just in front of and below it.

Gerdy's tubercle is the tibial reference in front, where the iliotibial band attaches. 2.2.4 covers it.

The fibular head and styloid carry the lateral attachments: the collateral ligament on the lateral face of the head, the popliteofibular ligament on the posteromedial styloid.

The biceps tendon is the fourth, and it is the only soft tissue landmark on the list. It is used to find the common peroneal nerve.

Relations

An approach from the outside meets the layers in order: skin, fascia with the iliotibial band and biceps in layer one, the retinaculum in layer two, then the capsule in layer three with the collateral ligament in its superficial lamina and the popliteus tendon in its deep one.

The common peroneal nerve lies outside all of that, behind the biceps tendon. It is met before the ligaments rather than after them.

The inferior lateral genicular artery runs between the two laminae of layer three, close to the joint line.

Conventional teaching places the nerve about 2 cm posteromedial to the biceps tendon at the fibular head.

Function

Finding the bone first is the rule here as on the medial side. Three of the four landmarks are bony and they do not change after injury.

The nerve is the exception and it is found from the fourth landmark, the tendon.

Operative technique belongs to Section 7, chapters 7.45 to 7.50. This page covers what is where.

Clinical Relevance

The nerve is identified before anything else is done. Everything on this side of the knee is approached around it.

The two lateral fibular attachments are on different parts of the bone, a few millimetres apart, so naming the fibular head alone is not enough.

The two femoral attachments are about 18 mm apart, which is close enough that each is described from the epicondyle rather than from the other.

MRCS Level

Structure and Location

Learn the two attachment fields as sets of offsets. On the femur, the collateral ligament sits about 1 mm proximal and 3 mm posterior to the lateral epicondyle, and the popliteus tendon about 18 mm anterior and distal to the ligament.

On the fibula, the collateral ligament sits about 8 mm behind the front edge of the lateral head, and the popliteofibular ligament on the posteromedial styloid.

The fibular styloid carries three attachments in all: the popliteofibular ligament, the arcuate ligament's lateral limb, and the fabellofibular ligament where present.

Conventional teaching places the nerve about 4 cm below the styloid tip where it wraps the fibular neck, which is the point at which it lies on bare bone.

Relations

The interval between the iliotibial band and biceps femoris is the standard posterolateral window. The nerve lies at its posterior edge.

Between the two laminae of layer three is the plane that separates the collateral ligament from the popliteus tendon, marked by the inferior lateral genicular artery.

The popliteal hiatus connects the joint to the posterolateral compartment, which means a structure can be reached from inside the knee as well as from outside.

The lateral head of gastrocnemius covers the posterior corner and is retracted rather than divided.

Blood Supply and Innervation

The lateral superior and lateral inferior genicular arteries supply the field. The inferior is the one encountered, running between the laminae.

The nerve's own supply runs segmentally in its epineurium, so mobilising it over a distance divides the vessels feeding that length. 2.10.6 covers it.

Preserving vascularity matters less here than medially, because lateral repair is less often the plan, but it still decides whether repair remains an option.

Function

Plan the exposure from the nerve outwards rather than from the skin inwards. The nerve is the fixed constraint and the incision is arranged to find it early.

The two femoral points are close enough that a tunnel for one can take the bone the other needs. Both are planned before either is drilled.

Working with the knee flexed relaxes the nerve and opens the posterolateral window, so position is part of the exposure. 7.46 carries the technique.

Clinical Relevance

Identify the nerve first in any posterolateral approach, and record that it was identified.

Mark the two femoral points before drilling either, because 18 mm does not leave room for a correction by eye.

Name the fibular attachment by head or by styloid, since the two lateral structures use different bone.

Flex the knee while working near the fibula. The position relaxes the nerve and improves the view at the same time.

FRCS Level

Relations

Two crowded fields and one nerve describe the lateral side. The femoral field is 18 mm across and holds two attachments; the fibular field is smaller and holds three; the nerve is about 2 cm behind the second of them.

The lamina split is the only true interval and it is available where layer three is intact. In a knee that has been injured or operated on, it may not be.

The popliteal hiatus gives access from inside the joint, which is occasionally the shorter route to a structure the outside approach reaches through scar.

Function

Treat the nerve as the constraint and the attachments as the problem. The nerve limits where an approach can go; the crowding limits where fixation can sit.

Tunnel convergence on the lateral femoral condyle is three dimensional and includes a cruciate tunnel when one is being drilled in the same condyle. The surface distance describes none of that.

Lateral reconstructions are judged on whether they cross the fibula as well as the femur, because rotation is restrained from the fibular attachments. 2.10.3 covers it.

Clinical Relevance

Identify and protect the nerve before any other step, and say so in the operation note.

Plan every tunnel in the condyle together, including the cruciate tunnel where one is planned, and plan them in three dimensions.

Assess whether the lamina split is still available in a revision, and plan from bone where it is not.

Flex the knee for fibular work and keep it flexed, since the nerve relaxes and the window opens together.

Fellowship Level

Clinical Relevance

The approach is chosen by what is being reconstructed. A collateral ligament alone is reached through a short lateral incision over the epicondyle and the fibular head. A corner needs the incision carried proximally and posteriorly, the iliotibial band and biceps interval opened, and the nerve found before anything else.

Revision changes what is available. The bony landmarks remain and the lamina split usually does not, so a revision is planned from the epicondyle, the styloid and the offsets rather than from tissue that will not separate.

Previous tunnels are the harder problem on this side than on the medial, because the lateral condyle is asked to hold more of them. A tunnel from a previous lateral construct, a cruciate tunnel and a popliteus tunnel in one condyle is a planning problem before it is a drilling one.

The nerve in a revision is a different nerve. It has been mobilised, it sits in scar, and the fascial plane that made it findable has been crossed before. Start proximally, in tissue that has not been entered, and work down to it.

Combined medial and lateral reconstruction raises the sequence question, and the vascular asymmetry answers part of it: the medial side repairs and the lateral side usually does not, so the lateral construct is the one that has to be right first time.

Position is a tool throughout. Flexion relaxes the nerve, opens the posterolateral window and changes the angle at which a fibular tunnel meets the bone, and it is available at any point without changing the plan.