Surgical Anatomy

For Medical Students

Structure and Location

Anterior cruciate surgery is done through the notch, reached through the standard anterior portals with the camera usually anterolateral.

The notch is a fixed space containing both cruciates, their synovial covering, fat and the entering middle genicular vessels. Working in it means removing or displacing some of that.

The landmarks are the lateral wall of the notch with its intercondylar ridge, the articular margins, the notch roof, and the tibial footprint with the tibial spines behind it.

Relations

In front of the notch: the fat pad, which obstructs the view and is partly resected.

Behind the notch: the posterior capsule, then the popliteal vessels. Anything passed posteriorly from inside the notch is directed at them.

Laterally: the lateral wall and, beyond the condyle, the lateral structures and the iliotibial band where a femoral tunnel exits.

Below: the tibial footprint, the meniscal anterior horns and the intermeniscal ligament.

Function

The notch is the only route to both footprints, and it is a space shared with the posterior cruciate. Everything about access is a compromise between seeing the footprint and preserving what is around it.

Flexion angle changes what is reachable. The femoral footprint is reached at different angles depending on the technique, and the trajectory available changes with the knee's position.

Clinical Relevance

The structure most at risk from a posteriorly directed instrument is the popliteal artery, and the capsule is all that separates them.

Clearing the lateral wall to bone to find the intercondylar ridge is part of the operation, because the footprint cannot be located reliably without it.

Operative technique belongs to 7.20 onwards. This page is the working space.

MRCS Level

Structure and Location

Name the landmarks in the order they are used. The fat pad, partly resected for the view. The lateral wall, cleared to bone. The lateral intercondylar ridge, marking the anterior limit of the femoral footprint. The bifurcate ridge where present. The posterior articular margin, limiting how posteriorly a tunnel can go. The notch roof, which an anteriorly placed graft meets. The tibial footprint and the medial tibial spine behind it.

Portals. Anterolateral for the camera. Anteromedial for instruments, placed under needle localisation at a level and angle chosen for the femoral wall. An accessory anteromedial portal is made lower and more medially where a femoral tunnel is to be drilled through it, and the trajectory it gives is the reason it exists.

A transtibial trajectory reaches the femoral footprint through the tibial tunnel and constrains both. An independent femoral trajectory separates them. 7.20 owns the comparison; the anatomical point is that one tunnel constrains the other only in the first.

Relations

Posterior capsule and popliteal vessels behind. The margin is capsule alone and flexion does not reliably increase it.

The posterior wall of the lateral condyle behind the femoral footprint, thinner than it appears, and assessed before drilling.

The articular cartilage of the medial femoral condyle, which an instrument passed through a low anteromedial portal can scuff. That is the commonest iatrogenic injury in this operation.

The lateral meniscal anterior root at the tibial footprint, overlapping it.

At the femoral tunnel exit, the lateral condyle's outer surface and the lateral structures. 2.1.4 covers them.

Blood Supply and Innervation

The middle genicular artery enters the notch from behind and supplies both cruciates. Debriding the notch divides it.

The stump carries the vascular and neural supply, so remnant preservation preserves both and costs visualisation. 2.7.4 and 2.7.5 cover the trade.

The fat pad is richly innervated and routinely disturbed, which is a source of postoperative anterior knee pain independent of the graft.

Function

Visualisation and trajectory are the two problems and they compete. A remnant that is preserved obscures the footprint; a fat pad that is preserved obscures the notch; a knee flexed for one trajectory closes another.

The notch is a fixed volume, so graft diameter, notch width and the presence of the posterior cruciate together determine whether impingement occurs.

Every trajectory is bounded by four things: the posterior wall, the articular margins, the notch roof and the physes in an immature knee.

Clinical Relevance

Localise the anteromedial portal with a needle and choose its level for the femoral wall, not by habit. An accessory portal placed late is harder than one planned.

Protect the medial femoral condyle cartilage when passing instruments through a low medial portal. Scuffing it is common, avoidable and permanent.

Clear the lateral wall and identify the intercondylar ridge before drilling. Where no ridge is visible, the articular margin is the fallback reference.

Check extension after fixation to exclude impingement, which is a placement problem detectable at the time.

No portal measurement appears on this page. Published portal positions are distances from the tendon and the joint line and none could be verified here.

FRCS Level

Relations

In revision the landmarks may be gone. Previous tunnels, hardware and scar alter the wall, and the references that survive are the articular margins and the overall geometry of the notch.

The relation between existing hardware and the intended trajectory is a preoperative question answered on computed tomography, not an intraoperative discovery.

Function

Access determines placement and placement determines outcome, so access is not a preliminary to the operation; it is the operation.

The notch's fixed volume is the constraint that does not yield. A larger graft, a retained remnant and a narrow notch cannot all be accommodated, and choosing which to give up is the decision.

Clinical Relevance

Plan the portals, the trajectory and the staging from preoperative imaging in every revision. Converting a plan mid procedure in a notch with altered landmarks is where placement errors are made.

Where hardware obstructs the trajectory, decide in advance whether it is removed, worked around, or the procedure staged.

In the immature knee the trajectory is constrained by both physes, and the femoral one is closer to its footprint. Section 10 owns the technique choice.

In the multi-ligament knee the notch is approached in a knee that may have a devascularised capsule and an altered posterior margin, and the vessels are the limit rather than the landmarks.

Fellowship Level

Clinical Relevance

Four situations where the notch is the operation rather than the route to it.

The revision with converging tunnels. Whether a new femoral tunnel can avoid the old one is geometry, answered on computed tomography. One stage where it can, bone graft and stage where it cannot. Deciding at arthroscopy means deciding with a drill in hand.

The narrow notch with a large graft. The options are a smaller graft, a notchplasty, or accepting impingement. A notchplasty alters the wall the footprint sits on, which matters if the knee is ever revised, so it is not a free choice.

The multi-ligament knee. The capsule may be injured, the posterior margin altered and the vessels closer than normal. The notch landmarks are intact and the thing limiting the operation is behind them. Vascular assessment precedes reconstruction.

The immature knee. Both physes bound the trajectory and the femoral footprint is the closer of the two to its physis. Physeal sparing, partial transphyseal and transphyseal techniques are three answers to that geometry, and skeletal age decides. Section 10 owns it.

In all four the notch is the same space described on the first page of this chapter. What changes is how much room there is in it.