Distal Femur

For Medical Students

Structure and Location

Look at a distal femur from below and you see two convex articular surfaces separated by the intercondylar notch. From the front you see a single saddle, the trochlea, with a groove running down its middle.

The two views are of one continuous surface. The trochlea becomes the condyles at the point where the knee is in early flexion, which is why the patella leaves the trochlea and sits between the condyles as the knee bends further.

On the outside of each condyle, away from the joint, are the epicondyles. Above the medial epicondyle is the adductor tubercle, a small prominence that is easier to find by following the adductor magnus tendon down to it than by palpating for it directly.

Relations

The notch is roofed by bone and floored by the two cruciate ligaments, which cross within it. The middle genicular artery enters the notch from behind to supply them.

The capsule attaches around the articular margin, close to it anteriorly and further from it posteriorly, so the posterior condyles have an intracapsular portion that the anterior surface does not.

The epicondyles are extracapsular. That is why the collateral ligaments arising from them are outside the joint while the cruciates arising inside the notch are within it.

Function

The condyles roll and glide on the tibia. Their profile is not a circle, so the instantaneous centre of rotation moves rather than staying fixed.

The notch holds the cruciates in a position where they stay tensioned through the range rather than becoming slack at one end of it.

The trochlea constrains the patella in the coronal plane while leaving it free to slide proximally and distally.

Clinical Relevance

The adductor tubercle and the epicondyles are the landmarks used to locate the medial and lateral soft tissue attachments through intact skin.

The notch roof appears on a lateral radiograph as Blumensaat's line, which is the single most useful bony landmark on that view.

MRCS Level

Structure and Location

Describe the condyles by comparison rather than by dimension. The medial condyle is longer in the sagittal plane, extends further distally, and its articular surface is more curved. The lateral condyle is broader where it meets the trochlea, projects further anteriorly, and its surface is flatter in the sagittal plane.

The lateral wall of the notch is formed by the medial surface of the lateral condyle and carries the femoral attachment of the anterior cruciate ligament. The medial wall of the notch is the lateral surface of the medial condyle and carries the posterior cruciate attachment. Both are inside the notch, on the surface facing the other condyle, which is the point candidates most often get the wrong way round.

The posterior condyles each carry a facet for the corresponding meniscus at full flexion, and the medial condyle has a flattened area where the posterior horn of the medial meniscus sits.

Relations

The notch contains both cruciates, the fat and synovium around them, and the entering middle genicular vessels.

Immediately posterior to the condyles is the posterior capsule, reinforced by the oblique popliteal ligament, and behind that the popliteal vessels.

The popliteal sulcus on the lateral condyle lies within the capsule, so the popliteus tendon is intra-articular where it crosses from its origin to the muscle belly. The lateral collateral ligament, arising just above and behind it, is not.

The adductor tubercle, the medial epicondyle and the region between them carry the medial patellofemoral ligament, the superficial medial collateral ligament and the adductor magnus insertion in that neighbourhood.

Blood Supply and Innervation

The condylar epiphyses are supplied by branches of the superior and inferior genicular arteries entering through the capsular attachments, and by the middle genicular artery supplying the notch and the cruciates.

The middle genicular is the vessel to name for the intra-articular structures. It arises from the popliteal artery, pierces the posterior capsule, and is the main supply of both cruciate ligaments and of the posterior part of the notch.

Innervation of the condyles and notch is from articular branches of the tibial nerve posteriorly and the femoral nerve anteriorly, with the obturator contributing medially.

Function

Through flexion the contact point on each condyle moves posteriorly while the condyle also rotates, so motion is neither pure rolling nor pure sliding.

The flatter lateral condyle in the sagittal plane allows the lateral side to translate further than the medial, which is the bony reason tibial rotation accompanies flexion.

The difference in curvature between the anterior and posterior parts of each condyle means the ligaments are not tensioned equally at every angle. 3.13 takes that further.

Clinical Relevance

The lateral wall of the notch is the surface the femoral tunnel is placed on in anterior cruciate reconstruction, and the landmarks on it are the subject of 2.7.6.

The posterior condylar surfaces are the reference for femoral component rotation, and their asymmetry means that reference and the transepicondylar axis diverge.

A notch that is narrow leaves less room for the anterior cruciate, and notch shape is cited in discussions of ligament injury risk. The shape is anatomy and belongs here. Whether it predicts injury is an evidence question owned elsewhere.

Because the popliteus tendon is intra-articular, a lateral condylar injury can present with an effusion from a tendon sheath that elsewhere would be outside the joint.

FRCS Level

Relations

The notch is a closed space with fixed walls and a soft tissue content that competes for it. The clinically important relations are therefore between contents rather than between the notch and anything outside it.

Posteriorly the capsule, the oblique popliteal ligament and the popliteal vessels lie in series. The distance between articular cartilage and artery is small and is not increased by flexion as reliably as is often assumed.

Function

Condylar geometry determines which alignment philosophy reproduces a given patient's own kinematics, because the surface being replaced is the surface that produced them.

Two features recur. The asymmetry between the condyles means a symmetrical implant cannot reproduce both sides. The changing radius of curvature means a single radius implant does not reproduce the native relationship between flexion angle and ligament tension.

Neither observation settles a choice. Both explain why the choice exists.

Clinical Relevance

Notch anatomy constrains cruciate reconstruction in three ways: the available volume, the position of the native attachment on the lateral wall, and the obliquity that the wall imposes on any tunnel drilled through it.

Posterior condylar anatomy constrains arthroplasty rotation, and the disagreement between available references is anatomical rather than technical.

The notch is also where bone is removed in a range of procedures. Removing it changes the wall that the cruciate attaches to, which matters in a staged or revision setting in a way it does not in a primary one.