Gerdy's Tubercle

For Medical Students

Structure and Location

Gerdy's tubercle is a smooth prominence on the anterolateral surface of the proximal tibia, below the level of the lateral plateau and lateral to the tibial tubercle.

It is palpable in most people, and it is found by following the iliotibial band distally until it stops.

Relations

The iliotibial band inserts on it. That is its defining attachment.

Below and behind it, the muscles of the anterior compartment arise from the lateral surface of the tibia, so the tubercle is the upper limit of that origin.

The anterolateral capsule attaches above it, between the tubercle and the plateau margin.

The lateral collateral ligament and the biceps femoris do not attach here. They pass to the fibula, which lies behind and below.

Function

The tubercle transmits the pull of the iliotibial band to the tibia. Because the band runs from the pelvis, that pull contributes to lateral stability of the knee as well as to extension of the hip's abductor mechanism.

Its position in front of the joint's rotational axis means the band resists internal rotation of the tibia as well as resisting varus.

Clinical Relevance

Gerdy's tubercle is the standard landmark for the anterolateral side of the knee. It locates the iliotibial band's insertion, the upper limit of the anterior compartment, and the starting point for a lateral approach.

It is also the reference used when describing the anterolateral capsular structures, which is where current argument about rotational control is concentrated.

MRCS Level

Structure and Location

The tubercle is a flattened, slightly raised area rather than a sharp prominence, and its upper border blends into the anterolateral capsular attachment while its lower border gives origin to the anterior compartment.

Its relationship to the three other landmarks of the region is what makes it useful: it lies lateral to the tibial tubercle, distal to the lateral plateau margin, and anterior to the fibular head.

Relations

Iliotibial band insertion on the tubercle itself, with the band's deeper fibres attaching more proximally to the lateral femoral condyle before the band reaches the tibia. 2.11.1 owns the band.

The anterolateral capsule and whatever structure is accepted within it attach between the tubercle and the plateau margin.

Tibialis anterior and the extensor group arise below.

The anterior tibial recurrent artery ascends in front of the tubercle to join the genicular anastomosis.

The infrapatellar branch of the saphenous nerve crosses medial to it, and the common peroneal nerve lies posterolaterally at the fibular neck, well away from it.

Blood Supply and Innervation

The tubercle and the surrounding anterolateral cortex are supplied by the inferior lateral genicular artery and by the anterior tibial recurrent artery.

The periosteum is innervated by the recurrent branch of the common peroneal nerve, which also supplies the anterolateral capsule. A painful Gerdy's tubercle therefore refers in the territory of that nerve.

Function

The band acts through this single point, so the whole of its tensile load passes through a small area of cortex.

Because the insertion lies anterior to the axis of tibial rotation and lateral to the sagittal plane, the band restrains both internal rotation and varus, and the relative contribution of each changes with flexion angle. 3.7 owns that.

Clinical Relevance

The tubercle is the starting point for the lateral approach to the plateau, where the band is elevated from it to expose the lateral metaphysis.

It is the tibial fixation point in the lateral tenodesis procedures used for rotational control, and the anatomical argument about those procedures is about where the tibial and femoral points should be. Section 7 owns the procedures.

An avulsion of the anterolateral capsule and bone adjacent to the tubercle is the Segond fracture, associated with anterior cruciate injury. The fracture is pathology and belongs to Section 6; the attachment that avulses is here.

Because the band inserts here and arises from the pelvis, a problem at the tubercle can have its cause above the knee.

FRCS Level

Relations

The structure that matters most here is the one whose identity is disputed. The anterolateral capsule between the tubercle and the plateau margin has been described as a discrete ligament and as a thickening of capsule, and the description chosen changes what a reconstruction is trying to reproduce.

What is not disputed is the tubercle itself, which is why reconstructions are described from it.

Function

Lateral tenodesis works by changing the moment arm of a structure that already resists internal rotation, rather than by adding a new restraint. The tubercle's position is what sets that moment arm.

Moving the tibial fixation point away from the tubercle alters the restraint's direction and therefore the angle at which it is tight, which is the same principle as the femoral attachment argument in the previous chapter.

Clinical Relevance

In anterolateral reconstruction the tibial point is the tubercle or close to it in almost every described technique, and the variation between techniques is at the femoral end. That asymmetry of opinion is itself informative.

In plateau fracture work the band's insertion is the structure released to gain exposure and the structure that must be repaired afterwards.

The anatomical literature on the anterolateral structures is quantitative and contested at once. None of its measurements appears here, and a reviewer should treat this page's description as the uncontested part only.