Popliteus Tendon

For Medical Students

Structure and Location

Popliteus is a short triangular muscle on the back of the upper tibia. Its tendon runs upwards and laterally, enters the joint, and attaches to the lateral femoral condyle.

The femoral attachment is in a groove on the lateral condyle called the popliteal sulcus, in front of and below the attachment of the lateral collateral ligament. Conventional teaching separates the two centres by about 18 mm.

The tendon is intra-articular but outside the synovium, the same arrangement as the cruciate ligaments.

On its way it passes through the popliteal hiatus, a gap in the attachment of the lateral meniscus to the capsule. That gap is why the lateral meniscus is attached around only part of its border.

Fibres run from the tendon to the lateral meniscus as the popliteomeniscal fascicles, which 2.6.2 covers.

Relations

Above and behind it: the lateral collateral ligament, crossing superficial to it.

Below it: the popliteofibular ligament running down to the fibular styloid, which 2.10.3 covers.

Medially, as the muscle: the posterior tibia and the popliteal vessels lying on it.

Through the hiatus: the lateral meniscus, which it is attached to by the fascicles and separated from by the gap.

Function

As a muscle it rotates the tibia internally, or the femur externally when the foot is on the ground. Either way it unlocks the knee from full extension, which is the function it is known for.

As a tendon it is a static restraint to external rotation and to varus.

Through the fascicles it pulls the lateral meniscus backwards in flexion, keeping it out of the way of the advancing femoral condyle, the same job semimembranosus does on the medial side.

Clinical Relevance

The popliteal hiatus is the anatomical reason the lateral meniscus moves roughly twice as far as the medial one through flexion.

Because the tendon is both muscle and ligament, a lateral injury can leave the static restraint intact and the dynamic one gone, or the reverse.

The tendon is a landmark at arthroscopy: finding it identifies the lateral compartment and the hiatus beside it.

MRCS Level

Structure and Location

Call the whole thing the popliteus complex: the muscle, the tendon and the popliteofibular ligament. Treating any one alone misdescribes the function.

The muscle arises from the posterior tibia above the soleal line and runs upwards and laterally. Conventional teaching gives the tendon a length of about 55 mm from musculotendinous junction to femoral attachment.

The femoral attachment is anterior and distal to the collateral ligament's, which is the opposite of what most people guess from the muscle's position. The tendon crosses under the ligament to reach it.

Three popliteomeniscal fascicles are usually described, anteroinferior, posterosuperior and posteroinferior. 2.6.2 carries them.

Relations

The tendon lies in the deep lamina of layer three, and the collateral ligament in the superficial lamina. That is what lets the two be separated at operation.

The inferior lateral genicular artery runs between the laminae, close to the hiatus.

The popliteofibular ligament leaves the musculotendinous junction and runs to the fibular styloid, so the complex is anchored to two bones.

The common peroneal nerve lies posterolateral to the whole complex, outside the capsule and behind the biceps tendon.

Blood Supply and Innervation

Blood supply to the muscle is from the popliteal artery directly and from the inferior genicular arteries; to the tendon, from the lateral genicular vessels.

The nerve supply is the tibial nerve, which is worth stating beside 2.10.5: biceps femoris has one head on each division of the sciatic nerve, and popliteus has only the tibial.

The tendon carries mechanoreceptors near its femoral attachment, consistent with a structure that reports rotation.

Function

Through flexion the muscle's internal rotation moment keeps the lateral femoral condyle tracking on the lateral plateau as the femur rolls back.

The static restraint to external rotation is shared between this tendon and the popliteofibular ligament, with the ligament carrying more. 3.10.4 and 3.10.5 carry the proportions.

The fascicles make meniscal position partly dynamic, so a working muscle changes where the lateral meniscus sits under load.

Clinical Relevance

Read the dial test as a test of this complex rather than of a single structure. 3.10.7 covers the biomechanics and 4.13 the examination.

Expect lateral meniscal mobility to be the normal finding at arthroscopy. The hiatus is anatomy, not pathology.

Identify the tendon at arthroscopy before working in the lateral compartment, because it and the fascicles are the landmarks that orient the hiatus.

Protect the fascicles during lateral meniscal work. They are the meniscus's attachment where the coronary ligament is absent.

FRCS Level

Relations

The femoral attachments of the tendon and the collateral ligament sit about 18 mm apart in a field where a reconstruction needs two tunnels. The anatomy sets the spacing and the spacing sets the convergence risk.

The tendon crosses from deep to superficial relative to the collateral ligament as it runs forward, so a graft routed along the tendon's path is not routed along the ligament's.

The hiatus is a defect in the meniscal attachment and a route into the posterolateral compartment. Both matter and they are the same opening.

Function

Treat the complex as the rotational restraint of the lateral side and the collateral ligament as the coronal one. An anatomical reconstruction reproduces both because the anatomy separates them.

Its dynamic component cannot be grafted, as on the medial side. A reconstruction restores the static tendon and not the muscle that tensions it.

Loss of the complex changes lateral meniscal position as well as rotation, which is a second consequence of a single injury.

Clinical Relevance

Plan the femoral tunnels for this tendon and the collateral ligament together and in three dimensions. Eighteen millimetres on the surface is not 18 mm along the tunnel.

Assess rotation at 30 and at 90 degrees before deciding what the complex has lost. 3.10.7 covers why both angles are needed.

Preserve the fascicles where a repair allows it, because they carry meniscal position and nothing else does at the hiatus.

Avoid treating an isolated popliteus injury as a common finding. The anatomy binds the three primary structures closely enough that one rarely fails alone.