Retinacula

For Medical Students

Structure and Location

The retinacula are the fibrous sheets on either side of the patella that hold it in place and transmit part of the quadriceps pull to the tibia.

The medial retinaculum carries the medial patellofemoral ligament in its deep layer, together with the medial patellotibial and patellomeniscal ligaments below it.

The lateral retinaculum has a superficial oblique layer from the iliotibial band to the patella, and a deep transverse layer running from the band directly to the patellar border.

The deep transverse part of the lateral retinaculum is the strongest component and it is sometimes called the lateral patellofemoral ligament.

Both retinacula blend with the joint capsule beneath them, so neither has a clean deep border.

Relations

Medially: vastus medialis obliquus above, the medial patellofemoral ligament within, and the capsule beneath. 2.12.2 covers the ligament.

Laterally: the iliotibial band above and behind, the vastus lateralis expansion in front, and the capsule beneath. 2.11.1 covers the band.

In front of both: the prepatellar tissues and skin.

Below both: the patellotibial parts running to the tibia on either side of the patellar tendon.

Function

They hold the patella centred, with the medial side resisting lateral movement and the lateral side resisting medial movement.

They transmit part of the quadriceps force to the tibia directly, bypassing the patella, which is why a patient with a fractured patella can sometimes still extend the knee.

The patellotibial parts restrain the patella from riding up as the knee extends.

Clinical Relevance

The lateral retinaculum is tight in some patellofemoral problems and releasing it is an old operation. The anatomy says why that is not minor: the deep transverse layer is a ligament and dividing it removes a restraint.

Over-release of the lateral side can let the patella move medially, which is harder to treat than the problem it was meant to fix.

Because the retinacula transmit force to the tibia, an intact retinaculum can mask a patellar or tendon injury on examination.

MRCS Level

Structure and Location

Set the medial side out by layer: layer one fascia, layer two carrying the patellofemoral ligaments, layer three the capsule. The retinaculum is layers one and two together.

On the lateral side, name three components: the superficial oblique retinaculum from the iliotibial band, the deep transverse retinaculum or lateral patellofemoral ligament, and the patellotibial band running to the tibia.

Conventional teaching gives the lateral patellofemoral ligament a width of the order of 15 mm where it reaches the patella.

The iliopatellar band is the anterior expansion of the iliotibial band into the lateral retinaculum, which is why lateral patellar restraint depends partly on a structure that crosses the hip. 2.11.1 covers it.

Relations

The lateral superior and inferior genicular arteries run in the lateral retinaculum, and a lateral release divides them.

The infrapatellar branch of the saphenous nerve crosses the medial side, as 2.9.7 covers.

The medial and lateral patellomeniscal ligaments attach to the anterior horns of the menisci, linking patellar position to meniscal position.

Both retinacula blend with the capsule, so a release that is intended to be extracapsular often is not.

Blood Supply and Innervation

The genicular anastomosis runs in and around both retinacula, with the superior and inferior genicular arteries on each side.

Dividing the lateral retinaculum divides part of that anastomosis, which matters for patellar vascularity when other procedures have also been done.

Both retinacula are richly innervated by articular branches, and the lateral retinaculum in particular carries nerve fibres that have been implicated in anterior knee pain. 6.59 covers that.

Function

The medial side's passive restraint is mostly the medial patellofemoral ligament, so the retinaculum around it contributes less than its size suggests.

The lateral side's deep transverse layer is the main passive medial restraint and is loaded when the patella is pushed medially.

Retinacular force transmission to the tibia means the extensor mechanism has a path that does not pass through the patella at all. 3.12.1 covers tracking.

Clinical Relevance

Test medial and lateral patellar translation separately, because the two sides restrain in opposite directions and one can be lax while the other is tight.

Expect a lateral release to divide vessels and a ligament, and record what was divided.

Consider medial patellar instability in a patient with pain after a previous lateral release, since the anatomy makes it possible.

Preserve the deep transverse layer where a lengthening rather than a release will serve, and 7.55 covers the techniques.

FRCS Level

Relations

The lateral retinaculum's continuity with the iliotibial band means lateral patellar tightness can originate above the knee. That is an anatomical route for a hip problem to present at the patella.

Both retinacula blend with capsule, so the distinction between a retinacular and a capsular procedure is not as clean as the names imply.

The genicular anastomosis in the lateral retinaculum is part of the patella's blood supply, which constrains how much can be divided in a knee that has had other anterior surgery.

Function

Treat the lateral deep transverse layer as a ligament and not as tight tissue. Releasing a ligament is a decision, and the fact that it was done routinely for years does not make it a small one.

Medial restraint is concentrated in the medial patellofemoral ligament, so medial retinacular plication reproduces little of what that ligament does. 3.12.5 covers it.

Retinacular transmission to the tibia is the reason an extensor mechanism can be partly competent with a disrupted patella, which affects what a straight leg raise actually tests.

Clinical Relevance

Assess for iliotibial band tightness and hip function when the lateral side is tight, because the anatomy connects them.

Prefer lengthening to release where the deep transverse layer is the tight structure, since removing it risks medial instability. 7.55 carries the technique.

Consider patellar vascularity before dividing the lateral retinaculum in a knee with previous anterior surgery.

Avoid relying on medial plication to do the work of a ligament reconstruction. The anatomy puts the restraint in the ligament.