Blood Supply

For Medical Students

Structure and Location

The anterior cruciate ligament is supplied by the middle genicular artery. It arises from the popliteal artery, pierces the posterior capsule, and reaches the ligament through its synovial covering.

There is a small additional contribution at the tibial end from the inferior genicular arteries through the fat pad and the infrapatellar synovium.

The vessels run on the surface of the ligament in the synovial sheath and send branches inwards between the fascicles, running along the ligament rather than across it.

The mid substance is the least well supplied part. The tissue near each insertion is better supplied, partly from the bone.

Relations

The artery reaches the notch from behind, so it crosses the posterior capsule with the posterior cruciate's supply.

It supplies both cruciates. The two ligaments share one main vessel, which is unusual for two structures that fail independently.

The synovial sheath is the route. Anything that strips the sheath removes the supply, whatever happens to the collagen.

Function

A tissue with a blood supply can mount a healing response. A relatively avascular tissue cannot do so reliably.

The middle genicular supply is adequate to maintain the ligament and inadequate to heal a complete mid substance rupture. That is the practical summary.

Clinical Relevance

Mid substance anterior cruciate rupture does not heal reliably, and this is why. It is not a matter of the ends being apart; it is the vascular and cellular state of the tissue between them.

A medial collateral ligament injury heals because it is extracapsular with a soft tissue supply. A cruciate does not because it is intra-articular with one vessel. Comparing the two is the quickest way to make the point.

Haemarthrosis after injury comes partly from this artery, which is why an acute cruciate rupture usually produces a tense swollen knee within hours.

MRCS Level

Structure and Location

Name the route in order: popliteal artery, middle genicular artery, posterior capsule, notch, synovial sheath, periligamentous vessels, endoligamentous branches between fascicles.

The periligamentous plexus on the surface is richer than anything inside the ligament. The intraligamentous supply is sparse and longitudinal.

At the tibial insertion the inferior genicular arteries and the fat pad contribute, so the distal end has a second source. The femoral insertion depends more completely on the middle genicular and on the bone.

Conventional teaching describes the mid substance as relatively hypovascular rather than avascular. It has a supply; it is a poor one.

Relations

The middle genicular artery is a relation of the posterior capsule before it is a supply of the ligament. A posterior capsular injury or a posteriorly directed instrument threatens it.

It supplies both cruciates, the posterior part of the notch, and the meniscal roots and meniscofemoral ligaments in that region. Everything intra-articular in the posterior notch shares it.

The synovial sheath is continuous with the notch synovium and with the fat pad anteriorly, which is the route of the secondary supply.

Blood Supply and Innervation

Supply and innervation share the route, both arriving through the posterior capsule alongside the artery and travelling in the synovial sheath.

The consequence is that a procedure or an injury that devascularises the ligament also denervates it, and the sensory loss after rupture is not separable from the vascular loss.

Vascularity falls with age, which is one of several age related changes in the ligament and is relevant to the discussion about repair in younger patients.

Function

The supply maintains matrix turnover rather than supporting repair. A ligament that is intact remodels; one that has ruptured in its mid substance does not reconstitute.

Proximal avulsion behaves differently. Where the tear is at the femoral end and the synovial sheath is intact, the vascular route is preserved and the tissue is better supplied, which is the biological basis of the repair argument.

Partial tears with an intact sheath may heal, and that observation is consistent with the anatomy rather than contradicting it.

Clinical Relevance

Preserving the stump at reconstruction preserves a vascular and neural source, which is the rationale behind remnant preserving techniques. Section 7 owns the comparison and the anatomy is here.

Repair candidacy is a vascular judgement: tear level, sheath integrity and tissue quality. All three are assessed arthroscopically and all three are anatomical.

Haemarthrosis volume and timing reflect this artery. A knee that swells within an hour of a twisting injury has bled, and the differential is cruciate rupture, patellar dislocation, osteochondral fracture or peripheral meniscal tear.

Devascularisation and denervation occur together, so a reconstructed knee is not simply a mechanically restored one.

FRCS Level

Relations

The middle genicular artery's course through the posterior capsule makes it a relation of posterior cruciate surgery as well as a supply of the anterior. A transtibial posterior cruciate tunnel is directed at the region it crosses.

In revision, previous surgery may have divided the periligamentous plexus and the synovial sheath, so a remnant that looks preserved may not be vascularised.

Function

This page is the biological ceiling on everything in Section 7. No technique changes the supply, and the supply is why reconstruction rather than repair became standard.

The current interest in repair is an argument about which subgroup has favourable vascular anatomy, not an argument that the anatomy has changed.

Clinical Relevance

Select repair candidates on sheath integrity and tissue quality, and accept that the evidence for durability is not settled. The anatomy supports the attempt in a narrow group and does not support it generally.

Remnant preservation has a vascular and a proprioceptive rationale, and its cost is visualisation. That trade is anatomical.

In multi-ligament injury the middle genicular artery may be injured along with the capsule, and a devascularised notch changes what any reconstruction can achieve.

No quantitative vascular data appears on this page. Vessel density and perfusion measurements exist in the literature and none could be verified here.