Tibial Footprint

For Medical Students

Structure and Location

The tibial footprint lies in the anterior intercondylar area, in front of and lateral to the medial tibial spine, on a slightly depressed area of bone.

It is broader than the femoral footprint. Conventional teaching gives it as of the order of 17 mm front to back and 11 mm across, and it is roughly oval with the long axis running anteroposteriorly.

It is a shallow fossa rather than a ridge bounded area, so there is no equivalent of the lateral intercondylar ridge to work from.

The anteromedial fibres attach anteromedially within it and the posterolateral fibres posterolaterally, which is where the bundles get their names.

Relations

In front: the anterior horn of the medial meniscus and the transverse intermeniscal ligament.

Laterally and overlapping: the anterior root of the lateral meniscus. The two footprints share bone, which 2.6.4 covers.

Behind: the medial tibial spine, then the posterior intercondylar area with the posterior cruciate.

Above: the roof of the notch, which the ligament runs parallel to in extension. A graft placed too far anteriorly on this footprint meets that roof.

Function

The footprint spreads the ligament's load into bone over an area several times the mid substance cross section.

Its anteroposterior extent is what makes anterior placement possible as an error: the fossa is long enough that a tunnel can sit within the footprint and still be too far forward.

Clinical Relevance

A tibial tunnel placed too anteriorly produces roof impingement in extension, and the knee loses extension or the graft fails.

A tunnel placed on the footprint can still take part of the lateral meniscal anterior root, because the two overlap. Respecting the cruciate footprint does not protect the root.

In a child the footprint sits close to the proximal tibial physis, which is the paediatric constraint on this end.

MRCS Level

Structure and Location

Describe the landmarks in order, because this footprint has to be located without a ridge. The medial tibial spine lies behind and medial. The anterior horn of the lateral meniscus lies lateral and overlaps. The posterior cruciate lies further back. A line between the two tibial spines, and the position of the lateral meniscal anterior horn, are the two references used most often.

The footprint is wider posteriorly than anteriorly in most descriptions, and its centre is the point surgical descriptions refer to rather than its whole area.

A fibrous band often runs forwards from the footprint towards the anterior horn of the lateral meniscus and the intermeniscal ligament, which is why a torn ligament can leave an anteriorly tethered stump.

The bone of the fossa is relatively soft cancellous bone, which matters for fixation at this end.

Relations

The anterior root of the lateral meniscus overlaps the footprint laterally. The anterior root of the medial meniscus lies anteromedial to it. Both are at risk from a tunnel.

Posteriorly, the medial tibial spine and then the posterior cruciate's tibial attachment. A tunnel drilled too posteriorly compromises the notch contents rather than the roof.

Above, the roof of the notch. The relationship between the footprint, the roof and the ligament's obliquity is the geometry behind impingement.

In the immature knee, the proximal tibial physis lies below, and it is further from the footprint than the femoral physis is from its own.

Blood Supply and Innervation

The footprint is supplied from the inferior genicular arteries and from the fat pad anteriorly, in addition to the middle genicular supply reaching the ligament from behind. The tibial end therefore has a second source that the femoral end lacks.

That is relevant to stump preservation and to tunnel healing at this end.

Mechanoreceptors are present near this insertion as well as the femoral, though several descriptions place the higher density proximally.

Function

Load transfer into cancellous bone over a broad area. The breadth is why aperture fixation at the tibia behaves differently from the femur and why tibial fixation is often the weaker end early.

The anteroposterior extent gives the footprint a range of positions with different obliquities, and 3.7 owns what each does.

Roof impingement is a geometric consequence of placement rather than a property of the graft.

Clinical Relevance

Use the posterior aspect of the footprint rather than the anterior when in doubt. Posterior placement risks the notch contents and anterior placement risks extension, and the second is the harder problem to live with.

Inspect the lateral meniscal anterior root after drilling, because overlap means it can be injured without the footprint having been missed.

Expect the tibial end to be the weaker fixation early, because the bone is cancellous and the tunnel is in metaphysis rather than condyle.

The footprint dimensions here are standard teaching values, registered and unchecked, and published measurements differ by method.

FRCS Level

Relations

The relation that decides the tunnel is between the footprint, the notch roof and the intended graft obliquity. Those three cannot be chosen independently.

In revision, the previous tunnel occupies part of the fossa and the bone around it may be poor. The references that survive are the tibial spines and the meniscal horns.

Function

This footprint offers a range of positions rather than a point, and the choice within it trades impingement against notch crowding. That is the practical content of the anatomic placement argument at the tibial end.

Fixation behaves differently here. Cancellous bone, a metaphyseal tunnel and a graft loaded along the tunnel axis combine to make this the end that slips.

Clinical Relevance

Assess extension intraoperatively after graft passage and fixation. Impingement is a placement problem detectable at the time and expensive afterwards.

In revision, grade the tibial bone and the tunnel position preoperatively. A tibial tunnel that has widened is a staging decision, and it is made on imaging.

Where a previous tunnel is anterior, a new posteriorly placed tunnel may be achievable in one stage. Where it is already posterior, it usually is not.

Every published description of this footprint is quantitative and the figures differ. The two here are conventional teaching and registered as unchecked.

Fellowship Level

Clinical Relevance

Three situations where the tibial footprint decides the plan.

The widened tibial tunnel at revision. Tunnel widening is commoner at the tibia, the bone is cancellous, and a graft cannot be fixed in a cavity. The decision is bone graft and stage, or divergent tunnel in one stage, and it is made on preoperative computed tomography rather than at arthroscopy.

The reconstruction with a fixed flexion deficit. Where the tunnel is anterior, the graft meets the roof in extension. Notchplasty treats the symptom; revising the tunnel treats the cause. Which is appropriate depends on how far forward the tunnel is, which is measurable.

Combined cruciate and lateral meniscal root injury. The footprints overlap, so the tunnel and the root repair compete for the same bone. Sequence matters and so does fixation choice, because an anchor placed for the root can occupy the tunnel's path.

In all three the footprint is where it always was. What changes is how much of the fossa is still bone.