Tunnel View

For Medical Students

What It Shows

A tunnel view projects through the intercondylar notch with the knee flexed, so the notch is seen open rather than foreshortened. 5.2.2 covers the image formation.

That brings the notch walls, the posterior parts of the condyles and the intercondylar region into view. 5.3.14 covers avulsion injuries.

It matters because a loose body, an osteochondral lesion or a notch osteophyte can be invisible on the standard views and visible here. 5.11.5 covers osteochondral lesions.

How It Is Acquired

Flex the knee and angle the beam so the notch is projected along its own axis. 5.2.5 covers magnification.

Keep the flexion and beam angle consistent, since both change which part of the condyle is profiled. 5.3.5 covers the Rosenberg view.

Look specifically in the notch and at the posterior condylar surfaces, which is what the view is for. 5.11.6 covers OCD.

Assess the notch width, since notch narrowing accompanies arthritis and has been associated with cruciate injury. 5.7.1 covers the normal cruciate.

Pair it with the standard views rather than using it alone. 5.3.1 covers the anteroposterior view.

What Normal Looks Like

An open intercondylar notch with smooth walls and no bony fragment within it.

Smooth posterior condylar articular surfaces. 5.11.1 covers normal cartilage.

A notch of proportionate width relative to the condyles. 5.7.1 covers the normal cruciate.

No separate ossific density in the joint. 5.14.6 covers synovial chondromatosis.

What Abnormal Looks Like

A loose ossific body within the notch or the posterior joint. 5.14.6 covers synovial chondromatosis.

A lucent or fragmented area of the condyle, typically the lateral aspect of the medial condyle. 5.11.6 covers OCD.

Notch osteophyte narrowing the notch. 5.3.18 covers osteophytes.

An avulsed bony fragment at the cruciate attachment. 5.3.14 covers avulsion injuries.

MRCS Level

How It Is Acquired

In a viva this is the view to request when a loose body or an osteochondral lesion is suspected and the standard films are normal.

The expected points are the flexion and beam angle, the consistency, the notch and posterior condyles, the notch width, and the pairing.

Say that this view finds what the standard views foreshorten. 5.3.1 covers the anteroposterior view.

Say that the classic osteochondritis dissecans site is seen here. 5.11.6 covers OCD.

Say that magnetic resonance imaging characterises what this view detects. 5.11.5 covers osteochondral lesions.

What Abnormal Looks Like

The reasoning expected is that the notch is a recess, so a beam crossing it obliquely superimposes its walls and anything inside it on the condyles. 5.2.2 covers the image formation.

Projecting along the notch axis removes that superimposition, which is why the same fragment appears here and not on the anteroposterior view. 5.2.5 covers magnification.

The posterior condyle contacts the tibia in flexion, so a lesion there is loaded in flexion and is both clinically relevant and radiographically hidden on an extended view. 3.5.4 covers the effects of flexion.

Notch narrowing in arthritis is osteophyte, and its association with cruciate injury is a separate and weaker claim. 5.7.1 covers the normal cruciate.

How Good It Is

The tunnel view detects what the standard views conceal and characterises nothing.

Its best contribution is a loose body or an osteochondral fragment that would otherwise be missed, which is a detection role. 5.11.5 covers osteochondral lesions.

It is limited to detection, since staging an osteochondral lesion needs magnetic resonance imaging. 5.11.6 covers OCD.

No figures appear for accuracy on this page, under decision 028, and no notch width index or beam angle appears either: those are published protocol quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level this view is worth requesting when the question is a fragment and the standard films are unremarkable.

A locking knee with normal standard films is the clearest indication, because a loose body has a mechanical answer. 5.6.6 covers bucket handle tears.

A suspected osteochondritis dissecans lesion in a young patient is detected here and staged elsewhere. 5.11.6 covers OCD.

Notch osteophyte limiting extension is a finding with a surgical answer. 5.3.18 covers osteophytes.

A normal tunnel view does not exclude a cartilaginous loose body, which is invisible on any radiograph. 5.14.6 covers synovial chondromatosis.

Where It Misleads

The commonest error is excluding a loose body because the radiographs are normal, when a cartilaginous body is radiolucent. 5.14.6 covers synovial chondromatosis.

A normal standard series is accepted without the tunnel view being considered. 5.3.1 covers the anteroposterior view.

An osteochondral lesion is staged from this view. 5.11.6 covers OCD.

A fabella or a normal ossicle is read as a loose body. 5.3.12 covers patellar fractures.

Notch narrowing is interpreted as cruciate risk on weak grounds. 5.7.1 covers the normal cruciate.

Fellowship Level

Where It Misleads

At fellowship level the tunnel view is a cheap film with a narrow indication that is both under-requested and over-interpreted.

Its detection advantage is real and its characterisation ability is nil, so a positive finding always leads to another study and a negative finding excludes less than it appears to. 5.11.5 covers osteochondral lesions.

The notch width index and its association with cruciate injury has a literature that predates routine magnetic resonance imaging, and the association has not translated into a usable risk measure. 5.21.2 covers the cruciate imaging literature.

Magnetic resonance imaging detects everything this view detects and more, so the view survives on cost and availability rather than on capability. 5.1.5 covers the cost effectiveness of imaging.

Where a cross sectional study is already planned, this view adds nothing, and requesting it reflexively is the commoner waste. 5.1.4 covers imaging pathways.

The defensible position is that this is a useful first line film where cross sectional imaging is not immediately available, and redundant where it is. 5.1.3 covers choosing the correct investigation.