POL Assessment

For Medical Students

What It Tests

The posterior oblique ligament is the posterior part of the medial complex, and assessing it means asking what the medial side does in extension and in rotation rather than in valgus alone.

It tightens as the knee extends, which is why a knee with a torn superficial ligament can still feel firm in full extension. 3.9.5 covers its function.

It also resists internal rotation of the tibia, which is why its loss shows up as a rotational complaint rather than as a bigger valgus grade. 3.9.2 covers rotational stability.

How It Is Performed

Perform valgus stress in full extension first, because opening there is the finding that implicates this structure or a cruciate. 4.12.2 covers that angle.

Palpate the posteromedial corner of the knee, behind the superficial ligament's course and above the joint line, with the knee flexed to about thirty degrees.

Test the anteromedial drawer. Flex the knee to about ninety degrees, rotate the tibia externally by about fifteen degrees, and draw the tibia forwards while watching the medial plateau rather than the whole tibia.

Note whether the medial plateau rotates forwards more than the other side, which is the finding rather than the amount of straight translation.

Examine the cruciates, because an anterior cruciate rupture produces anterior translation that has to be separated from this rotation. 4.10.4 covers the Lachman test.

What a Positive Means

Increased anteromedial rotation of the tibia, with the medial plateau coming forwards more than the lateral, indicates a deficient posteromedial corner including this ligament.

Valgus opening in full extension points the same way and is the easier finding to obtain. 4.12.2 covers it.

A knee that is lax at thirty degrees, firm in extension and has no anteromedial rotation has an isolated superficial ligament injury, and that is most medial injuries. 4.12.3 covers that grade.

A knee with all three findings has a severe medial injury, and that is the combination that is reconstructed rather than braced.

MRCS Level

How It Is Performed

In a viva this is the structure to name when asked what makes a medial injury surgical, because that is almost always why the question is being asked.

The expected points are the extension test, the posteromedial palpation, the anteromedial drawer with the tibia externally rotated, and watching the medial plateau.

Say that you would separate the rotation from the translation, since an anterior cruciate rupture gives translation and this gives rotation, and a knee can have both. 4.12.6 covers the pattern.

Say that the structure is a capsular thickening continuous with the superficial ligament rather than a separate cord, so it is assessed by the pattern of laxity rather than by palpating a structure.

Say that you would repeat the examination after a period of bracing, because the superficial ligament heals and this one less reliably does, so the difference between the two examinations is the information. 4.12.8 covers it.

What a Positive Means

The reasoning expected is that the medial restraints divide their work by flexion angle, and this structure's share is greatest in extension, so its loss is read there. 3.9.9 covers the angles.

Its loss also removes a restraint to internal rotation, which allows the medial plateau to rotate anteriorly under an anterior force and produces the anteromedial pattern. 3.9.7 covers the biomechanics.

The pattern requires the anterior cruciate to be deficient as well in most descriptions, because the cruciate resists the anterior component, which is why anteromedial rotatory instability is usually a combined diagnosis. 4.14.4 covers that pattern.

A knee with a healed superficial ligament and an unhealed posteromedial corner is the common chronic presentation, and it is the knee in which the valgus grade looks acceptable and the patient still complains. 4.12.8 covers it.

How Good It Is

The examination for this structure is indirect and is the best available, because no test loads it in isolation.

The extension test is the most reliable part of it and is reproducible between examiners.

The anteromedial drawer is less reliable, because it asks the examiner to separate rotation from translation by feel, and that is a judgement rather than a measurement.

Magnetic resonance imaging identifies the structure and says less about whether its loss matters, so the examination keeps the decision even where the imaging has the better picture. 4.1.6 covers that relationship.

No figures appear for any of these comparisons, under decision 023, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level this is the structure the medial decision rests on, and the chapter is arranged around getting to it.

A medial injury with an intact posteromedial corner is braced, and almost all of them are. A medial injury with a deficient corner is the one that is reconstructed, and the examination is what identifies it.

In a combined medial and anterior cruciate injury the corner decides whether the medial side is addressed at the time of the cruciate reconstruction, and the examination repeated after bracing is what settles it. 3.9.10 covers the combination.

In the chronic knee the corner is the structure behind a persistent valgus and rotational complaint over an acceptable grade, and reconstructing the superficial ligament alone in that knee leaves the complaint. 4.12.8 covers the assessment.

Where the examination is equivocal, stress radiographs in extension and magnetic resonance imaging are read together, since the question is both how lax and which structure.

Where It Misleads

The commonest error is omitting the extension test, which is the only reliable clinical route to this structure.

The second is reading the anteromedial drawer as an anterior drawer and attributing the laxity to the cruciate alone.

The third is examining once. A corner that is lax acutely and firm at six weeks has healed, and treating the acute finding as definitive leads to operations that were not needed.

The fourth is reconstructing a superficial ligament in a knee whose complaint is rotational, which is a technically successful operation for the wrong structure.

Fellowship Level

Where It Misleads

In referred practice the posteromedial corner is the structure that explains the patient whose medial reconstruction worked and whose knee still gives way on turning.

That patient has a rotational deficiency over a corrected valgus laxity, and the examination that finds it is the anteromedial drawer rather than any valgus test. 4.12.6 covers it.

A corner that healed in a lengthened position gives a firm endpoint over a rotationally lax joint, which is the same misleading combination the whole medial chapter keeps producing, and it needs the comparison with the other side to reveal it. 4.12.3 covers that trap.

In a knee with a previous posteromedial repair, scar can hold the extension test firm while the rotational examination stays abnormal, so the two tests disagree and the rotational one is the one to believe. 4.2.30 covers previous surgery.

A patient with an anteromedial pattern and a varus alignment is at risk from a medial reconstruction, because the medial side is unloaded in varus and the reconstruction has nothing holding it. Alignment is assessed before the ligament work.

In the multiligament knee this structure is routinely the one not recorded, because the examination has already found larger problems, and the plan is built without it. 4.11.7 covers that sequence.