Assessment at 30 Degrees

For Medical Students

What It Tests

Valgus stress applied with the knee flexed to thirty degrees tests the superficial medial collateral ligament with the least help from anything else.

Flexing the knee relaxes the posterior capsule and the posterior oblique ligament, which leaves the superficial ligament as the structure taking the valgus load. 3.9.3 covers its function.

That isolation is the point of the angle. It is the same logic as the Lachman test, where a particular flexion angle removes the structures that would otherwise share the work. 4.10.4 covers that test.

How It Is Performed

Lay the patient supine and flex the knee to about thirty degrees, with the leg relaxed and the foot resting on the couch or supported by your forearm.

Place one hand along the lateral side of the knee as the fulcrum, with your fingers over the medial joint line.

Hold the ankle with the other hand and apply a valgus force through it, keeping the tibia in neutral rotation.

Feel the medial joint line open under your fingers and note the endpoint as the opening stops.

Grade the opening against the other knee and record both the grade and the endpoint. 4.1.8 covers the record.

What a Positive Means

Increased opening at thirty degrees with a firm endpoint in full extension indicates an injury confined to the superficial medial ligament.

The grade is conventionally described in three degrees. A few millimetres of extra opening with a firm endpoint is first degree, a moderate increase with a discernible endpoint is second degree, and a large increase with a soft or absent endpoint is third degree.

A first or second degree injury heals in a brace in almost every case, which makes this the one grade in the chapter that reliably predicts the treatment.

A third degree injury at thirty degrees should send you back to full extension, because the two findings together mean something different from either alone. 4.12.2 covers extension.

Tenderness over the ligament's course with no increase in opening is a sprain rather than a laxity, and it is treated as pain rather than instability.

MRCS Level

How It Is Performed

In a viva the expected points are the flexion angle, the fulcrum, the fingers on the joint line, neutral rotation, the endpoint, and the grade against the other side.

Say why thirty degrees, because the reason is the whole content of the question and the follow up is usually what else resists valgus.

Say that you would keep the tibia in neutral rotation, since external rotation opens the medial side and internal rotation closes it, and a rotated tibia turns a grade into a guess.

Say that you would palpate the ligament's course from the femoral epicondyle to the tibia, because the site of tenderness localises the tear within the ligament. 4.12.7 covers the discrimination from meniscal pain.

Say that you would grade against the other knee rather than in absolute millimetres, and that stress radiographs supply the millimetres when a plan needs them.

What a Positive Means

The reasoning expected is that the superficial ligament is the principal valgus restraint through mid flexion and supplies most of that restraint itself. 3.9.1 covers valgus stability.

Its proximal fibres and distal fibres tighten at different parts of the range, which is why a partial injury can give a firm endpoint with increased opening rather than a clean grade. 3.9.9 covers the angles.

The deep ligament lies beneath it and attaches to the meniscus, and its contribution to valgus restraint is small enough that this test does not separate it. 4.12.4 covers it.

A grade that improves between two examinations indicates healing in continuity, which is what this ligament does and what the brace is protecting. 4.12.8 covers the later assessment.

How Good It Is

The thirty degree test is the most reproducible ligament examination in the knee, and more reproducible between examiners than any cruciate test.

The reason is that the force has one direction, the fulcrum is fixed, and the joint line can be felt opening rather than inferred.

It grades well and localises poorly. It cannot tell the superficial ligament from the deep one and cannot tell a proximal tear from a distal one, both of which affect healing.

It is reliable acutely, which is why it is the medial examination that is actually performed in the emergency department.

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 the thirty degree grade sets the length of the brace and little else, which is a modest role performed reliably.

A first degree injury needs support and early movement, a second degree injury needs a hinged brace for weeks, and a third degree injury needs the extension test and the corner assessed before anything is decided. 4.12.5 covers the corner.

Where the grade does matter beyond bracing is in a knee listed for cruciate reconstruction, because an unhealed medial side changes the timing of that operation and occasionally its content. 3.9.10 covers the combination.

The site of the tear matters more than the grade for healing. A tear at the tibial attachment, where the ligament ends can displace, heals less reliably than one at the femoral end, and that is a palpation finding rather than a grading one.

Stress radiographs at this angle are the reference for comparison over time and are worth obtaining where a surgical decision will rest on whether the laxity changed.

Where It Misleads

The commonest error is grading without the extension test, which leaves a severe injury looking like a moderate one.

The second is grading a rotated knee.

The third is recording a grade with no endpoint, which makes the later comparison impossible and is the error this whole section keeps naming.

The fourth is treating tenderness as laxity. A painful medial side with no increased opening is common in meniscal injury and is a different diagnosis. 4.12.7 covers it.

The fifth is examining through a brace or a bulky dressing, where the fulcrum is wrong and the joint line cannot be felt.

Fellowship Level

Where It Misleads

In referred practice a residual grade at thirty degrees is usually asymptomatic, and the work is deciding whether it explains the complaint.

A patient with a second degree residual laxity, a firm endpoint and pain on twisting is more likely describing the meniscus than the ligament. 4.12.7 covers the separation.

A patient with the same laxity and a sense of the knee opening on cutting is describing an anteromedial rotatory pattern, which is graded with rotation added rather than with valgus alone. 4.12.6 covers it.

Chronic medial laxity after a tibial sided tear can be larger than the acute grade recorded, because the ligament healed in a lengthened position rather than failing to heal, and the endpoint stays firm throughout. That combination of a firm endpoint over a lax joint is the chapter's most misleading finding.

In a varus aligned knee a medial laxity is usually irrelevant and in a valgus aligned knee it is usually not, because alignment decides whether the medial side is loaded at all. 4.11.5 covers dynamic assessment.

After a medial reconstruction the grade is read against the contralateral side and against the operation note, and a grade that is better than normal is a tight reconstruction rather than a success. 4.12.8 covers the assessment.