Paediatric ACL Injury

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Paediatric ACL Injury

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Student MRCS FRCS Fellow

For Medical Students

What It Tests

A cruciate tear in a child presents as it does in an adult, with a twisting injury, an immediate effusion and a feeling of the knee giving way. 4.10.1 covers the history of the injury.

The examination is the same set of tests, and the difference is that a positive finding in a growing knee leads to a different discussion. 4.10.5 covers the anterior drawer test.

The first task is separating a cruciate injury from a physeal injury, since both follow a twisting injury and both produce an effusion. 4.19.1 covers the growth plate assessment.

How It Is Performed

Establish the age, the maturity and the mechanism, because a twisting injury in a young child is more likely to involve the physis or a tibial spine. 4.19.6 covers developmental variants.

Assess the effusion, since an immediate haemarthrosis after a twisting injury narrows the differential sharply. 4.8.7 covers the acute haemarthrosis.

Palpate the physeal lines before any stress test, as in any immature knee. 4.6.1 covers systematic palpation.

Perform the Lachman test, which is the most informative single test and the gentlest of the anterior tests. 4.10.4 covers the Lachman test.

Perform the anterior drawer if the Lachman is equivocal, accepting that it is less sensitive. 4.10.5 covers it.

Defer the pivot shift in an acute injury, since it needs a relaxed knee and it is uncomfortable. 4.10.6 covers the pivot shift.

Assess the collaterals and the posterior structures gently, so a combined injury is not missed. 4.12.1 covers valgus stress testing.

What a Positive Means

An increased anterior excursion with a soft end point on the Lachman test indicates a cruciate injury, in a child as in an adult. 4.10.4 covers the test.

A haemarthrosis with a twisting mechanism and a normal Lachman raises a tibial spine avulsion instead, which is the paediatric equivalent. 4.10.1 covers the history of the injury.

Physeal tenderness with anterior laxity means both structures may be injured and the physis is examined first. 4.19.1 covers the growth plate assessment.

A positive finding in a skeletally immature knee changes the treatment timing and the technique rather than the diagnosis. 4.20.1 covers the reconstructed knee.

A normal examination with a convincing history in a child deserves repeating, since guarding hides laxity. 4.10.4 covers the test.

Key Learning Points

The tests are the same as in an adult and the consequences differ.
A twisting injury in a young child may involve the physis or a tibial spine.
The Lachman is the most informative and the gentlest anterior test.
The physis is palpated before any stress test.
A guarded examination hides laxity and deserves repeating.

MRCS Level

How It Is Performed

In a viva this is the adolescent knee injury station and the expected answer covers maturity, the physis and the tibial spine before the ligament.

The expected points are the age and maturity, the mechanism, the haemarthrosis, the physeal palpation, the Lachman, the drawer, the deferred pivot shift, the collaterals and the decision on imaging.

Say that you would assess skeletal maturity clinically and confirm it, since it determines the treatment options. 4.19.6 covers developmental variants.

Say that you would consider a tibial spine avulsion in a younger child with the same history. 4.10.1 covers the history of the injury.

Say that you would defer the pivot shift acutely and perform it later, with the reason. 4.10.6 covers it.

What a Positive Means

The reasoning expected is that the cruciate's bony attachments are stronger than the ligament in an adult and relatively weaker in a child, so the failure moves to the bone. 2.7.7 covers the tibial footprint.

A tibial spine avulsion is therefore the younger child's version of the same injury, and it produces the same laxity with a different lesion. 4.10.1 covers the history of the injury.

The Lachman tests the ligament at a position where the hamstrings cannot easily resist, which is why it outperforms the drawer in a guarding patient. 4.10.4 covers the test.

Skeletal maturity governs the treatment because a reconstruction crossing an open physis risks a growth disturbance. 4.19.1 covers the growth plate assessment.

How Good It Is

The Lachman test performs as it does in an adult in a cooperative child and poorly in a guarding one.

Its best contribution is the same as in the adult knee, which is detecting anterior laxity with a single gentle manoeuvre. 4.10.4 covers the test.

It cannot distinguish a midsubstance tear from a tibial spine avulsion, since both produce anterior laxity.

Magnetic resonance imaging distinguishes them, so the examination establishes the laxity and the imaging establishes the lesion. 4.1.6 covers that relationship.

No figures appear for any accuracy comparison on this page, under decision 023, and the comparison is the claim being made.

Key Learning Points

The cruciate's bony attachment is relatively weaker in a child.
A tibial spine avulsion is the younger child's version of the same injury.
The Lachman works at a position where the hamstrings cannot easily resist.
Skeletal maturity governs the treatment, not the diagnosis.
The examination cannot separate a tear from an avulsion.

FRCS Level

How Good It Is

At decision level the examination establishes the laxity and the maturity, and the combination of those two decides the pathway.

An immature knee with anterior laxity is a different decision from a mature one, and the examination contributes the laxity while imaging contributes the physeal status. 4.19.1 covers the growth plate assessment.

Associated meniscal injury changes the urgency, and the examination for joint line tenderness and a block to extension is how it is raised. 4.9.3 covers the McMurray test.

A tibial spine avulsion with a block to extension is urgent, and the block is a clinical finding. 4.5.4 covers the flexion deformity.

Recurrent giving way in a child with laxity is a functional finding that moves the decision, and it is asked for rather than assumed. 4.2.6 covers giving way.

Where It Misleads

The commonest error is examining the ligament and not the physis, so a physeal injury is called a cruciate injury. 4.19.1 covers the growth plate assessment.

Guarding in an acute paediatric knee produces false reassurance on the Lachman, and the examination is repeated rather than trusted once. 4.10.4 covers the test.

Physiological laxity is greater in children, so a soft end point is harder to call abnormal than in an adult. 4.19.6 covers developmental variants.

A tibial spine avulsion is attributed to a midsubstance tear, and the two have different urgency.

A combined meniscal injury is missed because the attention goes to the ligament. 4.9.3 covers the McMurray test.

Key Learning Points

Examining the ligament and not the physis is the commonest error.
Acute guarding produces false reassurance on the Lachman.
Physiological laxity is greater in children, so the end point is harder to call.
An avulsion attributed to a tear loses the difference in urgency.
A combined meniscal injury is missed when attention goes to the ligament.

Fellowship Level

Where It Misleads

At fellowship level the examination's limits in the growing knee are about degree rather than about presence.

Physiological laxity varies with age and with generalised laxity, so a given excursion means different things at different ages and the examination has no age adjusted reference. 4.19.6 covers developmental variants.

A partially torn cruciate in a child can produce a soft end point with a firm stop, and the clinical distinction between partial and complete is unreliable here as it is in adults. 4.10.4 covers the test.

The examination cannot assess the physeal status, which is the finding that governs the operation rather than the laxity. 4.19.1 covers the growth plate assessment.

Repeat examination under anaesthesia resolves the guarding problem and introduces its own, because an anaesthetised child's laxity is not the laxity being treated. 4.10.6 covers the pivot shift.

Functional instability in a child is reported by a parent as often as by the patient, and the two reports differ. 4.2.6 covers giving way.

Key Learning Points

Physiological laxity varies with age and the examination has no age adjusted reference.
Partial and complete tears are not reliably separated clinically.
The physeal status, not the laxity, governs the operation.
Examination under anaesthesia removes guarding and changes what is measured.
Parent and patient reports of instability differ.

Explore Further

Where this topic came from and where it goes next in the spiral.

References

No reference list is attached to this draft. Evidence verification has not run, because source retrieval was unavailable at generation time. Under the Operations Handbook a missing reference is acceptable and an invented one is a critical failure, so nothing has been cited and no citation marker appears in the text. This page carries no diagnostic accuracy figure, which is decision 023 rather than an omission. The comparative standing of these tests is standard teaching and a specific sensitivity written from memory is the same class of claim as an invented citation, so ACC-001 refuses the number and the page states the comparison. A reviewer with the literature can add the figures into How Good It Is without restructuring the page, and chapter 3.17 lists the studies the figures would come from. Any measurement here, including a flexion angle, is written from standard teaching, has not been checked, and is registered under decision 006 in pipeline/config/figures with a verification state of UNVERIFIED_FROM_MEMORY.

Safety. KneeSchool is educational and does not give individual medical advice. Seek urgent assessment for a knee that cannot bear weight after an injury, a hot swollen knee with a fever, or new numbness, weakness or coldness in the leg or foot.