Non-contact Injury

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Student MRCS FRCS Fellow

For Medical Students

What It Tests

A non-contact injury is one where nothing struck the knee. The patient produced the forces that injured it.

Asking about this tests whether the injury was generated by the patient's own movement, which points strongly towards the cruciate and the menisci rather than towards the collaterals.

The majority of anterior cruciate ruptures happen this way, which is why this page opens the injury history section. 3.7.14 covers the mechanisms.

How It Is Performed

Ask whether anything or anybody hit the knee. A patient will often describe a tackle that happened nearby rather than to them.

Ask what the foot was doing: planted, turning, or landing.

Ask what the body was doing: decelerating, changing direction, or landing from a jump.

Ask whether they heard or felt a pop, whether they fell, and whether they could carry on.

Ask about swelling timing, which is the single most discriminating follow-up. 4.2.3 covers it.

What a Positive Means

A planted foot with a sudden change of direction, a pop, immediate swelling and inability to continue is an anterior cruciate rupture.

Landing from a jump with the knee collapsing inwards is the same injury by a different route, and is the classic mechanism in female athletes. 3.7.15 covers it.

Deceleration with a twist and pain but the ability to continue, with slower swelling, fits a meniscal tear.

Hyperextension during a kick or a missed step raises the cruciate and the posterior structures. 4.2.19 covers hyperextension.

A patella that moved laterally during a twist on a flexed knee is a dislocation event, which patients usually describe clearly. 4.2.22 covers it.

Key Learning Points

A non-contact injury is one where the patient produced the forces themselves.
Most anterior cruciate ruptures happen this way.
Ask what the foot was doing and what the body was doing separately.
Planted foot, change of direction, pop, immediate swelling, could not continue: a cruciate.
Swelling timing is the most discriminating follow-up question.

MRCS Level

What a Positive Means

The expected reasoning connects the mechanism to the loading, which Section 3 establishes.

A planted foot with internal rotation of the femur on the tibia loads the anterior cruciate and the anterolateral structures together, which is why isolated cruciate injuries are less common than the teaching implies.

Valgus collapse during landing adds the medial structures to the same event. 4.12.7 covers separating medial meniscus from collateral injury.

A deep squat or a forced flexion with rotation loads the posterior meniscal attachments, which is a root tear mechanism. 4.9.9 covers root tears.

The combination that should always be sought is a cruciate injury with a meniscal injury, because the mechanism produces both and the second is the one whose repair has a window.

How Good It Is

The non-contact mechanism is one of the better recalled parts of the knee history, because it happened during a deliberate movement the patient was concentrating on.

It performs well for identifying which structures were loaded and poorly for grading what happened to them.

The pop is reasonably discriminating when present and absent in a substantial proportion of genuine ruptures, so its absence excludes little.

The inability to continue is among the more reliable features, because it is a behaviour rather than a sensation.

Key Learning Points

A planted, rotating knee loads the cruciate and the anterolateral structures together.
Valgus collapse on landing adds the medial structures to the same event.
Forced flexion with rotation is a meniscal root mechanism.
Always seek the combination of cruciate and meniscal injury, because the mechanism produces both.
Inability to continue is more reliable than the pop, because it is a behaviour.

FRCS Level

How Good It Is

At decision level the mechanism shapes what to look for and how urgently, because the repairable injuries have windows.

A non-contact cruciate injury with a locked knee is a displaced meniscal tear and is urgent, because a bucket handle tear in a young knee may be repairable now and not later. 4.2.5 covers locking.

A non-contact injury with valgus collapse should prompt a deliberate search for medial and rotational injury rather than a cruciate-only assessment.

The mechanism also predicts recurrence. A patient who injured the knee in a movement central to their sport will meet that movement again, and the rehabilitation has to address it. 4.21.7 covers return to sport testing.

Where It Misleads

The commonest error is accepting a non-contact label from the referral without asking. Patients and clinicians both use contact loosely.

The second is treating a non-contact mechanism as a cruciate mechanism and stopping there, missing the associated injuries that the same event produces.

The third is attributing a non-contact injury in an older patient to the same pathology as in a young one. A degenerate structure fails under lower loads and the history may sound trivial. 4.9.11 covers the degenerate version.

And a non-contact injury in a child needs the growth plate considered before the ligament. 4.19.1 covers it.

Key Learning Points

Repairable injuries have windows, so the mechanism shapes urgency.
A non-contact cruciate injury with a locked knee is urgent.
Valgus collapse should prompt a deliberate search for medial and rotational injury.
A degenerate structure fails under lower loads, so the history may sound trivial.
In a child the growth plate comes before the ligament.

Fellowship Level

Where It Misleads

In referred practice the non-contact mechanism matters most for what it says about recurrence risk and about what the first operation did not address.

A graft that failed during the same movement that caused the original injury raises rotational control and tunnel position, and the mechanism is the clue that the rotational component was never addressed. 4.14.3 covers the pattern.

A graft that failed during a trivial movement raises biological failure, fixation failure or an undiagnosed cause of abnormal loading such as malalignment or a deficient meniscus. 4.9.10 covers meniscal deficiency.

In a revision assessment the mechanism of the re-injury is usually recorded poorly and is worth reconstructing carefully, because the two scenarios above lead to different operations. 4.10.12 covers revision assessment.

No figure here supports which mechanism features discriminate, under decision 023.

Key Learning Points

The mechanism of a re-injury points at what the first operation did not address.
Failure during the original movement raises rotational control and tunnel position.
Failure during a trivial movement raises biology, fixation, alignment or meniscal deficiency.
The two scenarios lead to different operations, so reconstruct the mechanism carefully.

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 either, which is decision 023 rather than an omission: the comparative value of the history questions is standard teaching and a specific sensitivity written from memory is not, so ACC-001 refuses the number and the page states the comparison. Any measurement on this page is written from standard teaching, has not been checked against a source, 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.