Onset

For Medical Students

What It Tests

Asking about onset tests whether there was an event, and that single distinction divides the knee differential almost in half.

A sudden onset during a defined activity means a structure failed. A gradual onset over weeks or months means a process rather than an event.

Patients frequently supply an event that did not cause the problem, because the mind looks for one, so the question has to establish whether symptoms genuinely began then.

How It Is Performed

Ask when the knee was last completely normal, which is more reliable than asking when the problem started.

If there was an event, ask whether they could continue, whether they needed help to get off the pitch or out of the building, and what they did that evening.

If it was gradual, ask what changed around the time it began: new training, new footwear, new work, weight change, or a period of inactivity.

Ask whether there were earlier, milder episodes, since a sudden onset on a background of warning symptoms is a different story.

What a Positive Means

A sudden onset with an audible pop, immediate swelling and inability to continue is a structural failure and usually a cruciate. 4.2.3 covers swelling.

A sudden onset while twisting, with pain but the ability to continue, fits a meniscal tear.

A gradual onset with activity-related pain fits a tendinopathy, an overuse problem or early degenerative change. 4.16.3 covers one version.

A gradual onset with rest pain, night pain or systemic features is a different category and needs a different workup. 4.2.13 covers night pain.

MRCS Level

What a Positive Means

At this level the onset is paired with the mechanism and the aftermath to produce a diagnosis before examination. 4.2.16 covers non-contact mechanisms.

A sudden onset in a knee with prior warning symptoms frequently means a degenerate structure finally failed, which changes the expectation of healing and of repair.

A gradual onset that accelerated suddenly suggests a new element on an old problem, such as a fragment displacing in a previously torn meniscus.

An onset the patient cannot date at all is itself informative, and in a degenerate knee it is the commonest answer.

How Good It Is

Onset is one of the more reliable parts of the knee history, because an event is a memorable thing and patients recall whether they could carry on.

It performs best at separating traumatic from atraumatic presentations, which is the division that most changes the subsequent pathway.

It performs worst at dating a gradual problem, where recall compresses time and patients systematically under-estimate duration.

Asking when the knee was last normal recovers some of that, and is the better form of the question for a gradual presentation.

FRCS Level

How Good It Is

The decision onset informs most is whether tissue is likely to be repairable, and timing is what makes that question answerable.

A peripheral meniscal tear in a young patient presenting within weeks is a different surgical proposition from the same tear at a year, and the difference is in the history rather than the imaging.

An acute cruciate injury with a repairable meniscal tear has a window, and the onset date is what defines it.

In degenerative disease onset carries less weight, because the process predates the symptoms and the date the patient gives is when it became intrusive rather than when it began.

Where It Misleads

The commonest error is accepting an attributed event. A patient with a degenerate knee who noticed it after a long walk did not injure the knee on that walk.

The second is accepting a date without checking what the patient means. A knee that started hurting six months ago in a patient who stopped running two years ago has a longer history than the date suggests.

The third is in medicolegal and occupational contexts, where the date carries consequences and the account is shaped accordingly. That is a reason for care rather than suspicion. 4.23.7 covers medicolegal assessment.

And a sudden onset with no mechanism at all, particularly with night pain or systemic features, should raise causes outside the knee before it is managed as mechanical.

Fellowship Level

Where It Misleads

In referred practice onset has usually been recorded already, and the useful question becomes the onset of the current complaint rather than of the original injury.

A patient referred years after a reconstruction has two onsets and conflating them is the commonest error in the letter.

The onset of a post-operative symptom relative to rehabilitation milestones is particularly informative: a symptom that began when loading increased behaves differently from one present from the first week. 4.2.34 covers rehabilitation.

In a multiply operated knee the sequence of onsets is the history, and constructing a timeline of operations and symptom changes is usually the single most useful thing the consultation produces. 4.23.5 covers revision patients.

The limit of this page is that no figure supports which onset features discriminate; they are standard teaching and the numbers were refused under decision 023.