The knee was fine on Monday. The grade is only half the story.

POST-TRAUMATIC KNEE INJURY

A knee that took a dashboard, a twisting fall or a planted-foot pivot has two problems, and only one of them is structural. Something tore or bruised. And on the same day, the chemical environment inside that joint changed and stayed changed.

What actually turns an injury into arthritis

The impact itself kills chondrocytes. Blood and debris inside the joint provoke a synovial response, and the fluid that bathes the cartilage shifts to a catabolic state — more degradative enzyme activity, less matrix synthesis. Altered kinematics then load a surface in a pattern it was not built for. Reviews of post-traumatic osteoarthritis after cruciate ligament injury are consistent on the uncomfortable part: reconstructing the ligament restores stability and does not reliably prevent the arthritis.

Stability is a mechanical fix for a problem that is mechanical and biochemical. That is the whole argument for treating the joint environment rather than only the torn structure, and it is why a knee after a ligament injury is a joint to be managed for a decade rather than signed off when the graft is stable.

The terrain the joint is being asked to repair in

A joint recovering from trauma is fighting a local inflammatory state. If it is also sitting inside a systemic one, the two add. Insulin resistance, visceral adiposity, poor sleep and nicotine exposure are the background against which every repair signal in that knee has to be read. We measure them before we treat, and where they can be moved, we move them first.

The honest qualifier: the direct evidence linking a specific marker to a specific injection outcome is thinner than the enthusiasm for it. In a secondary analysis of a randomized trial, body mass index predicted outcome after microfragmented adipose tissue but not after platelet-rich plasma. We publish that because it complicates our own position. What it argues for is measuring rather than assuming, which is what the metabolic health page describes.

Post-traumatic arthritis is a category, not a turn of phrase

About 12% of the overall prevalence of symptomatic hip, knee and ankle osteoarthritis in the United States is post-traumatic in origin. That is roughly 5.6 million people carrying arthritis that began with an event, and about $3.06 billion a year in direct cost. It has been a described population estimate in the orthopedic literature since 2006.

So the sequence — an injury, then years, then a joint that grades badly — is a recognized disease process. It is also the reason a young knee is the highest-stakes version of this conversation rather than the lowest.

What the grade tells you, and what it does not

Kellgren-Lawrence grades a radiograph from 0 to 4 on joint space narrowing, osteophytes and sclerosis. It is useful, coarse, and blind to the two things that matter most after an event: how the joint got there, and what state its environment is in now. Our knee osteoarthritis page works through what each grade means for treatment.

Two cautions specific to a knee injured in an event. A grade found on a film taken after the injury does not date the change; in most adults past forty some degenerative finding is available. And a grade does not decide a treatment by itself — the consensus documents rate scenarios, not radiographs, with age, compartment, effusion and prior treatment all moving the rating. Where a degenerate structure had less reserve and an event exceeded what remained, that is a clinical description first; its use in a file is set out on the collision page.

What the knee guidance supports, grade by grade

The ESSKA-ORBIT consensus issued three grade A statements: sufficient evidence supports platelet-rich plasma in knee osteoarthritis; effectiveness is shown in mild to moderate disease, Kellgren-Lawrence grade 3 or below; and the effect lasts longer than corticosteroid with a safer profile. The ESSKA-ICRS consensus rated 216 clinical scenarios by the RAND/UCLA method — 38.9% appropriate, 4.2% inappropriate, 56.9% uncertain — with strongest agreement for use after other injective treatment has already failed.

Underneath sit the trials. Against hyaluronic acid across eighteen level-1 studies, platelet-rich plasma produced a mean total WOMAC improvement of 44.7% versus 12.6%, with leukocyte-poor preparations outperforming leukocyte-rich. A 2024 network meta-analysis found corticosteroid beaten on both pain and function at six months or beyond by all three of platelet-rich plasma, bone marrow concentrate and hyaluronic acid. A 2025 meta-analysis found the improvement clinically significant and dependent on how much platelet concentration was actually delivered — which is why what is in the syringe is a clinical decision here and not a purchasing one.

The meniscus answer is no, and we are not going to soften it

The 2019 ESSKA meniscus consensus addresses traumatic tears at length and does not establish biologics as a meniscal healing agent. A platelet injection does not knit a torn meniscus. What it can address is the inflamed joint environment the tear sits inside — which is a different claim, with different evidence, and it is the claim we make. The detail is on the meniscus page.

Grade 4, and where we part company with the consensus

ESSKA-ICRS does not rate platelet-rich plasma appropriate at grade 4. Be precise about what that means: grade 4 fell into the uncertain band, not the inappropriate one, in a document where 56.9% of all scenarios landed there.

Our position at grade 4 is that an injection buys time and reduces medication in a patient who is not ready for, or not a candidate for, arthroplasty — and that it is not a substitute for the operation when the operation is the right step. A placebo-controlled study of serial injections was run specifically in Kellgren-Lawrence grade IV knees, and a four-year follow-up of 37 grade III and IV knees treated with bone marrow aspirate concentrate exists as well. That is a thinner base than grade 2, and we say so while treating it. Where a replacement is the better decision has its own page.

Why a result from one joint does not travel to another

The knee has the deepest evidence base of any joint here, and that is precisely why it gets quoted at joints where it does not apply. Cartilage thickness, load distribution, joint volume, synovial behavior and the accessibility of the target are all different in the hip, the ankle and the shoulder, and so is the literature. We make the case joint by joint rather than transferring one, which is why the hip has its own page rather than a paragraph on this one.

Questions about a knee injured in an accident

Does an injection stop my knee turning into arthritis?

Nothing has been shown to do that, and we will not claim it. What can be treated is the inflammatory environment the joint is living in, and what can be changed is the load and the systemic state it is repairing under — the measurable part of which is on the metabolic health page.

Which grades does the evidence actually cover?

The ESSKA-ORBIT grade A statement on clinical effectiveness sits at Kellgren-Lawrence grade 3 or below, and the ESSKA-ICRS scenario ratings are strongest after other injections have already failed. Grade by grade, with what each means for you, is on the knee osteoarthritis page.

Should I have this instead of the cortisone shot I was offered?

On the six-month-and-beyond horizon the meta-analytic answer is yes on pain and function, with a longer effect and a safer profile per the consensus. Cortisone still has a role when a hot, swollen joint has to be calmed before anything else is possible — the trade is on the cortisone comparison page.

Will an injection heal my torn meniscus?

No. The 2019 ESSKA meniscus consensus does not establish biologics as a healing agent for a torn meniscus and we will not tell you otherwise. The joint environment around the tear is a different target, described on the meniscus page.

Does bone-on-bone rule me out?

It does not rule you out here, and it does change what we promise: at grade 4 the realistic goal is time and reduced medication rather than restoration. Where a replacement is the better decision we say so, on the surgery page.

Everything hurts less than it did. Do I still need to be seen?

Yes, and improving pain is exactly when it is worth doing, because pain settles before function does and the weeks that set the ceiling are the early ones. Being assessed early is not the same as being injected early — the sequence is on the tissue timeline page.

Where the knee thread continues

• Terrain first, then the catalyst
• PRP for knee osteoarthritis, grade by grade
• The meniscus, and what an injection cannot do
• PRP against cortisone
• When a replacement is the better decision
• Why we ask for bloodwork