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

POST-TRAUMATIC KNEE INJURY

A post-traumatic knee injury is two problems. Something tore or bruised. And on the same day, the chemical setting inside the joint turned catabolic (tissue-breaking) and stayed that way. That second problem is what turns an injury into arthritis. Rebuilding the ligament does not reliably prevent it.

Think of a knee that hit a dashboard, took a twisting fall or pivoted on a planted foot. It has two problems, and only one of them is structural. Something tore or bruised. And on the same day, the chemical setting inside that joint changed and stayed changed.

What actually turns an injury into arthritis

The impact itself kills chondrocytes (cartilage cells). Blood and debris inside the joint stir up the joint lining (a synovial response). The fluid that bathes the cartilage shifts to a catabolic state — more enzymes breaking tissue down, less new matrix being built. Then the joint moves differently (altered kinematics) and loads a surface in a pattern it was not built for. Reviews of post-traumatic osteoarthritis after cruciate ligament injury agree on the hard part. Rebuilding the ligament restores stability. It does not reliably prevent the arthritis.

Stability is a mechanical fix for a problem that is mechanical and biochemical. That is the whole case for treating the joint setting, not only the torn part. It is why a knee after a ligament injury is a joint to manage for a decade, not one to sign off when the graft is stable.

The terrain the joint is being asked to repair in

A joint healing from trauma is fighting a local inflammatory state. If it also sits inside a body-wide one, the two add up. Insulin resistance, visceral adiposity (fat packed around the organs), poor sleep and nicotine form the background. Every repair signal in that knee has to be read against it. We measure them before we treat. Where they can be moved, we move them first.

Here is the honest qualifier. The direct evidence that ties one marker to one injection outcome is thinner than the hype. Take a secondary analysis of a randomized trial. In it, body mass index predicted outcome after microfragmented adipose tissue but not after platelet-rich plasma. We publish that because it makes our own position messier. It argues for measuring, not assuming. That is what the metabolic health page describes.

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

About 12% of all symptomatic hip, knee and ankle osteoarthritis in the United States is post-traumatic in origin. That is roughly 5.6 million people with arthritis that began with an event. Direct costs run about $3.06 billion a year. This population estimate has been 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 why a young knee is the highest-stakes version of this talk, not the lowest.

What the grade tells you, and what it does not

Kellgren-Lawrence grades an X-ray from 0 to 4. It scores joint space narrowing, bone spurs (osteophytes) and hardening of the bone (sclerosis). It is useful but coarse. It is 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 apply to a knee hurt in an event. First, a grade found on a film taken after the injury does not date the change. In most adults past forty, some degenerative finding is there to be found. Second, a grade does not decide a treatment by itself. The consensus documents rate scenarios, not X-rays. Age, compartment, effusion (fluid in the joint) and prior treatment all move the rating. Sometimes a degenerated structure had less reserve and an event went past 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. One: sufficient evidence supports platelet-rich plasma in knee osteoarthritis. Two: it is shown to work in mild to moderate disease, Kellgren-Lawrence grade 3 or below. Three: the effect lasts longer than corticosteroid, with a safer profile. The ESSKA-ICRS consensus rated 216 clinical scenarios by the RAND/UCLA method. It found 38.9% appropriate, 4.2% inappropriate and 56.9% uncertain. Agreement was strongest for use after other injection treatment has already failed.

Under those sit the trials. Eighteen level-1 studies tested it against hyaluronic acid. Across them, platelet-rich plasma produced a mean total WOMAC improvement of 44.7% versus 12.6%. Leukocyte-poor preparations did better than leukocyte-rich. A 2024 network meta-analysis found corticosteroid beaten on both pain and function at six months or beyond by all three: platelet-rich plasma, bone marrow concentrate and hyaluronic acid. A 2025 meta-analysis found the improvement clinically significant. It also found it depended on how much platelet concentration was actually delivered. That is why what is in the syringe is a clinical decision here, not a purchasing one.

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

The 2019 ESSKA meniscus consensus covers traumatic tears at length. It 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. That 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. And in that document, 56.9% of all scenarios landed in the uncertain band.

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. That is exactly why it gets quoted for joints where it does not apply. Cartilage thickness, load spread, joint volume, joint lining behavior and how easy the target is to reach all differ in the hip, the ankle and the shoulder. So does the literature. We make the case joint by joint rather than carrying one over. That is why the hip has its own page rather than a paragraph on this one.

Balance and joint control come back with work like vibration therapy for knee stability.

Questions about a knee injured in an accident

Does an injection stop my knee from 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 lives in. What can be changed is the load and the body-wide state it is repairing under. The measurable part of that is on the metabolic health page.

Which grades does the evidence actually cover?

The ESSKA-ORBIT grade A statement on how well it works sits at Kellgren-Lawrence grade 3 or below. 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?

Over six months and beyond, the meta-analytic answer is yes on pain and function. Per the consensus, the effect lasts longer and the profile is safer. Cortisone still has a role when a hot, swollen joint has to be calmed before anything else is possible. The trade-off 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. 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. It does change what we promise. At grade 4 the realistic goal is time and less medication, not 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. Improving pain is exactly when it is worth doing. That is because pain settles before function does, and the early weeks set the ceiling. Being assessed early is not the same as being injected early. The order of steps 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