The astute clinician must be alert to knee rehabilitation that is not taking its expected course.

First published by Dr Noyes in 2008, and reviewed August 2023 by Dr Sheila Strover (Clinical Editor)


Inflammation and limitation of knee motion is normal in the early days after surgery.

However, when the normal sequence of events turns into an abnormal arthrofibrosis reaction, the surgeon and therapist must be able to immediately identify that something is going wrong, as there is only a small window of opportunity to resolve this problem.


Normal healing response after joint injury or surgery

Following surgery or injury, the body sets off what is termed an 'inflammatory cascade' - a process that it uses to fight infection and protect itself. This involves the production of cytokines - the whole family of chemical mediators which can mediate the response of the white blood cells, growth factors, and TGF-beta products ('transforming growth factors') which control scarring. These produce:

This inflammatory response usually becomes quiescent at approximately 2-4 weeks after surgery. The body needs to go through this whole predictable process in order to heal and rebuild. Because this response occurs in all patients, the surgeon and therapist need to have a well-defined postoperative protocol. During the first month after surgery, this should include the classical RICE concept of rest, ice, compression, elevation, and as well, exercises to regain normal knee motion and muscle function.


But in arthrofibrosis the inflammatory response becomes exaggerated!

In cases of arthrofibrosis, the same initial sequence occurs, but it then becomes an unpredictable and exaggerated cascade which is destructive rather than constructive, leading to considerable tissue damage and scarring.

On the left - a view down the arthroscope of a normal knee, showing the rounded end of the femur (condyle), the flattened top of the tibia, and the meniscus wedged between them.

inside the knee joint

scar tissue inside knee

On the right - a similar view in a knee with advanced arthrofibrosis - shows a dense growth of fibrous scar tissue and overgrown synovium obscuring the normal anatomy.



Abnormal healing response in arthrofibrosis

In my experience, approximately 10% of patients have an exaggerated inflammatory response where, at 2 to 3 weeks postoperative, they are not regaining knee motion as I normally expect. These patients require special treatment which, when initiated this early after surgery, will be successful. I always stress that treatment for a knee motion problem must be initiated within these first few weeks to prevent a permanent loss of flexion or extension (ref 1).

I have found that 1% of patients do not respond to treatment. These patients represent very difficult cases and have what surgeons refer to as primary arthrofibrosis. Occasionally, these patients will have had prior surgery performed elsewhere where they experienced exactly the same problem - a genetically-based exaggerated inflammatory response which will always be a problem for them. Incidentally, in our study on 443 consecutive ACL reconstructions (ref 1), we found that females were not more prone to knee motion problems than males - there was no gender difference.

So, to sum up - 89% are going to do well, 10% are going to have a problem that you can address, and 1% are going to have residual problems requiring major knee surgery. Note, I am talking major knee surgery.

Some conditions are more commonly associated with the developent of arthrofibrosis -


The surgeon must always exclude infection - infection is the number one cause of arthrofibrosis - I repeat - THE number one cause. When a knee is not responding in a normal manner and scar tissue has formed, infection must be suspected until proven otherwise.

Infection comes in acute case where it is obvious; the knee is drained and surgery performed immediately. There are also sub-acute cases where the joint shows very little (if any) swelling - but scar tissue has developed and the joint is warm.

Commonly, there will be chemical abnormalities that can be measured in the blood. However, in some instances all cultures are negative and it becomes a dilemma as to how to treat the patient. In these cases, we use infectious disease consultants to administer empiric large doses of antibiotics because we suspect an infection (as the joint is red and there may be a mild temperature elevation), even though we were not able to culture a specific bacteria.

Haemarthrosis (bleeding into the joint)

There are different types of haemarthrosis which may occur after surgery - one is mild which has approximately 25 cc in the joint - this does not require draining.

A moderate haemarthrosis - 50 cc in the joint - definitely requires draining because it will shut down the quadriceps and hamstrings - patients may lose 30-40% of their strength. Severe haemarthrosis also requires draining as the knee joint is very tense and painful.

After long periods of immobilisation in a cast

Orthopaedic surgeons sometimes have to immobilise the knee after surgery, but today this is kept to a minimum. However, a major problem is that the knee may have been immobilised for several weeks after injury before the surgeon first sees the patient.

After fractures around the knee joint/high tibial osteotomy

Of course, immobilisation is likely to be part of the necessary management after a fracture. While we use immediate knee motion following high tibial osteotomy, some surgeons may still use a cast postoperatively.

Post ACL surgery

It is a clinical decision when to perform ACL reconstruction without risking triggering arthrofibrosis. Before reconstruction, we follow these steps to avoid the development of a postoperative knee motion problem. The patient should regain full motion unless a mechanical block exists (such as a meniscus tear), swelling and pain from the injury should be resolved, and most importantly, a strong muscle contraction should be demonstrated. I think that if you ask, 90% of the surgeons would state that this requires at least 4-6 weeks. There are special patients who have minimal swelling and good return of muscle function within 1-2 weeks of their ACL rupture. Some surgeons will say (correctly) that these cases do not pose special problems because they have fulfilled all the preoperative goals. It is a clinical decision for the surgeon to determine that these goals have been met and decide that surgery is now safe for the patient. The other factor which is particularly important is the surgical technique itself. A poorly positioned graft may cause mechanical problems and also trigger arthrofibrosis.

Post arthroplasty (knee replacement)

Stiffness after arthroplasty may be due to a number of factors besides arthrofibrosis. Pre-op flexion, for example, is an established predictor of poor post-op ROM due to stiffness of the extensor mechanism. When arthrofibrosis does develop, the patient may notice a 'clunk' due to the development of a fibrotic band stretching from the top of the patella to the femur.

Patellofemoral joint surgery

This includes other procedures altering the extensor mechanism.


1 Frank R. Noyes, Sandra Berrios-Torres, Sue D. Barber-Westin, Timothy P. Heckmann. Prevention of permanent arthrofibrosis after anterior cruciate ligament reconstruction alone or combined with associated procedures: a prospective study in 443 knees. Knee Surg, Sports Traumatol, Arthrosc (2000) 8 : 196-206

PREVIOUS PART: Anatomic classification of arthrofibrosis

NEXT PART: Early signs and symptoms of arthrofibrosis