Range of Movement After a Knee Replacement

Two numbers get quoted constantly after a knee replacement — how far the knee bends, and how far it straightens. They are worth understanding properly, because patients are frequently more worried about them than the numbers warrant, and occasionally less worried than they should be.

This page covers what the figures mean, which direction matters more, what the timeline realistically looks like, and what to do when progress stalls.

What you actually need

The honest answer is that the number matters less than what it lets you do. These are the approximate requirements for ordinary activities:

Most knee replacements settle somewhere between 110 and 125 degrees, which covers everything on that list except comfortable kneeling. A knee at 110 degrees is a knee that does what you need it to do.

The single most reliable predictor of where you will finish is how far the knee bent before surgery. A knee that was stiff for years going in is more likely to be stiff coming out. This is not a rule without exceptions, but it is the reason your pre-operative movement gets measured and recorded.

Straightening matters more than bending

This is the part that surprises people, and it is the thing worth taking away from this page.

Patients arrive at reviews concerned about the bend, because bending is what you can see and what everybody asks about. Straightening attracts far less attention and causes far more trouble.

A knee that does not fully straighten changes how you walk. The quadriceps has to work continuously to hold you up rather than resting each time the leg is straight, so walking becomes tiring, the limp persists, and the knee aches at the end of the day. A loss of even 10 degrees of extension is noticeable in a way that a loss of 10 degrees of bend simply is not.

It is also considerably harder to regain than bend. Getting the last few degrees of straightening back once the knee has settled bent is genuinely difficult, where bend can usually be worked on for months.

Why the knee resists straightening

Several things at once, which is why it takes deliberate work:

• Swelling inside the joint holds it in the position of greatest capacity, which is slightly bent. This is why swelling control is range-of-movement work, not just comfort
• Tightness at the back of the knee — if the knee had a fixed bend before surgery, the hamstrings, capsule and ligaments behind it have been short for years. The joint can now extend; the soft tissues have not caught up
• The comfortable position is the bent one, so the knee drifts there whenever it is not being thought about — resting on a pillow, sitting with the foot tucked back, sleeping with the leg curled

What helps

Prop the heel, not the knee. Lying flat with the heel on a rolled towel or a block so the calf is supported and the knee hangs free lets gravity do the work. Fifteen minutes several times a day. It is uncomfortable, which is the point — a position that feels pleasant is not stretching anything.

Never put a pillow directly under the knee. It is the most comfortable thing available in the first fortnight and it quietly works against you. Five Things Not to Do Straight After a Knee Replacement covers this in more detail, and it is the first item on that list for a reason.

Heel slides and active straightening. Your physiotherapist will give you specific work. Do it on the ordinary days as well as the motivated ones.

Treat swelling seriously. Ice, elevation, compression. Less swelling means more movement, immediately and measurably.

What the timeline usually looks like

These are patterns, not targets to be measured against. Being a fortnight behind this table is common and is not, by itself, a sign that anything has gone wrong. Age, the state of the knee going in, body shape and how much swelling you are carrying all shift it.

What matters more than the absolute number is whether it is still moving. A knee at 95 degrees that gained 10 degrees this month is in a better position than a knee at 100 degrees that has not changed in six weeks.

The window

Movement is easiest to gain in the first three months, while the scar tissue inside and around the knee is still forming and remodelling. After that the tissue matures, and range becomes harder — not impossible, and many people keep gaining slowly through the first year, but the easy gains are early.

This is the whole argument for doing the exercises consistently in weeks two to twelve, including on the days the knee is unimpressive and you cannot be bothered.

When bend stalls

If the knee has stopped moving well short of where it needs to be — commonly taken as under 90 degrees at six weeks with no recent progress — say so rather than waiting for the next scheduled appointment.

A stalled knee is not a verdict on how hard you have worked. Some knees lay down scar tissue far more readily than others, and that tendency is largely outside anyone’s control.

What is usually happening

The knee heals by forming scar tissue, inside the joint as well as along the incision. In most people that tissue stays soft enough to stretch out with rehabilitation. In some it becomes thick, tight and adherent — binding the surfaces that need to glide past each other. When it is severe enough to restrict movement it is called arthrofibrosis, and the bands of tissue responsible are adhesions.

It is important to know that this is not always about effort, and that the tendency towards it varies between people for reasons that are not well understood.

The steps, in order

Rather than one decision, it is a sequence — and the earlier steps resolve most cases.

1. Sort out the pain relief. This is first because it is the most common reversible cause and the most often missed. A knee that hurts too much to be exercised will not gain movement, and no amount of physiotherapy overcomes inadequate analgesia. Sometimes it is the whole answer.

2. Change the rehabilitation. Intensity, frequency, technique, or the physiotherapist. Adding strength work where the problem turns out to be weakness rather than stiffness — see the section below, because this is a genuinely common mix-up.

3. Manipulation under anaesthetic. A short procedure under a general anaesthetic in which the knee is bent firmly through its range, breaking the adhesions. There is no incision and you go home the same day or the next.

Two things matter about it. The first is timing: it is usually considered between six and twelve weeks, because adhesions are still immature enough to give way readily. Much beyond about three months the tissue has toughened, the manipulation has to be more forceful, and the risks — including fracture around the implant — rise. The second is that the gain has to be held. The movement is won in theatre and kept in the weeks afterwards, with intensive physiotherapy starting immediately. Without that, a knee can tighten back up.

4. Arthroscopic release. Keyhole surgery through small incisions, in which the scar tissue is divided under direct vision. Used when a manipulation has not achieved enough, when the problem is recognised too late for manipulation to be the sensible first move, or where the pattern suggests dense adhesions rather than general tightness. It is often combined with a manipulation in the same anaesthetic. Rehabilitation afterwards is much like it was the first time, which people find dispiriting and worth knowing in advance.

5. Revision surgery. Reserved for stiffness with an identifiable mechanical cause — a component that is too large, poorly positioned or rotated, for example — rather than for scar tissue alone. It is a considerably bigger operation, and its results for stiffness by itself are less predictable than for a clear mechanical problem, which is why it sits at the end of the list rather than in the middle. Knee revision surgery covers what it involves.

Alongside all of this, investigation — X-rays, and sometimes further imaging or blood tests — to check that something other than scar tissue is not responsible. Infection, in particular, presents as a stiff painful knee and has to be excluded rather than assumed against.

Stiffness that is actually weakness

This distinction is genuinely useful and rarely explained.

If your measured movement is good — say 0 to 115 — but the knee still feels stiff, heavy, and as though it might not hold you, the problem is usually not stiffness at all. It is the quadriceps.

The thigh muscle shuts down after a knee replacement. It is partly the surgery, partly the swelling, partly weeks of not using the leg normally, and partly that the muscle was already weak from years of an arthritic knee. A weak quadriceps produces exactly the sensations people describe as stiffness: the knee feels unreliable going downstairs, gives a sense of buckling, feels heavy to lift, and aches after standing.

More stretching will not fix it. Strengthening will, and the work is different — straight leg raises, controlled step-downs, sit-to-stands, progressive resistance, and eventually loaded work.

It is worth telling your physiotherapist which of the two it feels like, because the answer changes the programme.

Numbers are not the point

It is easy to become fixated on the measurement, particularly when comparing notes with other people. Two things are worth holding onto.

The first is that these numbers are measured differently by different people. A physiotherapist pushing firmly at the end of range will record more than you will get on your own, and neither is wrong. Comparing your figure to someone else’s is comparing two things measured two ways.

The second is that a knee that straightens fully and bends to 110 degrees does everything on the list at the top of this page. Chasing 130 degrees has little practical return, where getting extension from 8 degrees to 0 changes how you walk every day for the rest of your life.

If you are unsure where your own knee sits or whether it is where it should be, the recovery timeline sets out the broader picture, and it is a reasonable thing to ask about directly at a review.

If your movement has stalled, or something about your recovery does not seem right, phone the rooms on (08) 6332 6365 rather than waiting for your next appointment. Appointments can also be made through the contact page.