Pain guide · Knee pain
This guide is about operations on the smooth cartilage that covers the ends of the bones: microfracture, cell transplants (autologous chondrocyte implantation, ACI) and grafts of bone and cartilage. If you had a torn meniscus trimmed or repaired, our meniscus surgery guide is the one you need. Recovery is long: the new surface is protected for about the first 6 weeks, usually with crutches and sometimes a brace, and the full rehab takes 6 to 12 months.
Your surgical team's plan comes first: the weight you can take and how far you can bend depend on the operation and where the damage was. This guide sets out the usual stages from NHS and specialist protocols, with a 3D demo of each exercise, what trials found about putting weight through the leg, the return to sport, what a scan after surgery does and doesn't mean, and the signs of a blood clot and other warning signs.
Exercise is for pain that has been checked or is clearly mild and settling.
Articular cartilage is the smooth, shiny layer on the ends of the bones, and this guide is about surgery on it. The meniscus is the C-shaped cushion between the bones: the NHS page on knee cartilage damage is about meniscus tears, and our meniscus surgery guide covers those operations. Your operation note or your surgeon can tell you which you had.
Damage to the joint surface can follow an injury, especially a sports injury in young people, or come from osteochondritis dissecans or an unstable kneecap. It can cause pain, swelling, a knee that gives way, catching or locking, and it may lead to osteoarthritis over time. Cartilage doesn't heal itself well, which is why surgery tries to fill the defect.
These operations are often combined with others, such as straightening the leg or rebuilding a ligament, which bring their own limits.
The National Institute for Health and Care Excellence (NICE) says supportive care comes first: exercise, weight loss, physiotherapy, painkillers, injections and braces that take the load off. Surgery is considered only if symptoms persist. NICE recommends ACI only for people who haven't had cartilage repair surgery before, with minimal arthritis and a defect larger than 2 cm², in a specialist centre.
The AAOS says most people who have these operations are young adults with a single damaged patch, and that an earlier microfracture can make a later restoration work less well. In a UK trial, an earlier operation that stimulates the bone marrow, such as microfracture, worsened the results of ACI at 5 years, though not in the ACI group at 10 years.
NHS and specialist protocols agree on the shape of recovery, with different timings. Your own team's plan comes first.
In a Norwegian trial of 80 people, ACI and microfracture did the same at 14 to 15 years, and about half the knees still working had early arthritis on X-ray (57% and 48%). For defects of 3 cm² or more, MACI did better than microfracture on pain and function at 2 and 5 years, in a trial of 144 people. For medium and large defects, results after microfracture declined over 10 years or more, with arthritis getting worse in 40% to 48%.
In a UK trial of 390 people whose first cartilage operation hadn't worked, ACI and other surgery did the same at 5 years. At 10 years, ACI was ahead by 7.3 points on a 100-point knee score, but once later operations were allowed for, the difference shrank to 3.8 points, which could be no real difference at all. Failure rates were similar (29% and 25%). Only the abstract of the 10-year report was available.
In a review of 32 studies (1,019 people), most magnetic resonance imaging (MRI) measures of a cartilage repair matched how people did poorly or not at all. In one trial, MACI felt better than microfracture, though the defects looked similarly filled on MRI. So incomplete filling on a scan doesn't on its own mean the repair has failed, and a well-filled defect doesn't guarantee a pain-free knee.
The exception is a mechanical problem: a graft can lift off (delamination, in about 5 in 100 after MACI, usually in the first 6 months), which can cause new catching or locking and needs your team.
NHS and US plans range from full weight with crutches to partial weight (about half your body weight) or none for the first 6 weeks. After MACI, one US hospital's guideline builds from 20% to 75% of body weight over 6 weeks, and NICE says no weight for 4 to 8 weeks is usual after mosaicplasty. Across US protocols, full weight was allowed at an average of about 6 weeks after microfracture of the thigh bone, sooner for the kneecap joint, and at 5 to 6 weeks after grafts. Most trials of ACI used partial weight straight away and full weight within 12 weeks.
In trials from one Australian group, reaching full weight 8 weeks after MACI did as well as 11 weeks at 2, 5 and 10 years, and 6 weeks did as well as 8 weeks, with no harm to the graft. These are small trials in specialist hands, so keep to the limits your team sets.
In a study of 43 small defects, taking weight as comfortable without a continuous passive motion (CPM) machine did as well as 6 weeks without weight and with the machine. A review concludes that weight limits may not be needed for small defects on the main weight-bearing surfaces, but the evidence is low level, so your team's limits still apply.
Across 2,549 athletes, 76% went back to sport: 93% after an osteochondral autograft (at about 5 months), 88% after a donor graft (about 10 months), 82% after ACI (about 12 months) and 58% after microfracture (about 9 months). An earlier review found 73% went back, at 7 to 18 months. In 7 trials (346 people), autografts gave a better return to sport and fewer failures than microfracture. These reviews pool mostly low-quality studies.
NHS and US protocols set criteria rather than dates: running from about 12 to 20 weeks, and competitive sport from about 20 weeks after microfracture in one NHS protocol, once strength and control allow and the knee isn't swelling.
In 11 studies (6 of them trials, 664 people), adding platelet-rich plasma (PRP) to microfracture improved pain and function scores at some time points but not others, and the authors call for better studies. It's an add-on with uncertain benefit.
Source 31
NICE says medicine to prevent clots is generally not needed after keyhole knee surgery when the anaesthetic is under 90 minutes and the risk is low, and to consider it for 14 days when the operation is longer or the risk is higher, and for other knee surgery when the risk of a clot outweighs the risk of bleeding. One NHS trust gives daily injections for about 14 days when they're needed, and advises no flying for 8 weeks after microfracture.
One NHS trust's leaflet says the exercises should be pain-free, and a US hospital's guideline says to avoid pain during exercise and daily activities, with no pain or swelling after activity before moving on. Another NHS leaflet says extra discomfort for up to an hour after the exercises is normal, and another says to avoid activities that are painful and make the knee swell.
So, borrowed from our knee osteochondritis dissecans (OCD) guide's rule: for walking, running and jumping, no pain in the knee joint during, straight after or the next morning; for strength exercises, no pain in the joint, though a working ache in the thigh or hip muscles that settles within the hour is fine. Catching, locking, giving way, new swelling, or a knee that doesn't straighten as far as before are never part of the rule: stop and contact your team.
Swelling is the other gauge, borrowed from our anterior cruciate ligament (ACL) guide: measure round the middle of both knees with a soft tape, and if the operated knee is more than about 1 cm bigger after a session, let it settle before carrying on. This is stricter than our knee pain hub's rule for long-standing knee pain, because the joint surface is healing.
Start at the first stage. Each move opens a full guide with a 3D demo.
As your team allows. Keep exactly to the weight your team sets for about the first 6 weeks: none, part of your weight, or full weight with crutches, depending on the operation and where the defect is. Wear any brace as you're told, often all the time, including at night. Get the knee fully straight, get the bend back within your limits, and keep the thigh working, with the exercises 3 to 4 times a day. Keep the leg raised with nothing under the knee, and use ice for 15 to 20 minutes. The exercises should be pain-free; some extra discomfort for up to an hour afterwards is normal.
3D demoAnkle circlesBeginner · No equipmentPump the ankle up and down 10 times every waking hour · An NHS leaflet's dose; up-and-down pumps rather than the move page's circles
3D demoQuad set (static quads)Beginner · No equipmentHold 10 s, 10 times, 3 to 4 times a day · An NHS leaflet's dose
Harder: Straight-leg raise
3D demoSupine heel slideBeginner · No equipment10 slides, 3 to 4 times a day, only within your bending limit · An NHS leaflet's dose, a little more often than the move page's
Harder: Hip windshield wipers
3D demoStraight-leg raiseBeginner · No equipmentHold 5 s, 10 times, when your team says · NHS leaflets' dose
Easier: Quad set (static quads) · Harder: Leg extension
3D demoSide-lying leg raiseBeginner · No equipment10 times, operated leg on top, when your physiotherapist says · An NHS leaflet's dose
Easier: Lateral band walk · Harder: Lateral band walk, band at the feet
Move on when: Your team lifts the weight limit (often at about 6 weeks, sooner after some operations and later after others), you can lift the straight leg without the knee bending, the swelling is settling, and the knee straightens fully.
As your team allows. Come off the crutches as your team says, and walk normally, heel first and without a limp. Get the bend back. Start loading the leg standing up: in an NHS and a US protocol, the bike, step-ups, chair squats and a light leg press start in or just before this window. Keep exercises out of any range your team gives you to avoid. Doses are editorial.
3D demoStationary cyclingBeginner · Cardio machine10 to 20 minutes, easy, with the saddle high · Editorial dose
Easier: Recumbent exercise bike · Harder: Air bike intervals
3D demoSit to stand from a chairBeginner · A bench or box2 to 3 sets of 10, from a higher chair at first · Editorial dose
Easier: Sit to stand, pushing on the thighs · Harder: Bodyweight squat
3D demoLeg pressBeginner · Strength machineLight, 3 sets of 10 to 12, in the range your team allows · Editorial dose
Harder: Bodyweight squat
3D demoGlute bridgeBeginner · No equipment2 to 3 sets of 10 · Editorial dose
Easier: Pelvic tilt into bridge · Harder: Single-leg glute bridge
3D demoLow step-upBeginner · A step2 sets of 10 on each leg, from a 10 cm step, building towards 20 cm · Editorial dose; a US guideline builds the step height the same way
Harder: Step-up
3D demoSingle-leg standBeginner · A wall3 holds of up to 30 s, near a support · Editorial dose
Easier: Tandem stance and heel-to-toe walk · Harder: Single-leg reach matrix
Move on when: You walk normally, have full movement (or as much as your team allows), and can step up onto a 20 cm step, squat evenly to a right angle and stand on the operated leg for more than 30 seconds, with no swelling after sessions. These are a US hospital's criteria.
As your team allows. Heavier and single-leg strength work 2 to 3 times a week, keeping the knee in line over the middle of the foot, and low-impact cardio such as the cross-trainer. In one NHS protocol after microfracture of the kneecap groove, strength without range limits starts at 12 weeks, with light jogging, changes of direction and jumping drills from 12 to 16 weeks; a US guideline starts running from about 20 weeks after MACI. Doses are editorial unless named.
3D demoDumbbell goblet squatIntermediate · A dumbbell3 sets of 8 to 12, to a box at first, going deeper over the weeks · Editorial dose
Easier: Bodyweight squat · Harder: Barbell front squat
3D demoSplit squatIntermediate · No equipment3 sets of 8 on each leg, holding a support · Editorial dose
Easier: Bodyweight squat · Harder: Reverse lunge
3D demoPatrick step-downIntermediate · A step3 sets of 8 to 10 on each leg, from a low step · Editorial dose
Easier: Bodyweight squat · Harder: Skater squat
3D demoSingle-leg Romanian deadliftAdvanced · A dumbbell3 sets of 8 on each leg · Editorial dose
Easier: Dumbbell Romanian deadlift
3D demoLateral band walkBeginner · A band3 sets of 10 steps each way · Editorial dose
Easier: Hip abduction machine · Harder: Lateral band walk, band at the feet
3D demoElliptical trainerBeginner · Cardio machine10 to 20 minutes at a moderate effort, building towards 30 · The move page's dose
Harder: Stair-stepper machine
Move on when: Thigh strength is at least 80% of the other side's (a physiotherapist can test it), there's no pain or swelling after activity, and you can step down from 20 cm and squat on one leg to 45 to 60° with control. These are a US hospital's criteria.
As your team allows. Running starts from about 12 to 16 weeks after microfracture of the kneecap groove in one NHS protocol, and from about 20 weeks after MACI in a US hospital's guideline. Agility, cutting and twisting come next, and competitive sport from about 20 weeks after that microfracture. Across studies, going back to sport took about 5 months after an osteochondral autograft and about 12 months after ACI. Doses are editorial unless named.
3D demoTreadmill joggingIntermediate · Cardio machineWalk-jog intervals every other day, building to continuous running; stop if the knee swells · Editorial dose
Easier: Treadmill walking · Harder: Sprint intervals
3D demoSnapdown to athletic landingBeginner · No equipment2 to 3 sets of 5, freezing each landing · Editorial dose
Harder: Box drop landing
3D demoSingle-leg hop and stickIntermediate · No equipment3 sets of 5 on each leg, forwards then sideways · Editorial dose
Easier: Standing broad jump with stuck landing · Harder: Alternate-leg bounding
3D demoLateral bound (skater jump)Beginner · No equipment3 sets of 6 to 8 bounds (3 or 4 on each leg), resting a minute between sets · The move page's dose
Harder: Bench jump-over
3D demoShuttle runsAdvanced · No equipmentShort sets with wide, easy turns at first, building speed over the weeks · Editorial dose
Easier: Treadmill jogging
Move on when: Your team clears you for sport: no swelling or pain in the joint after training, full movement, and strength and hops close to the other leg's (90% in a US hospital's guideline). Keep a strength day or two a week, and use a knee control warm-up before pivoting sport.
These come from NHS leaflets, NICE and a US hospital's guideline, and they differ. Your own team's timings come first.
From the Gateshead and Worcestershire NHS leaflets.
From the Worcestershire NHS leaflet, with our suggestion marked.
Source 9
From the Worcestershire NHS leaflet. Some teams use a continuous passive motion (CPM) machine to bend the knee for you in the first weeks, as most ACI trials did; this is the home version.
From the Liverpool NHS leaflet. Take only the weight your team allows through the operated leg.
Source 4
From about 6 weeks: the cardio intervals workout (on the bike), the low-impact leg workout and the balance exercises routine; skip the leg workout's wall sit if your defect is on the kneecap or its groove, until your team allows. From about 3 months: the knee strengthening workout, leaving out its heel-elevated deep squat and reverse Nordic until your team allows deep bending (our meniscus surgery guide makes the same exception), and its wall sit with a kneecap or groove defect. Save the knee control warm-up for the return to sport.
| Habit or position | Why it matters | Instead |
|---|---|---|
| Putting more weight through the leg than your team allows in the first 6 weeks | The new surface needs protecting while it forms. The trials of earlier weight-bearing were planned protocols in specialist centres. | Crutches, with only the weight you're allowed. |
| Bending past your limit, or outside the brace's setting | Limits protect the repaired area, especially on the kneecap or its groove. | Heel slides within your limit, and bending the knee with a towel.Try: Supine heel slide |
| A pillow under the knee | The knee can stiffen bent; NHS leaflets say rest with it straight. | The heel prop in the written steps. |
| Deep squats before your team allows deep bending | Deep bending loads the joint surface heavily (our reasoning). | The bike, and a leg press in the range your team allows.Try: Leg press |
| Wall sits with a kneecap or groove defect, before your team allows | Holding a bent knee under load presses the kneecap into its groove (our reasoning); one NHS protocol keeps thigh exercises out of the defect's range. | The bike, in the range your team allows.Try: Stationary cycling |
| Knee extensions against a weight with a kneecap or groove defect, before your team allows | They load the kneecap joint through a range your team may want to avoid. | Tightening the thigh with the leg straight.Try: Quad set (static quads) |
| The reverse Nordic, before your team allows deep bending | It bends the knee deeply under load (our reasoning). | Split squats in a short range.Try: Split squat |
| Long walks in the first week | One NHS leaflet advises no more than 15 minutes at a time in the first week. | Short, frequent walks on crutches. |
| Running and jumping before your team allows | Protocols wait until about 12 to 20 weeks, and a graft can lift off in the first months. | The cross-trainer and the bike.Try: Elliptical trainer |
| Pushing through pain or swelling in the joint | Pain in the joint, swelling or catching means the healing surface is being overloaded. | Drop back a step, not to nothing. |
A 25-minute interval session on a bike or rower: one-minute hard efforts with two minutes easy, building from 4 to 8 rounds.
25 minIntermediate1 movesCardio machineA gentle leg strength routine with no jumping: sit-to-stands, step-ups, wall sits, bridges and calf raises.
20 minBeginner7 movesA bench or box, A stepBalance practice in 10 minutes: tandem stance, single-leg stands, marches, heel walks, tree pose and floor transfers.
10 minBeginner7 movesA wall, A bench or boxA 25-minute session for knees that don't currently hurt: thigh and hamstring strength, single-leg control, then an optional full-range block with knees over toes.
25 minBeginner13 movesA bench or box, A wallA 20-minute warm-up that trains your knees to track over your toes: side-hip strength, squats and lunges with alignment practice, balance and quiet landings.
20 minBeginner10 movesA wall, A bandNo. This guide is about the smooth cartilage on the ends of the bones. The NHS's knee cartilage damage page is about meniscus tears, the cushions between the bones, and our meniscus surgery guide covers those. Your operation note or surgeon can tell you which you had.
The new surface is protected for about the first 6 weeks, usually with crutches. Rehab takes 6 to 12 months, and one NHS trust says most people notice a big improvement by 6 months, but full recovery can take 12 to 18 months.
The clot or graft that forms the new surface needs protecting while it settles in, so most teams limit weight for about 6 weeks. How much depends on the operation and where the defect is: defects on the kneecap often allow more weight than those on the main weight-bearing surfaces. Follow your team's limits exactly.
ACI means two operations, and recovery is long. Weight is built up over about 6 to 12 weeks, running may start from about 20 weeks, and going back to sport took about 12 months on average in studies. In trials, people were still doing well 10 years later.
Some teams use a continuous passive motion (CPM) machine to bend the knee gently in the first weeks. Others ask you to bend it yourself with a towel or your other leg, many times a day. For small defects, going without a machine did no worse in one study.
Usually not while your weight is limited: one NHS trust says at least 6 weeks. You need to walk without crutches and be able to do an emergency stop, and you should tell your insurer.
Running often starts from about 12 to 20 weeks, and competitive sport from about 5 months after microfracture in one NHS protocol. Across studies, 76% went back to sport: fastest after a graft from your own knee (about 5 months) and slowest after ACI (about a year). Your team decides, often using strength and hop tests.
Not exactly: microfracture makes a tougher, less smooth repair tissue called fibrocartilage. Many people still do well. Results after microfracture of larger defects tend to decline over the years, while grafts and cell implants held up better in some trials.
Not necessarily. Most MRI measures of a cartilage repair match how people feel poorly, and in one trial, two operations with similar filling on MRI felt different. Your surgeon will weigh the scan alongside your symptoms.
Some people do, years later: in a 15-year trial, about half the knees still working had early signs of arthritis on X-ray after either ACI or microfracture. Keeping the thigh strong and staying active within your team's advice gives the knee its best chance.
A desk job may be possible within days to a couple of weeks if you can keep your leg up. Jobs on your feet usually wait until your weight limits are lifted and walking is comfortable. Your team will advise.
Exercise education, not a diagnosis or treatment plan. It is written from the guidelines and studies listed above; review by a clinician is pending. If your pain follows an injury, is severe, is getting worse, or comes with any warning sign listed on this page, get it assessed. Health disclaimer.
