Pain guide · Knee pain
A plica is a fold in the knee's lining left over from before birth, and most knees have one. Plica syndrome is when the fold becomes thickened and irritated, usually on the inner edge of the kneecap, causing pain at one spot and often a click or snap as you bend, worse on stairs and after sitting.
Because plicae are so common, a scan showing one isn't a diagnosis: other causes are ruled out first. Most people start with about 3 months of thigh and hip strengthening and stretching, and many improve; if that doesn't work, removing the fold by keyhole surgery did better in two small trials. This guide covers how it's recognised, what the trials found and a staged plan with 3D demos.
Exercise is for pain that has been checked or is clearly mild and settling.
Plicae are folds of the knee's lining (the synovium). They are left over from thin walls that divide the knee early in its development, before birth, and are only partly absorbed. There are four: above the kneecap, along its inner edge (the medial plica), below it, and rarely on the outer side. The medial plica is the one that usually causes trouble.
In 3,889 knees seen at keyhole surgery in Japan, 80% had a medial plica. On MRI (magnetic resonance imaging) of 342 painful knees, 48% had one. A normal plica is thin, flexible and almost see-through: on dynamic ultrasound of 60 knees of volunteers without symptoms, 23 showed a plica, and none of them looked abnormal.
A blow, a sudden increase in activity, or inflammation inside the knee can irritate the plica. It thickens, scars and loses its stretch, then rubs over the inner bump of the thigh bone or tugs on the lining, causing pain and sometimes wear of the cartilage next to it. An injury started it in 57% of 969 operated patients in a review, but only 16% of the 48 people in a Danish trial recalled one.
Mostly teenagers and young adults: the average age was 25 in the review of 969 patients and 27 in the Danish trial, and a British trial was in children and teenagers.
The main symptom is pain at one spot on the inner front of the knee. In the Danish trial, 67% also had clicking, 67% pain when sitting, 25% snapping, 25% a feeling of instability and only 8% swelling. Stairs, squatting, bending and getting up after sitting for a long time bring it on, and some people feel the knee catch.
It's a diagnosis of exclusion. Other causes of pain at the front of the knee, such as runner's knee, a meniscus tear, cartilage damage or tendon problems, are ruled out first, often with an MRI. The plica is then diagnosed from tenderness over a band on the inner edge of the kneecap, sometimes with a snap you can feel.
In a review of 7 studies (492 knees) checked against keyhole surgery, an examination test picked up 90% of painful plicae and was correctly negative in 89% of knees without one, and ultrasound did nearly as well (90% and 83%). MRI picked up 77% but wrongly flagged 42% of knees without plica syndrome. In another study, an examination method was confirmed at keyhole surgery in 44 of 48 people, and a 2026 study of 156 knees found MRI showed the plica well but classified it poorly. A scan can show a plica, but not whether it's the cause of your pain.
It's an uncommon cause of knee pain. In one Brazilian clinic, 63 of about 3,200 people with knee problems (2%) were thought to have it, and in one US series, 76 of nearly 2,000 keyhole examinations (4%) found a thickened plica as the only problem. Estimates range from 3 to 30%, depending on the group studied.
Many people improve with about 3 months of conservative care: 55 of 63 in one series. Results were more mixed in another, with 40% good, 20% average and 40% poor results in 136 people, and at a German surgical centre, 76 of 117 people (65%) went on to surgery after 3 months. People who stopped their exercises tended to slip back.
Runner's knee hurts around or behind the kneecap more widely; the Danish trial left out people with that kind of pain for this reason. Jumper's knee hurts on the tendon below the kneecap, a meniscus tear hurts on the joint line and can lock, and pes anserine pain sits lower, on the inner shin. Each has its own guide.
Source 7
The usual first treatment is about 3 months of changing your activities, anti-inflammatory painkillers if they suit you, strengthening of the thigh and hips, and stretching of the hamstrings, calves and quadriceps, ideally with a physiotherapist. A US professional body says physical therapy is the most common treatment. This rests on case series and expert advice: no trial has compared exercise with no treatment.
In one series of 63 people, 90 days of changing activity, stretching and knee-straightening exercises, especially the last part of straightening, helped 55, and 8 had surgery. In another of 136, stretching gave good results in 40%, average in 20% and poor in 40%, which the authors judged enough to try it before surgery. The Danish trial's programme, which the plan below follows, used quadriceps strengthening, straight-leg raises, the leg press, an exercise bike and an elliptical trainer, with stretches.
Two small randomised trials compared keyhole removal of the plica with leaving it, and both favoured removal for symptoms that persisted. Each has limits:
Across 23 studies (969 patients), 64% were free of symptoms after removal, 26% improved and 10% didn't, at about 2 years. A review of 12 studies (643 knees) estimated good or excellent results in 84%, and in 76% of people who had tried non-surgical care first. Results were poorer with cartilage damage under the plica, an unclear diagnosis and older age. There were no surgical complications in the Danish trial.
In one series, an injection of steroid and local anaesthetic into the plica gave complete relief and a full return to activity in 22 of 30 people (73%), with 3 poor results; a local anaesthetic alone helped only while it lasted. Reviews suggest an injection early, while the plica is inflamed rather than scarred, as a help to exercise rather than on its own, and note that placing it accurately in such a thin fold needs image guidance.
In 117 people treated for 3 months at a German surgical centre, a thicker plica, a plica touching the cartilage behind the kneecap, and persistent pain with snapping as the knee bends and straightens went with conservative care failing. This was a surgical centre's patients looked at afterwards, so the figures may not apply to everyone.
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Rate your pain from 0 to 10 during and after exercise. In the pain-monitoring model used in knee trials, 0 to 2 counts as safe, up to 5 as acceptable and above 5 as too much; aim for 0 to 3 most of the time. It's borrowed from our other knee guides: no plica study has tested a pain rule.
The spot on the inner edge of the kneecap should be no sorer the next morning. If it is, shorten the range or drop back a step. In the Danish trial, the programme was adjusted when symptoms flared.
Painless clicking is normal. A painful catch or snap during an exercise means make the range smaller or swap the exercise (our suggestion), and painful catching that keeps happening is a reason to get it checked.
Start at the first stage. Each move opens a full guide with a 3D demo.
Cut back on what brings the pain on, without stopping activity altogether: long sits with the knee bent, deep squats and lunges, jumping, and lots of stairs. Ice and painkillers can help a flare. The exercises follow the choice in the Danish trial's physiotherapy programme, whose doses couldn't be found, so the doses here are borrowed from our other knee guides as editorial starting points. Do them daily.
3D demoQuad set (static quads)Beginner · No equipment10 holds of 5 s, 2 to 3 times a day · Works the last part of straightening
Harder: Straight-leg raise
3D demoStraight-leg raiseBeginner · No equipment2 sets of 10 each leg · In the trial's programme
Easier: Quad set (static quads) · Harder: Leg extension
3D demoStationary cyclingBeginner · Cardio machine10 to 15 min easy, seat high · In the trial's programme
Harder: Air bike intervals
3D demoSupine hamstring stretch with a strapBeginner · No equipment2 to 3 holds of 30 s each leg · Back off if you feel burning or tingling down the leg
Easier: Leg-up hamstring stretch · Harder: Contract-relax hamstring stretch (PNF)
3D demoWall calf stretch (gastrocnemius)Beginner · A wall2 to 3 holds of 30 s each leg
Easier: Seated calf stretch with a towel · Harder: Toes-tucked kneeling (toe squat)
3D demoStanding quad stretchBeginner · A wall2 rounds of 30 to 45 s each side · Only if the knee bend doesn't pinch; hold your trouser leg rather than the ankle if it does
Harder: Couch stretch
Move on when: Stairs and sitting are within the pain rule, and the spot on the inner edge of the kneecap is less tender.
Strength 2 to 3 days a week, with the feet on the floor or a footplate and a shallow range first, plus the stretches from stage 1.
3D demoLeg pressBeginner · Strength machine3 sets of 10 to 12 · Limited depth at first; in the trial's programme
Harder: Bodyweight squat
3D demoElliptical trainerBeginner · Cardio machine10 to 20 min at a moderate effort · In the trial's programme
Harder: Stair-stepper machine
3D demoSit squat (partial squat)Beginner · No equipment3 sets of 10 · To about 45 degrees of knee bend
Harder: Bodyweight squat
3D demoStep-upBeginner · A step3 sets of 8 to 10 each leg · Low step first
Easier: Low step-up · Harder: Dumbbell step-up
3D demoClamshellBeginner · No equipment3 sets of 12 to 15 each side · Hip strength, as a US professional body advises
Harder: Lateral band walk
3D demoSide-lying quad stretchBeginner · No equipment20 to 30 s, 2 to 4 times each side · Use a belt if the full knee bend pinches
Move on when: Shallow squats, step-ups and the leg press are within the pain rule with no painful catching, and the knee settles by the next morning.
Heavier and single-leg work 2 to 3 times a week, then running and sport. Keep the exercises going afterwards: in the Danish trial, people who stopped tended to slip back.
3D demoDumbbell goblet squatIntermediate · A dumbbell3 sets of 8 to 12 · Deeper as it allows
Easier: Bodyweight squat · Harder: Back squat with bands
3D demoSplit squatIntermediate · No equipment3 sets of 8 each leg
Easier: Bodyweight squat · Harder: Reverse lunge
3D demoPatrick step-downIntermediate · A step3 sets of 8 to 10 each leg
Easier: Bodyweight squat · Harder: Skater squat
3D demoLateral band walkBeginner · A band3 sets of 10 to 15 steps each way
Easier: Hip abduction machine · Harder: Lateral band walk, band at the feet
3D demoSingle-leg standBeginner · A wall3 holds of 30 s each leg
Easier: Tandem stance and heel-to-toe walk · Harder: Single-leg reach matrix
3D demoTreadmill joggingIntermediate · Cardio machineWalk-jog intervals on the flat, if you run · Build time before speed or hills
Easier: Treadmill walking · Harder: Sprint intervals
Move on when: Daily life and sport stay within the pain rule. If there's no clear improvement after about 3 months of doing this well, ask about a referral to discuss an injection or surgery.
Long sits with the knee bent, deep squats and lunges, jumping and lots of stairs bring the pain on. Stretch the leg out when you sit for a while, use shallow squats, and spread stairs through the day. The trial's programme avoided exercises that straighten the knee against a weight with the foot free, such as the leg extension machine, when they irritated the plica.
In the Danish trial, most people in the physiotherapy group said they stopped after 3 to 6 months, and their scores slipped by 2 years. Two short sessions a week once you feel better is a reasonable way to keep the gains (our suggestion).
Source 7
| Habit or position | Why it matters | Instead |
|---|---|---|
| Long sits with the knee bent, deep squats and lunges, and lots of stairs in a flare | These bring the pain on. | Shorter sits with the leg stretched out, shallow squats, and stairs spread through the day.Try: Sit squat (partial squat) |
| The leg extension machine, or full-range knee extensions, if they catch | The trial's programme avoided exercises like these when they irritated the plica. | The leg press and shallow squats, and quad sets for the last part of straightening.Try: Leg press |
| Pushing through painful catches or snaps | Persistent pain with snapping went with conservative care failing. | A smaller range, or a different exercise (our suggestion).Try: Quad set (static quads) |
| Stopping the exercises as soon as it feels better | In the trial, people who stopped after 3 to 6 months tended to get worse again. | Keep two short sessions a week going.Try: Split squat |
| Asking for an MRI to find the plica | Most knees have one, and MRI is less accurate than examination for plica syndrome. | Examination first, with scans to rule out other causes. |
| Relying on stretching alone | The programmes in the studies combined strengthening and stretching. | Strength work plus stretches.Try: Straight-leg raise |
A 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 stepSeven stretches for after a run: calves, soleus, quads, hip flexors, hamstrings and glutes.
10 minBeginner7 movesA wallA 12-minute routine to loosen tight hamstrings with strap stretches, PNF, folds and hinges.
12 minBeginner7 movesNo equipmentA fold of the knee's lining left over from its development before birth. Most people have one: 80% of knees at keyhole surgery in a large Japanese study. It only causes trouble when it becomes thickened and irritated.
It's an uncommon cause of knee pain: about 2% of people at one knee clinic, and 4% of nearly 2,000 keyhole examinations in another series. It's most often seen in teenagers and young adults.
Pain at one spot on the inner front of the knee, often with clicking or snapping as you bend, worse on stairs, squatting and sitting for a long time. Swelling is unusual.
By examination, after other causes have been ruled out. An MRI is mostly for ruling out other problems: it can show a plica, but most knees have one, and an examination test or ultrasound diagnosed plica syndrome more accurately.
Strengthening the thigh, especially the last part of straightening, and the hips, with stretches of the hamstrings, calves and quadriceps, for about 3 months. The plan on this page follows the choice of exercises in a Danish trial's physiotherapy programme.
For now, deep squats and lunges, jumping, long sits with the knee bent, and any exercise that makes the plica catch painfully, such as the leg extension machine. Build them back gradually.
Programmes in the studies ran for about 3 months, and many people improved over that time. If there's no clear improvement after about 3 months of good rehab, ask about a referral.
If symptoms persist despite a good programme, removal is a reasonable option. In two small trials it did better than a keyhole examination that left the plica alone and, at 2 years, better than physiotherapy, though only 33 of 48 people were assessed then and many had stopped their exercises. Results were poorer with cartilage damage under the plica.
A steroid injection into the plica gave full relief in 73% of 30 people in one series. Reviews suggest it early, as a help to exercise rather than on its own.
No. Runner's knee is pain around or behind the kneecap; plica syndrome is pain at one spot on its inner edge, often with a click. They're treated in similar ways, and runner's knee has its own guide.
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.
