Pain guide · Knee pain
Pain behind the knee is less common than pain at the front or sides, and it has a wide range of possible causes. A soft lump that is tight to bend and worse after walking is usually a Baker's cyst, which in adults usually comes with arthritis or a meniscus tear; otherwise it is often a hamstring or calf tendon, the back of the meniscus or, after a fall onto a bent knee, the posterior cruciate ligament (PCL).
Because a blood clot can also cause pain behind the knee and in the calf, this guide starts with the National Health Service (NHS) clot signs and the other signs that need help today, from a 999 call or accident and emergency (A&E) to NHS 111 or a general practitioner (GP). It then maps the causes by the exact spot, explains when an ultrasound scan helps and why draining a cyst rarely fixes it for good, and gives a three-stage plan, with a joint lane and a tendon lane, that ends with walking, bending, kneeling and sport.
Exercise is for pain that has been checked or is clearly mild and settling.
Location narrows the likely causes; it does not diagnose.
Often a Baker's cyst, usually with arthritis or a meniscus tear.
Read: Baker's cyst →A possible clot (deep vein thrombosis, DVT): get help the same day, as the warning signs say.
A burst cyst or a clot: they look alike and need the same same-day check.
Read: Baker's cyst →The semimembranosus (hamstring) tendon: this guide's tendon lane.
The biceps femoris (hamstring) tendon: this guide's tendon lane.
A hamstring strain.
Read: Hamstring strain →The upper calf just below the back of the knee, sore with calf raises and bending the knee against resistanceThe calf muscle (gastrocnemius).
Read: Calf pain →Deep at the back outer corner, sore taking weight with the knee slightly bent, especially after a twist or a blowThe popliteus, often hurt with the back outer corner of the knee.
Read: LCL sprain →Catching or locking with pain at the back, after a twist or at the bottom of a squatPossibly the back of the meniscus: get it assessed.
Read: Meniscus tear →A single painful pop in mid-lifeIt can be a tear at the root of the inner meniscus: see a GP.
Read: Meniscus tear →After a fall onto a bent knee or a dashboard injury: pain, swelling and a knee that may give outA possible PCL injury: get it assessed.
Read: PCL injury →After the knee was forced past straightA hyperextension injury.
Read: Hyperextended knee →A squeezed feeling only at the deepest bend, with no lump, swelling or catchingCommon, as our knee pain when squatting guide explains.
Read: Knee pain when squatting →A sudden, painful tightening of the calf at night or at rest that passes within 10 minutesCramp.
Read: Leg cramps →Pain from the buttock down the back of the leg, often to the foot, with tingling or numbnessSciatica, from a nerve in the back.
Read: Sciatica →Rarely, popliteal artery entrapment: see a GP.
It needs a GP's check: other lumps include a swelling of the artery and, rarely, a tumour.
Growing pains. Hip problems in children can be felt in the knee, so sudden knee pain or a limp needs an urgent GP appointment or NHS 111.
Read: Growing pains →Pain mostly when you bend or straighten the kneeOur knee pain when bending guide.
Read: Knee pain when bending →Pain mostly when you walkOur knee pain when walking guide.
Read: Knee pain when walking →Pain mostly on stairsOur knee pain on stairs guide.
Read: Knee pain on stairs →Pain mostly when you cycleOur knee pain when cycling guide.
Read: Knee pain when cycling →Pain behind the knee is less common than pain at the front or sides. A review lists tendon and other soft tissue causes as commoner than nerve and blood vessel ones, and a family medicine review says pain only at the back may come from a Baker's cyst; after an injury, from the PCL or the back of the meniscus; and, when it lasts, from a hamstring tendon. Pain can also be felt there from the hip, the lower back and the kneecap joint.
A Baker's cyst is a fluid-filled lump at the back of the knee that connects with the joint. It may show more when you stand, and it can cause pain, tightness, stiffness, difficulty bending and clicking, often worse after walking, the NHS says. In adults it usually comes from another knee problem, such as osteoarthritis, a meniscus tear, rheumatoid arthritis or gout.
On 1,001 knee magnetic resonance imaging (MRI) scans, cysts were seen in 4.7%, and 94% came with another problem in the knee, a meniscus tear in 83%, often at the back of the inner meniscus. An NHS trust leaflet says cysts are commonest in children aged 4 to 7 and adults aged 35 to 70.
About 1 to 2 in 20 cysts are thought to burst, an NHS trust leaflet says, and a burst cyst is hard to tell from a deep vein thrombosis (DVT), a clot in a deep vein of the leg. Of 3,072 people scanned for a suspected clot, 95 had cysts, and 7 of those also had a clot. Cysts don't seem to cause clots, though: across 357,703 leg vein scans, cysts were not a risk factor.
The NHS lists the signs of a DVT separately, and any of them can be a clot: throbbing pain in one leg (rarely both), usually the calf or thigh; swelling in one leg; red, blue or darkened skin around the painful area; or swollen veins. A suspected clot is referred for an ultrasound scan within 24 hours, and the National Institute for Health and Care Excellence (NICE) asks for the result within 4 hours if possible when a clot is likely.
The semimembranosus, a hamstring tendon at the back inner corner, aches with tenderness just below the joint; it's uncommon, often seen in runners, and little studied. The biceps femoris, the outer hamstring, runs to the bony bump below the outer knee. The calf muscle (gastrocnemius) hurts when you bend the knee against resistance or rise onto your toes, and the popliteus, deep at the back outer corner, hurts bearing weight with the knee bent 15° to 30°.
Meniscus tears rarely show up as pain at the back, mostly tears of the back of the inner meniscus. A single painful pop in mid-life can point to a tear at the root of the inner meniscus, as one study of people already having keyhole surgery found; in 234 people whose root tears were repaired, about 80% were women and the average age was 65.
In 494 people with a long-standing PCL injury, traffic accidents (45%) and sport (40%) were the causes, a dashboard injury the commonest way (35%), and 53% had other ligaments injured too. The American Academy of Orthopaedic Surgeons (AAOS) describes pain and swelling that come quickly, a stiff knee, a limp and a knee that may feel it will give out.
A popliteal artery aneurysm, a swelling of the artery behind the knee, is the commonest aneurysm in the limbs; 95% to 99% are in men, about half are in both legs, and 30% to 50% come with an aneurysm of the aorta. A clot in one can threaten the leg, and a review lists it among the lumps that can be mistaken for a cyst.
Popliteal artery entrapment, where a muscle squeezes the artery, causes calf and foot pain after exercise that eases with rest in young, active people without the usual risk factors for narrowed arteries, sometimes in both legs. It's uncommon, and diagnosing it early helps prevent clots.
For a lump, an ultrasound scan confirms a cyst and shows what's inside it, and an MRI shows the problems inside the knee that cause it; a GP may arrange either. A possible clot needs an ultrasound scan, within 24 hours, the NHS says. After an injury, the Ottawa knee rule decides on an X-ray, and an MRI looks at the PCL and the meniscus.
Artery problems are checked by comparing the blood pressure at the ankle and the arm, or with a Doppler ultrasound scan while the foot is pushed or pulled, then a scan of the arteries; an aneurysm is followed with ultrasound scans.
A Baker's cyst may go away on its own, especially in children, or when its cause is treated, and the NHS says it can take a few months to a few years; a burst cyst makes symptoms worse for a few weeks until the swelling goes down, and cysts often come back after draining. A clot is treated with blood-thinning medicine, usually for at least 3 months. Mild hamstring injuries get better in a few days and severe ones take weeks or months; a cramp lasts from a few seconds to 10 minutes. No one can promise a date.
If a cyst comes from another knee problem, the NHS says it often gets better when that problem is treated, and lists physiotherapy among the treatments; an NHS trust leaflet says keeping the knee moving and strengthening the muscles around it may help. For osteoarthritis, NICE makes exercise a core treatment, and for a worn meniscus tear, 12 weeks of exercise did as well as keyhole surgery at 2 years. No trial has tested exercise for the cyst itself.
Draining the fluid and a steroid injection ease a cyst, but it commonly re-forms, an NHS trust leaflet says. The NHS lists a painkilling injection into the knee, draining the fluid and surgery to repair damage inside the knee, and says surgery to remove the cyst itself is rare. In knee osteoarthritis, a steroid injection into the knee shrank cysts in a study a review describes.
For the semimembranosus, the treatment evidence is scant, so a review suggests modelling rehabilitation on other tendon problems: progressive tendon loading and hamstring strength. After a fresh hamstring injury, the NHS advises protection, rest, ice, compression and elevation for the first 2 to 3 days, and no heat, massage or alcohol for the first 3 days; a physiotherapist's exercises can speed recovery and help prevent another injury.
A DVT is treated with blood-thinning medicine, usually for at least 3 months, the NHS says. To lower the chance of a clot on journeys of 4 hours or more, it advises getting up and moving around every hour or so, drinking plenty of water and avoiding alcohol. Our exercise after a blood clot page covers getting active again.
Source 9
Strengthening the front of the thigh is a key part of recovery from a PCL injury, the AAOS says, with surgery for combined injuries or instability that persists; our PCL guide has the plan. A popliteal aneurysm is watched with scans or repaired with open surgery or a stent, and entrapment is treated by freeing the artery from the muscle.
For a Baker's cyst and most joint pain, this guide uses our Baker's cyst guide's rule. Rate your knee 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.
By the next morning your knee should be back to its usual level. If it isn't, or the swelling behind the knee is bigger or tighter, drop back one step next time: fewer sets or a smaller bend. The swelling check is our suggestion; this rule has never been tested for Baker's cysts. NICE says joint pain may rise when you start exercising with osteoarthritis, and regular exercise still helps.
For a sore tendon at the back of the knee, we borrow the stricter limit our tendon guides use: keep tendon pain during the exercise to about 3 out of 10, settling by the next morning. No trial has tested a rule for hamstring, calf or popliteus tendon pain at the knee; in trials of long-lasting muscle and joint pain, exercise that allowed some pain did no worse than pain-free exercise.
New calf pain, swelling, warmth or redness is not a pain-rule question: stop and get a same-day check. Nor are red, blue or darkened skin, a cold or pale foot, a lump that is growing, or calf pain on exercise in a young athlete.
Start at the first stage. Each move opens a full guide with a 3D demo.
About the first 2 weeks. Joint lane (a cyst, arthritis or the back of the meniscus): rest, an ice pack wrapped in a tea towel for around 10 minutes at a time and the leg raised, as the NHS advises for a cyst; bend only as far as the back of the knee is comfortable, and take shorter walks spread through the day (our Baker's cyst guide). Tendon lane (a hamstring or calf tendon, or the popliteus): cut back the load that provokes it, such as hills, sprints or long rides, without stopping altogether (our suggestion). Nobody starts either lane with a swollen, throbbing calf, red, blue or darkened skin, a cold or pale foot, or a growing lump; with a cyst, a meniscus tear, a PCL injury or arthritis, that guide's plan can replace this one.
3D demoQuad set (static quads)Beginner · No equipmentHold 10 s: 2 to 3 at a time, building to 8, 2 to 3 times a day · NHS inform's knee exercise, with its pacing; it also works straightening, which a cyst can make stiff
Harder: Straight-leg raise
3D demoSupine heel slideBeginner · No equipment10 slow reps, once or twice a day, bending only as far as the back of the knee is comfortable · The move page's dose, an editorial starting point; the comfort limit is our Baker's cyst guide's
Harder: Hip windshield wipers
3D demoStationary cyclingBeginner · Cardio machine10 minutes, easy, seat high so the knee never bends fully · As in our Baker's cyst guide
Easier: Recumbent exercise bike · Harder: Air bike intervals
3D demoGlute bridgeBeginner · No equipment2 sets of 10 · As in our Baker's cyst guide; a gentle hamstring load for the tendon lane
Easier: Pelvic tilt into bridge · Harder: Single-leg glute bridge
3D demoIsometric calf raise holdBeginner · A wall5 holds of 30 to 45 s, once or twice a day, at a gentle effort (tendon lane, calf) · The move page's dose, an editorial starting point; keep tendon pain to about 3 out of 10, as the pain rule says
Easier: Seated bent-knee calf raise (soleus raise) · Harder: Slow calf raise
Move on when: Joint lane: the swelling behind the knee is no bigger the next morning and your calf feels normal (our Baker's cyst guide's check). Tendon lane: walking and stairs are comfortable and the tender spot is calmer (our suggestion).
About weeks 2 to 6, 2 or 3 days a week: standing strength in a comfortable range for the joint lane, and slow, progressive loading of the sore tendon for the tendon lane, borrowed from other tendon problems.
3D demoSit to stand from a chairBeginner · A bench or box3 sets of 8 to 12, a higher seat first · As in our Baker's cyst guide
Easier: Sit to stand, pushing on the thighs · Harder: Bodyweight squat
3D demoSeated knee extension (chair)Beginner · A bench or box + Something with weight3 sets of 10 to 15 each leg, 2 to 3 days a week · The move page's dose, an editorial starting point; our Baker's cyst guide uses it too
Easier: Quad set (static quads) · Harder: Leg extension
3D demoStep-upBeginner · A step3 sets of 8 to 10 each leg, low step · As in our Baker's cyst guide
Easier: Low step-up · Harder: Dumbbell step-up
3D demoSlow calf raiseBeginner · A wall3 sets of 12, holding a support · As in our Baker's cyst and knee pain guides
Easier: Seated bent-knee calf raise (soleus raise) · Harder: Standing dumbbell calf raise
3D demoSeated leg curlBeginner · Strength machine2 to 3 sets of 8 to 12, stopping with 2 or 3 reps in reserve (tendon lane) · The move page's dose, an editorial starting point; start light and keep tendon pain to about 3 out of 10
Easier: Seated band hamstring curl · Harder: Stability ball leg curl
3D demoWall sitBeginner · A wall3 to 4 holds of 20 to 40 s, shallow · As in our Baker's cyst guide. Breathe normally through the hold, as the move page says
Easier: Straight-leg raise · Harder: Spanish squat (band squat hold)
Move on when: Joint lane: 12 sit-to-stands and 10 step-ups each leg leave the swelling and the ache no worse the next day (our Baker's cyst guide's check). Tendon lane: 3 sets of 12 calf raises and the leg curls stay within the pain rule (our suggestion).
From about week 6, 2 days a week and ongoing: heavier and single-leg strength, with the hamstrings working as they lengthen for the tendon lane, while everyday bending and sport come back by the written steps below. With a cyst from arthritis or a meniscus tear, carry on with that guide's plan: NICE says exercise keeps helping when you keep it going.
3D demoSplit squatIntermediate · No equipment3 sets of 8 each leg, holding a support, only as deep as is comfortable · As in our Baker's cyst guide. Pad the back knee, as the move page says
Easier: Bodyweight squat · Harder: Reverse lunge
3D demoDumbbell goblet squatIntermediate · A dumbbell3 sets of 8 to 12, to a box · As in our Baker's cyst guide
Easier: Bodyweight squat · Harder: Barbell front squat
3D demoSingle-leg calf raise from a stepIntermediate · A step + A wall3 sets of 8 to 10 each leg · As in our Baker's cyst guide. Face the step and keep a hand on a rail, as the move page says
Easier: Slow calf raise · Harder: Single-leg pogo hops
3D demoSingle-leg Romanian deadliftAdvanced · A dumbbell3 sets of 8 each leg, fingertips on a wall at first · As in our LCL guide; it loads the hamstrings as they lengthen (tendon lane)
Easier: Dumbbell Romanian deadlift
3D demoSlider hamstring curlIntermediate · No equipment2 to 3 sets of 6 to 8 (tendon lane) · Editorial. Expect strong cramping at first, so start with fewer reps and less range, as the move page says
Easier: Machine leg curl · Harder: Full Nordic curl
3D demoTreadmill walkingBeginner · Cardio machineBuild to 30 minutes on most days · Editorial, as in our pes anserine guide; walking outdoors counts the same
Harder: Treadmill jogging
Move on when: Our suggestion: walking, bending, kneeling and your sport stay within the pain rule, with the swelling and the tendon no worse the next morning. Keep two strength days a week; if a big day flares it, drop back a stage for a few days rather than stopping.
Our 3D figure can't show these changes. They come from the NHS and an NHS trust's leaflet; where a step is our suggestion or another of our guides' advice, it says so.
No trial has tested how to bring these back after pain behind the knee. These steps are our suggestion unless a source is named.
| Habit or position | Why it matters | Instead |
|---|---|---|
| Massaging, stretching or walking off a swollen, throbbing calf | It can be a clot or a burst cyst, and they look alike. | A same-day check. |
| Holding a deep squat, kneeling or full knee bends while the back of the knee is tight | A cyst can make bending difficult, and our Baker's cyst guide eases off deep bending for now. | Bend only as far as is comfortable; a higher seat.Try: Sit squat (partial squat) |
| Long walks that leave the back of the knee aching | The NHS says a cyst's symptoms may be worse after walking. | Shorter walks spread through the day, or cycling with a high seat.Try: Stationary cycling |
| Expecting draining or an injection to fix a cyst for good | Cysts commonly re-form after draining, an NHS trust leaflet says. | Treat the cause with exercise.Try: Seated knee extension (chair) |
| Hard hamstring stretches or Nordic curls with a sore tendon at a back corner | Tendons respond to graded, progressive loading, and the Nordic curl's page warns of delayed soreness at first. | Light seated leg curls, built up slowly.Try: Seated leg curl |
| Sprints and hill repeats with a sore hamstring or calf tendon | Speed and hills load the back of the leg most (our suggestion). | Flat, steady running first. |
| Sitting still for hours on a long journey | The NHS advises getting up and moving around every hour or so on journeys of 4 hours or more. | Move every hour, with ankle circles while you sit.Try: Ankle circles |
| Heat, massage or alcohol in the first 3 days after a hamstring injury | The NHS advises avoiding them for the first 3 days. | Protection, rest, ice, compression and elevation. |
| Ignoring a lump that is hard, painless or growing | The NHS says get any lump you don't know checked by a GP. | See a GP. |
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 stepA 30-minute joint-friendly circuit built like the GLA:D and ESCAPE-pain programmes: a gentle warm-up, chair, step and band strength moves, balance, then stretches.
30 minBeginner14 movesA bench or box, A stepA 25-minute calf workout with a step and a dumbbell: single-leg raises for the big calf muscle, then seated raises for the soleus, with gym swaps for each move.
25 minIntermediate7 movesA wall, A stepA 35-minute gym hamstring workout: Romanian deadlifts for the hip, seated leg curls for the knee, single-leg Romanian deadlifts, then Nordic curls when ready.
35 minIntermediate7 movesA dumbbell, Strength machineA 15-minute calf pump routine for varicose veins and heavy, swollen legs: ankle pumps, calf raises, a brisk walk, calf stretches and legs up to finish.
15 minBeginner10 movesA bench or box, A wallA 20-minute seated workout for older adults who cannot stand for long: marching, leg and arm strength, posture, and sit-to-stands that lead back to standing.
20 minBeginner11 movesA bench or box, Something with weightA Baker's cyst, a soft lump that usually comes with arthritis or a meniscus tear, is the classic cause. Tendons at the back corners, the calf muscle, the back of the meniscus, a PCL injury and, rarely, the blood vessels can also hurt there. Throbbing pain or swelling in one leg needs a same-day check for a clot.
Usually not, but know the NHS's signs, any of which can mean a clot: throbbing pain in one leg, usually the calf or thigh; swelling in one leg; red, blue or darkened skin; or swollen veins. Ask for an urgent GP appointment or call NHS 111, and call 999 if you're also breathless or have chest pain. A burst Baker's cyst looks the same and needs the same check.
A soft lump at the back of the knee that may show more when you stand, sometimes with pain, tightness, stiffness, difficulty bending the knee or clicking, and often worse after walking. If it bursts, fluid leaks into the calf and causes pain and swelling, which looks like a clot.
A cyst can make the knee tight to bend fully, a tendon at a back corner hurts when you bend against resistance, and the popliteus hurts when you load a slightly bent knee. A squeezed feeling only at the deepest bend, with no lump or swelling, is common. A knee that is stuck and can't straighten needs advice from NHS 111 now.
A Baker's cyst often aches more after walking. Take shorter walks spread through the day while it's sore, and build up gradually. Calf, thigh or buttock pain that comes on with walking and goes within minutes of standing still is a different pattern, covered in our calf pain when walking guide.
Usually a hamstring tendon at one of the back corners (often the semimembranosus on the inner side, which is seen in runners) or the calf muscle. Cut back the hills, speed or riding time that bring it on, then build strength slowly; on a bike, our cycling guide covers the saddle.
No: behind the kneecap means the front of the knee, and it's usually kneecap (patellofemoral) pain, worse on stairs, squatting and after sitting. Our runner's knee guide covers it. Pain in the hollow at the back of the knee is what this guide is about.
Not usually: it often settles when its cause is treated, and the NHS says surgery to remove it is rare. Draining and a steroid injection can ease a large or painful cyst, but it commonly comes back. Treating the cause with exercise is the long-term answer.
A burst Baker's cyst, a clot, a calf strain or cramp can all cause both, so sudden swelling or throbbing needs a same-day check. A cramp tightens the calf just below the back of the knee and passes within 10 minutes. Pain down the back of the leg with tingling can come from your back (sciatica).
For a cyst or arthritis, gentle bending, thigh strengthening and cycling with a high seat, with a check that the swelling is no worse the next day. For a tendon, slow, progressive loading such as calf raises and light leg curls, borrowed from other tendon problems. No trial has tested exercise for pain behind the knee as such.
Call 999 for leg pain or swelling with breathlessness or chest pain, or a leg that is suddenly cold, pale or numb. Get help the same day for throbbing pain or swelling in one leg, sudden worse pain and swelling around a lump, or a tight, very painful calf after a burst cyst. See a GP for any lump you don't know, especially one that is hard or growing.
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.
