Baker's Cyst
Lower LimbOverview
A Baker's cyst is a fluid-filled sac that forms in the popliteal space behind the knee, typically arising from the gastrocnemius-semimembranosus bursa. While often asymptomatic and discovered incidentally, it can cause posterior knee pain, swelling, and restricted motion, particularly with flexion activities. The cyst frequently develops secondary to underlying knee pathology such as meniscal tears or osteoarthritis.
Pathophysiology
Baker's cysts form when synovial fluid from the knee joint herniates through a weakened posterior joint capsule into the popliteal space, commonly via a one-way valve mechanism near the gastrocnemius-semimembranosus bursa. Increased intra-articular pressure forces fluid into the bursa, which distends over time. The cyst may enlarge, compress surrounding neurovascular structures, or rupture, causing acute swelling mimicking deep vein thrombosis.
Patient Education
A Baker's cyst often develops because of underlying knee problems that cause fluid to accumulate; addressing the root cause through activity modification and strengthening can help prevent cyst enlargement and symptoms.
Typical Presentation
Site
Posterior knee in the popliteal fossa, occasionally extending down the calf
Quality
Dull, aching, or tightness; may feel like a palpable lump or fullness
Intensity
Mild to moderate; often painless but uncomfortable with activity; can be severe if ruptured
Aggravating
Deep knee flexion, squatting, climbing stairs, prolonged standing, repetitive knee movement
Relieving
Rest, knee extension, ice application, anti-inflammatory medication, activity modification
Associated
Swelling in popliteal fossa, restricted knee flexion, knee effusion, clicking or locking if meniscal pathology present, calf pain or swelling if cyst ruptures or compresses tissues
Orthopaedic Tests
Test descriptions are written with AI assistance from standard clinical texts. Where a test lists Sources, its description has been checked against them; those sources are independent and do not endorse OsteoKit. Accuracy figures and grades (A–D) appear only when checked against the published study; tests without one are marked “No accuracy study”.
Further reading: full test procedures are described in standard clinical examination texts, e.g. Magee & Manske, Orthopedic Physical Assessment (7th ed.), and Cook & Hegedus, Orthopedic Physical Examination Tests: An Evidence-Based Approach (2nd ed.).
Ultrasound (Popliteal Fossa Scanning)
Procedure
Arranged by the treating doctor or performed by a trained sonographer: ultrasound of the back of the knee, often with a scan of the calf veins.
Positive Finding
A fluid collection between the medial gastrocnemius and semimembranosus tendons, connecting to the joint.
Interpretation
Confirms the cyst, shows whether it has ruptured into the calf, and can exclude a DVT or aneurysm in the same visit. Ultrasound is a useful confirmatory imaging modality for a popliteal (Baker’s) cyst, but the ranges previously shown are not traceable to a single confirmed diagnostic-accuracy study and are not a verified sensitivity/specificity pair.
MRI (Magnetic Resonance Imaging)
Procedure
Arranged by the treating doctor: MRI of the knee.
Positive Finding
A fluid-filled cyst connecting to the joint, often with a meniscal tear or osteoarthritis.
Interpretation
Shows the cyst and, more usefully, the joint problem causing it, which is the main target of treatment. MRI reliably characterises a popliteal cyst and its communication with the joint, but the ranges previously shown are not traceable to a confirmed diagnostic-accuracy study reporting a sensitivity/specificity pair.
Lachman Test (or ACL assessment)
Procedure
Patient supine, knee bent to 20–30°. Stabilise the lower femur with one hand and pull the upper tibia forwards with the other, comparing with the other knee.
Positive Finding
More forward movement than on the other side, with a soft or absent end-point.
Interpretation
Checks for an ACL injury as a possible cause of ongoing joint fluid. It does not test the cyst itself. The Lachman test assesses anterior cruciate ligament integrity, not a Baker’s cyst; the figures previously shown were attributed to the fabricated "Hegedus 2015 BJSM" citation.
Sources
Posterior Knee Palpation
Procedure
Patient prone. Palpate the back of the knee, especially the inner side, with the knee straight and then bent to about 45°.
Positive Finding
A soft, smooth swelling at the back of the inner knee that feels firmer with the knee straight and softer with it bent (Foucher's sign).
Interpretation
Supports a popliteal (Baker's) cyst. A swelling that pulsates may be a popliteal artery aneurysm, and a hard or growing mass needs imaging. Calf pain and swelling can come from a burst cyst but also from a DVT, which must be excluded first.
McMurray's Test (with posterior palpation)
Procedure
Patient supine. Fully bend the knee, then rotate the tibia out and straighten the knee (medial meniscus); repeat with the tibia rotated in (lateral meniscus). Keep a hand on the joint line.
Positive Finding
A painful click or clunk at the joint line, reproducing the familiar symptoms.
Interpretation
Checks for a meniscal tear, a common cause of the joint fluid that feeds a Baker's cyst. It does not test the cyst itself.
Sources
Knee Extension Lag or Swelling Assessment
Procedure
Check for a joint effusion with the bulge sign or patellar tap, and measure active and passive knee extension, comparing with the other side.
Positive Finding
A joint effusion, or loss of full extension.
Interpretation
An effusion means a problem inside the joint is producing fluid that can feed the cyst. Loss of extension may come from the cyst itself or from the joint problem.
⚠ Red Flags
- •Sudden onset severe calf swelling with warmth and erythema suggesting ruptured cyst or DVT
- •Signs of deep vein thrombosis (unilateral calf swelling, warmth, deep-vein tenderness) - a ruptured Baker's cyst can mimic DVT closely, so refer for duplex ultrasound rather than attempting to distinguish them clinically. Homan's sign is unreliable (sensitivity roughly 10-54%, specificity roughly 39-89%) and must not be used to include or exclude DVT
- •Neurovascular compromise (foot paresthesia, colour changes, absent pulses, weakness)
- •Systemic signs suggesting infection or inflammatory arthropathy (fever, night sweats, polyarticular symptoms)
- •History of malignancy with new knee symptoms
⚡ Yellow Flags
- •High fear-avoidance beliefs limiting activity and rehabilitation engagement
- •Catastrophizing about cyst causing serious complications
- •Poor understanding of benign nature leading to health anxiety
- •Avoidance of activity due to symptom hypervigilance
- •Psychosocial stressors affecting pain perception and recovery
Osteopathic Techniques
A cyst with no symptoms needs no treatment. Symptomatic cysts are managed with activity changes, NSAIDs and rehab, and care for the knee itself (often arthritis or a meniscal tear) is part of it.
- Reference bookLeib et al. · StatPearls 2023
Safety: A swelling behind the knee is not always a cyst: the differential includes deep vein thrombosis, an arteriovenous fistula, an abscess and a tumour. Rule these out before hands-on work.
- Reference bookLeib et al. · StatPearls 2023
Region
Tibiofemoral and patellofemoral joints
Technique
Rationale
Gentle, rhythmic glides of the knee and kneecap within their range to ease pain and stiffness.
How it's done, cautions & evidence
How it's done
Passive, low-velocity glides of the knee within its range, with no thrust: distraction and front-to-back glides of the tibia on the femur, and glides of the kneecap in each direction, usually 2–3 oscillations a second for 1–2 minutes. A Mulligan variant holds a sustained glide of the tibia while the patient actively bends and straightens the knee.
Cautions
In knee osteoarthritis trials, no serious adverse events were reported with manual therapy.
Evidence in Baker's Cyst
Searched 24 Oct 2026: no trials of knee mobilisation in Baker cysts.
Sources
- Journal articleCoulter et al. · Spine J 2018
- Journal articleLi et al. · World J Clin Cases 2022
- Journal articleZhu et al. · Syst Rev 2024
Region
Posterior knee capsule and popliteal fascia
Technique
Rationale
Hands-on work to the quadriceps and the tissues around the knee to ease tension and pain.
How it's done & evidence
How it's done
Hands-on kneading, stroking and sustained pressure to the quadriceps, the patellar and quadriceps tendons, the iliotibial band near the knee and the tissues around the joint. Transverse friction massage across a tendon is one form. In trials it was given alongside exercise.
Evidence in Baker's Cyst
Searched 24 Oct 2026: no trials of soft tissue technique in Baker cysts.
Sources
- Journal articleFurlan et al. · Cochrane 2015
- Journal articleRagone et al. · Healthcare (Basel) 2024
Region
Gastrocnemius and soleus
Technique
Rationale
Low-force, patient-powered stretch for a tight calf.
How it's done, cautions & evidence
How it's done
The calf is taken to its barrier by dorsiflexing the ankle. The patient pushes the foot gently down, at about 10–20% effort, against resistance for 5–10 seconds, relaxes for 3–5 seconds, and the new barrier is taken up.
Cautions
Not used with an acute fracture, a joint infection or a bone malignancy; take care with severe osteoporosis or after surgery that limits muscle contraction. Use the least force needed: too much can tear a muscle or pull off a tendon, especially in older patients.
Evidence in Baker's Cyst
Searched 24 Oct 2026: no trials of calf muscle energy technique in Baker cysts.
Sources
- Reference bookWaxenbaum & Sina · StatPearls 2026
Rehabilitation Exercises
Supine Knee Flexion and Extension
Supine Gastrocnemius Stretch with Towel or Strap
Standing Hamstring Stretch at Wall
Supine Quadriceps Setting with Isometric Hold
Seated Knee Extension Lifts
Standing Hamstring Curls
Glute Bridges on Supine Position
Single Leg Standing on Firm Surface
Wall Squats with Controlled Depth
Step-ups with Handrail Support
Stationary Cycling with Seat Height Adjustment
Tandem Walking in Supportive Environment
Referral Criteria
- •Signs suggestive of deep vein thrombosis (calf swelling, warmth, positive Wells score)
- •Neurovascular compromise with sensory or motor deficits in lower limb
- •Failure to improve with conservative management after 6-8 weeks
- •Recurrent rupture or significant functional limitation despite rehabilitation
- •Evidence of underlying significant pathology requiring surgical intervention (large symptomatic meniscal tear, severe osteoarthritis, inflammatory arthropathy)
- •Imaging findings suggesting malignancy or other serious underlying pathology
- •Acute exacerbation with severe pain unresponsive to conservative measures
- •Diagnostic uncertainty requiring imaging correlation (ultrasound or MRI)