Baker's Cyst
What is a Baker's cyst?
A Baker's cyst — also called a popliteal cyst — is a fluid-filled swelling that forms in the back of the knee, in the popliteal fossa (the hollow behind the knee joint). It typically feels like a soft, rounded lump that may be painless or produce a sense of tightness, particularly when the knee is fully bent or fully straightened. Larger cysts can cause aching behind the knee and into the calf.
If you've found a lump behind your knee and are concerned about what it is, a Baker's cyst is by far the most common cause of swelling in this location and is not dangerous. It is not a tumour and does not require urgent treatment in most cases — though a proper assessment to identify the underlying cause is important.
What causes a Baker's cyst?
This is the most important thing to understand about Baker's cysts: they are almost never a primary condition. They are a secondary response to excess fluid production within the knee joint — the body's synovial membrane produces more fluid than normal in response to joint irritation or damage, and this excess fluid accumulates in a naturally occurring bursa at the back of the knee, forming the cyst.
The question that matters clinically is what is causing the excess fluid production. The most common underlying causes include osteoarthritis of the knee, meniscal tears, rheumatoid arthritis, cartilage damage, ACL injuries and other forms of intra-articular inflammation. In children, Baker's cysts more commonly occur without an underlying joint problem and often resolve spontaneously.
This is why treating the cyst directly — by aspiration (draining the fluid with a needle) or injection — without addressing the underlying cause produces a recurrence rate of over 50%. The body simply refills the cyst because the joint problem driving the fluid production hasn't changed. The cyst is a symptom, not the disease.
What are the symptoms?
The primary symptom is the swelling itself — a soft lump behind the knee that may be barely noticeable or quite prominent. Associated symptoms depend largely on the underlying cause: knee pain, stiffness, swelling within the joint, clicking or catching, and reduced range of motion are all common. The cyst itself may contribute to a feeling of tightness or pressure behind the knee, particularly when squatting or kneeling.
Occasionally a Baker's cyst ruptures, causing sudden onset of pain and swelling tracking down into the calf. This can mimic the presentation of a deep vein thrombosis (DVT) and should be assessed promptly — an ultrasound will differentiate the two.
How is it diagnosed?
Clinical assessment by a physiotherapist will identify the posterior knee swelling and assess the knee joint for signs of the underlying pathology. Ultrasound is the most useful imaging modality for confirming the diagnosis and assessing cyst size. MRI provides more detailed information about the underlying joint pathology — meniscal tears, cartilage damage and ligament injuries are all well visualised on MRI and help guide treatment planning.
How can physiotherapy help?
Because the Baker's cyst is secondary to intra-articular pathology, physiotherapy focuses on treating the underlying knee condition rather than the cyst directly. When the joint problem is managed effectively — inflammation controlled, the mechanical factors contributing to excess fluid production addressed, and the knee's function restored — the cyst typically reduces in size and often resolves completely without direct intervention.
For patients with osteoarthritis as the underlying cause, physiotherapy focuses on quadriceps and gluteal strengthening to reduce mechanical load on the articular surfaces, activity modification to manage flare-ups, and an education-based approach to long-term self-management. Clinical Pilates is particularly well suited to this group — the low-impact, load-controlled environment allows meaningful strengthening without provoking the joint irritation that drives fluid production.
For patients with a meniscal tear or other structural pathology, physiotherapy either manages the condition conservatively or provides pre and post-operative rehabilitation if surgery is indicated. In either case, addressing the underlying structural issue is central to resolving the cyst.
For inflammatory arthritis conditions including rheumatoid arthritis, management is coordinated with the patient's rheumatologist — physiotherapy contributes joint protection education, targeted exercise and functional rehabilitation alongside medical management of the inflammatory condition.
Real time ultrasound can assist in assessing deep muscle activation patterns around the knee where inhibition from pain and swelling is affecting rehabilitation progress.
Our physiotherapists Eliane Machado, Bethany Kippen and Emma Cameron all have experience in knee pain management across a range of underlying conditions and are members of the Australian Physiotherapy Association.
To book or find out more, call us on 07 3706 3407 or book online below. We see patients from across Brisbane's southside including Tarragindi, Coorparoo, Holland Park, Greenslopes and Mt Gravatt.
A Baker's cyst — also called a popliteal cyst — is a fluid-filled swelling that forms in the back of the knee, in the popliteal fossa (the hollow behind the knee joint). It typically feels like a soft, rounded lump that may be painless or produce a sense of tightness, particularly when the knee is fully bent or fully straightened. Larger cysts can cause aching behind the knee and into the calf.
If you've found a lump behind your knee and are concerned about what it is, a Baker's cyst is by far the most common cause of swelling in this location and is not dangerous. It is not a tumour and does not require urgent treatment in most cases — though a proper assessment to identify the underlying cause is important.
What causes a Baker's cyst?
This is the most important thing to understand about Baker's cysts: they are almost never a primary condition. They are a secondary response to excess fluid production within the knee joint — the body's synovial membrane produces more fluid than normal in response to joint irritation or damage, and this excess fluid accumulates in a naturally occurring bursa at the back of the knee, forming the cyst.
The question that matters clinically is what is causing the excess fluid production. The most common underlying causes include osteoarthritis of the knee, meniscal tears, rheumatoid arthritis, cartilage damage, ACL injuries and other forms of intra-articular inflammation. In children, Baker's cysts more commonly occur without an underlying joint problem and often resolve spontaneously.
This is why treating the cyst directly — by aspiration (draining the fluid with a needle) or injection — without addressing the underlying cause produces a recurrence rate of over 50%. The body simply refills the cyst because the joint problem driving the fluid production hasn't changed. The cyst is a symptom, not the disease.
What are the symptoms?
The primary symptom is the swelling itself — a soft lump behind the knee that may be barely noticeable or quite prominent. Associated symptoms depend largely on the underlying cause: knee pain, stiffness, swelling within the joint, clicking or catching, and reduced range of motion are all common. The cyst itself may contribute to a feeling of tightness or pressure behind the knee, particularly when squatting or kneeling.
Occasionally a Baker's cyst ruptures, causing sudden onset of pain and swelling tracking down into the calf. This can mimic the presentation of a deep vein thrombosis (DVT) and should be assessed promptly — an ultrasound will differentiate the two.
How is it diagnosed?
Clinical assessment by a physiotherapist will identify the posterior knee swelling and assess the knee joint for signs of the underlying pathology. Ultrasound is the most useful imaging modality for confirming the diagnosis and assessing cyst size. MRI provides more detailed information about the underlying joint pathology — meniscal tears, cartilage damage and ligament injuries are all well visualised on MRI and help guide treatment planning.
How can physiotherapy help?
Because the Baker's cyst is secondary to intra-articular pathology, physiotherapy focuses on treating the underlying knee condition rather than the cyst directly. When the joint problem is managed effectively — inflammation controlled, the mechanical factors contributing to excess fluid production addressed, and the knee's function restored — the cyst typically reduces in size and often resolves completely without direct intervention.
For patients with osteoarthritis as the underlying cause, physiotherapy focuses on quadriceps and gluteal strengthening to reduce mechanical load on the articular surfaces, activity modification to manage flare-ups, and an education-based approach to long-term self-management. Clinical Pilates is particularly well suited to this group — the low-impact, load-controlled environment allows meaningful strengthening without provoking the joint irritation that drives fluid production.
For patients with a meniscal tear or other structural pathology, physiotherapy either manages the condition conservatively or provides pre and post-operative rehabilitation if surgery is indicated. In either case, addressing the underlying structural issue is central to resolving the cyst.
For inflammatory arthritis conditions including rheumatoid arthritis, management is coordinated with the patient's rheumatologist — physiotherapy contributes joint protection education, targeted exercise and functional rehabilitation alongside medical management of the inflammatory condition.
Real time ultrasound can assist in assessing deep muscle activation patterns around the knee where inhibition from pain and swelling is affecting rehabilitation progress.
Our physiotherapists Eliane Machado, Bethany Kippen and Emma Cameron all have experience in knee pain management across a range of underlying conditions and are members of the Australian Physiotherapy Association.
To book or find out more, call us on 07 3706 3407 or book online below. We see patients from across Brisbane's southside including Tarragindi, Coorparoo, Holland Park, Greenslopes and Mt Gravatt.
