What knee bursitis actually is

A tender, puffy lump near the knee — sometimes warm to the touch and sore when kneeling or climbing stairs — is often the first sign that a bursa has become inflamed. A bursa is a small sac filled with synovial fluid; its job is to reduce friction between the knee's bones, tendons, and overlying skin. The knee contains several of these sacs, and when one becomes irritated or injured, the result is bursitis.

Three types account for the great majority of cases seen in clinical practice:

• Prepatellar bursitis ('housemaid's knee') — the sac sitting directly over the kneecap becomes swollen, producing a visible dome of fluid at the front of the knee. Chronic kneeling on hard surfaces is the classic cause, which is why carpet layers and cleaners are particularly affected.
• Pes anserine bursitis — located on the inner side of the knee, roughly 2–3 cm below the joint line. It is more common in runners and people with osteoarthritis, and the pain often worsens when climbing stairs or after a period of rest.
• Infrapatellar bursitis ('clergyman's knee') — involves the sac just below the kneecap, with superficial and deep subtypes that carry slightly different implications for management.

The distinction between types is clinically meaningful, not merely academic. Because the location of each bursa differs, so does the most likely cause, the pattern of symptoms, and the appropriate management — all of which the following sections explore in turn. One subtype, septic (infected) bursitis, stands apart from the others entirely and is covered in detail later because it demands a different and more urgent response.

Causes and who tends to get it

Occupation and activity are the most useful starting point for working out which type may be involved. People who spend long periods kneeling on hard surfaces — gardeners, floor fitters, cleaners, and plumbers among them — are disproportionately represented among prepatellar and infrapatellar cases, where sustained pressure on the front of the knee is the primary driver. A single direct blow to the kneecap can produce the same result in someone with no kneeling history.

Pes anserine bursitis tends to follow a different pattern. Runners with tight hamstrings, flat feet, or knock-knee alignment place repeated mechanical stress on the inner-knee bursa; so do people with established knee osteoarthritis, for whom abnormal load distribution plays a central role. Carrying excess weight increases the force through this particular bursa and is considered an independent risk factor.

Septic bursitis operates on a separate mechanism entirely. It typically begins with a break in the skin close to the knee — a graze, cut, or insect bite — which allows bacteria to enter the bursa directly. The resulting infection produces fever and intense redness alongside swelling, and it warrants prompt medical attention rather than watchful waiting at home.

Symptoms and what else it could be

The pain in knee bursitis is characteristically localised — dull and achy rather than sharp, centred over whichever bursa is affected. Pressing the area directly usually reproduces tenderness, and in many cases a soft, fluid-filled lump is visible and slightly warm to the touch. Some people also experience stiffness that limits bending or straightening the knee, particularly after sitting still for a while.

The location and timing of discomfort carry diagnostic weight. Inner-knee pain that reliably worsens on stair climbing and eases as the day progresses, for instance, points more specifically towards the pes anserine bursa than towards a generalised arthritic flare — though the two conditions frequently coexist in the same patient, which complicates the picture.

When symptoms suggest something more urgent

If swelling comes with fever, shivering, or skin that appears intensely red and hot across a wide area, septic bursitis should be considered. These systemic signs indicate infection rather than sterile inflammation and change the clinical priority: antibiotics are required, and watchful waiting is not appropriate. Any combination of swelling and fever in the same knee warrants same-day or urgent GP assessment.

What else could be causing the symptoms?

Knee osteoarthritis, tendonitis, and gout can all produce a similar mix of localised pain, stiffness, and visible swelling. No symptom alone reliably separates these conditions without clinical examination and, in most cases, imaging. Fluid analysis may be needed when gout or infection is possible. It is also worth noting that mild bursitis sometimes presents mainly as swelling with little accompanying pain — so the absence of significant discomfort does not exclude the diagnosis.

Which specialist to see and when

For most people, the GP is the right first call. A primary care assessment can confirm that the knee needs specialist attention, start the process of excluding infection, and point the referral in the right direction — whether that is musculoskeletal or systemic.

The majority of knee bursitis cases are referred to an orthopaedic surgeon or sports medicine physician. These specialists lead the MSK-focused workup: physical examination, imaging, and decisions about aspiration or injection. If the history or examination raises the possibility that a systemic inflammatory condition — rheumatoid arthritis or gout, for example — is driving the bursitis, a rheumatologist is the more appropriate specialist; they can investigate and manage the underlying disease alongside the local joint problem.

Physiotherapy enters the pathway after the acute inflammatory phase has settled. Its role is rehabilitative — rebuilding the muscle support around the knee and restoring range of motion — rather than diagnostic.

When to seek urgent care

If fever, rapid-onset swelling, or intense spreading redness accompanies the knee symptoms, septic bursitis should be treated as urgent. These are signs of infection, covered in the earlier sections of this article, and same-day GP or emergency assessment is appropriate rather than waiting for a routine referral.

What the assessment and diagnosis involves

Arriving at a diagnosis follows a clear sequence, and knowing what to expect at each step can make the appointment feel less daunting.

History first

The clinician will begin by asking about symptom duration, what triggered or worsened them, and whether the knee has been exposed to repetitive kneeling or recent direct trauma. Occupational and recreational history matter here, as does any recent skin break — a cut, scrape, or insect bite near the knee raises the possibility of septic bursitis and changes the urgency of the workup.

Physical examination

Examination focuses on palpating the affected area for localised swelling, warmth, and point tenderness, and on assessing how far the knee can comfortably flex and extend. Where the tenderness sits — directly over the kneecap, just below it, or on the inner side — helps the clinician determine which bursa is involved.

Imaging

An X-ray is typically requested to exclude fracture or underlying arthritis rather than to see the bursa itself, which plain X-ray cannot image directly. Ultrasound or MRI can visualise the inflamed sac and confirm its size and location. These scans are useful corroborating tools, but they form one part of the diagnostic picture alongside the history and examination — a scan result is interpreted in clinical context, not read in isolation.

Aspiration

When infection or gout is a realistic possibility, a clinician may draw a small sample of fluid from the bursa using a fine needle. The fluid is then analysed in a laboratory for bacteria (confirming or excluding septic bursitis) and for uric acid crystals (confirming or excluding gout). This single step materially changes the treatment chosen, which is why it is performed whenever either diagnosis remains open.

Questions worth asking at a first consultation

Preparing a handful of questions before the appointment makes it easier to leave with a clear picture of what is happening and what comes next.

• Which bursa is affected, and is this mechanical, inflammatory, or infectious? The answer shapes everything else — treatment for septic bursitis is entirely different from treatment for overuse-related swelling, and knowing the type also clarifies what you can reasonably expect by way of recovery.
• Do you recommend aspiration at this stage? Fluid analysis is the only way to definitively rule out infection or gout. Understanding whether the clinician considers it necessary — and why, or why not — helps set realistic expectations about the workup.
• What is the first-line treatment, and what should I expect over the next four to six weeks? This gives a baseline: whether that means a short course of anti-inflammatories, a corticosteroid injection, or antibiotics, knowing the plan and its rough timeline reduces uncertainty.
• Are there activities I should stop or modify while this settles? Continuing to kneel or load the bursa during recovery can prolong inflammation; specific guidance is more useful than general rest advice.
• What signs should prompt me to contact you sooner? Understanding the warning signs — particularly those that suggest infection — means a deterioration is caught early rather than managed at home for too long.

Taken together, these questions move the consultation from a passive examination into an active conversation — and a confident grasp of the diagnosis, the next investigation, and the treatment plan is exactly what makes that conversation worth having.