Bursitis Around the Knee

What a Bursa Is and Why the Knee Has Several

A bursa is a small, fluid-filled sac that sits wherever a tendon or the skin needs to glide smoothly over bone, cutting down on friction. The knee has more than a dozen of these cushions scattered around it, but two account for most of the swelling people notice: the prepatellar bursa, sitting just in front of the kneecap between skin and bone, and the pes anserine bursa, sitting on the inner knee below the joint line where three tendons converge. When a bursa is irritated enough, by repeated pressure, a direct blow, or overuse, it fills with extra fluid and becomes bursitis.

The location tells you which bursa is involved almost by itself. Prepatellar bursitis sits directly over the kneecap and is visible as a rounded lump. Pes anserine bursitis sits a few inches lower and to the inside, over soft tissue rather than bone, and is felt more than seen. Neither one is the joint itself, which is part of why bursitis, unlike arthritis of the knee, usually does not cause the joint's cartilage-related deep ache or stiffness 1Ref 1American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Arthritis of the Knee.Knee arthritis symptoms are centered at the joint itself, distinct from bursitis, which affects soft-tissue cushions outside the joint..

Prepatellar Bursitis: The Kneeling Swelling

Prepatellar bursitis, sometimes called housemaid's knee, develops when the bursa in front of the kneecap is compressed repeatedly, classically from kneeling on hard surfaces for work like flooring, gardening, or plumbing, though a single hard fall onto the knee can also trigger it. The hallmark is a soft, well-defined, movable swelling directly over the kneecap that can range from grape-sized to noticeably large, often with only mild pain unless it is pressed on directly.

Because the swelling sits close to the skin, it is also the type most prone to infection if the skin over it is broken, which changes it from a nuisance into something needing prompt evaluation. Uncomplicated prepatellar bursitis generally responds to avoiding kneeling, padding the area if kneeling can't be avoided, and giving the bursa time to settle; it is a soft-tissue problem outside the joint, distinct from bursitis around the shoulder in mechanism but similar in how it resolves 2Ref 2American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Shoulder Impingement / Rotator Cuff Tendinitis.Bursitis around a joint such as the shoulder shares a similar mechanism and first-line nonsurgical management (rest, activity modification) with bursitis elsewhere, including the knee..

Pes Anserine Bursitis: The Inner-Knee Ache

Pes anserine bursitis affects a bursa on the inner side of the knee, a couple of inches below the joint line, where the tendons of three muscles, the sartorius, gracilis, and semitendinosus, converge before attaching to the shin bone. Unlike prepatellar bursitis, this swelling is rarely visible; instead it produces localized tenderness and an ache that can be mistaken for arthritis on the inner knee, especially since both are common in the same population: people who are overweight, have knee osteoarthritis, a degenerative joint condition that becomes more common with age 3Ref 3National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023).Osteoarthritis.Osteoarthritis is a degenerative joint disease with cartilage breakdown that becomes more common with age, and it frequently coexists with pes anserine bursitis in the same population., or run or cycle with tight hamstrings.

The distinguishing clue is location relative to the joint line. Arthritis pain tends to be felt at the joint line itself and deeper, while pes anserine tenderness is reliably found a couple of inches below it, over soft tissue rather than bone or cartilage. Because the two so often coexist, particularly in people with knee osteoarthritis, a clinician examining inner-knee pain typically checks both sites rather than assuming one explains it entirely 1Ref 1American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Arthritis of the Knee.Knee arthritis symptoms are centered at the joint itself, distinct from bursitis, which affects soft-tissue cushions outside the joint..

How the Two Types Compare

Both types are usually diagnosed from the history and a focused exam rather than imaging. Ultrasound or MRI is reserved for swelling that doesn't fit the typical pattern, doesn't improve with initial care, or raises concern for infection or a coexisting problem such as a meniscus tear.

What Actually Helps

For both types, the first move is reducing whatever is loading the bursa: kneeling on a pad or avoiding it for prepatellar bursitis, and addressing hamstring tightness and training load for pes anserine bursitis. Rest, ice, and time resolve most uncomplicated cases over a few weeks. When swelling persists, a clinician may aspirate fluid from a prepatellar bursa to relieve pressure and check it isn't infected, or use a corticosteroid injection for a stubborn pes anserine bursitis that hasn't responded to activity changes.

Most knee bursitis is a soft-tissue problem outside the joint itself, not a sign of arthritis or a structural knee injury, and it responds to time and avoiding the trigger far more often than it needs a procedure. Persistent or recurrent swelling in either location is still worth having examined, since chronic pressure or an underlying joint problem can keep re-triggering it.

Reducing the Chance It Comes Back

Prepatellar bursitis tends to recur in people whose work or hobbies involve regular kneeling, since the bursa can re-inflame each time the same pressure returns before the tissue has fully settled. Padding, a cushioned kneeling pad for flooring, gardening, or plumbing work, or simply shifting position more often during a task, addresses the mechanical cause directly rather than only treating each flare after it starts. Pes anserine bursitis tends to recur when the underlying hamstring tightness or training-load imbalance that triggered it in the first place goes unaddressed between episodes, so an ongoing stretching routine and a more gradual return to running or cycling volume matter as much as treating the current flare.

Chronic or repeatedly recurring bursitis in either location is sometimes a sign that an underlying factor hasn't been dealt with, added weight increasing pressure across the pes anserine bursa, or a job that genuinely can't avoid kneeling for long stretches. In those situations, a longer-term plan built around padding, posture changes, or a more gradual return to activity tends to hold up better than repeated short courses of rest that only address whichever flare is happening right now.