High-yield overview
Housemaid's Knee
In frontSuperficial swelling over the patella
KneelingChronic microtrauma the commonest cause
Septic?The key distinction (aspirate if suspected)
S. aureusCommonest organism in septic cases
Key features
What it is
PatternInflammation of the superficial PREPATELLAR BURSA (in FRONT of the patella) - 'housemaid's knee' - producing a localised, fluctuant SUPERFICIAL swelling anterior to the patella; the knee joint itself is normal (this is NOT an intra-articular effusion).
Treatment
Causes
PatternCHRONIC microtrauma from KNEELING is the commonest cause; also acute trauma/haemorrhage, inflammatory/crystal disease (gout, rheumatoid arthritis) and INFECTION (septic bursitis - usually Staphylococcus aureus).
Treatment
The key question
PatternIs it SEPTIC? Distinguish septic from non-septic clinically (warmth, marked tenderness, erythema, fever) and by ASPIRATION when infection is suspected; ultrasound distinguishes bursitis from cellulitis. Do NOT routinely aspirate a non-infected microtraumatic bursa (iatrogenic infection risk).
Treatment
Critical Must-Knows
- Prepatellar bursitis ('housemaid's knee') is inflammation of the superficial prepatellar bursa, which lies in FRONT of the patella, producing a localised, well-circumscribed, fluctuant SUPERFICIAL swelling over the kneecap; because the bursa is superficial and extra-articular, the knee joint itself is normal and the swelling must be distinguished from a true intra-articular EFFUSION (which is deep, fills the suprapatellar pouch and balloons around the joint line).
- The COMMONEST cause is CHRONIC microtrauma from repetitive KNEELING (the occupational 'housemaid's/carpet-layer's/roofer's knee'); other causes are acute trauma or haemorrhage, inflammatory and crystal arthropathies (gout, rheumatoid arthritis), and INFECTION (septic bursitis), with the olecranon and prepatellar bursae being the commonest sites of superficial bursitis.
- The single most important clinical task is to distinguish SEPTIC from NON-SEPTIC bursitis, because the superficial location makes the prepatellar bursa prone to infection (often from a breach in the overlying skin); features suggesting sepsis include marked warmth, tenderness, erythema, fever and cellulitis, and ULTRASOUND can help distinguish a bursitis from surrounding cellulitis while blood tests/MRI help separate infectious from non-infectious causes.
- If infection is suspected, ASPIRATE the bursa and examine the fluid with Gram stain, culture, cell count, glucose and crystal analysis; STAPHYLOCOCCUS AUREUS is the predominant organism in septic bursitis (with streptococci next), so empirical antibiotics should cover S. aureus, given orally in the well patient and intravenously in those who are febrile/acutely ill or have extensive cellulitis.
- CONVERSELY, a non-infected chronic MICROTRAUMATIC bursa should generally NOT be aspirated, because aspiration carries a risk of introducing infection (iatrogenic septic bursitis); microtraumatic and acute traumatic bursitis are treated conservatively (rest, ice, compression, activity modification/kneeling avoidance, analgesia), and intrabursal corticosteroid injection has weak evidence and is not routinely recommended for microtraumatic cases.
- MANAGEMENT therefore depends on the TYPE: acute traumatic/haemorrhagic - conservative (aspiration may shorten symptoms in selected cases); chronic microtraumatic - conservative and address the cause (knee protection); inflammatory/crystal - treat the underlying condition (steroid injection often used); and SEPTIC - anti-staphylococcal antibiotics (a course of adequate duration; a course shorter than about two weeks is associated with more failures), with surgical drainage/bursectomy reserved for bursitis not responding to antibiotics or for recurrent disease.
Clinical Pearls
- “Prepatellar bursitis = superficial swelling IN FRONT of the patella ('housemaid's knee') - distinguish from an intra-articular effusion (deep). Commonest cause = chronic KNEELING microtrauma.
- “KEY task: septic vs non-septic. Aspirate if infection suspected (Gram/culture/crystals); S. aureus predominates. Ultrasound separates bursitis from cellulitis.
- “Do NOT routinely aspirate a non-infected microtraumatic bursa (iatrogenic infection). Septic -> anti-staph antibiotics (adequate duration); surgery for non-response/recurrence.
In Front of the Patella - and Is It Infected?
Recognise
A localised, fluctuant superficial swelling in front of the patella ('housemaid's knee') - the knee joint is normal (not an intra-articular effusion). Commonest cause: chronic kneeling.
The key decision
Septic or not? Aspirate if infection suspected (S. aureus); ultrasound separates bursitis from cellulitis. Don't routinely aspirate a non-infected microtraumatic bursa.
Recognition, Causes & the Septic Question
Superficial Swelling - and the Crucial Septic Distinction
Prepatellar bursitis is inflammation of the superficial bursa in front of the patella - 'housemaid's knee'
- giving a localised, fluctuant superficial swelling over the kneecap with a normal underlying knee joint (distinguish it from a deep intra-articular effusion). The commonest cause is chronic kneeling microtrauma; others are acute trauma/haemorrhage, gout/rheumatoid disease, and infection. The crucial clinical task is to decide whether it is septic, because the superficial bursa is prone to infection from a skin breach: warmth, marked tenderness, erythema, fever and cellulitis suggest sepsis. Ultrasound helps distinguish bursitis from cellulitis, and if infection is suspected the bursa is aspirated (Gram stain, culture, cell count, glucose, crystals); Staphylococcus aureus predominates. A non-infected microtraumatic bursa should NOT routinely be aspirated, because of the risk of iatrogenic septic bursitis.
Management by Type
Treat According to the Cause
- Acute traumatic/haemorrhagic: conservative - rest, ice, compression, elevation, analgesia; aspiration may shorten symptoms in selected cases.
- Chronic microtraumatic (kneeling): conservative and address the cause (knee protection / avoid kneeling); generally do NOT aspirate (iatrogenic infection risk); intrabursal corticosteroid has weak evidence and is not routinely recommended.
- Inflammatory/crystal (gout, RA): treat the underlying condition; intrabursal corticosteroid is often used.
- Septic: anti-staphylococcal antibiotics for an adequate duration (a course shorter than about two weeks is associated with more failures); oral in the well patient, IV if febrile/acutely ill or extensive cellulitis; surgical drainage/bursectomy for bursitis not responding to antibiotics or for recurrent disease.
Septic Until Proven Otherwise If Hot - But Don't Needle a Quiet Bursa
The two errors to avoid in prepatellar bursitis are opposite. The first is missing SEPTIC bursitis: because the prepatellar bursa is superficial and easily seeded through a skin breach, a hot, very tender, erythematous bursa
- especially with fever or cellulitis - should be treated as septic until proven otherwise, with aspiration for Gram stain and culture and anti-staphylococcal antibiotics, since untreated septic bursitis can progress. The second is needlessly aspirating a QUIET, non-infected microtraumatic bursa, which risks introducing infection and converting a benign problem into an iatrogenic septic bursitis - so a chronic kneeling-related bursa is managed conservatively with knee protection rather than routine aspiration. Distinguishing the superficial bursitis from a true intra-articular effusion, and septic from non-septic, is what guides safe management.
Evidence & Key Studies
Evidence
Common superficial bursitis (olecranon and prepatellar): diagnosis and management
Khodaee M • American Family Physician (2017)
Key Findings:
- Chronic microtrauma (e.g. kneeling on the prepatellar bursa) is the most common cause of superficial bursitis; other causes include acute trauma/haemorrhage, inflammatory disorders (gout, rheumatoid arthritis) and infection.
- Diagnosis is clinical with a focus on septic signs; ultrasound distinguishes bursitis from cellulitis, and if infection is suspected the bursa should be aspirated (Gram stain, crystals, glucose, cell count, culture).
- Bursal aspiration of a non-infected microtraumatic bursa is generally not recommended (iatrogenic septic-bursitis risk); septic bursitis is treated with antibiotics effective against Staphylococcus aureus, with surgery reserved for non-responsive or recurrent cases.
Evidence
Clinical characteristics and management of olecranon and prepatellar septic bursitis
Charret L, Bart G, Hoppe E, Dernis E, Cormier G, Boutoille D, Le Goff B, Darrieutort-Laffite C • Journal of Antimicrobial Chemotherapy (2021)
Key Findings:
- In 272 patients with septic bursitis, a microorganism was identified in about two-thirds, with staphylococci in 73% and streptococci in 19%.
- Septic bursitis resolved in the majority even with exclusively medical (antibiotic) treatment, with an equivalent success rate to surgical management.
- A treatment duration shorter than 14 days was associated with more failures in both medically and surgically treated patients.
Evidence Attribution
According to PubMed, the predominance of chronic kneeling microtrauma as the cause, the diagnostic focus on septic signs (with ultrasound distinguishing bursitis from cellulitis), the aspiration approach, the caution against aspirating a non-infected microtraumatic bursa, and the anti-staphylococcal treatment of septic cases come from the cited Khodaee review; the microbiology (staphylococci predominant), the equivalent success of medical and surgical management, and the higher failure rate with antibiotic courses shorter than 14 days from the cited Charret study. The distinction of a superficial bursitis from a true intra-articular effusion is standard, well-established teaching. (See also our Olecranon Bursitis and Septic Arthritis topics.)
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioStandard
Clinical prompt
“A patient who kneels at work has a swelling in front of the kneecap. How do you assess it?”
Practical approach
The history of occupational kneeling and a swelling in front of the kneecap is the classic picture of prepatellar bursitis, or housemaid's knee, which is inflammation of the superficial prepatellar bursa from chronic kneeling microtrauma. On examination I would confirm that the swelling is superficial and localised in front of the patella, fluctuant, with a normal underlying knee joint - this distinguishes a bursitis from a true intra-articular effusion, which is deep, fills the suprapatellar pouch and balloons around the joint line. The single most important task is to decide whether it is septic, because the superficial bursa is easily infected through a skin breach; I would look for warmth, marked tenderness, erythema, fever and overlying cellulitis, and I would examine the skin for a portal of entry. Ultrasound can help distinguish the bursitis from surrounding cellulitis, and blood tests and MRI can help separate infectious from non-infectious causes. If I suspect infection, I would aspirate the bursa and send the fluid for Gram stain, culture, cell count, glucose and crystal analysis, expecting Staphylococcus aureus as the commonest organism. If there are no features of infection and this is a chronic microtraumatic bursa, I would not routinely aspirate it, because aspiration risks introducing infection.
Key clinical points
Kneeling + anterior swelling = prepatellar bursitis (housemaid's knee)
Superficial/in front of patella, knee joint normal - distinguish from intra-articular effusion
Decide septic vs non-septic (warmth/tenderness/erythema/fever/cellulitis; ultrasound vs cellulitis)
Aspirate if infection suspected (Gram/culture/crystals; S. aureus); don't aspirate a quiet microtraumatic bursa
Common pitfalls
Mistaking a superficial bursitis for an intra-articular effusion
Missing septic bursitis (hot, tender, febrile)
Aspirating a non-infected microtraumatic bursa (iatrogenic infection)
Further questions
“How distinguish bursitis from effusion? - Superficial/in front of patella vs deep intra-articular”
“Commonest organism in septic bursitis? - Staphylococcus aureus”
Viva scenarioStandard
Clinical prompt
“How does your management differ for septic versus non-septic prepatellar bursitis?”
Practical approach
Management depends entirely on the type. For a non-septic, chronic microtraumatic bursa - the typical kneeling-related case - I would manage conservatively with rest, ice, compression, activity modification and knee protection to avoid further kneeling, and analgesia, and I would specifically NOT routinely aspirate it, because aspirating a non-infected bursa risks introducing infection and turning it septic; intrabursal corticosteroid has weak evidence and is not routinely recommended for microtraumatic bursitis. An acute traumatic or haemorrhagic bursa is also treated conservatively, though aspiration may shorten symptoms in selected cases. If the cause is inflammatory or crystal-related, such as gout or rheumatoid arthritis, I would treat the underlying condition, and intrabursal corticosteroid is often used. For septic bursitis, I would aspirate to confirm the diagnosis and obtain cultures, then give antibiotics effective against Staphylococcus aureus, orally in a well patient and intravenously if they are febrile, acutely ill or have extensive cellulitis; the evidence shows most septic bursitis resolves with medical treatment alone, with success equivalent to surgery, but a course shorter than about two weeks is associated with more failures, so I would ensure an adequate duration. Surgical drainage or bursectomy is reserved for bursitis that does not respond to antibiotics or for recurrent disease.
Key clinical points
Non-septic microtraumatic: conservative + knee protection; do NOT routinely aspirate
Acute traumatic: conservative (aspiration may shorten symptoms in selected cases)
Inflammatory/crystal: treat underlying condition (steroid injection often used)
Septic: anti-staph antibiotics (adequate duration, at least about 2 weeks); surgery for non-response/recurrence
Common pitfalls
Steroid-injecting or aspirating a possibly septic bursa inappropriately
Too short an antibiotic course in septic bursitis (more failures)
Defaulting to surgery (medical management usually succeeds)
Further questions
“Why avoid aspirating a non-infected microtraumatic bursa? - Iatrogenic septic bursitis risk”
“Medical vs surgical success in septic bursitis? - Equivalent (most resolve medically)”
Mnemonics & Memory Aids
Mnemonic
KNEEL
K
Kneeling microtrauma - the commonest cause
N
Not intra-articular - superficial swelling in front of patella
E
Evaluate for sepsis (hot/tender/erythema/fever) - the key question
E
Examine the skin / ultrasound (bursitis vs cellulitis)
L
Leave it alone if quiet (don't aspirate); aspirate + anti-staph if septic
Hook:KNEEL: Kneeling cause, Not intra-articular, Evaluate for sepsis, Examine skin/ultrasound, Leave quiet bursa alone (aspirate/treat if septic).
Exam day cheat sheet
Prepatellar Bursitis - Exam Day Cheat Sheet
Recognition
- Superficial, fluctuant swelling in front of the patella ('housemaid's knee')
- Knee joint normal - distinguish from intra-articular effusion
- Commonest superficial bursitis site along with the olecranon
Causes
- Chronic kneeling microtrauma (commonest)
- Acute trauma/haemorrhage; gout/rheumatoid arthritis
- Infection (septic bursitis - usually S. aureus)
Septic vs non-septic
- Septic signs: warmth, marked tenderness, erythema, fever, cellulitis
- Ultrasound separates bursitis from cellulitis; aspirate if infection suspected (Gram/culture/crystals)
- Do NOT routinely aspirate a non-infected microtraumatic bursa (iatrogenic infection)
Management
- Traumatic/microtraumatic: conservative (rest/ice/compression; knee protection)
- Inflammatory/crystal: treat underlying condition (steroid injection often used)
- Septic: anti-staph antibiotics (adequate duration); surgery for non-response/recurrence