Housemaid's Knee
- Superficial, not articular - the bursa lies in front of the patella, so the swelling is localised and fluctuant over the kneecap and the knee joint is normal, unlike a deep intra-articular effusion
- Chronic kneeling microtrauma is the commonest cause; acute trauma or haemorrhage, gout or rheumatoid arthritis, and infection are the others
- Septic or not is the key question - warmth, marked tenderness, erythema, fever and cellulitis suggest sepsis; aspirate if infection is suspected and expect Staphylococcus aureus
- Do not routinely aspirate a quiet microtraumatic bursa - aspiration risks an iatrogenic septic bursitis
- Treat by type - conservative for traumatic and microtraumatic bursitis, the underlying disease for inflammatory or crystal bursitis, anti-staphylococcal antibiotics of adequate duration for septic bursitis, and surgery for non-response or recurrence
- “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.
Overview and Causes
What it is. Prepatellar bursitis, or housemaid's knee, is inflammation of the superficial bursa in front of the patella. It gives a localised, well-circumscribed, fluctuant swelling over the kneecap, and the knee joint beneath is normal. The olecranon and prepatellar bursae are the commonest sites of superficial bursitis.
Causes. The commonest is chronic microtrauma from repetitive kneeling, which is where the occupational names come from: housemaid's, carpet-layer's and roofer's knee. The others are:
- Acute trauma or haemorrhage
- Inflammatory and crystal arthropathies, gout and rheumatoid arthritis
- Infection (septic bursitis), usually Staphylococcus aureus
The question that matters. The single most important clinical task is to decide whether the bursa is septic. Its superficial position makes it prone to infection, often through a breach in the overlying skin, and whether you put a needle in it turns on the answer.
Anatomy and the Anterior Knee Swelling Differential
Where the bursa sits. The prepatellar bursa is a subcutaneous bursa, superficial to the patella and lying between the skin and the patella and patellar tendon; subfascial and subtendinous extensions have been described. It is extra-articular and does not communicate with the joint, which is why the knee itself is normal.
Bursa or effusion. A true intra-articular effusion is deep. It fills the suprapatellar pouch, is fluctuant and balloons around the joint line, and makes the patella ballottable. Prepatellar bursitis is a swelling in front of the patella over a normal joint.
The differential of anterior knee swelling. Position relative to the patella and the patellar tendon names the bursa.
- Infrapatellar bursitis ("clergyman's knee"): swelling over the tibial tubercle and patellar tendon from more upright kneeling, where housemaid's knee comes from kneeling flat over the patella
- Pes anserine bursitis, medial and below the joint line, and the other periarticular bursae (see Pes Anserine Bursitis)
- A true intra-articular effusion
- A gouty tophus (see Gout and Crystal Arthropathy)
- A ganglion or cyst
- A Morel-Lavallée lesion (see Morel-Lavallée Lesion)
- Rarely, a soft-tissue tumour
Clinical Assessment
Is it septic? Marked warmth, tenderness, erythema, fever and cellulitis suggest sepsis. Examine the skin over the knee for the breach that let organisms in.
The two errors in prepatellar bursitis are opposite. The first is missing septic bursitis: a hot, very tender, erythematous bursa, especially with fever or cellulitis, should be treated as septic until proven otherwise, because untreated septic bursitis can progress. The second is needling a quiet, non-infected microtraumatic bursa, which risks introducing infection and converting a benign problem into an iatrogenic septic bursitis. A non-infected chronic kneeling bursa should generally not be aspirated; it is managed conservatively with knee protection instead.
Anatomical reasoning tells you the prepatellar bursa is extra-articular, but the bedside test is dynamic and takes seconds. Passive knee movement is preserved and relatively comfortable in bursitis, because the inflamed structure lies in front of the patella and is not stretched by moving the joint. In septic arthritis any movement is agonising, because a distended, inflamed capsule is loaded through range.
That matters more than it first appears. A hot, swollen, erythematous knee in a febrile patient prompts a septic-joint pathway; if the pathology is actually a superficial bursa, the joint is normal and does not need an arthrotomy. Conversely, a knee that resists all movement is not a bursitis, whatever the anterior swelling looks like. (The joint's own pathway is in Septic Arthritis Pathophysiology.)
Investigations
Ultrasound and blood tests. Ultrasound helps distinguish a bursitis from surrounding cellulitis, and blood tests and MRI help separate infectious from non-infectious causes.
Plain radiograph. On the horizontal-beam lateral the bursa is a prepatellar soft-tissue opacity silhouetted against the fat planes, and the film shows the bone clean, with the patella and the joint untouched.
MRI. When the question is deeper, MRI separates a simple bursa from a joint effusion and from the deep infection it can hide.
Aspiration. When infection is suspected, aspirate the bursa and send the fluid for Gram stain, culture, cell count, glucose and crystal analysis. Staphylococcus aureus is the predominant organism, with streptococci next.
Reading the aspirate. Bursal fluid does not follow the septic-joint rules.
- White-cell count. There is no single agreed threshold, and an infected bursa often has a much lower count than an infected joint. The joint's ~50,000 figure does not apply, so a "low" count does not exclude infection; a high count with neutrophil predominance supports it.
- Gram stain. Positive in only about half of septic bursitis, so a negative stain does not exclude infection. Culture is the gold standard.
- Glucose. A low bursal glucose relative to serum supports infection.
- Crystals. Gout or CPPD crystals can be present, and gouty bursitis looks infected on the ward and crystalline under polarised light. A tophus shows at urate density on CT. Crystals and infection can coexist, so culture is sent even when crystals are seen.
When the fluid is equivocal. Treat as septic if the clinical picture fits, even when the fluid is equivocal or culture-negative; the diagnosis may then rest on the clinical picture and the response to antibiotics. Full septic-bursitis management is in Septic Bursitis.
Where the needle goes. Enter through healthy skin, away from the most inflamed area, on an oblique rather than a perpendicular track. Needling through cellulitic skin drives surface organisms into the bursa, and a puncture at the point of maximum tension over a subcutaneous bursa can fail to seal and become a chronic sinus.
Why the sinus matters. A discharging sinus over the patella is considerably harder to treat than the bursitis was, because the skin there is thin, poorly vascularised and loaded every time the patient kneels.
Management by Type
Treat according to the cause. Each type has its own management.
- Acute traumatic or haemorrhagic. Conservative: rest, ice, compression, elevation and analgesia. Aspiration may shorten symptoms in selected cases.
- Chronic microtraumatic (kneeling). Conservative, with rest, ice, compression, activity modification and analgesia, and address the cause with knee protection and avoidance of kneeling. Intrabursal corticosteroid has weak evidence and is not routinely recommended.
- Inflammatory or crystal (gout, rheumatoid arthritis). Treat the underlying condition; intrabursal corticosteroid is often used.
- Septic. Antibiotics effective against Staphylococcus aureus, with surgery for the indications below.
Antibiotics for septic bursitis. Give them orally in the well patient and intravenously if the patient is febrile or acutely ill, or has extensive cellulitis. Duration matters: a course shorter than about two weeks is associated with more failures.
Medical or surgical. Antibiotics alone resolve most septic bursitis, with success equivalent to surgery in the Charret series. In that retrospective series surgery went to worse or non-responding cases, so the equal success shows that surgical rescue works rather than that the two strategies are interchangeable.
When to operate. Surgical drainage or bursectomy is reserved for bursitis not responding to antibiotics, recurrent disease, an abscess or a foreign body. The threshold is genuine failure, not impatience.
If you do operate, respect the skin over the patella. The anterior knee is the worst place on the body to make a healing problem: the skin is thin, its blood supply is modest, and it is the surface the patient kneels on.
- Incision. Do not place a longitudinal incision down the midline over the patella. Use a transverse or parapatellar approach, so the scar is off the kneeling surface and away from the point of maximum tension.
- Healing. Expect slower healing than the operation seems to justify, and protect it. The commonest complications of bursectomy are wound breakdown and a persistent sinus, not recurrence of the bursitis.
- Excision. Excise the bursa completely rather than partially, since a retained bursal remnant is a route to recurrence, and counsel the patient to keep off the knee until the wound is sound.
Mnemonics & Memory Aids
KNEEL
Hook:KNEEL: Kneeling cause, Not intra-articular, Evaluate for sepsis, Examine skin/ultrasound, Leave quiet bursa alone (aspirate/treat if septic).
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A patient who kneels at work has a swelling in front of the kneecap. How do you assess it?”
“How does your management differ for septic versus non-septic prepatellar bursitis?”
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
Evidence & Key Studies
Common superficial bursitis (olecranon and prepatellar): diagnosis and management
- 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.
Clinical characteristics and management of olecranon and prepatellar septic bursitis
- 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.
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. Aspirating through healthy skin away from the inflamed area to avoid a chronic sinus, and the preserved passive joint movement that separates a bursitis from septic arthritis, follow Septic Bursitis, which covers the olecranon bursa alongside this one, so the two pages give the same technique. (See also Septic Arthritis Pathophysiology, Pes Anserine Bursitis and Gout and Crystal Arthropathy.)