Housemaid's Knee (Prepatellar Bursitis)

Definition & Anatomy

Housemaid's knee is inflammation of the prepatellar bursa - a small fluid-filled sac lying directly anterior to the patella and between the skin and the bone. It is also called nun's knee or carpet-layer's knee, reflecting the occupational pattern.

The anatomy of the knee bursae is shown below - note the prepatellar bursa sitting anterior to the patella:

Multiple bursae around the knee joint including the prepatellar bursa

(Campbell's Operative Orthopaedics, Fig. 10.6 - Multiple bursae around the knee)

Cause

Friction between the skin and patella from repetitive kneeling on hard surfaces (housemaids cleaning floors, carpet layers, plumbers, wrestlers)
Can also result from an acute direct blow (fall onto patella)
The resulting swelling covers the lower half of the patella and the upper half of the ligamentum patellae

Clinical Features

Feature	Finding
Location	Fluctuant swelling anterior to patella
Pain	Frequently mild in nonseptic form
Range of motion	Usually preserved; only end-range flexion may cause discomfort (as the inflamed bursa is compressed)
Skin	May be thickened/calloused in chronic cases; does NOT communicate with the joint space
Bursal margins	Often palpable

Clinical photo of prepatellar bursitis (left knee swollen, right knee normal for comparison):

Prepatellar bursitis showing local bursal swelling of the left knee

(Tintinalli's Emergency Medicine, Fig. 281-9)

Key distinguishing point: Because the prepatellar bursa does NOT communicate with the joint space, the swelling is anterior and fluctuant, and passive/active ROM is largely preserved - unlike a true intra-articular effusion.

Differential Diagnosis

Infrapatellar bursitis (Clergyman's knee) - also from kneeling, but the bursa lies on the lower half of the ligamentum patellae
Septic arthritis of the knee - distinguished by joint-wide effusion, significant ROM restriction, and constitutional features
Joint effusion - swelling fills the suprapatellar pouch and parapatellar gutters rather than being confined anteriorly
Gout / pseudogout / rheumatoid arthritis (which can also cause bursitis)

Types

1. Traumatic (Nonseptic) Bursitis

Chronic or progressive enlargement
No tenderness, no erythema
Skin over bursa may be thickened
No limitation of joint movement or pain on movement
Associated with repetitive trauma

2. Septic Bursitis

The prepatellar bursa is the most common site for septic bursitis (50-53% of cases)
Especially common in children
Caused by bacterial spread from skin flora (not hematogenous)
Presents with acute pain, tenderness, erythema, and warmth
Fever present in 20-77% of cases
Most common organism: Staphylococcus aureus

Bursal Fluid Analysis

Feature	Septic	Traumatic/Idiopathic	Crystal-Induced
Appearance	Purulent/serosanguineous	Straw-colored or bloody	Straw-colored to bloody
WBC/mm³	Mean ~54,000; >3000 diagnostic	Mean ~2475	Mean ~2900
Differential	>50% PMNs diagnostic	Predominantly mononuclear	Highly variable
Bursal:serum glucose	<50% in 90% of septic cases	>50% in 98%	Unknown
Gram stain	Positive in 70%	Negative	Negative
Culture	Positive	Negative	Negative

(Tintinalli's Emergency Medicine, Table 204)

Treatment

Nonseptic Bursitis

NSAIDs and activity modification (eliminating the precipitating kneeling activity)
Aspiration is controversial - fluid often reaccumulates
If fibrosis or painful nodules fail conservative treatment: surgical excision of the bursa (open or endoscopic)

Septic Bursitis

Aspiration - once or twice daily
Antibiotics - covering skin flora (anti-staphylococcal)
Immobilization
If no significant improvement in 36-48 hours: proceed to incision and drainage

Related Conditions

Clergyman's knee (infrapatellar bursitis) - infrapatellar bursa, lying on the lower half of the ligamentum patellae, also from repetitive kneeling
Student's elbow (olecranon bursitis) - analogous condition at the elbow

Sources: Campbell's Operative Orthopaedics 15th Ed 2026, p. 593; Tintinalli's Emergency Medicine; Rosen's Emergency Medicine; S Das Manual on Clinical Surgery 13th Ed

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