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Prepatellar bursitis

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Prepatellar bursitis
Other names: Carpet layer's knee, coal miner's knee, housemaid's knee,[1] carpenters knee,[2] beat knee,[3] rug cutter's knee,[4] nun's knee[5]
Aseptic prepatellar bursitis of the knee near the camera
SpecialtyOrthopedics, sports medicine
SymptomsSwelling, redness, and tenderness in front of knee[2]
CausesRepetitive minor trauma, acute injury, gout, rheumatoid arthritis, infection[2]
Risk factorsProfessions that require frequent kneeling, poor immune function[1][2]
Diagnostic methodBased on symptoms and examination, potentially aspiration to rule out infection[2]
Differential diagnosisPatellar tendonitis, patellar subluxation, tibial apophysitis, septic arthritis, cellulitis,[2] Morel-Lavallée lesion[6]
TreatmentRest, NSAIDS, applying ice[2]
PrognosisGenerally good[2]
FrequencyRelatively common[1]

Prepatellar bursitis is inflammation of the prepatellar bursa at the front of the knee.[2] Symptoms generally include swelling, redness, tenderness, and possibly minor decrease in range of motion.[2][4] Cases of longer duration generally have little pain.[2]

It most commonly due to repetitive minor trauma to the knee, such as from kneeling.[1] Other causes may include a single injury, gout, rheumatoid arthritis, or infection.[2] Risk factors include professions that require frequent kneeling and poor immune function.[1][2] Diagnosis is usually based on symptoms and examination, with potentially aspiration to rule out infection.[2]

Treatment may include rest, NSAIDS, and applying ice.[2] If infected 7 days of antibiotics are generally sufficient.[7] Steroid injection maybe used for long term cases.[2] In cases that fail other measures, bursectomy may be carried out.[2] Outcomes are generally good.[2]

Prepatellar bursitis is relatively common, estimated to affect about 1 in 10,000 people a year; second in frequency only to olecranon bursitis.[1][2] It occurs more commonly in males than females.[2] Those between the ages of 40 and 60 are most commonly affected.[2] It has historically been called housemaids, carpet layers, or carpenters knee.[2]

Signs and symptoms

Left sided aseptic prepatellar bursitis in a concrete finisher.

The primary symptom of prepatellar bursitis is swelling of the area around the kneecap. It generally does not produce a significant amount of pain unless pressure is applied directly.[8] The area may be red (erythema), warm to the touch, or surrounded by cellulitis, particularly if infection is present, often accompanied by fever.[9]: p. 608  Unlike arthritis, except in severe cases prepatellar bursitis generally does not affect the range of motion of the knee, though it may cause some discomfort in complete flexion of the joint.[10]: p. 360  Flexion and extension of the knee may be accompanied by crepitus, the audible grating of bones, ligaments, or particles within the excess synovial fluid.[11]: p. 20 


In human anatomy, a bursa is a small pouch filled with synovial fluid. Its purpose is to reduce friction between adjacent structures. The prepatellar bursa is one of several bursae of the knee joint, and is located between the patella and the skin.[12] Prepatellar bursitis is an inflammation of this bursa. Bursae are readily inflamed when irritated, as their walls are very thin.[11]: p. 22  Along with the pes anserine bursa, the prepatellar bursa is one of the most common bursae to cause knee pain when inflamed.[13]

Prepatellar bursitis is caused by either a single instance of acute trauma to the knee, or repeated minor trauma to the knee. The trauma can cause extravasation of nearby fluids into the bursa, which stimulates an inflammatory response.[14] This response occurs in two phases: The vascular phase, in which the blood flow to the surrounding area increases, and the cellular phase, in which leukocytes migrate from the blood to the affected area.[11]: p. 22  Other possible causes include gout, sarcoidosis, CREST syndrome,[10]: p. 359  diabetes mellitus, alcohol use disorder, uremia, and chronic obstructive pulmonary disease.[11]: p. 22  Some cases are idiopathic, though these may be caused by trauma that the patient does not remember.[9]: pp. 607–8 

The prepatellar bursa and the olecranon bursa are the two bursae that are most likely to become infected, or septic.[15] Septic bursitis typically occurs when the trauma to the knee causes an abrasion, though it is also possible for the infection to be caused by bacteria traveling through the blood from a pre-existing infection site.[16] In approximately 80% of septic cases, the infection is caused by Staphylococcus aureus; other common infections are Streptococcus, Mycobacterium, and Brucella.[10]: p. 359  It is highly unusual for septic bursitis to be caused by anaerobes, fungi, or Gram-negative bacteria.[9]: p. 608  In very rare cases, the infection can be caused by tuberculosis.[17]


Lateral section of the knee

There are several types of inflammation that can cause knee pain, including sprains, bursitis, and injuries to the meniscus.[13] A diagnosis of prepatellar bursitis can be made based on a physical examination and the presence of risk factors in the person's medical history; swelling and tenderness at the front of the knee, combined with a profession that requires frequent kneeling, suggest prepatellar bursitis.[14] Swelling of multiple joints along with restricted range of motion may indicate arthritis instead.[9]: p. 608 

A physical examination and medical history are generally not enough to distinguish between infectious and non-infectious bursitis; aspiration of the bursal fluid is often required for this, along with a cell culture and Gram stain of the aspirated fluid.[10]: p. 360  Septic prepatellar bursitis may be diagnosed if the fluid is found to have a neutrophil count above 1500 per microliter,[9]: p. 608  a threshold significantly lower than that of septic arthritis (50,000 cells per microliter).[10]: p. 360  A tuberculosis infection can be confirmed using a radiograph of the knee and urinalysis.[17]


It is possible to prevent the onset of prepatellar bursitis, or prevent the symptoms from worsening, by avoiding trauma to the knee or frequent kneeling.[9]: p. 610  Protective knee pads can also help prevent prepatellar bursitis for those whose professions require frequent kneeling and for athletes who play contact sports, such as American football, basketball, and wrestling.[18]


Non-septic prepatellar bursitis can be treated with rest, the application of ice to the affected area, and anti-inflammatory drugs, particularly ibuprofen. Elevation of the affected leg during rest may also expedite the recovery process.[18] Severe cases may require fine-needle aspiration of the bursa fluid, sometimes coupled with cortisone injections.[16] However, some studies have shown that steroid injections may not be an effective treatment option.[19] After the bursitis has been treated, rehabilitative exercise may help improve joint mechanics and reduce chronic pain.[20]: p. 2320 

Opinions vary as to which treatment options are most effective for septic prepatellar bursitis.[10]: p. 360  McAfee and Smith recommend a course of oral antibiotics, usually oxacillin sodium or cephradine, and assert that surgery and drainage are unnecessary.[9]: p. 609  Wilson-MacDonald argues that oral antibiotics are "inadequate", and recommends intravenous antibiotics for managing the infection.[3] Some authors suggest surgical irrigation of the bursa by means of a subcutaneous tube.[10]: p. 360 [21] Others suggest that bursectomy may be necessary for intractable cases; the operation is an outpatient procedure that can be performed in less than half an hour.[22]: p. 357 


The various nicknames associated with prepatellar bursitis arise from the fact that it commonly occurs among those individuals whose professions require frequent kneeling, such as carpenters, carpet layers, gardeners, housemaids, mechanics, miners, plumbers, and roofers.[14][8][9]: p. 607  The exact incidence of the condition is not known; it is difficult to estimate because only severe septic cases require hospital admission, and mild non-septic cases generally go unreported.[9]: p. 607  Prepatellar bursitis is more common among males than females. It affects all age groups, but is more likely to be septic when it occurs in children.[23]


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