1
Background
Bursae are located between surfaces exposed to friction and movement, often between different types of tissues like tendons and bones. Knee bursitis is a disorder related to an inflammation of any of the bursa in the knee joint region. It is a common clinical disorder that may lead to functional impairments. The clinical presentation of a bursitis depends on its location, size, mass effect, and relationship to surrounding structures. They are often asymptomatic and may be incidentally found on inspection or imaging examinations [ ]. Occasionally, they may cause pain, swelling, nerve compression, erosion, or joint impairment. In rare cases, the clinical presentation of a knee bursitis may be misleading. For example, parameniscal cysts are always associated with meniscal tears and popliteal cysts are highly associated with osteoarthritis of the medial compartment of the knee [ ].
Asymptomatic knee bursitis is often treated with observation alone, while the treatment of symptomatic cysts depends on the underlying cause. Microtrauma-related bursitis is usually treated with steroid injection and immobilization. Bursitis that impairs joint function may require aspiration or resection. If a bursitis is associated with underlying joint disease, it is important to address the underlying joint abnormality to prevent recurrence [ ].
Eleven bursae are found within the knee region [ ] ( Fig. 11.1 ).
Three bursae communicate with the knee joint. Four of them are associated with the patella, two are related to the semimembranosus tendons and two are related to the collateral ligaments of the knee [ ].
2
Clinical Study
2.1
Symptoms
The patient usually complains of mild local pain which may be associated with swelling in the affected site. The pain is worse with flexion and usually occurs at night or after activity. In some cases, the pain may be intense and accompanied by morning stiffness [ ].
Walking promptly becomes painful and limping may be present. A limitation in knee range of motion (ROM), especially in flexion, may impair driving and sitting at a desk at work.
Patients will also have problems leaning, kneeling, crawling, or climbing, which may interfere with professional and recreational activities. Athletes such as runners may have diminished performance or may be even put off play [ ].
2.2
Physical Examination
The patient may have an antalgic gait, with a shortened stance phase on the affected side. There is tenderness to palpation associated with swelling at the site of the involved bursa, and there may be associated to local inflammatory signs and crepitation [ ].
If the bursa connects with the knee joint, there may be an associated joint effusion.
Knee ROM is often limited by pain and increased intraarticular tension.
The neurologic examination findings should be normal.
Decreased balance is often seen in older patients, sometimes necessitating assistive devices such as a walker, crutches, cane, or even a wheelchair [ ].
2.3
Topographic Forms
The most common knee bursitis conditions are the following.
2.3.1
Prepatellar bursitis (Housemaid’s knee)
Prepatellar bursitis can be caused by microtrauma such as frequent kneeling on a hard surface or direct trauma, such as falling on a bent knee [ ]. It has been reported to be associated with knee osteoarthritis in 3.1% of cases [ ].
2.3.2
Infrapatellar bursitis (Vicar’s knee)
Infrapatellar bursitis is usually due to repetitive knee flexion in weight bearing, such as deep knee bends, squatting, or jumping. It can be associated with patellar and quadriceps tendinopathies [ ]. It is associated with knee osteoarthritis in 10.6% of patients [ ].
2.3.3
Anserine bursitis
Anserine bursitis is commonly seen in individuals who participate in sports that require running, side-to-side movement and cutting and in overweight older women with knee osteoarthritis [ ]. It is responsible for 2.5% of medial knee pain [ ].
2.3.4
Medial collateral ligament bursitis
Medial collateral ligament bursitis refers to inflammation of a bursa located between the deep and superficial parts of the medial collateral ligament [ ]. It is associated with degenerative disease of the medial joint compartment [ ]. This bursitis may be seen in horse-riding and motorcycle athletes because of the friction applied to the medial side of the knee [ ].
2.3.5
Semimembranosus bursitis
Semimembranosus bursitis is usually seen in runners and may be associated with hamstring tendinitis [ ]. This bursitis was seen in 4.4% of subjects with knee pain explored with magnetic resonance imaging (MRI) [ ].
3
Differential Diagnosis
Necrotic or mucinous neoplasms.
There is usually some solid component that differentiates these more serious masses from the benign cystic lesions.
4
Imaging
The aim of knee bursitis imaging is to confirm the cystic nature of the lesion, determine its relationship with the joint and the surrounding structures, and to evaluate the joint for associated disorders.
4.1
Standard X-rays
Standard radiographs have a limited value for assessing soft tissue abnormalities. They may demonstrate soft tissue swelling, effusion, signs of associated degenerative joint disease, bone erosion, calcification, or intraarticular calcifications in case of a communicating bursa [ ].
4.2
Arthrography
Arthrography can be helpful in demonstrating the communication of a cyst with the joint cavity. However, when the communication is very narrow or when the bursa is filled with highly viscous fluid, it may not be filled with the contrast product and in these cases, arthrography offers little information [ ].
4.3
Ultrasound
Ultrasound (US) is adapted to study suspected bursitis. It can be used to demonstrate the location and extent of cysts and can differentiate cysts from noncystic masses. However, US has limited ability to evaluate for associated intraarticular abnormalities. Furthermore, cysts containing debris or hyperplastic synovium may simulate solid mass lesions [ ] ( Figs. 11.2 and 11.3 ).
