Ultrasound-Guided Injection Technique for Prepatellar Bursitis Pain
Prepatellar bursitis, which is also known as housemaid’s and coal miner’s knee, is a common cause of anterior knee pain. The prepatellar bursa lies between the anterior subcutaneous tissues of the knee and the anterior surface of the patella (Fig. 144.1). The bursa serves to cushion and facilitate sliding of the skin and subcutaneous tissues of the anterior knee over the patella. The bursa is subject to inflammation from a variety of causes with acute trauma to the knee and repetitive microtrauma being the most common. Acute injuries to the bursa can occur from direct blunt trauma to the anterior knee from falls onto the knee as well as from overuse injuries including running on uneven or soft surfaces or jobs that require crawling on the knees like carpet laying and coal mining. If the inflammation of the bursa is not treated and the condition becomes chronic, calcification of the bursa with further functional disability may occur. Gout and other crystal arthropathies may also precipitate acute prepatellar bursitis as may bacterial, tubercular, or fungal infections.
The patient suffering from prepatellar bursitis most frequently presents with the complaint of pain in the anterior knee, which may radiate over the entire knee. The patient may find walking down stairs and kneeling increasingly difficult. Physical examination of the patient suffering from prepatellar bursitis will reveal point tenderness over the anterior knee. If there is significant inflammation, rubor and color may be present and the entire area may feel boggy or edematous to palpation. At times, massive effusion may be present, which can be quite distressing to the patient (Fig. 144.2). Active resisted extension and passive flexion of the affected knee will often reproduce the patient’s pain. Sudden release of resistance to active extension will markedly increase the pain. If calcification or gouty tophi of the bursa and surrounding tendons are present, the examiner may appreciate crepitus with active extension of the knee, and the patient may complain of a catching sensation when moving the affected knee, especially on awaking. Often, the patient will not be able to sleep on the affected side. Occasionally, the prepatellar bursa may become infected, with systemic symptoms, including fever and malaise, as well as local symptoms, with rubor, color, and dolor being present.
Plain radiographs are indicated in all patients who present with knee pain to rule out occult bony pathology (Fig. 144.3). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound imaging of the affected area may also confirm the diagnosis and help delineate the presence of other knee bursitis, calcific tendonitis, tendinopathy, quadriceps tendonitis, or other knee pathology (Fig. 144.4). Rarely, the inflamed bursa may become infected, and failure to diagnose and treat the acute infection can lead to dire consequences.
CLINICALLY RELEVANT ANATOMY
There is significant intrapatient variability in the size of the prepatellar bursa. The prepatellar bursa lies between the anterior subcutaneous tissues of the knee and the anterior surface patella (see Fig. 144.1). The bursa serves to cushion and facilitate sliding of the skin and subcutaneous tissues of the anterior knee over the patella (Fig. 144.5). The prepatellar bursa is held in place by patellar tendon patellae, which is an extension of the common tendon of the quadriceps tendon. Both the quadriceps tendon and its expansions and the patellar tendon and the prepatellar bursa are subject to the development of inflammation caused by overuse, misuse, or direct trauma. The quadriceps tendon is made up of fibers from the four muscles that comprise the quadriceps muscle: the vastus lateralis, the vastus intermedius, the vastus medialis, and the rectus femoris. These muscles are the primary extensors of the lower extremity at the knee. The tendons of these muscles converge and unite to form a single, exceedingly strong tendon. The patella functions as a sesamoid bone within the quadriceps tendon, with fibers of the tendon expanding around the patella and forming the medial and lateral patella retinacula, which help strengthen the knee joint. These fibers are called expansions and are subject to strain; the tendon proper is subject to the development of tendonitis. The prepatellar, infrapatellar, and suprapatellar bursae also may concurrently become inflamed with dysfunction of the quadriceps tendon.