Suprapatellar Bursa Injection

Indications and Clinical Considerations

Bursae are formed from synovial sacs, and their purpose is to allow easy sliding of muscles and tendons across one another at areas of repeated movement. These synovial sacs are lined with a synovial membrane that is invested with a network of blood vessels that secrete synovial fluid. Inflammation of the bursa results in an increase in the production of synovial fluid with swelling of the bursal sac. With overuse or misuse, these bursae may become inflamed, enlarged, and on rare occasions infected. Although there is significant intrapatient variability as to the number, size, and location of bursae, anatomists have identified a number of clinically relevant bursae, including the suprapatellar bursa. The suprapatellar bursa extends superiorly from beneath the patella under the quadriceps femoris muscle ( Fig. 157.1 ). This bursa may exist as a single bursal sac or in some patients as a multisegmented series of sacs that may be loculated.

The suprapatellar bursa is vulnerable to injury from both acute trauma and repeated microtrauma. Acute injuries frequently take the form of direct trauma to the bursa via falls directly onto the knee or patellar fractures, as well as overuse injuries, such as from running on soft or uneven surfaces or from jobs that require crawling on the knees, such as carpet laying ( Fig. 157.2 ). If the inflammation of the suprapatellar bursa becomes chronic, calcification of the bursa may occur.

The patient with suprapatellar bursitis frequently reports pain in the anterior knee above the patella that can radiate superiorly into the distal anterior thigh. Often the patient is unable to kneel or walk down stairs. The patient also may note a sharp, “catching” sensation with range of motion of the knee, especially on first rising. Suprapatellar bursitis often coexists with arthritis and tendinitis of the knee joint, and these other pathologic processes may confuse the clinical picture.

Physical examination may reveal point tenderness in the anterior knee just above the patella. Passive flexion, as well as active resisted extension of the knee, reproduces the pain. Sudden release of resistance during this maneuver markedly increases the pain. There may be swelling in the suprapatellar region with a “boggy” feeling on palpation. Occasionally, the suprapatellar bursa may become infected, with systemic symptoms, including fever and malaise, as well as local symptoms, with rubor, color, and dolor present.

Plain radiographs of the knee may reveal calcification of the bursa and associated structures, including the quadriceps tendon, consistent with chronic inflammation. Magnetic resonance imaging and/or ultrasound imaging is indicated if internal derangement, occult mass, or tumor of the knee is suggested, as well as to help confirm the clinical diagnosis of suprapatellar bursitis ( Fig. 157.3 ). Electromyography helps distinguish suprapatellar bursitis from femoral neuropathy, lumbar radiculopathy, and plexopathy. The injection technique described later serves as both a diagnostic and a therapeutic maneuver.

Clinically Relevant Anatomy

The suprapatellar bursa extends superiorly from beneath the patella under the quadriceps femoris muscle and its tendon (see Figs. 157.1 and 157.4 ). The bursa is held in place by a small portion of the vastus intermedius muscle, called the articularis genus muscle. Both the quadriceps tendon and the suprapatellar 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 4 muscles that constitute 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 patellar 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 tendinitis. The suprapatellar, infrapatellar, and prepatellar bursae also may concurrently become inflamed with dysfunction of the quadriceps tendon.