Biomechanics of the Knee Complex : 5DR. DIBYENDUNARAYAN BID [PT] THE SARVAJANIK COLLEGE OF PHYSIOTHERAPY, RAMPURA, SURAT
Bursae The extensive array of ligaments and muscles crossing the tibiofemoral joint, in combination with the large excursions of bony segments, sets up the potential for substantial frictional forces among muscular, ligamentous, and bony structures. Numerous bursae, however, prevent or limit such degenerative forces.
Three of the knee joint’s bursae, the suprapatellar bursa, the sub-popliteal bursa, and the gastrocnemius bursa, :are not separate entities but either are invaginations of the capsule’s synovium or communicate with the synovial lining of the joint capsule through small openings (see Fig. 11-12).
The anteriorly located suprapatellar bursa lies between the quadriceps tendon and the anterior femur, superior to the patella. The posteriorly located subpopliteal bursa lies between the tendon of the popliteus muscle and the lateral femoral condyle, and the gastrocnemius bursa lies between the tendon of the medial head of the gastrocnemius muscle and the medial femoral condyle.
The gastrocnemius bursa continues beneath the tendon of the semimembranosus muscle to protect it from the medial femoral condyle.
The three bursae that are connected to the synovial lining of the joint capsule allow the lubricating synovial fluid to move from recess to recess during flexion and extension of the knee. In extension, the posterior capsule and ligaments are taut, and the gastrocnemius and subpopliteal bursae are compressed. This shifts the synovial fluid anteriorly (Fig. 11-23A). In flexion, the suprapatellar bursa is compressed anteriorly and the fluid is forced posteriorly (see Fig. 11- 23B).
When the knee joint is in the semiflexed position, the synovial fluid is under the least amount of pressure (see Fig. 11-23C). Clinically, when there is excess fluid within the joint cavity as a result of injury or disease (termed joint effusion), the semiflexed knee position helps to relieve tension in the capsule and, therefore, minimizes discomfort.
Besides the bursae that communicate with the synovial capsule, there are several other bursae associated with the knee joint (Fig. 11-24). The prepatellar bursa, located between the skin and the anterior surface of the patella, allows free movement of the skin over the patella during flexion and extension. The infrapatellarbursa lies inferior to the patella, between the patellar tendon and the overlying skin.
Both the infrapatellar bursa and the prepatellar bursa may become inflamed as a result of direct trauma to the front of the knee or through activities such as prolonged kneeling. The deep infrapatellar bursa, located between the patellar tendon and the tibial tuberosity, helps to reduce friction between the patellar tendon and the tibial tuberosity.
This bursa is separated from the synovial cavity of the joint by the infrapatellar (Hoffa’s) fat pad. There are also several small bursae that are associated with the ligaments of the knee joint. There is commonly a bursa between the LCL and the biceps femoris tendon.
On the medial side of the joint, small bursae can be found both superficial and deep to the superficial portion of the MCL to protect it from the deep portion of the MCL and the tendons of the semitendinosus and gracilis muscles, respectively.