1. Biomechanics
of the
Knee Complex : 5
DR. DIBYENDUNARAYAN BID [PT]
THE SARVAJANIK COLLEGE OF PHYSIOTHERAPY,
RAMPURA, SURAT

2. 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.

3.  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).

5.  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.

6.  The gastrocnemius bursa continues beneath the
tendon of the semimembranosus muscle to protect it
from the medial femoral condyle.

7.  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).

9.  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.

10.  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.

12.  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.

13.  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.

14.  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.

15. End of Part - 5