The document discusses the anatomy and structure of the knee joint capsule. It describes how the capsule consists of an outer fibrous layer and inner synovial membrane. The synovial membrane folds and invaginates within the joint, surrounding structures like the cruciate ligaments. The fibrous layer provides passive support and is reinforced by capsular ligaments. The intricate structure of the capsule plays an important role in joint stability and function.

1. Biomechanics
of the
Knee Complex : 3
DR. DIBYENDUNARAYAN BID [PT]
THE SARVAJANIK COLLEGE OF PHYSIOTHERAPY,
RAMPURA, SURAT

2. Joint Capsule
 Given the incongruence of the knee joint, even with
the improvements provided by the menisci, joint
stability is heavily dependent on the surrounding
joint structures.
 The delicate balance between stability and mobility
varies as the knee is flexed from full extension
toward increased flexion.
 Bony congruence and overall ligament tautness are
maximal in full extension, representing the close-
packed position of the knee joint.

3.  In knee flexion, the periarticular passive structures tend
to be lax, and the relative bony incongruence of the joint
permits greater anterior and posterior translations, as
well as rotation of the tibia beneath the femur.
 The joint capsule that encloses the tibiofemoral and
patellofemoral joints is large and lax.
 It is grossly composed of an exterior or superficial fibrous
layer and a thinner internal synovial membrane that is
even more complex than the already complex fibrous
portion.

4.  In general, the outer or fibrous portion of the capsule
is firmly attached to the inferior aspect of the femur
and the superior portion of the tibia.
 Posteriorly, the capsule is attached proximally to the
posterior margins of the femoral condyles and
intercondylar notch and distally to the posterior
tibial condyle.

5.  The patella, the tendon of the quadriceps muscles
superiorly, and the patellar tendon inferiorly
complete the anterior portion of the joint capsule.
 The anteromedial and anterolateral portions of the
capsule, as we shall see, are often separately
identified as the medial and lateral patellar
retinaculae or together as the extensor retinaculum.
 The joint capsule is reinforced medially, laterally,
and posteriorly by capsular ligaments.

6.  The knee joint capsule and its associated ligaments
are critical in restricting excessive joint motions to
maintain joint integrity and normal function.
 Although muscles clearly play a dominant role in
stabilization,
it is difficult to stabilize the knee with active
muscular forces alone in the presence of substantial
disruption of passive restraining mechanisms of the
capsule and ligaments.

7.  The joint capsule plays a role beyond that of a simple
passive structure, however.
 The joint capsule is strongly innervated by both
nociceptors as well as pacinian and Ruffini corpuscles.
 These mechanoreceptors may contribute to muscular
stabilization of the knee joint by initiating reflex-
mediated muscular responses. In addition, the joint
capsule is responsible for providing a tight seal for
keeping the lubricating synovial fluid within the joint
space.

8. Synovial Layer of the Joint Capsule
 The synovial membrane forms the inner lining in
much of the knee joint capsule.
 The roles of the synovial tissue are to secrete and
absorb synovial fluid into the joint for lubrication
and to provide nutrition to avascular structures, such
as the menisci.
 The synovial lining of the joint capsule is quite
complex and is among the most extensive and
involved in the body (Fig. 11-12).

10.  Posteriorly, the synovium breaks away from the
inner wall of the fibrous joint capsule and
invaginates anteriorly between the femoral condyles.
The invaginated synovium adheres to the anterior
aspect and sides of the ACL and the PCL.
 Therefore, both the ACL and the PCL are contained
within the fibrous capsule (intracapsular) but lie
outside of the synovial sheath (extrasynovial).

11.  Posterolaterally, the synovial lining delves between
the popliteus muscle and lateral femoral condyle,
whereas posteromedially it may invaginate between
the semimembranosus tendon, the medial head of
the gastrocnemius muscle, and the medial femoral
condyle.

12.  The intricate folds of the synovium exclude several
fat pads that lie within the fibrous capsule, making
them intracapsular but extrasynovial, like the
cruciate ligaments.
 The anterior and posterior supra-patellar fat pads lie
posterior to the quadriceps tendon and anterior to
the distal femoral epiphysis, respectively.
 The infra-patellar (Hoffa’s) fat pad lies deep to the
patellar tendon (see Fig. 11-9).

13. Patellar Plicae
 Formation of the knee joint’s synovial membrane
occurs in early embryonic development.
 Initially, the synovial membrane may separate the
medial and lateral articular surfaces into separate
joint cavities.
 By 12 weeks of gestation, the synovial septae are
resorbed to some degree, which results in a single
joint cavity but with retention of the posterior
invagination of the synovium that forms some
separation of the condyles.

14.  The failure of the synovial membrane to become fully
resorbed results in persistent folds in specific regions
of the membrane.
 These folds are called patellar plicae.

15.  There are four potential locations where patellar
plicae may be found.
 Because size, shape, and frequency of these plicae
vary among individuals, descriptions also vary
among authors.

16.  The most frequent locations for the plicae, in
descending order of incidence, are:
 inferior (infrapatellar plica),
 superior (suprapatellar plica), and
 medial (mediopatellar plica) (Fig. 11-13).
 There is also the potential for a lateral plica,
although finding this lateral plica is relatively rare.

24.  Synovial plicae, when they exist, are generally
composed of loose, pliant, and elastic fibrous
connective tissue that easily passes back and forth
over the femoral condyles as the knee flexes and ex-
tends.
 On occasion, a plica may become irritated and
inflamed, which leads to pain, effusion, and changes
in joint structure and function,
called plica syndrome.

25. Fibrous Layer of the Joint Capsule
 Superficial to the synovial lining of the knee joint lies
the fibrous joint capsule, which provides passive sup-
port for the joint.
 The fibrous joint capsule itself is composed of two or
three layers, depending on location.
 Additional structural support to the incongruent
knee joint is provided by several capsular
thickenings (or capsular ligaments),
as well as both intracapsular and extracapsular
ligaments.

26.  The anterior portion of the knee joint capsule is
called the extensor retinaculum.
 A fascial layer covers the distal quadriceps muscles
and extends inferiorly.
 Deep to this layer, the medial and lateral retinacula
are composed of a series of transverse and
longitudinal fibrous bands connecting the patella to
the surrounding structures (Fig. 11-14).

28.  Medially, the thickest and clinically most important
band within the medial retinaculum is the medial
patellofemoral ligament (MPFL).

29.  Its fibers, oriented in a transverse manner, course
anteriorly from the adductor tubercle of the femur to
blend with the distal fibers of the vastus medialis and
eventually insert onto the superomedial border of the
patella.
 The transversely oriented fibers within the lateral
retinaculum, called the lateral patellofemoral
ligament, travel from the iliotibial (IT) band to the
lateral border of the patella.

30.  The remainder of the retinacular bands include the
obliquely oriented medial patellomeniscal ligament and
the longitudinally positioned medial and lateral
patellotibial ligaments (see Fig. 11-14).
 The medial portion of the joint capsule is com-posed of
the deep and superficial portions of the MCL.
 The most superficial layer of the joint capsule on the
medial side of the knee joint is a fascial layer that covers
the vastus medialis muscle anteriorly and the sartorius
muscle posteriorly.

31.  Laterally, the joint capsule is composed superficially
of the IT band and its thick fascia lata.
 The capsule is reinforced posterolaterally by the
arcuate ligament and posteromedially by the
posterior oblique ligament (POL).

32. End of Part - 3