Lecture 19: Knee joint Flashcards
what are the 2 articulations in the knee joint?
- between the femur and the tibia
- between the femur and the
patella (Patellofemoral joint). - The articular cavity of the knee
joint includes both the
patellofemoral joint and
the tibiofemoral joint. (share the cavity and synovial fluid)
what is the role of the meniscus?
The menisci increase stability for femorotibial articulation, distribute axial load, absorb shock, and provide lubrication and nutrition to the knee joint.
+increase SA for articulation between femur and tibia
what is the role of the patella( sesamoid bone )?
protects quad tendon
what is a sesamoid bone?
A sesamoid bone is a small bone that is commonly found embedded within a muscle or tendon near joint surfaces, existing as focal areas of ossification and functioning as a pulley to alleviate stress on that particular muscle or tendon
patella anatomy
- Patella has an upper and lower
pole - Patella is a sesamoid bone
It sits in the tendon of the
quadriceps muscles - Attaches to tibial tuberosity of
tibia - Protects the quadreceps
tendon
normal alignment
*Weight of body is transmitted to centre of
hip joints
*Then down leg
*If leg is aligned well weight is transmitted
through the knee joint and ankle joint
= “Normal alignment” of lower limb
Minimises wear on joints and energy
required to stand or walk
varus alignment
-normal in babies and older ppl (legs further apart to increase stability)
-knee joint is directed laterally
-apex of joint point out
valgus alignment
-common in young girls-> grow out of it
-if not fixed-> puts pressure on the lateral aspects+ and tension on the medial ligaments-> stretched and weakened
-apex point in
5 ligaments of the knee
-patellar lig/tendon
-the medial and lateral collateral ligs
-anterior and posterior cruciate lig
patellar lig/tendon
- The Patellar ligament is the continuation of
the quadriceps mechanism (making the patella a
sesamoid bone). - It is attached to the inferior margins of the
patella (superiorly) and the tibial tuberosity
(inferiorly). - Clinically call it patella tendon as patella
ligament is really continuation of quadriceps
tendon
The Medial and Lateral Collateral ligaments
- The Medial and Lateral Collateral
ligaments (MCL and LCL) attach at the sides
of the knee. - The MCL runs from the medial femoral
epicondyle to the medial tibia (posterior to the
attachment of the Pes Anserinus). - It is a broad ligament that blends with the
underlying joint capsule. - The LCL runs from the lateral femoral
epicondyle to the fibula head. - It is a cord-like ligament that is discrete from
the joint capsule. - Function – prevent knee going valgus or
varus
lateral collateral lig
medial collateral lig
Anterior and Posterior Cruciate ligaments
- Intracapsular
-inside the capsule BUT not inside the synovial cavity - The Anterior and Posterior Cruciate ligaments
(ACL and PCL) run from the intercondylar
region of the tibia ( ‘tibial spine’) to the distal
femur - Important in stabilizing the knee in the AP plane.
- The ACL runs from the anterior tibial spine to
the lateral condyle of the femur. It prevents
excessive anterior translation of the tibia on the
femur (prevents the tibia sliding forward on
femur) - The PCL runs from the posterior tibial spine to
the medial femoral condyle. It prevents
posterior translation of the tibia on the femur.
(prevents the tibia from sliding backwards on femur)
knee joint capsule structure
The joint capsule isolates and covers the entire joint. It consists of two layers, an outer fibrous layer and an inner layer known as the synovial membrane.
- The joint capsule is the fibrous membrane that
encloses the articular cavity. - Attached is where the cartilage finishes
- Anteriorly the membrane is reinforced by the quads tendon and patella ligament.
- The synovial membrane is deep to the fibrous membrane and excludes the anterior and posterior cruciate ligaments
bursae of the knee
The Prepatellar bursa is anterior to the patella.
* This can become inflamed with repeated
trauma e.g. kneeling for long periods of time.
- The Infrapatellar bursae are superficial and deep
to the patellar ligament (inferior to the patella itself)
and can also become inflamed and cause knee pain - The prepatellar and infrapatellar bursae do
not communicate with the knee joint - The Suprapatellar bursa is in continuity with the knee joint and sits between the quads tendon and the distal femur.
clinical relevance of suprapatellar bursa
- This is often where fluid will accumulate during a knee joint effusion.
- Good place to access the knee joint to aspirate fluid or inject into the knee
menisci
There are two fibrocartilaginous menisci
within the knee joint- medial and lateral.
They improve the articulation between
the femur and the tibia as shape of the
surfaces changes throughout the full range
of motion.
Also act as “shock absorbers”
The medial meniscus is attached to the joint
capsule and MCL, making it less mobile.
The lateral meniscus is not attached to the
joint capsule and hence is more mobile.
what is the problem with menisci?
fibrocartilage-> poor blood supply-> central meniscal tears won’t heal-> need to take out
which meniscus is more commonly injured?
medial
attached to the joint capsule and MCL making it less mobile
what is a good radiology scan to see tears in minisci?
MRI. White line= tear
what is a good radiology scan to see tears in menisci?
MRI. White line= tear
what is the most common knee dislocation?
hyperextension- anterior dislocation
risks associated with knee dislocation
Neurovascular structures at risk:
Popliteal artery and vein, Tibial and
common fibular nerves
+ damage to the ligaments
what is happening here?
risks/ consequences/ concerns
comminuted Tibial fracture involving the joint
-blood+ fat has come out of the bone into the joint capsule-> fat can get into the bloodstream -> fat emboli-> if in lungs- can die of hypoxia
+ trauma involving the joint predisposes to arthritis
vascular supply to the knee
The vascular supply to the knee comes from:
Branches of the femoral,
lateral femoral circumflex and
popliteal vessels (superiorly)
anastomosing with branches of the:
Anterior tibial and circumflex peroneal arteries (inferiorly).
Main concept: Anastomoses
Allow some blood to get to the leg if the
the popliteal artery is blocked.
nerve supply to the knee
- Knee joint is supplied by branches from the femoral, sciatic, and
obturator nerves, which move the joint. - Some of these nerves go to the fibrous capsule and ligaments; others
innervate this capsule and reach the synovial membrane.
dermatome
A dermatome is an area of skin that is mainly supplied by
cutaneous branches of a single spinal nerve
myotome
A myotome is a group of muscles derived from one somite and supplied by a single spinal nerve (it is the motor equivalent of a dermatome)
A myotome is defined as ‘a group of muscles innervated by a single spinal nerve root‘. They are clinically useful as they can determine if damage has occurred to the spinal cord, and at which level the damage has occurred.
Most muscles in the upper and lower limbs receive innervation from more than one spinal nerve root. They are therefore comprised of multiple myotomes.
Each muscle in the body is supplied by a particular level or
segment of the spinal cord and by its corresponding spinal
nerve.
The muscle and its nerve make up a myotome.
patterns/rules of myotomal supply:
- Muscles with common action have a common segmental supply i.e. all muscles which act to flex the hip have the same myotome(or two); they are innervated by L2 and L3.
- Opposing muscles supplied by subsequent segmental levels i.e. muscles acting to extend the knee are supplied by L3 and L4; Those acting to flex the knee are supplied by L5 and S1.
- Each joint distally supplied by 1 segment lower in the cord i.e. knee movements produced by muscles supplied by L3-S1; ankle movements produced by muscles supplied by L4-S2.
match spinal lvl to action
clinical importance of Pes Anserinus( goose foot)
The Pes Anserinus (meaning “goose’s foot”) is the insertion of the tendons of Sartorius,
Gracilis and Semitendinosus onto the medial surface of the proximal tibia. These tendons
can be used to reconstruct a torn ACL.
terrible/unhappy triad
This a common injury pattern resulting from a lateral (valgus) force to the knee. The three
structures involved are typically the medial collateral ligament, anterior cruciate ligament
and medial (or lateral) meniscus.
