8 - Knee Joint Flashcards
What are the articulations of the knee joint?
The knee joint has 2 articulations
> femur and tibia (tibiofemoral)
> femur and patella (patellofemoral)
> the fibula is NOT involved in the knee joint
What joints are included in the joint cavity of the knee joint?
Both the tibiofemoral and patellofemoral joints
What kind of joint is the knee joint and what does it allow?
A hinge joint - mostly allows flexion and extension
What does the locking mechanism of the knee allow?
The locking mechanism means when the leg/knee is fully extended the muscle energy to maintain a straight leg like when walking/standing is reduced
What way is the patella moved during movement?
- the quad muscles are the muscles that act on the patella
- patella generally moves superiorly and inferiorly to extend the leg
- the quad muscles are on an angle from ASIS so they also pull the patella LATERALLY (Q angle)
What is the Q angle?
The line of pull the patella is on due to the quadricep muscles compared to the line it wants to be on (directly up to acetabulum)
How big is the Q angle?
14 degrees in males
17 in females
> the bigger the carrying angle and so bigger the hips, the more likely lateral dislocation is
How does the patella sit in the femur?
The distal femur has a groove inbetween the 2 condyles and the patella has a corresponding on its deep side
What about the patella/femur is important in preventing dislocation?
People with a flat distal femur and patella allows the patella to move more; the contour of the distal femur and patella is important in keeping the patella in place
How can you tell which side of the body the distal femur is from?
The lateral condyle projects further forward/anteriorly to protect the patella from dislocating laterally
Important features of the femur and tibia
- tibial tuberosity (where patella tendon inserts)
- tibial plateau
- femoral condyles
- femoral epicondyles
Where does the patella sit?
Anteriorly on the femur attached superiorly to the quadriceps tendon and there is a ligamentous tissue connecting the patella to the tibial tuberosity (patellar tendon)
What connects the patella to the tibial tuberosity?
The patellar tendon - ligamentous tissue that is more like a tendon
What attaches laterally to the tibial tuberosity?
The iliotibial band
The patella is a … bone. Why is this significant?
Sesamoid bone. It sits WITHIN the tendon of a muscle, protecting it from rupturing
> if there was no sesamoid bone here the FORCES and FRICTION that occurs over the distal femur and tendon when bending/straightening would cause the tendon to rupture
The patella acts as part of the …
Quadriceps mechanism and so can be thought of as a continuation of the muscle so the ligamentous tissue acts as a tendon
What is the primary function of the the collateral ligaments of the knee?
Act as knee stabilisers
Where do the collateral ligaments attach?
> They run down the medial and lateral sides of the knee.
Where does the Medial Collateral Ligament (MCL) run?
> medial femoral epicondyle to the medial tibia (behind pes anserinus)
broad ligament that posteriorly attaches to the JOINT CAPSULE and MEDIAL MENISCUS
as it attaches to these other structures when you injure MCL you often injure other structures
stops VALGUS malignment of the knee
What does MCL prevent?
Valgus knee malalignment
Describe the lateral collateral ligament (LCL)
> runs from lateral femoral epicondyle to fibula head
compared to the MCL the LCL is more discrete and does NOT adhere to other structures
means the LCL is less prone to damage
prevents VARUS
the ITB attaches more anteriorly; may be why the ligament is more discrete?
What collateral ligament is more prone to damage?
The Medial Collateral Ligament. Attached to more structures (joint capsule and medial meniscus) while LCL is discrete and not as broad.
What does LCL prevent?
Varus
Where are the cruciate ligaments?
> they run from the intercondylar region of the tibia to the distal femur
What do the cruciate ligaments do?
They stabilise the knee in the AP plane (back/forwards). They are especially important when the knee is flexed like when walking and up/down stairs. Less important when leg is extended as it is locked/stable as the quadricep muscles hold it stable
Where does the Anterior Cruciate Ligament (ACL) run?
> from the anterior intercondylar tibia/anterior tibial spine on the tibial plateau to the LATERAL femoral condyle
Where does the Posterior Cruciate Ligament (PCL) run?
> from posterior intercondylar tibia/posteiror tibial spine on the tibial plateau to the MEDIAL femoral condyle
Where do both the ACL and PCL lie?
They lie WITHIN the knee joint but OUTSIDE of the articular cavity
What does the PCL prevent?
Posterior translation of the tibia on the femur
What does the ACL prevent?
Anterior translation of the tibia on the femur
What are the symptoms when you damage the cruciate ligaments?
Feeling of instability, like knee will give way, rather than pain
What are bursa?
‘water balloons’ found where friction is high such as ski/bone or muscle/bone. Normally only contain a few mL of fluid but when diseased can fill to 100mL
How many bursae are there in the knee?
There are 4
- Prepatellar Bursa
- The 2 infrapatellar bursae (subcutaneous and deep)
- Suprapatellar Bursa
What are the ligaments of the knee?
There are 5
- Patellar Tendon
- MCL
- LCL
- ACL
- PCL
What is the bursa anterior to the patella?
Prepatellar Bursa
What are the bursa inferior to the patellar, on either side of the patellar tendon?
Deep and Superficial Infrapatellar Bursae
What bursa sits beneath the patella?
Suprapatellar Bursa
Prepatellar Bursa?
- between front of patella and skin
- has minimal fluid so is hard
- protects when kneeling i.e. carpet layers/plumbers
- is a subcutaneous structure just below the skin so is prone to infection i.e. splinter
- “Housemaid’s Knee” - fills with fluid and tissue
Infrapatellar Bursae?
- below the patella, superficial and deep to the patellar tendon (skin/tendon and tendon/bone)
- Kluge Men’s Knee
- often inflammed in gardners (just on knees)
Suprapatellar Bursa?
- sits beneath and slightly above the patella, anterior to the femur, deep to the quad muscles
- is in continuation with the knee joint fluid
What bursa is in continuation with the knee joint fluid?
Suprapatellar Bursa
How can you sample the knee joint fluid?
- the knee joint itself is very small and a needle on bone that has a periosteal nerve supply hurts more than needle through muscle
- inject medicine/take sample from suprapatellar bursa just superior to patellar and deep to quad tendon
- if the knee joint IS inflammed then it WILL collect in the bursa rather than the joint space as the muscle has more give than the bones
What are the menisici are for?
> Shock absorbers
they improve the articulation between the femur and tibia as shape of the surfaces changes throughout the full range of motion
Describe the knee joint capsule
> A fibrous membrane that encloses the articular cavity
on the medial side the capsule fuses with the medial menisci and MCL; means the medial side is less mobile as is very adherent to the joint capsule
the lateral capsule is discrete so is less likely to be injured and is more mobile
What reinforces the capsule anteriorly?
Quadriceps tendon and patella tendon
The … … is deep to the fibrous membrane and EXCLUDES the cruciate ligaments
Synovial Membrane
How many menisci are there in the knee and what are they made of?
2 (lateral and medial) made of fibrocartilage
How is the lateral menisci kept discrete form the lateral joint capsule?
The popliteus muscle in the back of the knee has its tendon lieing between the lateral meniscus and joint capsule to keep them discrete
Which menisci are you more likely to damage?
The medial meniscus. Is attached to joint capsule and MCL so is less mobile. Lateral is more discrete and more mobile less prone to damage
What is the vascular supply to the knee?
Branches of the femoral, lateral femoral circumflex, and popliteal vessels anastomosing with branches of the anterior tibial and circumflex peroneal arteries
What are the actions, muscles and myotomes acting on the knee?
1. Extension > hamstrings > L3/L4 (kick the door) 2. Flexion > quadriceps > L5/S1 (kick my bum)
What is a myotome?
A movement affected by 1 or 2 of the spinal levels. Nerves remember where they came from and when they arrive at their destinations/peripheral nerves, the ones from the same segmental level line up
What is the clinical importance of Pes Anserinus
- where sartorius, semitendinosus, gracillus insert at medial prox tibia
> these tendons can be used in the knee to replace a torn ACL
What causes an unhappy triad?
Lateral/valgus force to the knee.
What are the 3 structures involved in an unhappy triad?
Medial meniscus, MCL, anterior cruciate ligament
How would you determine what spinal nerve is injured?
- test leg muscles strength. For example if can’t extend leg L3/L4 damaged
How may you injure the cruciate ligaments?
By hyperextending the leg. Or when the 2 bones twist in opposite directions
