Knee Anatomy Flashcards
What are the three joints at the knee?
Patella femoral joint (PFJ)
Tibiofemoral joint (TFJ)
Superior tibiofibular joint (STFJ)
What are the key bony points of the knee?
Tibial tuberosity
Medial and lateral femoral condyles
Patella
Superior tibiofibular joint
Knee Joint line
Tibial plateau
What attaches to the tibial tuberosity?
Patella tendon
What is key about the tibiofemoral joint?
Modified synovial hinge joint
Can only get rotation at the tibiofemoral joint when the knee is at 90 degrees flexion
Rounded surface of the femur comes into contact with flatter surface of the tibia meaning it isn’ as stable because the two bones aren’t ‘overlapping’ each other.
What is key about the articular surface of the knee?
The lateral and medial femoral condyles are not symmetrical
Lateral side is deeper to stop the patella dislocating and moving out of the lateral side of the femur.
What is key about the proximal tibia?
Slightly flatter tibia and different size areas which allows the femur to fit properly.
What is the ROM of flexion and extension at the knee?
130-150 degree flexion (depending on the hip)
0-10 degrees extension
What is the ROM of medial and lateral rotation at the knee?
30-35 degrees medial rotation (less than lateral because of the bony structure)
40-45 degree lateral rotation
What is the close packed position of the knee? (when the bones are closest together/ joint is most stable)
Full extension
What is the open packed position of the knee? (when the bones are furthest apart/ joint is least stable)
30 degrees flexion
What is the stability like in the knee?
Due to the femoral condyles being round and the tibial plateau being flatish it causes the knee to be unstable.
What adds stability to the knee?
Passive and dynamic stabilisers
What is a passive stabiliser?
A joint capsule
Intra and extra capsular ligaments
extracapsular ligaments are thickenings of the capsule
Menisci inside the joint
What are the extracapsular ligaments of the knee?
MCL
LCL
Oblique popliteal ligament (posterior)
Arcuate ligament
What do the MCL and LCL do in movements?
Both are taught in extension & prevent rotation at the knee; however, in knee flexion they become lax allowing rotation to occur
Describe the MCL
Triangular in shape
Blends with the medial meniscus
Medial stability to the knee
Stabilises and secures the medial meniscus
Most effective in flexion
Comes from the medial femoral condyle
What is the mode of injury for the MCL?
Medial valgus stress (struck on the lateral side of the leg when the foot is fixed)
Kicking the foot laterally when going in for a tackle
Describe the LCL
Thin and pencil like
Associated closely with the insertion of the tendon of biceps femoris
Prevents Varus stress of the knee (force coming from medial to laterally)
Much less common injury
Comes from the lateral femoral condyle onto the head of the fibula
How do you tension the MCL & LCL
When extended the MCL and LCL are under max tension to contribute to the locking mechanism.
When are the MCL and LCL slack?
Under flexion they both slacken to allow rotation
Flexion is much more unstable meaning more likely to get injures when flexed
What does the shape of the MCL allow
Due to the MCL being triangular shape some fibres will be in action during both flexion and extension
What are the functions of the LCL?
Resists adduction (varus) not strong
Helped by iliotibial band (IT band) and popliteus
Not a great deal in controlling rotary movements
What are the intracapsular ligaments of the knee?
They cross over so are referred to as the ‘cruciates’
From front to back (ACL)
From back to front (PCL)
They attach in the intracondricular area, in between the medial and lateral condyle on the femur
Stability in the anterior and posterior direction
Describe the ACL
Prevents anterior translation of the tibia on the femur
Checks external rotation of the tibia in flexion
Aids medial displacement of the tibia
Assists in controlling rolling and gliding in the knee
What is the mode of injury of the ACL?
Forced internal rotation of the knee, the foot is usually fixed
Common in football and skiing
What is the unhappy triad?
When you get force on the lateral side going medially which causes damage in the ACL, MCL and meniscal damage
What is the rolling and gliding of the tibiofemoral joint?
- From extension, popliteus unlocks the knee & the femoral condyles begin to roll (approx. 15-20 degrees)
- Then they begin to slide posteriorly as well
- By the end of knee flexion rolling has stopped and only gliding takes place
- Visa versa with extension but at 20 degrees to end of range the tibia laterally rotates to ‘lock the knee’ (closed-pack position)
- This complex mechanism is another example of joint accessory movements
Describe the PCL
Strongest ligament in the knee
Checks posterior translation of the tibia on the femur
Also aids to prevent lateral tibial displacement
Prevents hyperextension
Mode of injury of the PCL
Rarely injured
‘Dashboard ligament’
A positive sag may be seen - with the knees flexed you may see some posterior shift in the tibial tuberosity on the affected side - the horizon sign
Describe the Menisci
Medial and lateral meniscus
Shock absorbers of the knee
Two ‘c’ shaped structures
Fixed at either end – otherwise free to move
Thicker at the external margins
Continuous with the capsule
Lateral more mobile than medial, translated backwards during flexion by popliteus
In the knee extension the menisci translate anteriorly
What is the function of the menisci?
Deepen the articular surface
Shock absorbers - transmit 50-70% of the load
Provide stability - allows the rounded surface to fit to the flat surface
Proprioception
Nutrition
Removal may hasten arthritic changes
Mode of meniscal injury
Twisting on a semi-flexed knee with the foot fixed on the floor
Medial meniscus tears occur 10 times more frequently than lateral ones
Medial tears more longitudinal, lateral more radial
What is the blood supply like in the meniscus?
The outer rim of the meniscus has a good blood supply
This reduces as we move inwards
What muscles cause flexion of the knee?
The hamstrings:
- Semimembranosus
- Semitendinosus
- Biceps Femoris
What muscles cause extension of the knee?
The Quadriceps:
- Rectus Femoris
- Vastus lateralis
- Vastus medialis
- Vastus intermedius
What muscle causes internal rotation of the knee?
Popliteus unlocks the knee
What muscle causes external rotation of the knee?
Biceps femoris locks the knee
Describe the patello-femoral joint
Modified synovial plane joint - patella (sesamoid bone)
Patellar tendon attaches the apex of patella to the tibial tuberosity
What are the movements of the patella-femoral joint?
Shift - tilt - rotate
Moves up (caudad) on femur with knee extension
Moves down (cephalad) on femur with knee flexion
What is patellar tracking?
During knee flexion and extension the patella is not static but undergoes a degree of shift, tilt and rotation on the patellar surface of the femur as well as supero-inferior movement.
Different parts of the patella will articulate with the femur at different parts of the flexion/extension range
The posterior surface of the patella has different facets for changing areas of articulation
