M: The knee joint Flashcards
What 2 conditions are the common causes of chronic knee pain/swelling?
1) Osteoarthritis
2) Burisitis
What 3 atraumatic conditions can result in acute knee swelling/pain?
1) Acute gout
2) Flare of OA or RA
3) Septic joint
What kind of joint is the knee joint?
Synovial hinge joint
Which 3 bones are involved in the knee joint?
1) Distal femur
2) Proximal tibia
3) Patella
What 3 articulations make up the knee joint?
1) Medial femorotibial
2) Lateral femorotibial
3) Femoropatellar
The medial and lateral femorotibial articulations are between which joint surfaces?
Medial and lateral tibial plateaus (flattened top surfaces of tibial condyles) and the medial and lateral femoral condyles
What are the 4 possible movements of the knee joint?
1) Extension
2) Flexion
3) Medial rotation of leg when knee joint flexed at 90 degrees
4) Lateral rotation of leg when knee joint flexed at 90 degrees
Why is some knee flexion lost when the hip is extended?
Due to loss of tension on hamstrings
When can rotation of the knee occur?
Only when the knee is flexed and the collateral ligaments are relaxed
What is locking of the knee, when does it occur?
Occurs as the joint approaches full extension, femur undergoes a few degrees of medial rotation on the tibia
Why is locking of the knee important?
It provides a very stable position when the leg is in full extension so that the thigh muscles can relax
Which muscle is involved in unlocking the knee, why is this necessary?
Popliteus muscle - laterally rotates the femur
Knee need to be unlocked in order to flex the knee from extension
Why is the knee joint said to be incongruent, what structures improves the congruency of the knee joint?
Tibial plateau is a poor fit for the rounded femoral condyles
Tibial plateau is deepened - thus congruency is improved - by 2 plates of fibrocartilage called the menisci
Is the knee joint more or less stable in extension or flexion, why?
Most stable in extension
because the joint is most congruent in this position
What are the menisci?
2 c-shaped wedges of fibrocartilage which are thicker at the external margins
What are the 4 functions of the menisci?
1) Increase joint congruency
2) Distribute weight evenly across the knee joint
3) Shock absorption
4) Assist in locking mechanism
What do the menisci attach to?
The external edges of both menisci attach to the fibrous capsule of the joint
The medial meniscus is also firmly attached to the tibial collateral ligament
What is the clinical significance of the relationship between the medial meniscus and the tibial collateral ligament?
Rupture to the tibial collateral ligament will also result in injury to the medial meniscus
Unlike the lateral meniscus which is not attached to the fibular collateral ligament and you can therefore get isolated injuries
What is the likely cause of a meniscal tear?
Sports injury or degenerative changes
Why does the knee become painful or lock in a meniscal tear?
Get displaced cartilage which can become trapped during knee movement
What is the treatment for a meniscal tear?
Repair or resection
Damage to the menisci is associated with development of what condition?
Osteoarthritis
Which 3 things increase the stability of the joint, which has the most effect?
1) Ligaments inside the joint - intra-articular
2) Ligaments outside the joint - extra-articular
3) Surrounding muscles - have the biggest influence on stability
What are the 2 intra-articular ligaments of the knee?
Anterior and posterior cruciate ligaments
What are the 2 extra-articular ligaments of the knee?
The fibular and tibial collateral ligaments
Are the cruciate ligaments inside or outside of the joint capsule?
Inside
How do the cruciate ligaments relate to eachother?
Cross eachother obliquely in the centre of the knee
What are the attachments of the posterior cruciate ligament?
From the posterior intercondylar region of the tibia, travels supero-anteriorly to insert onto the medial femoral condyle
What are the attachments of the anterior cruciate ligament?
From the anterior intercondylar region of the tibia, travels supero-posteriorly to insert onto the lateral femoral condyle
Which of the cruciates is stronger?
The posterior cruciate ligament
What are the 3 functions of the posterior cruciate ligament?
1) Prevents posterior displacement of the tibia on the femur
2) Prevents hyperflexion
3) Main stabiliser of the flexed knee when weight bearing eg. walking down a hill
What are the 2 functions of the anterior cruciate ligament?
1) Prevents anterior displacement of the tibia on the femur
2) Prevents hyperextension
When does PCL injury occur?
When landing on the tibial tuberosity with the knee flexed
When does ACL injury occur?
When the knee is hyperextended of force is applied anteriorly
What is the nature of the tibial (medial) collateral ligament and what is its function?
Flat band attached to the medial meniscus
Prevents abduction of the leg at the knee
What is the nature of the fibular (lateral) collateral ligament and what is its function?
Cord like band which is NOT attached to the lateral meniscus
Prevents adduction of the leg at the knee
What 3 things occur in a combined knee injury (the unhappy triad)?
1) Torn medial collateral ligament
2) Torn medial meniscus
3) Torn anterior cruciate ligament
What causes a combined knee injury?
Excessive lateral twisting of the flexed knee or blow to the lateral side of an extended knee - common when flexed knees are twisted
What is the sequence of events in a combined knee injury?
1) Tibial (medial) collateral ligament is torn
2) Which leads to a tear in the medial meniscus
3) ACL then also tears as it is very taught - under alot of tension - in flexion
Which 5 muscles (or muscle groups) are the main stabilisers of the knee?
1) Quadriceps
2) Hamstrings (posterior thigh)
3) Sartorius
4) Gracilis
5) Iliotibial tract
What is the mainstay of treatment in ligament injuries which cannot be repaired?
Building up of the quads through physio/exercise can compensate for the ligament damage and avoid surgery
What are the bursae of the knee?
Fluid filled pouches in and around the knee
What are the 2 most important bursae of the knee in terms of developing bursitis?
1) Suprapatellar bursa - above the patella
2) Prepatellar bursa - infront of the patella
When does bursitis commonly occur?
In people who spend alot of time on their knees
What are the 3 types of fracture that can occur to the knee?
Fractures of the patella, tibia or distal femur
Can be traumatic, insufficiency fractures (in osteoporotic bone) or peri-prosthetic (near a knee replacement)
In which direction does patellar dislocation almost always occur?
Laterally
Why does patellar dislocation almost always occur laterally?
Because of the direction in which the muscles pull
Rectus femoris, vastus intermedius and vastus lateralis all pull superolaterally
This is counteracted by the more horizontal pull of vastus medialis, but sometimes this is overcome
Why is dislocation of the patellar more common in females?
because of the alignment of the femur and tibia
The Q angle is larger in females due to wider pelvis
Large Q angle + strong quad contraction leads to dislocation
What is the Q angle?
The knee is positioned under the hip - this returns the center of gravity to the midline and distributes weight evenly across the knee. This is achieved by the obliquity of the femur
The angle between the femur on the tibia from vertical is the Q angle
What does abnormal alignment of the tibia result in?
Osteoarthritis
What is genu varum, what condition does this lead to and why?
Genu varum = bow leg
Condition of disalignment of the tibia which is adducted with respect to the femur
Leads to more weight bearing on medial tibial condyle - osteoarthritis in medial part of knee
What is genu valgum, what condition does this lead to and why?
Genu valgum = knock knee
Conditions of disalignment of the tibia which is abducted with respect to the femur
Leads to more weight bearing on the lateral tibial condyle - osteoarthritis in lateral part of knee
What are the 3 main changes in osteoarthritis of the knee?
1) Reduced joint space - little menisci or cartilage there, bone on bone which is very painful
2) Osteophyte formation - bone spur which form when the bone is damaged and tries to remodel itself but does so abnormally
3) Sclerosis of bone - abnormal density of bone also to do with remodelling and repair of damaged bone
Development of OS is normal with aging but what 2 things could lead to early development of OA?
1) Meniscal tear
2) Obesity - excessive pressure on joint
What is it important not to confuse a patellar fracture with, how could you differentiate?
Anatomical quirk which is a bipartite patellar (normally in 2 pieces)
Bipartite patellar would be in 2 smooth pieces, patellar fracture broken edges are jagged
What occurs in a dislocation of the knee?
Distal end of femur moves posteriorly with respect to the proximal tibia
What is the biggest concern in a dislocation of the knee?
Damage to the blood supply and nerves
Check blood supply by feeling for distal pulses
Why is normal alignment of the knee crucial?
For even distribution of weight across the joint
What commonly happens to the knee joint with a meniscal tear?
Locking of the knee joint
