Download TSM97 - The Knee Joint

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Describe the functional anatomy of the knee joint
The knee joint is the site of articulation between the distal femur, proximal tibia and the patella
o Synovial hinge joint between the two long bones
o Two articulations between the femur and tibia; one between the femur and patella
The distal femur does not articulate directly with the lateral leg bone the fibula (compare to elbow)
o Posteriorly the linea aspera divides into the medial and lateral supracondylar lines
o Also protruding posteriorly are the medial and lateral condyles and intercondylar fossa
o Anteriorly the medial and lateral epicondyles are divided by the patellar surface
o Just above the medial epicondyle is the adductor tubercle where adductor magnus attaches
The proximal tibia has a small supero-lateral articular facet posteriorly for the fibular head
o Superiorly the medial and lateral condyles have two broad flat articular surfaces (plateaux)
o Also superiorly the intercondylar eminence is elevated with two intercondylar tubercles
o Anteriorly the tibial tuberosity protrudes centrally just below the condyles
o Posteriorly the soleal line descends and crosses medially from the superior tibio-fibular joint
The patella is the largest sesamoid bone (‘intra-tendinous’) in the body within quadriceps femoris
o Roughly triangular with its apex facing inferiorly for attachment to the patellar ligament
o Broad base superiorly for attachment of the quadriceps femoris tendon
o Posterior surface has medial and lateral facets that articulate with patellar surface of femur
A fibrous capsule extends around the articular margins of the femoral and tibial condyles
o Covers the posterior and lateral regions of the joint but is replaced by the patella anteriorly
o Extracapsular medial and lateral collateral ligaments limit lateral displacement on either side
 Medial collateral ligament is continuous with the capsule
 Lateral collateral ligament joins to the fibula
o Intracapsular anterior and posterior cruciate ligaments limit antero-posterior displacement
 Arise from the tibia (area of origin determines name) and cross over
 Insert onto the lateral and medial femoral condyles respectively
 Anterior ligament is tensed in extension; posterior is tensed in flexion
 Posterior ligament is much thicker and stronger
The femoral condyles are rounded whereas they articulate with the flat superior facets of the tibia
o Normal articular (hyaline) cartilage covers the facets on the tibial plateaux
o Lateral and medial fibro-cartilaginous interarticular rings called menisci also line the facets
 Wedge-shaped – broader at the edges; thinner but more firmly attached centrally
 Mostly avascular so do not repair well – complete excision prompts regeneration
 Medial meniscus is continuous with the capsule and hence prone to rupture
Explain the anatomical basis of injuries to the collateral ligaments, cruciate ligaments and the menisci of the knee
The knee joint is adapted for weight-bearing and stability but is essentially not a very strong joint
The associated ligaments and muscles are mostly responsible for strengthening the joint
The collateral ligaments can be damaged in lateral displacement at the knee joint
o Blow to the lateral knee can rupture the medial collateral ligament, capsule and meniscus
o Tearing of the lateral collateral ligament can cause damage to the common peroneal nerve
 Supplies the dorsiflexors of the foot – damage results in ‘foot drop’
The cruciate ligaments can be damaged in antero-posterior displacement at the knee joint
o Injury to the extended knee can easily damage the anterior cruciate as it will be tensed
o Injury to the flexed knee can similarly damage the posterior cruciate
Demonstrate the range of normal movements of the knee joint
The majority of movement at the knee is flexion facilitated by the hamstrings
o Normal range of knee flexion is up to 150˚
o Limited by posterior thigh
Small amount of hyperextension possible up to 10˚ facilitated by quadriceps femoris
During extension of the knee to a ‘locked’ stable position (i.e. standing) the femur laterally rotates
o Passive rotation of about 5˚ – a normal physiological mechanism
o In unlocking of the knee the femur is actively medially rotated by the popliteus muscle
 Arises from the lateral femoral condyle within the fibrous capsule then pierces it
 Inserts on the postero-medial surface of the proximal tibia (crosses the midline)
Describe the tests for instability of the knee joint
The Q-angle can be measured as the angle between the two imaginary lines:
o From ASIS through the middle of the patella (roughly along the angle of the femur – oblique)
o From the tibial tuberosity through the middle of the patella (vertical)
This angle is around 14˚ in males and 17˚ in females
o Reduced values indicate genu varum (varus – twisting towards midline) – ‘bow-legged’
o Elevated values indicate genu valgum (valgus – twisting away from midline) – ‘knock-knee’)