Knee Flashcards
Briefly describe the knee joint
- The largest synovial joint in the body
- Modified hinge joint
- Composed of two condylar joints between the femur and tibia and one saddle joint between the femur and patella.
- Allows flexion, extension, and limited rotation in flexion. ^[also some varus and valgus action, rotation – these actions are controlled by the ACL]
List the muscles responsible for flexion and extension at the knee
FLEXION
- Primary movers are the hamstrings – semimembranosus, semitendinosus (medial), and biceps femoris (lateral)
- Lesser flexors – gracilus, sartorius, popliteus, gastrocnemius, and plantaris
EXTENSION
- Primary mover – quadriceps femoris
Note that there is a complex rotation mechanism with flexion and extension
Describe the joints and joint surfaces
- Two distal joint surfaces – anterior patello-femoral, inferior tibio-femoral ^[note that there is no direct contact between fibia and femur]
-
Patello-femoral – femur
- Patellar groove or trochlea
- Distally the groove becomes the intercondylar notch
- Saddle shaped, asymmetrical
- Lateral face larger and more convex than the medial face
- Lined with articular cartilage
-
Tibio-femoral – femur
- Flattened anteriorly, curved posteriorly
- Two condyles separated by a deep U-shaped notch, the intercondylar fossa
- Two articular surfaces- medial and lateral
- Two surfaces arch up towards each other and are separated by two bony spines – intercondylar eminence.
- Covered by articular cartilage 3-4cm thick.
- Vaguely triangular with a rounded base and sharper but still rounded inferior point.
- The “extensor mechanism” – quadriceps - quadriceps tendon – patella –patella tendon – tibial tuberosity. ^[i.e. patella sites within quadriceps tendon] ^[note also that patella tendon may be interchanged with patellar ligament]
- Posterior surface is wedge shaped with three facets.
- Lateral facet is longer
- Median ridge orientated in the long axis separates the medial and lateral facets
- “Odd” facet – along the medial border of patella
- Thick articular cartilage: 6-7x the weight of the body is applied on patella during 90 degrees squat, so it protects against stress on patella
- Glides in the trochlea of the femur
List the stabilisers of the patella and briefly describe their function
Keeps patella within groove and prevents wear and tear and associated pain
- Superior – quadriceps tendon
- Inferior – patellar tendon
- Medial – medial retinaculum, vastus medialis
- Lateral – lateral retinaculum, vastus lateralis, ilio-tibial tract
Describe the ACL, its function and associated clinical problems
- Prevents anterior translation of the tibia on a fixed femur
- FFAATT
- Controls rotation
- From the area between the posterior ends of the menisci
- Passes forwards, medially, and upwards
-
To antero-lateral surface of medial condyle of the femur
Note mechanism of ACL injury: non-contact injuries e.g. landings. Recurrent collapses of the knee increase the risk of osteoarthritis.
Describe the PCL, its function and associated clinical problems
- Prevents posterior translation of the tibia on a fixed femur
- Increases stability in knee extension
Describe the MCL and LCL
Medial collateral
- Superficial and capsular ligaments
- Superficial – from the medial femoral epicondyle to the medial tibia just below the level of the articular cartilage
- Wide thinner ligament, difficult to palpate
- Damaged by valgus stress
Lateral collateral
- Firm, round, distinct band - difficult to rupture
- From lateral epicondyle of the femur to head of the fibula
- Injured in varus stress
Describe the menisci
- semilunar Cartilages
- Medial and lateral
- Crescentic pieces of fibrocartilage
- Lateral meniscus is a fuller crescent
- Attached to the periphery of the articular surfaces of the lateral and medial tibial condyles by the adjacent deep parts of the capsule – the coronary ligaments.
- Thick at the periphery, thin inner edges (wedge in cross-section)
- Upper femoral surface is concave
- Lower tibial surface is flat
- Improve congruence of joint surfaces
- Guide movement
-
Shock absorption
Mechanism of injury to menisci: semi-flexed, weight-bearing, and twist
Describe the two big bursae at the anterior knee joint
SUPRAPATELLAR
- Lies above the patella
- Extends for 5-7cm
- Communicates with knee joint – site for effusion
PREPATELLAR
-
In front of the patella
Affects work on knees.
An infection of the prepatellar bursae involves hospitalisation and a strong course of antibiotics.
Describe the popliteal bursae and associated clinical issues
Sits in popliteal fossa behind knee
Baker’s cyst
can be confused with an aneurysm
Describe the blood supply to the knee
- From the popliteal artery
- Five geniculate branches – middle, and medial and lateral superior and inferior geniculate arteries
- Superiors curve around the femoral condyles proximal to the epicondyles
- Inferiors course around the margins of the tibial plateau, passing under the collateral ligaments
- Anastomoses around the knee joint
- Middle and inferior arteries supply the menisci, the outer ¼ of which are vascular.
Describe the nerve supply of the knee
-
Three sources
- Sciatic nerve – branches from tibial and common peroneal nerves
- Femoral nerves – branches travelling via the vastus muscles
-
Obturator nerve – small nerve from posterior division, accompanies femoral artery to popliteal fossa ^[relevant in paeds: knee looks fine]
- May explain referral of hip pain to the knee
Describe the quadriceps
- Rectus femoris – anterior inferior iliac spine
- Vastus lateralis – proximal part of intertrochanteric line, anterior greater trochanter, proximal half lateral aspect of linea aspera.
- Vastus intermedius – anterior and lateral surfaces of proximal 2/3 of the body of the femur, distal ½ linea aspera.
- Vastus medialis – distal ½ intertrochanteric line, medial lip of linea aspera, tendons of adductor longus and adductor magnus, and medial intermuscular septum.
- Insertion – proximal border of the patella and via the patellar tendon to the tuberosity of the tibia.
- Action – extension of the knee, rectus femoris section also flexes the hip.
- Nerve supply – femoral nerve (L2,3,4)
Describe hamstrings
- Biceps femoris – long head – ischial tuberosity, short head – linea aspera and lateral supracondylar line of the femur.
- Semitendinosus – ischial tuberosity
-
Semimembranosus – ischial tuberosity
Note: sufficient to say origin = ischial tuberosity -
Insertion
- Biceps femoris – head of fibula and lateral condyle of tibia
- Semitendinosus – upper part of medial surface of the shaft of the tibia
- Semimembranosus – posterior part of the medial condyle of the tibia
- Action – flexion of the knee, extension of the hip (except short head of biceps femoris)
- Nerve supply – sciatic nerve (L5,S1,2)
Describe gastrocnemius
- Origin – ‘posterior surface of distal femur’: two heads from just superior to medial and lateral condyles of the femur
- Insertion – via the Achilles tendon to the posterior surface of the calcaneus
- Action – plantar flexion of the foot, flexion of the knee
- Nerve supply – tibial nerve (S1,2)
