session 3 Flashcards
The knee joint The anterior and medial thigh
Describe normal ‘locking and unlocking’ of the knee
In the erect position, when the knee is fully extended, internal (medial) rotation of the femur on the tibia leads to locking of the knee joint.
What is the mechanical advantage of locking the knee in the extended position?
In the locked position, the thigh and leg muscles can relax without making the knee joint unstable.
Which muscle assists unlocking of the knee?
Contraction of the popliteus muscle which rotates the femur externally (laterally) on the tibia so that flexion of the knee can take place.
Describe the anatomy and composition of the menisci of the knee joint
- fibrocartilaginous structures in the knee joint.
- crescentic (C-shaped) and thicker peripherally than centrally
- attach at both ends to the intercondylar area of the tibia.
- medial meniscus is attached peripherally to the medial (tibial) collateral ligament and the joint capsule.
What is the role of menisci?
- deepen the articular surface of the tibia, increasing the stability of the joint.
- act as shock absorbers by increasing surface area to further dissipate forces.
What is the physical difference between the lateral and medial menisci?
The lateral meniscus is smaller than the medical meniscus and is not attached to the lateral (fibular) collateral ligament, rendering it fairly mobile.
What connects the menisci anteriorly?
The menisci are connected to each other anteriorly by the transverse ligament of the knee.
What does the posterior meniscofemoral ligament do?
helps stabilise the posterior horn of the lateral meniscus by attaching it to the medial femoral condyle.
Describe the vascular supply to the menisci
The blood supply to the menisci is from the periphery and they are relatively avascular centrally.
Which meniscus is most commonly torn and why
- medial meniscus
- firmly adherent to the medial (tibial) collateral ligament.
Although the medial collateral ligament is broad, it is weaker than the lateral (fibular) collateral ligament Excessive lateral displacement of the tibia may cause the medial collateral ligament to tear, and this often results in tearing of the medial meniscus.
Define the ‘unhappy triad’ injury
refers to tears to the medial collateral ligament, medial meniscus and anterior cruciate ligament.
Why do meniscal tears often heal poorly?
- blood supply to the meniscus is from the periphery
- blood flow decreases with age and the central meniscus is avascular by adulthood, leading to impaired healing after trauma.
why might a ‘locked’ knee be the presenting sign of a torn meniscus?
A torn meniscus may result in a fragment becoming dislodged and trapped within the knee joint cavity causing the knee to become ‘locked’.
Describe ‘Housemaid’s knee’
inflammation of the pre-patellar bursa
- the bursa becomes distended with fluid and forms a swelling anterior to the knee.
- Pre- patellar bursitis usually results from friction caused by excessive rubbing of the skin against the patella e.g. whilst leaning forward in the kneeling position to scrub the floor.
Describe ‘Clergyman’s knee’
inflammation of the subcutaneous/superficial infrapatellar bursa
- the bursa becomes distended with fluid because of microtrauma caused by extensive kneeling in the upright position. It is most commonly described in clergymen and plumbers.
What structures does the femoral sheath enclose?
- Femoral artery
- femoral vein
- femoral canal (with associated lymph
nodes)
-> but not the femoral nerve
What is the function of the femoral Canal?
The canal only contains a couple of lymph nodes. It acts as a “dead space” to allow for the distension of the femoral vein, particularly during heavy exercise, to accommodate venous return from the limb.
Describe the surface anatomy of the femoral vein
The femoral vein lies within the femoral triangle, medial to the femoral artery.
The femoral artery enters the thigh by passing underneath the inguinal ligament at the mid-inguinal point (midway between the pubic symphysis and anterior superior iliac spine) and the pulsation can usually be palpated.
The femoral vein is situated immediately medial to the arterial pulsation.
Which muscles form the quadriceps femoris?
Rectus femoris, vastus lateralis, vastus intermedius, vastus lateralis.
What are the actions of the quadriceps femoris?
The quadriceps extend the knee and are some of the important stabilisers of the knee joint. As the rectus femoris originates proximal to the hip joint, it also assists iliopsoas in flexion of the hip.
In a patient with a traumatic division of the femoral nerve at the level of the inguinal ligament (e.g. a stab wound), why would sensation be preserved over the lateral thigh?
The lateral side of the thigh is supplied by the lateral cutaneous nerve of the thigh (lateral femoral cutaneous nerve) which is a direct branch from the lumbar plexus.
The distal segment of vastus medialis, the vastus medialis obliquus (VMO) sends some fibres horizontally to insert onto the patella. What is the function of these fibres?
During movements of the knee, there is a tendency for the patella to become displaced laterally (due to the angle between the line of pull of quadriceps femoris and the line of insertion of the patellar ligament). In order to prevent this, the horizontal fibres of vastus medialis contract to pull the patella back into line.
