thigh & knee region Flashcards
Describe the frontal plane alignment of the lower limb using mechanical axes.
Described by the hip-knee-ankle (HKA) angle, which is the angle formed by the intersection of femoral mechanical axis and the tibial mechanical axis. HKA angle average slightly <180 degrees, described as a varus alignment of approx. 1 degree (+/-2 degrees).
Femoral mechanical axis (FM): line from centre of femoral head to centre of intercondylar notch
Tibial mechanical axis (TM): line from centre of proximal tibia to centre of tibial plafond / ankle joint
What are the implications of having a varus knee alignment using mechanical axis?
A varus alignment means the centre of the knee is lateral to the load-bearing axis which means vertical ground reaction forces cross the knee medially causing an adduction moment. This causes increased compression and load in the medial compartment of the knee.
What are the implications of having valgus knee alignment using mechanical axis?
In valgus alignment, the centre of the knee is located medially to load-bearing axis (ground reaction force ascends lateral to centre of the knee). This causes an abduction moment, with increased load and stress on the lateral compartment of the knee.
Describe frontal plane alignment of the lower limb using anatomical axis.
The frontal plane alignment using anatomical axis is found through the angle formed between the shaft of the femur and the shaft of the tibia. Tibia is lateral relative to the femur therefore making a valgus alignment (normal is approx. 5 degrees genu valgus)
What are the 3 joints of the knee?
Tibiofemoral joint and patellofemoral joint (enclosed by the knee joint capsule)
Superior tibiofibular joint (separate to the ‘knee joint’)
What are the articulations and classification of the tibiofemoral joint?
The tibiofemoral joint is a bicondylar (predominantly uniaxial) joint between the femoral condyles and the tibial plateau. It mainly performs flexion-extension in the sagittal plane (around ~coronal axis through posterior femoral condyles)
What is the screw-home mechanism?
The screw home mechanism describes the medial rotation of the femur on the tibia during full extension of the lower limb in weight bearing. The screw home mechanism occurs due to the longer articular surface on the medial epicondyle
What mechanisms cause tibial rotation?
Screw-home mechanism, popliteus (lateral rotation of femur on tibia to unlock knee and allow flexion), movements of the foot (i.e., pronation of the midfoot) due to movement of talus causing tibial movement
What factors of the knee joint promote stability in anatomical position?
- Screw-home mechanism: medial roation when extending leg promotes locking of the joint and contributes to stability in full extension (needs popliteus muscle to flex knee)
- Centre of gravity falls anterior to the axis of the tibiofemoral joint which creates an extension moment and thus keeps us in extension
- Shape of femoral condyles: flat femoral condyles articulating with flat tibia surfaces promote stability when compressive vertical (weight-bearing forces) forces are applied = stable orientation of joint surfaces)
when in flexion = less stable, due to round portion of epicondyles articulating with flat tibial surface
What is the purpose of the menisci?
Increase congruency and contact area between the femoral condyles (round) and tibial plateau (flat). This decreases stress, protects articular cartilage and stabilises the joint
what are the differences between the medial and lateral menisci?
Medial menisci is longer in the anterior-posterior direction, having a larger posterior horn and also capsular attachment. This makes it less mobile than the lateral menisci. Therefore the lateral menisci is more mobile and variable (more C shaped)
Which meniscis provides greater coverage of its plateau? and what are the consequences of this?
The Lateral menisci provides greater coverage of its plateau. Medial menisci is larger but the medial epincondyles and medial compartment of knee is also larger therefore the medial menisci does not provide as much coverage. Considering weight bearing force travelling down medial compartment - osteoarthritis is more commonly seen on medial compartment
What are the tibiofemoral ligaments and what forces do they resist?
- Tibial collateral - resists valgus
- fibular collateral - resists varus
- anterolateral - resists tibial IR <35 degrees flexion (provides anterolateral stability)
- anterior cruciate - resists anterior translation of tibia on femur and posterior translation of femur on tibia, valgus force (rotational stability)
- posterior cruciate - resists posterior translation of tibia on femur (femur moving forward on tibia)
- oblique popliteal
(iliotibial band) although not a ligament
Describe the functional fibre bundles of the anterior cruciate ligament.
The Posterolateral band (PLB) is the largest and will be tight during extension, contributing to knee stability). The Anteromedial band (AMB), tightens during flexion
Describe the mechanisms of ACL injuries.
Often non-contact during the weight loading phase (“knee in-toe out”), creates a valgus moment + tibial IR/ER which causes rupture of ACL
- most commonly occurs in pivoting sports and females
