Knee Biomechanics Flashcards
What are the biomechanic functions of the knee joint?
i) gait
ii) stair climbing
What is a Q angle? What is the normative value?
The angle between the ASIS, patella and tibial tuberosity (aka quads line of pull). Normative is 15’ (13’-18’) with females > males.
What knee injury is predisposed by a large Q angle?
ACL tear.
What are the functions of the menisci in the knee?
i) absorb shock
ii) lubricate joint
iii) provide stability
iv) prevent capsule from entering joint space
How do the menisci move relative to knee joint osteokinematic movement?
They move anteriorly with extension and posteriorly with flexion.
Name three differences between the medial and lateral menisci.
i) medial meniscus is larger
ii) medial meniscus is C shaped, lateral meniscus is O shaped
iii) medial meniscus attaches to deep fibres of MCL, lateral meniscus projects posterior meniscofemoral ligament to PCL.
What is the general purpose of the cruciate ligaments?
Prevent multidirectional instability in both flexion and extension.
What is the “terrible triad” of the knee?
Simultaneous injury to the ACL, MCL and medial meniscus. These structures are closely attach and resist valgus force therefore are often injured together.
What might be expected is a patient has more global than local knee pain?
i) more likely OA
ii) more likely higher level of functional disability
What is the type of joint of the knee? (all categories)
i) synovial
ii) modified hinge
iii) modified ovoid - bicondylar
iv) complex
v) compound
What is the resting position of the knee?
Approx. 30’ of flexion. Neutral rotation.
What is the close packed position of the knee?
Full extension with tibial ER.
What is the capsular pattern of the knee joint?
Flex > Ext.
What are the normal end feels of the knee joint?
i) flexion - soft tissue approximation
ii) extension - capsular tissue stretch
iii) IR/ER - capsular tissue stretch
What are the osteokinematic movements of the knee joint and their normative ROM values?
i) flexion (135’)
ii) extension (5’-15’)
iii) tibial IR (20’)
iv) tibial ER (30’-40’).
What position of the knee maximizes tibial rotation?
Flexion.
Describe the planar and axial movement of knee flexion/extension.
i) sagittal plane
ii) coronal axis
What is conjunct rotation at end range knee position?
In max flexion, the tibia passively internally rotates. In extension, the tibia passively externally rotates. These movements are mechanically coupled and cannot be performed independently.
What causes conjunct tibial rotation of the knee at end range?
i) larger medial femoral condyle
ii) passive tension from the ACL
iii) lateral pull of the quads
Describe the arthrokinematics of knee flexion.
Posterior roll, posterior glide.
Describe the arthrokinematics of knee extension.
Anterior roll, anterior glide.
Describe the arthrokinematics of tibial internal rotation.
Spin.
Describe the arthrokinematics of tibial external rotation.
Spin.
Which passive structures limit knee extension?
i) ACL
ii) posterior joint capsule
iii) MCL (posterior bands)
iv) LCL
v) popliteal ligament
What is the type of joint of the patellofemoral joint? (all categories)
i) synovial
ii) plane
iii) compound
iv) modified sellar
Describe the osteokinematic movements of the patello femoral joint.
Apparently 1 DOF (?). Inferior glide with flexion (2X its length) and superior glide with extension. These are associated with M/L tilting and M/L rotation.
Which direction does the patella track on extension and why?
Superior and lateral. This is due to pull of quadriceps - the lateral tracking is due to pull of vastus lateralis via lateral patellar retinaculum.
In which direction is the base of the patella displaced with IR and ER of the tibia?
i) IR - lateral
ii) ER - medial
Describe which facet articulates with the femur at which angle of knee flexion.
i) inferior facet - 20’
ii) lateral facet - 45’
iii) medial facet - 60’
iv) superior facet - 90’
v) odd facet - 135’
Describe the arthrokinematics of a superior patellar pull.
Superior glide.
Describe the kinematics of an inferior patellar pull.
Inferior glide.
What is the resting position of the patellofemoral joint?
Knee flexed 25’.
What is the close packed position of the patellofemoral joint?
Unknown (not likely knee extension).
What is the capsular pattern of the patellofemoral joint?
Flex > ext.
What is the normal end feel of the patellofemoral joint?
Tissue stretch - ligamentous.
How might patients with knee medial compartment steoarthritis compensate to avoid pain? What type of strategy is this?
Lateral co-contraction to resist adductor moment and prevent condylar lift off that would load the medial compartment. This is directed co-contraction (rather than general). This also increases muscle activity about the joint and adds to stability.
