Knee Biomechanics

Question 1

What are the biomechanic functions of the knee joint?

Answer 1

i) gait

ii) stair climbing

Question 2

What is a Q angle? What is the normative value?

Answer 2

The angle between the ASIS, patella and tibial tuberosity (aka quads line of pull). Normative is 15’ (13’-18’) with females > males.

Question 3

What knee injury is predisposed by a large Q angle?

Answer 3

ACL tear.

Question 4

What are the functions of the menisci in the knee?

Answer 4

i) absorb shock
ii) lubricate joint
iii) provide stability
iv) prevent capsule from entering joint space

Question 5

How do the menisci move relative to knee joint osteokinematic movement?

Answer 5

They move anteriorly with extension and posteriorly with flexion.

Question 6

Name three differences between the medial and lateral menisci.

Answer 6

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.

Question 7

What is the general purpose of the cruciate ligaments?

Answer 7

Prevent multidirectional instability in both flexion and extension.

Question 8

What is the “terrible triad” of the knee?

Answer 8

Simultaneous injury to the ACL, MCL and medial meniscus. These structures are closely attach and resist valgus force therefore are often injured together.

Question 9

What might be expected is a patient has more global than local knee pain?

Answer 9

i) more likely OA

ii) more likely higher level of functional disability

Question 10

What is the type of joint of the knee? (all categories)

Answer 10

i) synovial
ii) modified hinge
iii) modified ovoid - bicondylar
iv) complex
v) compound

Question 11

What is the resting position of the knee?

Answer 11

Approx. 30’ of flexion. Neutral rotation.

Question 12

What is the close packed position of the knee?

Answer 12

Full extension with tibial ER.

Question 13

What is the capsular pattern of the knee joint?

Answer 13

Flex > Ext.

Question 14

What are the normal end feels of the knee joint?

Answer 14

i) flexion - soft tissue approximation
ii) extension - capsular tissue stretch
iii) IR/ER - capsular tissue stretch

Question 15

What are the osteokinematic movements of the knee joint and their normative ROM values?

Answer 15

i) flexion (135’)
ii) extension (5’-15’)
iii) tibial IR (20’)
iv) tibial ER (30’-40’).

Question 16

What position of the knee maximizes tibial rotation?

Answer 16

Flexion.

Question 17

Describe the planar and axial movement of knee flexion/extension.

Answer 17

i) sagittal plane

ii) coronal axis

Question 18

What is conjunct rotation at end range knee position?

Answer 18

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.

Question 19

What causes conjunct tibial rotation of the knee at end range?

Answer 19

i) larger medial femoral condyle
ii) passive tension from the ACL
iii) lateral pull of the quads

Question 20

Describe the arthrokinematics of knee flexion.

Answer 20

Posterior roll, posterior glide.

Question 21

Describe the arthrokinematics of knee extension.

Answer 21

Anterior roll, anterior glide.

Question 22

Describe the arthrokinematics of tibial internal rotation.

Answer 22

Spin.

Question 23

Describe the arthrokinematics of tibial external rotation.

Answer 23

Spin.

Question 24

Which passive structures limit knee extension?

Answer 24

i) ACL
ii) posterior joint capsule
iii) MCL (posterior bands)
iv) LCL
v) popliteal ligament

Question 25

What is the type of joint of the patellofemoral joint? (all categories)

Answer 25

i) synovial ii) plane iii) compound iv) modified sellar

Question 26

Describe the osteokinematic movements of the patello femoral joint.

Answer 26

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.

Question 27

Which direction does the patella track on extension and why?

Answer 27

Superior and lateral. This is due to pull of quadriceps - the lateral tracking is due to pull of vastus lateralis via lateral patellar retinaculum.

Question 28

In which direction is the base of the patella displaced with IR and ER of the tibia?

Answer 28

i) IR - lateral | ii) ER - medial

Question 29

Describe which facet articulates with the femur at which angle of knee flexion.

Answer 29

i) inferior facet - 20' ii) lateral facet - 45' iii) medial facet - 60' iv) superior facet - 90' v) odd facet - 135'

Question 30

Describe the arthrokinematics of a superior patellar pull.

Answer 30

Superior glide.

Question 31

Describe the kinematics of an inferior patellar pull.

Answer 31

Inferior glide.

Question 32

What is the resting position of the patellofemoral joint?

Answer 32

Knee flexed 25'.

Question 33

What is the close packed position of the patellofemoral joint?

Answer 33

Unknown (not likely knee extension).

Question 34

What is the capsular pattern of the patellofemoral joint?

Answer 34

Flex > ext.

Question 35

What is the normal end feel of the patellofemoral joint?

Answer 35

Tissue stretch - ligamentous.

Question 36

How might patients with knee medial compartment steoarthritis compensate to avoid pain? What type of strategy is this?

Answer 36

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.