Week 9: knee

Question 1

WEEK 8: Joints

Answer 1

 The knee complex consists of 3 articulations:
Tibiofemoral joint
- Between the large femoral condyles and the smaller and
nearly flat tibial plateaus

Patellofemoral joint
- Between the patella and the trochlear notch of the femur
(gliding joint)

Proximal tibiofibular joint
- Between the head of the fibula and the posterolateral and
inferior aspect of the tibial condyle

Question 2

Tibiofemoral joint – factor 1

Answer 2

 Differences between the size of the medial and
lateral femoral condyles
 The lateral femoral condyle has a shorter
straight articular surface while the medial
femoral condyle has a larger curved
articular surface
 Pure flexion-extension fails to use the
entire articular surface of the medial
femoral condyle so additional movements
in the transverse (in particular) and frontal
planes are necessary

Question 3

Tibiofemoral motion in flexion-extension

Answer 3

 During FLEXION the tibia
INTERNALLY ROTATES in
relation to the femur
 During EXTENSION the tibia
EXTERNALLY ROTATES in
relation to the femur
 Differences in the size and
shape of the articular
surfaces account for the
internal-external rotation

Question 4

Screw home mechanism

Answer 4

 As the knee moves towards full extension,
external rotation of the tibia is required
 Full extension increases joint congruence (close
packed position), promoting stability and allows
the overall contact area to be maximised
(reducing stress)

Question 5

Screw home mechanism (2)

Answer 5

Speculation about cause
 To accommodate the larger curved
surface of the medial femoral condyle
 Passive tension in both the ACL and
PCL
 Slight lateral pull of the quadriceps
muscle group
 Iliotibial band (ITB)?

Question 6

Screw home mechanism (3)

Answer 6

A similar but less obvious mechanism occurs
during femoral on tibial extension
When a person rises up from a squat position the
knee locks into extension as the femur internally
rotates relative to the fixed tibia

From full extension the knee must internally
rotate as flexion is initiated
 This is driven primarily by the popliteus muscle

Question 7

Tibiofemoral joint - factor 2

Answer 7

 Differences between the size of the femoral and
tibial articular surfaces
 The femoral articular surfaces are
larger than the tibial articular surfaces
 For pure rolling to occur at a joint the
articular surfaces must be equal in
size
 The articular surfaces on the medial
aspect have reasonable congruence
but the articular surfaces on the lateral
aspect do not
*roll & glide
- tibial on femoral extension
- femoral on tibial extension

Question 8

Tibiofemoral joint - factor 3

Answer 8

 Variation in the curvature from anterior to
posterior in all of the articular surfaces
 There will be differences in the relative amount of roll
and glide depending on joint position (i.e. which part of
the articular surfaces are actually in contact)

Question 9

Menisci

Answer 9

 Lateral meniscus is almost a
complete circle whereas the
medial meniscus is a half circle
(crescent shaped)
 Lateral meniscus is smaller but
covers a larger area of its tibial
plateau
 The menisci are bound to the tibia by ligaments
and are further reinforced via muscle attachments

Question 10

Menisci (2)

Answer 10

 Viewed in the frontal plane each
meniscus is wedge shaped,
thicker at its periphery, and this
creates a concave surface for
the femoral condyles
 The primary function of the
menisci is to increase the contact
area between the femur and
tibia, thereby reducing the
compression stress on the
articular cartilage

Question 11

Menisci (3)

Answer 11

 The menisci move in concert
with the rolling femoral condyles
 As the menisci remain attached
at their poles as they slide
anteriorly and posteriorly on the
tibia, they undergo considerable
distortion in shape

Question 12

Menisci (4)

Answer 12

 The menisci are susceptible to tears because:
-Large compression forces are experienced
-The gliding and rotatory motion between the femur
and tibia create large shear forces
-The twisting motion of the tibia and femur cause large
deformations
 The periphery of the menisci has a blood supply
but the thin inner portion does not. This has a
bearing on whether healing can occur

Question 13

Patella

Answer 13

 Large triangular sesamoid
bone embedded in the
tendon of the quadriceps
 Its apex points distally
 The posterior articulating
surface is covered in the
thickest articular cartilage
found in any joint

Question 14

Patella (2)

Answer 14

 Although the patella
protects the quadriceps
tendon from excessive
friction from the femur
during knee flexion, its
primary function is to
increase the length of the
moment arm for the
quadriceps tendon
 Moment arm is largest
between ≈ 20-60° flexion

Question 15

Movement of the patella

Answer 15

The area of articular contact increases with knee flexion, reaching a maximum
between 60-90° flexion

Question 16

Patella position

Answer 16

 As the patella moves it should remain equidistant
between the medial and lateral epicondyles
 Excessive deviation medially, or more commonly
laterally, is known as medial or lateral tracking

Question 17

Patella position (2)

Answer 17

 Rectus femoris & vastus intermedius
are centrally located and have a line
of action along the length of the femur
 The line of action of vastus lateralis is
slightly lateral to the femur
 As the femur deviates laterally from
the tibia contraction of the these
muscles pulls the patella proximally
and laterally
- The Q angle is generally between 10-20°
(10-15° in males and 15-20° in females)

Question 18

Systems to prevent lateral deviation (1)

Answer 18

 The surface of the
lateral femoral condyle
extends further
anteriorly and acts as
a buttress against the
lateral displacement of
the patella
- A lateral condyle with a large buttress
helps to deepen the groove (trochlea)
- A deep ‘hull’ on the posterior surface of
the patella also helps to keep the patella
in the groove

Question 19

Systems to prevent lateral deviation (2)

Answer 19

 A medially directed
stabilising force
provided by the
oblique fibres of
vastus medialis
- Unfortunately the VMO is the
first portion of muscle to be
inhibited with swelling or pain

Question 20

Systems to prevent lateral deviation (3)

Answer 20

 The medial extensor
retinaculum also
provides passive
resistance to the lateral
pull of the patella

Question 21

Other alignment considerations

Answer 21

The femur should be aligned at ≈
170-175° relative to the tibia
 This is referred to as genu valgum
 An angle of < 170° is excessive
genu valgum or “knock knees”
 An angle > 180° is called genu
varum or “bow leg”

Question 22

Other alignment considerations (2)

Answer 22

 In the sagittal plane, hyperextension
of the knee is called genu recurvatum
 It frequently results from postural
anomalies and muscle imbalance at
the ankle or knee
 This type of alignment results in
increased stress on the posterior joint
capsule and ACL

Question 23

Pes Anserinus (goose’s foot)

Answer 23

 The semitendinosus, gracilis and
sartorius all insert close together on the
medial aspect of the knee
 All flex & IR the knee
 Work together to dynamically stabilise
the knee against valgus and external
rotatory forces
 Important during movement patterns
requiring running and quick turning

Question 24

Popliteus (unscrews the screw home mechanism)

Answer 24

 Rotates the tibia internally to initiate tibial on
femoral flexion OR for closed chain tasks
 Rotates the femur externally to initiate femoral
on tibial flexion
It is also an important dynamic stabilizer:
 Reinforces the PCL
 Helps to prevent posterior translation of the tibia
 Supports the knee medially by controlling ER
 Its strong tendon helps to resist knee varus
 Proprioception?

Question 25

TFL & Gluteus maximus

Answer 25

 It provides dynamic stability to the
lateral aspect of the knee via its
attachment to the ITB, increasing its
activity when there are varus forces
 Tightness is associated with medial
and lateral knee pain
 ITB ‘friction’ syndrome - common in runners – WAS
thought to be due to repeated rubbing or excessive friction
between the band and the lateral epicondyle BUT NOW it
is understood that repeated tension under compression
leads to progressive stages of insertional tendinopathy

Question 26

Ligaments

Answer 26

 The medial collateral ligament
(MCL) has two portions
 Anterior superficial portion is
considerably stronger than the
posterior deep portion and is
the primary restraint against a
valgus force (particularly when
the knee is in flexion)
 It is taut in extension

Question 27

Ligaments (2)

Answer 27

 The lateral collateral ligament
(LCL) is the primary restraint
against a varus force
 It is taut in extension
 Both the MCL and the LCL
offer some resistance against
axial rotation

Question 28

Ligaments (3)

Answer 28

 The cruciate ligaments are located
between the synovial and fibrous
layers of the joint capsule so they
are intracapsular and extrasynovial
 The anterior cruciate ligament (ACL)
limits anterior translation of the tibia
on the femur
 It is considered to be taut in
extension (and perhaps IR)

Question 29

Ligaments (4)

Answer 29

The posterior cruciate ligament (PCL) has a larger
CSA than the ACL and is therefore stronger
 It limits posterior translation
of the tibia on the femur
 It is considered to be taut in
maximum knee flexion

Question 30

Summary

Answer 30

 The collateral ligaments provide mediolateral stability
with the cruciate ligaments contributing important
secondary support
 The cruciate ligaments provide anterior-posterior stability
with the collateral ligaments contributing important
secondary support
 Both cruciate and collateral ligaments contribute to
rotatory stability
 NB The joint capsule will also contribute to stability in all directions

Question 31

ACL injury

Answer 31

 Reasons are likely to be
multifactorial but there are
probably at least 6 causes:
1. Landing and cutting mechanics (see
figure)
2. Quadriceps pull
3. Ground reaction forces (GRF) e.g.
wall squat, skiing (power out or ski
snag/rotation)
4. Medial shear?
5. Dummying?
6. Direct blow (bumper)

Question 32

ACL injury (2)

Answer 32

Reasons are likely to be
multifactorial but from a movement
perspective sportswomen have been
shown to:
 Land with more hip adduction & IR
and more apparent knee valgus
 Land with less knee & trunk flexion
and maintain a more extended knee
during the stance phase
 Higher quadriceps activation during
the landing phase

Question 33

ACL injury (3)

Answer 33

 With the knee near full extension contraction of the
quadriceps produces an anterior shear force
(tends to translate the tibia anteriorly on the femur)
 In closed chain
activities the ground
reaction force may
produce large
anterior shear forces

Question 34

ACL injury (4)

Answer 34

 Males have also been shown to have
significantly higher hamstring recruitment
 The hamstrings produce a posterior shear force
that reduces the load on the ACL, particularly
when the knee is flexed