Biomechanics of knee complex 9 frontal plane patellofemoral jt stability

Biomechanics
of the

Knee Complex : 9
1

DR. DIBYENDUNARAYAN BID [PT]
THE SARVAJANIK COLLEGE OF PHYSIOTHERAPY,
RAMPURA, SURAT

dnbid71@gmail.com 6/12/2012

2

Frontal Plane Patellofemoral
Joint Stability


3

 The patellofemoral joint is unique in its potential for
frontal plane instability near full knee extension, as
well as for degenerative changes resulting from
increased patellofemoral joint stresses (in flexion).

 This multifaceted problem makes understanding the
control of the patella’s frontal plane motion
particularly important.


4

 In the extended knee, instability can be a problem
be-cause the patella sits on the shallow aspect of the
superior femoral sulcus.


5

 There is less bony stability and less patellofemoral
compression from the quadriceps.

 Because of the physiologic valgus that normally
exists between the tibia and femur, the action lines of
the quadriceps and the patellar tendon do not
coincide.

 This results in the patella’s being pulled slightly
laterally by the two forces (Fig. 11-46).

6


7

 The presence of a resultant lateral pull on the
patella suggests that soft tissue stabilizers must
assume more responsibility for medial-lateral
stability in the absence of suitable bony stability.


8

 Once knee flexion is initiated and the patella begins
to slide down the femur and into the femoral sulcus
(at about 20 of flexion), medial-lateral stability is
increased by the addition of the bony stability of the
femoral sulcus.

 However, the concomitant increased compression of
the patella against the femoral condyles can present
another problem.


9

 Whether the patella is at risk for instability or for
increased medial-lateral compression, the position,
mobility, and control of the patella in the frontal
plane are of utmost concern.

 These factors are determined by the relative tension
in both the transverse and longitudinal stabilizers of
the patella.


10

 The longitudinal stabilizers of the patella consist of
the patellar tendon inferiorly and the quadriceps ten-
don superiorly.

 The patellotibial ligaments that are part of the
extensor retinaculum and reinforce the capsule also
are longitudinal stabilizers (see Fig. 11-14).


11


12

 The longitudinal stabilizers are capable of providing
medial-lateral stability of the patella in knee flexion
through increased patellofemoral compression (see
Fig. 11-45).


13


14

 In the extended knee, this compression is minimal,
however, leaving the patella relatively unstable in
this position.

 When extension is exaggerated, as in genu
recurvatum, the pull of the quadriceps muscle and
patellar tendon may actually distract the patella
somewhat from the femoral sulcus, further
aggravating the relative patella instability.


15

 The transverse stabilizers are composed of the
superficial portion of the extensor retinaculum.

 This retinaculum connects the vastus medialis and
vastus lateralis muscles directly to the patella for
improved muscular stabilization.


16

 In addition, passive stabilizers such as the medial
and lateral patellofemoral ligaments firmly attach
the patella to the adductor tubercle medially, and the
IT band laterally.

 The role of the medial patellofemoral ligament in
assisting normal patellar tracking should not be
understated.


17

 As the thickest portion of the medial retinaculum,
the medial patellofemoral ligament alone provides
approximately 60% of the passive restraining force
against lateral translation (lateral shift) of the
patella.


18

 An additional passive stabilizer that is sometimes
overlooked is the large lateral lip of the femoral
sulcus (see Fig. 11-2).

 The steep lateral facet acts as a buttress to excessive
lateral patellar shift.

 Therefore, even large lateral forces can be prevented
from subluxing or dislocating the patella, provided
that the lateral lip of the femoral sulcus is of
sufficient height.


19


20

 In the case of trochlear dysplasia, however, even
relatively small lateral forces imposed on the patella
can cause the patella to sublux or fully dislocate.


21

 Both the transverse and the longitudinal structures
will influence the medial-lateral positioning of the
patella within the femoral sulcus, as well as influence
patellar tracking as the patella slides down the
femoral condyles and into the intercondylar groove.


22

 The passive mobility of the patella and its medial-lateral
positioning are largely governed by the passive and
dynamic pulls of the structures surrounding it.

 This is important because the presence of hypermobility
could result in patellar subluxations or dislocations,
whereas hypomobility could yield greater patellofemoral
stresses.

 Passive mobility of the patella is maximal when the knee
is fully extended and the musculature is relaxed.


23

 An imbalance in the passive tension or a change in the
line of pull of the dynamic structures will substantially
influence the orientation of the patella.

 This is predominantly true when the knee joint is in
extension and the patella sits on the relatively shallow
superior femoral sulcus.

 Abnormal forces, however, may influence the excursion
of the patella even in its more secure location within the
intercondylar groove with the knee in flexion.


24

 As already noted, tension in the active and/or stretched
quadriceps muscle helps create compression between the
patella and the femur to increase patellofemoral stability.

 The force on the patella is determined by the resultant
pull of the four muscles that constitute the quadriceps
and by the pull of the patellar tendon.

 Each of the segments of the quadriceps can make some
contribution to frontal plane mobility and stability.


25

 As noted earlier, the pull of the vastus lateralis
muscle is normally 35° lateral to the long axis of the
femur,

whereas the pull of the proximal portion of the
vastus medialis muscle (VML) is approximately 15°
to 18° medial to the femoral shaft with the distal
fibers (VMO) oriented 50° to 55° medially (see Fig.
11-34).


26


27

 Because the vastus medialis and vastus lateralis muscles
not only pull on the quadriceps tendon but also exert a
pull on the patella through their retinacular connections,
complementary function is critical.

 Relative weakness of the vastus medialis muscle may
substantially increase the resultant lateral forces on the
patella.

 The individual pulls of each respective portion of the
quadriceps is impossible to measure in vivo, however.


28

 Although measurements of muscular force cannot be
made, the literature supports the contention that
muscle activity of the two portions of the vastus
medialis (VMO and VML) and the vastus lateralis
muscles are not selectively altered in patients with
patellofemoral pain.


29

 Anatomic variations may contribute to asymmetrical
pulls on the patella.

 In general, the VMO inserts into the superomedial aspect
of the patella about one third to one half of the way down
on the medial border.

 In instances of patellar malalignment, the VMO insertion
site may be located less than a fourth of the way down on
the patella’s medial aspect, and as a result, the vastus
medialis muscle cannot effectively counteract the lateral
motion of the patella.


30

 Although individual components of the quadriceps
may not necessarily be influenced by pain, the
quadriceps muscle as a whole does appear to be
susceptible to the inhibitory effects of the acute joint
effusions caused by injury.

 This inhibition can result in hypotonia and atrophy,
minimizing the compressive role of the quadriceps
and thus altering the resultant pull on the patella.


31


32


Asymmetry of Patellofemoral Stabilization
33

 The orientation of the quadriceps resultant pull with
respect to the pull of the patellar tendon provides
information about the net force on the patella in the
frontal plane.

 The net effect of the pull of the quadriceps and the
patellar ligament can be assessed clinically using a
measurement called the Q-angle (quadriceps angle).


34
 The Q-angle is the angle
formed between a line
connecting the ASIS to
the midpoint of the
patella and a line
connecting the tibial
tuberosity and the
midpoint of the patella
(Fig. 11-47).


35


36

 A Q-angle of 10 ° to 15 ° measured with the knee either in
full extension or slightly flexed is considered normal.

 Any alteration in alignment that increases the Q-angle is
thought to increase the lateral force on the patella.

 This can be harmful because an increase in this lateral
force may increase the compression of the lateral patella
on the lateral lip of the femoral sulcus.


37

 In the presence of a large enough lateral force, the
patella may actually sublux or dislocate over the
femoral sulcus when the quadriceps muscle is
activated on an extended knee.


38

 The Q-angle is usually measured with the knee at or
near full extension because lateral forces on the
patella may be more of a problem in these
circumstances.

 With the knee flexed, the patella is set within the
intercondylar notch, and even a very large lateral
force on the patella is unlikely to result in
dislocation.


39

 Furthermore, the Q-angle will reduce with knee
flexion as the tibia rotates medially in relation to the
femur.


40

 It has been postulated that women have a slightly
greater Q-angle than do men because of the presence
of:
 a wider pelvis,
 increased femoral anteversion, and
 a relative knee valgus angle.

 However, other authors have disputed this, and the
presence of a gender difference in the Q-angle is still
a matter of debate.


41

 Although an excessively large Q-angle of 20° or
more is usually an indicator of some structural
malalignment,

>an apparently normal Q-angle will not necessarily
ensure the absence of problems.


42

 Large Q-angles are thought to create excessive lateral
forces on the patella that may predispose the patella
to pathologic changes.

 One problem with using the Q-angle as a measure of
the lateral pull on the patella is that the line between
the ASIS and the mid-patella is only an estimate of
the line of pull of the quadriceps and does not
necessarily reflect the actual line of pull in the
patient being examined.


43

 If a substantial imbalance exists between the vastus
medialis and vastus lateralis muscles in a patient, the
Q-angle may lead to an incorrect estimate of the
lateral force on the patella because the actual pull of
the quadriceps muscle is no longer along the
estimated line.


44

 Furthermore, a patella that sits in an abnormal
lateral position in the femoral sulcus because of
imbalanced forces will yield a smaller Q-angle
because the patella lies more in line with the ASIS
and tibial tuberosity.


45

 There are several abnormalities that can yield increased
lateral forces.

 There is a potential for imbalance between the vastus
lateralis and vastus medialis muscles, although, as
identified earlier, this imbalance cannot be measured in
vivo.

 The presence of a tight IT band could also limit the
mobility of the patella and restrict its ability to shift
medially during flexion, contributing to increased stress
under the lateral facet of the patella.


46

 When the IT band moves posteriorly with knee
flexion, it exerts an even greater lateral pull on the
patella, which results in a progressive lateral tilting
as knee flexion increases.

 The increased lateral tilt could further load the
lateral facet, increasing joint stress.


47

 The frontal plane deviation of genu valgum increases
the obliquity of the femur (see Fig. 11-7A) and,
concomitantly, the obliquity of the pull of the
quadriceps.

 In contrast, individuals with genu varum exhibit less
obliquity of the femur (see Fig. 11-7B), and therefore
should have a diminished lateral quadriceps pull.


48


49

 The transverse plane deviation of medial femoral
torsion (or femoral aneversion) generally results in
the femoral condyles being turned in (medially
rotated), carrying the patella medially with the
femoral condyles and increasing the Q-angle by
increasing the obliquity of the pull of the quadriceps
on the patella.

 Medial femoral torsion is often associated with
lateral tibial torsion in the older child or adult, or it
may exist independently.


50

 In lateral tibial torsion, the tibial tuberosity lies more
lateral to the patella, increasing the Q-angle by
increasing the obliquity of the patellar tendon.

 When medial femoral torsion and lateral tibial
torsion coexist, the Q-angle will increase
substantially, resulting in a substantial lateral force
on the patella (Fig. 11-48).


51


52

 As we will see in Chapter 12,
the presence of excessive or prolonged pronation in
the foot can contribute to excessive or prolonged
medial rotation of the lower extremity that moves
the patella medially, increasing the Q-angle and
promoting a greater lateral force on the patella in a
way similar to that of medial femoral torsion.

 Each of these conditions can predispose the patella
to excessive pressure laterally or to lateral
subluxation or dislocation.


53

 Forces other than the alignment and balance of the
quadriceps muscle components may influence
patellar positioning.

 Either laxity of the medial retinaculum or
excessive tension in or adaptive shortening of the
lateral retinaculum >
may contribute to a laterally tilted patella in the
femoral sulcus (Fig. 11-49).


54


55

 In addition, a tight IT band may exert an excessive
lateral pull on the patella through the lateral
patellofemoral ligament.

 Such deficits in the passive stabilizers, as well as
weakness in the medial active stabilizers, result in
increased lateral compressive forces.

 It is currently unknown whether such changes in the
passive structures are primary or are secondary to
abnormalities in the dynamic stabilizers.


Weight-Bearing
versus
56

Non-Weight-Bearing Exercises
with
Patellofemoral Pain


57

 Both weight-bearing and non-weight-bearing
exercises are often prescribed for patients with
patellofemoral pain.

 Each mode of exercise influences the patellofemoral
joint differently on the basis of the knee’s position
within the ROM.


58

 Effective quadriceps strengthening in a patient with
pain must be performed in a pain-free range.

 This necessitates a complete understanding of how
both weight-bearing and non-weight-bearing
exercises influence the contact area and force across
the patellofemoral joint.


59

 We already noted that in non-weight-bearing
extension, such as the seated knee extension, the
quadriceps must work harder as extension
progresses (quadriceps force increases with
decreasing knee flexion angle) (see Fig. 11-37).


60

 The increased work of the quadriceps near extension
is necessary to compensate for the increased MA of
the resistance.

 However, the greater compressive force generated
by the increased quadriceps contraction can be
detrimental for an individual with patellofemoral
pain,
especially if the degeneration is located on the
inferior aspect of the patella that is in contact with
the femur near extension.


61

 In contrast, a weight-bearing exercise requires
greater quadriceps activity with greater knee flexion
(e.g., at the bottom of a squat) as the MA of the
resistance increases (see Fig. 11-38).


62

 During weight-bearing exercise, greater knee flexion
will therefore increase the compressive force across
the patellofemoral joint both because of increased
force demands on the quadriceps muscle and
because of the increased patellofemoral
compression that occurs even with passive knee
flexion.


63

 The substantial patellofemoral compression
will aggravate patellofemoral pain.


64

 Exercise recommendations for the person with
patellofemoral pain can be based on
changing patellofemoral joint stress
with weight-bearing and non-weight-bearing
exercises and knee flexion angle (Fig. 11-50).


65

Figure 11-50  Pending….
Simulations showed
patellofemoral joint stress
to be greater during loaded
non–weight-bearing
exercises than weight-
bearing exercises when the
knee was closer to knee
extension. Patellofemoral
joint stress was higher,
however, during weight-
bearing exercises when
knee flexion exceeds
approximately 50. [Data
from Cohen ZA, Roglic H,
Grelsamer RP, et al:
Patellofemoral stresses
during open and closed
kinetic chain exercises. An
analysis using computer
simulation. Am J Sports
Med 29:483–484, 2001.]


66

 It has been recommended that those with
patellofemoral pain:

 Avoid deep flexion while doing weight-bearing extension
exercises and

 Avoid the final 30° of extension during non-weight-
bearing knee extension exercises.


67


Effects of Injury and Disease
68

 The joints of the knee complex, like other joints in
the body, are subject to:
 developmental defects,

 injury, and

 disease processes.


69

 A number of factors, however, make the knee joint
unique in its development of various pathologies.

 The knee, unlike the shoulder, elbow, and wrist,
must support the body weight and at the same time
provide considerable mobility.


70

 Although the hip and ankle joints similarly support
the body’s weight, the knee is a more complex
structure than either the hip or ankle.

 The anatomic complexity is necessary to dissipate
the enormous forces applied through the joint as
two of the longest levers in the body meet at the knee
complex.


Tibiofemoral Joint Injury
71

 The tremendous forces applied through the knee
have the potential to contribute to numerous injuries
and degenerative damage.

 In addition, participation in physical fitness and
sports activities that involve jumping, pivoting,
cutting, or repetitive cyclic loading among all age
groups and both sexes can subject the knee complex
to risk of injury.


72

 Injuries to the knee complex may involve the
menisci, the ligaments, the bones, or the
musculotendinous structures.


73

 Meniscal injuries are common and usually occur as a
result of sudden rotation of the femur on the fixed
tibia when the knee is in flexion.

 The pivot point during axial rotation in the flexed
knee occurs through the medial meniscus.

 Therefore, the more rigidly attached medial
meniscus may tear under the sudden load.


74

 Ligamentous injuries may occur as a result of a force
that causes the joint to exceed its normal ROM,
usually the translational ROM.

 Although excessive forces may cause ligamentous
tears, lower-level forces may similarly cause
disruption in ligaments weakened by aging, disease,
immobilization, steroids, or vascular insufficiency.


75

 Cyclic loading (whether short term and intense or over a
prolonged period) may also affect visco-elasticity and
stiffness.

 A weakened ligament may take 10 months or
more to return to normal stiffness once the
underlying problem has been resolved.

 After a ligament injury or reconstruction, the new or
damaged tissue must be protected to minimize excessive
stress through the healing tissue.


76

 Absence of tissue stress, however, is also
detrimental, because the new tissue will not adapt
and become stronger under unloaded conditions.

 Rehabilitation of the repaired or reconstructed
ligament,
therefore,
is a balance between too much applied stress and
too little.


77

 The bony and cartilaginous structures of the
tibiofemoral joint may be injured either
by the application of a large direct force, such as
during a twist or fall, or
by forces exerted by abnormal ligamentous and
muscular forces.

 Knee osteoarthritis is often seen in older adults and
is particularly common in women.


78

 This progressive erosion of articular cartilage may be
initiated by:
a previous traumatic joint injury,
obesity,
malalignment,
instability, or
quadriceps muscle weakness,
to name just a few of the many suspected contributors to
the development of osteoarthritis.

 Tibial plateau fractures can occur when large magnitudes
of force are applied through the joint.


79

 Knee joint instability, as frequently seen in the knee
after ACL injury, can lead to progressive changes in
the articular cartilage, in the menisci, and in the
other ligaments attempting to restrain the increased
joint mobility.

 The presence of ligamentous instability induces
abnormal forces through the joint, inasmuch as
excessive shearing can often occur.


80

 In addition, this excessive laxity must be controlled
in order to avoid episodes of giving way.

 Because the knee has poor bony congruency, the
muscles must provide greater control of all fine
movements of the tibiofemoral joint in the absence
of ligaments.


81

 Increased muscular co-contraction, however, may
generate greater compressive forces through the
joint, contributing to articular cartilage
degeneration.

 An improved method of providing dynamic stability
to a lax joint, therefore,
is to generate isolated muscle contractions as
needed,
rather than a massive co-contraction to stiffen the
joint.


82

 The numerous bursae and tendons at the knee are
also subject to injury.

 The cause of injuries to these structures may be
either a direct blow or prolonged compressive or
tensile stresses.

 Bursitis is common after either blunt trauma or
repetitive low-level compressions, which can irritate
the tissue.

83

 The pre-patellar bursa, the superficial infra-patellar
bursa (known as housemaid’s knee when it is
inflamed), and the bursa beneath the pes anserinus
are common locations for injury.

 Tendinitis results from repetitive low-level stresses
to the tissues of the tendon.


84

 Frequently this is caused by an overworking of the
muscle and can occur in response to a previous
ligamentous injury.

 Another potential source of pain and dysfunction in
the knee joint is the irritation of a patellar plica.

 Classic symptoms include pain with prolonged
sitting, with stair climbing, and during resisted
extension exercises.

85

 In flexion, the medial patellar plica is drawn over the
medial femoral condyle and can become pressed
beneath the patella.

 The resulting tension in the band may cause plica to
become inflamed.


86

 If the inflamed plica becomes fibrotic, it may create a
secondary synovitis around the femoral condyle, and
deterioration of the condylar cartilage may occur.

 A thickened or inflamed superior plica may erode the
superior aspect of the medial facet of the patella.


Patellofemoral Joint Injury
87

 We have presented the mechanics of a number of
problems that may predispose the knee to
patellofemoral dysfunction.

 Any one problem in isolation or various
combinations of problems may lead to excessive
pressure on the lateral facets of the patella, to lateral
subluxation, or to lateral dislocation.


88

 Both patellar instability and increased
patellofemoral compression are commonly
associated with:
 knee pain,
 poor tolerance of sustained passive knee flexion (as in
sitting for long periods),
 “giving way” of the knee, and

 exacerbation of symptoms by repeated use of the
quadriceps on a flexed knee.


89

 Often this results in diminished use of the
quadriceps, leading to atrophy and subsequently a
further deterioration of patellar control.

 As muscle function declines, patellofemoral
dysfunction may progress,
necessitating a reversal of muscle function under a
series of controlled situations to generate
hypertrophy of the quadriceps,
while minimizing discomfort.

90

 Among the causes of increased patellar compression
include:
 a tight IT band,
 large Q-angle (e.g., as in genu valgum or femoral
anteversion with lateral tibial torsion),
 relative vastus medialis muscle weakness, or

 patellar hypomobility.


91

 With patellar hypermobility, lax medial structures,
and a short lateral femoral condyle, the risk of lateral
patellar subluxation or dislocation is increased.

 After a lateral patellar subluxation or dislocation, the
medial retinaculum is stretched as the patella
deviates toward or slips over the lateral lip of the
femoral sulcus or condyle.


92

 The return of the patella into the intercondylar notch
may affect the medial patella (occasionally causing
an osteochondral fracture).

 There are a host of other pathologies that can occur
around the patellofemoral joint, including:
 pain from the lateral patellofemoral ligament,
 inflammation of the medial patellar plica, and

 pain from the quadriceps tendon above or the patellar
ligament below.


93

 Patellofemoral pain is most often observed in
adolescents and may resolve spontaneously.

 In addition, patellar subluxation is more often seen
in younger patients, who may have a less
developed patella and lateral condyle to resist
an excessive lateral force on the patella.


94

 Cartilaginous changes seen on the lateral patellar
facet were once considered to be diagnostic of
patellofemoral dysfunction, and the term
chondromalacia patella (softening of the cartilage)
was assigned.


95

 With the knowledge that similar cartilaginous
changes can be found in asymptomatic knees and
that the medial patellar facet can show greater
change without symptoms or progressive cartilage
deterioration, more general diagnoses have been
used,
including patellofemoral arthralgia or patellofemoral
pain syndrome.


96

 The use of this more general terminology suggests
that the damage extends beyond the articular
cartilage.

 Cartilage is aneural and therefore cannot be
the cause of pain.

 Instead, patients with patellofemoral pain can
experience discomfort from damage to
subchondral bone, the synovial membrane, and
ligamentous or musculotendinous structures.


Summary
97

 A thorough knowledge of normal structure and
function, however, can be used to predict or
understand the immediate impact of a specific
injury and the secondary effects on intact
structures.


98

 The variety of forces transmitted through the knee
complex arises from gravity (weight-bearing
forces), muscles, ligaments, and other passive soft-
tissue structures.


99

 Any alteration of the knees anatomy can
substantially influence these forces and can have a
dramatic impact on the function of the knee joint.

 Damage to the tibiofemoral joint or the
patellofemoral joint can result from either:
A large rapid load or
 The accumulation of smaller repetitive loads.


100

 An understanding of both the primary and
secondary effects of injury is important in order to
gain a full appreciation for the pathogenesis of
knee disorders.


101

Thanks for your
attention………………….


102

End of Part - 9


Biomechanics of knee complex 9 frontal plane patellofemoral jt stability

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