pfs

varaiaty of disease :

patellofemoral pain

1-patellar instability

2-lateral patellar compression

3-idiopathic chondromalacia of patella

4-quadrecepes tendon rupture

5-patella tendon rupture

6-artiucular cartillage defect of knee

7-osteonecrosis of the knee

8- SONK

9- plica

Contact area: maximum contact area at 45 deg.

- in this position: both the central ridge and the medial and lateral facets area in contact with the sulcus;

- in full extension: the lower most portion of the patella is in contact, and it progresses proximally as the knee is flexed;

- odd facet: contacts the femur only at maximum flexion;

- relative lack of conformity that contributes to many of the problems noted in patellar tracking;

it is the principal site of insertion of quadriceps, it transmits tensile forces generated by quadriceps to patellar ligament;

- despite low friction in the patello femoral joint, tension in the tendon above patella differs from that in the patellar ligament below it;

- tension in extensor mechanism can be considerable in the normal patient, even under static conditions, rising to 6 times half the body

wt in each knee during crouching;- at 25 deg, the force at the patello femoral joint is equal to that passing thru the tibio femoral joints;

- at nearly full bend (before pts buttocks touch his heels) this value has risen to nearly 150% of force passing through tibiofemoral

joints;

- this explains need for large area of thick articular cartilage on normal patella and on the femoral condyles;

- max patellofemoral joint reaction loads occur at 35 deg of flexion & may approach a max of 3.5 to 4 times body wt w/ stair climbing

or descent;

- beyond 90 deg of flexion, posterior surface of quadriceps tendon also comes into contact with the trochlea;

- when this occurs, compressive forces on the patellofemoral articulation are diminished owing to division of the load bearing

between patellofemoral joint and the tendon of quadriceps mechanism;

patella is subjected to complex loading

- w/ knee extension, it transmits almost all of force of quadriceps contraction and thus is loaded primarily in tension;

- w/ knee flexion, its post surface contacts distal aspect of femur & is subjected to compressive force = patellofemoral joint rxn force;

-

loading on the surface creates 3-point bending configuration in patella.

- this bending load results in tension at ant surface of patella, which is additive to that naturally generated by distraction from contraction of

the quadriceps.

-relative contribution of these modes of loading of patella depends primarily on position of knee joint;

- as knee moves into flexion, bending forces become increasingly important.

- magnitude of tensile forces in anterior surface of patella reaches maximum near 45 degrees of knee flexion;

- loads across patella have not been precisely measured, but they probably are on order of 3000 newtons of tensile load and may rise

to 6000 newtons in young, trained men.

- during normal activities such as stair-climbing, joint reactive forces may equal 3 time body wt, and doing deep knee bends can

increase JRF to 7-8 times body wt

acute traumatic

occurs equally by gender

may occur from a direct blow (ex. helmet to knee collision in football)

chronic patholaxity

recurrent subluxation episodes

occurs more in women

associated with malalignment

habitual

usually painless

occurs during each flexion movement

pathology is usually proximal (e.g. tight lateral structures - ITB and vastus lateralis)

ligamentous laxity (Ehlers-Danlos syndrome)

previous patellar instability event

"miserable malalignment syndrome"

a term named for the 3 anatomic characteristics that lead to an increased Q angle

femoral anteversion

genu valgum

external tibial torsion / pronated fee

patella alta

causes patella to not articulate with sulcus, losing its constraint effects

trochlear dysplasia

excessive lateral patellar tilt (measured in extension)

lateral femoral condyle hypoplasia

dysplastic vastus medialis oblique (VMO) muscle

overpull of lateral structures

iliotibial band

vastus lateralis

usually on noncontact twisting injury with the knee extended and foot externally rotated

patient will usually reflexively contract quadriceps thereby reducing the patella

osteochondral fractures occur most often as the patella relocates

direct blow

less common

ex. knee to knee collision in basketball, or football helmet to side of knee

acute dislocation usually associated with a large hemarthrosis

absence of swelling supports ligamentous laxity and habitual dislocation mechanism

medial sided tenderness (over MPFL)

increase in passive patellar translation

measured in quadrants of translation (midline of patella is considered "0"), and also should be compared to contralateral side

normal motion is <2 quadrants of patellar translation

lateral translation of medial border of patella to lateral edge of trochlear groove is considered "2" quadrants and is considered abnormal amount of translation

patellar apprehension

passive lateral translation results in guarding and a sense of apprehension

increased Q angle

J sign post

x rays

A

x rays

CT

mri

help further rule out suspected loose bodies

osteochondral lesion and/or bone bruising

medial patellar facet (most common)

lateral femoral condyle

tear of MPFL

tear usually at medial femoral epicondyle

cons

or