CHAPTER 60 • THE PATELLOFEMORAL JOINT 357of the patella moves proximally and medially with
the most extensive contact being made at approxi-
mately 45°. Contact stresses on the patellofemoral
joint are higher than any other major weight bearing
joint in the body. The contact area and load across
the joint increases with knee flexion. Compressive
forces on the patella can range from 3.3 times body
weight with stair climbing up to 7.6 times body
weight with squatting.- The patellar medial facet varies anatomically. It may
be divided into a medial facet proper and a small odd
facet. The odd facet may develop as a response to
functional loads and does not contact the medial
femoral condyle except in extreme flexion.
•Several ossification centers contribute to the patella.
Failure of fusion can lead to bipartite patella that can be
classified into three types: type I—inferior; type II—
lateral; and type III—superolateral (most common).
Bipartite patella is most often discovered accidentally
during radiographic examination of the knee for
another disorder. - The medial retinaculum is composed of the medial
patellofemoral ligament and the medial patellotibial
ligament. The medial patellofemoral ligament(MPFL)
originates from the adductor tubercle and inserts on
the medial border of the patella. This ligament plays a
major role in preventing lateral displacement of the
patella. The lateral retinaculum is composed of a
superficial and deep layer and runs from lateral margin
of the patella and patellar tendon to the anterior aspect
of the iliotibial band. - The patellar tendon varies in length (average 4.6 cm).
It connects the apex of the patella to the tibial tuberos-
ity and is slightly wider proximally than distally.
PATELLAR PAIN
- The single most common cause of knee pain involves
pathology related to the patella. Patellar pain or dis-
comfort may be the result of direct trauma, repetitive
direct pressure, constant repetitive movements with
the knee in a flexed position, malalignment, or a com-
bination of these factors. - Symptoms of patellar pain that begin during relatively
normal activities/sports should alert the physician that
the knee was not normal in the first place. If the knee
swells significantly within the first 12 to 24 h after
traumatic knee injury, this signifies that there is blood
or a hemarthrosis within the joint. The most common
cause of an acute hemarthrosis after a sports related
knee injury is a tear of the anterior cruciate ligament
with the second most common cause being a trau-
matic patellar dislocation/subluxation with bleeding
as a result of either soft tissue tearing, osteochondral
fracture or both.PHYSICAL EXAMINATION- The physical examination should begin with general
inspection for skin abrasions, contusions, or lacera-
tions. - It is important to document the overall alignment of
the leg while the patient is standing, seated, and
supine. With the patient supine, patellar alignment and
Q angle (angle between anterior superior iliac spine
(ASIS), patella, and tibial tubercle) are measured. A Q
angle of less than 15°is generally considered normal.
The Q angle should be assessed with the knee
extended and also with the knee flexed 90°. An angle
greater than 8°with this method is indicative of an
abnormally lateralized patellar vector. If the patella is
subluxed, the Q angle reverts to within normal range.
Along with Q angle determination, the amount of
varus/valgus should be noted. Thigh circumference
should be measured at a consistent level above the
knee to assess for quadriceps atrophy. Observe
patellofemoral tracking with the patient seated over
the edge of the table while slowly flexing and extend-
ing the knee from 0 to 90°. Observe for high or lateral
patellar positioning (grasshopper eyes), small patella,
patella alta (the patella faces the ceiling rather than
straight ahead), vastus medialis oblique(VMO) dys-
plasia, excessive hit anteversion. Also the examiner
should observe for signs of J tracking (the patella
deviates laterally in terminal extension).
•Palpate for crepitation, suggesting possible chondral
injury, noting the degree of knee flexion that crepitus
is present to delineate between proximal and distal
lesions. Patellofemoral crepitus is best elicited by
having the patient standing and then squatting down
with the examiners hands over the patella noting at
what arc of motion the crepitus occurs. Retropatellar
crepitus that is painful and occurs in either early flex-
ion or terminal extension indicates disease on the
distal part of the patella. A painful arc with crepitus in
greater degrees of flexion indicates disease on the
more proximal portion of the patella. One finger pal-
pation is important to localize tenderness whether it is
in the retinaculum or the medial and lateral patellar
facets. These are best palpated by placing one finger
under the respective facet and pushing the patella over
to that side with the other hand. The quadriceps
tendon and patellar tendon are also best palpated in a
resting position with the knee extended. Point tender-
ness at the inferior pole of the patella at the attach-
ment of the patellar tendon is typically consistent with