Herv? e Collado, MDa,b,c,*, Michael Fredericson, MDd,e,f
The average recreational runner has a 37% to 56% incidence of being injured during
the course of a year’s training.1The knee is the most common site of injury and patel-
lofemoral pain (PFP) syndrome constitutes nearly 25% of injuries to the knee.2The
cause of PFP, however, is not clearly understood and may have multiple origins.
The most commonly accepted hypothesis is related to increased patellofemoral joint
stress (force per unit area) and subsequent articular cartilage wear.
There are many classification systems for PFP. Most of these are based on radio-
graphic findings and grading of the extent of chondral injury or patellar position. These
systems are devised to help in surgical planning, but are not easily applicable in the
clinical setting. An innovative classification system by Holmes and Clancy3(Box 1)
allows classification of the various patellofemoral pathologies seen in a runner’s injury
clinic, and particularly in clarifying PFP or instability related to malalignment.
PREDISPOSING FACTORS FOR PATELLAR MALALIGNMENT AND INSTABILITY
As the knee begins to flex, the articular surface of the patella comes into contact with
the lateral femoral condyle and the patella then follows an S-shaped curve through the
aDepartment of Medicine & Rehabilitation and Sport Medicine, University Hospital la Timone,
Boulevard Jean Moulin, 13005 Marseille, France
bDivision of Physical Medicine & Rehabilitation, Stanford University School of Medicine, Stan-
ford, CA, USA
cDepartment of Orthopaedic Surgery, PM&R and Sports Medicine, Stanford University School
of Medicine, Stanford, CA, USA
dOrthopaedics & Sports Medicine, Stanford University School of Medicine, Stanford Center for
Medicine, 450 Broadway Street, Redwood City, CA 94063, USA
ePM&R Sports Medicine Service, Stanford University School of Medicine, Stanford Center for
Medicine, 450 Broadway Street, Redwood City, CA 94063, USA
fStanford Cross-Country & Track, Stanford University School of Medicine, Stanford Center for
Medicine, 450 Broadway Street, Redwood City, CA 94063, USA
* Corresponding author. Department of Medicine & Rehabilitation and Sport Medicine, Univer-
sity Hospital la Timone, Boulevard Jean Moulin, 13005 Marseille, France.
E-mail address: firstname.lastname@example.org
? Patellofemoral ? Pain ? Syndrome
Clin Sports Med 29 (2010) 379–398
0278-5919/10/$ – see front matter ª 2010 Elsevier Inc. All rights reserved.
Classification of Patellofemoral Pain and Dysfunction
1. Subluxation or dislocation, single episode
2. Subluxation or dislocation, recurrent
? Lateral subluxation or dislocation
Normal functional Q-angle
Increased functional Q-angle
Grossly inadequate medial stabilizers
Tight lateral retinaculum
? Medial subluxation or dislocation
3. Chronic dislocation of patella
4. Associated fractures
Patellofemoral pain and malalignment
1. Increased functional Q-angle
? Femoral anteversion
? External tibial torsion
? Genu valgum
? Foot hyperpronation
2. Tight lateral retinaculum (lateral patellar compression syndrome)
3. Grossly inadequate medial stabilizers
4. Electrical dissociation
5. Patella alta
6. Patella baja
7. Dysplastic femoral trochlea
Patellofemoral pain without malalignment
1. Tight medial and lateral retinacula
3. Osteochondritis dissecans
? Femoral trochlea
4. Traumatic patellar chondromalacia
5. Fat pad syndrome
Collado & Fredericson
trochlea. Part of the patellar surface remains in contact with the trochlea throughout
the remainder of the flexion arc. This contact between the femur and patella prog-
resses from a distal to a proximal direction on the patella.4Helping to keep the patella
centered inthe trochlear groove is the V-shaped anatomy of the patella and the config-
uration of the femoral condyles. In normal knees the lateral condyle is higher than the
medial one. There may be various degrees of true dysplasia of the medial or lateral
portions of the trochlear groove, leading to decreased stability of the patellofemoral
joint.5This instability can be caused by either excessive thickness of the floor of the
trochlea or insufficient height of one or both trochlear femoral condyles. Asymmetry
of patellar facets also affects patellar congruity. The normal ratio of the lateral to
medial facet is 3:2, such that the lateral facet is longer and more sloped, matching
the higher and wider lateral femoral condyle.6
Lower Extremity Malalignment
Torsional or angular malalignment of the lower extremity has a significant influence on
the patellofemoral joint mechanics. Significant deviations in patella alignment
secondary to patella alta, trochlear dysplasia, femoral anteversion, knee valgus, and
a laterally displaced tibial tuberosity could cause PFP.7For example, anteversion of
the femoral neck is frequently associated with external torsion of the tibia and,
frequently, compensatory pronation of the foot. Hyperpronation of the foot is a causa-
tive factor for PFP syndrome (PFPS).8In theory, increased pronation causes the tibia
to internally rotate during the weight acceptance phase of gait, thereby preventing the
6. Patellofemoral osteoarthritis
7. Patellar tendinitis
8. Quadriceps tendinitis
9. Prepatellar bursitis
? Osgood-Schlatter syndrome
? Sinding-Larsen-Johanssen disease
11. Symptomatic bipartite patella
12. Other trauma
? Quadriceps tendon rupture
? Patellar tendon rupture
? Patella fracture
? Proximal tibial epiphysis (tubercle) fracture
? Turf knee/wrestler’s knee
? Cruciate ligament instability
13. Reflex sympathetic dystrophy
From Holmes WS, Clancy WG. Clinical classification of patellofemoral pain and dysfunction.
J Orthop Sports Phys Ther 1998;28(5):300; with permission.
Patellofemoral Pain Syndrome
tibia from fully externally rotating during midstance. In turn, this prevents the knee from
fully locking via the screw-home mechanism. To compensate, the femur internally
rotates to allow the knee to fully lock. Increased femoral internal rotation leads to
increased contact pressure between the patella and the lateral trochlear groove,
which can increase subchondral bone stress and symptoms of PFPS.
Muscle and Soft Tissue Imbalances
One of the most important anatomic factors proposed for affecting dynamic patellar
stabilization is the balance between the medial and lateral quadriceps muscles. It is
thought that the vastus medialis obliquus (VMO), the primary active medial stabilizer of
the iliotibial tract, the lateral retinaculum, and the vastus lateralis.10In some runners the
VMO is weak; however, many runners with sufficient VMO strength still exhibit timing
deficit with delayed onset of the VMO when compared with the vastus lateralis.11,12
Abnormal soft tissue length can also affect patellofemoral mechanics. For example,
tightness in the quadriceps muscle can directly increase the contact pressure
between the articular surfaces of the femur and patella, whereas tightness in the
hamstrings and gastrocnemius can indirectly increase patellofemoral joint reaction
forces by producing a constant flexion moment to the patella.13Tightness in the
hamstrings or gastrocnemius will also restrict talocrural dorsiflexion, producing
compensatory pronation in the subtalar joint14and an increase in the dynamic
Q-angle. The talocrural joint requires 10?of dorsiflexion for walking and 15?to 25?
of dorsiflexion for running. If this motion is not available, compensatory pronation
occurs to allow dorsiflexion of the midfoot on the rearfoot.15
Tightness of the iliotibial band (ITB) can affect normal patella excursion. The distal
ITB fibers blend with the superficial and deep fibers of the lateral retinaculum, and
tightness in the ITB can contribute to lateral patellar tilt and excessive pressure on
the lateral patella.7There is an association between patellar hypomobility and a tight
ITB. Hypermobility with increased lateral patellar glide is correlated with laxity of the
medial patellofemoral ligament or patellomeniscal ligament, and is often noted in
association with patellar subluxation or dislocation.
The pathophysiology of PFP is not well understood. Studies of the biomechanical
factors that potentially contribute to PFPS demonstrate conflicting results, a lack of
reproducibility, and no firm conclusions. Investigators consistently cite the difficulty
of research due to the syndrome’s probable multifactorial nature. Proper tracking
requires balanced forces acting on the patella. If any force acting on the patella is
too large or too small then the movement of the patella may be altered, thereby placing
additional stresses on the soft tissue of the joint. As the stress exceeds the tissues’
mechanical strength, microdamage, inflammation, and pain result.16Altered stresses
in the cartilage may also play a role in a pain response by transferring stresses into the
underlying subchondral bone and exciting nociceptors. Increased cartilage and sub-
chondral bone stress have been postulated as mechanical causes for PFP,17sup-
ported, in part, by estimates of average joint stresses (force/area) in patients with
PFP.18The lateral retinaculum also plays an important role in PFP. The chronic lateral
subluxation of the patella can lead to shortening of the retinaculum with secondary
nerve damage, resembling the histopathologic picture of a Morton neuroma.13,19
The synovium, medial patellofemoral ligament, and fat pad of Hoffa, along with the
loss of tissue homeostasis, have also been highlighted as potent sources of pain.20,21
Collado & Fredericson
Runners note the insidious onset of an ill-defined ache localized to the anterior knee,
behind the knee cap. The onset of anterior knee pain may be gradual or acute and may
be precipitated by trauma. Pain may occur in one or both knees. Knee pain worsens
with squatting, running, prolonged sitting, or when ascending or descending steps.22
The pain is often poorly localized under or around the patella, and is usually described
as ‘‘achy’’ but may be ‘‘sharp.’’ The pain may vary throughout the run and is particu-
larly aggravated by hills. Some patients may describe the affected knee as ‘‘giving
way’’ or ‘‘buckling.’’ In PFPS this perceived instability may be due to pain inhibiting
proper contraction of the quadriceps; but it must be distinguished from instability
arising from a patellar dislocation, subluxation, or ligamentous injury of the knee. There
may be occasional complaints of mild swelling but it is rare for there to be a gross effu-
sion seen with a traumatic knee injury. In the subset of patients with patellar instability,
there is often a sensation of patellar slippage or a feeling of actual bony subluxation,
particularly with twisting, cutting, or pivoting activity. Only rarely,however, willa runner
turn sharply enough to sustain a dynamic force sufficient to cause an acute dislocation
of the patella.
The positive findings in PFP are often subtle, and it is not always clear if they correlate
with the patients’ symptoms. Clinical studies have not been able to consistently
demonstrate biomechanical or alignment differences between patients with PFP
and healthy individuals.23–25Some of this relates to the difficulty defining where the
range of normal alignment ends and malalignment begins. Physical examination for
static malalignment has a place in clinical and scientific evaluation. However, many
of these malalignments change once movement is initiated. Furthermore, additional
malalignment may exist during movement as a result of poor muscular control of
the segments.16Given this, the authors still believe that the physical examination,
when systematically performed, can highlight predisposing static and dynamic factors
to patellofemoral malalignment that are important to address in the design of an indi-
vidualized treatment program.26
The anatomic alignment of the pelvis and lower extremity may play a role in the devel-
opment of PFPS in some individuals, and is referred to as ‘‘static alignment’’ because
it is identifiable when the patient is not moving. Static alignment is not easily modified
with conservative rehabilitation. Alignment of the lower extremity is evaluated by
noting evidence of femoral anteversion; knee position (genu varum, valgum, or recur-
vatum); external tibial rotation; and foot and ankle weight-bearing alignment. A
common clinical measurement of the alignment of the lower extremity is the Q-angle.
The Q-angle is formed by the line connecting the anterosuperior iliac spine to the
center of the patella and the line connecting the center of the patella to the middle
of the anterior tibial tuberosity. This angle is thought to represent the line of action
of the quadriceps force. Although many sources report that a Q-angle greater than
16?is a risk factor for developing PFPS, the literature is inconsistent in supporting
this finding.16,24Although some investigators27,28have found a difference between
the Q-angles of men and women, a study by Grelsamer and colleagues29concluded
that when measurement data are corrected for the average height between men and
women, the difference in the Q-angle between men and women disappears.
Patellofemoral Pain Syndrome
Dynamic malalignment may exist during movement as a result of poor muscular
control of the lower extremity segments. Dynamic alignment can be tested by having
the runner step slowly upon and down from a 6-inch stool or perform single-leg
squats. The presence of any abnormal movements of the patella as it engages and
disengages the trochlea, and any body shifting, trunk rotation, or loss of hip control
are noted. The ‘‘dynamic Q-angle’’ that causes dysfunction has been described.
The concept of poor dynamic alignment took form when clinicians observed a consis-
tent pattern when patients performed a single-leg squat or step-down of excessive
contralateral pelvic drop; hip adduction and internal rotation; knee abduction; and
tibial external rotation and hyperpronation. Several investigators have described this
movement pattern and its link to PFPS.30–32Dynamic magnetic resonance imaging
(MRI) has shown that during weight bearing, PFPS subjects had greater femoral
internal rotation than control subjects.33
This concept supports the idea that poor control of the femur may contribute to
PFPS symptoms in some patients. The excessive frontal and transverse plane motion
seen in women during functional tasks has been attributed to weakness in the hip
abductors and external rotators.30,31,34,35Gluteus medius weakness allows the
contralateral pelvis to drop, and puts the stance leg in an adducted position; this is
accompanied by excessive internal rotation of the femur and tibia and hyperpronation
of the subtalar joint.36,37Normally the patella travels smoothly through the trochlear
groove and follows a straight or slightly curved path. An abrupt or sudden lateral
movement of the patella as the knee nears full extension is considered abnormal.
Called a positive J-sign, this movement is caused by excessive lateral forces as the
patella exits the femoral trochlea at 10?to 30?of flexion,6,38and is seen in a small
number of patients with patellar malalignment and in the majority of patients with frank
In the sitting position, patellar height for signs of alta or baja position can also be
assessed. A prominent infrapatellar fat pad often accompanies patella alta, as does
genu recurvatum. Patella alta is more frequently seen in women and is a common
finding in a congenitally subluxing patella, as it causes the patella to enter the femoral
sulcus late in knee flexion. Patella baja is rarer and is sometimes seen as a complica-
tion of anterior cruciate ligament reconstruction. The path of the patellar tendon inser-
tion into the tibial tuberosity is also noted. When the tibial tubercle is situated more
laterally than normal, such that the patellar tendon descends at an angle rather than
directly downward, proximal external tibial torsion is present.
Dynamic patellar tracking is a measure of patellar instability. During this evaluation,
the examiner asks the seated patient to actively extend the knee from 90?to full exten-
sion, and observes the movement pattern of the patella from the front. In most individ-
uals, the patella seems to move straight proximally, with a slight lateral shift near
terminal extension (J-sign). The term J-sign describes the path of the patella with
mal-tracking. Instead of moving superiorly with knee extension, the patella suddenly
deviates laterally at terminal extension as it exits the trochlear groove, to create an
inverted J-shaped path.22,39
Leg length discrepancies can be screened by measuring the distance from the ante-
rior superior iliac spine to the highest point of the medial malleolus. Leg length discrep-
ancy greater than 1.0 cm may have adverse effects on the lower extremity while
Collado & Fredericson
running.40The knee joint is then observed and palpated for any swelling. As little as 20
to 30 mL of fluid in the knee joint can inhibit VMO function.41It is unusual, however, to
have any more than a mild synovitis of the knee with chronic extensor mechanism
The examination then focuses on palpation of the patella and peripatellar soft
tissues for tenderness. The lateral retinaculum interdigitates with fibers from the
vastus lateralis and ITB, and tenderness is frequently palpated in this area related to
the chronic, recurrent stress of a maligned patella.38,42Several studies have presented
evidence of nerve damage and hyperinnervation into the lateral retinaculum in patients
with patellofemoral malalignment.43,44In these individuals, the neural growth factor is
overexpressed in the nerve fiber and vessel wall, and stimulates the release of
substance P in the free nerve endings.44This condition is often associated with
tenderness along the medial patellar facet, and less often, the lateral patellar facet.
These areas are best palpated by curling the fingers around the border of the patella.
The examiner next palpates along the patellar tendon, specifically at its attachment to
the distal pole of the patella. Patellar tendinitis is demonstrated by tenderness to
palpation in this area. Tenderness directly ventral or dorsal to the patellar tendon is
associated with patellar bursitis and tendinopathy, whereas tenderness along either
side of the patellar tendon is associated with inflammation of the fat pad of Hoffa.
Less commonly, tenderness is located at the proximal pole of the patella at the quad-
riceps insertion, indicating quadriceps tendinitis.
Close observation of the patella in relation to the femur is continued. Grelsamer and
McConnell10describe 4 components that are believed to affect patellar position stat-
ically or dynamically: glide, tilt, rotation, and anterior-posterior position. The glide test
is an assessment of lateral/medial displacement of the patella, and measures the
distance from the midpole of the patella to the medial and lateral femoral epicondyles
with the knee flexed to 20?. The patella may sit equidistant to the condyles, but moves
laterally when the quadriceps contract, indicating a dynamic problem. The glide
component is examined by use of a tape measure to record the distance from the mid-
patella to the lateral femoral epicondyle and the distance from the midpatella to the
medial femoral epicondyle. The midpatella point is determined by visual assess-
ment.10A 5-mm lateral displacement of the patella caused a 50% decrease in vastus
medialis oblique tension.45While it is common for patients with PFP to have some
degree of lateral displacement, these clinical measurements should be interpreted
with caution, because they may not be a true reflection of anatomic position. Powers
and colleagues46found that the clinical assessment of patellar glide (medial/lateral
displacement) overestimated the true amount of lateral displacement assessed on
Patellar tilt compares the height of the anterior aspect of the medial patellar border
with the height of the anterior aspect of the lateral patellar border. This tilt is consid-
ered normal when the 2 borders are level in the frontal plane. In mild tilt, more than
50% of the depth of the lateral border can be palpated but the posterior surface is
not palpable; and in more severe tilt less than 50% of the depth of the lateral border
can be palpated. To determine the presence of a dynamic tilt problem, an active
contraction is simulated by passively moving the patella medially. If the depth of the
lateral border becomes more difficult to palpate, a dynamic tilt is present. If the lateral
tilt is severe, this can lead to lateral patellar compression syndrome, sometimes
requiring surgical release (Fig. 1).
Rotational measurements help to determine any deviation of the long axis of the
patella from the long axis of the femur, and are believed to be another indication
that a particular part of the retinaculum is tight and a potential source of symptoms.
Patellofemoral Pain Syndrome
In normal rotation a line connecting the superior and inferior poles of the patella is
parallel to the long axis of the femur. If the inferior pole is medial to the long axis of
the femur, this signifies internal rotation; if the inferior pole of the patella is lateral to
the long axis of the femur, this signifies external rotation.
The evaluation of anteroposterior (A-P) alignment is to assess if the inferior pole is
tilted posteriorly compared with the superior pole. Such tilting can irritate the fat
pad and is common in patients who have pain on extension or hyperextension of
the knee, because the inferior pole gets buried in the fat pad. These patients are often
diagnosed as having a patellar tendonitis, and usually have pain with quad sets and
straight leg raises. A-P tilt occurs when the distal one-third of the patella, or the inferior
pole of the patella, is not as clear to palpate as the superior one-third and superior
pole. These individuals often present with a dimple in their knees. Dynamically ante-
rior-posterior tilt can be determined during a maximal quadriceps contraction. If the
inferior pole disappears as a dimple, then the test is positive.
Also important is assessment of patellar mobility.47The test is performed with the
knee flexed 20?to 30?and the quadriceps relaxed. The test can be done either by
resting the patient’s knee over the examiner’s thigh or with a small pillow underneath
the patient’s knee. The patella is divided into 4 longitudinal quadrants, and the patella
is displaced medially and laterally with the examiner’s thumb and index finger to deter-
mine the amount of patellar tightness (Fig. 2). A lateral displacement of 3 quadrants
suggests an incompetent medial restraint. A lateral displacement of 4 quadrants
defines a dislocatable patella. A medial displacement of only 1 quadrant indicates
a tight lateral retinaculum and usually correlates with an abnormal passive patellar
tilt test. There is an association between patellar hypomobility and a tight ITB.48Medial
displacement of 3 or 4 quadrants suggests a more globally hypermobile patella
without tightness of the lateral restraints, and is often seen in patients with other stig-
mata of generalized ligamentous laxity. Hypermobility with lateral patellar glide is
correlated with laxity of the medial patellofemoral ligament or patellomeniscal liga-
ment, and is often noted in association with patellar subluxation. During these maneu-
vers, the examiner should look not only for patellar mobility but also for any associated
apprehension. When positive, this is a very specific test for patellar instability.
The ligamentous stability of both knees is assessed, particularly if there is a previous
history of knee injury. Both anterior and posterior cruciate deficiencies are associated
with peripatellar pain. Careful evaluation for meniscal pathology is noted by palpation
of the medial and lateral joint lines and McMurray testing. Joint-line tenderness can be
present with patellar pathology if there is an associated synovitis, and does not neces-
sarily indicate a meniscal injury or femorotibial arthritis.10Identification of a symptom-
atic synovial plica is equally important.
Hip range of motion, femoral acetabular impingement tests, and the Faber
maneuver should be thoroughly assessed to rule out referred pain to the knee from
Fig. 1. Example of patellar orientation with a lateral glide and/or tilt component.
Collado & Fredericson
intra-articular hip pathology. Internal rotation that exceeds external rotation is sugges-
tiveof femoral anteversion, and following this, soft tissue lengthshould be measured in
the hamstrings and hip flexors.
In the side-lying position, with the knee flexed at 20?, the lateral retinaculum can be
evaluated for excessive tightness by passively moving the patella in a medial direc-
tion.10The superficial retinacular fibers are believed to be tight if the femoral condyle
is not easily exposed. To test the deep fibers, the hand is placed on the middle of the
patella, the slack of any lateral glide is removed, and an anteroposterior pressure on
the medial border of the patella is applied. The lateral border of the patella should
move freely away from the femur, and on palpation the tension in the retinacular fibers
should be similar.
In this position ITB tightness can be evaluated with Ober’s test, and the gluteus
medius can be tested for strength deficits.
This position allows a more accurate assessment of rearfoot and forefoot alignment,
subtalar position, gastroc-soleus, and quadriceps muscle length.
Observational Gait Analysis
Observational gait analysis is one of the most important aspects of the examination—
the evaluation of dynamic function by observing the runner’s angle of gait while
walking and running. In more complicated cases, it may be helpful to use treadmill
running or even more sophisticated video taping to analyze the runner’s gait. The find-
ings of Thijs and colleagues49suggest that an excessive impact-shock during heel-
strike and at the propulsion phase of running may contribute to an increased risk of
developing PFP. Dierks and colleagues50have also shown that runners with PFPS
Fig. 2. Assessment of patellar mobility medially and laterally. (From Assessment of patellar
mobility medially and laterally. In: DeLee JC, Drez D, editors. Orthopaedic sports medicine,
vol. 2. Philadelphia (PA): W.B. Saunders Co; 1994. p. 1179; with permission.)
Patellofemoral Pain Syndrome
displayed weaker hip abductor muscles that were associated with an increase in hip
adduction during running. This relationship became more pronounced at the end of
The diagnosis of PFPS depends primarily on the history of the patient. Radiography is
an adjunct to history and physical examination. It is important to obtain radiographs in
the runner who has apparent PFP and does not demonstrate improvement after
several weeks of conservative treatment, or if there has been a history of recent
trauma or dislocation. Radiographic findings do not correlate well with clinical
complaints and frequently the injured side is difficult to differentiate from the uninjured
side.51When imaging is indicated, plain films of the knee (weight-bearing A-P, weight-
bearing lateral, and axial view) are useful to rule out other sources of anterior knee
pain, including bipartite patella, osteoarthritis, loose bodies, and occult fractures.
On standard A-P radiographs of the knee, one can identify accessory ossification
centers, degenerative joint disease, and other unrelated conditions, such as bone
The lateral view is most helpful for assessing patellar height. There is a plethora of
measurement techniques described in the literature for this purpose.10The Black-
burne and Peel53technique is easy to use and fairly reliable. This technique measures
the distance from the tibial plateau to the inferior pole, which should equal the length of
the patellar articular surface (Fig. 3). Normal values are approximately 1.0, with higher
values indicating patellar alta. The technique should be used with caution in adoles-
cent patients with skeletally immature proximal tibial epiphysis, certain patellar mor-
photypes with short articular surface, or when there is an abnormal slope of the
Fig. 3. Technique of Blackburn and Peel to assess patella alta on lateral radiographs of the
Collado & Fredericson
Axial or Merchant views of the patellofemoral joint are recommended with the knee
flexed 30?.10Some subluxation can be detected at 30?that could be missed at 45?.
This view allows evaluation of degenerative changes in the patellofemoral joint, osteo-
chondritis dissecans of the patella, patellar morphology, dysplasia of the trochlear
groove, and accessory ossification centers and ectopic calcifications in the retinac-
ulum. The position and orientation of the patella relative to the trochlear groove are
also evaluated with the sulcus angle, congruence angle, and the patellar tilt angle.
The sulcus angle measures the angle of the bony trochlea. With the knee flexed at
30?to 45?, the normal sulcus angle is approximately 140?.54Patellar instability is asso-
ciated with a more shallow trochlea, whereas too steep a trochlea is associated with
patellar pain without instability.55
The congruence angle is an index of medial/lateral subluxation of the patella within
the trochlear groove, similar to the physical examination assessment of patellar glide,
and in nondislocators the average angle is ?6?(standard deviation 11?) (Fig. 4A).42
Although this measurement has been widely used, drawing and bisecting an angle
can prove to be time-consuming and difficult with both plain radiographs and digital
radiography. A new axial linear displacement measurement presented in the study
by Urch and colleagues56provides a simple alternative method for evaluating the posi-
tion of the patella relative to the trochlear groove that is similar to that of the congru-
ence angle measurement (see Fig. 4B).
The patellar tilt angle is an index of the medial/lateral tilt of the plane of the patella
relative to the femur (Fig. 5). In the normal patellofemoral joint, the angle formed by the
lateral patellar facet and any horizontal line should open laterally, whereas in patients
with patellar subluxation the lines used to define the angle are parallel or open medi-
ally.57For this evaluation to be accurate and repeatable, the radiograph must be taken
with the foot vertical and the cassette maintained parallel to the ground. If the patient
exhibits external tibial torsion, the natural position of the feet is maintained. A tilt angle
between 0?and 5?is normal, 5?to 10?is borderline, and an angle greater than 10?is
considered abnormal. In a study by Grelsamer and colleagues58abnormal tilt was
detected in 85% of patients suffering from malalignment pain. The 15% of patients
whose malalignment was not detected exhibited either abnormal tilt that became
normal at 30?of flexion or malalignment that was not related to tilt (ie, patella alta or
Fig. 4. (A) Congruence angle. Line BO is the bisector of angle ABC. Line BX passes through
the lowest point on the median ridge of the patella. Angle OBX is the congruence angle. If
line BX falls to the medial side of line BO, the angle is expressed as negative degrees. If it
falls to the lateral side of line BO, it is expressed as positive degrees. (B) A reference line
is drawn by connecting the most anterior aspects of the lateral (A) and medial (C) trochlear
facets. A line is drawn perpendicularly from the depth of the sulcus (B) through the refer-
ence line (AC). Another line is drawn perpendicularly from the posterior aspect of the
patellar spine (X) through the reference line. To obtain the lateral displacement measure-
ment, the distance (d) between the 2 intersections is measured.
Patellofemoral Pain Syndrome
Because the patella usually becomes unstable as it nears extension, a lateralized
patella may not be detected by an axial-view radiograph that requires the knee be
flexed to at least 30?. Thus if surgery is contemplated and plain films are negative,
an MRI scan or computed tomography (CT) scan should be used to further evaluate
patellar tracking. Serial CT scans taken at knee flexion angles in the range of 0?to
30?can provide even greater information about the tracking of the patella in the troch-
lear groove. Measurements of sulcus angle, congruence angle, and patellar tilt angle
can be performed on CT scans just as they can be performed on conventional axial
radiographs, and may be helpful in understanding the patient with a difficult patellofe-
moral problem.59,60Three patterns of malalignment can be characterized by the
congruence angle and patellar tilt angle: lateral subluxation without lateral tilt, sublux-
ation with tilt, and tilt without subluxation.
Kinematic studies can also be accomplished with MRI61,62without exposure to radi-
ation. In addition to defining tracking abnormalities, MRI is particularly helpful in
assessing any degenerative joint changes, such as cartilage fissuring or thinning, sub-
chondral bone marrow edema, subchondral cysts, and other pathologic entities such
as synovial plica and patellar tendinitis. A new method using real-time MRI allows
measurement of patellofemoral joint motion during weight-bearing and non–weight-
bearing dynamic tasks (Fig. 6).63The aim is to define the cause of PFP using real-
time MRI in experimental research. Single-slice, spiral, real-time MR images of all
subjects performing knee flexion/extension were obtained in a 0.5-T open MRI
scanner (Fig. 7).
Fig. 5. Patellar tilt angle. The tilt angle is measured by a line joining the corners of the
patella and any horizontal line. (From Grelsamer RP, McConnell J. The patella. Gaithersburg
(MD): Aspen Publishers; 1998. Adapted from Grelsamer, RP, Bazos AN, Proctor CS. Radio-
graphic analysis of patellar tilt. J Bone Joint Surg Br. 1993 Sep ;75(5):822–4; with permission.)
Fig. 6. (A) Open-bore MRI scanner with subject performing a weight-bearing squat. (B) Side
view of scanner and backrest used to stabilize subjects as they moved in the scanner.
Subjects supported about 90% of their body weight.
Collado & Fredericson
The management of PFPS should include a comprehensive rehabilitation program.
Symptom control (activity modification, nonsteroidal anti-inflammatory drugs, ice or
cold application, patellar taping, or patellar bracing) is the first stage, then patients
should be classified by suspected contributing mechanisms: abnormal patellofemoral
joint mechanics, altered lower extremity alignment and/or motion, and overuse.7
Abnormal Patellofemoral Tracking and Alignment
Tightness of soft tissue structures
Soft tissue inflexibilities, particularly in the hamstrings and ITB, can also affect normal
patella excursion and should be addressed.7,64Soft tissue mobilization and stretching
techniques are also important to address tight retinaculum structures contributing to
abnormal patellar tracking.
Decreased patellar mobility
Patellar mobilization techniques should be performed if evidence of decreased
patellar mobility is noted. These techniques should be performed with care to prevent
excessive patellofemoral joint compression.
Quadriceps muscle strengthening
Restoration ofquadriceps strength and function has been demonstrated to be asignif-
icant contributing factor to recovery from patellofemoral symptoms.65However, the
mechanism by which strengthening improves PFP symptoms and functional ability
is not entirely clear.
Choosing the correct exercises to prescribe for an individual with PFP requires an
understanding of patellofemoral joint biomechanics. During open chain exercises,
the amount of quadriceps muscle force required to extend the knee steadily increases
as the knee moves from 90?to full knee extension.11In addition, the patellofemoral
joint contact area decreases as the knee extends, thereby increasing patellofemoral
joint stress. By contrast, during closed chain exercises the quadriceps muscle force
is minimal at full knee extension and therefore, patellofemoral joint stresses are
Fig. 7. (A) Real-time MR images of the patellofemoral (PF) joint of a pain-free control
subject during upright, weight-bearing knee extension. (B) Real-time MR images of the
PF joint of a subject with pain during upright, weight-bearing knee extension. Notice the
lateral position and rotation of the patella relative to the femur.
Patellofemoral Pain Syndrome
reduced.11Examples of closed chain exercises include lunges, wall slides, and leg
Both open and closed chain strengthening exercises should be performed so that
strengthening can be performed throughout a large arc of motion. Isometrics and
open kinetic chain exercises, such as knee extensions, are recommended if there is
significant quadriceps weakness or pain with weight bearing.66As quickly as possible,
however, patients should be progressed to the core of the rehabilitation program that
includes a closed kinetic chain quadriceps strengthening regimen, which is more
effective than isokinetic joint isolation and open chain exercises in improving
To improve eccentric control of the quadriceps, the rehabilitation program also
should include exercises performed while standing on one leg. In this position, the
lower abdominals and the gluteals work together to maintain a level pelvis, simulating
the activity of the stance phase ofgait.10Activation of the lower abdominal and oblique
muscles helps to decrease the anterior rotation of the pelvis and the resultant internal
rotation of the femur (step-down exercises: Fig. 8).
In addition, Souza and Powers69have demonstrated abnormal hip kinematics in
women with PFP that seem to be the result of diminished hip-muscle performance
rather than altered femoral structure. The results suggest that assessment of
Fig. 8. Step-down exercise. The pelvis should remain parallel with the floor; the hip, knee
and foot should be aligned, avoiding excessive hip adduction or internal rotation. The
goal is to activate the gluteal and quadricep muscles by maintaining erect posture, and
avoiding forward body lean as one steps down. Start on a step only a few inches off the
ground and increase the distance as stability improves.
Collado & Fredericson
hip-muscle performance should be considered in the evaluation and treatment of
patellofemoral joint dysfunction.
Role of the Vastus Medialis Obliquus
Isolated recruitment of the VMO, proposed by many therapists, has not been proven
to occur with exercises that are commonly prescribed for the treatment of PFP. One
electromyographic study examined 9 commonly used strengthening exercises and
found that the activity of the VMO was not significantly greater than that of the vastus
lateralis, the vastus intermedius, and the vastus medialis longus, suggesting that iso-
lated recruitment or strengthening ofthe VMOthrough selected exercises isunrealistic
and probably translates into a general quadriceps muscle strengthening effect.7,70
Correcting abnormal patella posture using the Grelsamer and McConnell10taping
technique is one way of optimizing the entry of the patella into the trochlea, and is
a transitional step in the rehabilitation process in those patients who are unable to
perform strengthening exercises due to their pain. Taping the patella of symptomatic
individuals during stair ascent and descent exercises can diminish symptoms by 50%.
In addition, it has been shown to increase quadriceps activity and permit increased
loading of the knee joint.11
Patients with patellar pain may report decreased pain from wearing properly fitted
dynamic patellar stabilization braces. Powers and colleagues71found that 50% of
subjects experienced an improvement in symptoms with the use of patellar stabilizing
braces. Further study64evaluating the same brace, however, did not find it was able to
consistently correct patellar tracking patterns as measured quantitatively by kinematic
MRI. However, a more recent study by Draper and colleagues63evaluated women
with PFP during dynamic, weight-bearing knee extension, and assessed the effects
of knee braces on patellofemoral motion with real-time magnetic resonance images
of the patellofemoral joints of 36 women volunteers. The results suggest that different
subsets of women with PFP exist and that bracing seems to have a mechanical effect
in only one group compared with the controls: those with abnormal kinematics. With
application of the brace, the lateral translation and tilt of the patella were reduced but
were not restored to normal. A simple patellar sleeve provided more mild correction of
lateral translation of the patella but did not alter patellar tilt.
Lower Kinetic Chain Problems
Subtalar joint pronation
Excessive pronation whether secondary to abnormal compensation as a result of
abnormal structure in the trunk or lower extremity, or secondary to pathology in the
foot itself, should also be addressed. Excessive pronation can increase the Q-angle,
causing a dynamic abduction moment at the knee and a consequent increase in the
laterally directed force on the patella. It should be noted that not all patients with
excessive pronation need an orthotic. In fact, a recent study72showed that although
foot orthoses are superior to flat inserts according to participants’ overall perception,
they are similar to physiotherapy and do not improve outcomes when added to phys-
iotherapy in the short-term management of PFP.
In those runners who seem to benefit from an orthotic, a custom-molded orthotic for
maximal biomechanical control is recommended. Most over-the-counter orthotic
devices have been designed to address primary control of rearfoot motion.
Patellofemoral Pain Syndrome
Three-dimensional studies, however, have shown that forefoot stability may play an
integral role in rearfoot stability.73These studies indicate that instability in the forefoot
at push-off may create instability in the rearfoot. For this reason an orthotic that
extends all the way to the sulcus or web-space of the toes is considered crucial for
control of forefoot instability in runners.10
Hip internal rotation
The functional significance of an internally rotated femur is that the trochlear groove
can rotate beneath the patella, placing the patella in a fairly lateral position. If it is
observed that the femur collapses into internal rotation during gait, and this motion
seems to originate from the pelvis, then strengthening of the external rotators
including gluteus maximus, gluteus medius, and the deep rotators may be indicated.
If the femur remains in a constant state of internal rotation during the gait cycle (rather
than collapsing inward), femoral anteversion should be suspected. As femoral ante-
version is a fixed bony deformity, little can be done from a nonsurgical standpoint
to correct this abnormality.
The restoration of normal gait function is essential to the overall treatment plan.
Preliminary work from Noehren and Davis74suggests that gait retraining with real-
time visual feedback can alter faulty mechanics, such as increased hip adduction
and internal rotation and pelvic drop. Research in cadavers has shown that decreasing
hip adduction or internal rotation decreases the compression on the lateral facet of the
patella.75,76In addition, decreased pelvic drop reduces the strain on the ITB, which in
turn reduces its lateral force on the patella and allows more normal alignment.77
The lack of significant findings on physical examination (ie, normal patellar mechanics,
normal lower extremity function) suggests that the source of PFP symptoms may be
related to overuse. This overuse is often seen in an athletic population. The treatment
program should focus on relative rest with activity modification. The training program
also should be evaluated for obvious errors, including increasing exercise intensity too
quickly, inadequate time for recovery, and excessive hill work.
Most runners with PFP and malalignment, including those with minor instability
problems, will respond to nonoperative treatment. The lateral retinacular release is
perhaps the most frequently performed surgical procedure, but is only indicated if
a major contributor to malalignment is a tight lateral retinaculum causing isolated
patellar tilt.47A common complication of lateral retinacular release is an incomplete
release, which most commonly is the failure to release the patellar tibial portion of
the lateral retinaculum along with the patellofemoral portion. By contrast, an over-
zealous release can lead to medial subluxation or dislocation. A lateral release will
not correct more global patellar hypermobility or an abnormal anatomic Q-angle. In
these cases, more extensive realignment surgery may be contemplated but is unlikely
to permit a return to serious running.14,42
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