Patella Instability

Transcription

Patella Instability

280
Bulletin of the NYU Hospital for Joint Diseases 2007;65(4):280-93
Patella Instability
Reuven Minkowitz, M.D., Chris Inzerillo, M.D., and Orrin H. Sherman, M.D.
P
atellofemoral instability is a common cause of knee
pain and disability. Patellar instability can be defined
in different ways,1 the first as a clinical entity or diagnosis of a traumatic dislocation. It can also describe a sign
on physical examination, signifying the ability of the patella
to be translated out of the trochlear groove of the femur in
a passive manner. Furthermore, patellofemoral instability
can be a symptom, typically if the knee “gives-way” as a
result of the patella slipping out of the trochlear groove. The
relationships between the symptoms, injuries, and diseases
of the patellofemoral joint are particularly confusing.1,2 Addressing the specifics of anatomy, biomechanics, history,
physical examination, and radiographic interpretation can
shed important light on the treatment options of acute and
recurrent patellar dislocation and subluxations.
Bony Anatomy
The patella is the largest sesamoid bone in the body, and
resides within the complex of the quadriceps and patellar
tendons. The patella assists in coordinating the forces of
these tendons. The patella functions both as a lever and a
pulley. As a lever, the patella magnifies the force exerted by
the quadriceps on knee extension. As a pulley, the patella
redirects the quadriceps force as it undergoes normal lateral
Reuven Minkowitz, M.D., was a Chief Resident in the NYU Hospital for Joint Diseases Department of Orthopaedic Surgery, New
York, New York. Chris Inzerillo, M.D., was a Fellow in the Sports
Medicine Service, NYU Hospital for Joint Diseases Department
of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New
York, New York. Orrin H. Sherman, M.D., is Associate Professor
of Orthopaedic Surgery, New York University School of Medicine,
and Chief of the Division of Sports Medicine, NYU Hospital for
Joint Diseases Department of Orthopedic Surgery, NYU Medical
Center, New York, New York.
Correspondence: Orrin Sherman, M.D., Suite 8U, New York
University Medical Center, 530 First Avenue, New York, New
York 10016.
tracking during flexion. The lateral trochlear facet, which is
normally 1 cm higher than the medial, provides a buttress to
lateral patellar subluxation and helps maintain the patella’s
centered position in the trochlea (Fig. 1).
Soft Tissue Anatomy
Passive stabilizers are present as uniform restraints of
abnormal joint motion. In the patellofemoral joint, these
structures include the patellar ligament or patellar retinacular complexes, which include the patellofemoral and
patellotibial ligaments. Warren and Marshall3 published a
thorough description of the medial aspect of the knee, basing their description on the dissection of 154 fresh-frozen
cadavers. They considered the medial patellofemoral ligament (MPFL), along with the superficial medial collateral
ligament (MCL), to be part of layer 2, which is an extracapsular structure.
The MPFL is a continuation of the deep retinacular surface of the vastus medialis obliques (VMO) muscle fibers.
The patellofemoral ligament extends from the superior medial border of the patella (approximately at the two o’clock
position on a right knee) and attaches firmly to bone just
anterior to the MCL, on the medial epicondyle (Fig. 2). Some
superficial fibers of the MPFL can be seen to cross over the
epicondyle and blend into the soft tissue posterior to the
medial epicondyle. The medial epicondyle is the attachment
site for the MCL and the MPFL. The size and thickness of
the ligament varies considerably among individuals, but it
is relatively constant within a given person.4,5
The quadriceps functions as a dynamic stabilizer of the
patella, while the MPFL acts as a static checkrein to resist
lateral translation of the patella. Conlan and colleagues6
reported that the MPFL contributes an average of 53% of the
restraining force against lateral patellar displacement. Desio
and associates5 reported that the MPFL contributes 60%
(range, 41% to 80%) of the total restraining force against
Minkowits R, Inzerillo C, Sherman O. Patella instability. Bull NYU Hosp Jt Dis. 2007;65(4):280-93.
Figure 1 Lateral tilt of the patella on an axial view being buttressed
by the lateral trochlea.
lateral patellar displacement. The patellomeniscal ligament
and associated retinacular fibers were also found to be important medial stabilizers, contributing an average of 22% of
the total restraining force. The remaining transverse fibers of
the medial patellotibial band and ligament were found to be
less important restraints to lateral subluxation of the patella.
Anatomical studies by Lieb and Berry7 have shown
the contributions of the various portions of the quadriceps
muscle to knee extension. They demonstrated that the vastus
lateralis pulls laterally to the frontal plane of the femur at an
angle of 7° to 10°. The vastus medialis is divided into two
parts, the vastus medialis longus (with its muscle fibers pulling at 15° to 18° medially) and the vastus medialis obliques
(with its muscle fibers pulling at a relatively horizontal 50°
to 55° medially). The primary function of the VMO muscle
is to stabilize the patella against the lateral pull of the vastus
lateralis, making the VMO the dynamic stabilizer of the
patella.
Biomechanics
Stress encountered by the patellofemoral joint can be mathematically defined as the sum of joint reactive force (JRF)
divided over the surface area of force distribution. From 0°
to 60°, the surface area of the patella that comes in contact
with the femur enlarges as the knee is increasingly flexed.
Beyond 60° of flexion, the studies have been inconclusive.
With greater patellofemoral joint loads, the contact surface
area is larger between the patella and femur. The location of
contact for the patella and femur varies with different degrees
of flexion and joint load. At 0°, no contact occurs. At early
flexion, the distal patella contacts the proximal trochlea. At
90°, the superior aspect of the patella contacts the femur as
the patella glides further inferiorly. When flexion is greater
than 90°, the contact area returns to the center of the patella;
and when the knee is fully flexed, the inner border of the
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Figure 2 Image of the medial patellofemoral ligament (black oval)
femoral attachment. (From Nomura E. Classification of lesions
of the medial patello-femoral ligament in patellar dislocation. Int
Orthop (SICOT). 1999;23:262. Copyright © 1999 Springer-Verlag,
with permission of Springer Science).
medial femoral condyle is in contact with the small vertical
ridge of the medial facet.8
Lateral tracking of the patella leads to decreased efficiency
of the quadriceps extensor mechanism and increased patellofemoral joint stress. A lateral patellar subluxation of only
a few millimeters results in decreased contact surface area
between the patellar and trochlear surfaces. Lateral tracking
pushes the lateral facet closer to the lateral side of the trochlear
groove, thus, creating a greater distance between the medial
facet and the medial side of the trochlear groove. The total
JRF, distributed over both patellar facets, is now completely
transmitted through the lateral patellar facet, increasing lateral
facet stress. The result can be pain and chondromalacia. A
2-cm elevation of the tibial tubercle has demonstrated a 50%
reduction of the JRF when the knee is flexed to 45°.9
“Q Angle”
Both static and dynamic forces tend to displace the patella
laterally. Brattström10 first described the “Q angle” (Fig.
3) as an angle formed by the line of pull of the quadriceps
mechanism and that of the patellar tendon as they intersect at
the center of the patella. Clinically, this angle is represented
by the intersection of a line drawn from the anterosuperior
iliac spine to the center of the patella, with a second line
drawn from the center of the tibial tuberosity to the center of
the patella. For this measurement to be accurate, the patella
must be centered on the trochlea. In males, the Q angle,
normally, is about 8° to 10°; in females, the normal angle is
15°, plus or minus 5°. This valgus angle gives a lateral force
vector to the patellofemoral joint as the knee is extended.
The factors that can increase this Q angle are genu valgum,
increased femoral anteversion, external tibial torsion, or a
laterally positioned tibial tuberosity. The Q angle also can
be increased in a dynamic mode by internally rotating the
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30 and 59 years of age to 1.5 to 2.0 per 100,000. This study
did find that differences in the prevalence of injury based
on gender showed a higher average annual risk for females
in the second decade, but a higher risk for males in the third
decade.
Mechanism
Two mechanisms of acute lateral patellar dislocations have
been proposed.14 An indirect injury and a direct blow. The
indirect mechanism is more common and involves the combination of a strong quadriceps contraction, a flexed and
valgus knee position, and an internally rotated femur on an
externally rotated tibia. An example of this mechanism is a
baseball batter’s hind leg when he misses while swinging for
a pitched ball. Patients with dislocations frequently have one
or more predisposing risk factors (mentioned below). Medial
dislocation and subluxation are much less common, usually
iatrogenic, and are beyond the scope of this review.
Figure 3 Q angle. (From Insall J, Falvo KA, Wise DW. Chondromalacia patellae. A prospective study. J Bone J Surg Am. 1976;58:1,
with permission)
femur on a fixed tibia, as in a “cutting” maneuver. Any of
these factors that increase the Q angle can be a contributing
element in recurrent patellar instability.
Acute Patella Dislocation
Epidemiology
Nietosvaara and coworkers11 studied the annual incidence
of acute patellar dislocations in Finnish children younger
than 16 years of age. The investigators found an annual
incidence of 43 per 100,000 children. Over a 2-year period,
a total of 72 children demonstrated patellar dislocations. Of
these, 28 (39%) of the knees had associated osteochondral
fractures. Of the 28 osteochondral fractures, 15 had capsular avulsions of the medial patellar margin, and a different
15 had intra-articular fragments from the patella or lateral
femoral condyle.
The true incidence of acute patellar dislocation in the adult
is difficult to discern from the literature. This is primarily
due to the lack of population-based prospective studies and
a prevalence of retrospective evaluations and case series.12
The largest North American study to date is that by Atkin
and colleagues in 2000.13 They prospectively studied a group
of Kaiser Permanente patients from the greater San Diego
area of Southern California. The average plan enrollment
included more than 360,000 patients, with approximately
1000 of these patients referred each year for evaluation of
knee injury. During the three-year study period, 74 patients
from this group were diagnosed with primary patellar dislocation. Broken down by age, at 31 per 100,000, the highest
annual risk was noted for patients in the second decade.
The average annual risk dropped to 11 per 100,000 in the
third decade and dropped still further for patients between
Pathology (Figs. 4 and 5)
Acute lateral patellar dislocation has been associated with
medial retinacular injury. As described in an article by Elias
and White,15 Marangi and associates reported on a consecutive series of 74 cases of acute lateral patellar dislocation
using MRI. Evidence of medial retinacular injury was seen in
75% (56) of patients. In 44% of knees, complete retinacular
disruption was noted near the patellar attachment.
Burks and coworkers16 reported a simulation of patellar
dislocation using a cadaveric model. They compared MRI
and gross anatomic findings in 10 fresh-frozen cadaveric
knees. After MRI imaging, they dissected the medial structures to determine where the ligamentous injury occurred.
The MPFL was injured in eight out of the 10 knees. Although
the location can vary, the most frequent site found was the
femoral attachment of the MPFL.
In 2003, Nomura17 studied 39 consecutive knees with
initial lateral patellar dislocation. Articular cartilage injuries
were examined using arthroscopy or macroscopic observation. Thirty-seven knees (95%) had articular cartilage
injuries of the patellofemoral joint and two knees (5%) had
no cartilage injury. In all 37 knees (95%), articular cartilage
injuries were observed in the patella, showing that articular
cartilage injuries, especially of the patella, seem to be common occurrences after acute patellar dislocation.
Physical Exam
Acute dislocation of the patella in the adult requires disruption of the medial patellar restraints. Swelling associated with the acute injury is often rapid, and a significant
hemarthrosis frequently develops, especially if there is an
associated osteochondral fracture. This swelling may mask
a persistent lateral subluxation of the patella within the
trochlea and may be noted on physical examination. As well,
loose chondral or bony fragments may be palpable in the
joint, and attached osteochondral fragments may be felt in
A
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B
Figure 5 Patellar dislocation. A, Anteroposterior view. B, Sunrise
view.
Figure 4 Axial gradient-echo image (TR/TE, 450/10, Flip angle
30°) of complete retinacular disruption near the patellar insertion
(white arrow). (From Arendt EA. Current concepts of lateral patella
dislocation. Clin Sports Med. 2002;21(3):509. Copyright © 2002,
WB Saunders, with permission from Elsevier.)
the medial parapatellar retinaculum. A thorough palpation
of the knee should be performed to detect focal areas of
maximum tenderness that suggest soft tissue injury.
The examiner may find a palpable defect at the medial
patellar margin, tenderness along the course of the MPFL
and the other medial retinacular ligaments, or tenderness
near the medial femoral epicondyle at the MPFL insertion
site. Tenderness at the medial femoral condyle may suggest
an injury to the MCL of the knee. If significant disruption
of the VMO insertion has occurred, there may be a palpable
defect at its distal insertion, as well as a visible change in
its symmetry. A positive apprehension test at 30° of flexion
is the classically described examination finding (Fig. 6).
With or without apprehension, the physician may be able to
demonstrate increased medial retinacular laxity that is not
symmetrical with the contralateral knee.12
Management
Acute dislocations of the patella usually are managed by
closed methods.18 The patella is almost always dislocated
laterally; extension of the flexed knee with pressure applied
to the lateral margin of the patella results in reduction. After
an acute dislocation, the knee is immobilized in a commercial immobilizer with a Jones-type compressive dressing,
and crutches are used for ambulation. If a large hemarthrosis
is present, causing significant pain and tightness, aspiration
under sterile conditions is indicated before the extremity is
immobilized.
Early short arc (0° to 45°) range of motion is begun in
order to prevent arthrofibrosis and to promote the formation
of strong collagen along the lines of stress. Roentgenograms (Fig. 5) should be carefully evaluated to be certain
that no osteochondral fragments are displaced within the
joint. The patient should be warned of the possibility of
future episodes of recurrent patellar subluxation or dislocation.
Rehabilitation
Quadriceps setting exercises and three sets of 15 to 20
straight leg raises are done four or five times a day during the
acute period. Ice is applied for 20 minutes every 2 to 3 hours
to reduce swelling. The knee immobilizer and compressive
wrap are discontinued approximately 2 to 3 weeks after the
acute reaction has resolved. The crutches are discontinued
when the patient is able to do straight leg raises with a 5-lb
ankle weight and is able to walk with a near normal gait.
Rehabilitation should emphasize closed chain exercises,
including wall sets, in which the patient squats to approximately 40° while keeping his back flat against the wall for
15 to 20 seconds, for a total of 10 to 15 repetitions. Side
and forward step-up exercises using a 6 to 8 inch platform
should be performed after the acute inflammatory reaction
has resolved. These are followed by short arc leg presses
and endurance-type strengthening using a stationary bike
and StairMaster® or similar stepping machine. The patient
can return to sports activity when quadriceps and hamstring
muscle strength is normal and sport-specific agility has
been regained. Generally, a patellar stabilizing brace is
prescribed for the first 2 or 3 months after return to athletic
activities.19
McConnell taping techniques or patellar stabilizing
braces have both been commonly used during rehabilitation
and when the athlete first returns to sports participation.13
Although these techniques and braces may serve a protective or proprioceptive function, no outcome studies in the
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literature prove that they reduce the rate of redislocation.20
Nonoperative Outcomes
Redislocation or recurrent subluxation rates after nonoperative
treatment have been reported to be as high as 48%.21 Cofield
and Bryan22 reported that in patients considered athletes, at
an average of 5 years after injury, 52% remained unable to
return to vigorous sports. Even in more recent literature, there
is significant variability among both patient population and
treatment methods. Garth and Pomphrey19 reported on an
aggressive, modern rehabilitation protocol in 58 athletically
active patients. They began a functional rehabilitation program without antecedent immobilization. At the initial visit,
patients were instructed in isometric and isotonic quadriceps
strengthening and active and active-assisted range of motion
exercises with a stationary bicycle were begun. Patients wore
a lateral buttressing knee sleeve, initially for ambulation, until
muscle strength was documented to be at least 80% that of
the opposite extremity. They reported a return to full activity, with resolution of all significant tenderness, and a return
of full isotonic quadriceps strength after, generally, 3 to 8
weeks. Sixty-eight percent of the patients who were treated
after acute patellar dislocation without previous symptoms
had good or excellent results, with 30% experiencing impairment in athletics.
In 2000, Atkin and colleagues13 studied the early recovery
phase (at 6 months); almost 60% of patients continued to
have limitations with strenuous activities. These results show
that, unfortunately, a large percentage of patients are left with
recurring problems of patellofemoral pain and instability.
Operative Treatment
Operative indications for treatment of an initial dislocation
of the patella in the adult continue to be controversial.23 In
the current literature, the most commonly cited indications
for operative treatment in the adult without predisposing
malalignment include the following: patients with evidence
of osteochondral loose bodies, patients with large palpable
defects in the VMO insertion, those with obvious tears of the
medial peripatellar retinaculum, and those with persistent
asymmetrical subluxation. Elite athletes and, more recently,
patients thought to have an avulsion of the MPFL are also
operative candidates.24 Use of a realignment procedure
assumes that there was an underlying, predisposing malalignment (discussed below). Lateral release is performed
if there is an associated tilt. Repair and reconstruction are
appropriate if there is an identifiable soft tissue injury. Arthroscopy is usually adequate for a thorough diagnosis and
for treating osteochondral injuries and may be used alone
or in combination with other procedures.
Generally, surgical repair of acute patellar dislocation is
best performed within 2 to 3 weeks of injury in order to avoid
operating through early scar tissue formation. A diagnostic
arthroscopy is utilized to inspect the joint for evidence of
soft tissue or capsular injury and to repair or remove osteo-
chondral or chondral loose bodies. The MPFL is external
to the synovial layer and, usually, is not visible directly by
arthroscopy. Repair of MPFL avulsions or VMO insertional
tears is performed through a 4-cm to 6-cm incision just anterior to the medial femoral epicondyle, at the distal edge
of the VMO muscle belly. The MPFL is identified confluent
with the deep fascia of the VMO and can be demonstrated,
usually, to have a direct connection to the superior medial
border of the patella. In most of these cases, the MPFL can
be found to have avulsed off the femur and may be repaired
directly by adhering to bone with suture anchors. Complete
intrasubstance tears are repaired with permanent suture.
Overlying retinacular tears are then repaired with absorbable
suture. If the retinaculum and capsule are disrupted near
the patella, this is usually clear from the examination and
MRI, and repair is performed through a medial parapatellar
incision. In patients without a substantial MPFL, repair can
be supplemented with a hamstring graft from the patella to
the femoral attachment site of the MPFL. The retinaculum
and VMO are also slightly imbricated in the repair.
Postoperative treatment consists of progressive weightbearing as tolerated in a postoperative brace, followed by
early range of motion and quadriceps strengthening exercises. Regaining flexion can be difficult, even if range of
motion is started early. Occasionally, manipulation under
anesthesia is required. The athlete is allowed to return to
sport-specific training when he or she has regained full,
nontender functional range of motion and demonstrates muscular strength equal to 80% to 90% that of the contralateral
limb. Return to play follows a demonstration of adequate
recovery during functional testing.12,14
Operative Outcomes
In recent reports of operative treatment, rates of recurrence
have ranged from 0% to 17%.23-28 At first glance, these
results appear superior to those attained with nonoperative
treatment, but few randomized, truly prospective studies
have been done. Follow-up is generally limited, the numbers
of patients are small, and the operative methods as well as
results are varied.
Vainionpaa and colleagues26 reported the results of open
repair in 55 patients followed prospectively after their first
patellar dislocation. At 2 years, subjective results were good
or excellent in 80%, with a redislocation rate of 9%.
Sallay and associates27 reported on 16 patients and found
94% to have had the MPFL avulsed from the femur. Suture
repair was performed and, with an average 3-year follow-up,
no recurrences were seen; 58% of patients returned to their
previous sport.
Nikku and Nietosvaara,28 in 1997, reported on the results
of a prospective randomized trial of nonoperative versus
operative treatments in 176 consecutive patients, all of whom
had sustained primary patellar dislocation. In the group
randomized to operative treatment, patients had individually
adjusted procedures that consisted of a mixture of medial
retinacular repair or duplication, adductor magnus tenodesis,
and lateral release. In this report of 2-year results, recurrent
instability episodes were equivalent, and both function and
subjective results were better in the nonoperative group. The
investigators felt surgery gave no additional benefit, and it
remains to be seen whether long-term follow-up will change
their findings.
Summary
In summary, the literature suggests that two main groups
of patients suffer acute dislocation of the patella, those
with and those without significant predisposition. In young
athletically active adults without previous history of subluxation, who sustain an acute patellar dislocation, the surgeon
can focus on addressing specific pathology. It is clear that
some patients do well with nonoperative treatment. There
is, however, significant enough incidence of occult intra-articular injury that arthroscopic evaluation should be strongly
considered in most patients.2,28,29 In addition, repairing the
main medial stabilizer to the patella, the MPFL, may restore
patellar stability.
Owing to the lack of long-term, prospective study results,
however, it continues to be unclear as to whether operative
treatment consistently provides significantly improved
outcomes, reliably preventing recurrent subluxation or
dislocation. Guidelines are as follows:
•Since it is not possible to predict who will do well
with nonoperative treatment, operative treatment
should be avoided unless there is a displaced articular
surface fragment or any acquired lateral displacement of the patella that is unreduced.
•Only do an acute release in patients who have a very
tight lateral retinaculum associated with imaging
evidence of tilt.
•Avoid excessive medial imbrication, which may
overload the medial facet and predispose the patient
to medial facet arthrosis.
•Tear of the MPFL is not always at the adductor
tubercle and is frequently multifocal. Obtain preoperative MRI image if acute surgery is planned
Recurrent Patellofemoral Instability
Risk Factors
The “typical” physical characteristics of the patellar dislocator have been characterized as an adolescent female with
ligamentous laxity and multiple developmental anomalies,
including trochlear dysplasia, patella alta, and rotational and
angular bony alignment.14 Trochlea dysplasia and patella
alta reduce the containment of the patella within the femoral
trochlea at any given angle. This contributes directly to the
risk of recurrent patellar dislocation by reducing the relative
height of the trochlear buttress to the patella.
Dysplasia of the lateral femoral condyle can be a contributing factor. Patients with a hypoplastic lateral femoral
condyle have lost a bony support that prevents lateral sub-
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luxation of the patella from the intercondylar groove. Amis
and Dejour30 reported that simulation of a shallow trochlea
in cadaver knees dramatically increases mediolateral patellar
mobility. Additional factors that may contribute to recurrent
dislocation of the patella include a change in orientation of
the fibers of the vastus medialis muscle, atrophy of the vastus
medialis, hypertrophy of the vastus lateralis, and generalized
ligamentous laxity.
In 2004, Fithian and coworkers31 prospectively followed
189 patients who had a patella dislocation. They found
the risk was highest among females 10 to 17 years of age.
Patients presenting with a prior history of instability were
more likely to be female and were older (median age, 21
years) than first-time dislocators. Fewer first-time dislocators (17%) had episodes of instability during follow-up than
patients with a previous history of instability (49%). After
adjusting for demographics, patients with a prior history had
a seven-fold increase in probability for subsequent instability
episodes during follow-up than first time dislocators.
Clinical Features
History
In patients with recurrent dislocation or subluxation of the
patella, an accurate history is still one of the most important
diagnostic tools. Patients who have recurrent dislocation frequently report diffuse pain about the knee that is aggravated
by going up and down stairs or climbing hills. Usually, the
pain is located anterior in the knee and often is described as an
aching pain with intermittent episodes of sharp, severe pain. A
feeling of insecurity in the knee and occasionally of “giving
way” of the knee or the knee “going out” may be present.
Physical Exam
Patellar crepitation and swelling of the knee are common.
Physical findings include the previously cited factors that
contribute to the Q angle. In addition, patellofemoral crepitus
may be palpable, and an effusion may be present. Several
testing maneuvers are helpful in evaluating patients with recurrent patellar dislocation or subluxation. The patellar grind
test is done by applying pressure to the patella and manually
displacing it medially, laterally, superiorly, and inferiorly in
the trochlear groove. This test reproduces anterior knee pain
when a patellofemoral pathological condition is present.
In the “apprehension test,” (Fig. 6) the examiner holds the
relaxed knee in 20° to 30° of flexion and manually subluxes
the patella laterally. When the test is positive, the patient
suddenly complains of pain and resists any further lateral
motion of the patella.
The same controlled maneuver is done while slowly flexing and extending the patient’s knee. The examiner visually
divides the patella into four quadrants and passively moves
the patella medially and then laterally, measuring the amount
of excursion in the patellar quadrants (Fig. 7). This is done
with the knee at 0° and at 20° of flexion. Normally, passive
patellar glide is one but not more then two quadrants, both
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Figure 6 “Apprehension test.” (From Walsh WM: Recurrent dislocation of the knee in the adult. In: DeLee J III, Drez D IV, Miller MD
(eds): DeLee & Drez’s Orthopaedic Sports Medicine: Principles
and Practice. (2nd ed). Philadelphia: Saunders, 2003, p. 1715.
Copyright © 2003 Saunders, with permission from Elsevier.)
Figure 8 “Patellar tilt test.” In this left knee, the patella can be
tilted so that the lateral edge is well anterior to the medial edge.
(From Walsh WM: Recurrent dislocation of the knee in the adult.
In: DeLee J III, Drez D IV, Miller MD (eds): DeLee & Drez’s
Orthopaedic Sports Medicine: Principles and Practice. (2nd ed).
Philadelphia: Saunders, 2003, p. 1721. Copyright © 2003 Saunders,
with permission from Elsevier.)
Figure 7 Depiction of two quadrants of lateral translation of
the patella. (From Arendt EA. Current concepts of lateral patella
dislocation. Clin Sports Med. 2002;21(3):504. Copyright © 2002
WB Saunders, with permission from Elsevier.)
medially and laterally. Excessive lateral retinacular tightness
is indicated by limited medial passive patellar glide and by
a negative patellar tilt.
The patellar tilt test is done with the knee in extension (Fig.
8). The examiner’s fingers are placed along the medial side
of the patella and the thumb on the lateral aspect. Inability to
raise the lateral facet to the horizontal plane or slightly past
indicates excessive lateral retinacular tightness.
Dynamic patellar tracking is evaluated with the examiner
standing in front of the seated patient while the patient slowly
extends the knee. A positive J sign, lateral subluxation of
the patella as the knee approaches full extension, indicates
some degree of maltracking. Active patellar tracking also
should be examined with the knee in the extended relaxed
position. The quadriceps is tightened, and motion of the
Figure 9 A, Knee in flexion. B and C, Positive J sign, or lateral
subluxation of the patella as the knee approaches full extension.
(From Walsh WM: Recurrent dislocation of the knee in the adult.
In: DeLee J III, Drez D IV, Miller MD (eds): DeLee & Drez’s
Orthopaedic Sports Medicine: Principles and Practice. (2nd ed).
Philadelphia: Saunders, 2003, p. 1718. Copyright © 2003 Saunders,
with permission from Elsevier.)
patella is examined. Normally, the patella should move more
superiorly than laterally (Fig. 9)
Tenderness may be palpated at the quadriceps or patellar tendon insertion on the patella or at the medial or lateral
retinaculum; defects in the retinaculum also may be palpable.
Tenderness along the medial or lateral facets of the patella
may be noted on direct palpation of the facet as the patella
is manually subluxed and rotated to expose these articular
surfaces. This patellar tenderness may indicate a pathological
condition of the articular cartilage.
Thigh circumferences, measured proximal to the patella,
often show quadriceps atrophy on the involved side. With the
patient sitting and the knees flexed 90°, a lateral or superior
position of the patella sometimes can be seen. After careful
examination of the uninvolved and injured knees, other joints
should be examined for hyperlaxity. Hyperextension of the
knees or elbows past 10°, ability to touch the thumb passively
to the forearm, hyperextension of the metacarpophalangeal
joint of the index finger, and multidirectional laxity of the
shoulder joint all are indicative of generalized ligamentous
laxity. Stanitski32 found that patients with generalized ligamentous laxity did worse than patients without ligamentous
laxity.
Imaging
Radiographic Exam
The AP roentgenogram is of limited use regarding patellofemoral problems. This view may reveal a bipartite patella,
which is a variant of normal. Occasionally, an osteochondral
Figure 10 Assessment of patella alta (technique of Insall and
Salvati). The ratio of the longest diagonal of the patella to the
length of the patellar tendon should be 1.0 ± 20%. (From Walsh
WM: Recurrent dislocation of the knee in the adult. In: DeLee J
III, Drez D IV, Miller MD (eds): DeLee & Drez’s Orthopaedic
Sports Medicine: Principles and Practice. (2nd ed). Philadelphia:
Saunders, 2003, p. 1725. Copyright © 2003 Saunders, with permission from Elsevier.)
287
fracture of the medial patellar edge can be seen. Loose bodies
or osteochondral fractures occasionally are present.
The lateral view yields more commonly used information relating to patella alta or excessively low (patella infra
or baja) patella. The method of Blumensaat is of historical
significance only33 and related the position of the patella to
a line projected along the roof of the intercondylar notch.
Investigators such as Insall and Salvati have found the Blumensaat line to be an inexact index of patella alta.
In a review of 114 lateral roentgenograms of normal knees,
Insall and colleagues33 found that the length of the patellar
tendon (LT) and the diagonal length of the patella (LP) had
a ratio of 1.0, with less than 20% variation. They concluded
that patella alta is likely to be present if LT exceeds LP by
more than 20% (ratio of 1.2 or more) (Fig. 10).
The most widely used axial views are those described
by Merchant and associates34 and Laurin and coworkers.35
In the Merchant technique, the patellofemoral joint is
viewed with knees flexed to 45°. The radiographic tube
is positioned above the knee, with the radiographic plate
positioned distal to the knee. These investigators originally described the “congruence angle” (Fig. 11) and the
technique of measuring the angle. The average congruence
angle in 100 normal subjects was found to be 6°, with a
standard deviation of 11°. This means that a congruence
angle of greater than +16° is abnormal at the 95th percentile. Aglietti and colleagues36 are credited with providing
a more accurate definition of the congruence angle. Their
study found an average congruence angle of 8°, with a
Figure 11 Congruence angle of Merchant. 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. (From Walsh WM: Recurrent dislocation of the knee in the adult. In: DeLee J III, Drez D IV, Miller MD
288
A
B
Figure 12 Measurement of lateral patellofemoral angle. Line YY
is drawn across the most anterior portions of the femoral trochlea
in the axial view of this left knee. Line XX follows the slope of the
lateral patellar facet. A, Demonstration of a normal angle in which
the angle opens laterally. B, Demonstration of an abnormal angle
with the angle open medially. (From Walsh WM: Recurrent dislocation of the knee in the adult. In: DeLee J III, Drez D IV, Miller MD
standard deviation of 6°.
Laurin and associates35 described a technique in which
the knees are flexed to 20° to 30°. The radiographic tube
is positioned between the ankles, with the cassette held
proximal to the knees by the patient. On this view, these
authors defined a “lateral patellofemoral angle” (Fig. 12).
They indicated that, normally, this angle is open laterally,
whereas in patients with patellar tilt, the lines used to define
the angle are parallel or open medially.
Teitge and coworkers37 described a radiographic technique that can be a helpful adjunctive test for diagnosing
patellar instability. They first obtained bilateral axial radiographs of the patellofemoral joints in anatomic position. A
constant medial and lateral force was applied to the patella
with an instrumented device, and axial radiographs were
repeated. They found that a 4 mm increase in medial or
lateral patellar excursion, compared with the asymptomatic
knee, correlates with patellar instability. These dynamic
radiographs are thought to be more reliable than static
films.
Computed Tomography
Inoue and colleagues38 described a group of patients with
minimal subluxation in whom the condition was determined
more accurately by using computed tomography (CT) with
the knee in full extension. They found that, with the knee
extended, the lateral tilt of the patella was more pronounced
in patients who had patellar subluxation than in patients of
the normal control groups. The patients with patellar subluxation had a lesser degree of abnormality, and the subluxation
was not seen with the knee flexed 30° to 45°, as is usual in
most routine axial views.
Another role for CT is identifying lateralization of the
tibial tubercle as measured by the distance between the
tibial tubercle and the trochlear sulcus. An axial CT image
demonstrating the femoral groove is superimposed on an
axial image of the tibial tubercle. A line is drawn on this
superimposed image between the posterior margins of the
femoral condyles. Two lines are drawn perpendicular to this
line, one bisecting the femoral trochlear groove (TG) and
the other bisecting the anterior tibial tuberosity (ATT). The
distance between these two lines determines the extent of
lateralization of the tibial tubercle. Values greater than 9 mm
have been shown to identify patients with patellofemoral
malalignment with a specificity of 95% and a sensitivity of
85%.39 More recently, Shakespeare and Fick,40 in 2005, tried
to measure theses parameters by clinical exam only. They
concluded that examination alone is not reliable and that CT
is the only accurate way to measure the ATT-TG distance.
Magnetic Resonance Imaging (MRI)
Pathologic entities such as chondromalacia, articular cartilage injuries and degeneration, synovial plicae, and patellar tendinitis can be visualized on MRI. Studies similar to
those made with CT scans can easily be accomplished with
MRI without exposure to radiation, although they involve
considerable expense.
Recent interest has been generated in the determination of
what MRI can show regarding the acute lesion associated with
patellar instability, as mentioned above. Among the first to
describe this were Sallay and coworkers.27 They demonstrated
how clearly the rupture of the MPFL from the femur could
be seen on both sagittal and axial T2-weighted views.
Shellock and associates41 described a medial subluxation
of the patella that could be demonstrated only by kinematic
MRI of the patellofemoral joint done with the knee at 0°,
5°, 10°, 15°, 20°, 25°, and 30° of flexion. Identifying these
subluxations is important, because releasing the lateral side
of this patella would make the condition worse. MRI can
be helpful in determining the site of retinacular or patellofemoral ligamentous injury if the physical examination
is equivocal and surgical repair is contemplated.
One must bear in mind that, although these roentgenographic techniques are important in evaluation of the patellofemoral joint, the diagnosis of patellar dislocation or
subluxation is made by clinical evaluation and not only by
roentgenogram.
Conservative Management
Surgery is not needed in all patients with patellofemoral
malalignment or recurrent subluxation of the patella. Satisfactory results may be achieved with a conservative exercise
treatment program. A rehabilitation program to strengthen
289
the quadriceps muscle and VMO is of primary importance.
A program similar to that followed after acute dislocation,
with the addition of more resistive exercises, can be started
early, and a patellar stabilization brace may help prevent
chronic recurrent subluxation. Using kinematic MRI, Muhle
and coworkers42 demonstrated no significant effect on patellar tracking when bracing was used. It is unknown whether
the brace benefits proprioception as above.
Operative Management
If clinical improvement with nonoperative treatment has
plateaued, operative intervention may be required. Repeated subluxations or dislocations may cause continued
apprehension and progressive joint damage. An abnormal
patellofemoral articulation, abnormal quadriceps pull, osteochondral free fragments, chondromalacia of the patella,
meniscal tears, and degeneration all contribute to progressive
deterioration of the knee joint.
No single operation is universally successful in correcting
recurrent patellar dislocation and subluxation. The operation
must be chosen insofar as possible with the needs of the
individual patient as the foremost consideration. The extent
of the malalignment, the patient’s age, the level of activity,
and the condition of the joint also are important. Over 100
operations have been described for the treatment of recurrent
subluxation or dislocation of the patella. These procedures
can generally be divided into categories:
1. Proximal realignment of the extensor mechanism.
These procedures alter the medial-lateral position of
the patella through manipulation of the soft tissues
proximal to its inferior pole. Included in this category
are lateral retinacular release, medial plication, vastus medialis obliques advancement, and MPFL repair
and reconstruction.
2. Distal realignment of the extensor mechanism. These
operations modify the positions of the patella by
way of transferring the tibial tuberosity or through
surgery on the soft tissues distal to the inferior pole.
Most commonly, this method involves medial or
anteromedial displacement of the tibial tuberosity.
3. Combined proximal and distal realignment.
Proximal Realignment
Proximal realignment of the patella is a realignment of the
quadriceps muscle to the patella, with or without a lateral
release. As emphasized by Insall and colleagues,33 in 1972,
and Insall,43 in 1982, the operation is not a capsular procedure
but rather a quadricepsplasty. Proximal realignment is indicated for patellar instability when the Q angle is the normal
range. When the Q angle approaches 20°, additional distal
realignment should be considered. Further indications are
asymmetrical lateral patellar translation at 30°, significant
trochlear dysplasia, normal or mild tubercle malalignment,
and absence of severe medial patella arthrosis.2,18,41,44 These
procedures may be performed by open or mini imbrication,
Figure 13 Insall technique of proximal realignment of the patella.
A, Medial and lateral vasti are separated from rectus femoris tendon.
B, Lateral release is performed; synovium is left intact. C, Completed closure is tight to hold patella securely in femoral groove.
D, Remaining medial flap sutured without further overlap. (From
Phillips BB: Recurrent dislocations. In: Canal ST (ed): Campbell’s
Operative Orthopaedics. (10th ed). Philadelphia: Mosby, 2003, p,
2384. Copyright © 2003 Elsevier. Sources for illustration. A and C
redrawn from Insall JN, Aglietti P, Tria AJ Jr: Patellar pain and incongruence. II: Clinical application. Clin Orthop 1983;(176):225-32;
B, redrawn from Insall JN, Falvo KA, Wise DW: Chondromalacia
patellae. A prospective study. J Bone Joint Surg Am.1976;58;1:1-8.
Copyright ©1976, The Journal of Bone and Joint Surgery, Inc.; D,
redrawn from Insall J, Bullough PG, Burstein AN. Proximal “tube”
realignment of the patella for chondromalacia patellae. Clin Orthop
Relat Res. 1979;(144):63-9. All sources, with permission.)
as well as arthroscopic medial imbrication.
A proximal “tube” realignment of the patella was described by Insall and associates (Fig. 13). In this technique,
the vastus medialis is brought laterally and sutured to the free
edge of the vastus lateralis, forming a flattened tube proximal
to the patella (Fig. 13). Their results in 53 knees showed
81% excellent or good results and 19% fair or poor.
290
under 15° (Fig. 14); 87% of patients had good to excellent results. The medial patellotibial ligament was also reconstructed
using a portion of the autograft. The investigators admitted
that the patellotibial ligament may not contribute significant
stability, as evidenced by prior anatomic studies. Additionally, although the MPFL reconstruction was performed with a
lateral release, they contended, and previous studies support,
that lateral release alone would have led to inferior results.
Figure 14 The reconstructed medial patellofemoral ligament and
the medial patellotibial ligament. (Reprinted from Drez D Jr, Edwards TB, Williams CS. Results of medial patellofemoral ligament
reconstruction in the treatment of patellar dislocation. Arthroscopy.
2001;17(3):298-306. Copyright © 2001, with permission from the
Arthroscopy Association of North America.)
Halbrecht,45 in 2001, reported his results of arthroscopic
all-inside medial reefing and lateral release. Arthroscopic
reefing was performed by percutaneous passage of suture,
followed by arthroscopic retrieval and knot tying inside the
joint. Ninety-three percent had significant subjective improvement, as well as improvement of the congruence and
lateral patellofemoral angle. This procedure is indicated for
mild to moderate insufficiency of the MPFL, with a normal
Q angle, and without trochlear dysplasia or patella alta.
MPFL Reconstruction
Since recognition of the important role of the MPFL, techniques have begun to emerge addressing this pathologic
process. Hautamaa and colleagues4 believe that proximal
realignment should always repair the MPFL and they demonstrated the effectiveness of this in restoring balance in
cadaver knees. Key points to MPFL reconstruction are that
isometry is a critical factor and the MPFL should not be
over tensioned. In chronic dislocations, reconstruction of
the MPFL is performed rather than repair.
Avikainen and coworkers46 presented a technique of
augmentation of the MPFL with a strip of adductor magnus
tendon. There was one redislocation in 14 patients. Muneta
and colleagues47 reconstructed the MPFL with a double
strand gracilis tendon in five cases and an iliotibial band
allograft in one.
Drez and colleagues,48 in 2001, presented a series of 19
patients who underwent reconstruction of the MPFL with a
lateral release using autogenous hamstrings or iliotibial band
and a minimum 2-year follow-up with an average Q angle of
Lateral Release
The treatment of choice for patellar tilt is an arthroscopic
release. This procedure has been shown to be most effective in patients with patellar tilt49 (as mentioned above). The
lateral release does not substantially reduce the active lateral
vector of the quadriceps and, therefore, has less satisfactory
results in patients with subluxation. Arendt2 showed that
lateral patellar tilt could be a function not only of lateral
retinacular tension but also of isolated medial retinacular
laxity. Therefore, most investigators2,49 would recommend
that a lateral release be used only when there is residual
patellar tilt (a physical examination sign) after restoration
of the medial retinacular structures or limited medial passive
patellar displacement.
The arthroscopic release is performed 5 mm lateral to the
patellar border, covering the distance from 1 cm superior to
the patella to the anterolateral portal. Hemarthrosis, the most
common postoperative complication, inhibits the quadriceps
and delays rehabilitation. This can be minimized by using
electrocautery and deflating the tourniquet before closure.
Distal Realignment
Reducing the Q angle by medializing the tibial tubercle
insertion has long played a role in patellar realignment surgery. One of the more popular current operations is one that
involves medial displacement of the anterior tibial tubercle.
This operation was originated and performed by Roux50 in
1887. The principles were modified by Elmslie and published
by Trillat and associates.51 The intent of the operation was to
diminish the Q angle and effectively medialize the extensor
mechanism to correct lateral tracking of the patella. Current
indications for distal realignment are:
•Increased quadriceps angle or ATT-TG distance,
•Normal lateral patellar glide (intact MPFL),
•Static malalignment of patella with tilt,
•Medial facet arthrosis, and
•Patella alta.
In 1994, Shelbourne and coworkers52 reported 45 patients
with a 2-year follow-up using a modified Elmslie-Trillat
procedure for refractory patellar instability (34 knees) or
painful patellofemoral syndrome with malalignment (11
knees). The postoperative congruence angle (mean, +3.4°) was
significantly improved when compared with the preoperative
value (mean, +21.5°). The “normal” congruence angle is on
average -8°. Even though their results were better than prior
Elmslie-Trillat osteotomies,51,53 nine knees (20%) had some
291
however, is an anomaly that is difficult to correct. A trench
type trochleoplasty is technically difficult to perform, and
there is concern that there is potential disruption of the
cartilage surface or change in contact pressure that may
lead to postoperative pain and arthrosis. Clinical outcome
seemingly would depend also on the type and shape of the
patella, which are factors particularly difficult to simulate
and by which to predict an outcome.
In 2005, Verdonk and coworkers58 performed a Henri Dejour trochleoplasty on 13 patients complaining of recurrent
patellar dislocations or persistent retropatellar pain due to
a dysplastic femoral trochlea. In this technique, the femoral
trochlea is deepened by removing the subchondral trochlear
bone, followed by incision, impaction, and fixation of the
cartilage flange along the trochlear groove. They achieved
77% good to very good subjective results. Although the
outcome was not perfect, the patients were satisfied with the
procedure. The investigators suggested that this technique
might be a valuable alternative in cases of frank trochlear
dysplasia associated with persistent retropatellar pain or
recurrent patellar dislocations.
Figure 15 The direction and extent of the tibial tubercle displacement in the Fulkerson anteriomedialization osteotomy. (From
Fulkerson JP, Hungerford DS. Surgical treatment of patellofemoral
chondrosis and arthrosis. Disorders of the Patellofemoral Joint.
(2nd ed). Baltimore: Williams & Wilkins, 1990, p. 237. Copyright
© 1990 Williams & Wilkins, with permission Lippincott Williams
& Wilkins, Wolters Kluwer.)
postoperative subluxation. Furthermore, medial tibial tubercle
transfer may lead to medial patellofemoral arthrosis.54
To avoid potential loading of the medial patellar facet or
to unload potential damage to patellar articular cartilage in
recurrent patellar dislocations, some investigators advocate
anteriorization of the tibial tubercle and medialization. Maquet53 and Bandi55 first introduced elongation of the extensor
lever arm by anterior displacement of the tibial tuberosity.
This operation has been modified further by Fulkerson and
colleagues.56
Anteromedial Tibial Tubercle Transfer (Fulkerson
Procedure)
This procedure corrects the Q angle with medialization of
the tibial tubercle and unloads the patellofemoral articulation with anteriorization of the tubercle (Fig. 15). A hinge
of bone is maintained intact at the distal tubercle to facilitate healing. After the transfer, the bone pedicle is locked
into position with two cortical screws. Patients are made
non-weightbearing for 6 to 8 weeks to avoid tibia fracture.
Fulkerson and associates56 reported 93% good and excellent results subjectively and 89% good and excellent results
objectively.
Trochleoplasty
Trochlear dysplasia is identified as a predominant factor
in symptomatic patellar dislocation.57 Trochlear dysplasia,
Combined Proximal and Distal Realignment
Indications for a combined proximal and distal procedure
are a combination of tubercle malalignment and traumatic
incompetency of the medial restraints. Hughston and Walsh59
reported satisfactory results using a technique for reconstruction of the extensor mechanism that combines many aspects
of other procedures. They emphasized the importance of
a proximal extensor mechanism reconstruction, including
careful placement of the vastus medialis muscle. Distal
realignment is indicated for knees in which the Q angle is
increased beyond 20° in skeletally mature patients.
The surgeon should first correct tubercle malalignment and
then reassess patellar tracking, in combination with lateral
retinacular release. If patellar tracking is still not corrected and
lateral instability is still present, the surgeon should perform
medial augmentation or reconstruction of the MPFL.
More recently, in 2004, Palmer and colleagues60 reported
their results of a lateral release, a VMO advancement, and
an anteromedial tibial tubercle transfer to correct all the abnormalities of patellofemoral maltracking, including patella
alta. One hundred seven knees in 84 patients were reviewed,
with a mean follow-up of 5.6 years. Seventy-nine percent
of patients had a good to excellent functional outcome, and
84% of patients stated they would have the operation again.
Two patients with marked generalized ligamentous laxity
had recurrent dislocation of the patella.
Conclusions
Patellofemoral instability can be difficult to treat. Surgical
treatment of patellar dislocations both acute and chronic
have evolved significantly with the advancement of biomechanical knowledge of patellofemoral restraints and injury
patterns identified by physical examination and improved
292
imaging techniques.
For acute dislocations, nonoperative therapy should be
a mainstay of treatment. Arthroscopy should be indicated
for symptomatic osteochondral injury, with or without medial repair and lateral release. In recurrent dislocations or
subluxations, nonoperative therapy is still the predominant
form of treatment as well. For patients who fail conservative
treatment, proximal, distal, and combined realignments can
be performed and should be based on the specific dysfunction of each patient.
Disclosure Statement
None of the authors have a financial or proprietary interest
in the subject matter or materials discussed, including, but
not limited to, employment, consultancies, stock ownership,
honoraria, and paid expert testimony.
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Patella Instability

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