1. health and fitness
2. disease
3. arthritis

REVIEW ARTICLE
First-Time Patellar Dislocation: Surgery
or Conservative Treatment?
Petri J. Sillanpa¨a¨, MD, PhD and Heikki M. Ma¨enpa¨a¨, MD, PhD
Abstract: Primary patellar dislocation injures the medial patellofemoral ligament (MPFL), the major soft-tissue stabilizer of the patella, which may lead to recurrent patellar instability. Recurrent
patellar dislocation are common and may require surgical intervention. The variation in location of injury of the MPFL and the
presence of an osteochondral fracture produces challenges in clinical
decision making between nonoperative and operative treatment, including the surgical modality, to repair or reconstruct the MPFL.
Current evidence suggests that not all primary dislocations should
undergo the same treatment. MPFL reconstruction may theoretically
be more reliable than repair, but the optimal time to perform additional bony corrections is not known. A normal or minor dysplastic
patellofemoral joint may be suitable for nonoperative treatment,
whereas a higher grade of trochlear dysplasia or other significant
abnormalities may benefit from surgical treatment. In this paper, we
present a treatment algorithm for primary patellar dislocation.
Key Words: patella, medial patellofemoral ligament, dislocation,
injury, knee, magnetic resonance imaging
(Sports Med Arthrosc Rev 2012;20:128–135)
F
irst-time (primary) patellar dislocation commonly occurs
in the young physically active population1 and is associated with a high rate of recurrent patellar instability. Depending on the patient cohort, 44% to 70% patients sustain
recurrent dislocations.2–4 With a complete dislocation of the
patella, the primary stabilizer, the medial patellofemoral
ligament (MPFL), is frequently torn. A total or partial
MPFL disruption can be observed by magnetic resonance
imaging (MRI).5,6 Biomechanical studies7–9 reveal that the
MPFL is the major ligamentous restraint against lateral
patellar dislocation. The MPFL extends from the medial
margin of the patella and attaches firmly to the femur between the adductor tubercle and the medial epicondyle.10,11
The MPFL is estimated to contribute 50% to 60% of the
restraining force against lateral patellar displacement.7–9
Patellar dislocation and MPFL injury can be diagnosed
using MRI.5,6,12 A variable amount of anatomic abnormalities may be involved in patients with primary patellar
dislocation.13 Primary dislocation might thus be related to
trochlear dysplasia, patella alta, or malalignment, whereas
primary dislocation can occur in a normal patellofemoral
joint if extensive external forces twist or rotate the knee in
certain way.1 Primary patellar dislocations quite often involve an osteochondral fracture that may require surgical
fixation.2,14 Therefore the significant variation in the injury
From the Department of Orthopaedic Surgery, Tampere University
Hospital, Tampere, Finland.
Disclosure: The authors declare no conflict of interest.
Reprints: Petri J. Sillanpa¨a¨, MD, PhD, Department of Orthopaedic
Surgery, Tampere University Hospital, Teiskontie 35, Tampere
33521, Finland.
Copyright r 2012 by Lippincott Williams & Wilkins
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pattern and other associated factors such as alignment, dysplasia, and osteochondral injury can make treatment challenging. The majority of primary dislocations can be managed
nonsurgically, although occasionally surgery is warranted and
a thorough evaluation of each case is required.15 The optimal
strategy is not yet established.
The aim of this paper is to review the evidence in the
treatment of primary patellar dislocation. Surgical techniques for acute MPFL injuries and additional injuries are
also discussed. A treatment algorithm for primary patellar
dislocation, based on the evidence from current literature, is
presented.
ETIOLOGY AND RISK FACTORS FOR PRIMARY
DISLOCATION
When the patella dislocates laterally, the medial patellar restraints are injured, particularly the MPFL.1,9,16
The patella may spontaneously relocate back to the femoral
trochlear groove. The force required to dislocate the patella
most likely depends on the individual patellofemoral morphology. When the femur rotates internally and the tibia
externally, with the foot fixed on the ground, the patella
may dislocate without any pathologic structures in the patellofemoral joint.1,17 Quite often, however, patellar dislocation occurs in a knee that has predisposing anatomic
features for patellar instability. These include trochlear
dysplasia, patella alta, increased femoral antetorsion, increased external tibial torsion, and valgus alignment of the
lower limb.13 Rarely, ligamentous laxity can be present.
The incidence of primary patellar dislocation is reported to range from 6 to 112 per 100,000 persons depending on the age of the population.1,16,18–20 In a study of
military conscripts, the calculated incidence of acute traumatic primary patellar dislocation was 77.4 per 100,000
persons per year; in females 104.6 per 100,000 persons per
year.1 In that study, 63% of the injuries occurred during
sports activities and 37% occurred during military training,
indicating that injury was related to physical activity. The
mechanism of injury is reported to be knee valgus stress and
internal rotation of the femur with the foot fixed on the
ground.1,16,17,21 The risk factors for primary patellar
dislocation are tall height and excess weight (Table 1).1
The risk factors for recurrent patellar instability are well
described and include anatomic predisposing factors;
trochlear dysplasia, patella alta, variations of limb
alignment, connective tissue laxity, and insufficiency of
previously injured medial restraints.3,13,22
DIAGNOSIS OF PRIMARY PATELLAR
DISLOCATION
Patellar dislocation is usually diagnosed on the basis of
the clinical findings and the patient may describe “kneecap
was out of place.” Clinical findings include tenderness of the
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TABLE 1. Risk Factors for Acute Traumatic Primary Patellar
Dislocations Among Military Conscripts (Median and SD)
Risk Factors
Sex
Male
Female
Age (y)
Height (cm)
Weight (kg)
Muscle
strength
Run test (m)
Body mass
index
Acute Traumatic
Primary Patellar
Dislocation (n = 75)
Healthy
Controls
(n = 130,421)
73
2
19.8 (0.8)
180.3 (7.2)
77.2 (4.3)
16.4 (3.5)
128,642
1992
20.0 (1.3)
178.5 (6.7)
73.2 (12.7)
16.4 (3.6)
0.287
0.031*
0.014*
0.960
2500 (371)
23.7 (3.8)
2520 (355)
22.9 (3.5)
0.703
0.105
P
0.283
*Considered significant with P-value <0.05.
Reprinted with permission of Wolters Kluwer Health Sillanpaa et al.1
medial restraints. A medial hematoma may be observed.
The patella may be lateralized, and an apprehension test
positive. The knee is acutely swollen and hemarthrosis can
be aspirated for pain relief. The patella is usually spontaneously reduced, and is quite rarely still dislocated when the
patient arrives at the hospital. Children and adults may have
quite different symptoms. Children can have a relatively
atraumatic dislocation with slight or no effusion, indicating
dysplasia in the patellofemoral joint, which allows the patella to dislocate without extensive soft-tissue damage. The
primary dislocation can then be an atraumatic primary dislocation, because of patellofemoral joint laxity. This situation is nearly impossible in mature skeletons. In adults
who sustain a primary dislocation without prior knee complaints, soft-tissue damage and medial restraint injury with
acute hemarthrosis occur.1,2,23 Additional injuries such as
osteochondral fractures are more frequent in traumatic primary dislocations.2,14 Traumatic dislocation means a twisting, bending, rotating, or valgusing movement of the lower
limb, and that tissue damage has occurred. Both conditions,
atraumatic dislocation in young children and traumatic dislocation in young adults, can sometimes be difficult to diagnose, because of the lack of clinical findings or painfully
swollen knee. Radiographs are therefore always needed to
confirm the diagnosis.
IMAGING
Imaging of the patellofemoral joint is described more
thoroughly in another chapter in this issue. Primary patellar
dislocation has certain important signs that affect decision
making between surgical and nonsurgical methods. First,
First-Time Patellar Dislocation
plain radiographs are always needed to evaluate patellar
position and assess osteochondral fractures. Sagittal and
anteroposterior views with axial Merchant view are essential.24 Axial views are particularly important, and both
patellae should be included in this view. The patella may be
lateralized if compared with the contralateral side (Fig. 1),
and fragmentation of the medial patella, a defect of the
patellar articular surface, or a loose osteochondral fragment may be observed (Fig. 2). MRI is recommended to
assess the cartilage more precisely.25 MPFL injury location
can be assessed reliably by MRI.6 MPFL injuries are classified in 3 categories based on location: at the level of the
MPFL patellar insertion, at the midsubstance of the MPFL
and medial retinaculum, and at the femoral origin of the
MPFL (Table 2).6,12 Therefore, MRI is recommended in
cases of primary dislocation to verify the diagnosis, evaluate
additional injuries, and, importantly, describe the anatomic
factors of the patellofemoral joint.6,26–30 Because of the
high prevalence of osteochondral fractures, MRI should be
performed quite soon after the injury.
REVIEW OF THE CURRENT CLINICAL EVIDENCE
A recent Cochrane Review concluded that there was
insufficient evidence to confirm a significant difference in the
outcome between surgical or nonsurgical initial management in those who have sustained a primary patellar dislocation.4 A meta-analysis regarding nonsurgical and surgical
care of acute primary patellar dislocation concluded that
surgery was not better than nonsurgical treatment.3 Below,
we discuss prospective studies that include primary patellar
dislocation and factors affecting clinical decision making
between surgical and nonsurgical treatment.5,21,23,31
Generally, prospective studies report variable results
after surgical treatment for patellar dislocation.3 Studies
initiated >10 years ago mainly utilized surgical techniques
that were nonanatomic and are no longer used.5,21,23 Therefore, those results are considered less reliable than modern
surgical techniques. MPFL repair by sutures is not better
than nonsurgical treatment, and does not decrease recurrent
instability rate in skeletally immature children and do not
improve subjective results in adults.5,21,23 Acute arthroscopic MPFL repair is also not superior to nonsurgical
management.12 Arthroscopic repair is likely an insufficient
method to approach the MPFL injury locations. Delayed
repair is usually not targeted to the previous injury location
and is therefore not useful.32–34
Two prospective randomized studies described better
patellar stability after MPFL repair compared with conservative treatment.5,31 However, only 1 study described clinically significant improvement in subjective outcome.31 An
older study included a suture repair technique5 and a recent
FIGURE 1. Axial Merchant radiographic view after primary patellar dislocation. Right side (R) has been dislocated and the patella is
abnormally lateralized. Left side (L) is normal.
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(Fig. 2). On the basis of these previous findings, MPFL
repair may be considered more unreliable than MPFL reconstruction, in terms of providing sufficient medial softtissue stability.
Studies of the long-term clinical outcome of primary
patellar dislocation regarding the injury location are limited
to retrospective studies28 and are insufficient to prove any
clear benefits of certain treatment modalities.
PRINCIPLES OF NONSURGICAL MANAGEMENT
FOR PRIMARY DISLOCATION
FIGURE 2. Medial osteochondral avulsion fracture with articular
surface involvement (at the patellar insertion of the medial patellofemoral ligament). Axial proton-density magnetic resonance
image.
study included MPFL reinsertion with anchors,31 showing
more favorable results with surgical treatment. The more
recent the prospective randomized study, the more favorable the result toward operative treatment. All of the prospective randomized studies utilized different kinds of
MPFL repair.5,21,23,31,33 To date, no study has compared
MPFL reconstruction to nonoperative treatment in a prospective and randomized study setting.
The clinical importance of an MPFL injury location
was evaluated in 1 study.28 In that study, MPFL disruption
at the femoral attachment was related to more frequent
subsequent instability than patellar or midsubstance MPFL
injuries.28 The study is limited by its retrospective nature
and the use of only male subjects. MPFL patellar attachment injury was recently reported to be at least as common
as femoral attachment injury.6,27,29,30 Midsubstance MPFL
disruption as an independent injury location is less common.6,28 Partial tears or wavy features of the midsubstance
MPFL structure are commonly seen in cases of patellar or
femoral attachment MPFL disruption.6,30 Patellar MPFL
injury may include an osteochondral avulsion fracture, in
which the MPFL structure is relatively intact and attached
to the avulsed bone from the medial margin of the patella.30
In some cases, articular cartilage involvement is seen14
Conservative treatment has been historically suggested
for patients with primary patellar dislocation. A short immobilization period is used for patient comfort and is followed by formal physiotherapy. A recent systematic review
regarding the clinical outcomes of rehabilitation for patients
after lateral patellar dislocation concluded that no randomized controlled clinical trials had been published that assessed different physiotherapy interventions.35 Therefore, the
optimal conservative management has yet to be established.
Acute primary patellar dislocation is painful. Hemarthrosis can be aspirated for pain relief, after which
clinical examination is controlled and the patient undergoes
diagnostic imaging studies. There is no clear evidence that
the knee should be immobilized after primary dislocation.
Studies have poorly described the primary and recurrent
nature of the patellar dislocation and the immobilization
period has varied widely between 0 to 6 weeks.5,31,35,36 A
recent report of preliminary results of a prospective randomized study in which immediate mobilization was compared with flexion restriction with a patellar brace found no
difference at 2 years.37 The study is ongoing and will provide additional information in a few years. A feasibility
study for a pragmatic randomized controlled trial comparing cast immobilization versus no immobilization for
patients after first-time patellar dislocation suggested better
short-term functional result for those not immobilized, but
the reported preliminary sample was too small to make any
conclusions.38
The aims of physiotherapy are to restore knee range of
motion, and to strengthen the quadriceps muscles to restore
the dynamic part of the patellar soft-tissue stabilizers.39
Patients should be encouraged to activate the quadriceps as
tolerated by pain and after a few weeks, strenuous exercises
should be started aimed at normalizing quadriceps strength
and control. At 4 to 6 weeks, by which point walking and
knee range of motion have been normalized, exercises continue with more extensive extension raises, proprioceptive
activities, and core stability training. Return to full activity
can be suggested at 3 months. Avoiding chronic muscle
weakness and imbalance is the main rehabilitation goal.
TABLE 2. Classification on MPFL Injuries Based on Injury Location and Reported Incidence in the Literature6,26–30
MPFL Injury
Classification
Anatomic
Description
Proportion in Primary
Dislocations
Mean Reported
Incidence (%)
Patellar
Midsubstance
MPFL patellar attachment
MPFL midsubstance (region between patellar
and femoral attachments)
MPFL femoral attachment
13%-76%
0%-30%
54
12
12%-66%
34
Femoral
MPFL indicates medial patellofemoral ligament.
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First-Time Patellar Dislocation
A variety of different clinical outcomes have been reported in patients after physiotherapy management after a
lateral patellar dislocation.35 The results are discussed more
thoroughly in another chapter in this issue.
In conclusion, because of the lack of clinical evidence,
it is not possible to determine the optimal nonsurgical schema after primary patellar dislocation. Most likely physiotherapy treatments are recommended for patients after
primary patellar dislocation, because quadriceps control and
strength can be compromised, thereby affecting long-term
clinical outcome. No evidence is available as to whether
quadriceps weakness and especially vastus medialis oblique
(VMO) muscle inactivity are an acquired clinical situation
after primary patellar dislocation or present before the injury.40 Because of the nature of the primary dislocation,
which is usually a sport-related injury or related to other
physical activities,1,16 muscle weaknesses or imbalances are
perhaps subsequent side effects of the injury resulting from
medial capsular disruption, potential neural injuries, and loss
of proprioceptive control.
SURGICAL OPTIONS FOR PRIMARY
DISLOCATION
As described earlier, in primary patellar dislocation,
MPFL injury location can be diagnosed by MRI.6 Secondary dislocation may not have a clear MPFL disruption
due to prior MPFL laxity, and MRI is less useful in secondary dislocations if surgery is not planned. MPFL injury
location should not be assessed surgically because it requires a large incision and involves dissecting the medial
capsular structures including VMO fascia, which can
potentially produce comorbidity to muscle function and
saphenous nerve branches.10,7,9
In primary patellar dislocation, the MPFL is the injured part of the patellar stability complex, whereas limb
alignment and patellofemoral joint morphology are individual persistent factors. Theoretically, repair of the injured part of this complex structure should be the primary
surgical option. Surgical stabilization of the patella can be
performed with MPFL repair or reconstruction. Surgical
repair can be performed if the injury location is known.28
Some patients, however, may have remarkable underlying
pathology that critically affects patellar stability, although
there is no evidence available when osseous abnormalities
should be addressed in addition to restoring the MPFL.
Additional procedures involving osseous anatomy should
be selected on an individual basis and are generally not
considered necessary as a first-line treatment after primary
patellar dislocation.
MPFL patellar or femoral attachment injury can be
surgically reinserted with satisfying results and may lead to a
better outcome than nonsurgical treatment,31 although
some controversy exists in the results of prospective studies.5,21,23,33 MPFL midsubstance injuries seem to not benefit
from acute repairs.28 MPFL injury at the femoral or patellar
attachment can be repaired with sutures or suture anchors
(Fig. 3).31 Midsubstance MPFL injury is difficult to repair
adequately and is not recommended.5,21 Midsubstance
MPFL injury should be repaired only in rare cases with
extensive VMO fascial disruption in a high-energy dislocation (Fig. 4). In such cases, the VMO detaches from the
medial patellar capsule (Fig. 4), and the quadriceps pull
vector may be significantly lateralized, therefore the patella
dislocates in extension when the quadriceps is activated.
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FIGURE 3. Medial patellofemoral ligament injury at the femoral
or patellar attachment is repaired with suture anchors.
Patellar attachment MPFL injury can be classified as a
ligamentous or bony avulsion from the medial margin of the
patella.28 A third type includes an osteochondral fragment
with articular cartilage involvement from the medial patella
(Fig. 2). According to a retrospective study, ligamentous
patellar MPFL avulsion is not associated with an increased
rate of recurrent instability compared with femoral MPFL
avulsion injury with similar nonsurgical management.28
Articular cartilage involvement can be considered an indication for surgery, and cartilage defects should be repaired
by reduction and fixation of the fragment (Fig. 5).14,15 In
particular, fractures located in a high-pressure area, central
or lateral patellar cartilage, or lateral trochlear wall, should
be repaired if possible. A fragment size >510 mm can be
fixated, and based on the experience of the authors, large
fragments heal well if fixation is performed within 1 week of
the injury. Fixation is performed with bioabsorbable nails,
pins, small screws, or sutures. Small osteochondral fractures
can be managed nonsurgically, especially in cases when the
fracture is located in a low-pressure area, the distal lateral
margin in the lateral condyle of the femur, which normally
does not carry weight or articulate with the patella. In such
cases, a small fracture may be arthroscopically removed if it
acts as a loose body and produces symptoms.28 Symptoms
usually persist >4 weeks in cases of loose body formation
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FIGURE 4. Extensive, combined medial patellofemoral ligament
patellar attachment (small arrow) and midsubstance injury with
vastus medial oblique muscular detachment (large arrow) from
the medial patellar capsule. Only skin and subcutaneous have
been incised before photography. All parts of the medial stabilizing structures of the patella (P) have been injured and the
patella does not stay its place when medial and lateral part of the
quadriceps muscle pulls patella cranially.
and disappear in cases of fracture incorporation with the
synovial tissue, indicating no need for fragment removal.
In some cases, the MPFL may be injured in 2 locations.6 Most likely, MPFL patellar or femoral attachment
disruption can be accompanied by a midsubstance total or
partial tear. Therefore, MPFL reconstruction may be more
reliable surgical method than MPFL repair. MPFL reconstruction cannot be safely performed at the time of injury if there is a medial patellar margin MPFL avulsion
fracture (Fig. 2).28 MPFL reconstruction requires experience in patellofemoral surgery and is considered technically
more demanding than repair. MPFL reconstruction produces good stability in the majority of cases with few
complications, as described in many studies.41 MPFL reconstruction techniques are described in another chapter of
this issue. Current evidence for MPFL repair is, however,
very limited compared with that for MPFL reconstruction.
MPFL repair cannot be performed without MRI verification of the injury location and repair is inappropriate if
performed later in cases of chronic patellar instability.32
Repair is perhaps best indicated in acute cases with MRIverified patellar or femoral attachment MPFL disruption
within a few weeks of the injury. An additional indication
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Volume 20, Number 3, September 2012
could be an osteochondral fragment from the medial patella
with simultaneous patellar attachment MPFL avulsion
(Fig. 2).
To summarize, if surgical treatment has been chosen,
primary dislocation in adults without any prior knee complaints requires only MPFL reconstruction in most cases.
MPFL repair can be performed at the patellar or femoral
attachment, but may be more unreliable than reconstruction.
Skeletally immature patients and adolescents with primary
dislocation quite often have severe trochlear dysplasia or
alignment abnormalities that may need to be addressed if
surgery is performed after primary dislocation. The vast
majority of the primary dislocations belong to this group. It
might be that repair alone is especially insufficient in anatomically abnormal population, based on the high probability of recurrent patellar instability, which is reported to be
as high as 70%, especially in a very young population.23
A treatment algorithm, based on current evidence in
the literature and the experience of the authors, is shown
in Figure 6.
AFTER MANAGEMENT OF PRIMARY PATELLAR
DISLOCATION
After initial surgical or nonsurgical treatment for primary patellar dislocation, the knee is usually immobilized for
a short period to relief pain. If MPFL reconstruction is
performed, immobilization is usually not needed. Additional
surgical procedures may require their own specific aftercare,
which are discussed in other chapters of this issue. During
the first few weeks to 3 months, patients undergo physiotherapy to recover any muscle atrophy or joint range of
motion restrictions related to the injury. Patients are then
encouraged to return to physical activity after 3 months and
to sports when quadriceps strength and proprioceptive control are regained. The return to preinjury levels of physical
activity vary between 44% to 60% after primary patellar
dislocation, regardless of treatment modality.5,12,28,35
RECURRENT DISLOCATIONS
After primary dislocation, patients tend to have a
2-year period before the risk of recurrence increases.23 This
may be partly because of the inability to participate in
physical activities for a long time after injury. Many studies
have assessed the frequency of recurrent patellar dislocation
after primary dislocation. The findings indicate that 33%
(range, 6% to 100%) of patients experience patellar instability after primary dislocation.4,22 Reoperation rate
after primary dislocation varies between 10% and 55%.4
FIGURE 5. Acute osteochondral fracture (size, 10 18 mm) involving the medial facet and central articular surface of the patella (A). The
defect should be repaired by reduction and fixation of the fragment (B).
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First-Time Patellar Dislocation
Primary (First-time)
Patellar Dislocation
Clinical examination
and radiographs,
including axial view
No fractures, patella
highly unstable, pops
out of it place in
extension or flexion
No fractures, patella
is stable enabling
active knee extension
and flexion
Osteochondral
fracture
Immobilization, MRI
and operative
treatment (MPFL
reconstruction and
individual additional
procedures, if severe
abnormalities)
Short immobilization
for patient comfort,
MRI within 2 weeks,
assessment of MPFL
injury and additional
injuries
MRI, operative
treatment, fixation of
the fragment and
MPFL reinsertion or
reconstruction
MPFL disruption at
patellar attachment
MPFL patellar
insertion bony
avulsion with
articular cartilage
involvement,
operative treatment
MPFL patellar
insertion disruption
without articular
cartilage
involvement,
nonoperative
treatment
MPFL
midsubstance
disruption or partial
MPFL injury
MPFL
disruption at femoral
attachment
Nonoperative
treatment with
physiotherapy
initiated as tolerated
by pain
Nonoperative
treatment if no severe
dysplasia
Operative treatment
(individual) if severe
abnormalities
FIGURE 6. A treatment algorithm for primary patellar dislocation. MPFL indicates medial patellofemoral ligament; MRI, magnetic
resonance imaging.
Recurrent dislocations are exceptionally common in skeletally immature patients, as reported by Palmu et al23 and
Nikku et al21 (study included, but was not restricted to,
children), that 70% of their cohort presented with recurrent
patellar instability after rehabilitation.
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DISCUSSION
Primary patellar dislocation leads to MPFL injury.
Some studies advocate surgical management for primary
patellar dislocation whereas others recommend nonsurgical
treatment.21,23,31 Because of the insufficient amount of
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evidence in the literature, there is currently no universally
accepted, optimal strategy for primary patellar dislocation
available.4 The complexity of patellar instability leads to
challenges in decision making between different treatment
modalities. Most cases are suitable for initial nonsurgical
management with physiotherapy, although recurrent instability is very common.4 Osteochondral fragments amenable
for surgical fixation are an indication for surgery, and
MPFL reconstruction may be a more reliable method of
stabilizing the patella than MPFL repair, which has limitations related to the MPFL injury location. Osseous surgery is usually not needed if surgery is planned after primary
dislocation, but corrections are needed in cases with severe
bony abnormalities.
The MPFL injury location can be reliably assessed by
MRI.6 Several recent studies advocate MRI after acute
patellar dislocation,2,5,28 as the acutely injured knee usually
shows hemarthrosis as a sign of tissue damage and clinical
diagnosis can sometimes be difficult. MRI can be used to
diagnose the signs of acute patellar dislocation and associated injuries, such as osteochondral fractures and meniscal or ligament injuries.6 Previous randomized studies of
primary patellar dislocations concluded that surgery is not
superior to nonsurgical treatment if all the patients with
different types of MPFL injuries are treated similarly.5,21,23
In contrast, a recent prospective randomized study in which
nonsurgical treatment was compared with surgical reinsertion in either femoral or patellar attachment, surgery
resulted in better stability than nonoperative treatment.31
Because of the high, 44% to 70%, redislocation rate after
primary dislocation4 some cases might benefit from initial
surgery, and surgery should definitely be considered for
cases with a high risk of failure after nonsurgical treatment.
Patients with patellar MPFL avulsion fracture and femoral
attachment MPFL disruption may be at greater risk of
subsequent dislocation.28 In these patients, restoring the
integrity of the MPFL might be necessary to ensure better
stability. Ruptures at the MPFL midsubstance or patellar
insertion regions are generally not related to significant
subsequent patellar instability.28 We therefore suggest that
rupture of the MPFL at its midsubstance or near the patellar attachment should be treated nonsurgically.
The clinical outcome of various MPFL injuries, however,
remains highly uncertain with regard to the well-known
factors that predispose a patient to patellar instability, such
as trochlear dysplasia, axial and torsional lower-limb
alignment abnormalities, and MPFL injuries.13,22,42 Most
likely, the more dysplastic the trochlear shape, the more
devastating the injury to the MPFL is to patellar stability.
Surgical treatment needs to be tailored individually, based
on the MRI findings of the MPFL injury and osseous
anatomy, although nonoperative treatment is still preferred
in most cases.
In conclusion, primary patellar dislocation leads to
MPFL injury. MPFL injuries can occur in different locations and may be combined with an osteochondral avulsion
fracture of the medial patellar margin or an impact fracture,
which should be treated with initial fixation of the fragment.
MRI is recommended for assessment of the MPFL injury
and the exclusion of additional injuries. Current evidence
supports nonoperative management for primary patellar
dislocation in majority of the cases. Surgery should probably be considered for MPFL patellar or femoral attachment disruptions in cases with 1 or more dysplastic features,
especially if patella is highly unstable after dislocation. In
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some cases, osseous corrections may be needed, but the
majority will stabilize with MPFL reconstruction alone.
Because of the complex nature of patellar instability, treatment of primary patellar dislocation is challenging. The
optimal treatment has not yet been established and further
prospective randomized studies are required.
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2. Stefancin JJ, Parker RD. First-time traumatic patellar
dislocation: a systematic review. Clin Orthop Relat Res. 2007;
455:93–101.
3. Smith TO, Song F, Donell ST, et al. Operative versus nonoperative management of patellar dislocation. A meta-analysis.
Knee Surg Sports Traumatol Arthrosc. 2011;19:988–998.
4. Hing CB, Smith TO, Donell S, et al. Surgical versus nonsurgical interventions for treating patellar dislocation. Cochrane
Database Syst Rev. 2011;11CD008106.
5. Sillanpaa PJ, Mattila VM, Maenpaa H, et al. Treatment with
and without initial stabilizing surgery for primary traumatic
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Joint Surg Am. 2009;91:263–273.
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