Dr. Anthony A. Schepsis

Coastal Orthopedics
Beverly, MA
Professor of Orthopedic Surgery
Boston University School of Medicine

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patellar dislocation

Management of First-Time Patellar

Dislocations

MICHAEL GEARY, MD; ANTHONY SCHEPSIS, MD

OCTOBER 2004 | Volume 27 • Number 10 1059

■ sports medicine update

The average annual incidence

of first time patella

dislocation is 5.8 per 100,000.1

When risk is stratified by age

and gender, the risk of first time

dislocation is highest in females

aged 10-17 years. In this group,

the annual incidence of first

time patella dislocation is 33

per 100,000.1

Stability of the patellofemoral

joint against lateral dislocation

is based on osseous

constraint in 30° of flexion

and medial soft-tissue restraints

in the early flexion range where

instability usually occurs. The

medial patellofemoral ligament

is the most important of these

medial soft-tissue restraints.2

The typical mechanism of

injury is external rotation of the

tibia with concomitant contraction

of the quadriceps. Less frequently,

glancing blows to the

patella may produce a dislocation.

Factors that predispose to

dislocation include an

increased quadriceps angle,

trochlear dysplasia, patella alta,

vastus medialis obliques atrophy,

insufficient medial

patellofemoral ligament, genu

recurvatum, increased femoral

anteversion, external tibial torsion,

foot pronation, increased

patellar tilt, and patellar hypermobility.

With greater anatomic

predisposition, the force

required to dislocate the patella

decreases.

EVALUATION AND

MANAGEMENT

Patients having sustained a

first time traumatic patella dislocation

usually present with a

reduced patellofemoral joint

and a history of feeling their

knee “go out of place.” On

examination, a large hemarthrosis

is typically present,

with tenderness over the medial

femoral epicondyle and

medial border of the patella, in

addition to pain with lateral

translation of the patella.

Arthrocentesis should be considered

in the acute setting for

both patient comfort and to

allow for a more accurate physical

examination.

The typical lesion associated

with lateral patella dislocation

is injury to the medial

patellofemoral ligament.3-5

Associated injuries frequently

include osteochondral fractures,

and less frequently medial

collateral ligament (MCL)

sprain, anterior cruciate ligament

(ACL) injury, and meniscal

injury.3-5 Initial management

consists of immobilizing

the affected knee in extension.

Radiographic evaluation

should include anteroposterior

(AP), lateral, and tunnel views

of the affected knee and

Merchant or axial views of

both knees. These studies

should be reviewed for osteochondral

fracture and adequacy

of patellofemoral joint reduction.

Consideration should also

be given to magnetic resonance

imaging (MRI), which is more

sensitive for osteochondral

injury and can also aid in diagnosis,

given a characteristic set

of MRI findings seen with

patellar dislocation. These

findings include disruption of

the medial patellofemoral ligament

and osteochondral bone

bruises or fractures involving

the inferomedial patella and

lateral femoral condyle.3-5

Treatment recommendations

for first time patellar dislocations

are controversial. Our

practice has been to manage

first time patellar dislocations

nonoperatively, unless a displaced

osteochondral fracture

or asymmetric reduction of the

dislocated patella is noted

when compared to the normal

knee. In the latter two cases,

arthroscopy is performed and

the knee is surveyed. Smaller

displaced osteochondral frag-

From Boston University Medical

Center, Boston, Mass.

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Ste 808, 720 Harrison Ave, Boston,

MA 02118.

Patellofemoral instability represents a continuum of

abnormal patellofemoral joint mechanics, ranging from

infrequent subluxation to recurrent dislocation.

ments that are not amenable to

fixation are excised; larger

fragments are fixed in an

arthroscopic or open fashion

depending on the size and

location of the injury. If indicated,

tears of the medial

patellofemoral ligament are

repaired primarily in an open

fashion.

CASE REPORTS

Case 1

A 16-year-old high school

football defensive back sustained

a first-time lateral dislocation of

the left patella during a tackling

drill in practice. The patient

recalled sudden knee pain after

twisting his knee in the drill. He

was attended to by the athletic

trainer who diagnosed a lateral

patellar dislocation. This was

reduced on the field by extending

the injured knee and applying a

medially directed force on the dislocated

patella. The patient’s left

knee was then placed in extension

in a knee immobilizer.

On evaluation the following

day, the patient reported no history

of patella dislocation or instability

in either knee prior to the

current episode. The patient was

otherwise healthy.

On physical examination, the

patient had a large effusion in the

left knee and pain with minimal

range of motion. An arthrocentesis

was performed and 120 cc of

sanguineous fluid with fat globules

was removed. Crepitus was

noted with range of motion. The

patient was able to perform a

straight leg raise. The knee was

stable to varus and valgus stress at

0° and 30°. Lachman and anterior

and posterior drawer tests were

negative. The patient was most

tender along the medial patella

border and medial femoral epicondyle.

Pain occurred with lateral

translation of the patella.

Significantly increased asymmetric

lateral patellar translation was

noted at 30° of flexion.

Radiographs, consisting of AP,

tunnel, and lateral of the left knee

and Merchant views of both knees

were obtained. A displaced osteochondral

fragment could be seen

on the Merchant and lateral views

of the left knee (Figure 1). The left

patellofemoral joint was reduced

and symmetrical in appearance

with the right patellofemoral joint.

Magnetic resonance imaging of

the left knee demonstrated an effusion

and a midsubstance tear of the

medial patellofemoral ligament. In

addition, a displaced osteochondral

fracture measuring 2 cm in diameter,

involving the lateral femoral

condyle, was present. The ACL,

MCL, posterior cruciate ligament

(PCL), lateral collateral ligament

(LCL), and medial and lateral

menisci were intact.

Arthroscopy demonstrated a

displaced osteochondral fracture

of the lateral femoral condyle

measuring 2 cm in diameter, and

hemorrhage in the medial retinacular

region (Figure 2). Both

menisci and ACL were intact.

Open reduction and internal

fixation of the displaced osteochondral

fracture was performed

using Arthrex Chondral Darts

(Arthrex, Naples, Fla). A 4-cm

medial parapatellar arthrotomy

was performed and primary repair

of the medial patellofemoral ligament

was carried out.

Postoperatively, the patient

was placed in a hinged knee brace,

locked in extension, and he

remained partial weight bearing

for 6 weeks. Early range of

motion was instituted, initially at

0°-90°, and progressing to full

passive range of motion by 4

weeks. At 6 weeks the patient was

advanced to weight bearing as tolerated,

with full active range of

motion while wearing a dynamic

lateral buttress patellar stabilizing

brace. Strengthening exercises

were begun 12 weeks postoperatively,

and return to full activity

was accomplished 16 weeks postoperatively.

The patient returned to playing

football the following season with

no episodes of instability or subsequent

dislocation. At last follow-

up, approximately 2 years

postoperatively, the patient again

reported no symptoms of instability,

pain, or swelling.

Figure 1: Case 1. Merchant view demonstrating a displaced osteochondral fracture. Figure 2: Case 1. Arthroscopic picture demonstrating reduction of the

displaced osteochondral fracture to the lateral femoral condyle.

1 2

1060 ORTHOPEDICS | www.orthobluejournal.com

sports medicine update

Case 2

A 19-year-old female NCAA

division 1 soccer player presented

with a large effusion and knee pain

after sustaining a twisting injury to

the left knee during a game the previous

day. The patient reported

immediate onset of pain and the

sensation that her “knee had gone

out of place.” The patient was initially

evaluated by the athletic trainer,

and placed in a knee immobilizer.

No history of injury or surgery

of either knee was reported. In

addition, no history of patellofemoral

instability in either knee

was noted prior to the current

injury. She was otherwise in good

health.

On physical examination, a

large effusion was present and

range of motion was limited secondary

to pain. An arthrocentesis

was performed and 70 cc of sanguineous

fluid was obtained. The

patient had active and passive range

of motion of the knee from 0°-

100°. The knee was maximally tender

over the medial boarder of the

patella and the medial femoral epicondyle.

The knee was stable to

varus and valgus stress at 0° and

30°. Lachman and anterior and posterior

drawer tests were negative.

Pain occurred with lateral translation

of the patella, and increased

asymmetric lateral patellar translation

was noted at 30° of flexion.

Anteroposterior, lateral, and tunnel

views of the left knee and Merchant

views of both knees were normal.

A diagnosis of acute lateral

patella dislocation was made. The

patient was placed in a hinged knee

brace locked in extension.

Magnetic resonance imaging

demonstrated an effusion and disruption

of the medial patellofemoral

ligament at its insertions

on the medial border of the patella.

Magnetic resonance imaging also

revealed osteochondral bone bruises

of the medial facet of the patella

and lateral femoral condyle (Figure

3). The ACL, PCL, MCL, LCL,

medial and lateral menisci were

intact. No evidence of a displaced

osteochondral fracture was noted.

The patient remained in the

hinged knee brace, locked in extension

and partial weight bearing for

3 weeks. The patient was then

placed in a dynamic lateral buttress

TABLE

Summary of Studies on Treatment of Acute Patella Dislocation

Study Sample Mean Recurrence

Study Design Treatment Size Follow-Up Surgical Technique Outcome Rate (%)

Cofield7 Retrospective Conservative 35 11.8 y NA 91% satisfied 44

1977

Hawkins6 Retrospective Conservative 20 40 mo NA 50% moderate/ 15

1986 severe pain

Cash8 Retrospective* Conservative 69† 8 y NA 52% G to E 43

1988 34‡ 75% G to E 20

Garth9 Retrospective Conservative 69 2 y NA 78% satisfied 26

1996

Maenpaa10 Retrospective Conservative 100 13 y NA 37% no complaints 44

1997

Dainer13 Retrospective Surgery 29 25 mo Scope, Scope + LR 83% G to E 27% with

1988 LR, 0% no LR

Vainionpaa14 Prospective Surgery 55 2 y Medial repair +/- LR 80% G to E 9

1990

Avikainen15 Retrospective Surgery 14§ 6.9 y Augment of MPFL 86% G 7

1993

Harilainen12 Prospective Surgery 53 6.5 y Medial repair/reef +/- LR 60% satisfied 17

1993

Sallay16 Retrospective Surgery 12 36 mo MPFL repair +/- LR 58% G to E 0 (33% sublux)

1996

Ahmad11 Retrospective Surgery 8 3 y VMO, MPFL repair + LR 96% satisfied 0

2000

Nikku17 Prospective, Conservative 55 2 y NA 70% G to E 30

1997 randomized Surgery 70 Proximal realignment 70% G to E 20

Fithian1 Prospective Conservative, 64 2-5 y Scope 9%, stabilize 12% NA 49

2004 surgery 125 Scope 6%, stabilize 5% 17

Abbreviations: E=excellent, G=good, LR=ligament repair, MPFL=medial patellofemoral ligament, NA=not applicable, and VMO=vastus medialis

obliquus.

*2 groups.

Predisposed.

Normal.

§Chronic and acute.

History of patellofemoral instability.

No history of patellofemoral instability.

OCTOBER 2004 | Volume 27 • Number 10 1061

sports medicine update

patellar stabilizing brace and range

of motion and strengthening exercises

were instituted with physical

therapy. During this time, the

patient exhibited no signs or symptoms

of loose bodies in the left

knee. The patient returned to sports

8 weeks following injury and at 2-

year follow-up the patient reported

no recurrent dislocation of the left

patella.

DISCUSSION

Treatment goals for patients

who have sustained a first-time

patella dislocation, include

restoration of normal pain-free

patellofemoral joint mechanics

while minimizing the risk of

recurrent subluxation and patella

dislocation.

Numerous retrospective

studies exist in the literature,

which detail the success of nonoperative1,6,7-

10 and operative11-

16 treatment of first-time patella

dislocations. Comparison of

these studies is problematic

given their retrospective design,

small sample sizes, differing

follow-up times, varied surgical

techniques both between and

within individual studies, and

heterogeneous sample composition

where primary dislocators

and patients with previous

history of patellofemoral instability

are grouped together

(Table). Comparison of these

studies demonstrates equivalent

results between operative and

nonoperative treatment. One

prospective randomized study17

demonstrated equivalent results

between operative and nonoperative

treatment. Conservative

treatment has therefore become

our standard of care for initial

treatment of first time patellar

dislocations.

Typical rehabilitation regimens

include immobilization of

the knee in extension for 2-3

weeks. Range of motion and

strengthening can be instituted

with the use of bracing to protect

against lateral displacement

of the patella. Return to full

activity can typically be accomplished

8-12 weeks from the

time of injury.

Indications for acute surgical

intervention include unstable

osteochondral fractures and

asymmetric unreduced lateral

subluxation of the patella. If a

displaced osteochondral fracture

is diagnosed by examination

or imaging studies, it

should be evaluated arthroscopically

and either reduced and

fixed or excised depending on

the size of the lesion. Large

unstable osteochondral fragments

typically require open

reduction and internal fixation,

whereas smaller fragments can

be excised arthroscopically.

The incidence of chondral or

osteochondral injury following

acute patellar dislocation has

been reported to be as high as

95% of cases.18 Furthermore,

standard radiographs have been

reported to have a sensitivity of

only 32% for identifying articular

injury.19 A majority of these

articular injuries missed on

plain radiographs are non-displaced

chondral and osteochondral

fractures and of no clinical

significance. However, if

patients report loose-body

symptoms, despite negative

radiographs and MRI, these

symptoms should be further

investigated and treated, if necessary,

with arthroscopy.

The disruption of the medial

patellofemoral ligament may

occur as a midsubstance tear, an

avulsion from the patella, or an

avulsion from the medial

femoral condyle. Finally, the

disruption may be multifocal in

nature.3 An MRI is therefore

useful for determining the location

of the medial patellofemoral

ligament tear.

Variable rates of recurrent

patellofemoral instability and

subsequent dislocation following

first time patellar dislocation

have been reported in the

literature. In retrospective

studies in which treatment was

nonoperative, recurrence rates

range from 15%-44%.6,7

Recurrence rates following

surgical intervention range

from 0%-17%.11,12 Certain factors

have been associated with

increased risk of recurrent dislocation

following first-time

dislocation. These include

young age at the time of dislocation,

history of symptoms of

patellofemoral subluxation

prior to first-time dislocation,

and anatomic predisposition.1,6

Regardless, no study to date

has demonstrated any disadvantage,

in terms of surgical

outcome, in delaying surgical

repair until after a patient has

suffered a recurrent patella dislocation

or subluxation versus

operating after a first time dislocation.

Furthermore, the

results of delayed proximal

realignment, performed in an

open or arthroscopic fashion,

have been good.20,21 If surgery

was performed after all firsttime

dislocations, then many

individuals who could have

been successfully managed

nonoperatively would be subjected

to unnecessary surgery

and its associated risks.

3

Figure 3: Case 2. Axial T2-weighted MRI demonstrating an effusion (black

arrow), disruption of the medial patellofemoral ligament (white arrow), and

osteochondral bone bruise of the lateral femoral condyle (small white arrows).

1062 ORTHOPEDICS | www.orthobluejournal.com

sports medicine update

We therefore advocate for

nonoperative treatment of all

first-time patellar dislocations,

unless a displaced osteochondral

fracture or an asymmetric

unreduced patella is noted.

REFERENCES

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al. Epidemiology and natural

history of acute patellar dislocation.

Am J Sports Med. 2004;

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693.

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DC. Acute lateral patellar dislocation

at MR imaging: injury

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T. Acute dislocation of the

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results in 125 randomized

patients. Acta Orthop Scand.

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Section Editor: Darren L. Johnson, MD

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