Dr. Anthony A. Schepsis

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

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schepsis@comcast.net

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MPFL publication

www.ORTHOSuperSite.com 1

Reconstruction of the Medial Patellofemoral Ligament

for Recurrent Patellar Instability

 Jack Farr, MD

Anthony A. Schepsis, MD

Dr Farr is from Indiana University School of Medicine and OrthoIndy,

Indianapolis, Ind; and Dr Schepsis is from Boston University Orthopaedic

Surgical Associates, Boston, Mass.

Reprint requests: Jack Farr, MD, 5255 E Stop 11 Rd, Ste 300, Indianapolis,

IN 46237.

INTRODUCTION

Recurrent lateral patellar instability after traumatic

patellar dislocation or subluxation is a commonly encountered

problem. Fithian et al14 concluded that individuals

with a history of recurrent patellar instability had seven

times higher odds of subsequent instability episodes than

fi rst time dislocators. In recent years, the importance of

the medial patellofemoral ligament (MPFL) as the primary

soft-tissue restraint to lateral displacement of the patella

has been corroborated by several authors.4,6,10,16,18 As

an extension of these investigations, the MPFL has been

established as the primary passive restraint to pathologic

lateral displacement of the patella. Thus, by defi nition, the

MPFL is always injured to some extent during traumatic

lateral patellar dislocations.6,10,16 Repair or reconstruction

of the MPFL is often recommended for patholaxity

of the medial patellar stabilizers with the understanding

that other medial tissues contribute (eg, medial patellotibial),

but are much less biomechanically important.

Although numerous procedures have been described

for addressing insuffi ciency of the medial restraints (eg,

reefi ng, advancements, and nonanatomic tendon transfer

procedures), most were designed without the current

anatomic and biomechanical knowledge of the MPFL and

associated anatomic medial restraints. As a result, some

of these earlier procedures have, at times, created the potential

for abnormal forces and contact areas (leading to

elevated stress) of the patellofemoral articulation. The

current goal of patellofemoral surgery, in general, is to

correct pathology without infl icting iatrogenic pathology

by inadvertently increasing patellofemoral stress. Thus, in

MPFL reconstruction, the goal is to recreate the restraint

of the MPFL without creating abnormal biomechanics. To

further emphasize this point, reconstruction is not an overconstraining

procedure and does not seek to address static

patellar position, nor is it indicated for primary problems

of pain and/or arthritis.

The following technique describes an approach to

the reconstruction of the MPFL using a free tendon graft.

Proper selection of patellar and femoral attachment sites,

anatomometric testing (as opposed to isometric), length

establishment (in distinction from tensioning), and fi xation

will be described. The graft is secured to the femoral

attachment site with an interference fi t bioabsorbable

screw. Two variations for patellar attachment of the graft,

with either suture anchor fi xation or interference fi t, will

be detailed. This procedure may be performed in association

with tibial tubercle realignment and/or cartilage restoration

of the patellofemoral joint as per patient pathology

and surgeon discretion.

PREOPERATIVE PLANNING

Physical Examination

A thorough extremity, knee, and patellofemoral specifi

c physical examination is performed as detailed by

Boden et al3 and Post.21 Specifi c to the MPFL, the extent

of patellar medial/lateral displacement and patellar

apprehension are documented. The patellar displacement

examination is performed with the knee at approximately

20°-30° of fl exion. The examiner palpates and holds the

margins of the trochlea with the index fi nger and thumb.

The trochlea is mentally divided into four quadrants.

Using the index fi nger and thumb of the other hand, the

medial and lateral margins of the patella are secured. A

normally positioned patella will be central in the trochlea

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at this degree of fl exion. Any medial or lateral deviation

from this starting point is noted.

The patella is then displaced medially and laterally and

the trochlear quadrants of displacement (patellar glide) are

recorded and compared to the contralateral knee. Three

quadrants or greater of lateral patellar displacement suggest

patholaxity (injury) to the MPFL. At this same degree of

knee fl exion, the patella lateral margin is assessed for mobility

(tilt) in the axial plane, again gripping the patella with

the index fi nger and thumb. The patella tilt noted initially

should be reversible to neutral. Failure to reverse tilt is one

indication of lateral compression and usually is associated

with a decrease in medial glide (displacement) of the patella

to ó or less trochlear quadrant. A combination of increased

lateral displacement past three trochlear quadrants (usually

associated with marked apprehension) and clinical history

of recurrent lateral patellar instability should be present to

warrant MPFL repair or reconstruction.

The contralateral knee should be examined for comparison,

but these independent guidelines are sometimes

necessary as bilateral patellofemoral dysplasia and bilateral

recurrent lateral patellar instability are common. It is

important to use the Fulkerson test to rule out iatrogenic

medial dislocations (post excessive lateral release), which

can present with the patient reporting lateral dislocations

by mistake (ie, a lateral dislocation, but in fact, the patella

moves from an overly medial position laterally into

the proper central trochlea position). The Fulkerson test

is performed with the patient in the supine position. The

examiner manually pushes the patella medially with the

knee extended, which simulates the medial “drift” of the

medial tracking patella. The examiner then abruptly fl exes

the knee and releases the patella. If the test is positive,

the patient experiences the same feeling of instability, as

this reproduces the abrupt relocation of the patella into the

trochlea from its medial position in extension.

Preoperative Imaging

Three standard radiographs (anterior/posterior, lateral,

and low fl exion angle axial [Merchant]), in conjunction

with a thorough physical examination, usually are

suffi cient to plan MPFL surgery. Occasionally, stress radiography

can help substantiate the clinical medial and

lateral patellar displacement. True lateral radiographic

views are useful for classifi cation of trochlear anatomy/

dysplasia and to document patellar infera or alta. Note

that the radiographs are used in an accessory manner, ie,

the radiographs help with determining bony injury, patellofemoral

dysplasia, and patellar height, but the decision

for MPFL reconstruction is based on the patholaxity of the

MPFL. Magnetic resonance imaging (MRI) and computed

tomography tracking studies may in certain instances

contribute to planning information, especially in assessing

tibial tubercle to trochlear groove distance (“TT-TG

measurement”), tilt, and MRI evidence of chondrosis.22

The use of this information in planning trochlear and/or

tubercle surgery is beyond the scope of this technique article.

Nevertheless, it is worth reemphasizing that patellofemoral

problems often are multifactorial, and the debate

as to whether the MPFL reconstruction can address all

problems of patellar instability, or if it should be combined

with tubercle surgery or tubercle surgery should be

performed alone, is ongoing and long-term prospective

studies are needed to elucidate this issue.

Examination Under Anesthesia and Arthroscopy

In addition to documenting the MPFL patholaxity

during standard physical examination, the examination is

reevaluated under anesthesia. Without the limitations of

patient apprehension, further lateral patellar displacement

under anesthesia often is observed compared to the examination

in which the patient is awake. Arthroscopy allows

inspection for possible cartilage lesions, as they are

commonly associated with recurrent patellar instability as

reported by Nomura and Inoue.20 If cartilage lesions are

present, they are staged by documenting grade and dimension

on a patellofemoral region map of the International

Cartilage Repair Society (available at www.Cartilage.

org). The decision algorithm to treat patellar chondral lesions

is outside the scope of this article, but is discussed

in depth by Farr in a patellofemoral monograph.13 Briefl y,

small lesions may be debrided to avoid intermediate term

desquamation, whereas more extensive lesions may suggest

the need for cartilage restoration. At the time of cartilage

restoration decision, MPFL surgery may still be performed

or it may be postponed based on the arthroscopy

and conducted later at the time of a concomitant cartilage

restoration procedure to minimize surgical trauma. By using

all of the data obtained from the physical examination,

examination under anesthesia, and arthroscopy, the fi nal

decision is made in regards to MPFL surgery.

GRAFT SELECTION

Our preferred graft for this procedure is a doubled

semitendinosus autograft or allograft. The authors have a

slight preference for the use of a semitendinosus allograft

rather than autograft to avoid graft site/donor graft morbidity

(pain and any fl exor weakness). The potential disadvantages

of using an allograft are longer incorporation

time and the potential for disease transmission. The authors,

however, have found that these allografts performed

similar to the autograft tissue in this richly vascular extra-

articular environment. In summary, the use of either

allograft or autograft is dependent on surgeon and patient

preference. The doubled semitendinosus graft offers a wide

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“margin of safety” in terms of strength. In fact, the purpose

of a doubled graft is to match the attachment site area

at the patella and not for strength. The strength-to-failure

of an intact medial patellofemoral ligament is 208 N, with

a stiffness of 12 N/mm. The stiffness of a reconstructed

MPFL is approximately 12 N/mm, which is approximately

20% of the average stiffness recorded for looped 30-mm

long semitendinosus grafts.6,14 The strength-to-failure of a

double strand semitendinosus is 2330 N, with a stiffness of

469 N/mm. The strength-to-failure of a double strand gracilis

is 1550 N, with a stiffness of 336 N/mm. With any of the

graft choices discussed above (single or double stranded),

the stiffness and strength requirements of the native MPFL

are satisfi ed with a large margin of safety.

If autograft is used, it is harvested through a separate

small incision over the pes group tibial insertion after

examination under anesthesia and arthroscopy have confi

rmed the need for MPFL reconstruction. Alternatively,

this procedure can also be performed with two tendons,

particularly for smaller patients. When allograft is preferred

and a hamstring allograft is not available, a tibialis

or other foot/ankle fl exor tendon may be used, noting in

the case of the tibialis, it often will need to be trimmed

to a narrower width for proper fi t. For the doubled graft

technique, the graft is fi rst doubled upon itself. A running

baseball stitch (using #2 Fiberwire) for a distance of 25

mm is performed at each free end and the doubled end,

creating a Y-shaped graft (Figure 1). The graft tendon is

sized at the doubled end for the femoral attachment socket

fi t (for a single strand, the larger diameter end is sized).

SURGICAL APPROACH

For isolated reconstruction of the MPFL (without

arthrotomy or associated procedures), two incisions are

made over the respective attachment sites—a 3- to 4-cm

longitudinal incision along the proximal medial border of

the superior one half of the patella and a smaller longitudinal

incision over the femoral attachment site in the saddle

area between the medial epicondyle and the adductor tubercle

(Figure 2). Alternatively, one longer medial patellar

incision can be used to expose both sites, particularly

when an arthrotomy is necessary such as with cartilage

restoration of the patellofemoral compartment.

(If tubercle surgery [medialization or anteromedialization]

is planned, then it is typically performed through a

separate incision. Alternatively, a long anterior “universal

incision” may be used if an extensive cartilage restoration

procedure is performed concomitantly with proximal

and distal extensor mechanism surgery. As the tubercle

surgery alters the relative anatomic relationships of the

MPFL, as well as peripatellar soft-tissue tensions, the tubercle

procedures should be performed prior to completing

the MPFL reconstruction.)

In general, a lateral release is not routinely performed

with MPFL reconstruction, but rather on a case-by-case

basis. In fact, be aware that in patients with pre-existing

adequate soft-tissue laxity of the lateral retinaculum, a lateral

release could create medial subluxation. If the tubercle

malalignment is only mildly to moderately abnormal

(the TT-TG distance is in the gray area between normal

and abnormal) and questions arise regarding the extent or

need for tubercle surgery, the MPFL reconstruction can be

initiated, but using only pins at the attachment sites and

suture to duplicate the planned MPFL. At that point, the

potential effect of tubercle surgery can be reassessed. If

distal realignment is believed necessary to centralize the

patella, it can be performed and fi xed followed by completion

of the MPFL reconstruction with fi ne-tuning of the

MPFL lengths with this new patellar tracking position.

The patellar area incision is made fi rst. Dissection is

performed along the proximal two-thirds of the medial

patella to the interval between layer 2 and 3 (between the

MPFL and capsular layer). This interval is bluntly developed

medially towards the medial epicondyle, using a

curved Kelly clamp. The graft should always be placed extra-

articularly (superfi cial) to the capsule. A 2-cm femoral

incision is made over the tip of the clamp when it overlies

the saddle between the epicondyle and adductor tubercle.

The femoral attachment of the MPFL is identifi ed using

the landmarks of the medial epicondyle, medial collateral

ligament, and adductor tubercle. The femoral attachment

of the MPFL resides posteriorly in the “saddle”

Figure 1. Doubled semitendinosus graft sutured in a “Y”

confi guration ready for insertion at the femoral origin site.

1

Figure 2. The incisions centered over the patellar and

femoral attachment sites of the MPFL.

2

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between the adductor tubercle and medial epicondyle. The

fascia is incised and a 2.4-mm guide pin (Bio-Tenodesis

Fixation Set; Arthrex, Naples, Fla) is placed just proximal

to the epicondyle and distal and posterior to the adductor

tubercle. A #2 suture is wrapped around this guide pin and

is pulled to the patella with the clamp through the same

MPFL/capsular interval tunnel and sutured or clamped

into the patellar attachment site of the MPFL (which is

along the proximal two-thirds of the medial patella, noting

the arms of the suture are at the proximal and distal

extent of the patellar MPFL attachment footprint). The

suture is pulled so that it is not loose or tensioned with the

knee at approximately 30° of fl exion. This adheres to the

concept of setting the length of the MPFL at the region

where the distance between the patellar and femoral attachments

are furthest apart (the ligament length could be

considered the “longest” at this arc of motion). Although

this is conceptually different from using “tension” to determine

the graft position/length, the goal of optimally

placing the graft to function properly without capturing

the patella is shared by both approaches. The knee is then

placed through a range of motion. The suture should become

lax with increasing fl exion and minimally change

or slightly tighten in terminal extension (Figures 3 and

4). The planned attachment sites and MPFL length should

not over-constrain, tension, or tilt the patella medially at

any point during full range of motion. Again, the goal is to

create a passive checkrein only.

The femoral origin is much more sensitive than the

patellar attachment in terms of achieving an anatomometric

graft placement (ie, the femoral attachment site alters

the attachment site distances through range of motion

more than the patellar site, as a result of the “cam” shape

of the medial femoral condyle. This femoral sensitivity

of graft attachment site is somewhat analogous to the

femoral attachment site importance in an anterior cruciate

ligament [ACL] reconstruction relative to the tibial attachment

site). Slight variations in position of the femoral

attachment site can have major implications on the patellar

tracking and contact forces.12 If the suture does not

exhibit the desired length changes during range of motion,

the patellar attachment may remain constant while the pin

at the femur is repositioned. If excessive tightening occurs

in extension, the graft is too distal or posterior, and if

there is increased tension in fl exion, the femoral point is

too proximal or anterior. The most common error is overconstraining,

thus causing abnormal contact forces on the

medial facet of the patella, as well as making it more diffi

cult to regain fl exion in the postoperative rehabilitation.

After an anatomometric position is established, tenodesis

at the femoral attachment site is the next step.

FEMORAL SOCKET PREPARATION

The doubled femoral end of the graft has been sutured

and sized. With the femoral guide pin still in place, a cannulated

drill bit 0.5-mm larger than the graft size is chosen

from the biotenodesis system. The Table provides a guide

for details of socket preparation and screw selection.

The femoral socket is drilled to a depth 2-mm longer

than the designated screw size length (Figure 5).

The appropriately sized Tenodesis Screw (Table) is

loaded onto the Bio-Tenodesis driver (Arthrex). A #2

Figure 3. Anatomometric testing extension. Figure 4. Anatomometric testing fl exion.

3 4

Figure 5. Femoral socket preparation.

5

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Fiberwire suture loop or #2 Fiberwire Suture Snare is

passed through the center cannulation of the driver tip.

The sutures extending from the graft are placed through

the suture loop. The loop is tightened around the tip of the

graft (and knots of the graft suture) and secured as they

exit the Tenodesis Driver Handle. The graft is inserted

into the base of the femoral pilot hole with the screw on

the posterior aspect of the socket and the tendon exiting

anteriorly (Figure 6).

Adjustments can be made to place the tendon in different

aspects of the tunnel (with respect to the screw) to adjust

anatomometric characteristics of graft length, if necessary.

The Bio-Tenodesis Screw is advanced adjacent to the graft

until the screw is fl ush to the cortical bone rim. Security of

the graft is tested. The sutures exiting the Bio-Tenodesis

screw and graft sutures may be either tied together to lock the

screw and graft together or cut as per surgeon preference.

GRAFT LENGTH SELECTION AND PATELLAR FIXATION

Option A: Bio Suture Tak “Reverse Loop” Technique

Two doubly loaded Arthrex 3.0-mm (smaller patellae)

or 3.7-mm (larger patellae) Bio-Suture Tak anchors are reloaded

with the Fiberwire loop end rerouted through suture

anchor loop (Figures 7 and 8A). Alternatively, one 3.7-mm

anchor can be used for a single strand graft. The suture anchors

are placed in a cancellous trough (created with a 4-

mm round burr) in the medial edge of the patella (superior

two-thirds) anterior to the articular cartilage (Figure 8B).

The two free arms of the allograft tendon are routed in

the developed soft-tissue tunnel interval from the femoral

attachment to the patella (Figure 9).

The sutures of the graft double tail ends are passed

into the loops, which have been threaded through the suture

anchor loops. After pulling the sutures and graft tails

through the soft-tissue tunnel, the graft tails are pulled

through the suture loops. One tail of the “Y” graft is

pulled through the mid-waist loop and the other graft tail

through the proximal loop. The suture loops are temporarily

cinched tight around the graft and held with hemostats.

This initial graft length trial is set at approximately 30°

of fl exion with both grafts pulled to length with minimal

tension and no laxity. The knee fl exion position for the

fi rst estimation of the graft length is based on a review of

biomechanical studies, which together suggest that the attachment

site distance (femoral to patellar) is longest near

30° of fl exion. (Once again, this emphasis on graft length

is analogous to ACL graft “fi xation,” as length of the graft

determined by knee fl exion angle is more important than

initial tension on the graft, ie, the major infl uence of ACL

graft function is proper position and length of the graft

set at a specifi c degree of arc of motion rather than tension

at fi xation). As during the anatomometric testing

with sutures, the applied graft “tension” is primarily to

TABLE

GUIDE FOR BIO-TENODESIS GRAFT FIXATION:

RECOMMENDED GRAFT, SOCKET, AND SCREW SIZE

FOR MPFL RECONSTRUCTION

Graft

Diameter (mm)

Socket

Diameter

(mm)

Socket Depth

(mm)

Bio-Tenodesis

Screw Size

(mm)

5 5.5 17 5.515

5.5 6 17 5.515

6 6.5 17 6.2515

6.5 7 25 723

7 7.5 25 723

7.5 8 25 723

8 8.5 25 823

Figure 6. The femoral screw insertion on the posterior side

of the socket.

6

Figure 7. Bioabsorbable suture anchor.

7

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remove “slack” in the graft to assure the length is correct:

the object is to select the proper baseline graft length, not

a baseline graft tension (Figure 10).

With this “longest length” of the graft (range of motion

at which the femoral and patellar attachment sites

are furthest apart) selected at a specifi c range of motion

(probably somewhat different from knee to knee, but near

30°), the site of the graft in the suture loop is marked with

a marking pen. The knee is placed through full range of

motion. The purpose of this range of motion test is: 1) to

assure a smoothly and centrally tracking patella, and 2)

that the longest graft length was selected during the anatomometric

position analysis. If the graft becomes tensioned

(patellar/femoral distance is increasing) with fl exion, the

mark on the graft will change in respect to the loop. If

the graft does not move in the loop, the femoral site was

selected properly. Minor adjustments can be made in the

length of the graft (through the loop) after checking medial/

lateral translation. Optimum graft placement allows

the patella to balance in the trochlea or 2 medial/2 lateral

trochlear quadrants of displacement (or symmetrical

with the other knee, if unaffected). Once the appropriate

graft length is achieved, the loops are tied and the graft is

folded back onto itself and sutured (Figures 11 and 12).

PATELLAR FIXATION USING THE BIO-TENODESIS

TECHNIQUE

This method of fi xation is ideally suited for single

strand grafts. Using the patellar poles as a reference, the

Figure 8. Medial border of the patella trough created with a burr (A). Suture anchor embedded in bony trough, which has

been refi tted with looped Fiberwire (B).

8A 8B

Figure 9. Passage of the graft to the patella after femoral

fi xation.

9

Figure 10. With this cinch loop technique, fi ne adjustments

of graft length are possible independent of attachment

site selection.

10

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2.4-mm guide pin is placed at the junction of the proximal

third and distal two-thirds of the patella. The Bio-Tenodesis

fi xation will be placed on the distal part of the socket,

in the wider portion of the patella.

The pin is advanced transversely across the patella until

it just exits laterally to ensure placement parallel with

the dorsal surface. Anatomometric characteristics should

be checked again by placing a temporary suture through

the graft at the patellar border under appropriate tension.

A suture is placed through the dorsal patellar soft tissues at

the edge of the socket and the same tensioning check is performed

as described before, securing the suture temporarily

through the graft and holding it with a hemostat. Once determined,

the graft is marked at this point (Figure 13).

The graft is cut 17 mm distal to this point. This portion

of the graft up to the mark should be sized and trimmed

as well as tapered slightly to between 5 and 6 mm, taking

into account that the baseball suture will slightly bulk up

the graft. A graft larger than this would require too large a

socket and screw for patellar fi xation. A baseball suture is

placed in this 17-mm free end of the graft and sized once

more. An acorn reamer 0.5-mm larger than the graft size

is chosen as per the same guidelines in the Table and a 17-

mm socket is created (Figure 14).

The appropriate sized screw, most commonly the 5.515

mm or the 6.2515 mm, is placed on the appropriate driver

(Table). The graft is pulled up to the tip of the driver with a

suture loop through the cannulation of the driver.

The knee is placed in 30° of fl exion as the Bio-Tenodesis

screw is inserted on the inferior portion of the graft

until fl ush with the cortical rim of the patella. The graft

sits superiorly and the screw is in the thicker portion of

the patella. Additional backup fi xation is possible with

a 3.0-mm Bio-Suture-Tak placed next to the socket, but

this usually is unnecessary. Soft-tissue sutures through the

graft and patella can also be used (Figure 15).

The soft tissues of layer 2 can then be reapproximated

over the graft and imbricated if necessary. The remaining

wound is closed in standard fashion (Figure 16).

POSTOPERATIVE MANAGEMENT

Postoperative Weeks 1-6

A compressive soft dressing and range of motion

Figure 11. After tying the anchor suture loops, additional

sutures can be added, further securing the graft to the

soft-tissue sleeve at the medial edge of the patella, and the

remaining graft can be passed back towards the femoral

attachment and sutured to itself.

11

Figure 12. The completed reconstruction using suture anchors.

(Reprinted with permission from Arthrex, Naples, Fla.)

12

Figure 13. The guide pin has been placed, and a temporary

suture placed at the edge of the patella is used to

determine tension. The corresponding location on the graft

is marked and the graft is measured and cut 17 mm distal

to this point.

13

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brace, initially locked in extension, are applied. The brace

is opened to allow full extension to 30° of fl exion as muscle

control is reestablished. Quadriceps isometrics are allowed,

unless the surgeon has elected to perform vastus

medialis obliquis advancement. Early motion is important

to prevent excessive scarring. Because the graft is placed

in an “anatomometric” fashion, there should not be excessive

graft tension with range of motion as the graft becomes

more lax with fl exion past 20°-30°. An optional

continuous passive motion machine may be used in the

postoperative period.

During ambulation, the use of crutches and a knee

brace in extension are recommended until the patient has

good quadriceps control without lag. Weight bearing as

tolerated is allowed. Crutches are gradually weaned and

discontinued when operative extremity control is excellent

and no limping occurs. Standard patellofemoral proximal

and core functional muscular exercises are performed

throughout the postoperative period. Close monitoring

of motion is essential to assure full range of motion is

achieved in the early postoperative setting, as this procedure

can initiate a vigorous scar response. If articular cartilage

procedures are performed concomitantly, progression

of exercises, range of motion, and weight bearing are

modifi ed accordingly.

After Postoperative Week 6

Progressive strengthening and functional exercises are

continued postoperatively until full strength, endurance,

and agility have been reestablished. Once all goals are

met, activities are advanced through a functional progression

program. Patellofemoral bracing may be used per patient

and surgeon preference.

DISCUSSION

Although recurrent patellar instability is a relatively

common occurrence after acute patellar subluxation or

dislocation, a review of the literature indicates a wide

variation in reported recurrence rates. A common theme

among authors is the need for a thorough examination and

rational patient-specifi c plan. Although numerous studies

exist in the literature detailing the success of nonoperative

and operative treatments of fi rst-time patellar dislocations,

comparison of these studies is problematic given

their retrospective design, small sample sizes, different

follow-up times, and heterogeneous sample composition.3

In an analysis of studies and treatment of acute patellar

dislocations by Geary and Schepsis,15 the recurrence rate

after conservative treatment of acute traumatic fi rst patellar

dislocations was between 15% and 44%. Likewise, an

analysis of recurrence after an acute surgery indicated a

recurrence rate between 7% and 33%. Most of these studies

are retrospective in nature. Recently, however, one

prospective study by Fithian et al14 indicated a recurrent

Figure 14. Drilling of the patellar socket.

14

Figure 15. The graft is secured to the patella, placing the

screw inferiorly in the thicker portion of the patella.

15

Figure 16. The completed reconstruction using the patellar

tenodesis technique. (Reprinted with permission from

Arthrex, Naples, Fla.)

16

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rate of 49% in patients treated conservatively and 17%

in patients with early surgery. They also found that older

females had a higher risk of recurrent patellar instability.

Multiple risk factors have been associated with patellar instability

including tubercle malalignment secondary to either

increased femoral anteversion or external tibial torsion,

trochlear dysplasia, patella alta, vastus medialis obliquis

atrophy, insuffi ciency of the MPFL, patellar hypermobility,

and increased patellar tilt with tight lateral retinaculum.

With greater patellofemoral dysplasia, the forces required

to dislocate the patella decrease substantially.21

Multiple studies agree that the MPFL is the primary

static restraint to lateral displacement of the patella.4,6,16

An MPFL tear is the “essential lesion” after acute traumatic

patellar dislocation.2,4 In patients with recurrent lateral

patellar instability, by defi nition the MPFL must be attenuated,

torn, or insuffi cient. Although 100 operations

exist to treat patellofemoral instability, it now appears

essential to address the core lesion. Multiple proximal

procedures have been described to treat the MPFL pathology.

5,7,9,20,22,24 These procedures include arthroscopic and

open approaches, reefi ng, and some non-anatomic tethering

grafts. Those procedures, which are not anatomic,

may create abnormal tracking patterns and abnormal contact

forces on the patella. Therefore, an attempt has been

made to restore a portion of the normal anatomy without

over-constraint. Reconstruction of the MPFL is indicated

in patients with recurrent lateral patellar instability due to

excessive laxity of the medial soft-tissue patellar stabilizers.

Medial patellofemoral ligament laxity must be documented

by history, physical examination, and in some

cases, with imaging and stress radiography. Examination

under anesthesia and arthroscopy routinely precede the

reconstruction, not only to document the laxity, but also

to document tracking patterns as well as to stage and treat

associated articular cartilage lesions. Nomura et al19 recently

reported that up to 95% of patients with fi rst time

dislocation suffered from articular cartilage injuries (osteochondral

fracture and or longitudinal cracks).

The current procedure represents an incremental

modifi cation of the multiple procedures described to reconstruct

the MPFL.4,8,11,17 Most of these procedures are

performed with a free tendon hamstring graft, which is

signifi cantly stronger than the native MPFL. It is suggested

that an “anatomometric” approach may be valuable, as

an option to an “isometric” approach (choosing the length

of the graft, rather than tension). With any approach, careful

review of the relevant biomechanics of the MPFL is a

critical aspect of reconstruction so as not to over-constrain

the patellofemoral joint, particularly the medial facet. In

light of the cam shape of the femur, the MPFL is most

sensitive to the femoral attachment site. Therefore, it is

critical to pick the appropriate points of attachment and

test the anatomometric behavior to plan the fi nal fi xation

points for the procedure. Elias et al12 have shown that a 4-

mm proximal shift in the femoral attachment point of the

reconstructed MPFL signifi cantly increases the compressive

forces on the medial facet of the patella, as well as

increasing medial patellar tilt. In the same study, they also

showed that increasing the tension excessively by a length

change of as little as 4 mm in the graft also overloads the

medial patellofemoral cartilage.

A common problem is placement of the femoral origin

too proximally near the adductor tubercle, such that

the graft tightens in fl exion, leading to markedly increased

compressive forces on the medial patellofemoral cartilage

in fl exion and diffi culties in regaining range of motion.

Because the MPFL primarily functions from 0°-30°,8 it

would follow that maximum resistance to abnormal lateral

tension be in this range. Likewise, it is critical that the

ligament reconstruction should act not as a tether, but only

as a “checkrein” to prevent excessive lateral displacement

of the patella. Normal physiological glide should be reestablished

at the end of the procedure. The currently

described technique allows a reproducible method, not

only to examine the anatomometric measurements of the

MPFL, but also to fi ne tune the graft lengths to reestablish

normal physiological patellar tracking.

Pullout strength studies of the fi xation used demonstrate

that the fi xation of the grafts is more than adequate to allow

for immediate range of motion after these procedures are

performed.1 With secure fi xation at both attachment sites

and a strong graft tissue, an aggressive early rehabilitation

program is not only allowable and safe, but also essential to

decrease scarring and muscular dehabilitation.

As mentioned previously in the technique section, in

some cases it may be necessary to combine MPFL reconstruction

with distal realignment. If distal realignment is

believed necessary to centralize the patella, the osteotomy

should be performed fi rst and tracking reassessed, followed

by completion of the MPFL reconstruction with

fi ne-tuning of the MPFL lengths with this new patellar

tracking and position. The goal of the MPFL is to provide

a checkrein, stopping laterally abnormal displacement,

and is not used to “pull” the patella into the trochlea. In

general, distal tubercle transfer combined with the MPFL

reconstruction is reserved for those patients with a markedly

abnormal lateral tubercle position associated with

moderate to severe insuffi ciency of the medial restraints

of the patella. The controversy over when to perform a

distal versus proximal realignment and when they should

be combined is a volatile topic, beyond the scope of this

article. The important point is to “fi ne-tune” each procedure

when they are combined, particularly in the sense

that fi ne-tuning the MPFL reconstruction should be performed

after the distal tubercle transfer. The postopera-

JKS0406FARR.indd 9 8/30/2006 1:31:36 PM

10

THE JOURNAL OF KNEE SURGERY

October 2006 / Vol 19 No 4

tive radiographs of patients with preoperative static patellar

subluxation will vary, depending on whether distal or

proximal realignment was performed. On a low-fl exion

axial view (eg, Merchant radiograph), the patella will remain

statically subluxed when treated by those surgeons

whose philosophy is to treat only the MPFL and not the

tubercle. On the other hand, for surgeons who treat increased

TT-TG distances with tubercle medialization,

postoperative radiographs may show a more centralized,

static Merchant view.

CONCLUSION

Regardless of the means of addressing MPFL patholaxity,

the goal is to duplicate the MPFL anatomy and

biomechanics. Although the precise anatomometric characteristics

of the MPFL graft have not been universally

agreed upon in the literature, within the range of reported

MPFL characteristics, the currently described technique

is reproducible in restoring “near normal” MPFL attachment

site positions. This allows the reestablishment of patellar

stability without creating abnormal tracking, which

is paramount as the MPFL serves as a “checkrein” against

laterally directed displacement forces and should not overconstrain

the patellofemoral compartment. The adherence

to attachment site anatomy and graft length selection allows

correction of the pathophysiology of lateral patellar

instability and an aggressive rehabilitation program.

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