The complex anatomy of the posterolateral corner of the knee
is due largely to the evolutionary changes in the anatomic relationships
of the fibular head, the popliteus tendon, and the biceps femoris muscle.
Recent research has improved our understanding of the popliteus
complex, particularly the role of the popliteofibular ligament.
Biomechanical studies provide a scientific basis for clinical
examination of the knee with suspected injury of the posterolateral
corner.
All grade-I and most moderate grade-II injuries of the posterolateral
structures can be treated nonoperatively, but residual laxity may
remain, especially in knees with grade-II injury.
Acute grade-III isolated or combined injury of the posterolateral
corner is best treated early, by direct repair, if possible, or
else by augmentation or reconstruction of all injured ligaments.
Chronic injury of the posterolateral corner, whether isolated
or combined, is probably best treated by reconstruction of the posterolateral
corner along with reconstruction of any coexisting cruciate ligament
injury.
Failure to diagnose and treat an injury of the posterolateral
corner in a patient who has a known tear of the anterior or posterior
cruciate ligament can result in failure of the reconstructed cruciate
ligament.
Injuries of the posterolateral corner of the knee are infrequent
but can cause severe disability due to both instability and articular
cartilage degeneration1-3. These
injuries do not usually occur in isolation but are often associated
with injury of the anterior or posterior cruciate ligament4,5. The diagnosis of subtle lesions
of the posterolateral corner can be elusive unless there is a high degree
of clinical suspicion for possible injury of this region. The consequence
of missing a posterolateral injury in the presence of a known tear
of the anterior or posterior cruciate ligament can be failure of
the reconstructed cruciate ligament6-8.
Recent studies have shed new light on the complex anatomy and functional
mechanics of the posterolateral corner of the knee, and they provide
a framework for improved diagnosis and treatment of these often
disabling injuries.
The posterolateral corner of the knee, with its complicated and
varying anatomy of static and dynamic stabilizers, is probably the
least understood region of the knee; it was once considered the
"dark side" of the knee9. The
inconsistent terminology used to describe the structures in the
posterolateral corner has added to the confusion10,11.
This is underscored by the varying nomenclature applied to the popliteofibular
ligament, which has been called the short external lateral ligament12, the popliteofibular fascicles13, the fibular origin of the popliteus14, the popliteus muscle with origin
from the fibular head11, and the
popliteofibular fibers15. In fact,
because of an oversight, mention of this structure disappeared from
standard anatomy texts and the orthopaedic literature during the
middle of the twentieth century, only to be rediscovered recently16.
Evolutionary and Developmental Anatomy
To conceptualize the morphology of the posterolateral corner,
an understanding of the evolutionary and developmental anatomy helps
to explain some of the confusing structural relationships.
The complex anatomy of the posterolateral corner of the knee
is due largely to the evolutionary changes in the anatomic relationships
among the fibular head, the popliteus tendon, and the biceps femoris
muscle17. In paleontologic specimens
dating back 360 million years, in extant lower vertebrates, and
in early human embryonic development, both the fibula and the tibia
articulate with the femur18-20.
However, as the vertebrate knee evolved, the fibula and the attached
lateral portion of the joint capsule moved distally to form a new
capsular layer between the distal part of the femur and the proximal
popliteus muscle, resulting in the popliteal hiatus and an intra-articular
popliteus tendon. In early evolution, when the fibula articulated
with the femur, the popliteus tendon inserted on the fibular head.
With subsequent distal migration of the fibular head, the popliteus
tendon acquired a femoral attachment while retaining its original
fibular insertion17. There also
was an evolutionary change in the location of the biceps femoris
tendon attachment, from the lateral aspect of the capsule and the
proximal part of the tibia to the fibula21.
The major components of the posterolateral corner of the knee
appear early in the course of human development. Between seven and
eight weeks of embryonic development, the fibular head has completed
its distal migration to reach a definitive location with respect
to the proximal part of the tibia, and the lateral collateral ligament,
popliteus tendon, and lateral meniscus are identifiable22-24. At eight weeks, the embryonic
knee has assumed a shape similar to that of the adult joint; three
weeks later, the popliteofibular ligament can be seen, having formed
during the process of fibular migration, with the attached popliteus
tendon. By the sixteenth week of development, the connections among
the popliteus tendon, the lateral meniscus, and the fibular head
that are seen in the adult knee are fully formed24.
Macroscopic Anatomy
The major structures of the posterolateral corner of the knee
include the iliotibial tract, the lateral collateral ligament, the
popliteus complex consisting of both dynamic components (the popliteus
muscle-tendon unit) and static components (the popliteofibular ligament,
popliteotibial fascicle, and popliteomeniscal fascicles), the middle
third of the lateral capsular ligament, the fabellofibular ligament,
the arcuate ligament, the posterior horn of the lateral meniscus,
the lateral coronary ligament, and the posterolateral part of the
joint capsule14,16,17,25. This
anatomy can be quite variable.
In their study of thirty-five cadaver knees, Seebacher et al.25 described the lateral structures
of the knee as comprising three distinct layers (Fig. 1Fig. 1). The
most superficial layer consists of the iliotibial tract, including
its anterior expansion, and the superficial portion of the biceps
and its expansion posteriorly. The middle layer is formed by the quadriceps
retinaculum anteriorly but is incomplete posteriorly, being represented
by the two patellofemoral ligaments. It also contains the patellomeniscal
ligament. The third and deepest layer forms the lateral part of
the joint capsule. This layer is divided into a superficial lamina,
which encompasses the lateral collateral ligament and ends at the fabellofibular
ligament, and a deep lamina, which forms the coronary ligament and
the popliteal hiatus, terminating at the arcuate ligament. The popliteofibular
ligament is a component of this deep layer. Seebacher et al. noted
three anatomic variations in their knee dissections. The arcuate
ligament alone reinforced the posterolateral part of the capsule
in 13% of the knees, the fabellofibular ligament alone reinforced
it in 20%, and both reinforced it in 67%.
On the basis of their dissections of fifty cadaver knees, Sudasna
and Harnsiriwattanagit14 also
found variability in the posterolateral corner structures. They
identified a fibular origin of the popliteus (now termed the popliteofibular
ligament) in 98% of the knees, a fabellofibular ligament in 68%,
and a thin, membranous arcuate ligament in 24%.
In a study of 115 cadaver knees, Watanabe et al.11 identified seven anatomic variants
by including the presence or absence of what they termed the popliteus
muscle with origin from the fibular head (the popliteofibular ligament)
in a classification scheme that also included the variability of
the arcuate and fabellofibular ligaments previously noted by Seebacher
et al.25. They found a lateral
collateral ligament and a popliteus tendon in all knees and a popliteofibular ligament
in 94%. Terry and LaPrade17 recently
performed dissections of thirty cadaver knees to provide a detailed
description of the complex anatomy and to develop a dependable operative
approach to the posterolateral structures. They used this operative
approach in a series of seventy-one patients and noted that it provided
excellent access for inspection and repair of injured components
of the posterolateral corner of the knee.
Blood Supply
The blood supply to the posterolateral corner of the knee comes
from named and unnamed branches of the popliteal artery. The lateral
superior genicular artery is divided into three branches. The articular branch
supplies the lateral collateral ligament and the lateral region
of the knee. This branch anastomoses with the ascending branch of
the lateral inferior genicular artery that runs anteriorly, deep
to the lateral collateral ligament17,26.
The middle genicular artery provides an important contribution to
the posterior capsular region27.
Additional contributions come from the posterior tibial recurrent
artery that ramifies into small branches to supply the popliteus
muscle, the tibial condyle, and the joint area superior to the fibular head26. Small branches off of the popliteal
artery also supply the posterior capsular region26.
Innervation
The posterolateral structures of the knee are innervated from
several sources. With contributions from the posterior articular
nerve (a prominent branch of the posterior tibial nerve) and from
the terminal portions of the obturator nerve, the popliteal plexus
supplies the posterolateral part of the capsule and the external
portion of the lateral meniscus28,29.
The terminal portion of the nerve to the vastus lateralis supplies
the superior portion of the lateral part of the capsule. The lateral
articular nerve arises from the common peroneal nerve and innervates the
inferior portion of the lateral part of the capsule and the lateral
collateral ligament28,30.
The knee contains complex mechanoreceptors that play an important
role in proprioceptive reflex arcs. Ruffini endings, found in the
capsule, menisci, and ligaments, are slowly adapting static and
dynamic mechanoreceptors that signal static joint position; changes
in intra-articular pressure; and the direction, amplitude, and velocity
of knee movements30,31. Pacinian
corpuscles and Golgi-tendon organ-like endings have also been identified
in meniscal, capsular, and ligamentous tissues. The former rapidly adapt
to signal joint acceleration and deceleration, while the latter
are high-threshold, slowly adapting mechanoreceptors that are activated
when high stresses are generated in ligaments or when the knee is
at the extremes of motion30,31.
Free nerve-endings, which are widely distributed throughout most
of the articular tissues, are high-threshold, nonadapting pain receptors
that respond to mechanical deformation or inflammatory mediators30,31. Any injury of the posterolateral
structures affects not only knee kinematics but also afferent signals
to the central nervous system.
Operative procedures for the treatment of lesions of the posterolateral
corner of the knee can be broadly categorized as primary repair,
augmentation, and advancement and reconstruction.
Acute Injury of the Posterolateral Corner
of the Knee
Operative treatment of acute lesions of the posterolateral corner
of the knee is generally more successful than is surgery for chronic
posterolateral injury4,5,53,54,56,58-60.
When grade-III injuries of the posterolateral corner are diagnosed
acutely, direct anatomic repair of all injured structures within
three weeks has the highest likelihood of giving the patient an
optimal result5,28,60,65,75,94,99.
Arthroscopy performed before open repair facilitates the diagnosis
of lateral compartment injury and allows treatment of any associated
meniscal or cruciate ligament pathology13,97.
Cruciate ligament reconstruction is indicated when a tear is present,
and it is usually performed before repair or reconstruction of the
posterolateral structures5,28,97,98.
The posterolateral corner of the knee can be adequately exposed
through a lateral hockey-stick-shaped, straight, or curvilinear
incision4,57,100,101. An operative
approach through the injured structures has been recommended, but
this requires a thorough understanding of the anatomic relationships
to be accomplished safely17. Terry
and LaPrade17 described three
fascial incisions and one lateral capsular incision that provide
access to the individual components of the posterolateral corner,
but they noted that it was rarely necessary to use all four incisions
in the same knee. Major structures that should be evaluated during
the exposure include the iliotibial tract, biceps femoris, peroneal nerve,
lateral collateral ligament, popliteus muscle and tendon, and popliteofibular
ligament101. Treatment of posterolateral
injuries should proceed from deep to superficial, with repair of
structures by direct suture, sutures via drill-holes through bone,
or suture anchors as appropriate28,94.
In the acute situation where the severity of injury precludes direct
repair, involved structures can be augmented with hamstring tendon,
biceps femoris tendon, iliotibial band, or allograft28,75,101.
Chronic Injury of the Posterolateral Corner
of the Knee
Chronic injury of the posterolateral corner of the knee usually
presents a more complex problem than acute injury because of extensive
scarring, secondary changes to other structures, and possible limb malalignment.
The goals of operative treatment include restoration of knee stability
and kinematics, a return to preinjury activity levels without pain
or instability, and a reduction of the likelihood or severity of
long-term knee arthrosis. Reconstructive procedures can be broadly
classified as those that are intended to reproduce the normal anatomy
of the region or as those that are meant to stabilize the posterolateral
corner by tightening specific tissues. When a grade-III injury of
the posterolateral corner is associated with other ligamentous tears,
there is a general consensus that combined operative intervention
offers the potential for a better outcome than does treatment of
an isolated injury6,7,28,60,65,90,102.
There is a lack of consensus in the literature on the best technique
of operative treatment. This is a reflection of the low prevalence
of posterolateral injury, the various ways of measuring the results
of treatment, differences in the nature and chronicity of injury,
and variations in postoperative rehabilitation.
In cases of marked varus alignment and a lateral thrust in the
stance phase of gait, consideration should be given to performing
a valgus tibial osteotomy as an initial procedure to prevent excessive
loads on the lateral capsular structures that are to be reconstructed65,101,103. Full-length weight-bearing
radiographs of both lower extremities can aid in evaluating the
overall limb alignment. In patients with chronic posterolateral
instability and valgus alignment of the lower limb, the pathology
of the posterolateral corner is directly addressed101. Noyes et al.98 found
that preoperative gait-training was a useful adjunct to reconstructive
surgery in patients with chronic combined cruciate and posterolateral
knee injuries.
Hughston and Jacobson4 followed
ninety-five patients (ninety-six knees) for an average of four years
after anterior and distal advancement of the osseous attachment
of the arcuate ligament complex (the lateral gastrocnemius tendon,
lateral collateral ligament, and popliteal tendon). Of these ninety-six
knees, 85%, 78%, and 80% were rated as good objectively, subjectively, and
functionally. This technique does not address injury to the popliteofibular
ligament or the popliteus musculotendinous junction, and it also
moves the attachments of the lateral collateral ligament and the
popliteus tendon anterior and distal to their normal locations90, which could result in progressive
attenuation of these structures.
Noyes and Barber-Westin100 reported
the results in twenty-one patients with combined posterolateral
and cruciate ligament injuries after proximal advancement of the
posterolateral complex and cruciate ligament reconstruction. Their
procedure was modified from that of Hughston and Jacobson4 in that the tissue was advanced with
the knee in 30° rather than 90° of flexion and the lateral collateral ligament
was fixed at its normal anatomic attachment100,104.
The posterolateral advancement was fully functional in 64% of the
patients, partially functional in 27%, and nonfunctional in 9% at
an average of forty-two months postoperatively. Noyes and Barber-Westin
emphasized that the posterolateral structures must have sufficient
intact collagenous tissue and that, if poorly organized scar tissue
or tissue without adequate distal attachment is advanced, the procedure
will fail. These investigators57,75 also
used Achilles tendon allograft or bone-patellar tendon-bone autograft
to reconstruct the lateral collateral ligament, and they used autogenous
hamstring tendon to reconstruct the popliteus complex in combination
with plication or advancement of the posterolateral structures as
indicated. Of twenty-one patients who were followed for an average
of forty-two months postoperatively, 76% had a good-to-excellent
functional result and 10% had failure of the reconstruction57.
Clancy and Sutherland105 reported
that tenodesis of the biceps femoris tendon to the lateral femoral
epicondyle could negate the deforming force of the biceps femoris
muscle and create an approximation of the lateral collateral ligament.
Thirty-nine patients with chronic posterolateral rotatory instability,
usually from combined cruciate ligament and posterolateral injuries,
were followed for an average of thirty-two months after this procedure106. The authors found that 77% of
the patients had no restrictions in their activities of daily living
and that 54% were able to return to their previous competitive level
in sports. Factors associated with inferior results were degenerative
changes involving the knee joint and receipt of Worker's Compensation. Fanelli
et al.107 also used the biceps
tenodesis procedure along with arthroscopically assisted reconstruction
of the posterior cruciate ligament to treat combined injury of the
posterolateral complex and the posterior cruciate ligament in twenty-one
patients. At a minimum of two years postoperatively, all patients
had either correction or overcorrection of the posterolateral instability
as measured by the tibial external rotation test. A study in cadaver
knees showed that biceps tenodesis could be effective in statically eliminating
abnormal external rotation and varus rotation, but it did so by
overconstraining these motions3.
Whether initial static overconstraint in vivo would
remain or attenuate over time to produce a normal or pathologic
laxity pattern is not known. Veltri et al.44 noted
that biceps tenodesis did not reproduce the popliteofibular ligament
or popliteus tendon attachment to the tibia, both of which are important
stabilizers.
Jakob and Warner108 suggested
that recession of the popliteus and lateral collateral ligaments
into the lateral femoral condyle can restore tension yet maintain
the anatomic attachment sites. This procedure would be appropriate
in cases of mild attenuation when the popliteus musculotendinous
junction and the popliteofibular ligament are intact (Fig. 3Fig. 3). Depending
upon the amount of attenuation, this reconstruction may be augmented
with other tissue.
Albright and Brown83 described
a posterolateral corner sling procedure for the treatment of posterolateral
rotatory instability. Their technique involved use of an autograft
(a central slip of the iliotibial band) or an allograft (Achilles
tendon or iliotibial band) to approximate reconstruction of the
popliteus tendon and thus improve stability. The graft (acting as
a sling) is passed through a tunnel in the proximal part of the tibia
and is fixed just proximal to the origin of the lateral collateral
ligament on the femoral condyle. Thirty patients, all of whom had
at least a combination of varus laxity and anterolateral or posterolateral
rotatory instability prior to surgery, were available for follow-up
at an average of four years postoperatively. According to the International Knee
Documentation Committee knee-rating system, the patients had improvement
from an average of 50 points preoperatively to an average of 70 points
postoperatively83. Eight patients
(27%) who had an excellent score had no intra-articular pathology.
Ten patients received an initial poor rating because of joint pathology
and residual laxity, and six of these patients underwent additional
stabilizing procedures that improved their scores. The sling procedure
was successful in eliminating the reverse pivot shift, hyperextension,
and varus laxity in twenty-six of the thirty patients. This technique,
however, does not include reconstruction of the lateral collateral ligament
or the popliteofibular ligament. Bousquet et al.109 described
a similar procedure.
Veltri and Warren76 recommended
that all injured posterolateral structures be anatomically reconstructed.
A lateral collateral ligament with a chronic tear can usually be reconstructed
with a distally based section of biceps femoris tendon (Fig. 4Fig. 4) or, alternatively,
with autograft or allograft76.
For tears that involve the popliteus complex, both the tibial and
the fibular (popliteofibular ligament) attachments of the popliteus
tendon should be addressed. With isolated injury of either the tibial or
the fibular component of the popliteus complex, the surgeon can
use a single graft fixed within the lateral femoral condyle that
extends distally through a tunnel in the tibia or fibula, respectively
(Fig. 5Fig.
5). In cases where both the tibial and the fibular component of
the popliteus complex are torn, a single split Achilles-tendon allograft
or patellar tendon autograft or allograft can be used. With this
technique, the graft bone-plug is fixed in the lateral femoral condyle;
the graft is split distally and then passed through tunnels in the
proximal parts of the tibia and fibula (Fig. 5Fig. 5). Bullis and Paulos110 used a similar technique employing
a bifid Achilles-tendon allograft to reconstruct the popliteus complex.
Latimer et al.102 reconstructed
the knees of ten patients who had combined cruciate ligament and
posterolateral instability. They used a 9-mm-wide bone-patellar tendon-bone
allograft secured with interference screws to reconstruct only the
lateral collateral ligament, and they also performed arthroscopically assisted
reconstruction of the anterior or posterior cruciate ligament. At
an average of twenty-eight months, nine patients had decreased varus
laxity and normal or slightly decreased external rotation at 30°
of knee flexion. These authors suggested that, because the allograft
was much larger than the patient's own lateral collateral ligament,
it might have served as a functional substitute for the nearby arcuate
and popliteofibular ligaments. Further study is needed to determine
whether this procedure will be beneficial in the long term.
Potential complications associated with the operative treatment
of posterolateral corner injuries include peroneal nerve injury
during the operative approach or reconstruction, wound problems
such as infection and hematoma, loss of knee motion postoperatively,
failure of the reconstruction, and irritation from hardware used
in the reconstruction28,83.
New studies on the anatomy and biomechanics of the posterolateral
corner of the knee are helping to refine the treatment of these
injuries. The preponderance of basic research shows that each component
of the posterolateral complex is important for proper functioning
of the knee. All grade-I and most moderate grade-II injuries of
the posterolateral structures can be treated nonoperatively, but residual
laxity may remain, especially in patients with a grade-II injury.
Acute grade-III isolated or combined injury of the posterolateral
corner of the knee is best treated early (within three weeks) by direct
repair if possible, or else by augmentation or reconstruction of
all injured ligaments. Chronic injury, whether isolated or combined
with other tissue injury, is probably best treated by reconstruction
of the posterolateral corner along with reconstruction of any coexisting
cruciate ligament injury. A number of operative techniques have
been devised to treat posterolateral injuries, but most have achieved
only modest success. With our redefined understanding of the complex
morphology of the posterolateral aspect of the knee, it appears
that anatomic reconstruction, with use of modern techniques that
restore normal tibiofemoral stability and kinematics, offers the
best potential for long-term excellent results. However, determination
of the efficacy of anatomic reconstruction awaits the outcomes of
long-term clinical studies.