Injury to the posterolateral corner structures of the knee can cause
posterolateral rotatory instability, a condition that has attracted increased
attention over recent
years1. This injury
is often associated with cruciate ligament injury, and its diagnosis can be
difficult unless one has a high degree of clinical suspicion for an injury to
the posterolateral corner
structures2,3.
Although a number of treatment methods have been proposed over the past twenty
years2,4-12,
there has been considerable controversy regarding the optimal method of
surgical treatment for this injury. The consequences of missed or
unsuccessfully treated posterolateral rotatory instability can be profound:
reconstructed anterior or posterior cruciate ligaments can fail, and
persistent posterolateral rotatory instability may eventually cause pain,
instability, and even degenerative
changes13-17.
In this report, we describe the use of an external rotation-valgus stress
radiograph for the evaluation and diagnosis of posterolateral rotatory
instability, and we describe a new anatomical reconstruction procedure
involving use of a split Achilles tendon allograft for its treatment.
Background
Although several physical examination techniques for the detection of
posterolateral rotatory instability of the knee have been
described18,19,
no widely accepted method of objective documentation, such as the use of
posterior stress radiographs to identify a posterior cruciate ligament injury,
has been established for posterolateral rotatory instability. Consequently,
assessment of posterolateral rotatory instability is very subjective and
dependent on the examiner's experience.
Several biomechanical studies have documented that sectioning of the
posterolateral corner structures markedly increases external rotation of the
tibia at 30° of knee flexion, whereas sectioning of the posterior cruciate
ligament alone does not have the same
effect20-22.
Consequently, increased external rotation of the tibia relative to the femur
at 30° of knee flexion has been regarded as a specific finding indicating
posterolateral rotatory instability of the knee. Clinically,
posterolateral rotatory instability of the knee refers to a
ligamentous lesion that allows posterolateral subluxation of the tibial
plateau23. In
addition, coupled valgus or posterior translation and an external rotational
force have been found to increase the degree of posterolateral
subluxation19,21.
On the basis of these findings, we hypothesized that increased posterolateral
subluxation of a knee with posterolateral rotatory instability could be
demonstrated radiographically as increased lateral translation of the proximal
part of the tibia in relation to the femur with an external rotation-valgus
stress.
Position and Technique for the External Rotation-Valgus Stress
Radiograph
Figures 1-A through 1-E show
the position and technique used to make the external rotation-valgus stress
radiograph. Stress radiography is performed with the subject in the supine
position. The examiner grips the subject's heel with one hand, supports the
lateral aspect of the thigh with the other, and flexes the knee to about
30°. The subject is then encouraged to relax, and the examiner rotates the
distal part of the leg externally while applying a valgus stress to translate
the proximal part of the tibia posterolaterally. The hip is internally rotated
20°, and an anteroposterior radiograph is made with the beam angled
caudally 10°. Internal rotation of the hip allows the posterolateral
translation to appear as lateral translation on the radiographs, and the
caudal angle of the beam provides a tibial plateau view to facilitate
measurement. During a pilot trial, we found that about 20° of internal
rotation of the hip and 10° of caudal tilt of the radiographic tube were
the optimal positions to provide the best image for measurement. However,
rather than requiring exact positioning of the limb by applying the same
protocol (i.e., an identical amount of internal rotation of the hip and caudal
tilt of the radiographic tube to the contralateral knee), a companion
radiograph can be made to achieve the most accurate evaluation.
Materials and Methods
From January 2004 to March 2006, seventeen consecutive patients diagnosed
as having posterolateral rotatory instability and the same number of normal
healthy volunteers were evaluated with the external rotation-valgus stress
radiograph. The inclusion criteria for the patient group (the
posterolateral-rotatory-instability group) were (1) unilateral posterolateral
rotatory instability with an uninjured contralateral knee, (2) >10° of
side-to-side difference demonstrated by the tibial external rotation (dial)
test at 30° of knee flexion, and (3) a positive posterolateral drawer
test. The inclusion criteria for the healthy volunteers (the control group)
were (1) the absence of knee pain, (2) no history of knee injury and no
obvious knee deformity, (3) <5° of side-to-side difference demonstrated
by the tibial external rotation (dial) test at 30° of knee flexion, (4) a
negative posterolateral drawer test, and (5) a negative varus stress test at
0° and 30° of flexion. In addition, eight patients who were diagnosed
as having a posterior cruciate ligament injury without evident posterolateral
rotatory instability (the posterior-cruciate-injury group) were evaluated.
Table I summarizes the
characteristics of the three groups. This study was approved by the
institutional review board of our hospital, and informed consent for the use
of their medical information was obtained from all study subjects.
Before the stress radiographs were made, side-to-side differences in
thigh-foot angles (as demonstrated with the dial test) at 30° of knee
flexion were determined for all subjects by two examiners. Angle measurements
were carried out with use of a goniometer in triplicate by each examiner.
Average values were regarded as true values.
To analyze the stress radiograph, two fixed landmarks were defined: the
lateral edge of the lateral femoral condyle and the lateral border of the
lateral tibial condyle. At first, a baseline connecting the medial and lateral
edges of the tibial plateau was drawn, and then lines tangential to each
landmark were drawn perpendicular to the baseline. The degree of lateral
displacement of the proximal part of the tibia relative to the distal part of
the femur was measured as the distance D (in millimeters) between the two
tangential lines (Fig. 2). The
side-to-side difference in displacement between the injured knee and the
uninjured contralateral knee was then calculated. All measurements were
performed with use of digital images, which were acquired with a picture
archiving and communication system (PACS) on a 21-in (53.3-cm) LCD (liquid
crystal display) monitor (ME315L; Totoku, Nagaoka, Japan) with use of V-works
software (version 5.0; CyberMed, Seoul, South Korea). This computerized system
made it possible to carry out measurements on magnified images and allowed
vertical lines to be easily drawn to the baseline. Measurements were performed
by one of us (C.B.C.) and were repeated three times at intervals of two days.
The average of the three measurements was regarded as the true value.
The intrarater reliability of the radiographic measurements was assessed
with use of the intraclass correlation coefficient, which quantifies the
variance of ratings—i.e., the variability between measurements. The
intraclass correlation coefficient can range from 0 to 1, and a higher value
means better agreement. In general, values of >0.75 are considered to
represent good agreement, whereas values of <0.40 are considered to reflect
poor
agreement24.
The differences among the posterolateral-rotatory-instability, normal
control, and posterior-cruciate-injury groups were examined with use of the
Kruskal-Wallis H test for nonparametric data. When a significant difference
was detected, post hoc intergroup comparisons were made with use of the
Mann-Whitney U test. The association between the degree of side-to-side
difference shown by the dial test and that shown by the stress radiograph in
the posterolateral-rotatory-instability group was evaluated with use of the
Pearson correlation test. In all analyses, a p value of <0.05 was
considered significant.
Results
The intrarater reliabilities of the measurements on the stress radiographs
were almost perfect (intraclass correlation coefficient, 0.98 in the patient
group and 0.99 in the normal control group). The maximum discrepancy among the
measurements was 0.5 mm.
Table II summarizes the
results of the dial test and of the measurements on the stress radiographs in
the three groups. In the posterolateral-rotatory-instability group, the
side-to-side difference in displacement measured on the stress radiographs
averaged 6.2 mm, whereas it averaged 0.9 mm and 1.5 mm, respectively, in the
normal control and posterior-cruciate-injury groups
(Figs. 3-A and 3-B). Intergroup
comparisons revealed that side-to-side differences in displacement measured on
the stress radiographs were significantly larger in the
posterolateral-rotatory-instability group than they were in the normal control
and posterior-cruciate-injury groups (p = 0.001 for both comparisons). With
the numbers studied, there was no significant difference in the
stress-radiograph measurements between the normal control and
posterior-cruciate-injury groups.
In the posterolateral-rotatory-instability group, the side-to-side
differences in displacement measured on the stress radiographs were
significantly correlated with the side-to-side angle differences demonstrated
by the dial tests at 30° of flexion (correlation coefficient = 0.44 and p
= 0.01).
Background
On the basis of several anatomical and biomechanical
studies20,21,25-27,
it has been generally agreed that the most consistent and important structures
of the posterolateral corner of the knee are the popliteus tendon, the
popliteofibular ligament, and the lateral collateral ligament. The
posterolateral reconstruction procedures that are currently used to treat
posterolateral instability, with respect to the principal anatomical
structures, have been reported to be effective in providing satisfactory
stability. However, these procedures have several shortcomings, including
difficulty with concurrent reconstruction of the three important
posterolateral structures and failure to restore the isometric point of each
structure. In 2003, we reported a new reconstruction method for treating
posterolateral rotatory instability that involves use of a split Achilles
tendon allograft; this method allows concurrent reconstruction of the three
important posterolateral structures and restores the isometry of the lateral
collateral ligament and the popliteus
complex7. In this
report, we introduce the new reconstruction method and describe its clinical
outcomes.
Operative Technique
Approach
With the knee flexed, a curvilinear incision through the skin and
subcutaneous tissue is made beginning 5 cm proximal to the lateral epicondyle
of the femur and extending just distal to the point between the fibular head
and the Gerdy tubercle. After the common peroneal nerve is exposed below the
fibular head, it is protected with a nerve sling. The interval between the
biceps femoris and the iliotibial band is then developed with use of blunt
dissection. The plane between the lateral head of the gastrocnemius and
popliteus muscle and the posterior aspect of the capsule is also developed.
The lateral head of the gastrocnemius is retracted posteriorly to allow
identification of the target point, where the drill will exit during the
tibial tunneling procedure. An incision is then made along the midportion of
the iliotibial band over the lateral femoral epicondyle and is continued
proximally and distally down to the popliteal hiatus to expose the insertion
of the popliteus tendon. The anterior tibial muscle is released from the
anterolateral aspect of the tibial crest just below the Gerdy tubercle.
A guide pin is then passed from just inferior to the Gerdy tubercle to the
desired point on the posterior aspect of the tibia anteroposteriorly and
slightly oblique to the joint line. After proper pin placement, 1.5 to 2 cm
below the joint line, has been confirmed, a tunnel of 7 mm in diameter is
established with a cannulated reamer (Fig.
4-A). From the point near the superior surface of the fibular
head, a guide pin for a second tunnel is passed by aiming it
posteroinferiorly. After an oblique tunnel of 6 mm in diameter is made with a
cannulated reamer, a curet and a 7-mm reamer are used to enlarge the tunnel.
The tunnel should lie completely within the fibular head, as the neck is much
too narrow to accept a reamer (Fig.
4-B).
The femoral tunnel is established along the most proximal portion of the
popliteus insertion. A guide pin is placed initially, and a femoral tunnel, 11
mm in diameter and 20 mm in length, is created with a cannulated reamer.
We use fresh-frozen Achilles tendon allograft for the reconstruction. The
bone-plug portion of the chosen allograft is fashioned into a 11 × 20-mm
shape with a tapered tip, and the tendinous portion is prepared to allow a
sufficient length of 20 cm and is split longitudinally into 2 limbs, 7 mm and
6 mm in width (Fig. 4-C). The
free tendinous end of each limb is trimmed and is rolled into a compact tube
shape and prevented from unrolling with number-1-0 nonabsorbable suture. We
encircle one-fourth of the entire circumference of the tendon with each throw.
The suture forms a criss-crossing weave that further tapers the tendon when
pretension is applied to it, making it easier to draw it through the formed
tunnels.
Tunnel Passage and Graft Fixation
The tapered bone plug of the allograft is placed into the femoral tunnel
with the cancellous bone facing upward and is secured with an appropriately
sized cannulated interference screw (Fig.
4-D). After the tendinous portion of each limb is passed below the
iliotibial band and the biceps femoris, the 7-mm anterior limb is passed
through the tibial tunnel, from posterior to anterior, with use of a silicone
tendon-passer to recreate the popliteus. The 6-mm limb, located posterior to
the 7-mm limb, is passed under the biceps and through the fibular tunnel from
posteroinferior to anterosuperior and then passed under the iliotibial band to
just reach the posterior aspect of the lateral femoral epicondyle, which is
the estimated isometric point of the lateral collateral ligament. The
posterior portion of the 6-mm limb (before it passes through the fibular
tunnel) is designed to recreate the popliteofibular ligament, and the anterior
portion (after it passes through the fibular tunnel) is designed to recreate
the lateral collateral ligament (Fig.
4-E). After the graft tension has been checked throughout the
range of knee motion and after pretension has been applied, the end of the
7-mm limb is fixed directly to the tibia near the outlet of the tibial tunnel
with use of a double-staple fixation technique with the knee held in 30°
of flexion and in neutral rotation. The end of the 6-mm limb is fixed to the
origin of the lateral collateral ligament, just posterior to the center of the
lateral epicondyle and posterior to the femoral tunnel, with use of a
double-staple fixation technique (Fig.
5).
Postoperative Rehabilitation
After the surgery, the knee is placed in an immobilizer in full extension
for three to four weeks, during which time weight-bearing is not allowed.
Isometric quadriceps-muscle exercises are started immediately. A
range-of-motion program and closed-chain kinetic exercises are begun at four
weeks, and a standard cruciate-ligament rehabilitation program is then
followed for the next six to twelve months.
Materials and Methods
The institutional review board of our hospital granted approval for a
clinical study of the results of this technique, and all patients gave
informed consent for the use of their medical information. Between January
2002 and March 2006, thirty-two consecutive patients with posterolateral
rotatory instability were treated with the new reconstruction method, and data
on all of these patients were entered prospectively into a database designed
to record patient demographics and characteristics, radiographic measurements,
findings of the physical examination, and preoperative and postoperative
clinical outcome scores, including the Tegner activity
level28 and the
Lysholm score29.
Twelve knees in twelve patients who were followed for more than two years
after the surgery were included in this study. All patients were male, and the
mean age was 30.6 years (range, eighteen to fifty-nine years). The mean time
from the injury to the surgery was eighteen months (range, two months to
sixteen years), and the mean duration of the follow-up period was thirty-seven
months (range, twenty-six to fifty months). The clinical details are shown in
Table III.
To evaluate the stability of the posterolateral corner after the procedure,
we compared the preoperative and postoperative results of the dial tests at
30° and 90° of knee flexion and the preoperative and postoperative
results of the varus stress tests at 0° and 30° of knee flexion. In
addition, we assessed whether the posterolateral drawer test, the reverse
pivot shift test, and the external rotation recurvatum test were positive
preoperatively and postoperatively. To assess the clinical outcomes, we
compared the preoperative and postoperative ranges of motion of the knee,
Tegner activity levels, and Lysholm scores.
The statistical comparisons between the preoperative and postoperative
functional outcomes were made with use of the Wilcoxon signed-rank test, and a
p value of <0.05 was considered significant.
Results
At the time of final follow-up, all twelve patients had significant
improvements in the stability of the posterolateral corner of the knee
(Table IV). The mean
preoperative Lysholm score was 39.5 points, and it improved to 78.1 points at
the time of the latest follow-up (p < 0.01). The mean Tegner score improved
from 1.9 points to 3.9 points (p < 0.01). All but one patient had a nearly
full active range of motion postoperatively. One patient, who was diagnosed as
having reflex sympathetic dystrophy, had 10° to 120° of passive knee
motion at two years after the surgery. He reported having considerable pain
during daily activity and had poor clinical outcome scores (26 points on the
Lysholm scale and a grade-0 Tegner activity level) at the time of the latest
follow-up.
We have described new methods for the diagnosis and treatment of
posterolateral rotatory instability of the knee. We developed the external
rotation-valgus stress radiograph at 30° of knee flexion as a diagnostic
tool on the basis of biomechanical studies and found it to be a practical and
valuable method for objective documentation of posterolateral rotatory
instability of the knee. To the best of our knowledge, this represents the
first application of stress radiography for the diagnosis of posterolateral
rotatory instability of the knee.
Several physical examination tests have been introduced to detect
posterolateral rotatory instability of the
knee18,19,30,31;
these include the dial test performed with the knee flexed 30° and
90°31,32.
However, these tests are subjective, and we believe that they are highly
dependent on the examiner's judgment in many cases. Among the examinations,
the dial test at 30° of flexion is known to be specific for posterolateral
rotatory instability; however, it is our anecdotal experience that accurate
measurement of the thigh-foot angle is difficult to perform, and the
interrater and intrarater variability of this examination can be considerable.
Among the imaging tools, magnetic resonance imaging is known to be helpful for
the diagnosis of a posterolateral corner injury, especially an acute injury.
However, the reported sensitivity of magnetic resonance imaging, used with a
standard protocol, for the detection of all posterolateral corner structures
has been found to be unsatisfactory; even with use of a specialized protocol,
its sensitivity has been found to be lower than that for the detection of a
cruciate ligament
injury33.
Furthermore, because magnetic resonance imaging provides static images, it
might not be able to demonstrate the true instability of the knee,
particularly in chronic cases.
In this study, we found that the degree of side-to-side difference
demonstrated by the dial test was significantly and positively correlated with
the amount of side-to-side difference measured on the stress radiograph. This
finding suggests that it might be possible to grade the amount of instability
seen on the stress radiograph. However, we do not believe that the present
study was comprehensive enough to allow us to propose a grading system because
accurate measurement of the thigh-foot angle during the dial test is
inconsistent, even with repeated measurements by two examiners. Moreover, the
number of subjects enrolled in the present study was limited. Nevertheless, as
the displacements on the stress radiographs in the
posterolateral-rotatory-instability group were significantly larger than those
in either the control or the posterior-cruciate-injury group, it is our
opinion that the external rotation-valgus stress radiograph can be of value in
the diagnosis of posterolateral rotatory instability of the knee.
Since several authors have demonstrated that failure to restore the
posterolateral corner is an important cause of failure of both a posterior
cruciate ligament and an anterior cruciate ligament
reconstruction14,16,17,
great efforts have been made to find the appropriate treatment for a
posterolateral corner injury. The surgical approach used to restore stability
to the injured posterolateral aspect of the knee has evolved substantially.
Early procedures involved the advancement of the femoral attachment of the
posterolateral structures. Hughston and Jacobson reported improved clinical
results in ninety-five patients who had undergone proximal bone-block
advancement of the posterolateral complex for treatment of chronic
posterolateral
instability5.
However, this advancement procedure did not restore isometry; therefore, many
patients had loosening with time. Clancy recommended biceps tenodesis to
reconstruct the posterolateral corner by transferring the biceps tendon to the
anterior aspect of the lateral epicondyle while leaving its distal attachment
to the fibula
intact34. However,
this reconstruction did not anatomically recreate the popliteus or the
popliteofibular ligament and, thus, represented only a partial reconstruction
of the posterolateral corner. Subsequent procedures involved the creation of
an extra-articular sling to restore posterolateral stability. Müller
introduced the popliteal bypass procedure, in which a graft was placed through
a tibial tunnel exiting at the posterolateral corner of the tibia and secured
to the anterior aspect of the lateral femoral
condyle8. Albright
and Brown reported on the posterolateral corner sling procedure, which
involved the use of an autograft or an allograft to approximate the
reconstruction of the popliteus
tendon2. More recent
studies have revealed that the lateral collateral ligament, the popliteus
tendon, and the popliteofibular ligament are the three key structures in the
posterolateral
corner27,35.
Interest has focused on the popliteal complex, particularly the
popliteofibular ligament, and several research efforts have improved our
understanding of the role of the popliteofibular
ligament26,36.
Consequently, there have been several reports on the anatomical reconstruction
of the lateral collateral ligament and the popliteal
complex9,11,37.
However, these concurrent reconstructions of all structures failed to restore
the optimal isometric points of each structure. To address these limitations,
we used a split Achilles tendon allograft to concurrently reconstruct the
three important structures and restore their
isometry7. In our
procedure, the posterior portion of the 6-mm limb (before it is passed through
the fibular tunnel) was designed to recreate the popliteofibular ligament and
the anterior portion (after it is passed through the fibular tunnel) was
designed to recreate the lateral collateral ligament with separate isometric
points. In addition, the 7-mm limb was planned to restore the popliteus tendon
as closely as possible to its original position. In addition, this technique
does not require an additional incision for a pull-out suture, which is needed
with some of the other
techniques11,38.
Although the number of patients in our study was limited, the results after
a minimum of two years of follow-up suggest that our anatomical reconstruction
is a reliable method that provides excellent stability and satisfactory
clinical results. We believe that the poor clinical outcome of one patient
stemmed from reflex sympathetic dystrophy and not from the ligament
reconstruction per se. None of the other thirty-one patients who had been
treated with this procedure had a similar outcome.
Recently, several procedures designed to concurrently reconstruct the three
major structures of the posterolateral corner have been
introduced6,10,12.
These procedures correspond to ours in terms of restoration of the isometric
points of each structure. Hopefully, the current reconstructive procedures
will allow us to achieve outcomes that will remain satisfactory after longer
follow-up. ?