Proximal fibular subluxation is a rare
condition1 that
mainly occurs as a result of isolated trauma or in combination with fractures
of the tibia and
ankle2,3.
Other, less frequent predisposing factors have been described, such as
generalized hyperlaxity or muscular
dystrophy4 as well
as tumors in the surrounding tissues, clubfoot, poliomyelitis, lower-extremity
amputation, rheumatoid arthritis, and septic
arthritis5. Four
types of proximal fibular subluxation and dislocation have been
described6,7:
(1) subluxation associated with generalized ligamentous laxity or muscular
dystrophy; (2) anterolateral dislocation, which mainly occurs during athletic
activity; (3) posteromedial dislocation, which is usually associated with
substantial trauma to the knee; and (4) superior dislocation, which is
invariably associated with a fracture of the tibial shaft.
Subluxation of the proximal tibiofibular joint has been observed after
tibial lengthening by distraction osteogenesis with use of a unilateral
external fixator8.
This is an inferior subluxation of the fibular head and, although it is a
common radiographic finding, little attention has been paid to this entity
clinically8,9.
In this study, inferior subluxation of the proximal part of the fibula as a
result of tibial lengthening with a unilateral external fixator was analyzed
clinically and radiographically, with particular attention focused on symptoms
or functional impairment.
From January 1995 to December 1999, thirty tibiae in seventeen patients
were lengthened by distraction osteogenesis with use of a unilateral external
fixator. The mean age at the time of the surgery was seventeen years (range,
eight to twenty-five years). Ten of the patients were female and seven were
male. Thirteen cases were bilateral and four were unilateral.
The indications for lengthening were grouped into five categories:
idiopathic short stature (five patients; ten tibiae), achondroplasia (five
patients; ten tibiae), lower-extremity length discrepancy (four patients; four
tibiae), Turner syndrome (two patients; four tibiae), and Down syndrome (one
patient; two tibiae).
The lengthening procedure was performed with use of distraction
osteogenesis through an anteromedial incision over the proximal part of the
tibia. A subperiosteal osteotomy was completed with an osteotome by connecting
drill holes made in a line perpendicular to the long axis of the tibia distal
to the tibial tubercle, in the proximal tibial metaphysis. The fibula was
osteotomized between its middle and distal one-thirds, and a segment of bone
approximately 1 cm in length was excised to avoid early consolidation. The
distal part of the fibula was stabilized to the tibia with a syndesmotic
screw. Intraoperatively, compression was applied to the tibial osteotomy site.
Distraction commenced on the tenth postoperative day at a rate of 0.25 mm
every six hours by means of a unilateral external fixator (Ex-fi-re; Osteo,
Selzach, Switzerland).
The syndesmotic screw was removed, with the patient under local anesthesia,
at the end of the lengthening period, just before partial weight-bearing was
allowed.
The relationship between the articular surfaces of the proximal parts of
the tibia and fibula was evaluated on standard anteroposterior and lateral
radiographs made preoperatively, postoperatively, on completion of the
lengthening process, and at the time of the last follow-up. All radiographs
were made in the same radiology department. Radiographs of both knees were
made, and when only one extremity was affected it was compared with the normal
side.
The anteroposterior radiographs were made with the patient supine, with the
knees in extension and in such a position that a maximal width of the femoral
and tibial condyles was shown together with the medial and lateral articular
surfaces and the superior margin of the fibular head.
The extent of inferior fibular subluxation was measured in centimeters by
comparing the positions of the fibular head relative to the tibial plateau on
the preoperative and final follow-up radiographs. Statistical analysis was
performed to determine whether there was a relationship between the degree of
tibiofibular subluxation and the sex of the patient, the initial diagnosis,
the initial tibial length, or the amount of lengthening.
After removal of the external fixation system and at the time of the final
follow-up, the patients were examined clinically for swelling and/or localized
tenderness at the proximal tibiofibular joint, pain on the lateral side of the
knee elicited by internal or external rotation of the tibia, pain on the
lateral side of the knee elicited by eversion or inversion of the foot,
limitation of knee flexion or extension, pain in the ankle joint, abnormal
mobility of the fibular head with the knee in 90° of flexion, muscle
strength as graded on a scale of 0 to 5 with the system of the British Medical
Research Council10,
or sensory disturbances in the distribution of the common peroneal nerve.
The mean duration of follow-up was two years and ten months (range, two to
four years) after removal of the fixator.
Statistical Methods
Relationships involving quantitative variables were analyzed with the
simple linear regression method, whereas relationships involving qualitative
variables were analyzed with the chi-square test or the Fisher test for small
samples. One-way analysis of variance was used to analyze the relationships
between qualitative and quantitative variables.
Amean of 8.1 cm (range, 3.5 to 13 cm) of tibial lengthening, which was 33%
(range, 9% to 67%) of the original tibial length, was obtained at the end of
the distraction period (see Appendix).
Radiographic Evaluation
The diagnosis of proximal tibiofibular subluxation was based mainly on the
radiographic findings (Figs. 1,
2-A, and
2-B). The mean amount of
subluxation of the fibular head as seen on the anteroposterior knee radiograph
was 1.6 cm (range, 0.4 to 3.3 cm). In patients with idiopathic short stature,
who had a mean tibial lengthening of 25%, the mean amount of fibular
subluxation was 1.2 cm (range, 0.5 to 1.8 cm). In patients with
achondroplasia, who had a mean tibial lengthening of 54%, the mean amount of
fibular subluxation was 2.4 cm (range, 1.3 to 3.0 cm). In patients with a
lower-extremity length discrepancy, who had a mean tibial lengthening of 12%,
the mean amount of fibular subluxation was 0.6 cm (range, 0.4 to 0.9 cm). In
patients with Turner syndrome, who had a mean tibial lengthening of 26%, the
mean amount of fibular subluxation was 1.2 cm (range, 1.0 to 1.4 cm). In the
patient with Down syndrome, who had a mean tibial lengthening of 20%, the mean
amount of fibular subluxation was 2.3 cm (1.3 and 3.3 cm)
(Table I).
In all but one of the patients who had bilateral tibial lengthening, the
amount of fibular subluxation was symmetrical. In one patient, a
seventeen-year-old girl with Down syndrome in whom both tibiae were lengthened
6 cm, the fibula subluxated 1.3 cm on the right and 3.3 cm on the left. Early
reossification of the left fibular osteotomy site was evident radiographically
in the fourth postoperative month in that patient. However, no other patient
had radiographic evidence of reossification at the osteotomy site of the
fibula at the end of the distraction period. At the time of the last
follow-up, twelve (40%) of the thirty fibulae had no radiographic signs of
union.
The degree of inferior subluxation of the fibula was linearly correlated
with the amount of tibial lengthening (Fig.
3). Once established, there was no subsequent change in the amount
of tibiofibular subluxation.
With the numbers available, there was no association between the extent of
the fibular subluxation and gender (p = 0.145). There was also no association
with the initial tibial length.
Clinical Evaluation
Preoperatively, all knees were asymptomatic. At the final assessment, no
patient was found to have swelling or localized tenderness at the proximal
tibiofibular joint and none complained of pain or discomfort involving the
proximal tibiofibular syndesmosis. No patient had pain on the lateral side of
the knee with rotation of the tibia or with eversion or inversion of the foot.
On examination, only one patient had abnormal movement of the fibular head.
This patient had achondroplasia with asymptomatic bilateral proximal
tibiofibular instability. No signs of peroneal nerve involvement and no muscle
weakness were found in any patient. Limitation of knee extension was noted
commonly during the lengthening procedure, but it had resolved completely with
physiotherapy by the end of the follow-up period. Flexion and valgus
deformities of the tibial axis were noted during the distraction period and
were corrected with the external fixator. No deformity was noted after removal
of the fixator. No symptoms or tenderness at the osteotomy site were found in
any of the fibulae with nonunion.
Ogden11
described two types of proximal tibiofibular joints, horizontal and oblique,
and he demonstrated that >70% of subluxations and dislocations involve
joints of the oblique type. While four types of proximal tibiofibular
subluxation and dislocation have been
documented6,7,
inferior subluxation of the fibular head during tibial lengthening has not
been previously described in detail, to our knowledge.
Meiss9 observed
inferior subluxation of the proximal tibiofibular joint in an illustration
from an article by
Aldegheri12.
Aldegheri8 agreed
with that observation and added that distal migration of the fibular head by 1
or even 2 cm was a frequent phenomenon in his series of patients treated with
tibial lengthening; however, he stated that it did not cause instability of
the knee.
In our study, we consistently found inferior subluxation of the proximal
part of the fibula following distraction osteogenesis of the tibia. The extent
of the inferior subluxation of the fibular head was directly proportional to
the amount of tibial lengthening (p = 0.001), with the patients with
achondroplasia, who had a mean tibial lengthening of 54%, demonstrating the
largest amount of fibular subluxation (p = 0.001)
(Table I).
Fibular lengthening appeared to progress more slowly than did tibial
lengthening, and there was less fibular lengthening overall (p = 0.01). This
can be explained by the fact that the fibular lengthening was not caused by a
rigid external fixator directly attached to the bone but evolved indirectly
through the tension exerted by the soft tissues, mainly by the intact distal
portion of the interosseous membrane.
The above observations led us to formulate a hypothesis regarding a cause
of fibular subluxation. Although the interosseous membrane stabilizes the
tibia and fibula, the proximal part, including the oval aperture that allows
passage of the anterior tibial vessels, is relatively
weak13. As the site
of the tibial osteotomy is just distal to the oval aperture, the part of the
interosseous membrane that remains intact and attached to the sliding part of
the tibia seems to pull the proximal part of the fibula distally. This
observation has to be further investigated by developing a mechanical model or
by performing a carefully designed cadaveric study. However, it should be
mentioned that this phenomenon has not been observed in patients in whom
tibial lengthening was done with the Ilizarov method, with which the proximal
part of the fibula is transfixed to the proximal part of the tibia by one
Kirschner wire in the frame
construct14. It
would be possible to also transfix the proximal part of the fibula to the
tibia with a screw when a unilateral lengthening device is used, although
doing so could be dangerous because of the proximity of the peroneal
nerve.
Many authors have reported that traumatic dislocations are associated with
swelling and/or localized tenderness of the proximal tibiofibular
joint3-7,15,
pain on the lateral side of the knee elicited by internal and external
rotation of the
tibia2,3,5
and by eversion or inversion of the
foot3,5,6,
limitation of knee flexion and
extension2,3,7,
pain in the ankle
joint5, abnormal
mobility of the fibular head with the knee in 90° of
flexion3,15,16,
and muscle weakness or sensory disturbances resulting from impaired peroneal
nerve
function3-7.
In our series, none of those symptoms or findings were noted except for
abnormal but painless movement of the fibular head in a patient with
achondroplasia. Peroneal nerve dysfunction was not observed in any of our
patients. Apparently, the slow elongation of the ligamentous complex of the
proximal tibiofibular joint protects against peroneal neuropathy, as was
mentioned by Paley et
al.17. While knee
flexion deformity was a problem during the lengthening procedure in our
patients, it had completely resolved with physiotherapy by the end of the
follow-up period.
In our series, subluxation of the fibula was a radiographic observation
that did not produce clinical symptoms or signs, at least not during the
follow-up period of more than two years, not even when the fibular subluxation
was as much as 3.3 cm. This is probably due to the fact that the capsule of
the proximal tibiofibular joint is gradually elongated. Since this subluxation
is asymptomatic, it does not require surgical intervention or any other
special treatment, and it is not a contraindication to the use of a unilateral
fixator.
A table showing detailed clinical and radiographic data on all study
patients is available with the electronic versions of this article, on our web
site at
(go to the article citation and click on "Supplementary Material")
and on our quarterly CD-ROM (call our subscription department, at
781-449-9780, to order the CD-ROM).