
COPYRIGHT © 2002
BY
THE JOURNAL
OF
BONE
AND JOINT
SURGERY, INCORPORATED
Treatment of Syndesmotic
Disruptions of the Ankle with
Bioabsorbable Screw Fixation
BY W. DAVID HOVIS, MD, BRYAN W. KAISER, MD,
JEFFRY T. WATSON, MD, AND ROBERT W. BUCHOLZ, MD
Investigation performed at the Department of Orthopaedic Surgery,
University of Texas Southwestern Medical Center at Dallas, and Parkland Memorial Hospital, Dallas, Texas
Background: Bioabsorbable implants have restricted indications because of their unique biochemical properties and their inferior biomechanical properties compared with those of conventional metallic implants. The purpose of this prospective study was to assess the efficacy of screws made of polylevolactic acid (PLLA) in the
treatment of syndesmotic disruptions associated with ankle fractures and fracture-dislocations.
Methods: Thirty-three consecutive patients with a syndesmotic disruption were managed with standard metallic
plate-and-screw fixation of the malleolar fracture and with 4.5-mm polylevolactic acid screws, with purchase in
four cortices, for fixation of the syndesmosis. Intraoperative radiographs confirmed reduction of the syndesmosis, and all of the patients were managed with a non-weight-bearing plaster splint or brace for six weeks.
Clinical and radiographic assessment and functional evaluation with use of the Olerud-Molander scoring system
were performed at the time of follow-up.
Results: Ten patients were lost to follow-up prior to the twenty-four-month evaluation, leaving twenty-three patients with an average duration of follow-up of thirty-four months (range, twenty-four to forty-three months). All
of the malleolar fractures healed in an anatomical position at an average of three months, and no postoperative displacement of the syndesmosis or widening of the medial clear space was detectable on radiographs.
No episodes of osteolysis or late inflammation secondary to the hydrolyzed polylactide occurred. Nineteen patients (83%) had an excellent result, and four patients (17%) had a good result. All twenty-three patients returned to their preinjury level of work and activities of daily living. No patient had malunion, nonunion, loss of
reduction, or complications attributable to the biomechanical or biochemical properties of the implants.
Conclusions: Polylevolactic acid screws are effective in stabilizing disruption of the syndesmosis during healing
of unstable ankle fractures. In this small series, the bioabsorbable screw was well tolerated, and there was no
need for a second operation to remove it.
T
he use of bioabsorbable polymers in fracture fixation
was shown to decrease the necessity for subsequent removal of hardware in certain situations1-4. The use of
these polymers may permit more complete bone-remodeling
after injury1,5 by allowing a gradual transfer of stress to the
healing bone. These theoretical benefits have encouraged clinical investigations of bioabsorbable polyesters for the internal
fixation of fractures.
Several different polyesters with different rates of hydrolysis and resorption have been investigated, including
polyglycolide, polylactide, polylevolactic acid (PLLA), and copolymers of polyglycolide and polylactide in various ratios.
A video supplement to this article is available from the Video Journal of Orthopaedics. A video clip is available at the JBJS web site,
www.jbjs.org. The Video Journal of Orthopaedics can be contacted
at (805) 962-3410, web site: www.vjortho.com.
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Each of these polymers has a different rate of degradation related to its chemical composition2,5-8. The compounds may be
drawn or molded into rod or screw shapes.
Because their mechanical properties are inferior to those
of conventional metal implants6-10, bioabsorbable implants
have been used predominantly in fracture patterns in which
internal fixation is subjected to minimal stress. These implants
are more expensive than the metal equivalents and are therefore best used in situations in which a second procedure for the
removal of metallic hardware would otherwise be anticipated.
Syndesmotic disruption of the ankle is such an indication because many surgeons believe that a second procedure for the
removal of hardware is necessary when conventional metal
screws are used. When absorbable implants are employed, the
syndesmosis can be protected with the use of crutches during
the healing process.
The purpose of this prospective study was to assess the
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efficacy of polylevolactic acid screws in the stabilization of a
syndesmotic disruption associated with an ankle fracture.
Materials and Methods
etween November 1995 and July 1997, thirty-three consecutive adult patients with a closed Weber type-C ankle
fracture11 and intraoperative fluoroscopic confirmation of
disruption of the syndesmosis were entered into this study.
Operative indications included any unstable trimalleolar, bimalleolar, lateral malleolar, or Maisonneuve-type ankle fracture in which the fibular fracture was proximal to the
syndesmosis. Fractures were judged to be unstable before the
operation when there was widening of the tibiofibular clear
space or evidence of a medial osseous or ligamentous injury
associated with the fibular fracture11. Polylevolactic acid
screws were approved for the internal fixation of fractures by
the United States Food and Drug Administration, and this
study protocol was approved by our Institutional Review
Board. A signed informed-consent form for enrollment in
this study was obtained from each patient before the operation. Patients who had sustained an open fracture, had a large
soft-tissue injury, or had preexisting hardware within the ankle were excluded from the study at this point. Patients were
also excluded from the study when the Weber type-C ankle
fracture failed to demonstrate syndesmotic disruption during
the operative procedure.
Open reduction and internal fixation of the ankle was
performed as soon as the patient’s condition was stabilized as
necessitated by associated injuries and as soon as soft-tissue
edema was controlled. Lateral fractures were approached
through a standard longitudinal incision, and internal fixation
was performed with a metallic one-third tubular plate and
3.5-mm cortical and 4.0-mm cancellous screws inserted with
standard AO technique12. The only exceptions to this protocol
were Maisonneuve-type fractures of the proximal third of the
fibula, which were not internally fixed. Medial fractures were
exposed through a straight medial incision, and all of the medial malleolar fragments were reduced and internally fixed
with either one or two 3.5-mm polylactide or 4.0-mm metallic
cancellous screws, at the discretion of the surgeon.
The ankle mortise was then stressed with an external
rotation load under intraoperative fluoroscopy to verify
disruption of the syndesmotic ligaments. Patients were included in the study only when radiographs demonstrated >3
mm of widening of the tibiofibular clear space. Approximately fifteen patients were excluded at this point because
the syndesmosis was deemed stable after internal fixation of
the fracture. Thirty-three consecutive patients underwent
fixation of a syndesmosis that had been identified as unstable in this manner.
Open reduction and internal fixation of the syndesmotic
disruption was performed with bioabsorbable screws as has
been previously described13. The syndesmosis was held reduced with a pointed reduction clamp with the foot in the neutral position. One 4.5-mm polylevolactic acid screw was placed
across the syndesmosis from the fibula to the tibia, with pur-
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chase obtained in four cortices approximately 1 to 2 cm proximal to the plafond. The screw was placed through a hole in the
plate when possible. For patients with a Maisonneuve-type
fracture pattern, one or two polylevolactic acid screws were
placed percutaneously, parallel to the tibial plafond. Intraoperative radiographs confirmed reduction of the syndesmosis.
The screws (SmartScrew; Bironx Implants, Blue Bell,
Pennsylvania) are made from polylevolactic acid, the levorotatory isomer of polylactic acid. The strength of the screw is increased by a self-reinforcing process known as orientrusion.
The implants, termed self-reinforcing polylevolactic acid (SRPLLA) implants, manufactured with this process have been
shown to be stronger in flexion and tension than their nonreinforced counterparts6. Each screw is fully threaded and has an
enlarged rectangular head over which a torque-limiting screwdriver fits for the purpose of insertion.
A 3.5-mm drill-bit was used to create the drill hole. The
hole was tapped along its entire length with a 4.5-mm tap, and
the screw was inserted. The most prominent portion of the
screw head was then smoothed with an electrocautery loop,
which removes polyester by melting it. Care was taken in each
case to leave most of the screw head intact to maintain adequate purchase on the fibula.
The average age of the patients was thirty-three years
(range, eighteen to fifty-three years). Nineteen left ankles
and fourteen right ankles were fractured in twenty-three
male and ten female patients. Six fractures involved disruption of the syndesmosis in a Maisonneuve pattern. Twelve
other syndesmotic disruptions included tearing of the deltoid ligament and a midshaft fracture or a distal-third fracture of the lateral malleolus. Of the remaining fifteen
fractures, five were trimalleolar and ten were bimalleolar.
The average time from injury to surgery was 1.5 days (range,
one to seven days).
Postoperatively, the patients were prohibited from
bearing weight on the affected ankle for a period of six weeks,
which is the standard protocol for unstable ankle fractures at
our institution. Immobilization was achieved with either a
plaster splint or a brace. Patients were instructed to gradually
increase weight-bearing and ankle motion beginning at six
weeks.
Clinical and radiographic follow-up was scheduled at
two weeks, six weeks, three months, six months, one year, and
yearly thereafter. At the one-year follow-up examination and
at each subsequent yearly follow-up visit, patient outcome was
assessed by means of the ankle fracture scoring scale as proposed by Olerud and Molander14. This 100-point scale provides a subjective evaluation of pain, stiffness, swelling, use of
supports, activities of daily living, and ability to climb stairs,
run, jump, and squat. The scoring system was applied as a discontinuous variable in 5-point increments.
Results
ive patients were lost to follow-up before the fracture
healed; the duration of follow-up of these patients ranged
from no follow-up to 3.5 months. No known complications
F
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TABLE I Patient Data
Case
Gender,
Side, Age
(yr)
1
Olerud and
Molander14
Score
(points)
Mechanism
of Injury
Fracture
Pattern
Medial
Injury
Lateral
Plate
Used
M, L, 32
Motor-veh.
acc.
Trimalleolar
Med. malleolar fract.
Yes
29
5-40
10-50
80
2
F, R, 18
Misstep
Unimalleolar
Deltoid lig. rupt.
Yes
39
15-30
15-30
100
3
M, R, 32
Sports inj.
Maisonneuve
Deltoid lig. rupt.
No
24
15-40
15-40
100
4
M, L, 33
Motor-veh./
pedest. acc.
Bimalleolar
Med. malleolar fract.
Yes
40
30-40
45-50
100
5
M, R, 39
Misstep
Unimalleolar
Deltoid lig. rupt.
Yes
39
5-60
10-60
80
6
M, L, 43
Assault
Bimalleolar
Med. malleolar fract.
Yes
31
10-35
20-40
85
7
M, L, 22
Motor-veh.
acc.
Bimalleolar
Med. malleolar fract.
Yes
24
10-50
10-50
95
8
M, L, 21
Motor-veh.
acc.
Bimalleolar
Med. malleolar fract.
Yes
38
10-30
20-35
95
9
F, L, 24
Fall from
height
Unimalleolar
Deltoid lig. rupt.
Yes
39
10-30
10-30
95
10
F, L, 25
Sports inj.
Bimalleolar
Med. malleolar fract.
Yes
24
10-60
10-70
100
11
M, R, 43
Misstep
Unimalleolar
Deltoid lig. rupt.
Yes
28
20-30
20-30
100
12
M, R, 24
Sports inj.
Maisonneuve
Med. malleolar fract.
No
26
40-60
45-50
100
13
M, L, 26
Work inj.
Trimalleolar
Med. malleolar fract.
Yes
37
40-60
40-60
85
14
M, L, 40
Sports inj.
Maisonneuve
Med. malleolar fract.
No
38
15-30
15-30
95
15
F, L, 42
Fall off stair
Bimalleolar
Med. malleolar fract.
Yes
27
30-50
30-50
90
16
F, R, 38
Fall off stair
Unimalleolar
Deltoid lig. rupt.
Yes
38
20-20
30-30
100
17
M, L, 24
Sports inj.
Trimalleolar
Med. malleolar fract.
Yes
43
10-30
35-45
90
18
M, L, 53
Motor-veh.
acc.
Bimalleolar
Med. malleolar fract.
Yes
35
10-30
10-30
95
19
M, R, 42
Misstep
Unimalleolar
Deltoid lig. rupt.
Yes
36
20-30
25-30
95
20
F, L, 35
Motor-veh./
pedest. acc.
Bimalleolar
Med. malleolar fract.
Yes
42
15-45
25-45
90
21
F, R, 26
Fall off stair
Bimalleolar
Med. malleolar fract.
Yes
39
20-50
20-50
100
22
M, L, 26
Sports inj.
Maisonneuve
Med. malleolar fract.
No
24
10-30
10-30
100
23
F, R, 49
Misstep
Trimalleolar
Med. malleolar fract.
Yes
37
30-45
30-45
90
occurred in these patients, but no functional ankle scores
were available for them.
Five additional patients were lost to follow-up after the
fracture had healed. The duration of follow-up of these five
patients ranged from eleven to fifteen months (average, 12.3
months), and the one-year follow-up ankle scores were 65, 90,
95, 100, and 100 points. All five fractures healed with no
known complications.
The remaining twenty-three patients were followed for
an average of thirty-four months (range, twenty-four to fortythree months; Table I).
At the time of the most recent follow-up, the average
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Duration
of Follow-up
(mo)
Range of
Dorsiflexion-Plantar
Flexion (deg)
Involved
Contralat.
dorsiflexion of the ankle was 17° (range, 5° to 40°) and the
average plantar flexion was 40° (range, 20° to 60°). The difference relative to the contralateral side averaged a loss of 5° of
dorsiflexion and 3° of plantar flexion.
The average ankle score for these patients was 94 points
(range, 80 to 100 points). Ankles that lost points did so only
because of mild swelling or stiffness, or both. All twenty-three
patients returned to levels of work and activities of daily living
similar to those before the injury.
Radiographs showed that all fractures had healed in an
anatomical position, with complete obliteration of all fracture
lines, at an average of three months (range, 2.5 to 4.0 months),
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Fig. 1-A
Fig. 1-B
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Fig. 1-C
Figs. 1-A, 1-B, and 1-C Case 1. Fig. 1-A Anteroposterior radiograph of a severe Weber type-C fracture-subluxation of the ankle in a thirty-two-year-old
man involved in a motor-vehicle collision. Fig. 1-B The syndesmosis was stabilized with one polylevolactic acid screw placed through the second
most distal hole in the plate. Fig. 1-C Two-year follow-up anteroposterior radiograph showing healing of the fracture with no widening of either the
syndesmosis or the ankle mortise. A tibiofibular synostosis is seen at the level of the fibular fracture.
and no postoperative displacement of the syndesmosis or widening of the medial clear space was detectable (Figs. 1-A, 1-B,
and 1-C). Radiographs revealed no evidence of osteolysis around
the implanted screws.
No episodes of drainage of the hydrolyzed polylactide
occurred, and there were no infections or wound-healing
problems.
Discussion
ioabsorbable implants offer several advantages compared
with conventional metallic implants for the internal fixation of fractures. Because the bioabsorbable implant is hydrolyzed and absorbed, there is less soft-tissue irritation from
prominent hardware, thus eliminating the need for subsequent
removal of the implant. The gradual resorption of the screw
permits a gradual transfer of stress to the bone, which results in
improved remodeling and healing without stress-shielding.
The material properties of the polylevolactic acid limit
its potential uses, however. The viscoelasticity and reduced
stiffness of these implants compared with stainless steel suggest that these screws are best suited for fracture patterns that
do not require compression for healing6. Polylevolactic acid
has a lower ultimate tensile strength; therefore, it is best utilized in cases in which the surgical construct can be unloaded
and subjected to minimal stress. Because polylevolactic acid
screws are more expensive than stainless-steel screws, the ideal
application is one in which a metal implant would have a high
likelihood of requiring removal, thus necessitating a second
surgical procedure.
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Disruption of the ankle syndesmosis fulfills all of these
qualifications. Internal fixation of the ankle syndesmosis is
positional fixation in which strong compression between the
tibia and fibula should be avoided11,15. The ankle can easily be
unloaded after the operation to protect the fixation. Finally,
fixation of the syndesmosis is viewed by many authors as temporary, meaning that a metal implant would have to be subsequently removed16,17.
In many fractured ankles, the syndesmosis is stable after
reduction and internal fixation of the fibular fracture and any
associated medial malleolar fracture18,19. Yablon et al.20 stated
that anatomical reduction of the fibula is the key factor in
achieving a good outcome of treatment of ankle fractures that
have accompanying syndesmotic disruption. Following these
principles, we determined the necessity for syndesmotic stabilization by applying intraoperative stress to the syndesmosis
under fluoroscopy after anatomic reduction and fixation of
the lateral and medial malleolar fractures.
Some authors11,16,17,21 have recommended placing the screw
across only three cortices so that some normal motion can occur at the syndesmosis. Compression can be generated when a
metal cortical screw traverses all four cortices. Such compression across the syndesmosis is not desired and may be detrimental to the achievement of a full range of motion of the
ankle15. However, Tornetta et al.22 recently challenged this principle in a cadaveric study by demonstrating no loss of passive
dorsiflexion with compression across the syndesmosis. Also, it is
our belief that the viscoelastic properties of the polylevolactic
acid polymer minimize any problem that may arise from this
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compression. Stress relaxation was demonstrated to occur in
these implants6, and any compression that may be generated
with these screws probably relaxes over time. Because of the
weaker mechanical properties of the polymer, fixation across
four cortices is recommended. We have found no difficulty in
obtaining purchase across four cortices with the use of standard
screws up to 70 mm in length.
Although we encountered no difficulties with insertion
of the screw in this series, we previously had a case of screw
breakage from overtightening. On insertion of the polylevolactic acid screw, a “squeak” can be heard as the screw fully
seats. The screw is then deemed to be fully tightened, and no
more torque is applied.
Hydrolysis and degradation of the implant cause its
strength to lessen with time. Rod implants made of self-reinforced polylevolactic acid lose 50% of their bending strength
and 10% of their shear strength at twelve weeks in vivo7. It is
therefore likely that, with polylevolactic acid screw fixation,
motion occurs at the syndesmosis when the patient begins to
bear weight. Although we cannot confirm it, we believe that
the implant fails at some point after the patient begins to bear
weight, thus restoring normal motion at the syndesmosis.
Several investigations6-8 have shown that polylevolactic
acid degrades more slowly and retains more strength than do
other polymers in clinical use, such as polyglycolic acid or
the racemic form of polylactic acid. The highly crystalline
polylevolactic acid isomer is less water-absorbent, so that it
degrades more slowly than other, less crystalline polymers6,7
and thus is perhaps better suited for fracture fixation than
other polymers that are available at the time of this writing.
The Olerud and Molander scoring system14 is a subjective outcomes tool for grading results after the treatment of
ankle fractures. In a large series of patients with ankle fractures, Olerud and Molander noted that the average score for
the good results was 78 points and the average score for the excellent results was 92 points. Of our twenty-three patients
with a minimum two-year follow-up, four (17%) had a good
result (an ankle score of 80 to 89 points) and nineteen (83%)
had an excellent result (a score of 90 to 100 points).
No patients were noted to have a complication due to
the biochemical properties of the implant. Rapidly degradable polymers such as polyglycolic acid have produced cystic
collections of the hydrolyzed polymer and have occasionally
formed draining sinus tracts4,23,24. To our knowledge, such
tracts have not been documented with the more slowly degrading polylevolactic acid polymer. None of our patients had
such a tract.
Additionally, areas of osteolysis have been seen adjacent
to some of these devices25-27. The rate of degradation of the
polymer and the ability of the body to clear the degraded debris determine the local concentration of the breakdown
products and the appearance of any cystic collection of degraded polymer. Osteolysis and a late foreign-body reaction
have been documented with the use of polylevolactic acid
screws. Böstman and Pihlajamäki27 described a case in which a
foreign-body reaction to degraded polylactide occurred four
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years after implantation of the screw. We performed a careful
periodic review of the radiographs to identify any evidence of
osteolysis in our series, and none was seen. Although the average duration of follow-up in our series was more than 2.5
years, the case reported by Böstman and Pihlajamäki demonstrates that reactions may occur much later as a result of the
highly crystalline, stable structure of polylevolactic acid. Consequently, the duration of follow-up represents a limitation of
the current study.
Other weaknesses of this study include the lack of control for fixation of the medial malleolus and the percentage of
patients lost to follow-up. Medial fractures were internally
fixed with either metallic or polymeric screws at the discretion
of the surgeon. All of the medial fractures healed, and no differences in healing could be identified according to the type of
screw fixation. Although controlling for this variable would
have produced a purer series, prior data from our institution
demonstrated equal outcomes with the use of metallic and
polylevolactic acid screws for fixation of medial malleolar
fractures3.
In this series of thirty-three patients, two-year followup data were available for twenty-three (70%) and one-year
follow-up data were available for twenty-eight (85%). All efforts (including the use of Internet search engines and private
investigators) were made to locate patients who were difficult
to find or had been lost to follow-up. To encourage patients to
return for scheduled follow-up appointments, a monetary incentive was given for the one-year and two-year visits. This incentive was offered solely and explicitly for the purpose of
increasing accrual of patient follow-up. This study was performed at a level-I trauma center with a large, indigent population. We would have preferred a more complete follow-up,
but we believe that these numbers are satisfactory given this
population of patients.
The biochemical and biomechanical properties of resorbable polymers must be taken into account when selecting
implants for fracture fixation. Disruption of the ankle syndesmosis appears to be a good indication for the use of selfreinforcing polylevolactic acid screws because the ankle can
be easily unloaded and the syndesmosis does not require
compression for healing. We recommend the avoidance of
any weight-bearing on the limb for a minimum of six weeks
after the operation to ensure that the screws do not fail before
osseous and ligamentous healing takes place. Therefore, polylevolactic acid screw fixation of the syndesmosis may be
contraindicated in a noncompliant patient. „
NOTE: The authors thank Shelly Whitlock for her diligent work assisting with this study.
W. David Hovis, MD
Hovis Orthopaedic Clinic, 501 19th Street, Suite 702, Knoxville,
TN 37916
Bryan W. Kaiser, MD
Robert W. Bucholz, MD
Department of Orthopaedic Surgery, University of Texas Southwestern
Medical School, 5323 Harry Hines Boulevard, Dallas, TX 75235-8883
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Jeffry T. Watson, MD
Anderson Orthopaedic Clinic, 2000 East Greeneville, Suite 3700,
Anderson, SC 29621
The authors did not receive grants or outside funding in support of
their research or preparation of this manuscript. They did not receive
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ANKLE
payments or other benefits or a commitment or agreement to
provide such benefits from a commercial entity. No commercial
entity paid or directed, or agreed to pay or direct, any benefits to any
research fund, foundation, educational institution, or other charitable
or nonprofit organization with which the authors are affiliated or
associated.
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