The use of absorbable materials in
surgery is not new, as gut suture
was described in the writings of
Galen in the second century. However,
recent improvements in polymer
science have led to the development
of new orthopaedic implants
made of bioabsorbable materials.
The chief advantage of these implants
is that there is initial stability
adequate for healing and then gradual
resorption after biologic fixation
has been established. In addition,
these materials limit stress shielding
of bone, gradually apply load as
they degrade, obviate hardware
removal procedures, and facilitate
postoperative radiologic imaging.
Polymers made from lactic acid,
glycolic acid, and dioxanone, as
well as copolymers of these materials,
have been studied and are readily
available for clinical use as implants
for both bone and soft-tissue
fixation.
Basic Science of
Bioabsorbable Implants
By definition, bioabsorbable implants
are degraded in a biologic
environment, and their breakdown
products are incorporated into normal
cellular physiologic and biochemical
processes. These materials
must also be biocompatible, with
degradation products that are well
tolerated by the host with no immunogenic
or mutagenic tendency. In
addition, for musculoskeletal applications,
these materials must maintain
adequate strength and not degrade
too rapidly, so that fixation is not lost
before adequate healing can occur.
The perfect bioabsorbable material
for orthopaedic use would initially
have mechanical characteristics
equal to those of standard stainless
steel implants. It would degrade
with the healing process so that load
is gradually transferred to the healing
tissue. The currently available
polymers still do not have mechanical
characteristics equal to those of
metal implants1-3 (Table 1), but
improvements continue to be made,
particularly with the use of reinforcing
techniques.
Polymer Science
Most research on the clinical applications
of bioabsorbable materials
has focused on the use of polymers
known as alpha-polyesters or poly-
(alpha-hydroxy) acids. These include
polylactic acid (PLA), polyglycolic
acid (PGA), and polydioxanone
(PDS). Combinations of these
materials allow optimization of
Dr. Ciccone is in private practice in Colorado
Springs, Colo. Dr. Motz is in private practice in
San Diego, Calif. Dr. Bentley is in private practice
in San Diego. Dr. Tasto is Associate Clinical
Professor of Orthopaedics, University of
California, San Diego.
One or more of the authors or the departments
with which they are affiliated have received
something of value from a commercial or other
party related directly or indirectly to the subject
of this article.
Reprint requests: Dr. Tasto, San Diego Sports
Medicine & Orthopaedic Center, #200, 6719
Alvarado Road, San Diego, CA 92120.

Abstract
The use of bioabsorbable implants in orthopaedic surgical procedures is becoming
more frequent. Advances in polymer science have allowed the production of
implants with the mechanical strength necessary for such procedures.
Bioabsorbable materials have been utilized for the fixation of fractures as well as
for soft-tissue fixation. These implants offer the advantages of gradual load
transfer to the healing tissue, reduced need for hardware removal, and radiolucency,
which facilitates postoperative radiographic evaluation. Reported complications
with the use of these materials include sterile sinus tract formation,
osteolysis, synovitis, and hypertrophic fibrous encapsulation. Further study is
required to determine the clinical situations in which these materials are of most
benefit.
J Am Acad Orthop Surg 2001;9:280-288
Bioabsorbable Implants in Orthopaedics:
New Developments and Clinical Applications
William J. Ciccone II, MD, Cary Motz, MD, Christian Bentley, MD, and James P. Tasto, MD
Perspectives on Modern Orthopaedics
William J. Ciccone II, MD, et al
Vol 9, No 5, September/October 2001 281
their biomechanical properties for
specific clinical uses.
Polymers are composed of covalently
bonded subunits that form
large macromolecules.4 These repeating
subunits are referred to as
monomers. A polymer made of a single
repeating monomer is a homopolymer.
A combination of two or
more different monomers results in a
copolymer. The various monomeric
units in a copolymer may be arranged
randomly (random copolymer)
or in long regions of one subunit
alternating with another (block
copolymer). The biomechanical
and biochemical properties of a
copolymer differ from those of its
constituent monomers.5
The polymer chains that constitute
the implant may be linear,
branched, or cross-linked to neighboring
chains. The microstructural
organization of the chains may be
amorphous or crystalline, as determined
by the orientation of the polymer
chains. The overall crystallinity
of a polymer affects its biomechanical
and degradation proerties. These
properties can be influenced by the
manufacturing technique, with elevated
temperatures and a slow rate
of cooling allowing the polymeric
chains to align themselves in an
ordered solid structure.6 Most bioabsorbable
implants are made of
“semicrystalline” materials containing
both amorphous and crystalline
regions, each of which plays a role in
strength and absorption rates.5,7,8
Many of the physical properties
of a polymer are dependent on the
chemical composition, the molecular
weight, and the arrangement of
the polymer chains. Polymers utilized
in orthopaedics are viscoelastic
in nature; therefore, their physical
properties change with the rate
of load application and are timedependent.
Increased molecular
weight implies an increased intrinsic
viscosity within the polymer,
leading to less deformability (i.e.,
less flow) with an applied load. In
general, high- to average-molecularweight
polymers that are highly viscous
will undergo slower biodegradation
than those of lesser molecular
weight and viscosity.
The mechanical properties of a
polymer are further influenced by
temperature. The glass-transition
temperature (Tg) is the temperature
below which the polymer is stiff and
hard and above which it is soft and
rubbery. The Tg will vary with the
chemical composition of the polymer,
the molecular weight, and the
percentage of the polymer involved
in amorphous domains. As a polymeric
implant is able to withstand
more load at temperatures below its
Tg, most polymers utilized clinically
have a Tg above body temperature.
Lactic acid is a small, hydrophobic
three-carbon molecule that
plays an important role in cellular
energy production. Due to the asymmetry
of the molecule, it has both a
dextrorotatory (D) and a levorotatory
(L) configuration. The D-form is
readily produced, but the L-isomer
is the biologically active form. Polymerized
L-lactic acid is referred to as
poly-L-lactic acid (PLLA). The copolymer
with the D-form (poly-DLlactic
acid) is termed PDLLA. The
mechanical and degradation properties
of these two enantiomers differ
markedly, with PLLA being
highly crystalline and PDLLA being
more amorphous.1 The characteristics
of the copolymers are intermediate
between those of the two
monomers.
Polyglycolic acid is synthesized
by ring-opening polymerization
from glycolide. It is a hard, tough,
crystalline molecule that is more
hydrophilic in nature than PLA. Its
self-reinforced form is stiffer than
other clinically utilized polymers.2
Polyglycolic acid has been utilized
extensively in orthopaedic implants.
This polymer has more rapid degeneration
rates than PLA; there
have been more synovitic reactions
with this material, probably secondary
to its rapid degradation.9
Polydioxanone was first described
in 1981.3 This material is
manufactured by polymerizing the
monomer para-dioxanone. In its
natural state, PDS is a colorless crystalline
polymer; its purple hue is
obtained with the addition of violet
dye. The PDS suture is created by
the melt-extrusion of polymer granules
through the appropriate dyes.
The inherent stiffness of PDS suture
has made it invaluable in applications
in arthroscopic procedures, as
it goes easily through suture passers.
Degradation
The degradation of bioabsorbable
implants follows a predictable
pattern. The rate of degradation is
dependent on the starting molecular
weight of the polymer and its crys-
Table 1
Mechanical Properties of Various Bioabsorbable Implant Materials1-3
Bending Bending Shear
Diameter, Modulus, Strength, Strength,
Implant Material mm GPa MPa MPa
Stainless steel (for comparison) … 200 280 …
Self-reinforced polyglycolic acid 2 13 320 240
Injection-molded polyglycolic acid 2 7 218 95
Self-reinforced poly-L-lactic acid 1.3 10 300 220
Injection-molded poly-L-lactic acid 2 3 119 68
Polydioxanone (suture) … … … 48
Bioabsorbable Implants
tallinity, the composition and porosity
of the implant, and other factors,
such as loading conditions and local
vascularity. In the degradation process,
there is first a loss in molecular
weight, followed by loss of strength
and finally loss of mass. The early
phase of degradation is chemical in
nature. Biologic processing and removal
of the implant occur later.10-12
Because of this pattern of degradation,
these materials lose functional
strength long before they are completely
absorbed.
The initial phase of degradation
is one of hydrolysis. Water molecules
enter the implanted material,
causing cleavage of the monomeric
molecular bonds. This leads to the
scission of long polymer chains into
shorter chains, reducing the overall
molecular weight. This process is
affected by implant porosity.13,14
Low porosity enhances autocatalysis
of the implant because the slow
clearance of degradation products
from within the material leads to
increased acidity and more rapid
molecular scission. The molecular
weight plays an important role in
the internal friction within the implant,
and thus its mechanical properties;
hydrolysis of these long
chains leads to a loss in mechanical
strength. As a result, implants with
low porosity may have a shortened
functional life.
As the implant loses integrity and
fragments, biologic removal of the
implant takes place. The rapid degradation
of these implants has been
postulated to be the cause of marked
foreign-body reactions, synovitis,
and even activation of the complement
cascade.8,15-17 Studies evaluating
the tissue response to PGA and
PLLA implants have shown foreignbody
reactions to the degradation
products. The degradation of PLLA
has been associated with a foreignbody
reaction as late as 143 weeks
after implantation.12 A foreign-body
response reaction to PGA has been
seen as early as 3 to 6 weeks.11 Differences
in the timing of the cellular
response to these materials are
probably secondary to the different
rates of degradation of PGA and
PLLA. Clinically, most symptomatic
foreign-body reactions have
been associated with the more
rapidly degrading PGA,9,18 but reactions
to PLLA have also been described.
19 The rates of degradation
of these materials can be optimized
for biologic fixation by changing the
copolymer ratios of PGA and PLLA.5
The most common soft-tissue
complications related to use of these
materials are sterile sinus tract formation,
hypertrophic fibrous encapsulation,
and osteolysis. These inflammatory
responses occur in
fewer than 10% of patients, but may
be severe enough to require surgery
for resolution of the reaction.16
Biochemical Degradative Pathway
Alpha polyesters, such as PLA,
PGA, and PDS, primarily degrade
by hydrolysis, with the release of
their respective monomers. The
monomers are then incorporated
into normal cellular physiologic
processes for further degradation.
Lactic acid, glycolic acid, and paradioxanone
have well-defined biochemical
pathways that lead eventually
to their excretion in the form of
carbon dioxide and water7,20 (Fig. 1).
Lactic acid is produced by the
hydrolytic degradation of PLA.
Lactic acid is normally produced at
the end of the glycolytic pathway
from pyruvate when the amount of
oxygen is limiting. The oxidation of
lactate to form pyruvate is catalyzed
by lactate dehydrogenase. In aerobic
conditions, pyruvate undergoes
oxidative decarboxylation to produce
acetyl coenzyme A. This molecule
may then enter the citric acid
cycle for further oxidation to produce
carbon dioxide, water, and
adenosine triphosphate by oxidative
phosphorylation.
Degradation of PGA and PDS
follows nearly the same pathway.
Hydrolysis of PGA produces glycolic
acid, which is either excreted
directly in the urine or converted to
glyoxylate. The PDS degradation
products enter the pathway at glyoxylate.
The amino acid glycine can
be produced from glyoxylate by a
transamination reaction. Glycine, a
glucogenic amino acid, can be further
converted to pyruvate through
a serine intermediate. Pyruvate is
then converted to acetyl coenzyme
A to enter the citric acid cycle, as
previously discussed.
Mechanical Properties
The mechanical properties of
bioabsorbable orthopaedic implants
must be considered both at the time
of insertion and throughout degradation.
The implants are initially subjected
to considerable loads, which
gradually decrease with tissue healing.
The perfect implant will de-
Figure 1 Biochemical degradation pathways
for PLA, PDS, and PGA.
Acetyl coenzyme A
CO2
H2O
Glycine Urine
Serine
Glycolic
acid
PLA PDS PGA
Citric acid cycle
Pyruvate
Lactic acid Glyoxylate
William J. Ciccone II, MD, et al
Vol 9, No 5, September/October 2001 283
grade at a rate that gradually transfers
load to healing tissue and does
not outpace the healing response.
Factors that affect the mechanical
properties of an implant include the
type of material, its processing, and
the local testing environment.21
Bioabsorbable polymers differ from
common stainless steel implants in
that they are more viscoelastic in
nature. Therefore, they exhibit enhanced
properties of creep and
stress relaxation. Claes21 exhibited
the importance of this property by
demonstrating that when used in
the form of an interfragmentary
screw, bioabsorbable polymers lost
20% of their force 20 minutes after
application, due to stress relaxation.
Reinforcing techniques have been
developed to improve the mechanical
characteristics of bioabsorbable
implants. Self-reinforced absorbable
components are polymeric materials
in which the reinforcing elements
and matrix material have the same
chemical composition. The most
effective way to manufacture the
self-reinforced structure into the
polymer is by the mechanical deformation
of the nonreinforced material.
7 This deformation process leads
to the formation of oriented polymeric
chains, the self-reinforcing
structures.
The reported properties of these
implants vary, due mostly to differences
in processing and testing conditions.
Overall, the self-reinforced
materials show an improvement in
their initial mechanical values compared
with the nonreinforced polymers
(Table 1). The initial bending
strength of self-reinforced PGA
exceeds that of stainless steel; however,
with rapid rates of degradation,
this strength is not maintained. In
general, the mechanical properties of
these polymeric implants do not
approach those of standard stainless
steel implants. While rapid loss of
the mechanical properties might be
expected to allow excessive motion
between fracture fragments, these
materials have been used successfully
in specific clinical situations.
Mechanical degradation studies
have been performed in both in
vivo and in vitro conditions. The
most important determinant of the
rate of degradation is the material
itself, but the environment surrounding
the implantation site can
also be an influence. There is evidence
that degradation rates are
more rapid with in vivo testing secondary
to enzymatic contributions.1
Areas of high tissue metabolism and
blood flow facilitate material degradation.
Furthermore, implants under
load tend to degrade faster, possibly
secondary to microfracture.
The mechanical degradation rate
of PDS suture has been studied by
Ray et al.3 The breaking strength of
PDS suture was tested after being
implanted in the subcutaneous
tissue of rats. The PDS suture retained
74% of its nonimplanted
strength at 2 weeks, but by 6 and 8
weeks that value had dropped to
41% and 14%, respectively. The
authors also determined, with the
use of radioactive labeling, that the
material absorption was complete
by 182 days after implantation.
Likewise, PGA materials lose their
mechanical strength by 6 to 8
weeks. The loss of the mechanical
properties of this material occurs at
varying rates, with the loss of shear
strength being slower than loss of
bending strength. In self-reinforced
materials, the matrix material loses
its strength more rapidly than the reinforcing
elements. Therefore, these
materials may be more suited for
the fixation of fractures involving
periarticular cancellous bone, where
high shear loads are common.
Clinical Applications
The use of bioabsorbable fixation for
the attachment of soft tissue to bone
is being increasingly utilized by
orthopaedic surgeons, especially in
the treatment of soft-tissue lesions in
the shoulder. These implants have
facilitated the repair and reconstruction
of labral and rotator cuff lesions.
The development of bioabsorbable
tacks, suture anchors, and screwand-
washer implants has given surgeons
more treatment alternatives
(Fig. 2).
Bioabsorbable suture anchors are
useful as an alternative to metal staples
and screws, which may have a
high profile. They also eliminate the
need for passing sutures through
bone tunnels. Pullout strengths for
bioabsorbable suture anchors are
comparable to those of their metallic
counterparts.22 These implants have
sufficient strength that the point of
failure is the suture–soft-tissue interface.
23
The complications observed with
the use of bioabsorbable suture
anchors are similar to those seen
with metallic anchors. Improper
insertion of the anchor too deep in
the bone can cause suture fraying or
failure. Superficial insertion of the
anchor can lead to cartilage wear on
the opposing articular surface. The
anchor can also fail by pullout from
bone and become an intra-articular
loose body. As these implants are
radiolucent, this diagnosis can be
difficult to make postoperatively in
a persistently painful joint. Unique
to bioabsorbable anchors is the potential
for eyelet failure with secondary
suture cutout.
Bioabsorbable suture anchor fixation
has several advantages. The
anchor undergoes reabsorption and
therefore reduces the need for removal
of a prominent implant. Resorption
also makes revision surgery
less complicated, as hardware
removal is not necessary. The fixation
does not obscure the anatomy
as depicted on radiographs and is
compatible with magnetic resonance
imaging if further evaluation
of the affected joint is necessary.
Improperly placed anchors may
simply be drilled out rather than
Bioabsorbable Implants
284 Journal of the American Academy of Orthopaedic Surgeons
unscrewed or pushed through, as is
necessary with metallic anchors.
Finally, stress is gradually transferred
to the healing soft tissue as
the anchor degrades.
Repair of Shoulder Lesions
The effectiveness of bioabsorbable
anchors for use in Bankart repairs,
as well as in treatment of rotator
cuff tears and “SLAP” lesions
(i.e., anterior-to-posterior lesions of
the superior labrum), is currently
under investigation. Warme et al24
compared the usefulness of bioabsorbable
and nonabsorbable suture
anchors in a prospective randomized
study of open Bankart repairs. At
an average follow-up interval of 25
months, there was one failure in the
18 patients treated with nonabsorbable
anchors, compared with two
failures in 20 patients treated with
absorbable anchors. Radiographs
obtained at the 2-year follow-up in
the absorbable group demonstrated
near-complete implant degradation
and osseous replacement. At 6
months, the anchor holes used for
nonabsorbable implants demonstrated
a sclerotic rim but no increase
in size from the measurements
on the initial postoperative
radiographs. There was no subsequent
radiographic change after that.
It must be noted that no reports of
complications attributable to the bioabsorbable
nature of these suture
anchors have been published.
The use of bioabsorbable tacks for
the repair of labral lesions has made
arthroscopic management of these
injuries technically less complicated.
The development of labral tacks,
such as Suretac (Smith&Nephew,
Andover, Mass), TissueTack (Arthrex,
Naples, Fla), ConTack (Mitek,
Westwood, Mass), and the Contour
Labral Nail (Bionx Implants, Blue
Bell, Pa), has led to the ability to
treat more patients with Bankart and
SLAP injuries arthroscopically. These
tacks are cannulated for ease of
insertion and allow the labrum to be
reattached to the glenoid in an anatomic
position. These devices eliminate
the risks of metal around joint
surfaces, do not require transglenoid
drilling or an accessory posterior
incision, and avoid technically difficult
arthroscopic knot tying.
The first absorbable tack was
constructed of PGA, which rapidly
loses strength over the first 4 to 6
weeks. Complete reabsorption occurs
in approximately 6 months.
This implant has been implicated in
several cases of aseptic synovitis
secondary to a histiocytic or phagocytic
reaction to the rapidly degrading
polymer.9 Currently, most tacks
are composed of longer-absorbing
materials such as PDLA, PLLA, or
composites, which may reduce the
rate of synovitis.
Warner et al25 reported on a
cohort of 15 patients who underwent
“second look” arthroscopy for a
failed arthroscopic Bankart repair
performed with the Suretac device.
These patients were a subgroup of 96
patients initially treated for posttraumatic
recurrent anterior dislocation
or subluxation. The repeat procedure
was necessitated by recurrent
instability in 7 patients, pain in 6,
and pain with stiffness in 2. When
reevaluated, the failure in the patients
with instability was considered
to be secondary to inadequate reconstruction
of either the anterior glenohumeral
ligaments or the anterior
labral complex. The cause of failure
in the 8 patients with either pain or
pain and stiffness was less clear, although
an indolent inflammatory
response to the PGA polymer was
found in several. Six of the patients
eventually had complete or partial
pain relief after a second arthroscopy
and subacromial decompression, biceps
tenodesis, or a capsular release
or manipulation.
Bioabsorbable fixation devices
are now also being used for the
repair of rotator cuff tears. These
procedures were initially performed
with suture anchors, but more re-
Figure 2 Currently available bioabsorbable implants for fracture fixation, interference fixation,
and meniscal repair.
William J. Ciccone II, MD, et al
Vol 9, No 5, September/October 2001 285
cently screw-and-washer–type devices
have become available. The
rationale behind the use of these
soft-tissue screws is to repair the
tendon to bone without a suture,
reducing the incidence of complications
at the tendon-suture interface
and increasing the surface area of
tendon contact with bone. These
devices (Bio-Headed Corkscrew,
Arthrex; Biocuff Screw, Bionx; Biotwist,
Linvatec, Naples, Fla) all
employ a screw-in device with a
large head for soft-tissue compression.
The Biocuff screw has an independent
spiked washer to prevent
tendon damage and reduce pressure
necrosis. No clinical studies on the
use of these devices are yet available.
Meniscal Repair
The “all inside” technique of meniscal
repair described by Morgan
was developed to safely repair the
posterior and central peripheral
portions of the meniscus, a location
difficult to reach with traditional
arthroscopic techniques because of
the risk of neurovascular injury.
The use of bioabsorbable implants
for use in all-inside meniscal repair
has now been described.26 These
devices eliminate the need for a posterior
incision, reduce the risk of
neurovascular injury, and simplify
the fixation procedure.
The Bionx Meniscal Arrow is a
well-characterized bioabsorbable implant
that has been approved by the
US Food and Drug Administration
for meniscal repair. It is a T-shaped
device composed of self-reinforced
PLLA with a 1.1-mm-diameter barbed
stem. The stem penetrates the meniscus
and capsule, and the bar portion
approximates the torn meniscal leaf
to the periphery. The arrows remain
in the joint for approximately 1 year
and are gradually absorbed through
hydrolysis to carbon dioxide and
water.
Biomechanical data reported by
Boenisch et al27 compared the pullout
strength and linear stiffness of
meniscal repair performed with
bioabsorbable arrows and vertical
and horizontal looped sutures in bovine
menisci. The pullout strengths
in both suture groups were significantly
(P<0.05) higher than those in
the arrow-fixation group. Further,
vertical-suture fixation was significantly
stiffer than fixation with
either horizontal sutures or arrows.
However, more recent data from another
bovine study28 demonstrated
no difference between the pullout
strength of the arrow and that of a
vertical PDS suture when the arrow
was inserted with a mechanical “gun.”
In fact, significantly greater pullout
strength for arrow fixation was noted
at 12 and 24 weeks compared with
PDS-based implants. Technical considerations
of insertion, such as keeping
the arrow parallel to the joint surface
and maximizing the number of
barbs engaging beyond the tear, have
been demonstrated to be essential to
the integrity of the repair.
Albrecht-Olsen et al29 performed
a randomized prospective study
comparing meniscal repair utilizing
the bioabsorbable meniscal arrow
implant to inside-out repair with
horizontal meniscal sutures. Sixtyeight
patients were divided evenly
between the two groups. Repairs
were performed only in red-red or
red-white zones, and rehabilitation
protocols were standardized. In all,
65 patients (96%) underwent repeat
arthroscopy at 3 to 4 months. A
healed meniscus was observed in
91% of the arrow repair group but
in only 75% of those in the suture
group. There were no complications
reported in the group with
bioabsorbable fixation. The operative
time for the procedures averaged
30 minutes for repair with the
arrow and 60 minutes for suture repair.
The advantages of decreased
operative time, ease of insertion,
and improved meniscal healing
with an all-inside meniscal repair
with a bioabsorbable implant were
confirmed by this study.
Complications with the Bionx
Arrow have been published in several
case reports.30-34 These include
hematoma formation, subcutaneous
migration, foreign-body reaction,
and loss of fixation. The use of
these newly developed implants
appears to be simple. However,
attention to technical detail in terms
of placement, choice of length, and
orientation is required to avoid
complications and ensure optimal
fixation.
Anterior Cruciate Ligament
Reconstruction
Graft fixation devices for anterior
cruciate ligament reconstruction
have been manufactured in the past
from nonabsorbable materials such
as metal and plastic. These devices
are often difficult to remove or
avoid if revision anterior cruciate
ligament reconstruction is required.
Furthermore, the evaluation of softtissue
lesions with MR imaging
after the use of metal fixation is difficult.
Additionally, aperture fixation
(soft-tissue fixation at the joint
line), which provides a stiffer construct,
is hampered by concerns
about graft severance by metal
interference screws. Use of bioabsorbable
fixation devices, such as
interference screws, can potentially
eliminate some of these problems.
Several different types of screws,
which vary in polymeric composition,
are currently available. Graft
fixation strength in anterior cruciate
ligament reconstruction is critical in
the period from initial fixation to osseous
integration of the graft. This period
ranges from 6 weeks for bone–
patellar tendon–bone fixation to
approximately 12 to 16 weeks for
hamstring fixation. Therefore, the
bioabsorbable interference screw
must maintain virtually all of its
structural integrity during that
entire interval. The initial pullout
strengths of these implants should
exceed the estimated 500-N load for
activities of daily living. For this
Bioabsorbable Implants
286 Journal of the American Academy of Orthopaedic Surgeons
reason, most screws on the market
are manufactured from PLLA or a
variant copolymer with a longer
half-life (Fig. 3). This composition
can lead to delayed osseous integration,
thus negating the main benefit
of the bioabsorbable fixation.
No consensus is supported by
the results of recent biomechanical
studies. Pena et al35 published data
on the insertion torques and fixation
strengths of bone–patellar tendon–
bone grafts fixed with PLA interference
screws (Bioscrew, Linvatec,
Key Largo, Fla) and compared them
with metal interference screws in
cadaveric specimens from young
and middle-aged individuals. With
use of a correction factor for bonemineral
density, the pullout forces
were 730 N for the metal screws and
668 N for the PLA screws. The insertion
torque was 1.52 N for the
metal screws and 0.30 N for the bioabsorbable
screws. Both pullout
force and insertion torque were significantly
(P>0.05) higher for metal
interference fixation. The authors
noted that loss of tensile strength of
bioabsorbable screws is possible
with excessive time in storage due to
hydrolysis or wetting the implant
before insertion.
Caborn et al36 have published the
results of a biomechanical comparison
of metal and bioabsorbable interference
screw fixation of quadrupled
semitendinosus-gracilis grafts. No
statistically significant difference was
found in the maximum load at pullout,
nor did the screw insertional
torques correlate with the maximum
load at pullout. However, a followup
study in which the bone tunnels
were specifically sized within 5 mm
of the graft diameter showed that the
bioabsorbable screw-insertion torque
correlated directly with ultimate
graft failure strength.37 Therefore, it
appears that bioabsorbable interference
screw fixation is not appropriate
for all patients, especially those
with poor bone quality. Careful
graft preparation and sizing can,
however, result in interference fixation
capable of withstanding the
forces of accelerated rehabilitation.
A recent prospective, randomized
study by McGuire et al38 compared
the Linvatec Bioscrew with metal
interference screws in 204 patients.
A variety of graft sources were used,
including autogenous and allograft
bone and patellar tendon and allograft
Achilles tendon. The average
follow-up interval was 2.4 years,
and the mean age of patients was 30
years. A standardized rehabilitation
protocol was used. No statistically
significant difference was noted in
the Lysholm or Tegner score, pain,
thigh size, Lachman test result, pivot
shift, patellofemoral crepitus, or
joint effusion. There was no statistically
significant difference in mean
maximum manual side-to-side KT-
1000 rating between the 1.8-mm bioabsorbable
screw and the 1.6-mm
metal screw. Twelve PLLA screws
broke during insertion without adverse
effects. There were no reported
complications related to loss of fixation,
toxicity, allergenicity, or osteolysis.
Excellent clinical results are possible
with bioabsorbable interference
screws, although there is no
consensus opinion as to whether
biomechanical strength is the same
between metal and bioabsorbable
screw fixation. Disadvantages of
bioabsorbable interference screws
include concerns about sterile
drainage, cyst formation, lack of
complete osseous ingrowth into the
defect, early loss of pullout strength
secondary to hydrolysis, and intraoperative
breakage of the device.
The reported rate of these clinical
complications is low and has not
resulted in a clinically significant
difference in outcome studies published
to date.
Fracture Fixation
Although bioabsorbable fracturefixation
devices appear to have obvious
advantages over metal implants,
concerns about the initial fixation
strength of these materials have limited
their widespread acceptance.
These materials must have the initial
fixation strength necessary to maintain
the reduction of bone fragments
during the healing process. Manufacturing
techniques are critical, as
melt-molded polymers do not possess
the strength necessary for reliable
fixation, whereas self-reinforced
materials have the mechanical characteristics
more suitable for this use.
In a review of more than 2,500
fracture-fixation cases in which bioabsorbable
implants were used,
Rokkanen et al39 reported that the
incidence of bacterial wound infection
was 3.6%; nonspecific foreignbody
reaction, 2.3%; and failure of
fixation, 3.7%. Compared with
metallic fixation, absorbable fixation
has shown a lower incidence of
infection.40
Bucholz et al41 performed a prospective
randomized trial comparing
PLA screws with stainless steel
screws for fixation of displaced
medial malleolar fractures. They
found no statistically significant difference
in operative or postoperative
complications between the two
groups.
Figure 3 MR image obtained 24 months
after interference fixation of hamstring
autografts with bioabsorbable PLLA
screws shows minimal degradation.
William J. Ciccone II, MD, et al
Vol 9, No 5, September/October 2001 287
Foreign-body reactions to PGA
have been described,9,18,39 but neither
Rokannen et al39 nor Bucholz et
al41 reported late reactions to PLA
screws. However, a recent case report
described an osteolytic reaction
to an intraosseous PLA screw 52
months after the operative procedure.
19 Longer-term follow-up may
be necessary to determine the actual
clinical biocompatibility of intraosseous
PLA.
The use of bioabsorbable implants
for pediatric fracture fixation
is particularly appealing because it
obviates implant removal. In experimental
studies, the presence of
an absorbable implant does not
seem to interfere with the growth
plate any more than an empty drill
hole does.42 Biodegradable implants
have shown satisfactory results,
especially in the treatment of distal
humeral physeal fractures.43-45
Böstman et al43 evaluated the use
of absorbable self-reinforced PGA
pins in the treatment of 71 physeal
and nonphyseal fractures in skeletally
immature patients, with a mean
follow-up interval of 15.8 months.
Anatomic reduction was maintained
until union in 87% of the fractures,
but in only 8 of 14 supracondylar
humerus fractures. The authors felt
that the displacement forces encountered
in supracondylar fractures
overwhelmed the mechanical properties
of the absorbable pins, resulting
in displacement. They concluded
that the preliminary results of fracture
treatment with self-reinforced
PGA were satisfactory except for
supracondylar humerus fractures.
Long-term clinical studies are still
required to determine the effects of
these implants on the growth plate.
Summary
The use of bioabsorbable implants in
musculoskeletal procedures is gaining
acceptance. While most commonly
utilized in the field of sports
medicine for soft-tissue fixation,
these implants may have applications
in other aspects of orthopaedics.
Complications associated with
the use of these materials have diminished
with the development of
newer, self-reinforced polymers.
Until more long-term, peer-reviewed
research becomes available, the
appropriate clinical usage of these
implants remains a concern for the
practicing orthopaedist.
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