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Bone Replacement of Fast-Absorbing Biocomposite Anchors in Arthroscopic
Shoulder Labral Repairs
Article in The American Journal of Sports Medicine · April 2012
DOI: 10.1177/0363546512441589 · Source: PubMed
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2. Bone Replacement of Fast-Absorbing
Biocomposite Anchors in Arthroscopic
Shoulder Labral Repairs
Matthew D. Milewski,* MD, David R. Diduch,y
MD, Joseph M. Hart,y
ATC, PhD,
Marc Tompkins,z
MD, Shen-Ying Ma,y
MD, and Cree M. Gaskin,y§||
MD
Investigation performed at the University of Virginia, Charlottesville, Virginia
Background: Newer generation biocomposite anchors are hypothesized to resorb more reliably and faster, while allowing for
bone ingrowth and replacement.
Purpose: The purposes of this study were to (1) assess anchor resorption and bone ingrowth over time, (2) identify tunnel wid-
ening or potential reactions to the implants, (3) compare imaging findings for different sites of labral repair, and (4) determine
patient subjective outcomes with the use of biocomposite anchors in glenoid labral repair.
Study Design: Case series; Level of evidence, 4.
Methods: We enrolled 22 patients to participate in a 24-month outcomes study that included subjective and objective outcome
assessments after glenoid labrum repair surgery. Magnetic resonance imaging (MRI) was performed at 6 and 12 months to iden-
tify any potential reactions to implants. Computed tomography (CT) scans were performed at 12 and 24 months to determine
anchor resorption and bone ingrowth. Sixteen patients and 47 anchors were available for follow-up at 24 months. An indepen-
dent, fellowship-trained musculoskeletal radiologist read the scans. Subjective outcome scores measured at 24 months post-
operatively included Simple Shoulder Test, Tegner activity scale, American Shoulder and Elbow Surgeons (ASES), and
University of California, Los Angeles (UCLA) shoulder scores.
Results: No adverse events were reported with the use of biocomposite anchors at the end of the study period. At 12 and 24
months, respectively, CT scans demonstrated that an estimated 68% and 98% of combined anchor material had been absorbed,
56% and 78% of the anchor material had been replaced by soft tissue of variable density, and 9% and 20% of total anchor vol-
ume was replaced by bone. No obvious mechanical failure of the labral repairs was detected on nonarthrogram MRI. Three of the
47 anchors showed bone cyst formation. Tunnel widening (expansion beyond tunnel diameter of 3 mm; 2.9-mm drill hole utilized)
was seen in 55% of the anchors but decreased between 12 and 24 months, consistent with bone replacement. Tunnel widening
was seen more in anteroinferior and posterior glenoid anchor locations (84% and 57%, respectively) than in superior labral an-
chors (13%). Subjective outcome scores at 24 months for ASES and UCLA shoulder scores averaged 88 and 30, respectively. All
but one patient were satisfied with their outcome at 24 months.
Conclusion: Our imaging evaluation indicates resorption of newer generation biocomposite anchors with progressive bone
replacement at 12 and 24 months while maintaining acceptable subjective outcomes.
Keywords: biocomposite; suture anchor; labral repair; shoulder; arthroscopy
The use of suture anchors for soft tissue to bone fixation
has facilitated the movement from open surgery to arthro-
scopic techniques for a variety of glenohumeral conditions
including Bankart and superior labrum anterior posterior
(SLAP) lesion repairs.16,25,27
Success of these arthroscopic
procedures depends on multiple factors including tissue
quality, patient selection, and compliance with postopera-
tive rehabilitation.26,38
Technique and technology-related
factors including anchor and suture material, knot secu-
rity, anchor geometry, and anchor biomechanics also play
a role.11,12,25,37
The first-generation suture anchors were
metallic devices that provided excellent fixation but were
associated with failures including loosening and breakage
that led to chondral damage.{
Metallic artifact also
||
Address correspondence to Cree M. Gaskin, MD, University of Vir-
ginia Health System, Department of Radiology and Medical Imaging,
PO Box 800170, Charlottesville, VA 22908 (e-mail: cmg9s@virginia.edu).
*Elite Sports Medicine / Connecticut Children’s Medical Center;
Farmington, Connecticut.
y
Department of Orthopaedic Surgery, University of Virginia, Charlot-
tesville, Virginia.
z
Department of Orthopaedics, University of Minnesota, Minneapolis,
Minnesota.
§
Department of Radiology and Medical Imaging, University of Virginia,
Charlottesville, Virginia.
One or more of the authors has declared the following potential con-
flict of interest or source of funding: Dr Gaskin is a consultant for DePuy
Mitek. This study was funded, in part, by a research grant from DePuy
Mitek.
The American Journal of Sports Medicine, Vol. 40, No. 6
DOI: 10.1177/0363546512441589
Ó 2012 The Author(s) {
References 4, 6, 10, 11, 13, 19, 30, 39.
1392

3. distorted postoperative imaging by computed tomography
(CT) and magnetic resonance imaging (MRI) in revision
scenarios.29
Bioabsorbable alternatives were therefore
developed to help address some of the disadvantages of
metallic anchors while providing appropriate soft tissue
fixation.2,9,24
Speer and Warren31
described 4 criteria for bioabsorbable
implants in the shoulder: (1) the bioabsorbable implant must
have adequate initial fixation strength to coapt the soft tis-
sues to bone, (2) the implant’s bioabsorption profile must
enable it to retain satisfactory strength while the healing tis-
sues are regaining mechanical integrity, (3) the implant
must not bioabsorb too slowly or it will behave like its metal
counterpart with breakage and migration, and (4) the
implant must be made of materials that are completely
safe: no toxicity, antigenicity, pyrogenicity, or carcinogeni-
city. One might consider adding a fifth criterion to Speer
and Warren’s criteria31
for bioabsorbable implants in the
shoulder: bioabsorbable implant replacement by bone.
Biocomposite anchors, which combine biodegradable co-
polymer and poly(lactic-co-glycolic acid) (PLGA) osteoconduc-
tive bioceramics such as b-tricalcium phosphate (TCP) or
hydroxyapatite, were developed to help bridge the gap
between adequate initial fixation and eventual bone replace-
ment without osteolysis or synovitis.21
We sought to investi-
gate one such biocomposite, Biocryl Rapide (BR) (DePuy
Mitek, Raynham, Massachusetts), which is used in 2 different
labral suture anchors, the Lupine BR anchor (DePuy Mitek)
and the Bioknotless BR anchor (DePuy Mitek).
We hypothesized that patients undergoing glenoid labral
repair with these new biocomposite anchors would demon-
strate radiographic evidence of labral healing with progres-
sive anchor resorption and replacement by bone while
maintaining good clinical outcomes based on subjective out-
come scores and minimizing adverse reactions such as
intra-articular inflammatory response and cyst formation.
MATERIALS AND METHODS
This longitudinal case series involving patients who had
undergone shoulder arthroscopy and labral repair by 3
senior surgeons at our academic sports medicine center
was approved by our institutional review board. Inclusion
criteria were patients between 18 and 60 years of age
who underwent arthroscopic capsulolabral repair using
anchors composed of this particular biocomposite and
who were willing to undergo postoperative MRI and CT
at the established time points. Anchors used included the
Lupine BR anchor and the Bioknotless BR anchor. Both
anchors were included in this study, focusing on anchor
bioabsorption and bioreplacement, because they have iden-
tical body types by both geometry and composition. They
both have suture loops and differ only in that one is knot-
less and the other allows suture tying of a suture attached
to the suture loop. Biocryl Rapide is made of 70% PLGA
and 30% TCP.
Exclusion criteria were previous shoulder surgery; chronic
or acute medical illness that may interfere with healing, such
as a neurological, collagenous, or circulatory disease; existing
pathological conditions or degenerative joint diseases includ-
ing rheumatoid arthritis, extensive osteoarthritis, or other
progressive collagen or bone conditions that would hinder
adequate anatomic visualization and prevent secure tissue
fixation; and women who were pregnant or lactating or
planned to become pregnant during the study. Sixteen
patients and 47 anchors were available for follow-up at 24
months. Enrollment and follow-up flow are shown in Figure 1.
Computed tomography was performed without intrave-
nous or intra-articular contrast at 12 6 1 months and 24 6
1 months utilizing multidetector CT scanners from GE
Medical Systems (Lightspeed 16, Lightspeed Pro 32, or
Lightspeed VCT 64, Little Chalfont, United Kingdom).
Patients were scanned with a 0.625-mm detector configu-
ration, with bone and soft tissue algorithms utilizing
140 kV and automatic mAs. Images were constructed pro-
spectively at 0.625 mm with 50% slice overlap. These direct
axial images were reviewed together with multiplanar
reformats at the radiologist’s workstation.
Magnetic resonance imaging was performed without
intravenous or intra-articular contrast at 6 6 1 months
and 12 6 1 months utilizing a 1.5-T scanner from Siemens
Medical Systems (Avanto, Erlangen, Germany). A dedi-
cated shoulder coil was utilized. Scan protocol included
axial, oblique coronal, and oblique sagittal conventional
spin echo T1 (repetition time [TR]/echo time [TE] =
625/16 msec); axial and oblique sagittal turbo inversion
recovery (TR/TE = 6350/25; inversion time = 160 msec);
and oblique coronal dual echo fast spin echo T2 and proton
density with fat saturation (TR/TE = 4130/102 and 4130/37).
A matrix of 512 3 512 was utilized.
Radiographic outcomes were based on postoperative
MRI scans obtained at 6 and 12 months to identify any
potential reactions to the implants and CT scans obtained
12 month MRI n=3
12 month CT scans n=3
6 month MRI scans: n=19
Initial Enrollment
12 month MRI scans: n=17
12 month CT scans: n=17
Lost to
follow-up
n=2
Supplemental Enrollment
Lost to
follow-up
n=4
24 month CT scans: n=13
24 month Evaluations: n=13
Lost to
follow-up
n=0
24 month CT scans: n=3
24 month Evaluations: n=3
Total 6 month MRI scans: N=19
Total 12 month MRI scans: N=20
Total 12 month CT scans: N=20
Total 24 month CT scans: N=16
Total 24 month Evaluations: N=16
Serial assessments:
Total 6+12+24 month scans on same patients: N=13
Total 6+12 month MRI: N=17
Total 12+24 month CT scans: N=16
Figure 1. CONSORT flowchart for study enrollment and
follow-up.
Vol. 40, No. 6, 2012 Biocomposite Anchors in Arthroscopic Shoulder Labral Repairs 1393

4. at 12 and 24 months to determine anchor resorption and
bone ingrowth. An independent and fellowship-trained
musculoskeletal radiologist with over 10 years of experi-
ence (C.M.G.) reviewed all scans. Nonarthrogram MRI
scans were examined for adequacy and integrity of labral
repair and to assess in vivo biological safety based on the
presence or absence of undesirable host responses includ-
ing joint effusion, synovitis, solid mass from foreign body
reaction, lymphadenopathy, edema, and/or cyst formation.
The CT scans were examined to determine anchor resorp-
tion, replacement by bone or soft tissue density, intraoss-
eous cyst formation, and anchor tunnel widening.
Data Analysis
A picture archiving and communication system (PACS) was
used for digital image review. Digital tools imbedded in our
PACS (version 10.2, Carestream, Rochester, New York)
were used to standardize measurements across patients
and scan dates. Specifically, we measured tunnel diameter,
cyst size (if present), and density of the tissue replacing the
anchors to support the determination of bone versus soft
tissue bioreplacement at each time point. Because of the
small size and complicated geometry of the anchors, precise
assessment or quantification of percentage of anchor resorp-
tion was not possible. The radiologist estimated the percent-
age of resorption by comparing the anchors across
examinations over 24 months and by referencing the
appearance of new (not yet absorbed) anchors. A similar
process was used for estimating quantity of anchor replace-
ment by bone or soft tissue density. Precise measurements
were again not possible, so the radiologist estimated the por-
tion of the anchor replaced. Although this technique of esti-
mation has limitations, it was considered satisfactory to
capture a general trend of progressive resorption.
To determine whether the tissue replacing the anchor was
bone or soft tissue, a semiquantitative or partially subjective
approach was employed. For the tissue replacing the anchor
to be considered as bone, it required 2 criteria to be met:
(1) the radiologist’s subjective interpretation of the density
and texture of the tissue needed to be consistent with bone,
and (2) the tissue density as objectively measured must be
similar to that of bone in Hounsfield units (HU). The use of
HU measurements to confirm bone replacement of bioabsorb-
able implants has been reported previously with interference
screws.7,8
The HU scale is based on linear attenuation coeffi-
cients and is a scale of relative radiodensity where, by defini-
tion, the radiodensity of distilled water under standard
pressure and temperature is 0 HU and the radiodensity of
air is –1000 HU. Typical HU measurements from the human
body are as follows: –120 for fat, 0 to 10 for simple fluid, 40
for muscle, over 150 for light trabecular bone, and 1000 for
cortical bone. The HU measurements were taken from the
tissue replacing the absorbed anchors, and these measure-
ments were considered additional support for the subjective
determination of whether a resorbed anchor had been
replaced by bone or soft tissue.
The MRI scans were reviewed for labral repair integrity,
with an intact repair defined as the experienced musculoskel-
etal radiologist’s subjective interpretation along with objective
criteria of labral tissue found in situ without linear increased
signal undercutting or coursing through it. Repair failure or
labral retear was defined as displaced labral tissue or in
situ labral tissue with linear high signal undercutting or
coursing through it. Indeterminate labrum was defined as
not being able to fit the definitions of intact or torn mentioned
above. Reasons for lack of clarity included patient motion and
postoperative related artifacts such as subtle signal changes
that were ambiguous for subtle retear versus normal postop-
erative changes of repaired tear. The authors emphasize,
however, that the primary imaging objective was focused on
the biological behavior of the implant with regard to biore-
sorption, host response, and bioreplacement.
Tunnel widening was defined as 3 mm or greater in
maximal cross-sectional diameter obtained orthogonal to
the long axis of the tunnel. This definition was based on
the geometry or size of the anchors and the pilot hole.
The anchors were 3 mm wide over much of their length
but varied from 2 mm (at deep tip) to 4 mm (near joint sur-
face) in width. The drill holes had a diameter of 2.9 mm for
both types of BR anchors as they had identical body types.
The radiologist was not specifically blinded to the time
interval between surgery and scanning. The studies were
read in 4 batches at different time points in the study,
and generally, the 6- and 12-month scans appeared in
the first and second groups, and 24-month scans appeared
in the third and fourth groups.
Follow-up clinical data included history and physical
examination as well as patient demographics. Subjective
outcome measures were recorded at 24 months postopera-
tively, which included Tegner activity scale, Simple Shoul-
der Test, American Shoulder and Elbow Surgeons (ASES),
and University of California, Los Angeles (UCLA) shoulder
scores.
Statistical Analyses
Percentage of resorption and percentage of replacement by
bone were compared among the 3 anchor locations (ante-
rior, posterior, and superior) at the 12- and 24-month
time points with a univariate analysis of variance
(ANOVA). Tukey least significant difference was used for
post hoc analyses. A test was considered statistically sig-
nificant if the P value was .05 or less. The data involving
the percentage of anchor resorption, percentage of anchor
replaced by bone, and the comparisons of these variables
between anchors of different locations were not normally
distributed. Kruskal-Wallis nonparametric analysis was
also completed and reported along with median values.
Both parametric and nonparametric analyses including
mean and median values were reported as the parametric
analysis and mean values may be easier to interpret both
scientifically and clinically.
RESULTS
A total of 22 patients were enrolled in our study, with 16
patients completing the clinical assessment, subjective out-
comes, and follow-up imaging at 24 months. Enrollment
1394 Milewski et al The American Journal of Sports Medicine

5. and follow-up flow are delineated in Figure 1. There was
73% patient follow-up at 24 months, with 6 patients having
withdrawn from the study or lost to follow-up. Three
patients were enrolled in a period of additional enrollment
after 2 patients were lost during early enrollment after
their 6-month follow-up scans. Four patients completed
MRI and CT scans at 12 months but were lost to follow-
up before 24 months. There were 11 male and 5 female
patients in our cohort, with a mean age of 35 years and
an age range of 18 to 60 years. A total of 48 BR anchors,
all composed of the same material, were utilized in these
16 patients’ labral repairs. One of these anchors could
not be evaluated on 24-month CT as it was obscured by
revision surgery that occurred between the 12- and 24-
month scans, leaving 47 anchors for 24-month analysis
by imaging. A total of 32 Bioknotless BR anchors and 16
Lupine BR anchors were utilized with an average of 3.0
suture anchors used per patient. Anchor type and number
utilized per patient were based on the surgeon’s prefer-
ence. Of the 47 anchors available for 24-month analysis,
25 anchors were placed for anteroinferior labral repairs
(19 Bioknotless BR and 6 Lupine BR anchors), 15 anchors
were placed for superior labral repairs (8 Bioknotless BR
and 7 Lupine BR anchors), and 7 anchors were placed for
posterior labral repairs (4 Bioknotless BR and 3 Lupine
BR anchors).
Thirteen of 16 patients (81%) underwent their MRI
examinations at 6 months, and 15 of 16 patients (94%)
completed their MRI examinations at 12 months. All 16
patients completed their CT scans at 12 months and 24
months along with their clinical examinations at 24
months.
The MRI scans performed at 12 months confirmed all 15
patients had no signs of effusion, synovitis, lymphadenopa-
thy, intra-articular masses, or soft tissue edema (Figure 2).
When assessed for labral integrity, 11 of 15 patients’ labral
repairs were deemed intact at the 12-month MRI examina-
tion. Three of the 15 labral repairs were deemed ‘‘indetermi-
nate’’ at the 12-month MRI examination. One of the 15
labral repairs was deemed ‘‘indeterminate’’ at 6 months
and was shown subsequently to be retorn intraoperatively
at 8 months.
The CT scan assessments at 12 and 24 months were used
to assess resorption of BR anchor material (Figures 3 and 4).
At 12-month follow-up, an estimated average of 68% 6 25%
resorption of BR anchor material was observed across the 47
anchors in 16 patients (median value of 70% resorption at
12 months). At 24-month follow-up, an estimated average
of 98% 6 10% resorption of BR anchor material was
observed, with 45 of 47 anchors having 100% resorption
(median value of 100% resorption at 24 months).
In terms of bone ingrowth, an estimated average of 9% of
total BR anchor material across all anchors was replaced by
bone at 12-month follow-up (median value of 0%) as deter-
mined from CT (mean, 423 HU; range, 250-800 HU). Eleven
of the 47 BR anchors (23%) exhibited replacement by bone,
and within this group of 11 anchors, an estimated average
of 39% 6 20% of BR anchor material was replaced by
bone. At 24 months, total bone replacement of anchors
had increased to an estimated average of 20% of the BR
Figure 2. Six-month postoperative axial inversion recovery magnetic resonance imaging (MRI) scan (A) and axial T1 MRI scan
(B) of a posterior labral repair utilizing a Lupine BR anchor (DePuy Mitek, Raynham, Massachusetts). Linear signal changes
are seen at the site of the anchor (long, thin white arrows) without adjacent bone or soft tissue changes. Twelve-month post-
operative axial inversion recovery MRI scan (C) and axial T1 MRI scan (D) show the anchor and tunnel (short, thick white arrows)
to be less perceptible over time. Axial and oblique sagittal reformat computed tomography images at 12 months (long, thin black
arrows) and 24 months (short, thick black arrows) postoperatively (E-H) show progressive bone replacement and less obvious
tunnel visualization in the midposterior labrum.
Vol. 40, No. 6, 2012 Biocomposite Anchors in Arthroscopic Shoulder Labral Repairs 1395

6. anchor material (median value of 0%). Twenty-two of the 47
BR anchors (47%) exhibited some replacement by bone at 24
months, and within this group of 22 anchors, bone replace-
ment averaged 42% 6 26%.
At 12-month CT scan evaluation, an estimated 56% of
BR anchor material in the 48 anchors was replaced by
soft tissue density (mean, 65 HU; range, 25-120 HU), and
this increased to 78% of BR anchor material in the 47
anchors at 24-month follow-up. The progression of percent-
age of anchor resorption and percentage of bone replace-
ment for anteriorly, posteriorly, and superiorly placed
anchors from 12-month and 24-month CT scan evaluations
are shown in Figure 5.
Our primary imaging focus was on overall anchor behav-
ior, and thus, we did not specifically power the study to per-
form subgroup analysis by anchor location or patient age;
however, we did perform such analyses to contribute to
our observations. Percentage of resorption was significantly
different among anchor locations at 12 months but not at 24
months after implantation (Figure 6). Specifically, at 12
months, the posterior anchors had a significantly higher
percentage of resorption than the superior (P = .03) and
anterior (P = .01) anchors. The percentage of resorption
was not different between the anterior and superior anchors
(P = .72). Percentage of replacement by bone was also signif-
icantly different among the anchor locations at both 12
months and 24 months after implantation (Figure 6). The
average percentage of replacement by bone was highest
for the superior anchors at 12 and 24 months. Percentage
of replacement by bone was significantly higher in the supe-
rior anchors compared with the anterior anchors at 12
months (P = .002) and 24 months (P = .01) after implanta-
tion but not significantly higher than the posterior anchors.
Kruskal-Wallis nonparametric analysis revealed a signifi-
cantly greater percentage of resorption of posterior anchors
at 12 months compared with anterior anchors (P = .04) and
a significantly greater percentage of replacement by bone of
superior anchors at 12 months compared with anterior
anchors (P = .01). Kruskal-Wallis nonparametric analysis
did not reveal significant differences in percentage of anchor
resorption and percentage of replacement by bone between
anchor locations at 24 months (P = .41 and P = .07, respec-
tively). Correlations were done to compare age and percent-
age of resorption and percentage of replacement by bone. At
12 months, age was related to percentage of resorption (r =
.30, P = .04) and percentage of replacement by bone (r =
–.04, P = .005), but these correlations were not significant
at 24 months (percentage of resorption: r = .15, P = .31; per-
centage of replacement by bone: r = .19, P = .19).
Bone cysts that communicated with the BR anchor tun-
nel were associated with 3 of the 47 BR anchors (6%). All 3
cysts were seen in anchors used for superior labral repair
(2 Bioknotless BR and 1 Lupine BR anchors). One was
a small cyst (5 mm in diameter) at the deep aspect of
the tunnel that developed between 12- and 24-month
follow-up CT scans even though the associated tunnel
decreased in size during that time period (Figure 4). The
second cyst was a 5-mm cyst present at 12-month follow-
up that enlarged to 8 mm at 24-month follow-up. This
Figure 3. Twelve- and 24-month postoperative axial com-
puted tomography images (A, B) of a superior labral repair
utilizing 2 Bioknotless BR anchors (DePuy Mitek, Raynham,
Massachusetts). Both anchor sites show interval anchor
resorption, tunnel width narrowing, and replacement by
bone between 12 months (black arrows) and 24 months
(white arrows).
Figure 4. Twelve-month postoperative axial (A) and oblique
sagittal reformat (B) computed tomography (CT) images of
an anteroinferior labral repair utilizing Bioknotless BR anchors
(DePuy Mitek, Raynham, Massachusetts). An enlarged cystic
cavity in the anterior glenoid is visualized surrounding
a vaguely linear calcific density thought to reflect partially
resorbed anchor material (black arrows). The oblique sagittal
reformat CT image (B) also shows a portion of a smaller tunnel
from another anchor (black arrowhead). Twenty-four-month
postoperative axial (C) and oblique sagittal reformat (D) CT
images show an interval decrease in the size of the cavity
(white arrows) with complete resorption of the anchor and par-
tial bone replacement. The oblique sagittal reformat image
(D) shows a more modest interval decrease in size of the tun-
nel from the other anchor (white arrowhead).
1396 Milewski et al The American Journal of Sports Medicine

7. patient also had some degree of glenohumeral osteoarthri-
tis (although still within inclusion criteria), which was
a confounding factor. The third cyst was 4 mm in size
and located at the deep aspect of the tunnel. It was present
on the 12-month CT scan, but it remained stable at 24-
month follow-up.
Tunnel widening, as defined as maximal tunnel width
greater than 3.0 mm, was associated with 26 of the 47
BR anchors (55%). The average diameter of the widened
tunnels was 4.4 mm at 12 months (range, 3.25-6.0 mm),
and this decreased to an average of 3.9 mm at 24 months
(range, 3.0-5.0 mm). Widening affected 2 of the 15 superior
labral BR anchors (13%) (1 Bioknotless BR and 1 Lupine
BR anchor). Widening affected 4 of the 7 posterior labral
BR anchors (57%) (1 Bioknotless BR and 3 Lupine BR
anchors). Widening affected 21 of the 25 anteroinferior lab-
ral BR anchors (84%) (14 Bioknotless BR and 7 Lupine BR
anchors).
Subjective outcome and clinical assessment data were
collected on 16 patients at a minimum of 24-month follow-
up. Clinical data were not available on the 6 patients lost
to follow-up because this was collected only at 24-month
follow-up. All but one patient were satisfied with their out-
come at 24 months (15/16 patients, 94%). One patient
sustained a repeat dislocation event at 8 months postopera-
tively and required a revision surgery. This patient was sat-
isfied with their outcome at most recent follow-up. The
ASES scores at most recent follow-up averaged 88 6 20.
The UCLA shoulder scores at most recent follow-up aver-
aged 30 6 6.7. Visual analog scale scores at most recent
follow-up averaged 1.5 6 1.8. Simple Shoulder Test scores
at most recent follow-up averaged 10 6 3.3 of a possible
12. Tegner activity scale scores preoperatively averaged
6.4 6 2.5 and postoperatively averaged 5.0 6 2.8.
Our primary focus was on the patients who completed
the 24-month clinical and imaging follow-up. However,
we did evaluate the 6- and 12-month imaging of those
patients who were lost to follow-up. For the sake of com-
plete reporting, we are providing a brief summary of data
from this group. These data are presented separately
from the data of the patients who completed the study
because patients dropped out at varying time points.
Figure 5. Top row graphs showing percentage of anchor resorption between 12 and 24 months (12-24M % Resorption) by com-
puted tomography (CT) scan evaluations for each superior, posterior, and anterior anchor. Bottom row graphs showing percent-
age of anchor replacement by bone between 12 and 24 months (12-24M % Bone) by CT scan evaluations for each superior,
posterior, and anterior anchor.
Vol. 40, No. 6, 2012 Biocomposite Anchors in Arthroscopic Shoulder Labral Repairs 1397

8. Overall, this small group demonstrated similar results to
those who completed the study. The 6 patients lost to fol-
low-up had 19 anchors placed. One of these 6 patients
could not be evaluated by MRI because of artifact from
a nearby metal foreign body. Fifteen anchors in 5 patients
were evaluated by MRI at 6 months, and 10 anchors in 3
patients were evaluated by MRI at 12 months. The find-
ings from the studies were negative for joint effusion,
edema, lymphadenopathy, soft tissue mass, or fluid collec-
tion. Only one anchor of 15 (7%) was associated with cyst
formation, and this 4-mm intraosseous cyst was stable
between 6 and 12 months. The repairs appeared intact in
3 of 5 patients. The integrity of repair was uncertain in 2
patients, although there was no overt evidence of failure
or retear in this group. Fourteen anchors in 4 patients
were evaluated by CT at 12 months. Six of 14 anchors
(43%) showed no evidence of tunnel widening, while 8 of
14 anchors (57%) were associated with tunnel widening
(mean, 4.3 mm; range, 3.6-4.6 mm). At 12-month CT, an
overall estimated 84% of anchor material was resorbed
and replaced by bone (9% of anchor material) and soft tis-
sue (75% of anchor material).
DISCUSSION
Bioabsorbable suture anchors are rapidly evolving and
supplanting metallic anchors in arthroscopic shoulder
surgery. These anchors offer some distinct advantages
from their metallic counterparts, particularly in cases of
failed tissue repairs. During revision cases, the need to
remove permanent implants is also avoided with biode-
gradable implants because they can often be drilled out
or through.
Bioabsorbable anchors also improve the quality of post-
operative imaging relative to metallic anchors. Bioabsorb-
able anchors cause less beam-hardening artifact on CT
scans, and more importantly, they minimize distortion on
postoperative MRI, which is often the study of choice to
evaluate the status of the repair.
In spite of these advantages, earlier generation bioab-
sorbable anchors have generated causes for concern. Multi-
ple different types and combinations of polymers have been
developed and utilized for anchors including polyglycolic
acid (PGA), poly-L-lactic acid (PLLA), and poly-D-L-lactic
acid copolymer polyglycolic acid (PDLLA-co-PGA). Early
bioabsorbable anchors and fixation devices such as the
Suretac (Smith & Nephew, Andover, Massachusetts) were
made of a synthetic copolymer of 67.5% polyglyconic acid
and 32.5% trimethylene carbonate.31
However, the degrada-
tion time reported with the PGA anchors was only 3 to 4
months, and they were associated with early loss of fixation,
osteolysis, loose body formation, and glenohumeral synovi-
tis.10,31,32
The PLLA anchors were developed to have a lon-
ger degradation time, between 10 and 30 months, but
concerns were raised as to whether this was an excessively
Figure 6. A, Percentage of anchor resorption by anchor location (superior, posterior, and anterior). Percentage of resorption was
highest in the posterior anchors at 12 months after implantation. B, Percentage of replacement by bone was highest for the supe-
rior anchors at 12 and 24 months after implantation.
1398 Milewski et al The American Journal of Sports Medicine

9. long degradation time, which may result in similar prob-
lems as metallic anchors with chondral damage from loosen-
ing as well as the fact that the anchors might not be
replaced by bone.4,6,22,23,36
The PLLA tack anchors have
been shown to have more radiographic evidence of persis-
tent drill holes at 7-year follow-up than PGA tack anchors.14
Also, there have been concerns raised over intra-articular
inflammatory response and cyst formation with PLLA
anchors.21,22,29,31
In one study, 55% of patients who had
anterior labral repairs with 3 polylactic acid (PLA) anchors
(Panalok, Mitek Ethicon, Somerville, New Jersey) showed
anchor tunnel enlargement greater than the mean plus
one standard deviation.34
The literature has also documented some unique com-
plications associated with use of bioabsorbable anchors.
Several case reports have identified a hyperinflammatory
response to bioabsorbable anchors, leading to synovitis,
bone osteolysis, cartilage damage, and adverse clinical out-
comes.#
These complications have been associated with
both PGA and PLLA implants alike, contributing to the
impetus to develop better implant materials.
Biocomposite anchors are composed of newer generation
materials with potential for improved performance over
earlier generation anchors. Biocomposites include a mix-
ture of biodegradable material, such as PLGA or PLA,
and osteoconductive bioceramics, such as TCP. Biocryl
Rapide (DePuy Mitek) is a composite between fast-
absorbing PLGA (70%) and osteoconductive TCP (30%).
The proposed advantages of the new material include
more timely and reliable resorption of the anchor with sub-
sequent replacement by bone at the site of the anchor.
Anchor resorption with bone replacement was hypothe-
sized to occur by 24 months. While cadaveric experiments
have demonstrated similar load-to-failure properties
between biodegradable anchors and more traditional
anchor materials, concern is still raised as to whether sim-
ilar results can be found in vivo.5
While suture anchors
made of newer generation biocomposite materials such as
Biocryl Rapide have found increasing utility in shoulder
arthroscopy, concern remains about the long-term effects
these materials have in the glenohumeral joint including
the effects that material resorption may have on repair
integrity and cyst formation and whether the material or
its resorption may induce an inflammatory response
within the glenohumeral joint that could lead to synovitis.
Also, there are little data in the literature regarding the
potential for bone replacement or remodeling as the bio-
composite material is resorbed.
We believe this is the first clinical study with 24-month
follow-up that radiographically demonstrates the extent of
bone replacement of biocomposite labral anchors. Barber
and Dockery7
have previously shown bone replacement of
TCP PLLA interference screws. On 24-month follow-up
with CT scans, our anchors appear to be largely resorbed
with some progressive replacement by bone. The replace-
ment of the rest of the anchor material by tissue not consti-
tuting bone was called ‘‘soft tissue density’’ because it
matched the density of noncalcified, nonfatty soft tissue
both subjectively and by HU density measurements but
was otherwise nonspecific. Without tissue samples, the
authors do not know whether this ‘‘soft tissue density’’
material represents immature osteoid, giant cell reaction,
fibrous tissue, or granulation tissue. Further long-term
studies will be needed to determine whether this material
continues to ossify.
Tunnel widening was seen in 55% of the anchors, but
this actually decreased between the 12- and 24-month
follow-up CT scans. The tunnel widening was not associ-
ated with clinical failures in this group and, as mentioned,
tunnel widening decreased as the anchors were resorbed
and partially replaced by bone. Tunnel widening is likely
multifactorial and may relate to implant material, implant
geometry and biomechanics, surgical technique, and gle-
noid location. The anchors used in this study were com-
posed of Biocryl Rapide but were also of a specific design
and geometry. Both anchors (Lupine BR anchor [DePuy
Mitek] and Bioknotless BR anchor [DePuy Mitek]) used
in this study have similar anchor body geometry, with
the Lupine BR anchor having a suture attached to its
suture loop for tying. These anchors can be described as
a toggle type of anchor and are triangular in shape, relying
in part on subcortical fixation with potential for space
around the distal aspect of the anchor within the drill
hole. We hypothesize that micromotion around the anchor
could occur during shoulder motion and result in pumping
of joint fluid in and around the anchor. Thus, anchor
design may also contribute to tunnel widening and cyst for-
mation. Changes in subsequent anchor designs and geom-
etry, such as with a cylindrical anchor that completely fills
the bone hole, may address these concerns. Tunnel widen-
ing was seen more in anteroinferior and posterior glenoid
anchor locations (84% and 57%, respectively) but was
only seen in 13% of the superior labral anchors. Identical
anchors examined at identical time points, while only dif-
fering in anchor position and having different widening
patterns, would support the idea that tunnel widening is
likely related to the forces across these anchors in situ at
different areas of the labrum.
Cyst formation reported with earlier generation bioab-
sorbable anchors has generated concern. We documented
3 cysts in our study or 6% of all anchors used. All 3 cysts
were seen with anchors used for superior labral repairs
(2 Bioknotless BR anchors and 1 Lupine BR anchor).
None of these 3 cysts were associated with anchor failure,
but rather they were associated with excellent clinical out-
comes. While cyst formation with these new biocomposite
anchors remains a concern, there have been few investiga-
tional studies documenting the clinical results of gleno-
humeral surgery utilizing this new generation of
material.7
Previous reports of cyst formation with PGA
and PLLA were usually associated with bioabsorbable
screws used for interference screw fixation in anterior cru-
ciate ligament reconstruction.18
Given the paucity of data
within the literature on biocomposite anchors, concern
therefore remains about the long-term performance of
these materials in the glenohumeral joint including the
effects of material resorption on repair integrity and cyst
#
References 1, 3, 15, 17, 20, 23, 25, 28, 33-35.
Vol. 40, No. 6, 2012 Biocomposite Anchors in Arthroscopic Shoulder Labral Repairs 1399

10. formation and whether the material or its resorption may
induce an inflammatory response within the glenohumeral
joint.
The strengths of this prospective study include the min-
imum 24-month follow-up including both CT and MRI
evaluations. In addition to the imaging findings, the BR
anchors were associated with good clinical outcomes, as
shown by ASES, UCLA shoulder, and Simple Shoulder
Test scores, with only one unsatisfied patient and one
repeat dislocation. We also had a broad age range of
patients and anchor location. We believe that a diverse
patient population including age range and anchor location
better characterizes the overall resorption profile of the
implant rather than a narrow patient population and loca-
tion. This allows us to make more broad and generalized
conclusions.
Weaknesses of this study include the lack of a control
group by which to compare these anchors directly. A con-
trol group would have required the use of another type of
anchor, which would have likely meant differences in
both anchor composition along with anchor geometry and
suture type. Subjective data were obtained in follow-up
but were not obtained preoperatively, which can limit the
conclusions drawn from the study in terms of subjective
improvement. We were not able to precisely quantify vol-
ume of anchor resorption or replacement because of small
anchor size and complex geometry, so we sought estima-
tions, which introduced some intrinsic bias. In addition,
we had a single fellowship-trained musculoskeletal radiol-
ogist read all of the scans, but he was not blinded to the
time points. While a single reader eliminates some vari-
ability, it does introduce potential bias especially when
he was not blinded to the time points of follow-up. While
we used a fairly wide age range of patients, we found
that age was not correlated at 24 months with anchor
resorption or bone replacement.
We had a 9% lost to follow-up rate at 12 months and
a 27% lost to follow-up rate at 24 months. The cause behind
these rates is likely multifactorial. This study was carried
out at an academic institution that is a large tertiary refer-
ral center attracting patients from several hours away.
Because of logistical issues, many of these patients were
unable to return for each follow-up time point. In addition,
many of these represent mobile patients, such as univer-
sity students, who were no longer in the area at the time
of follow-up. Lastly, during our study, there was heavy
public and media scrutiny on radiation risk associated
with CT, which may have affected patients’ willingness
to return for CT scans at 12 and 24 months after surgery.
In conclusion, this study documents good radiographic
and subjective outcomes following labral repairs using
a biocomposite anchor. We believe this study is the first
to document bone replacement of absorbed anchor material
and the first to determine the progression of absorption of
new-generation biocomposite anchors in humans. Compli-
cations related to biocomposite anchor resorption, includ-
ing cyst formation and tunnel widening, were mild and
not clinically important in this study. Cyst formation was
associated with only a small percentage of anchors, and
the cysts were small in size. Tunnel widening was common,
although mild, and improved during the time course of
radiographic follow-up as the anchors were resorbed and
partially replaced by bone. There was no evidence of syno-
vitis or intra-articular mass formation with absorption of
these anchors. Good clinical outcomes can be expected
using these new biocomposite faster absorbing suture
anchors. The residual soft tissue density at the anchor
sites at 2 years may contain nonmineralized osteoid
matrix, so there is theoretical potential for further bone
formation in time. Longer term CT follow-up will be
needed to examine this potential for further progression
of bone replacement of the resorbed anchors beyond 2
years.
ACKNOWLEDGMENT
The authors thank Christopher M. Kuenze, MA, ATC, for
his assistance in patient recruitment and data collection.
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