Abstract
Background: Following repairs of large-to-massive tears of the
rotator cuff, the rates of tendon retears are high and often involve tissue
deficiency. Animal studies of the Restore Orthobiologic Implant, a
collagen-based material derived from the small intestine mucosa of pigs, have
indicated that it might be used to help overcome such problems. We carried out
a study to determine whether patients who received this xenograft to augment a
rotator cuff repair exhibited greater shoulder strength, shoulder function,
and/or resistance to retearing.
Methods: We compared data from a group of patients who had undergone
conventional rotator cuff repair with xenograft augmentation (the xenograft
group) with data from a group in whom a repair had been done by the same
surgeon without augmentation (the controls). The groups were matched for
gender, mean age, and mean size of the rotator cuff tear. All subjects
completed a pain and function questionnaire and were given a systematic
clinical shoulder examination preoperatively and at three, six, and
twenty-four months postoperatively. The twenty-four-month visit included
magnetic resonance imaging to determine whether a retear had occurred.
Results: Four patients who had received a xenograft had a severe
postoperative reaction requiring surgical treatment. At two years after the
surgery, six of the ten tendons repaired with a xenograft and seven of the
twelve control tendons had retorn, as documented by magnetic resonance
imaging. The patients with a xenograft had significantly less lift-off
strength, as measured with a dynamometer, and significantly less strength in
internal rotation and adduction than the controls at two years after the
surgery (all p < 0.05). Also, the xenograft group had significantly more
impingement in external rotation, a slower rate of resolution of pain during
activities, more difficulty with hand-behind-the-back activities, and less
sports participation (all p < 0.05).
Conclusions: Two years after surgical repair of a large rotator cuff
defect supplemented with a xenograft, patients had several persisting deficits
and no recognizable benefit as compared with the results in a control group.
In view of these findings, together with the unsatisfactorily high proportion
of patients with a severe inflammatory reaction to the xenograft, we do not
recommend use of the Restore Orthobiologic Implant in its present form.
Level of Evidence: Therapeutic Level III. See
Instructions to Authors for a complete description of levels of evidence.
The retear rate after repairs of rotator cuff tendons is high, and there is
often a tissue deficiency, particularly when larger tears are involved.
Tendons with a repaired large or massive defect tear again more easily,
leading to weakness, chronic pain, severely impaired function, and an
inability to perform manual
labor1-5.
Large and massive rotator cuff defects are often more difficult to repair than
are small defects, and they are associated with a higher prevalence of
failure6.
Basic-science studies of the Restore Orthobiologic Implant (DuPuy
Orthopaedics, Warsaw, Indiana), a collagen-based material made from the small
intestine mucosa of pigs that has been approved by the United States Food and
Drug Administration, have indicated that this material may augment rotator
cuff repairs and provide new tissue when the tendon tissue is deficient. Thus,
we speculated that the addition of this product may enhance rotator cuff
repairs and reduce the rate of retears. We started a randomized controlled
trial whereby patients would be assigned to one of two groups: one treated
with a conventional repair with augmentation with the Restore Orthobiologic
Implant (the xenograft group) and one treated with a conventional repair
without the xenograft (the control group). The senior author (G.A.C.M.) used
the xenograft in nineteen open repairs of large-to-massive rotator cuff tears.
In half of these cases it was used to augment poor-quality tendon, and in the
other half it was employed to fill a remaining defect.
We abandoned the randomized controlled trial when it came to our attention
that, within two to four weeks after the surgery, four of the nineteen
patients had had a severe local inflammatory reaction that necessitated a
reoperation for irrigation and débridement of the affected rotator cuff
and removal of the
xenograft7. The
severe reaction initially appeared to be an infection, but since all
intraoperative cultures were negative it was deemed in retrospect to be an
inflammatory reaction to the xenograft.
We invited all patients who had undergone the xenograft procedure to
participate in a modified outcome study, and fifteen patients with sixteen
shoulders repaired with the xenograft consented to do so. A matched control
group comprising sixteen patients who had undergone conventional rotator cuff
repair by the same surgeon, and usually during the same period, was also
included in the study. We had previously obtained preoperative, three-month,
and six-month questionnaire responses and clinical test results from those
patients, as it is our standard practice to collect this information. All
patients in this study signed a consent form to participate in the study,
which involved returning for a follow-up examination at two years after the
surgery and undergoing a magnetic resonance imaging scan to determine whether
a retear had occurred because intact repairs yield substantially better
functional results than do
retears1,8,9.
Subjects
The protocols for the original study and this modified outcome study were
approved by the South East Sydney Human Research and Ethics Committee (Sydney,
New South Wales, Australia). Nineteen shoulders received a xenograft during
the course of the rotator cuff repair. To be included in the original study,
the patients had to have had poor-quality tendon or a large-to-massive
full-thickness tear of a tendon that could be attached to the greater
tuberosity after appropriate mobilization techniques as well as an intact
subscapularis tendon. One of the original nineteen subjects declined to
participate because the travel distance was excessive, and three others
declined for unknown reasons. Thus, fifteen subjects (with sixteen shoulders
repaired with the xenograft) consented to participate in the study.
Controls were then retrospectively matched with the xenograft group with
regard to the number of subjects, mean age, mean tear size, and gender ratio.
To the extent possible, we included controls from the original randomized
controlled trial.
The Xenograft
The Restore Orthobiologic Implant is a chemically sterilized ten-layer
implant prepared from porcine small intestine
mucosa10. The
implants were obtained in 2002 and 2003.
Instruments and Tests
The two groups were compared with regard to the data obtained
preoperatively and at the three-month, six-month, and two-year visits. Two
main instruments were used: (1) a pain and function questionnaire, which was a
modification of a validated
questionnaire11,
and (2) an examiner's form containing the results of a systematic clinical
shoulder
examination12.
Demographic information obtained from each patient included age, sex,
occupation, affected shoulder, hand dominance, date of injury, and cause of
injury (if known). The subjects were asked to rate, on a scale of 0 to 4, the
frequency of pain during activity and at night; the frequency of severe pain;
and the severity of pain during activity, during rest, and at night. Pain
scores were calculated by multiplying the frequency and severity for each type
of pain. In addition, the patients assessed the ease of carrying out overhead
activity and hand-behind-the-back activity, shoulder stiffness, shoulder
stability, previous and current activity and exercise levels, and their
overall shoulder condition.
The systematic clinical examination comprised twenty-three shoulder
tests12. During
this examination, each subject was assessed for atrophy of the supraspinatus,
infraspinatus, and deltoid muscles; tenderness of the sternoclavicular joint,
acromioclavicular joint, subacromial region, and biceps region; range of
motion of the neck and shoulder (passive forward flexion, abduction, internal
rotation, and external rotation as estimated on the basis of visual
inspection)13; the
Paxinos sign14; the
O'Brien sign15; the
drop arm sign16;
impingement during internal
rotation17; and
impingement during external
rotation18. The
strength of the
supraspinatus19 as
well as the strength in internal rotation, in external rotation, and of the
subscapularis20
were assessed with manual muscle tests on a scale of 0 to
521. At the
two-year visit, a dynamometer (modified Compact Gauge 200; RS, Smithfield, New
South Wales, Australia) was also used for all strength measurements.
Surgery
The subjects who received a xenograft and most of the controls underwent
the surgery during the nine-month period between April 2002 and January 2003.
All subjects in this study underwent diagnostic arthroscopy followed by tendon
repair performed with use of a standardized operative
technique22,23
by a single surgeon. An anterolateral deltoid-muscle-splitting approach to the
rotator cuff was used, and an anterior acromioplasty and bursectomy were then
performed. The distal edges of the torn rotator cuff tendons were
débrided, and the bone insertion site of the tendon was roughened to
create a bleeding surface. No osseous troughs were created. When possible, the
repair involved side-to-side sutures and tendon-to-bone reattachment. Mitek RC
titanium suture anchors (Mitek, Norwood, Massachusetts) containing number-2
Ethibond suture (Ethicon, Edinburgh, Scotland) were used for tendon-to-bone
reattachment. If a side-to-side repair was performed, a number-2 Ethibond
suture was passed in a simple stitch pattern. The torn rotator cuff tendons
were repaired as nearly as possible to their anatomic positions and were fixed
to the greater tuberosity with suture anchors. The number of suture anchors
used to reattach the tendon to bone was based on the size and configuration of
the tear. Suture anchors grasped the tendons, with the suture material being
passed in a horizontal mattress-stitch configuration.
In the procedures that included a xenograft, sutures were placed around the
repair after the conventional rotator cuff repair was completed. The sterile
xenograft was placed over the top of the rotator cuff repair as an
augmentation patch, in accordance with the manufacturer's instructions, and
was trimmed to the appropriate size. The xenograft was secured to the
anterior, medial, and posterior portions of the defective tendon by placing
four to twelve number-2 Ethibond sutures in native tendon and then passing
them through the xenograft in a horizontal mattress configuration. When all of
the sutures were in place, they were tied down. The xenograft was secured
laterally to bone with a single row of two or three suture anchors. The
muscle, subcutaneous tissue, and skin layers were closed with sutures, with
care taken to reattach the deltoid muscle and the coracoclavicular ligament to
their normal anatomic positions. All patients received three doses of
intravenous antibiotics (cefazolin routinely but clindamycin or vancomycin if
the patient had an allergy to penicillin or cephalosporin) immediately before
and one hour and four hours after the procedure.
Intraoperative data that were recorded included the range of motion,
shoulder stability, the number and types of suture anchors used in the repair,
and any additional findings or procedures. The size and location of the
rotator cuff tear were recorded on a specifically designed graph that allowed
measurement of the cross-sectional area of the tear in square centimeters. The
quality and mobility of the cuff tendon and the quality of the repair, as
judged by the surgeon, were recorded as excellent, good, fair, or poor.
For postoperative rehabilitation, the patients were provided with a sling
for four weeks and passive range-of-motion exercises were prescribed. After
four weeks, the patient began performing graduated active range-of-motion and
strengthening exercises.
Magnetic Resonance Imaging
A magnetic resonance imaging scan of the affected shoulder was performed at
the two-year follow-up visit. A well-experienced musculoskeletal radiologist
(J.L.) assessed whether or not a retear had occurred in the rotator cuff and
determined, from the magnetic resonance imaging scan, the minimum thickness of
the rotator cuff as measured immediately medial to the insertion of the
supraspinatus tendon into the greater tuberosity of the humerus, 1 cm
posterior to the biceps tendon. This measurement was recorded as 0 mm when the
tendon had retorn. The shoulders were examined with a 1.5-T magnetic resonance
imaging system (Signa; GE Medical Systems, Milwaukee, Wisconsin) and system
software 9.1 (slew rate, 77 T/m/sec, 33-mm T gradient amplitude), with use of
a high-resolution, non-arthrographic technique with a four-channel
phased-array shoulder coil (Medical Advances, Milwaukee, Wisconsin). Oblique
coronal proton-density and fat-suppressed T2, sagittal T2, and axial
proton-density sequencing were performed.
Statistical Analysis
Unpaired two-tailed t tests or Mann-Whitney rank-sum tests, performed with
SigmaStat software (Systat Software, Richmond, California), were used to
compare the results of the clinical shoulder tests and the scores on the pain
and function questionnaires in the control group with those in the xenograft
group. The controls were compared both with all of the patients in the
xenograft group and with all of the patients in that group except for the four
who had an inflammatory reaction. Fisher exact tests were used to evaluate the
significance of differences in the proportions of retears in the patients for
whom a readable magnetic resonance imaging scan was obtained. Results were
expressed as the mean and standard error, and significance was set at p
< 0.05.
Demographic Data
In the control and xenograft groups, respectively, the mean age was 59.6
± 3.1 years and 60.2 + 3.5 years and the mean tear size was 8.9
± 1.9 cm2 and 9.1 ± 1.6 cm2. The rotator
cuff repairs were carried out in five women and eleven men in the control
group and in five women and ten men in the xenograft group. One of the men in
the xenograft group had a xenograft repair in both shoulders, so there were
sixteen repairs in each group.
Pain and Function Questionnaire
At the two-year follow-up visit, the responses to the pain and function
questionnaires revealed that the xenograft and control groups perceived
similarly low levels of residual pain, including night pain, pain during
activity, and pain during rest. The only difference between the two groups was
that pain during activity took a mean of about three months longer to resolve
in the xenograft group than in the control group. The mean activity pain
scores at three months were 9.9 ± 1.6 points in the xenograft group and
4.0 ± 1.3 points in the control group (p < 0.01)
(Fig. 1).
At two years, the reported participation in sports activities in the
xenograft group was significantly less than that in the control group (p
< 0.01). All but two of those in the xenograft group indicated
that they refrained from participating in sports activities, whereas the
majority (eleven) of the sixteen subjects in the control group indicated that
they participated in sports either as a hobby or at the club sports level. The
patients with a xenograft also reported significantly more difficulty than the
control group with hand-behind-the-back activities (p < 0.05) at
two years after the surgery (Fig.
2).
At the time of the final follow-up, the median value for the patients'
overall satisfaction with their shoulder condition was 3.5 points (on a scale
of 0 to 4 points, with 0 points representing the least satisfaction) in the
xenograft group and 3.0 points in the control group. As these ratings were not
significantly different (p = 0.43, Mann-Whitney rank-sum test), it was
apparent that the two groups were equally satisfied with the outcomes of the
rotator cuff repair. There was a significant inverse correlation between a
retear and overall satisfaction with the shoulder condition in the control
group (r = — 0.588, p > 0.05) but not in the
xenograft group.
Clinical Shoulder Examination
With the numbers studied, no clinical test result obtained before the
surgery differed significantly between the two groups of patients. At two
years postoperatively, the ranges of forward flexion, internal rotation,
external rotation, and abduction remained similar between the xenograft group
and the control group. The strength in external rotation also did not differ
significantly between the groups (67 ± 11 N in the controls and 47
± 5 N in the xenograft recipients, p = 0.105), whereas the
xenograft group had significantly (36%) less strength in internal rotation
than did the control group (63 ± 6 N and 99 ± 11 N,
respectively, p < 0.01). The xenograft group also had
significantly (46%) less lift-off strength (28 ± 4 N compared with 61
± 11 N, p < 0.01) (Fig. 2,
B) and significantly (30%) less adduction strength (70
± 7 N compared with 100 ± 12 N, p < 0.05).
Supraspinatus strength was 36% lower in the xenograft group than in the
control group, but this difference was significant only at the p <
0.1 level (37 ± 7 N compared with 58 ± 9 N, p = 0.08.). Hence,
apart from strength in external rotation, the xenograft group exhibited an
almost global loss of strength compared with that of the control group. Median
scores for impingement in external rotation were significantly higher in the
xenograft group than in the control group (1.0 compared with 0.0, p < 0.05,
Mann-Whitney rank-sum test). With the numbers studied, the two groups
exhibited no significant difference in the drop arm sign, Paxinos sign, or
O'Brien sign.
Reanalysis of the data with omission of the four patients with the
inflammatory reaction to the xenograft indicated that the control group still
had significantly faster resolution of pain, greater sports participation,
significantly greater lift-off strength and strength in internal rotation, and
significantly less impingement during external rotation than did the subjects
in the remaining xenograft group (all p < 0.05).
Magnetic Resonance Imaging
At two years after the surgery, the retear rates, as determined with
magnetic resonance imaging, were comparable between the two groups (six of ten
in the xenograft group and seven of twelve in the control group [several
patients could not tolerate or did not arrange to have magnetic resonance
imaging, and one image was motion degraded]). Similarly, the mean tendon
thickness was not significantly different between the two groups, averaging
1.50 mm in the xenograft group and 1.58 mm in the control group.
The procedure for manufacturing the porcine small intestine submucosal
xenograft was originally described by Badylak et al. in
198924. The
material has been described as being a completely acellular collagenous
matrix25. In a
large number of studies, Badylak and his
collaborators25-28
and others 29
reported that sterilized porcine small intestine submucosal xenografts were
efficacious for orthopaedic, vascular, and dural repairs in dogs. However, the
xenograft does not appear to enhance rotator cuff repair in humans. We and
other research
groups30,31
have found tendon retear rates at least as high as those in patients who had
undergone repair without the xenograft.
Furthermore, several groups have reported that the tenply commercially
available xenografts marketed for human musculoskeletal repair can result in
an inflammatory reaction following a substantial proportion (~20%) of
rotator cuff repairs, probably as a result of an immune reaction to the
composition and/or structure of the
graft7,30,32,33.
One of these
groups32 also
implanted the xenograft material in the subcutaneous tissue of mice and in
rotator cuff tendons of rabbits, where it produced an obvious inflammatory
response involving lymphocytic infiltration and fibrosis. Surprisingly, that
group's histological examination revealed that the xenograft material was not
a cell-free collagenous matrix as reported in the literature but contained
multiple layers of cells with porcine
DNA32. Another
group, using a rabbit model, reported that rotator cuff repair with the
xenograft resulted in significantly more fatty infiltration near the
muscle-tendon junction than was found after rotator cuff repairs without a
xenograft (p <
0.05)34. Research
groups have also reported that the xenograft material is immunopositive for
transforming growth factor-ß
(TGF-ß)35,36
and is therefore biologically active. The authors of a clinical study of the
use of the xenograft for a nonorthopaedic
repair37 likewise
reported postoperative complications related to the xenograft that were
sufficient to require surgical intervention and to result in discontinuation
of the product's use. The preclinical testing of the xenograft was mainly
performed in dogs, and immunological reactions in this species were not
observed, not reported, or not considered to be problems.
In the present study of humans, we found that the xenograft failed to
augment tendon thickness or to protect rotator cuff repairs against retearing.
In another study, in which eleven patients had a repair of a large or massive
rotator cuff tear augmented with the same type of xenograft, ten had a
retear31. Moreover,
in our study the xenograft failed to improve supraspinatus strength. The
patients in the xenograft group had significantly more difficulty with
hand-behind-the-back activities than did the controls, a finding that is
consistent with their having significantly lower dynamometer-measured lift-off
strength than the control group. These patients also had significantly less
strength in internal rotation and in adduction, which persisted at the
two-year follow-up visit. In another
study31, five of
eleven patients who had undergone rotator cuff repair augmented with the
xenograft had worse scores for function postoperatively than preoperatively.
The other six patients showed no significant improvement at six to ten months
after the surgery. Thus, use of the xenograft apparently confers no
recognizable benefit for humans treated with rotator cuff repair.
Having been alerted to the possible problems with the xenograft as a result
of surgery performed by us and our affiliates, these outcome studies, and
subsequent careful review of the previous and current literature on the
subject, we no longer use the porcine small intestine submucosal xenograft or
recommend its use to others. If it is to be effective, this implant material
requires modifications to (1) overcome the apparent immunological response
that can accompany its use and (2) overcome the problem that interferes with
shoulder strength. In view of the lack of benefit in association with its
current form, we recommend that these modifications be made and the new
implant be more rigorously tested in species with immunoreactivity similar to
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