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Mechanical strength of repair of the rotator cuff

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  • Orthopaedic Clinic Lucerne OKL

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We have studied the mechanical properties of several current techniques of tendon-to-bone suture employed in rotator-cuff repair. Non-absorbable braided polyester and absorbable polyglactin and polyglycolic acid sutures best combined ultimate tensile strength and stiffness. Polyglyconate and polydioxanone sutures failed only at high loads, but elongated considerably under moderate loads. We then compared the mechanical properties of nine different techniques of tendon grasping, using 159 normal infraspinatus tendons from sheep. The most commonly used simple stitch was mechanically poor: repairs with two or four such stitches failed at 184 N and 208 N respectively. A new modification of the Mason-Allen suture technique improved the ultimate tensile strength to 359 N for two stitches. Finally, we studied the mechanical properties of several methods of anchorage to bone using typically osteoporotic specimens. Single and even double transosseous sutures and suture anchor fixation both failed at low tensile loads (about 140 N). The use of a 2 mm thick, plate-like augmentation device improved the failure strength to 329 N. The mechanical properties of many current repair techniques are poor and can be greatly improved by using good materials, an improved tendon-grasping suture, and augmentation at the bone attachment.
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VOL 76-B, No. 3, MAY 1994 371
MECHANICAL STRENGTH OF REPAIRS OF
THE ROTATOR CUFF
CHRISTIAN GERBER, ALBERTO G. SCHNEEBERGER, MARTIN BECK, URS SCHLEGEL
From the H#{244}pital Cantonal, Fribourg, the University ofBerne and the AO Research Institute,
Davos, Switzerland
We have studied the mechanical properties of several
current techniques oftendon-to-bone suture employed
in rotator-cuff repair.
Non-absorbable braided polyester and absorb-
able polyglactin and polyglycolic acid sutures best
combined ultimate tensile strength and stiffness.
Polyglyconate and polydioxanone sutures failed only
at high loads, but elongated considerably under
moderate loads.
We then compared the mechanical properties of
nine different techniques of tendon grasping, using
159 normal infraspinatus tendons from sheep. The
most commonly used simple stitch was mechanically
poor: repairs with two or four such stitches failed at
184 N and 208 N respectively. A new modification of
the Mason-Allen suture technique improved the ulti-
mate tensile strength to 359 N for two stitches.
Finally, we studied the mechanical properties of
several methods of anchorage to bone using typic-
ally osteoporotic specimens. Single and even double
transosseous sutures and suture anchor fixation both
failed at low tensile loads (about 140 N). The use of a
2 mm thick, plate-like augmentation device improved
the failure strength to 329 N.
The mechanical properties ofmany current repair
techniques are poor and can be greatly improved by
using good materials, an improved tendon-grasping
suture, and augmentation at the bone attachment.
J BoneJoint Surg [Br] 1994; 76-B:371-80.
Received 5 October 1993; Accepted 16 November1993
C. Gerber, MD, Professor and Chairman
M. Beck, MD, Resident
Department of Orthopaedic Surgery, H#{244}pitalCantonal, CH-1700 Fribourg
8, Switzerland.
A. G. Schneeberger, MD, Resident
Department of Orthopaedics, University of Berne, Berne, Switzerland.
U. Schlegel, Biomedical Engineer
AO Research Institute, 7270 Davos-Platz, Switzerland.
Correspondence should be sent to Professor C. Gerber.
©1994 British Editorial Society of Bone and Joint Surgery
0301-620X194/3787 $2.00
Recovery of shoulder strength after a tear of one or more
of the rotator-cuff tendons depends on the restoration of
the muscle-tendon-bone units, but repairs may fail more
often than previously suspected (Harryman et al 1991).
Failure may be due to muscular retraction with atrophy
and fatty degeneration (Goutallier, Bernageau and Patte
1989; Walch et a! 1992), neurovascular damage (Warner
et al 1992), loss of tendon substance or tendon degenera-
tion or both (Neer and Rockwood 1984; Walch et a!
1992), poor quality of the bone of the humeral head, or
lack of tendon-to-bone healing. Early failure is caused by
suture or knot failure, the suture pulling out of the tendon
or through the bone.
We have studied current techniques of rotator-cuff
repair to assess their mechanical properties and consider
potential improvements.
MATERIALS AND METhODS
To determine current practice by expert shoulder surgeons,
we interviewed ten members of the European Shoulder
and Elbow Society and 20 active members ofthe American
Shoulder and Elbow Surgeons. Each surgeon reported the
methods which he used for tendon grasping and for
tendon-to-bone fixation and the type and size of his
preferred suture material.
We then tested the suture materials most frequently
used (Table I), measuring elongation under load and
ultimate tensile strength of knotted threads on an Instron
universal testing machine 4302 (Fig. 1; Instron Limited,
High Wycombe, UK). One end of the tested threads was
tied around a bar, using six simple square knots
(1=1=1=1=1=1;TeraandAbergl976, 1977)and
fixing the other end under a preload of 2 N to a pneumatic
grip. We used both felt-tip pen marks on the threads and
force-displacement curves to ascertain the stability and
any knot slippage.
Tensile load was applied at 6 mm/mm, and elonga-
tion of the threads was determined from the crosshead
displacement of the Instron machine, for five dry and five
wet samples of each suture material. Wet sutures had
been immersed in Ringer’s lactate for 72 hours at room
temperature. Dry and wet threads were compared statist-
ically using the rank test X (van der Waerden and
Nievergelt 1956), and different suture materials were
2= 1
1=1
1=1=1
Crosshead
4
E
0
2= 1 =,,
E
0
Fig. 1 Fig. 2
Fig. 3
372
C. GERBER. A. G. SCHNEEBERGER, M. BECK, U. SCHLEGEL
ThE JOURNAL OF BONE AND JOINT SURGERY
Crosshead
,c’J
1=1=1=1
Pneumatic
Grip 1=1=1=1=1
Figure 1 - Use of the Instron testing machine to measure elongation under load and ultimate tensile strength of suture materials.
These were secured by six simple square knots to a bar attached to the crosshead. The other end was held by a pneumatic grip.
Figure 2 - The eight parallel knots which were tested, and the international knot nomenclature of Tera and Aberg (1976). Figure
3 - Use of the Instron testing machine to measure the mechanical properties of different knots.
Table I. Suture materials tested
Trade name Size (USP)
Manufacturer!
distributor
Non-absorbable
Braided polyester Ethibond
Mersilene
Tevdek II
Dacron
Ticron
(0, 1, 2, 3)
(2)
(0, 1, 2)
(2)
(0, 1)
Ethicon
Ethicon
Deknatel
Davis and Geck
Davis and Geck
Braided nylon Surgilon
Suturamid
(0, 1, 2, 3)
(1)
Davis and Geck
Ethicon
Monofilament nylon Dermalon
Ethilon
Prolene
(2)
(0)
(0)
Davis and Geck
Ethicon
Ethicon
Monofilament polybutester Novafil (0, 1, 2)
Davis and Geck
Absorbable
Braided polyglactin 910
Braided polyglycolic acid
Monofilament polyglyconate
Monofilament polydioxanone
Vicryl
Bondek
Dexon Plus
Maxon
PDS II
(0, 1, 2)
(0, 1, 2)
(0, 1, 2)
(0, 1)
(0, 1, 2)
Ethicon
Deknatel
Davis and Geck
Davis and Geck
Ethicon
* not all suture materials were av
ailable in all sizes
assessed by pooling the results for all ten specimens of
each suture.
We then used the most favourable sutures (Ethibond
1 and 3 and Tevdek II 1, both braided polyester) to
determine the mechanical characteristics of eight different
parallel knots (Fig. 2), each of which was tested ten times.
For comparison, we also tested a monofilament thread
( Maxon 1). The threads were knotted around two bars of
the Instron machine to form a loop (Fig. 3). The first two
throws of the simple square knots were formed from a
sliding knot (Tera and Aberg 1976; Mast, Jakob and Ganz
1989) which was tightened and locked by a simple square
knot to obtain firmly tightened loops. We recorded
slipping or failure of the knots in relation to the load
applied.
To assess the formation of a gap caused by the
stretching of suture material between tendon and bone in
vivo, we measured the elongation of the material under
tensile load in vitro. We recorded the length of suture
material used in eight human cadaver shoulders for a
rotator-cuff tendon-to-bone repair. The repairs were of
supraspinatus tendons sutured to a 5 mm deep trough in
the greater tuberosity by two mattress sutures (Fig. 4).
The length of these sutures averaged 7 ± 0.5 cm. Two
loops of 7 cm of each material were therefore fixed around
two bars and their elongation under load recorded five
times for each.
The four most common methods of suturing to a
tendon and five possible alternatives (Fig. 5) were then
tested on 159 infraspinatus tendons of 80 alpine sheep
with normal shoulders. The freshly removed tendons were
wrapped in saline-soaked gauze and stored at -20#{176}C.The
sheep were 9 months to 9.5 years old (mean 3 years) and
their weight averaged 55 kg (40 to 1 10). The sheep
infraspinatus tendon measured on average 21.5 mm in
/
Fig. 4a Fig. 4b Fig. 4c
Mod. 1 Kessler Mod. 2 Kessler
Mod. 3 Kessler
Fig. 5
The tendon-grasping techniques
which were used. Two, four and
six simple stitches were tested,
with two stitches for the other
techniques.
-I----
Locking loop
\#{231}\\\
Locking
Mod. Mason Allen
MECHANiCAL STRENGTh OF REPAIRS OF ThE ROTATOR CUFF 373
VOL. 76-B, No. 3, MAY 1994
Diagrams to show tests for gap formation: a) two mattress sutures, b) supraspinatus tendon fixed with two mattress sutures to the
greater tuberosity with a thread length of 7 cm for each suture, c) two 7 cm loops placed around two bars of the Instron testing
machine to measure elongation under load.
Simple stitCh
\#{149}\\
\ \\\
Mattress
\\\\
Kleinert
--
- -
-.-
-___
EiID
‘
c__#{149}_. EIID
Fig. 6
Details of the modified Mason-Allen grasping suture.
2
4
1
374
C. GERBER, A. G. SCHNEEBERGER, M. BECK, U. SCHLEGEL
ThE JOURNAL OF BONE AND JOINT SURGERY
width (18 to 26) and 3.9 mm in thickness (2.9 to 5.5). A
variety of age and tendon sizes was used for each suture
material.
The infraspinatus tendons of the sheep are similar to
those of the human rotator cuff in size and shape, with an
average thickness of 3.9 mm as against the reported
3.93 mm of the human supraspinatus tendon (France et al
1989). We carried out histological examination of two
sheep infraspinatus tendons and two human supraspinatus
tendons. The sheep tendons had slightly more bundles of
dense collagen fibres per unit area, but were almost
indistinguishable in all other aspects. In a pilot study, we
performed three pull-out tests on intact rotator-cuff
tendons of three human cadavers of 72 to 80 years of age.
One supraspinatus tendon and one subscapularis tendon
were grasped with the modified Mason-Allen technique
(Fig. 6), and one infraspinatus tendon was grasped with a
simple stitch technique. These gave pull-out strengths
within the standard deviations of the pull-out strengths of
the sheep tendons, confirming that the mechanical
properties of tendon tissue of other animals such as cattle,
pigs and dogs are similar to those of human tendons
( Yamada 1970). The sheep infraspinatus tendons were
therefore a suitable model, but since they lacked long-
standing cuff tears, the absolute results for tensile strength
are much less relevant than the differences between the
results of different surgical techniques.
We used an Instron universal testing machine to
record the ultimate strength and the gap between the
bottom of the bony trough and the end of the tendon
stump under tensile load. Each tendon was thawed at
room temperature, and the proximal part fixed to the
crosshead of the Instron machine (Fig. 7). For most of the
tests, two stitches were placed 1 cm proximal to the end
of the tendon, but the simple stitch (see Fig. 5), which
requires less space, was also tested with four and six
stitches. Eight specimens were tested for each tendon-
grasping technique. To match the clinical situation, when
a shortened and retracted tendon is sutured under tension,
the attachment was made under a preload of 30 N, using
Ethibond 3 for all sutures. The threads were knotted with
six simple square knots to one of three fixed bars of a
fixation device of the Instron machine (Fig. 7). Tendons
clamped proximally by a fixation device showed minimal
slippage, and the gap formed under load was therefore
measured at 0.5 cm from the stitches by an extensometer
and not from the crosshead displacement. The extension
rate was slow - at 1 mm/minute. Since tendon deformation
can jeopardise blood supply, we recorded strangulation
of tendon tissue and gap formation under load using
photographs and video recordings. The more successful
tendon-grasping techniques were retested using eight
specimens per technique with augmentation by 1.4 mm
thick, firm absorbable poly(L-/D-lactide) membranes
(Fig. 8).
The five satisfactory tendon sutures were retested
using cyclical loading (see Table VI), using five specimens
per technique. The crosshead moved cyclically at 200 mm/
mm at about 40 c/mm to a maximal load of 250 N, chosen
as about 70% of the ultimate tensile failure load for the
best grasping technique. We used this high cyclical load
because lower loads failed to show differences in
Fig. 7
Tests on the Instron machine: 1) three fixed bars to one of
which the tendon was sutured, 2) bar attached to the
crosshead, 3) extensometer, 4) distal tendon stump.
mechanical stability of the sutures. A maximum of 1000
cycles was performed; after this threads began to rupture
because of fatigue.
Finally, we tested differenttechniques for the fixation
of tendon to bone (Fig. 9). Two sutureless methods were
tested. First, a 4-hole, 2.7 mm AO/ASIF DC-plate
(STRATEC Medical, Waldenburg, Switzerland) was used
to compress and fix the tendon between a cortical graft
and the humeral head. Secondly, a metallic brush was
used to squeeze the tendon onto the bone. We then
evaluated the double and single transosseous, suture-bone
___
Fig. 8
Modification 1 of the Kessler suture augmented
with a 1.4 mm thick absorbable poly(L-/D-
lactide) membrane.
Single transosseous
Double transosseous
Fig. 9
MECHANICAL STRENGTh OF REPAIRS OF THE ROTATOR CUFF
375
VOL 76-B, No. 3, MAY 1994
fixation techniques, the Mitek G II anchor (Mitek Surgical
Products, Norwood, Massachusetts) and an augmented
technique using sutures knotted over a 2.0 mm thick, firm
poly(L-/D-lactide) membrane. The proximal humerus of
patients with chronic rotator-cuff tears is often osteo-
porotic, and we therefore tested fixation techniques on 18
osteoporotic humeral heads from cadavers of 65 to 80
years of age, all of which showed degenerative changes.
Fifteen of these had complete rupture of at least the
supraspinatus tendon, and the other three had partial
rotator-cuff defects. Osteoporosis was assessed by stand-
ardised radiography with an aluminium density gauge.
Densities were compared with those of standardised
radiographs of ten humeral heads in younger cadavers, 21
to 40 years old, with no rotator-cuff disorders.
For the bone tests we fixed the proximal humerus by
embedding in methylmethacrylate, leaving the head free.
The threads under test were passed around a bar on the
crosshead of the Instron machine, then through 2 mm drill
holes from the insertion of the supraspinatus to the greater
tuberosity and knotted over the cortex. Pull-out tests were
performed at an extension rate of 1 mm/mm, recording
ultimate tensile strength and modes of failure.
All measurements were statistically analysed using
the rank test X (van der Waerden and Nievergelt 1956).
Cortical graft
RESULTS
The currently used repair techniques of 30 surgeons are
shown in Table II. None of them used any augmentation
of tendon-to-bone sutures, and most employed non-
absorbable suture materials of sizes 0 to 2.
Elongation and ultimate tensile strength (Table III).
All tested threads failed at the knot. Non-absorbable
Metallic brush
Six methods of fixation to bone.
Mitek Gil anchor
Augmentation with membrane
Table II. Currently used techniques for grasping tendons and suture
materials for the repair of large rotator-cuff tears
Table III. Ultimate tensile strengths and elongations of all
tested suture materials (mean a so for ten measurements per
thread)
American
(n=20)
European
(n=1O)
Tendon grasping technique (see Fig. 5)
Simple stitch
10 2
Mattress
6 5
Mod 1 Kessler 1
3
Mod 2 Kessler
1 -
Mod 3 Kessler
2 -
Suture material
Size (USP)
0 7 3
I
6 2
2 5 5
lrnmtape 2
-
Non-absorbable
19 6
Absorbable
1 4
Bone fixation
Transosseous non-augmented sutures
20 10
braided polyesters (Ethibond, Mersilene and Tevdek II)
showed very high stiffness and high ultimate tensile
strength for all tested sizes, and were mechanically
superior to the other non-absorbable materials. Absorbable
braided sutures (Bondek, Dexon Plus and Vicryl) also
showed high stiffness and ultimate tensile strength for
sizes 0 to 2. The ultimate tensile strengths of the very
extensible monofilament absorbable Maxon and PDS II
were high but variable.
For the same suture material, one size larger increased
the ultimate tensile strength by an average of 35% ± 10%
from size 0 to size 1 and 30% ± 7% from size 1 to size 2.
Knots. Ethibond 3 and 1 and Tevdek II 1 were both
locked securely by either the 1 = 1 = 1 = 1 or the 2 = 1 = 1
knot configurations. More knots did not significantly
change either elongation or ultimate tensile strength. The
2 = 1 and the 1 = 1 knots both slipped badly, but the
1 = 1 = 1 knots of Ethibond 3 and Tevdek II 1 only
slipped under loads close to the ultimate tensile strength.
Any slippage appeared to damage the threads and cause
them to fail at lower ultimate tensile strengths (about 10%
lower for Ethibond, p < 0.05; 21% lower for Tevdek II 1,
p < 0.01). For the monofilament Maxon 1, stable knots
were achieved with 2 = 1 = 1 or 1 = 1 = 1 configurations
(p < 0.01). The ultimate tensile strength of the simple
square knots of Maxon 1, however, was on average 30%
lower than that of the surgeons’ knots (j < 0.01).
Elongation in tendon-to-bone fixation. The results for
elongation under load of two 7 cm loops of size 3 and
size 1 threads are shown in Table IV. Under a load of
200 N, two loops of Ethibond elongated 2.2 mm for size
3 and 3.5 mm for size 1 and Tevdek II 1 elongated
2.8 mm. By contrast, Surgilon 1 elongated by 7.4 mm and
PDS II 1 by 10.2 mm.
Tendon-grasping techniques. Table V records the
ultimate tensile strength, the separation at 200 N and the
mode of failure of all the tendon-grasping techniques.
Table IV. Gap in a tendon-to-
bone repair caused by the mechan-
ical properties of the suture
material alone (mean a SD for two
sutures of 7 cm length, 5 measure-
ments per thread)
Suture
Elongation under
200 N (mm)
Ethibond3 2.2 ±0.3
Surgilon 3 5.5 a 0.4
Tevdeklll 2.8±0.1
Bondeki
3.4±0.1
Ethibond 1 3.5 a 0.1
Vicryl 1 4.0 a 0.3
Dexon Plus I 4.2 a 0.2
Ticron 1 4.6 a 0.4
Maxon 1 7.0 a 0.2
Suturamid 1 7.3 a 0.9
Surgilon 1
7.4 a 0.4
PDSII1 10.2±0.6
Novaflll 11.3±0.3
Most techniques withstood loads of over 300 N; at
approximately 350 N, Ethibond 3 thread ruptured.
There was no slipping within the tendon of the
modified Mason-Allen technique, the locking suture or
the locking loop suture (Fig. 5); failure was by rupture of
376
C. GERBER, A. G. SCHNEEBERGER, M. BECK, U. SCHLEGEL
THE JOURNAL OF BONE AND JOINT SURGERY
Size Suture
No. 3 Ethibond 3
Surgilon 3
No. 2 Mersilene 2
Bondek 2
Tevdek II 2
Ethibond 2
Dexon Plus 2
Dacron 2
Vicryl 2
Dermalon 2
Surgilon 2
PDS II 2
Novafil 2
No. 1 Tevdek II 1
Bondek 1
Ethibond 1
Vicryl 1
Dexon Plus 1
Ticron 1
Maxon 1
Suturamid 1
Surgilon 1
PDS II 1
Novafll 1
No. 0 Ethibond 0
Tevdek II 0
Bondek 0
Ticron 0
VicrylO
Dexon Plus 0
Mason 0
Surgilon 0
PDS 110
Novafil 0
Prolene 0
Ethilon 0
Elongation under
40 N load
(mm crosshead
displacement)
6.5 ± 0.3
17.9± It)
7.5 ± 0.4
7.6 a 0.7
7.7 a 0.4
7.9 a 0.5
8.6 a 0.7
8.7±0.6
10.5 a 0.3
17.2 a 0.8
19.4± 1.3
20.6± 1.3
29.2 a 0.9
8.2 a 0.4
9.7 a 0.6
9.8 a 0.6
11.6 a 0.8
11.9 a 0.7
13.0± 1.3
20.7± 1.0
21.6± 1.3
22.3± 1.7
28.3 a 1.2
35.9± 1.0
10.9 a 0.5
11.7 a 0.6
12.0 a 0.8
16.1 a 2.7
16.8± 1.3
17.0± 1.2
28.5 a 2.3
35.6 a 2.9
37.4± 1.7
40.3 a 1.5
45.6 a 3.8
48.4 a 3.6
Ultimate tensile
strength (N)
106 a 9
88 a 6
83 a 7
125 a 13
84 a 7
82 a 3
101 a 7
73 a 8
90 a 7
69 a 9
82 a 5
109±15
77± 14
69 a 5
66 a 4
65 a 4
66 a 6
71 a 7
68 a 4
85 a 19
52 a 7
65 a 9
85 a 8
57 a 8
54 a 7
48 a 3
57 a 4
46 a 5
52±8
53 a 6
67 a 15
44±3
59 ± 6
41 a 6
42 a 2
41 a 3
Fig. 10 Fig. 11
I ‘-. I
Fig. 12
MECHANICAL STRENGTh OF REPAIRS OF THE ROTATOR CUFF 377
VOL 76-B, No. 3. MAY 1994
the suture material. By contrast, the simple stitches and
the mattress sutures slipped out at moderate loads of 184
to 270 N. The other techniques showed intermediate
results with a tendency to slip, especially within the
thinner tendons. Most techniques showed slight differ-
ences in ultimate tensile strength, but the simple stitch,
the augmented first modification of the Kessler stitch and
the mattress suture were significantly less strong than the
others (p < 0.05). The modified Mason-Allen suture
allowed the least gap formation, but the differences
between that and the first modification of the Kessler and
the Kleinert suture were not statistically significant.
The augmentation of the techniques with an absorb-
able poly(L-ID-lactide) membrane did not improve hold-
ing strength. The membrane acted as a gliding plane and
did not allow the suture to grasp the fibre bundles of the
tendon; the results were weaker and showed larger
separations.
Most techniques, other than the simple stitches,
caused definite deformation of the tendon by the loaded
Figure 10 - Modification 1 of the Kessler suture using Ethibond 3 thread in
20 mm wide, sheep infraspinatus tendon loaded with 300 N. Figure 11 -
Modified Mason-Allen suture using Ethibond 3 thread in 21 mm wide
infraspinatus tendon loaded with 300 N. Figure 12 - Modified Mason-Allen
suture using PDS II I thread in 22 mm wide infraspinatus tendon loaded
with 200 N. The threads elongated significantly.
and tightened sutures. The locking loop suture compressed
almost the entire tendon, and sutures such as the modified
Kessler grasped large fibre bundles with their transverse
loop, seeming to strangulate the tendon (Fig. 10). The
modified Mason-Allen suture required less substance for
stable fixation, and therefore strangulated a smaller part
of the tendon (Fig. 1 1). This seemed to be the best
technique: it did not slip and its ultimate tensile strength
was limited by the strength of the suture material.
Cyclical tests. Cyclical loading to 250 N at 40 c/mm gave
results for numbers of cycles withstood and separation
after 1000 cycles (Table VI). Only the modified Mason-
Allen technique withstood 1000 cycles in all measure-
ments. Separation was 4.9 mm in the unloaded state and
6.6 mm under 250 N of tensile load. There was no
slippage; progressive longitudinal pulling caused in-
creased transverse tightening of the suture loops.
Those sutures with a tendency to slip failed to resist
cyclical loading, especially in thin tendons. Only the third
modification of the Kessler suture resisted 1000 cycles,
378 C. GERBER, A. 0. SCHNEEBERGER, M. BECK, U. SCHLEGEL
THE JOURNAL OF BONE AND JOINT SURGERY
three times in larger tendons, but in smaller tendons it
slipped out, once after 475 and once after 25 cycles.
Bone-fixation techniques. The bone density of the
osteoporotic humeral heads was 20.1% ± 7% lower than
that of the younger, intact humeral heads (p < 0.05).
The results for ultimate pull-out strength and failure
modes of the different bone fixation techniques are listed
in Table VII. The use of a 4-hole AO/ASIF plate with a
cortical graft was unsatisfactory, the tendon slipping out
at 140 ± 31 N. The metallic brush grasped the tendon
better, to 299 ± 59 N, but under higher loads, the tendons
were cut longitudinally and slipped out. The Mitek G II
anchor pulled out of osteoporotic bone at 142 ± 55 N,
confirming the manufacturer’s statement that osteoporotic
Table V. Pull-out testing of different techniques by a slowly increasing
load (mean a SD for eight measurements per suturing technique). There were
two stitches per suture except for the simple stitch with two, four and six stitches
Technique
Extension
under
200 N (mm)
Ultimate
tensile
strength (N)
Failure mode
Rupture Slip
Mod Mason-Allen 3.5 a 0.6 359 a 28 8 0
Mod 1, Kessler 3.7 a 0.9
329 a 60 4 4
Kleinert 4.0 a 1.0
338 a 55 2 6
Mod 2, Kessler 4.2 a 0.6 350 a 53 7 1
Mattress
4.3 a 1.3 269 a 80 1 7
Locking 4.5±0.6 392±38 8 0
Mod3,Kessler 4.9±0.8
366±49 5 3
Kleinert augmented 4.9 a 0.9 329 a 82 4
4
Locking loop 5.1 a 1.0 383 a 23 8 0
Simple stitch (6 stitches) 5.3 a 1.4 273 a 72 0 8
Mod Mason-Allen
augmented 5.6 a 0.7
389 a 34 7 1
Mod 1, Kessler augmented 7.8 a 3.6 229 a 57 2 6
Simple stitch (4 stitches) - 208 a 68 0 8
Simple stitch (2 stitches) - 184 a 32
0 8
Table VI. Cycles to failure (mean, range) and diastasis (mean
a SD) of different suturing techniques using a load of 250 N (five
measurements per technique)
Technique Cycles to failure
Diastasis in mm
after 1000 cycles
0 N 250 N
Mattress
36 (1 to 140) - -
Modl,Kessler 115(89to440)
- -
Kleinert 217(12to445) - -
Mod 3, Kessler 700 (25 to 1000) 6.7 a 1.2 8.8 a 1.6
Mod Mason-Allen 1000 4.9 a 1.2 6.6 a 1.5
bone is a contraindication to its use. Single and double
transosseous sutures cut through osteoporotic bone at 139
± 38 N and 146 ± 41 N respectively. Only double
transosseous sutures augmented by a 2.0 mm absorbable
poly(L-fD-lactide) membrane gave significantly better
fixation strengths (329 ± 44 N; p < 0.05), limited only by
the ultimate strength of the Ethibond 3 sutures.
DISCUSSION
The ideal repair should have high initial fixation strength,
allow minimal gap formation and maintain mechanical
stability until solid healing. There is little experimental
documentation ofcurrent techniques (Forward and Cowan
1963; Robertson, Daniel and Biden 1986; France et al
1989), but it is clear that weak initial fixation leads to gap
formation under load, poor healing and possible complete
failure (Lindsay, Thomson and Walker 1960; Harryman
et al 1991).
We did not study tissue compatibility of suture
materials but used only those shown to have excellent
compatibility and a successful clinical record (Herrmann,
Kelly and Higgins 1970; Srugi and Adamson 1972; Craig
et al 1975; Sanz et al 1988).
Tendon-to-bone suturing gave the best results of the
techniques which we tested, but the elasticity of the suture
material with elongation under load precluded absolute
stability. Suture materials differed significantly, and we
agree with Trail, Powell and Noble (1989) who showed
that braided polyester (Ethibond, Mersilene, Tevdek II)
is an extremely stiff material with excellent ultimate
tensile strength. Only braided absorbable suture materials
(Bondek, Dexon Plus and Vicryl) have similar in-vitro,
mechanical properties (Herrmann et al 1970). Two weeks
after subcutaneous or submuscular implantation, however,
the ultimate tensile strength is reduced by 50% (Herrmann
et al 1970; Craig et al 1975; Stone, von Fraunhofer and
Masterson 1986; Bourne et al 1988; Sanz et al 1988),
while clinical experience suggests that at least six
weeks are necessary for the secure biological fixation
of a tendon-to-bone repair (Forward and Cowan 1963;
Ketchum, Martin and Kappel 1977; Clancy et al 1981).
Monofilament absorbable suture materials such as
Maxon and PDS II lose 50% of their in-vitro ultimate
tensile strength after implantation for three and four to
five weeks respectively (Stone, Masterson and von
Fraunhofer 1986; Bourne et al 1988; Sanz et al 1988),
and this degradation rate has been considered to be slow
enough to allow the use of PDS II for rotator-cuff repairs
(Bourne et al 1988). This suture material is extensible,
however, and the separation produced by its elongation
alone in a simulated repair is surprisingly large, at 10.2 ±
0.6 mm, as against the 2.8 ± 0.1 mm allowed by stiff
sutures such as braided polyester (Fig. 12). The choice of
suture material is therefore important for stability.
Few data are available regarding the so-called
‘sliding knot’ (Tera and Aberg 1976; Mast et al 1989).
This is often used in orthopaedic surgery, because it
allows easy tightening of the first two loose throws. We
tested this knot and the surgeons’ square knot with braided
Ethibond and Tevdek II and with monofilament Maxon.
The Ethibond 3 and 1 threads were both locked securely
by a 1 = 1 = 1 = 1 or 2 = 1 = 1 knot configuration. For the
monofilament Maxon 1, three throws of either type were
stable and showed no slippage.
The tendon-grasping techniques used in hand surgery
have been widely studied (Mason and Allen 1941; Cowan
and Courtemanche 1959; Schink and Gersbach 1961;
Kessler 1973; Urbaniak, Cahill and Mortenson 1975).
MECHANICAL STRENGTh OF REPAIRS OF THE ROTATOR CUFF
379
VOL 76-B, No. 3, MAY 1994
Table VII. Results of different bone-fixation techniques (mean a SD
for six measurements per technique)
Technique
Ultimate pull-out
strength (N)
Mode of failure
Cortical graft
140 a 31
Tendon pulled out
Metallic brush
299 a 59
Tendon pulled out
Double transosseous fixation 146 a 41
Suture pulled out
Single transosseous fixation
139 a 38
Suture pulled out
Mitek G II anchor
142 a 55
Anchor pulled out
Membrane augmentation 329 a 44 Suture ruptured
Our results confirm that different techniques vary consid-
erably in holding power in large, flat tendons such as
those of the rotator cuff. The commonly used simple
stitch was surprisingly weak, but does not strangulate the
tendon and it allows almost no separation in the absence
of significant tension. It may therefore be an excellent
technique for small cuff tears in which reinsertion to bone
can be obtained without tension and the repair can be
protected from tensile load during early healing. This
technique is probably not adequate for larger tears, in
which the tendon may be under tension and tensile loads
during wake-up from general anaesthesia and in the early
postoperative phase may be uncertain.
One new grasping technique showed significantly
better properties in vitro, with twice the holding strength
of the simple stitch, its strength being limited only by the
strength of the suture material. Two such stitches seemed
optimal for the 21 .5 mm wide infraspinatus tendon of the
sheep. The new suture grasps few fibre bundles and
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The weakest link in the chain was osteoporotic bone.
Threads pulled into such bone at moderate loads. In acute
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Any biocompatible material with adequate mechanical
properties could be used.
Little has been published about optimal surgical
techniques for rotator-cuff repairs. We have shown that
the mechanical properties of repairs can be improved
considerably by attention to techniques and materials. In
patients with large tears, retraction of muscle and
osteopenia of the proximal humerus, improved methods
are more likely to prevent early structural failure.
The authors wish to acknowledge the help of Mrs J. Buchanan, Mr J.
Cordey, PhD, Mr P. Imken, Mrs M. Tate, PhD, Mr R. Wurgler, Mech Ing,
and Mr W. Ziegler, PhD. The continuous help and support of Professor S.
M. Perren, MD, throughout this study is especially and gratefully
acknowledged.
This project was supported by a grant from the AO/ASIF-Foundation,
Switzerland.
No other benefits in any form have been received or will be received
from a commercial party related directly or indirectly to the subject of this
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Chapter
Most failures of rotator cuff repair occur at the tendon-suture junction, followed by anchor pullout. Various types of suture-tendon construct have been introduced to improve the strength. Meta-analyses have shown that double-row repair techniques are biomechanically superior to single-row repairs although there is no difference in the clinical outcome. Various reinforcement procedures such as adding augmentation sutures at the medial row, doubling the number of sutures, or using tapes wider than sutures seem to be effective in making the repair construct more durable. Information about triple-row repair is too limited to make any conclusions. In order to avoid anchor pullout, it is useful to estimate the anchor pullout strength using the CT data of the proximal humerus prior to surgery. A suture anchor should be inserted perpendicular to the bony surface to obtain the maximum pullout strength based on all the biomechanical studies and proper interpretation of the “deadman theory.”
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Absorbable sutures are initially equal or superior to nonabsorbable sutures in terms of tensile strength but are absorbed at variable rates by the action of hydrolysis. This study demonstrated that the in-vivo half-life tensile strength of the braided absorbable sutures polyglycolic acid (Dexon Plus) and polyglactin 910 (Vicryl) is 2 weeks, whereas those of the monofilament absorbable sutures polyglyconate (Maxon) and polydioxanone (PDS) are 3 and 6 weeks respectively. The addition of a single hitch or six knots reduced the in-vitro tensile strength by 30% to 35%. Polyglyconate (Maxon) suture demonstrated the best in-vitro knot security.
In-vivo maxon comparison & PDS
  • Rb Bourne
  • Bitarh
  • Vicryl
  • Pr
Bourne RB,BitarH,Andreae vicryl, PR, et plus, al.In-vivo maxon comparison & PDS. of J Surg four absorbable 1988; sutures:dexon Can 31:43-5
Anterior Rhesus and posterior J Bone cruciate Surg[Am] reconstruction 63-A:1270-84. inmonkeys. Joint CowanIU
  • Wg Clancy
  • Rg Narechania
  • Rosenberg
  • Td
Clancy WG,Narechania ligament 1981; RG, Rosenberg TD, et al. Anterior Rhesus and posterior J Bone cruciate Surg[Am] reconstruction 63-A:1270-84. inmonkeys. Joint CowanIU, Courtemanche Can J Surg AD. 1959; Anexperimental 2:373-80. study of tendonsuturing techniques
BidenE.Softtissuefixation tobone R, et aL PDS Comparison sutures of Maxon closure suture in rats
  • Caeds
  • Seconded
  • Med Robertsondb
  • Daniel
  • Patterson
  • Vicryl
  • Ja Gynecol
  • Kamath
CAeds. Seconded. RobertsonDB, Med Daniel 1986; DM, 14:398-403. BidenE.Softtissuefixation tobone. Am J Sports SanzLE, with Obstet Patterson vicryl, Gynecol JA,Kamath catgut 71 :418-22. R, et aL PDS Comparison sutures of Maxon closure suture in rats.chromic andin fascial 1988; SchinkW,Gersbach B