Keywords
rotator cuff - pressure - suture - suture techniques - tendon injuries - tendons
Introduction
Arthroscopic rotator cuff repairs have increased steadily in recent years.[1] Most cases show good to excellent clinical and functional outcomes both in the short
and long terms;[2]
[3]
[4]
[5] however, re-rupture rates are still considerable, ranging from 11% to 68% in some
series, and even 94% in selected studies.[6]
[7]
[8]
Rotator cuff repair surgery seeks to establish a fibrovascular interphase between
the tendon and the footprint, which is required for healing and restoration of the
fibrocartilaginous insertion (enthesis); this is achieved with a construct that maximizes
the pressurized contact between the tendon and the bone while maintaining mechanical
resistance against the physiological load.[9] Re-rupture is associated with patient- and repair-related factors (anatomical factors).
Patient-related factors include increasing age, larger tear size (compromise of multiple
tendons), lower tendon quality, muscle atrophy, fat degeneration (Goutallier classification
≥ 3), tendon retraction, longer evolution time, and comorbidities (smoking, diabetes,
hypercholesterolemia, alcoholism, obesity, and hypertension).[7]
[10] Anatomical, repair-related factors include construct tension, tissue perfusion,
micromotion at the tendon-footprint interphase, and the contact pressure and area
of the footprint.[11] The underlying principle is that a greater magnitude and distribution of the tendon-to-bone
contact area will increase the chance of tendon healing.[12]
Several biomechanical studies on double-row (DR) repair demonstrated an increased
resistance to load-related failure, improved contact pressures and areas, and decreased
gap formation at the tendon-footprint interphase when compared to the single-row (SR)
repair.[5]
[13] However, the anchors provide low resistance, are prone to loosen in osteoporotic
bone, lose optimal contact at the level of the supraspinatus tendon footprint, and
result in greater tuberosity osteolysis; in addition, they are associated with difficult
revision and increased costs.[14]
[15] Failure sites can include the tendon, the suture, the bone, or the anchor, as well
as the interphases between the bone and the anchor, the anchor and the suture, or
the suture and the tendon.[16] This has led to the creation of new types of anchors, such as suture anchors.[17]
[18]
The transosseous (TO) technique maximizes the contact area of the tendon-footprint
interphase,[19] and reduces movement at the tendon-bone interphase.[20] In addition to this mechanical aspect, the TO technique allows the bone side of
the lesion to be precisely prepared with no risks or complications, such as anchor
removal and/or osteolysis of the greater tuberosity.[21]
[22]
The TO suture techniques are efficient and reproducible in the arthroscopic repair
of rotator cuff tears.[23] In addition, the potential for healing is greater because of the direct contact
between the tendon and the bone (with no intervening anchor material) and mesenchymal
stem cells from proximal humeral tunnels.[24]
[25]
[26]
In 2009, Burkhart et al.[27] described a mechanism by which increased stress applied to the construct increases
resistance to structural failure due to a progressive increase in compressive forces
at the tendon footprint, and called it self-reinforcement. The compressive forces
created in the footprint increase the resistance to friction between the tendon and
the bone, thus reducing the formation of a gap between the two surfaces.
The SR repair with the modified Mason-Allen (MMA) technique according to Habermayer[28]
[29]
[30] is easily performed and provides excellent initial fixation strength, allowing long-lasting
osteofibroblastic integration of the reinserted sleeve; in addition, it has reproducible,
good to excellent clinical outcomes, with a 25% re-rupture rate, which is consistent
with the open repair.[30]
The present study aims to compare the average contact pressure curve and the percentage
of final residual contact pressure at the tendon-footprint interphase repaired with
a crossover TO (CTO) or MMA suture. Our hypothesis is that the CTO configuration will
have a higher average contact pressure curve and a higher percentage of final residual
contact pressure at the tendon-footprint interphase.
Materials and Methods
Animal Model
Eight 6-month-old fresh frozen lamb (Ovis orientalis aries) shoulders obtained from a local meat processing plant (oyster shoulder cut, Frigorífico
Simunovic Ltda., Punta Arenas, Región de Magallanes y Antártica Chilena, Chile) were
thawed at room temperature the night before the biomechanical tests (18 hours in total,
with fully thawed anatomical parts at room temperature). The infraspinatus tendon
was selected because its anatomical and functional characteristics are consistent
with those of the human supraspinatus tendon.[31] The specimens were dissected following a standardized technique, removing all soft
tissue associated with the humeral shaft, subscapular fossa, and supraspinatus fossa
to isolate the infraspinatus muscle and its tendon. No specimen showed rotator cuff
changes. Then, the infraspinatus tendon was dissected carefully and fixated to a polypropylene
nylon tape using a Krackow-type suture with MaxBraid #2 (Zimmer Biomet, Warsaw, IN,
US) to enable muscle and tendon manipulation without tearing them; the tape was clamped
to a linear actuator with an intermediate load cell ([Figure 1]). The parts were irrigated intermittently with saline solution (0.9% NaCl) throughout
each test to prevent dehydration of the specimens.
Fig. 1 Anatomical dissection of the infraspinatus tendon of a lamb. Standardized anatomical
dissection removing all soft tissue associated with the humeral shaft, subscapular
fossa, and supraspinatus fossa to isolate the infraspinatus muscle and its tendon.
The tendon was fixated to a polypropylene nylon tape using a Krackow-type suture with
MaxBraid #2 to enable muscle and tendon manipulation without tearing them.
A tailored system generated cyclical tensions at the level of the infraspinatus tendon
([Figure 2]). The model consisted of three fundamental parts: a modular support with adjustable
height, an adjustable support for guidance of the suture system, and a linear actuator
with an intermediate load cell. The actuator was programmed to cycle at a 2-Hz frequency
and a 30-N load for a total of 1,000 cycles. The contact pressure was recorded every
50 cycles. The humeral shaft was fixated with a metal clamp. Then, the modular support
was adjusted to ensure that the tendon was parallel to a vertical line (using a level),
generating a tendon traction vector at 0° of abduction and 0° of rotation. ([Figure 3]).
Fig. 2 The model consisted of three fundamental parts: a modular support with adjustable
height, an adjustable support for guidance of the suture system, and a linear actuator
with an intermediate load cell. The humeral shaft was fixated with a metal clamp.
Fig. 3 Modular support. The modular support was adjusted to ensure that the tendon was parallel
to a vertical line.
Rotator Cuff Tear
In each humeral head, the orientation of the greater tuberosity was identified and
demarcated with a 1.5 mm Kirschner wire. Next, the tip of the tuberosity was identified,
and a full-thickness, full-width tear was made with a #15 scalpel, releasing the entire
tendon attachment to the footprint, and then flattening it with a rasp to facilitate
the installation of pressure sensors ([Figure 4]).
Fig. 4 Rotator cuff tear. A full-thickness, full-width tear is made with a #15 scalpel.
The image shows the footprint of the infraspinatus tendon.
Pressure Measurement at the Tendon-footprint Interphase
A Tekscan FlexiForce digital pressure sensor (Tekscan, Inc., Boston, MA, US) was used
to measure the pressure at the tendon-footprint interphase. The sensor was positioned
between the tendon and the footprint, remaining fixated by the repair performed and
covering the total footprint area; it records pressure changes over time and stores
these readings in a computer for later analysis. The baseline pressure was recorded
at the beginning of the experiment (time 0), during cyclic loading (every 50 cycles),
and at the end of the intervention (1,000 cycles).
Repair of Rotator Cuff Tear with Transosseous Sutures and Modified Mason-Allen Suture
A braided, nonabsorbable, polyethylene polymer MaxBraid #2 suture was used for the
repair, which is consistent with the suture size most commonly used in arthroscopic
shoulder surgery. The TO tunnels were made with a device previously designed by our
team and used in other models to generate oblique architecture tunnels ([Figure 5]).
Fig. 5 Device for the design of oblique transosseous tunnels. Inset A shows the transosseous suture device used. Inset B shows the proper positioning of the instrument in relation to the greater tuberosity.
Inset C shows a section of a Sawbone (Pacific Research Laboratories, Vashon, WA, US) model;
note the oblique trajectory of the tunnel.
Two different repairs were performed: 2 CTO tunnels with MaxBraid #2 sutures (n = 4) ([Figure 6a]); and 2 MMA sutures using 2 double-titanium Ti-Screw anchors loaded with MaxBraid
#2 (n = 4) ([Figure 6b]).
Fig. 6 Repair configurations. Inset A shows the transosseous repair with crossover suture, and inset B shows the repair with modified Mason-Allen suture.
A prestressed repair was carried out with 10 N for 2 minutes. The load cell was then
programmed for 1,000 cycles at a 2-Hz frequency and 30-N load. These parameters were
consistent with those used in similar previous studies, and they reflect the initial
period of postoperative rehabilitation (two weeks) with passive exercises with pendular
movements.[32]
[33] No load-related failures were recorded regarding the repair, the tissue, or the
support.
Statistical Analysis
The results were presented as mean ± standard deviation values. Since the distribution
was normal, as revealed by the Shapiro-Wilk test, the statistical test for parametric
variables (Student t-test) was used. All data were analyzed using the Stata (StataCorp., College Station,
TX, US) software, version14. Statistical significance was set at p < 0.05.
Results
The pressure at the tendon-footprint interphase in response to cyclical loading (measured
with a digital pressure sensor) in both repair models presented the self-reinforcement
mechanism during increased cyclical stress ([Figure 7]).
Fig. 7 Self-reinforcement mechanism in transosseous repair. Example of pressure measurement
under cyclical loads, demonstrating the self-reinforcement phenomenon in transosseous
repair. The red arrow represents the traction exerted on the tendon. The green arrow
shows how the pressure increases at the footprint due to the applied load.
The average contact pressure curve at the tendon-footprint interphase after cycling
and the average final residual contact pressure (time = 1,000 cycles) at the tendon-footprint
interphase were compared. The average contact pressure curve was of 86.01 ± 8.43%
in parts repaired with CTO sutures, and of 73.28 ± 12.01% in those repaired with
MAM sutures (p < 0.0004). The average residual percentage at the end of cycling was of 71.57% for
CTO sutures, and of 51.19% for MMA sutures (p < 0.05) ([Figure 8]).
Fig. 8 Pressure percentage during cyclic loading. This figure shows how pressure (expressed
as a percentage) decreases throughout the loading cycles for both repairs. Abbreviations:
CTO, crossover transosseous suture; MMA, modified Mason-Allen suture.
Discussion
The main finding of the present study was that CTO repair presents a higher average
contact pressure curve and a higher percentage of final residual contact pressure
at the tendon-footprint interphase when compared to the MMA suture after standardized
cyclic loading. This may result in better healing rates regarding the footprint, leading
to better clinical outcomes.
This is consistent with biomechanical studies[5]
[13] on DR repair showing an increased resistance to load-related failure, improved contact
pressures and areas, and decreased gap formation at the tendon-footprint interphase
compared to SR repair.
Caldow et al.[9] demonstrated the biomechanical inferiority of the TO technique (regarding contact
area, contact pressure, tensile strength, and stiffness) compared to the MMA and DR
repairs. Contact pressure for the TO repair was significantly lower compared to the
MMA and DR repairs. The MMA repair demonstrated significantly higher maximum tensile
strength compared to the TO repair; the DR repair had a significantly higher maximum
tensile strength compared to the MMA and TO repairs. However, these findings are from
a simple TO suture model, and the crossover repair was not evaluated. In a study not
published by our group, the biomechanical properties of the crossover configuration
were superior to those of the simple configuration in terms of contact area and pressure
regarding the footprint.
Hinse et al.[34] compared the TO suture, TO tape and TO-equivalent technique, and demonstrated that
the load at failure was not different in the TO tape and TO-equivalent technique.
However, the TO suture had statistically significant lower resistance compared to
the TO-equivalent technique, indicating that the material could be an important factor
to consider. Furthermore, despite the lack of significant differences, this study
revealed a trend to a greater loss of footprint coverage with pure TO techniques.
Our study used MaxBraid #2, a high-strength suture recognized for its lower abrasive
properties compared with other similar sutures,[35] but there are no studies comparing tapes in this type of model. We can infer that
tapes from the same material would provide greater resistance to failure. Nevertheless,
in this model, we did not register material failures under the loads of an initial
rehabilitation.
Park et al.[12] compared simple TO, interrupted SR, and mattress SR sutures, demonstrating that
the TO tunnel rotator cuff repair technique creates significantly greater contact
and a greater overall pressure distribution on the defined footprint compared to the
other techniques. However, they did not compare these techniques to the CTO or MMA
configurations, which were evaluated in the present study. Tuoheti et al.[36] compared simple TO, SR and DR sutures, and found out that the DR was superior to
the TO suture; however, this was a simple TO technique and DR with mattress suture,
presenting weaknesses similar to those of the Park et al.[12] study.
However, these studies only evaluate biomechanical properties regarding pressure magnitude
and distribution, as well as load to failure. The TO technique apparently has healing
benefits due to the mesenchymal cell supply and better tendon vascularization.[24]
[25]
[26] Urita et al.[37] revealed that vascularization demonstrated by an ultrasound scan is superior in
patients submitted to TO arthroscopic repair compared to equivalent TO techniques.
This could reflect another benefit of the TO technique in improving healing.
Self-reinforcement is a mechanism described by Burkhart et al.[27] in 2009, in which an increased stress applied to the construct increases resistance
to structural failure by progressively increasing compression forces at the tendon
footprint. The compressive forces created at the footprint increase the resistance
to friction between thehe tendon and tbone, thus reducing the formation of gaps between
these two surfaces.[27] This phenomenon was observed in both repair techniques. The angle between the suture
material and the bone is probably reduced as the tendon is progressively stressed;
in addition, suture geometry at the coronal plane changes from rectangular to trapezoidal
as the tensile load increases.[27] This results in an elastic deformation of the tendon, creating a compression force
perpendicular to the bone surface, which increases as the tensile load increases ([Figure 9]).[27]
Fig. 9 Scheme of self-reinforcement in transosseous repair. Schematic illustration of the
angle between the suture material and the bone as the tendon is progressively stressed,
and suture geometry at the coronal plane changes from rectangular to trapezoidal as
tensile load increases.
Lastly, in addition to the biomechanical and biological advantages of the TO technique,
it can present a better cost-effectiveness relationship due to device reuse and the
low cost of high-resistance sutures compared to other construct types. However, these
assertions were not evaluated here.
A limitation of the present study was the evaluation of biomechanical aspects alone
in an animal model; as such, the findings may be different in humans and under biological
conditions (consider mesenchymal cells and irrigation). Human cadaver shoulders would
best represent the clinical population. On the other hand, the use of this model standardizes
our results because each specimen is 6 months old; therefore, it is easily comparable
to the others. This is also true for bone mineral density, which was not calculated
for our specimens, but would have been very similar at the same age.
We conclude that the CTO repair presents superior biomechanical properties at the
tendon-footprint interphase than the MMA repair after standardized cyclic loading.
This finding may have important clinical repercussions on healing rates and functional
outcomes, but the applicability of this device in the surgical environment and its
potential use in an arthroscopic technique must be evaluated.
