Keywords
rotator cuff - suture - suture techniques - tendon injuries - tendons - bone tunnel wear - suture abrasion - cyclic abrasion
Introduction
Rotator cuff tears are a very common cause of pain and deficit in shoulder function.[1] Their estimated prevalence is of 20.7% in the general population, and it increases with age.[1]
[2] Repair of rotator cuff tears relieves pain and improves function.[3]
Ideally, the repair must have sufficient compressive force to minimize separation and maintain mechanical stability until healing is complete.[4] This is why the repair should also be able to withstand a cyclic physiological load.[5]
The most common treatment for a rotator cuff tear is reattachment with anchors, either in an open or arthroscopic procedure, with adequate functional outcomes;[6]
[7]
[8]
[9]
[10]
[11] however, the rate of repair failure remains high.[12]
[13]
[14] The most important clinical factors influencing the healing process are tear size, the degree of fatty degeneration of the muscles, tissue quality, and age.[13]
[14]
[15]
[16]
[17]
[18] Many biomechanical factors contribute to the healing process and prevent repair failure. These factors include the contact area and contact pressure of the tendon on the footprint,[19] and the tension of the moving suture at the tendon-footprint interface.[20]
Anchor repair systems are widely used, but often fail to fixate in osteoporotic bone, resulting in decreased contact pressure on the footprint.[21] New repair methods have been developed with classic transosseous suture techniques to reduce the rerupture[22] and anchor avulsion rates, decrease the costs,[23]
[24]
[25] and improve tendon healing.[26]
[27]
Transosseous fixation techniques can be performed arthroscopically or in an open procedure, and their efficiency in rotator cuff repair has been proven.[28] For the classic open technique, the transosseous tunnel is performed with large oblique needles;[29] this method has been reproduced arthroscopically.[30] However, the most popular systems are based on arthroscopic techniques that create perpendicular transosseous tunnels, intersecting a medial tunnel in the footprint with another one 1.5 cm below the tip of the tuberosity.[31] The passage of a suture through the bone adds a failure zone due to cyclic load abrasion that must be considered.[5]
Abrasion on cancellous and cortical bone may change during cyclic loading according to the shape of the transosseous tunnel. The present biomechanical study aims to compare the bone wear generated by the abrasion of a cyclic load in classic oblique and perpendicular tunnels. Our hypothesis is that the oblique tunnel presents less bone wear due to cyclic abrasion compared to the perpendicular tunnel.
Materials and Methods
Animal Model
Eight lamb (Ovis orientalis aries) shoulders were thawed at room temperature and dissected for biomechanical tests. All the soft tissue around the proximal humerus was removed to identify the greater tuberosity. No rotator cuff abnormalities were found in any specimen. All pieces were irrigated with saline solution to prevent tissue dehydration. There was no live animal processing; all specimens were sourced from an animal-handling company (Simunovic Ltda.).
Tunnel Design
Two tunnels with 2.5 mm in diameter were made at the greater tuberosity, 10 mm apart from each other. Compasses designed to make perpendicular and oblique tunnels (with a 15-mm radius) were used in each specimen. For both tunnels, the entrance was 10 mm lateral to the edge of the tuberosity, and the exit, 10 mm medial to the edge of the tuberosity, corresponding to the medial area of the infraspinatus footprint in lambs ([Figure 1]).
Fig. 1 Tunnel design. On the left, a perpendicular tunnel; on the right, an oblique (classic) tunnel. Compasses designed to make perpendicular and oblique tunnels (with a 15-mm radius) were used in each specimen. For both tunnels, the entrance was 10 mm lateral to the edge of the tuberosity, and the exit, 10 mm medial to the edge of the tuberosity.
Cyclic Micro-abrasion Model
A custom-made cycling motor that enabled back-and-forth suture traction at a frequency of 2.5 Hz, with 5 cm of excursion (speed of 150 cm/minute), and a 10-N load was used ([Figure 2]). These parameters were described in similar studies,[32]
[33] and they simulate physiological loads in daily living activities. The suture traction axis was 90° in relation to the bone surface of the transosseous tunnel ([Fig. 3]).
Fig. 2 Custom-made cyclic abrasion model. A custom-made cycling motor was used for back-and-forth suture traction. The proximal humerus was fixed with a clamp, and the perpendicularity of the suture was ensured at the time of testing.
Fig. 3 Greater tuberosity dissection and tunnel preparation. This figure shows that all the soft tissue around the proximal humerus was removed to identify the greater tuberosity and prepare the tunnels.
The abrasion test was performed with a polyethylene central core suture covered with multiple high-molecular-weight braided strands (USP No. 2; FiberWire, Arthrex, Naples, FL, US). The distance between the entry and exit points of the suture in the tunnel was measured before and after 1,400 cycles with a digital caliper (with 0.1 cm of resolution). The diameter of the cortical bone hole was not measured.
Main Outcome
The main outcome was the percentual change in suture length within oblique and perpendicular tunnels before and after the micro-abrasion cycle as an estimate of the degree of bone tunnel wear.
Statistical Analysis
Due to the small sample size, the non-parametric Mann-Whitney U test was performed for the statistical analysis. All data were analyzed using the STATA (StataCorp LLC, College Station, TX, US) software, version16. Statistical significance was established at p < 0.05 with two-tailed tests.
Results
The perpendicular tunnels had a precycling length of 1.93 ± 0.17 cm, and a postcycling length of 1.48 ± 0.22 cm (23.24 ± 7.44% decrease in length). The oblique tunnels had a precycling length of 1.83 ± 0.15 cm, and a postcycling length of 1.69 ± 0.14 cm (7.76 ± 4.32% decrease in length) ([Table 1]). The difference between the decrease in length of oblique and perpendicular tunnels was significant (p = 0.0003).
Table 1
|
Angle of the tunnel
|
|
|
|
|
|
Perpendicular
|
Preabrasion (cm)
|
Postabrasion (cm)
|
∆ Abrasion
|
Percentage
|
|
2.2
|
1.8
|
0.4
|
18.2%
|
|
1.8
|
1.3
|
0.5
|
27.8%
|
|
2
|
1.4
|
0.6
|
30.0%
|
|
1.9
|
1.65
|
0.25
|
13.2%
|
|
2.1
|
1.6
|
0.5
|
23.8%
|
|
1.9
|
1.5
|
0.4
|
21.1%
|
|
1.8
|
1.5
|
0.3
|
16.7%
|
|
1.7
|
1.1
|
0.6
|
35.3%
|
|
Mean value
|
1.93
|
1.48
|
0.44
|
23.24%
|
|
Standard deviation
|
0.17
|
0.22
|
0.13
|
7.44
|
|
Oblique
|
Preabrasion (cm)
|
Postabrasion (cm)
|
∆ Abrasion
|
Percentage
|
|
1.6
|
1.5
|
0.1
|
6.3%
|
|
1.85
|
1.7
|
0.15
|
8.1%
|
|
1.9
|
1.8
|
0.1
|
5.3%
|
|
1.9
|
1.6
|
0.3
|
15.8%
|
|
1.6
|
1.5
|
0.1
|
6.3%
|
|
1.9
|
1.8
|
0.1
|
5.3%
|
|
1.9
|
1.85
|
0.05
|
2.6%
|
|
2
|
1.75
|
0.25
|
12.5%
|
|
Mean value
|
1.83
|
1.69
|
0.14
|
7.76
|
|
Standard deviation
|
0.15
|
0.14
|
0.09
|
4.32
|
Discussion
Our main finding is that the length of the intraosseous tunnel decreases after cycling as a result of cancellous bone wear caused by suture movement. This wear was three-fold lower in oblique tunnels compared to perpendicular tunnels.
Rotator cuff repair requires an adequate initial fixation force, with minimal loss of footprint contact until healing is complete.[4]
[34] Moreover, the repair must withstand a cyclic load over time.[5] The factors contributing to the repair include adequate tissue quality, contact area and contact pressure,[19] and the movement of the tendon-footprint interface.[20] Several studies[35]
[36]
[37]
[38] have shown that the pressure at the tendon-footprint interface, determined as suture tension, is beneficial for healing. Although the optimal pressure for rotator cuff repair has not been established, its clinical impact in different models is uncertain.[19]
[27]
[39]
Several biomechanical studies show that repairs using transosseous techniques result in excellent pressure at the level of the footprint,[26]
[27] greater resistance to failure, and less movement of the tendon-footprint interface compared to techniques based on anchors.[20]
[40] Selected clinical series[22] have shown low rates of rerupture (6%) when using transosseous techniques.
Arthroscopic repair attempts to replicate open techniques, including the transosseous technique with different anchor configurations. The transition from open transosseous techniques to arthroscopic techniques is not easy because of the complexity of the preparation of the transosseous tunnel. A direct lateral tunnel can be made with an exit at the medial footprint, but the proximity of the entry point to the axillary nerve is a challenge;[41] an oblique needle may be used to spare this area, but planning the exit at the footprint level is difficult.[30] This is why the most widespread technique is based on a mechanical system that manages to intersect perpendicular tunnels pointing to the required footprint area.[23]
[42]
The clinical practice witnessed a transition from monofilament or braided polyester sutures to braided, mixed (polyblend) sutures. Kowalsky et al.[5] studied the abrasive properties of different types of sutures on tendon and bone, showing that they do not influence bone wear. However, further studies are required to determine the actual impact of suture type and abrasion on bone tunnel models.
The present study evaluated biomechanical properties related to cyclic abrasion of a bone tunnel in an animal model. The lamb shoulder was selected because it has anatomical and functional characteristics equivalent to those of the human supraspinatus tendon.[43] However, it remains to be determined whether interspecies differences may affect rotator cuff repair in humans. The present study has many limitations. The effect of intraosseous abrasion aims to evaluate the isolated effect of the angle of the transosseous tunnel with a traction vector of 90° to the bone surface; however, in an ideal model, a simulated rotator cuff tear would be submitted to a transosseous repair followed by cyclic traction on the relevant tendon. The bone density of the ovine proximal humerus is different when compared to that of middle-aged human beings, so interspecies variability cannot be ruled out. Human cadavers may better represent the clinical outcome; however, ex vivo studies provide no information on healing.
Finally, we conclude that the intraosseous abrasion generated by the cyclic suture movement in a transosseous tunnel is influenced by the shape of the tunnel (angle). Bone wear is lower in oblique tunnels compared to perpendicular tunnels.
