Suture strength and angle of load application in a suture anchor eyelet

Risk Factors and Corresponding Management for Suture Anchor Pullout during Arthroscopic Rotator Cuff Repair

INTRODUCTION

Due to the aging of the population, the incidence of rotator cuff tears is growing. For rotator cuff repair, arthroscopic suture-anchor repair has gradually replaced open transosseous repair, so suture anchors are now considered increasingly important in rotator cuff tear reconstruction. There are some but limited studies of suture anchor pullout after arthroscopic rotator cuff repair. However, there is no body of knowledge in this area, which makes it difficult for clinicians to predict the risk of anchor pullout comprehensively and manage it accordingly.

METHODS

The literature search included rotator cuff repair as well as anchor pullout strength. A review of the literature was performed including all articles published in PubMed until September 2021. Articles of all in vitro biomechanical and clinical trial levels in English were included. After assessing all abstracts (n = 275), the full text and the bibliographies of the relevant articles were analyzed for the questions posed (n = 80). Articles including outcomes without the area of interest were excluded (n = 22). The final literature research revealed 58 relevant articles. Narrative synthesis was undertaken to bring together the findings from studies included in this review.

RESULT

Based on the presented studies, the overall incidence of anchor pullout is not low, and the incidence of intraoperative anchor pullout is slightly higher than in the early postoperative period. The risk factors for anchor pullout are mainly related to bone quality, insertion depth, insertion angle, size of rotator cuff tear, preoperative corticosteroid injections, anchor design, the materials used to produce anchors, etc. In response to the above issues, we have introduced and evaluated management techniques. They include changing the implant site of anchors, cement augmentation for suture anchors, increasing the number of suture limbs, using all-suture anchors, using an arthroscopic transosseous knotless anchor, the Buddy anchor technique, Steinmann pin anchoring, and transosseous suture repair technology.

DISCUSSION

However, not many of the management techniques have been widely used in clinical practice. Most of them come from in vitro biomechanical studies, so in vivo randomized controlled trials with larger sample sizes are needed to see if they can help patients in the long run.

Does the immediate repair of Bankart lesion following first dislocation reduce the chances of recurrence after arthroscopic repair in soldiers?

PURPOSE

The study attempted to compare the effects of immediate and delayed arthroscopic Bankart repair on the shoulder dislocation recurrence.

METHODS

In total, 465 soldiers with first-time anterior shoulder dislocation were included in the study. Of the total, 285 soldiers underwent a quick arthroscopic Bankart repair procedure, whether 180 soldiers underwent a delayed repair procedure. The initial dislocation was traumatic in both groups and operated using the standard arthroscopic suture anchor repair technique. Patient's age, repair time since the first dislocation, number of dislocations before surgery, number of suture anchors used during the repair, duration of surgical procedure, duration from surgery to return to work, and recurrence of dislocation after surgery were recorded. Rowe score, Constant score, and American Shoulder and Elbow Surgeons score were used for clinical assessment.

RESULTS

The operating time and recurrence rate were higher in the group subjected to delayed repair procedure than in the group subjected to immediate repair procedure. Repair timing was found to be crucial for a successful outcome.

CONCLUSIONS

The findings suggest that Bankart repair must be performed immediately to minimize recurrence and other degenerative changes, which may require an additional surgical procedure for satisfactory repair. More studies are required to reach a definitive conclusion.

LEVELS OF EVIDENCE

Level III.

Introduction of a new repair technique in bony avulsion of the FDP tendon: A biomechanical study

The purpose of this study was to determine the biomechanical characteristics of an innovative surgical technique based on a tension banding principle using a suture anchor in the repair of bony avulsions of the flexor digitorum profundus tendon. After injury simulation in 45 fresh frozen distal phalanges from human cadavers, repair was performed with minifragment screws, interosseous sutures and the innovative technique (15 per group). All repairs were loaded for a total of 500 cycles. Subsequently the specimens were loaded to failure. Load at failure, load at first noteworthy displacement (>2 mm), elongation of the system, gap formation at the avulsion site, and the mechanism of failure were assessed. The new techniques’ superior performance in load at failure (mean: 100.5 N), load at first noteworthy displacement (mean 77.4 N), and gap formation (median 0 mm) was statistically significant, which implies a preferable rigidity of the repair. No implant extrusion or suture rupture during cyclic loading were recorded when the new technique was applied. This innovative repair technique is superior biomechanically to other commonly used surgical tendon reattachment methods, particularly with respect to an early passive mobilisation protocol. Further, due to its subcutaneous position, reduction of complications may be achieved.

Functionally Graded, Bone- and Tendon-Like Polyurethane for Rotator Cuff Repair

Critical considerations in engineering biomaterials for rotator cuff repair include bone-tendon-like mechanical properties to support physiological loading and biophysicochemical attributes that stabilize the repair site over the long-term. In this study, UV-crosslinkable polyurethane based on quadrol (Q), hexamethylene diisocyante (H), and methacrylic anhydride (M; QHM polymers), which are free of solvent, catalyst, and photoinitiator, is developed. Mechanical characterization studies demonstrate that QHM polymers possesses phototunable bone- and tendon-like tensile and compressive properties (12-74 MPa tensile strength, 0.6-2.7 GPa tensile modulus, 58-121 MPa compressive strength, and 1.5-3.0 GPa compressive modulus), including the capability to withstand 10 000 cycles of physiological tensile loading and reduce stress concentrations via stiffness gradients. Biophysicochemical studies demonstrate that QHM polymers have clinically favorable attributes vital to rotator cuff repair stability, including slow degradation profiles (5-30% mass loss after 8 weeks) with little-to-no cytotoxicity in vitro, exceptional suture retention ex vivo (2.79-3.56-fold less suture migration relative to a clinically available graft), and competent tensile properties (similar ultimate load but higher normalized tensile stiffness relative to a clinically available graft) as well as good biocompatibility for augmenting rat supraspinatus tendon repair in vivo. This work demonstrates functionally graded, bone-tendon-like biomaterials for interfacial tissue engineering.

Biomechanical evaluation of the long head of the biceps brachii tendon fixed by three techniques: a sheep model

OBJECTIVE

To evaluate the biomechanical properties of the fixation of the long head of the biceps brachii into the humeral bone with suture anchors, interference screw, and soft tissue suture, comparing strength, highest traction load, and types of fixation failure.

METHODS

Thirty fresh-frozen sheep shoulders were used, separated into three groups of ten for each technique. After fixation, the tendons were subjected to longitudinal continuous loading, obtaining load-to-failure (N) and displacement (mm).

RESULTS

The mean load-to-failure for suture anchors was 95 ± 35.3 N, 152.7 ± 52.7 N for interference screw, and 104.7 ± 23.54 N for soft tissue technique. There was a statistically significant difference (p < 0.05), with interference screw demonstrating higher load-to-failure than suture anchor fixation (p = 0.00307) and soft tissue (p = 0.00473). The strength of interference screw was also superior when compared with the other two methods (p = 0.0000127 and p = 0.00000295, respectively). There were no differences between suture anchors and soft tissue technique regarding load-to-failure (p = 0.9420) and strength (p = 0.141).

CONCLUSION

Tenodesis of the long head of the biceps brachii with interference screw was stronger than the suture anchors and soft tissue techniques. The other two techniques did not differ between themselves.

Comparison of fixation properties between coil-type and screw-type anchors for rotator cuff repair: A virtual pullout testing using 3-dimensional finite element method

BACKGROUND

Pullout of inserted anchor constitutes one of the pathomechanisms of re-tearing after rotator cuff repair. The purpose of the present study was to investigate the fixation properties of suture anchors using 3-dimensional finite element method.

METHODS

The computer models of three types of anchors (TwinFix Ti, HEALICOIL PK and HEALICOIL RG) were inserted into the isotropic cube model that simulated cancellous bone. In the virtual pullout testing, a tensile load (500 N) along the long axis of the inserted anchor was applied to the site of suture thread attachment to simulate a traction force. The distribution of von Mises equivalent stress, the failure patterns of elements inside the cube and the anchor displacement were compared among the three anchors.

RESULTS

In TwinFix Ti, the highest stress concentration was seen around the anchor threads close to the surface of the cube, which caused element failure at this site. On the other hand, both HEALICOIL PK and HEALICOIL RG demonstrated a high stress concentration as well as element failure around the anchor tip. Comparing the anchor displacement, HEALICOIL RG showed the smallest displacement among the three anchors. The tensile loads that required a 0.1-mm displacement for TwinFix Ti, HEALICOIL PK and HEALICOIL RG were 400 N, 370 N, and greater than 500 N, respectively.

CONCLUSIONS

The bony structures close to the footprint surface may be damaged during surgery due to preparation for the bony bed as well as the insertion of anchors. Thus, we assumed that HEALICOIL RG represented the best initial fixation properties among the three anchors tested. Virtual pullout testing using 3-dimensional finite element method could reveal the detailed biomechanical characteristics of each suture anchor, which would be important for shoulder surgeons to improve the clinical outcomes of rotator cuff repair.

Biomechanical evaluation of different suture materials for arthroscopic transtibial pull-out repair of posterior meniscus root tears

PURPOSE

To evaluate the biomechanical properties of four different suture materials for arthroscopic transtibial pull-out repair of posterior meniscus root tears, with special focus on the meniscus-suture interface.

METHODS

Forty fresh-frozen lateral porcine menisci were used. The posterior meniscus root was sutured in a standardized fashion with a simple stitch using four different suture materials: group A, No. 2 PDS™; group B, No. 2 Ethibond™; group C, No. 2 FiberWire™; and group D, 2-mm Fibertape™. Meniscus-suture constructs were subjected to cyclic loading followed by load-to-failure testing using a servo-hydraulic material testing machine.

RESULTS

During cyclic loading, group D showed a significantly higher displacement after 100, 500, and 1,000 cycles compared to group A (p < 0.001, p = 0.001, and p = 0.001), and a significantly higher displacement after 100 and 500 cycles compared to group B (p = 0.010 and p = 0.045). Group C showed a significantly higher displacement compared to group A after 100 cycles (p = 0.008). The highest maximum load was observed in group D, with significant differences compared to group A (p = 0.013). Group B showed a significantly higher stiffness compared to group A (p = 0.023), and both group C and group D showed a significantly higher stiffness compared to group A and group B (p < 0.001).

CONCLUSION

None of the evaluated suture materials provided clearly superior properties over the others during both cyclic loading and load-to-failure testing. Based on the results of this study, FiberWire™ may be the preferred suture material for transtibial pull-out repair of posterior meniscus root tears because of comparably low displacement during cyclic loading and high values for maximum load and stiffness. In the clinical setting, FiberWire™ may improve healing rates and avoid progressive extrusion of the meniscus after transtibial pull-out repair of posterior meniscus root tears.

Biomechanical study: determining the optimum insertion angle for screw-in suture anchors-is deadman's angle correct?

PURPOSE

To assess the effect of the insertion angle and the angle of applied load on the pullout strength of screw-in suture anchors.

METHODS

Screw-in metallic suture anchors were inserted into a 10-lb/cu ft synthetic cancellous bone block at 30°, 45°, 60°, and 90° to the surface. The suture pull angle was then varied in 30° increments between 0° and 180°. Five constructs were tested to failure (anchor pullout) for each combination of angles using a Zwick tensile testing machine (Zwick Roell, Ulm, Germany).

RESULTS

There were a total of 25 combinations. The greatest pullout strength was seen with a suture anchor inserted at 90° to the bone block with a pull angle of 90° to the bone (mean, 306 N; standard deviation [SD], 9 N). The weakest pullout strength was seen with a suture anchor inserted at 30° with the angle of pull at 120° (i.e., opposite to the direction of insertion of the anchor) (mean, 97 N; SD, 11 N). A simulated deadman's angle of 45° with an angle of pull of 150° produced a pullout strength of 127 N (SD, 4 N). The pullout strengths for each insertion angle were greatest when the angle of pull was similar to the angle of insertion (P < .0001, repeated-measures analysis of variance).

CONCLUSIONS

The angle of applied load to a suture anchor and the insertion angle significantly influence the biomechanical pullout strength of screw-in suture anchors. The insertion angle of the suture anchor should replicate the angle of applied load to ensure the optimum pullout strength.

CLINICAL RELEVANCE

The screw-in anchor insertion angle and angle of applied load may have an influence on pullout strength.

Anatomic medial patellofemoral ligament reconstruction using patellar suture anchor fixation for recurrent patellar instability

PURPOSE

The purpose of this study was to prospectively evaluate clinical and radiographic outcomes following anatomic medial patellofemoral ligament (MPFL) reconstruction using patellar suture anchor fixation for recurrent patellar instability.

METHODS

Twenty patients (20 knees) were enrolled in this study. The median age was 21 years, and the median follow-up was 34.5 months. Reconstruction was performed using a hamstring autograft fixed with two suture anchors at native patellar site of the MPFL. No patient had undergone additional medial tibial tuberosity transfer. Clinical scores (Kujala, Lysholm, and Tegner score) and apprehension test were completed preoperatively and at the follow-up. Preoperative and follow-up radiographic assessments included modified Insall-Salvati ratio, congruence angle, and lateral patellofemoral angle.

RESULTS

The preoperative Kujala and Lysholm scores were 52.6±12.4 and 49.2±10.7, and at follow-up visits, corresponding values were 90.9±4.5 (p<0.001) and 90.9±5.2 (p<0.001). Tegner score increased from 3.0 (range 1-4) to 5.0 (range 4-7) (p<0.001). The apprehension test was positive in all patients preoperatively, but only positive in one patient at follow-up. All radiographic assessments were significantly improved; modified Insall-Salvati index (from 1.75 to 1.65) (p=0.002), congruence angle (from 6.3° to -7.0°) (p<0.001), and lateral patellofemoral angle (from 2.1° to 4.9°) (p=0.008). No patient experienced a patellar fracture or redislocation.

CONCLUSION

These results are comparable to those of bone tunnel techniques reported in the literature. This study shows that anatomic MPFL reconstruction using two suture anchors is a reliable treatment option.

LEVEL OF EVIDENCE

Case series with no comparison group, Level IV.

The effect of insertion angle on the pullout strength of threaded suture anchors: a validation of the deadman theory

PURPOSE

To determine the effect of insertion angle, from 45° to 135° in 15° increments, on the number of cycles withstood, the ultimate pullout strength, and the stiffness of threaded suture anchors subjected to load.

METHODS

Threaded anchors were inserted into polyurethane foam at angles from 45° to 135°, in 15° increments, relative to the direction of pull. Five anchors were tested at each angle. The anchors were first cycled for 30 cycles (10 each at 100 N, 150 N, and 200 N). The surviving specimens were then tensioned to failure. The McNemar test was used to compare cyclic failure rates. Paired-samples t tests were used to compare load-to-failure (LTF) and stiffness data. All P values are multiplicity adjusted by the Hommel procedure.

RESULTS

Four of 5 anchors inserted at 45° failed during cyclic testing at a mean of 27 cycles (P = .13). One of 5 anchors placed at 60° failed after 29 cycles (P = .99). All other anchors survived cyclic testing. Mean LTF was 234 N, 243 N, 297 N, 373 N, 409 N, 439 N, and 417 N at insertion angles of 45°, 60°, 75°, 90°, 105°, 120°, and 135°, respectively. LTF was significantly less for the 60° group when compared with the 90°, 105°, 120°, and 135° groups (P < .05). LTF was significantly less for the 75° group when compared with the 105°, 120°, and 135° groups (P < .05). For the 90° group, LTF was only significantly less when compared with the 135° group (P = .022). The differences in LTF between the 105°, 120°, and 135° groups were not significant. Stiffness increased from 28.13 N/mm at 90° to 43.4 N/mm at 105° (P = .03), 61.48 N/mm at 120° (P = .003), and 86.83 N/mm at 135° (P = .008).

CONCLUSIONS

Anchors placed at more acute angles, that is, anchors placed closer to the so-called deadman's angle, failed at lower loads and provided less construct stiffness than anchors placed at angles greater than 90°. Stiffness also increased sequentially from an angle of insertion of 90° up to our maximum angle tested of 135°. For threaded metallic suture anchors, an obtuse insertion angle of 90° to 135° in relation to the line of pull of the suture and rotator cuff withstands a greater LTF and provides a stiffer construct than the more acute insertion angle advocated by the "deadman theory."

CLINICAL RELEVANCE

This study offers a biomechanical validation for optimal placement of threaded suture anchors at an angle of 90° or more, as anatomic restraints allow, from the vector of pull of the attached suture and rotator cuff, rather than the 45° angle recommended by the deadman theory.

A new anchor augmentation technique with a cancellous screw in osteoporotic rotator cuff repair: an in vitro biomechanical study on sheep humerus specimens

PURPOSE

The aim of this study was to test a simple technique to augment the pullout resistance of an anchor in an over-drilled sheep humerus model.

METHODS

Sixty-four paired sheep humeri were harvested from 32 male sheep aged 18 months. Specimens were divided into an augmented group and non-augmented group. FASTIN RC 5-mm titanium screw anchors (DePuy Mitek, Raynham, MA) double loaded with suture material (braided polyester, nonabsorbable USP No. 2) were used in both groups. Osteoporosis was simulated by over-drilling with a 4.5-mm drill. Augmentation was performed by fixing 1 of the sutures 1.5 cm inferior to the anchor insertion site with a washer screw. This was followed by a pull-to-failure test at 50 mm/min. The ultimate load (the highest value of strength before anchor pullout) was recorded. A paired t test was used to compare the biomechanical properties of the augmented and non-augmented groups.

RESULTS

In all specimens the failure mode was pullout of the anchor. The ultimate failure loads were statistically significantly higher in the augmented group (P < .0001). The mean pullout strength was 121.1 ± 10.17 N in the non-augmented group and 176.1 ± 10.34 N in the augmented group.

CONCLUSIONS

The described augmentation technique, which is achieved by inferior-lateral fixation of 1 of the sutures of the double-loaded anchor to a fully threaded 6.5-mm cancellous screw with a washer, significantly increases the ultimate failure loads in the over-drilled sheep humerus model.

CLINICAL RELEVANCE

Our technique is simple, safe, and inexpensive. It can be easily used in all osteoporotic patients and will contribute to the reduction of anchor failure. This technique might be difficult to apply arthroscopically. Cannulated smaller screws would probably be more practical for arthroscopic use. Further clinical studies are needed.

Effect of configuration on the biomechanical performance of three suture materials used in combination with a metallic bone anchor

OBJECTIVE

To determine whether different suture configurations could improve the biomechanical performance of 3 suture materials used with bone anchors.

SAMPLES

3 suture materials (60-lb test nylon leader line, size 2 polyblend polyethylene composite suture, and 150-lb test ultrahigh-molecular weight spun polyethylene). PROCEDURES-Each suture material was looped through the eyelet of a metallic bone anchor and constructs were evaluated by use of an acute uniaxial load. Three configurations were tested for each suture material: single stranded (SS), double stranded (DS), and single stranded plus plastic insert (SSP). Force at failure, extension at failure, force at 3 mm of extension, stiffness, and site of failure of the suture were recorded for each test.

RESULTS

For all sutures, the DS configuration was the stiffest and yielded significantly higher forces at failure and forces at 3 mm of extension. The SS configuration had the lowest forces at failure. The SSP configuration yielded greater forces at failure for all suture materials, compared with the SS configuration, with a comparable stiffness. All sutures failed at the eyelet in the SS and DS configurations. In the SSP configuration, 60-lb test nylon leader line and 150-lb test ultrahigh-molecular weight spun polyethylene failed at the eyelet less frequently than did the polyblend composite suture.

CONCLUSIONS AND CLINICAL RELEVANCE

Among the tested constructs, a DS suture configuration used in combination with the metallic bone anchor gave the best biomechanical results for all suture materials. Considering that the SSP configuration yielded greater forces at failure, compared with the SS configuration, covering metallic edges in bone anchors with softer materials might protect sutures and result in increased forces at failure.

Pullout strength of all suture anchors in the repair of rotator cuff tears: a biomechanical study

PURPOSE

We evaluated the biomechanical strength of two all suture anchors (ASA) of reduced diameter (1.4 mm) and compared them with the standard screw anchor (SA) with larger diameter (5.5 mm) used in rotator cuff tears.

METHODS

We conducted 30 uniaxial vertical pullout tests using Material Testing System Instron 5566A until failure of the anchorage defined as rupture of the threads or anchor or detachment of the anchor. Anchor fixation was on tuberosities of fresh bovine humerus bone. ASAs were spaced four millimetres apart and were compared with a control SA implanted on the same greater tubercle at two centimetres. The tests were all performed at room temperature in a dry environment. Tensile loads (10 mm/min) were applied parallel to the axis of insertion. A preloading of 10 N was used to overcome loading artifacts of the test sample at the beginning of the test.

RESULTS

Student's t test showed no statistically significant difference between anchors in terms of load to failure (ASA: force 265.06 ± 87.25 N versus SA : 325.35 ± 113.46 N; p = 0.09) and mean elongation at rupture (ASA : 23 ± 7 mm versus SA : 21 ± 6 mm; p = 0.46).

CONCLUSIONS

In vitro, this experimental study showed no statistically significant difference in pullout strength and displacement between ASA and SA at a chosen level of significance (p < 0.05).

In vitro acute load to failure and eyelet abrasion testing of a novel veterinary screw-type mini-anchor design

OBJECTIVE

To determine acute load to failure (ALF) and suture abrasion (SA) at 0° and 90° for a novel screw-type mini-anchor design.

STUDY DESIGN

Biomechanical in vitro study.

SAMPLE POPULATION

Synthetic bone.

METHODS

Twenty mini-anchors were inserted into synthetic bone blocks assigned to 1 of 2 groups (0° ALF, 90° ALF). Pullout was performed at 5 mm/min. ALF, yield strength and stiffness were calculated. SA constructs were created with 4 groups of 5 anchors each with either 30 lb nylon leader line (NLL), 40 lb NLL, #2 Fiberwire or #5 Fiberwire. SA was performed at 0° and 90° with a sinusoidal wave form at 0.5 Hz and 10 N load for 1000 cycles or until failure. Data were summarized as mean ± SD. ALF data were analyzed using t-tests. SA data were analyzed using log rank, Tukey-adjusted pairwise comparisons and sign tests. Significance was set at P = .05.

RESULTS

Mean ± SD ALF at 0° and 90° was 431.8 ± 70.8 N and 683 ± 48.7 N, respectively. 90° ALF was significantly higher. Yield strength and stiffness were not significantly different at 0° and 90°. #5 and #2 Fiberwire survived significantly more cycles than 40 lb and 30 lb NLL at 90°. At 0°, 30 lb NLL survived significantly less cycles than either Fiberwire size. Suture orientation did not have a significant effect on SA for Fiberwire constructs.

CONCLUSION

The novel mini-anchor has ALF comparable to other mini-anchors. Fiberwire survived more cycles in the novel anchor eyelet than NLL and FW suture orientation in the eyelet did not affect SA.

The effects of low-intensity pulsed ultrasound on tendon-bone healing in a transosseous-equivalent sheep rotator cuff model

PURPOSE

The purpose of this study was to examine the effects Low-intensity Pulsed Ultrasound has on initial tendon-bone healing in a clinically relevant extra-articular transosseous-equivalent ovine rotator cuff model.

METHODS

Eight skeletally mature wethers, randomly allocated to either control group (n = 4) or treatment group (n = 4), underwent rotator cuff surgery following injury to the infraspinatus tendon. All animals were killed 28 days post surgery to allow examination of early effects of Low-intensity Pulsed Ultrasound treatment.

RESULTS

General improvement in histological appearance of tendon-bone integration was noted in the treatment group. Newly formed woven bone with increased osteoblast activity along the bone surface was evident. A continuum was observed between the tendon and bone in an interdigitated fashion with Sharpey's fibres noted in the treatment group. Low-intensity Pulsed Ultrasound treatment also increased bone mineral density at the tendon-bone interface (p < 0.01), while immunohistochemistry results revealed an increase in the protein expression patterns of VEGF (p = 0.038), RUNX2 (p = 0.02) and Smad4 (p = 0.05).

CONCLUSIONS

The results of this study indicate that Low-intensity Pulsed Ultrasound may aid in the initial phase of tendon-bone healing process in patients who have undergone rotator cuff repair. This treatment may also be beneficial following other types of reconstructive surgeries involving the tendon-bone interface.

Bending and abrasion fatigue of common suture materials used in arthroscopic and open orthopedic surgery

In orthopedic surgery, the reattachment of tendon to bone requires suture materials that have stable and durable properties to allow time for healing at the tendon-bone interface. The suture, not rigidly restrained within the anchor eyelet, is free to move during surgery and potentially after surgery with limb motion. During such movement, the suture is subjected to bending and frictional forces that can lead to fatigue-induced failure. We investigated some common contemporary commercial number-two-grade suture materials and evaluated their resistance to bending abrasion fatigue and the consequent failure. Sutures were oscillated over a stainless steel wire at low frequency under load. Number of abrasion cycles to failure, changes in suture morphology, and fatigue-failure method was recorded for each material. Suture structure had a significant effect on abrasion resistance, with braided sutures containing large numbers of fine high tenacity core filaments performing 15-20 times better than other braided suture structures. Ultra high molecular weight polyethylene (UHMWPE) core filaments resisted bending abrasion failure better than other core materials due to the load spreading and abrasion resistance of these filaments. Sutures with UHMWPE cores also had high resistance to tensile failure. Limited correlation was observed between tensile strength and abrasion resistance.

Analysis of suture anchor eyelet position on suture failure load

OBJECTIVE

To compare mechanical performance of 2 orientations of the 5 mm Corkscrew® suture anchor with #5 Fiberwire® .

STUDY DESIGN

In vitro biomechanical study.

SAMPLE POPULATION

Suture anchor-suture constructs (n=40).

METHODS

Acute and cyclic tensile loads were applied to suture threaded through eyelets of 40 anchors perpendicular to the long axis of the anchor. Eyelets were positioned so that the suture pull was in line with (anchor rotation angle of 0° [ARA 0]) or 90° (ARA 90) to the eyelet plane. Load at failure, stiffness, and cycles to failure were determined.

RESULTS

All constructs failed by suture breakage at the eyelet. Mean load at failure was significantly higher in the ARA 90 group (634 ± 93 N) compared with the ARA 0 group (495 ± 52 N; P=.0015). No significant difference was found between groups for mean number of cycles to failure (270 ± 177 versus 178 ± 109; P=.2166) and stiffness (50 ± 4 versus 48 ± 5 N/mm; P=.3141).

CONCLUSIONS

The Corkscrew® 5 mm suture anchor with Fiberwire® suture fails via suture breakage at the eyelet under higher acute loads if the suture is loaded at an angle of 90° compared with 0° with respect to the plane of the eyelet.

A comparison of knot security and loop security in arthroscopic knots tied with newer high-strength suture materials

PURPOSE

The purpose of this study was to compare the knot security and loop security of 2 sliding and 1 static arthroscopic knot tied with different types of suture material.

METHODS

We evaluated 3 commonly used arthroscopic knots (surgeon's knot, Roeder knot, and Weston knot) tied with 6 different braided No. 2 sutures (FiberWire [Arthrex, Naples, FL]; Ethibond [Ethicon, Somerville, NJ]; Orthocord [DePuy Mitek, Raynham, MA]; Herculine [now called HiFi; ConMed Linvatec, Largo, FL]; MaxBraid [Arthrotek, Warsaw, IN]; and UltraBraid [Smith & Nephew, Andover, MA]). Each suture loop was then mounted on a materials testing system, and its circumference was measured at a 5-N preload to assess each knot's ability to maintain a tight suture loop without slippage (loop security). Knot security was measured as the maximum force to failure at 3 mm of crosshead displacement or suture breakage during single-pull load testing.

RESULTS

We found that tying knots with different types of suture material can affect both the knot security and loop security of various types of arthroscopic knots. When a Roeder knot or surgeon's knot was tied, No. 2 FiberWire had the highest force to failure when compared with similar knots tied with other suture material (P < .001). The loop security for many of the knot and suture configurations was not significantly different. However, No. 2 FiberWire consistently showed the smallest loop circumference when compared with other suture materials.

CONCLUSIONS

Arthroscopic knots tied with No. 2 FiberWire provide superior knot security and similar loop security compared with other commonly used high-strength polyethylene suture materials.

CLINICAL RELEVANCE

High-strength sutures exhibit unique mechanical characteristics that may vary significantly between suture types. In addition, knot configuration plays an important role in altering these characteristics as they relate to knot security.

Biomechanical stability of knotless suture anchors used in rotator cuff repair in healthy and osteopenic bone

PURPOSE

The primary stability of 5 new knotless suture anchors was compared in healthy and osteopenic humeri by use of the following anchor systems: Opus Magnum 2 (ArthroCare, Austin, TX), PushLock (Arthrex, Naples, FL), SwiveLock (Arthrex), Kinsa RC (Smith & Nephew, London, England), and Versalok (DePuy Mitek, Raynham, MA).

METHODS

Twenty healthy and 20 osteopenic, macroscopically intact humeri with mean ages of 47 and 72 years, respectively, and mean bone mineral densities of 139.8 mg of calcium hydroxyapatite (Ca2+-HA) per milliliter and 51.8 mg of calcium hydroxyapatite per milliliter, respectively, were used. Cyclic loading was performed to simulate postoperative conditions. The maximum failure load (F(max)), the system displacement, and the modes of failure were recorded.

RESULTS

SwiveLock had the highest mean F(max) in healthy humeri, followed by Versalok, PushLock, Kinsa RC, and Opus Magnum 2, with SwiveLock and Versalok being statistically superior to Opus Magnum 2. In osteopenic humeri Versalok had the highest mean F(max), followed by Opus Magnum 2, SwiveLock, Kinsa RC, and PushLock, with no significant differences between all tested anchors. The Versalok anchor showed the shortest system displacement in healthy humeri, with 1.06 mm, and in osteopenic humeri, with 1.47 mm. In healthy humeri the system displacement of all anchors lay under the clinical failure threshold of 5 mm. In osteopenic humeri the PushLock clearly exceeded the clinical failure threshold, with 16.11 mm, whereas the other anchors were notably below the 5-mm threshold, with solitary measurements exceeding it.

CONCLUSIONS

Every tested anchor presented different problems that may lead to premature failure of the rotator cuff reconstruction. Knotless suture anchors show differences in primary stability depending on the bone quality of the greater tuberosity, the anchorage mechanism in the bone, the suture-retaining mechanism, and the anchor design. Nevertheless, cortical screw type and subcortical wedging anchors tend to show better primary stability than other designs.

CLINICAL RELEVANCE

Anchor design and bone quality play important roles in the stability of the rotator cuff repair.

Techniques for suture anchor removal in shoulder surgery

Although suture anchor complications after arthroscopic shoulder surgery are uncommon, they can be devastating, such as articular cartilage or bone loss secondary to a dislodged or prominent suture anchor. Proper insertion of the anchor is the most important factor in the prevention of this complication, but if a complication occurs, prompt recognition and treatment are important to prevent damage to the shoulder. The goals were to (1) discuss strategies for preventing or dealing with dislodged or prominent suture anchors and (2) introduce techniques for removal of these implants.

The primary stability of the hip transposition type IIb: a biomechanical in vitro study

BACKGROUND

The hip transposition is firmly established in pelvic sarcoma surgery. However, the primary stability of the hip transposition has not been tested yet so that the mobilisation, respectively the immobilisation of the patient so far solely relied on the experience of the surgeon. The aim of this study was to test the primary stability reliably with the help of a model and to reveal possible differences in stability between currently used anchor systems (TwinFix 6.5 and MITEK SuperAnchor).

METHODS

A biomechanical model of porcine sacra was developed to document the maximum load capacity (load to failure test) and the performance under cyclic load (100 N, 200 N, 350 N, 700 N, 1400 N, each with 1000 cycles), 28 sacra were tested in total. Macroscopic damages, displacement, yield load, stiffness and F(max) were recorded as well.

FINDINGS

The load to failure test results showed a 3.9 times higher maximum load capacity for the TwinFix 6.5 anchor (1307 N) compared to the MITEK SuperAnchor (334N). The cyclical test revealed that nearly all MITEK SuperAnchors failed at a load of 350 N. In contrast, the TwinFix 6.5 anchors resisted 4000 cycles up to a load of 1400 N.

INTERPRETATION

The TwinFix 6.5 anchor proved to be clearly superior to the MITEK SuperAnchor, resulting in the adjustment of the reconstruction technique. Therefore, the immobilisation period of a patient after a hip transposition type IIb could be shortened according to the results of the primary stability test.

Rotator cuff tears: pathology and repair

By virtue of its anatomy and function, the rotator cuff is vulnerable to considerable morbidity, often necessitating surgical intervention. The factors contributing to cuff disease can be divided into those extrinsic to the rotator cuff (most notably impingement) and those intrinsic to the cuff (age-related degeneration, hypovascularity and inflammation amongst others). In an era of emerging biologic interventions, our interventions are increasingly being modulated by our understanding of these core processes, many of which remain uncertain today. When we do intervene surgically, the techniques we employ are particularly challenging in the context of the tremendous pace of advancement. Several recent studies have shown that arthroscopic repair gives similar functional results to that of mini-open and open procedures, with all the benefits of minimally invasive surgery. However, the 'best' repair construct remains unknown, with wide variations in surgeon preference. Here we present a literature review encompassing recent developments in our understanding of basic science in rotator cuff disease as well as an up-to-date evidence-based comparison of different techniques available to the surgeon for cuff repair.

Interference screw versus suture anchor fixation for subpectoral tenodesis of the proximal biceps tendon: a cadaveric study

PURPOSE

The purpose of this study was to compare the biomechanical properties of 2 fixation methods for subpectoral proximal biceps tenodesis.

METHODS

In 9 matched pairs of cadaveric shoulders, an open subpectoral tenodesis was performed 1 cm proximal to the inferior border of the pectoralis major tendon by use of either an 8 x 12-mm Bio-Tenodesis screw (Arthrex, Naples, FL) with No. 2 FiberWire sutures (Arthrex) or a 5.5-mm Bio-Corkscrew double-loaded suture anchor (Arthrex) with No. 2 FiberWire sutures. The specimens were dissected and mounted in a material testing machine. Cyclic loading (20 to 60 N, 100 cycles, 0.5 mm/s, 5-N preload) was performed, followed by an unloaded 30-minute rest, a 5-N preload, and a load-to-failure protocol (1.25 mm/s) with a 100-lb load cell. Ultimate load (in Newtons), stiffness (in Newtons per millimeter), and modes of failure were recorded. Data were analyzed by use of paired t tests and Wilcoxon signed rank tests.

RESULTS

Proximal biceps tenodeses with Bio-Tenodesis screws had a significantly higher mean load to failure (169.6 +/- 50.5 N; range, 99.6 to 244.7 N) than those with Bio-Corkscrew suture anchors (68.5 +/- 33.0 N; range, 24.2 to 119.4 N) (P = .002). Bio-Tenodesis screws also had a significantly higher stiffness (34.1 +/- 9.0 N/mm; range, 20.6 to 48.9 N/mm) than Bio-Corkscrews (19.3 +/- 10.5; range, 5.9 to 32.9 N/mm) (P = .038).

CONCLUSIONS

In this cadaveric study the Bio-Tenodesis screw showed a statistically significantly higher load to failure and significantly higher stiffness than the Bio-Corkscrew anchor when used for tenodesis of the proximal biceps tendon in a subpectoral location.

CLINICAL RELEVANCE

Biomechanical comparison of these 2 fixation techniques provides information on stiffness and load to failure of alternate fixation methods.

Influence of suture material on the biomechanical behavior of suture-tendon specimens: a controlled study in bovine rotator cuff

BACKGROUND

Despite technical advances in rotator cuff surgery, recurrent or persistent defects in the repaired tendon continue to occur. Improved strength of sutures and suture anchors has resulted in the most common site of failure being the suture-tendon interface.

HYPOTHESIS

The type of suture material used has a significant effect on the biomechanics of the suture-tendon interface.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-two bovine infraspinatus specimens were randomly assigned to simple suture fixation using No. 2 Fiberwire, Ultrabraid, Orthocord, or Ethibond. Each specimen was subjected to cyclic testing from 5 to 30 N for 30 cycles, followed by load-to-failure testing.

RESULTS

Cyclic testing revealed significantly greater elongation with Ultrabraid, whereas peak-to-peak displacements were lowest for Fiberwire and greatest for Orthocord. Load-to-failure testing revealed no significant differences between any suture material for ultimate tensile load. Fiberwire and Orthocord repairs had the highest stiffness. The most common failure mode during load-to-failure testing was suture breakage in Ethibond specimens and suture cutting through the tendon in the polyblend suture specimens.

CONCLUSION

The type of suture material has a significant effect on the biomechanical behavior of the suture-tendon interface.

CLINICAL RELEVANCE

The type of suture may influence early gap formation and ultimate healing of rotator cuff repairs.

In vitro characteristics of a bioabsorbable suspension screw and suture system for endoscopic brow lift surgery

The time requirement for endoscopic subperiosteal brow lift fixation is as little as 10-14 days. Many types of bioabsorbable fixation have been applied to this procedure, including bioabsorbable suture coupled with a bioabsorbable bone anchor, with excellent outcomes. Typically, the anchor and suture materials differ, each having their own hydrolytic strength loss profile. The dynamic relationship between the instantaneous state of degradation of the bone anchor and the suture components can affect fixation strength and failure mode, a poorly understood phenomenon. We examined the use of 2x5 mm PLLA-PGA (82:18) copolymer screws containing a suture eyelet in the head, paired with one of four types of bioabsorbable suture (2-0 and 3-0 Vicryl and 2-0 and 3-0 PDS-II), in a model system designed to mimic brow lift fixation. Constructs were inserted into a synthetic bone substrate and incubated in pH 7.4 buffer at 37 degrees C for up to 3 weeks, then loaded to failure. Initial failure loads were dependent upon suture size but not suture material, with 2-0 suture constructs (63-70N) failing at twice the load of the 3-0 suture constructs (30-35N). The following 3 week strength retentions were obtained: 40-55% for 2-0 and 3-0 Vicryl suture, 100% for 3-0 PDS-II suture, and 58% for 2-0 PDS-II suture constructs. The predominant failure mode was suture breakage at the knot, with the later intervals utilizing 2-0 PDS-II suture including some screw head failures. This suspension screw, when coupled with an appropriate suture, appears to have suitable mechanical properties for endoscopic brow lift fixation.

Biomechanical fixation in arthroscopic rotator cuff repair

Rotator cuff repair remains a challenging and rapidly evolving field. Several recent studies have shown that arthroscopic repair yields functional results similar to those of mini-open and open procedures, with all of the benefits of minimally invasive surgery. However, the "best" repair construct remains relatively unknown, with wide variations in surgeon preference and conflicting evidence in the literature. The most recent developments in basic science, suture and suture anchor technology, and innovative prospects for arthroscopic rotator cuff repair are reviewed.

Strength of damaged suture: an in vitro study

PURPOSE

To determine the mechanical properties of damaged suture.

METHODS

Undamaged and damaged sutures were tested by a single pull to failure. Sutures were damaged with a razor blade incorporated into a custom-designed jig. Sutures were tested to failure by straight pull and by pulling at 180 degrees through a suture anchor eyelet. The friction of sutures through anchors was also tested.

RESULTS

For the straight line pull test, undamaged FiberWire (Arthrex, Naples, FL) had the highest load to failure (LTF) and ultimate tensile strength (UTS) of all sutures tested. Undamaged Orthocord (Mitek, Somerville, NJ) ranked second in both properties. Uncut polydioxanone (PDS) suture (Ethicon, Somerville, NJ) had a higher LTF and a comparable UTS with respect to Tevdek (Deknatel, Mansfield, MA) and Ethibond (Ethicon). For cut sutures, FiberWire and Orthocord had a significantly higher LTF and UTS than the other sutures tested. Suture stiffness was not significantly affected when the suture was cut. For the suture anchor test, FiberWire and Orthocord had the highest LTF, whether undamaged or damaged. When cut, PDS had the greatest loss of LTF and UTS during both tests.

CONCLUSIONS

The newer polyethylene core sutures (FiberWire and Orthocord) have superior mechanical properties compared with other sutures. Their superior properties are maintained even when cut. Although uncut PDS had equivalent or superior strength compared with Ethibond and Tevdek, once cut, PDS suture was weakened significantly more compared with all other sutures tested.

CLINICAL RELEVANCE

The mechanical properties of damaged suture are important to all surgeons who use suture arthroscopically.

Triple-loaded single-anchor stitch configurations: an analysis of cyclically loaded suture-tendon interface security

PURPOSE

This study evaluated the strength and suture-tendon interface security of different suture configurations from triple-suture-loaded anchors.

METHODS

A juvenile bovine infraspinatus tendon was detached and repaired by use of 4 different suture combinations from 2 suture anchors: 3 simple sutures in each anchor (ThreeVo anchor; Linvatec, Largo, FL); 2 peripheral simple stitches and 1 central horizontal mattress suture passed deeper into the tendon, creating a larger footprint (bigfoot-print anchor); 2 peripheral simple stitches with 1 central horizontal mattress stitch passed through the same holes as the simple sutures (stitch-of-Burns); and 2 simple stitches (TwoVo anchor; Linvatec). The constructs were cyclically loaded between 10 N and 180 N for 3,500 cycles and then destructively tested. The number of cycles required to create a 5-mm gap and a 10-mm gap and the ultimate load to failure and failure mode were recorded.

RESULTS

The ThreeVo anchor was strongest and most resistant to cyclic loading (P < .01). The TwoVo anchor was least resistant to cyclic loading. The stitch-of-Burns anchor was more resistant to cyclic loading than both the bigfoot-print anchor and the TwoVo anchor (P < .03). The ThreeVo, stitch-of-Burns, and TwoVo anchors were stronger than the bigfoot-print anchor (P < .05).

CONCLUSIONS

Three simple sutures in an anchor hold better than two simple sutures. Three simple sutures provide superior suture-tendon security than combinations of one mattress and two simple stitches subjected to cyclic loading. A central mattress stitch placed more medially than two peripheral simple stitches (bigfoot-print anchor) configured to enlarge the tendon-suture footprint was not as resistant to cyclic loading or destructive testing as three simple stitches (ThreeVo anchor).

CLINICAL RELEVANCE

Placing a central mattress stitch more medially than 2 peripheral simple stitches to enlarge the tendon-suture footprint was not as resistant to cyclic loading or destructive testing as 3 simple stitches.