A biomechanical analysis of point of failure during lateral-row tensioning in transosseous-equivalent rotator cuff repair

All-Suture Anchors: Biomechanical Analysis of Pullout Strength, Displacement, and Failure Mode

PURPOSE

To evaluate the biomechanical and design characteristics of all-suture anchors.

METHODS

All-suture anchors were tested in fresh porcine cortical bone and biphasic polyurethane foam blocks by cyclic loading (10-100 N for 200 cycles), followed by destructive testing parallel to the insertion axis at 12.5 mm/s. Endpoints included ultimate failure load, displacement at 100 and 200 cycles, stiffness, and failure mode. Anchors tested included JuggerKnot (1.4, 1.5, and 2.8), Iconix (1, 2, and 3), Y-knot (1.3, 1.8, and 2.8), Q-Fix (1.8 and 2.8), and Draw Tight (1.8 and 3.2).

RESULTS

The mean ultimate failure strength of the triple-loaded anchors (564 ± 42 N) was significantly greater than the mean ultimate failure strength of the double-loaded anchors (465 ± 33 N) (P = .017), and the double-loaded anchors were stronger than the single-loaded anchors (256 ± 35 N) (P < .0001). No difference was found between the results in porcine bone and biphasic polyurethane foam. None of these anchors demonstrated 5 mm or 10 mm of displacement during cyclic loading. The Y-Knot demonstrated greater displacement than the JuggerKnot and Q-Fix (P = .025) but not the Iconix and Draw Tight (P > .05). The most common failure mode varied and was suture breaking for the Q-Fix (97%), JuggerKnot (81%), and Iconix anchors (58%), anchor pullout with the Draw Tight (76%), whereas the Y-Knot was 50% suture breaking and 50% anchor pullout.

CONCLUSIONS

The ultimate failure load of an all-suture anchor is correlated directly with its number of sutures. With cyclic loading, the Y-Knot demonstrated greater displacement than the JuggerKnot and Q-Fix but not the Iconix and Draw Tight. JuggerKnot (81%) and Q-Fix (97%) anchors failed by suture breaking, whereas the Draw Tight anchor failed by anchor pullout (76%).

CLINICAL RELEVANCE

All-suture anchors vary in strength and performance, and these factors may influence clinical success. Biphasic polyurethane foam is a validated model for suture anchor testing.

Comparison of Passive Stiffness Changes in the Supraspinatus Muscle After Double-Row and Knotless Transosseous-Equivalent Rotator Cuff Repair Techniques: A Cadaveric Study

PURPOSE

To investigate the alteration of passive stiffness in the supraspinatus muscle after double-row (DR) and knotless transosseous-equivalent (KL-TOE) repair techniques, using shear wave elastography (SWE) in cadavers with rotator cuff tears. We also aimed to compare altered muscular stiffness after these repairs to that obtained from shoulders with intact rotator cuff tendon.

METHODS

Twelve fresh-frozen cadaveric shoulders with rotator cuff tear (tear size: small [6], medium-large [6]) were used. Passive stiffness of 4 anatomic regions in the supraspinatus muscle was measured based on an established SWE method. Each specimen underwent DR and KL-TOE footprint repairs at 30° glenohumeral abduction. SWE values, obtained at 0°, 10°, 20°, 30°, 60°, and 90° abduction, were assessed in 3 different conditions: preoperative (torn) and postoperative conditions with the 2 techniques. The increased ratio of SWE values after repair was compared among the 4 regions to assess stiffness distribution. In addition, SWE values were obtained on 12 shoulders with intact rotator cuff tendons as control.

RESULTS

In shoulders with medium-large-sized tears, supraspinatus muscles showed an increased passive stiffness after rotator cuff repairs, and this was significantly observed at adducted positions. KL-TOE repair showed uniform stiffness changes among the 4 regions of the supraspinatus muscle (mean, 189% to 218% increase after repair), whereas DR repair caused a significantly heterogeneous stiffness distribution within the muscle (mean, 187% to 319% after repair, P = .002). Although a repair-induced increase in muscle stiffness was observed also in small-sized tears, there were no significant differences in repaired stiffness changes between DR and KL-TOE (mean, 127% to 138% and 127% to 130% after repairs, respectively). Shoulders with intact rotator cuff tendon showed uniform SWE values among the 4 regions of the supraspinatus muscle (mean, 38.2 to 43.0 kPa).

CONCLUSIONS

Passive stiffness of the supraspinatus muscle increases after rotator cuff repairs for medium-large-sized tears. KL-TOE technique for the medium-large-sized tear provided a more uniform stiffness distribution across the repaired supraspinatus muscles compared with the DR technique.

CLINICAL RELEVANCE

Based on this insight, investigating rotator cuff muscle stiffness changes, further studies using SWE may determine the optimal repair technique for various sizes of rotator cuff tears.

Biomechanical Effect of Margin Convergence Techniques: Quantitative Assessment of Supraspinatus Muscle Stiffness

Although the margin convergence (MC) technique has been recognized as an option for rotator cuff repair, little is known about the biomechanical effect on repaired rotator cuff muscle, especially after supplemented footprint repair. The purpose of this study was to assess the passive stiffness changes of the supraspinatus (SSP) muscle after MC techniques using shear wave elastography (SWE). A 30 × 40-mm U-shaped rotator cuff tear was created in 8 cadaveric shoulders. Each specimen was repaired with 6 types of MC technique (1-, 2-, 3-suture MC with/without footprint repair, in a random order) at 30° glenohumeral abduction. Passive stiffness of four anatomical regions in the SSP muscle was measured based on an established SWE method. Data were obtained from the SSP muscle at 0° abduction under 8 different conditions: intact (before making a tear), torn, and postoperative conditions with 6 techniques. MC techniques using 1-, or 2-suture combined with footprint repair showed significantly higher stiffness values than the intact condition. Passive stiffness of the SSP muscle was highest after a 1-suture MC with footprint repair for all regions when compared among all repair procedures. There was no significant difference between the intact condition and a 3-suture MC with footprint repair. MC techniques with single stitch and subsequent footprint repair may have adverse effects on muscle properties and tensile loading on repair, increasing the risk of retear of repairs. Adding more MC stitches could reverse these adverse effects.

Gap formation in a transosseous rotator cuff repair as a function of bone quality

BACKGROUND

The transosseous approach has been well known for a long time as a valid repair approach. Over time, various criticisms have been raised over this technique principally classifiable in two main categories: technical difficulty and related reproducibility in an arthroscopic environment, and repair stability (in the suture-bone contact area). About cyclic performance, several authors have conceived test setups with the aim of simulating a real environment in dynamic load conditions. The aim of this study was to monitor gap formation in a cyclic test setup.

METHODS

The performance (measured as gap formation) has been monitored as a function of bone density to verify the effect of the latter. The test blocks have been shaped using sawbones® test bricks (Malmo, Sweden) of different densities, and the following values have been tested: 10, 15, 20, 30 and 40pcf.

FINDINGS

The comparison has been made between the two groups: traditional transosseous and new approach with an interposed device. Regarding the traditional transosseous approach in a 10-pcf environment, not even the first loading cycle was completed, the whole bone bridge was destroyed in the first loading ramp and no further loading capability was present in the repair. By increasing the block density, the surface damage in the suture-block contact decreased.

INTERPRETATION

With this work, it has been demonstrated how the traditional transosseous approach is strongly influenced by the bone quality up to the point where, in certain conditions, a safe and reliable repair is not guaranteed.

Cyclic biomechanical testing of biocomposite lateral row knotless anchors in a human cadaveric model

PURPOSE

The purpose of this study was to assess the mechanical performance of biocomposite knotless lateral row anchors based on both anchor design and the direction of pull.

METHODS

Two lateral row greater tuberosity insertion sites (anterior and posterior) were identified in matched pairs of fresh-frozen human cadaveric shoulders DEXA (dual energy X-ray absorptiometry) scanned to verify comparability. The humeri were stripped of all soft tissue and 3 different biocomposite knotless lateral row anchors: HEALIX Knotless BR (DePuy Mitek, Raynham MA), BioComposite PushLock (Arthrex, Naples, FL), and Bio-SwiveLock (Arthrex). Fifty-two anchors were distributed among the insertion locations and tested them with either an anatomic or axial pull. A fixed-gauge loop (15 mm) of 2 high-strength sutures from each anchor was created. After a 10-Nm preload, anchors were cycled from 10 to 45 Nm at 0.5 Hz for 200 cycles and tested to failure at 4.23 mm/second. The load to reach 3 mm and 5 mm displacement, ultimate failure load, displacement at ultimate failure, and failure mode were recorded.

RESULTS

Threaded anchors (Bio-SwiveLock, P = .03; HEALIX Knotless, P = .014) showed less displacement with anatomic testing than did the nonthreaded anchor (BioComposite PushLock), and the HEALIX Knotless showed less overall displacement than did the other 2 anchors. The Bio-SwiveLock exhibited greater failure loads than did the other 2 anchors (P < .05). Comparison of axial and anatomic loading showed no maximum load differences for all anchors as a whole (P = .1084). Yet, anatomic pulling produced higher failure loads than did axial pulling for the Bio-SwiveLock but not for the BioComposite PushLock or the HEALIX Knotless. The nonthreaded anchor (BioComposite PushLock) displayed lower failure loads than did both threaded anchors with axial pulling.

CONCLUSIONS

Threaded biocomposite anchors (HEALIX Knotless BR and Bio-SwiveLock) show less anatomic loading displacement and higher axial failure loads than do the nonthreaded (BioComposite PushLock) anchor. The HEALIX Knotless BR anchor showed less displacement than did the BioComposite PushLock and Bio-SwiveLock anchors. Neither axial nor anatomic loading had an effect on overall anchor displacement.

CLINICAL RELEVANCE

Because of the strength profiles exhibited, this study supports the use of biocomposite anchors, which have definite advantages over polyetheretherketone (PEEK) and metal products. However, the nonthreaded BioComposite PushLock anchor cannot be recommended.

Cyclic loading biomechanical analysis of the pullout strengths of rotator cuff and glenoid anchors: 2013 update

PURPOSE

The purpose of this study was to evaluate the biomechanical and design characteristics of newer suture anchors under cyclic loading.

METHODS

Suture anchors were tested in fresh porcine cortical and cancellous bone by cyclic loading (10 to 100 N for 200 cycles) followed by destructive testing parallel to the insertion axis at 12.5 mm per second. End points included ultimate failure load, displacement at 100 and 200 cycles, failure mode, and stiffness. Anchors tested included ReelX (Stryker Endoscopy, San Jose, CA); Footprint Ultra PK (4.5 and 5.5 mm) (Smith & Nephew, Andover, MA); TwinFix (4.5, 5.5, and 6.5 mm made from polyether ether ketone [PEEK], hydroxyapatite [HA], and titanium [Ti]) (Smith & Nephew Endoscopy, Andover, MA); Morphix (2.5 and 5.5 mm) (MedShape Solutions, Atlanta, GA); CrossFT BC (ConMed-Linvatec, Largo, FL); JuggerKnot (1.5 and 2.8 mm) (Biomet Sports Medicine, Warsaw, IN); Healicoil (Smith & Nephew Endoscopy, Andover, MA); Quattro (X, Link, and GL) (Cayenne Medical, Scottsdale, AZ); Healix (Biocryl Rapide [BR], PEEK, and Ti) (DePuy Mitek, Raynham, MA); Twin Loop (3.5 mm, PEEK) (Stryker Endoscopy, San Jose, CA); PressFT (2.1 and 2.6 mm) (ConMed Linvatec, Largo FL); Y-Knot (ConMed Linvatec, Largo FL); Gryphon (BR and PEEK) (DePuy Mitek, Raynham, MA); and Iconix (1, 2, and 3) (Stryker Endoscopy, San Jose, CA).

RESULTS

Rotator cuff anchors showed greater failure loads than did glenoid anchors in metaphyseal bone (rotator cuff anchors 448 N v glenoid anchors 296 N) (P = .001) and cancellous bone (rotator cuff anchors 435 N v glenoid anchors 225 N) (P < .001). No anchors reached 5 mm of displacement during cyclic loading. TwinFix anchors showed greater displacement at 100 (P = .014) and 200 cycles (P = .036) than did other rotator cuff anchors, although the ReelX and Morphix showed the greatest displacements. Rotator cuff anchors failed principally by eyelet breaking, whereas glenoid anchors failed more often by anchor pullout than by any other mode. No differences in stiffness were observed across the different rotator cuff and glenoid anchors tested.

CONCLUSIONS

Rotator cuff anchors showed higher failure strengths than did glenoid anchors, regardless of bone type. TwinFix anchors showed more cyclic displacement than did other rotator cuff anchors (except the ReelX and Morphix anchors) and the glenoid anchors tested. The failure mode was dependent on the specific anchor.

CLINICAL RELEVANCE

Suture anchor constructs tested showed that failure load is dependent on anchor type (rotator cuff anchor or glenoid anchor) but not on anchor location (cancellous or cortical bone).

Arthroscopic rotator cuff repair: techniques in 2012

Techniques for arthroscopic partial-thickness and full-thickness RTC repairs continue to advance. When selecting an RTC repair technique, it is important to identify the tear pattern and adhere to the fundamentals of tendon mobilization and footprint preparation. Partial RTC tears greater than 50% in thickness can be reproducibly repaired with tear completion or transtendinous techniques with good clinical outcomes. Based on the available literature, small, less than 1-cm RTC tears can effectively be repaired with single-row techniques. Tears sized 1 cm to 3 cm can be repaired with either single-row, double-row, or transosseous-equivalent techniques based on surgeon comfort, tendon quality, and tissue mobility. Tears greater than 3 cm have shown superior results when transosseous-equivalent techniques are used. Further clinical studies are needed to definitively conclude the ideal RTC repair technique.