Knotless Rotator Cuff Repairs – Kevin Kaplan MD

By Kevin M. Kaplan, MD

Knotless Rotator Cuff Repair in an External Rotation Model: The Importance of Medial-Row Horizontal Mattress Sutures

Kevin Kaplan, M.D., Neal S. ElAttrache, M.D.,
Oscar Vazquez, M.D., Yu-Jen Chen, M.D., and Thay Lee, Ph.D.

 

Purpose of Knotless Rotator Cuff Repair

To evaluate the effect of the addition of 2 horizontal mattress knots to the medial row of a knotless rotator cuff construct on the biomechanical properties in terms of both cyclic and failure testing parameters in an external rotation model.

 

Methods

In 8 fresh-frozen human cadaveric shoulders, a knotless transosseous repair, whereas in 8 contralateral matching-pair specimens. The addition of 2 horizontal mattress knots to the medial-row fixation. Using a custom jig to allow external rotation (0° to 30°) with loading. Using a materials testing machine to allow cyclically load repairs from 0 to 180 N for 30 cycles and then to failure. Video digitizing software was done for analysis. Data from pairs of specimens were in comparison to pairs of Student t tests.

Results

Ultimate load to failure was significantly higher in the modified construct (549 N v 311 N, P = .01). Linear stiffness in the first cycle, at the 30th cycle, and at failure was significantly higher (P = .02, P = .02, and P = .04, respectively) in the modified construct as well. Energy absorption by the  tissue under repair was significantly less in the modified construct.  This was at the first cycle, at the 30th cycle, and at ultimate load to failure (P =.03, P = .02, and P = .04, respectively).

The occurrence was significantly greater for anterior gap formation with the knotless technique. This was at the first cycle (4.55 v 1.35) and 30th cycle (7.67 mm v 1.77 mm) (P = .02).

Conclusion

The modified construct shows improvements in biomechanical properties.  When allowing for external rotation during high-load testing. Using an additional horizontal mattress from separate sutures in the medial-row anchors. This helps to neutralize forces by the repair. Clinical Relevance: The addition of medial-row fixation to a knotless construct will enhance the stability of rotator cuff repairs.  With the goal of improving patient outcomes.

Rotator Cuff Pathology

Understanding of the biomechanics and anatomy of rotator cuff pathology is important.  The stress put on the tissues during postoperative rehabilitation was the recent focus.  The goal was to create a more durable repair that provides an optimal environment for potential tendon healing.

Numerous studies provide significant data regarding the high incidence of re-tears after rotator cuff repair.1-3.  However, recent data suggests that the re-tear rate with a transosseous-equivalent suture bridge may be lower.4 DuQuin et al.5.  Reviews of 1,252 repairs from 23 studies.  They found a significantly lower re-tear rate for tears greater than 1 cm. However, the literature comparing single and double row techniques remains controversial.

Other Research

Several studies suggest that no difference exists between single-and double row repairs.  Burkhart and Cole9, state that these Level I study comparing techniques yield invalid conclusions.  With regard to standardizing the method of repair in addition to tear pattern and size.  Although there is no controversy regarding the biomechanical superiority of the transosseous repair techniques.  Finally, level I evidence does not exist to support or refute the claim that these patients have better clinical outcomes.

Outcome Studies

To make that determination, large prospective outcome studies need to be done.  Comparing patients with similar tear patterns using standardization of a single and transosseous repair constructs. A previous study outlines the potential pitfalls using a medial-row anchor.  Loading with No. 2 high strength sutures with the fixation of knotless anchors laterally.10. This study did not take into account external rotation on the repair.  Therefore, this study demonstrates the same as by Park et al.11 to affect gap formation and differential tendon strain.

Hypothesis

In this paragraph, review of recent literature with the focus on enhancing the contact between the tendon and footprint. New technology continues to develop to accomplish this task.12.  Creation of stronger and wider suture materials continues to date.  In addition, to knotless fixation constructs to maintain the biomechanics of repair constructs while simplifying the technique.

Purpose

The purpose of this study was to determine whether the addition of two No. 2 high-strength sutures tied in horizontal mattress fashion in the medial row of a knotless construct would enhance the biomechanical characteristics of the repair. Our hypothesis was that the addition of fixation would enhance the linear stiffness and energy absorption by the construct.   Thus, decreasing anterior gap formation during loading in an external rotation model.

JOI and Kerlan Jobe 

From the Jacksonville Orthopaedic Institute (K.K.), Jacksonville, Florida; Kerlan Jobe Orthopaedic Clinic (N.S.E.), Los Angeles; and Orthopaedic Biomechanics Laboratory Long Beach VA Healthcare System (O.V., Y-J.C., T.L.), Long Beach, California, U.S.A. N.S.E. is a consultant for and has patent/royalty agreements with Arthrex, Naples, Florida. The Kerlan Jobe Orthopaedic Foundation receives research support from Arthrex.

METHODS

Specimen Preparation

The matching of 8 pairs of fresh-frozen human cadavers (mean age, 54 years; range, 33 to 68 years) without evidence of rotator cuff pathology or greater tuberosity asymmetry were in this study. Storage of specimens were at –20°C and thawed for 24 hours before use. All soft tissues were carefully dissected from the scapula and proximal humerus.

First, a sharp dissection of the supraspinatus was done from its scapular and humeral attachments. Secondly a scraping of the bony footprint was done with a fine rasp.  This  is routinely done with surgical rotator cuff repair.  Thirdly, standard rotator cuff tear was made in the specimen.  Sharply resecting the distal 10 to 12 mm of the supraspinatus tendon in a straight anterior-to-posterior fashion. Lastly, the humerus was cut in the midshaft region 10 cm distal to the surgical neck.

Surgery

A single surgeon performed all dissections and repairs to minimize technique variability between tested specimens. All humeri were mounted and clamped with a custom-machined testing apparatus with a  design to allow humeral external rotation with tendon loading as described by Park et al.11. Therefore, this is an attempt to more accurately simulate in vivo biomechanics.

Prior studies have shown that active external rotation with the arm at the side can result in 30% maximal contraction of the supraspinatus tendon. External rotation is applied to the specimen by the materials testing machine. The humerus is able to return to the starting position with a built-in spring load device. The testing apparatus has stop pegs that limit external rotation to 30°.  This is comparable to postoperative range of motion seen in patients (Fig 1).

Rotator Cuff Repair

In 8 specimens the knotless repair technique was done by the surgeon. Two 4.75-mm anchors loaded with 1 strand of wider dimension high-strength suture were placed in 2 medial bone sockets.  Just lateral to the articular margin 1.2 cm apart. The tail of each wider-dimension high-strength suture was passed through medial supraspinatus rotator cuff tissue. One tail from each medial anchor was then retrieved and inserted with an anchor into a lateral bone socket 1 cm.

 

Rotator Cuff Repair

RE 2. Knotless technique.

(A) Saw bone model with two 4.75-mm anchors (arrows) loaded with wider dimension high-strength sutures in medial bone sockets. (B) Wider dimension sutures passed through supraspinatus tissue (black arrows) and (C) then placed in 2 lateral bone sockets with two 4.75-mm anchors (black arrows). (D) Cadaver specimen showing the final repair with wider-dimension high-strength sutures passed through supraspinatus tissue (black arrow) and then placed in 2 lateral bone sockets with 2 anchors lateral to the edge of the footprint.

The other tail from each medial-row anchor was then retrieved and inserted with an anchor into the other lateral bone socket approximately 1.2 cm from the other lateral bone tunnel (Fig 2). In 8 matching  specimens, the modified construct was used. Two 4.75-mm anchors loaded with 1 strand of wider-dimension high-strength suture and 1 strand of No. 2 high-strength suture (FiberWire; Arthrex) were placed in 2 medial bone sockets just lateral to the articular margin 1.2 cm apart.

The Construct

This construct uses 2 horizontal mattress knots to approximate the rotator cuff to the medial aspect of the rotator cuff footprint. One high-strength suture and 1 wider-dimension high strength suture were passed through the supraspinatus. This step was done for each of the other suture tails.

The high-strength sutures from the same anchor, which were in a horizontal mattress configuration, were then tied on top of the rotator cuff, reapproximating it to the footprint. One tail from the wider dimension high-strength sutures from each medial anchor was then retrieved and inserted with an anchor into a lateral bone socket 1 cm lateral to the edge of the footprint. The other tail from the wider-dimension high-strength sutures from each medial-row anchor was retrieved and inserted with an anchor into the other lateral bone socket approximately 1.2 cm from the other lateral bone tunnel (Fig 3).

NET bridge

We named this technique the NET bridge.  Because the medial-row sutures are used to neutralize the forces on the repair.  While the wider-dimension high-strength sutures capture the torn tendon, compressing and securing it to the bone. The previously detailed rotator cuff repair constructs were tested with an Instron materials testing machine (Instron, Canton, MA) with a load capacity of 5 kN.  A custom shoulder fixture device, and a video digitizing system.

The proximal humerus was potted with plaster of Paris in rigid polyvinyl chloride piping with screws to secure them. The potted specimen was secured in the custom rotatory testing apparatus previously described. The humerus was held in 30° of abduction, and to minimize soft-tissue slippage or failure at the tendon-grip interface, a cryoclamp was used to secure the proximal part of the supraspinatus tendon. Care was taken to ensure equal and symmetric tension on the tendon before clamping.

Digitizing Video

When the specimen was mounted securely, nonreflective black paint was used to make 3-mm circular markers on the specimens to be used for the video digitizing system. The seven markers were : 1 on the clamp, 1 pair medial to the medial-row anchors, 1 lateral to the medial-row anchors, 1 pair on the tendon edge, and 1 off a fixed marker in the greater tuberosity. A video digitizing system that involves video recording of the markers.

Computer digitization of the markers, creation of centroids representing the center of the markers, and calculation of distances with ExpertVision software (Motion Analysis, Santa Rosa,CA).

FIGURE 3. Explanation

Modified construct.

(A) Saw bone model with two 4.75-mm anchors (arrows) loaded with wider-dimension high-strength sutures and No. 2 high-strength sutures in medial bone sockets. (B) No. 2 high-strength sutures and wider-dimension high-strength sutures from each medial anchor passed through supraspinatus tissue (arrows). (C) No. 2 high-strength sutures tied in horizontal mattress fashion (arrows).

(D) Wider

dimension high-strength sutures placed in 2 lateral bone sockets with two 4.75-mm anchors (arrows). (E) Cadaveric specimen showing final repair: dashed arrow, wider-dimension high-strength suture; solid arrows, No. 2 high-strength sutures from same anchor tied to each other in horizontal mattress fashion.

 

Cyclic and Tensile Testing:

The application of a 10-N preload was done for 1 minute.  Each specimen had a clinical load from 10 to 180 N at a rate of 5 mm/s for 30 cycles. After cyclic loading for 30 cycles, the clamp and the custom fixture device were rechecked for tightness. This was to ensure that there was no tendon slippage. Application of another  10-N preload and then the specimen was loaded to failure at a rate of 1 mm/s.

Statistical Analysis

Paired Student t tests were performed to compare the paired specimens based on their biomechanical properties. As with other studies in our laboratory, paired t tests were used given that matched-pair specimens were randomized to repair constructs. The level of statistical significance was set at P <05.

 

RESULTS

All measurements and calculations were made by a computer analysis of the video recording of the testing. Initial and linear stiffness for the first and last cycles were done.  With the use of data acquisition and analysis software (Series IX; Instron). The initial stiffness definition was as the slope of the toe region of the load-elongation curve. Whereas the linear stiffness definition was as the slope of the linear region of the load-elongation curve.

The energy absorption by the first and 30th cycles definition was as the area under the load-elongation curve. Linear stiffness of the NET construct was significantly greater at the first and 30th cycles (P ! .02).

More Results

In addition, the energy which dissipates through the lateral repair of the rotator cuff tissue,  was significantly greater in the knotless technique.  This was seen at the first and 30th cycles (P =.03 and P = .02, respectively) (Table 1). Gap formation of the repair and surface strain over the footprint area were in the calculation for the first and last cycles.

The gap formation definition was; as the space (measured in millimeters) created at the lateral edge of the tendon at the repair site. Finally, this gap was calculated by measuring the change in the position of the markers on the lateral edge of the tendon relative to the stationary markers on the lateral humerus.

Gap Formation

Gap formation show a significant difference between groups. The modified constructs show significantly less anterior gap formation at the first cycle (1.35 mm v 4.55 mm,P = .02) and 30th cycle (1.77 mm v 7.67 mm, P =.02) (Table 2). The structural properties of linear stiffness at failure, ultimate failure load, and hysteresis at failure calculation by use of data acquisition and analysis software (Series IX; Instron).

Calculation of Linear stiffness at failure were done as before. The ultimate failure load definition was as the peak force of the load-elongation curve. The definition of energy to failure was the area under the load-elongation curve from the start of loading until the ultimate failure. Linear stiffness at failure was significantly higher in the constructs in comparison with the knotless technique (P = .04). In addition, the ultimate load to failure was significantly higher for the modified construct (mean, 549 N v 311 N; P = .01).

Lateral Rotator Cuff Repairs

Repairs to the lateral rotator cuff tissue was also protected to a significantly greater degree at ultimate load as shown by the ultimate hysteresis values (P = .04) (Table 3).The mode of failure for the majority of the knotless constructs occur at the anteromedial anchor. Whereas the majority of NET constructs fail intramuscularly (Figs 4 and 5). As with similar biomechanical studies on rotator cuff repairs, the failure mechanisms are merely observations.  Ultimately, there were no statistically significant findings of the 8 matching pair specimens.

DISCUSSION
Rotator cuff repairs continue to evolve from open techniques to mini-open repairs.  Presently, these repairs are commonly being done arthroscopically. Initial arthroscopic repairs were done with a single-row technique. However, through anatomic studies, surgeons began to better understand the rotator cuff footprint on the humerus.13.  Double row rotator cuff fixation was thought to enhance tendon-to-bone contact.

Animal Studies

The exact time period for tendon-to-bone incorporation does not have a definition in the literature. However, animal studies have shown the importance of tendon-to-bone contact for healing.14-16/ Charousset et al.17, with the use of CT arthrography, compared  double row and single row constructs.  He found better healing rates with the former. The transosseous-equivalent technique helps to maximize compression of the tendon to the footprint.  It also was able to optimize the contact dimensions and to provide an increase in the repair strength.18.

Technique

This technique has been shown to have a significantly greater ultimate load to failure.  Also, there was a similar gap formation and stiffness in the literature from a comparison with a double row technique.19 Frank et al.20. With the use of magnetic resonance imaging to show high healing rates with the transosseous-equivalent repair.

Outcome Studies

Outcome studies have shown promising early results using these techniques.4,5,21-28. As the volume of shoulder arthroscopy continues to increase, the technology for rotator cuff repairs continues to improve. In other words, high-strength sutures are more durable and are there minimize a potential weak point in repair constructs.

The wider-dimension sutures aid in rotator cuff compression across the anatomic footprint. Finally, in attempts to simplify the surgical technique, the knotless technique eliminates the need to tie arthroscopic knots. However, as shown in this study, knotless fixation may lead to increases in the gap formation and failure of the repair. Thus, this simplification of the procedure may be detrimental to patient outcomes.

FIGURE 4.

View of lateral aspect of potted humerus after ultimate failure of knotless construct. The tendon (light arrow) has torn away from the footprint (dark arrow). Initial failure occurred anteriorly due to the external rotation and differential strain on the rotator cuff.

FIGURE 5.

View of lateral aspect of potted humerus after ultimate failure of modified construct. The medial-row sutures (dashed arrow) have neutralized the forces acting on the repair. (Light arrows, tendon; dark arrow, footprint.) Ultimately, the load to failure was significantly higher with this technique, with a significantly lower anterior gap formation.

Biomechanical Testing

Early biomechanical testing of rotator cuff repairs did not account for the rotational motion or external rotation.  Patients’ typically experience this during their postoperative rehabilitation. Thus, Park et al.11 created a model that provides cyclic external rotation. Implementation of that model was in this study. Finally, the literature has shown the significant effect that rotation has on repair constructs.

Double Row Repairs

Double row repairs had to have better fixation strength than single row repairs. When they was exposure to cyclic loading and changes in humeral rotational position.29,30. In addition, recent literature has shown differential tension between anterior and posterior sutures, when allowing for rotational motion during laboratory testing.31.  Therefore, this study is the first to compare a modified transosseous-equivalent suture repair technique with a knotless technique in an external rotation model.

Medial Row Fixation

This study shows that the addition of medial-row fixation to a knotless repair construct significantly increases the biomechanical characteristics of the repair (linear stiffness, ultimate load, and hysteresis).  While significantly decreasing gap formation regardless of tissue quality. Thus, the medial-row horizontal mattress sutures neutralized the force experienced by the repaired tissue.

Findings

This finding was also proven at ultimate load, with the majority of failures in the transosseous repair group occurring intramuscularly. At times leaving rotator cuff tissue under the repair construct. It is known that the maximal load during supraspinatus contraction is approximately 302 N.32.  In younger specimens, with better tissue quality by gross examination, the knotless construct failed at loads higher than the maximal contraction. However, with poor tissue quality observed by gross examination, the constructs failed at lower loads.

In addition, the majority of failures in the knotless construct occurred at the anterior medial anchor.  This was due to an increase in the differential stress on this area during external rotation. We believe that to provide the best biomechanical environment for healing regardless of tissue quality, medial-row knot fixation is paramount.

Although it was not part of our study, we hypothesize that the addition of medial-row knot fixation acts to seal the footprint from egress of synovial fluid.  Ultimately, this may aid in the healing of tendon to bone.

Recent Studies

A recent study by Ahmad et al.33 used a fluid-infusion model.  This model was to show that a single-row repair exposes the healing zone to a larger amount of fluid than a transosseous repair technique. Future studies need to be done with this type of model on the modified construct to determine its effect on footprint protection during tendon healing.

The main limitation of this study is the use of cadaveric specimens. Obviously, information regarding healing and long-term construct durability was not part of this result. Ultimately, the removal of the infraspinatus and subscapularis, may have affected our biomechanical results.

Previous Studies

As with previous studies using an external rotation model, external rotation loading is a simplification of the complex kinematics involved in postoperative motion.  Thus, it has been shown to replicate 1 commonly experienced shoulder motion after rotator cuff repair. Strengths of our study include the utilization of matching pair specimens.  Therefore, this is an attempt to eliminate variations in tissue quality being tested by the 2 techniques.

Moreover, 1 surgeon did perform all repairs to decrease variability in surgical technique. In addition, unlike previous experiments in our laboratory, the utilization of a cryoclamp provided a more stable construct for the experimental origin of the supraspinatus. Therefore, this modification improves the ability to analyze the cyclic load and load-to-failure data.

CONCLUSIONS

In conclusion, the modified construct shows improved biomechanical properties when allowing for external rotation during high-load testing. Therefore, using an additional horizontal mattress from separate sutures in the medial-row anchors helps to neutralize forces experienced by the repair.

Acknowledgment: Finally, the authors thank Arthrex for their support of this project.

REFERENCES

1. Anderson K, Boothby M, Aschenbrener D, van Holsbeeck M. Outcome and structural integrity after arthroscopic rotator cuff repair using 2 rows of fixation. American J Sports Med 2006;32:1899-1905.
2. Bishop J, Klepps S, Lo IK, Bird J, Gladstone J, Flatow E. Cuff integrity after arthroscopic versus open rotator cuff repair J Shoulder Elbow Surgery 2006;15:290-299.
3. Harryman D, Mack L, Jackins S, Richardson M, Matsen F. Repairs of the rotator cuff J Bone Joint Surgery Am 1991;73:982-989.

4. Cole B, McCarty L, Kang R, Alford W, Lewis P, Hayden J. Arthroscopic rotator cuff repair J Shoulder Elbow Surgery 2007;16:579-585.
5. DuQuin T, Buyea C, Bisson L. Which method of rotator cuff repair leads to the highest rate of structural healing? American J Sports Med 2010;38:835-841.
6. Burks R, Crim J, Brown N, Fink B, Greis P. A prospective randomized clinical trial comparing arthroscopic single and double row rotator cuff repair. American  J Sports Med 2009; 37:674-682.

Other References

7. Franceschi F, Ruzzini L, Longo U, et al. Equivalent clinical results of arthroscopic single-row and double row suture anchor repair for rotator cuff tears American J Sports Med 2007;35:1254-1260.
8. Sugaya H, Maeda K, Matsuki K, Moreishi J. Functional and structural outcome after arthroscopic full-thickness rotator cuff repair Arthroscopy 2005; 21:1307-1316.

9. Burkhart S, Cole BJ. Bridging self-reinforcing double row rotator cuff repair Arthroscopy 2010;26:677-680.
10. Busfield B, Glousman R, McGarry M, Tibone J, Lee TQ. A biomechanical comparison of 2 technical variations of double row rotator cuff fixation American J Sports Med 2008;36:901-906.

11. Park M, Bong J, Park C, Ahmad C, ElAttrache N, Lee T. The biomechanical effects of dynamic external rotation on rotator cuff repair compared to testing with the humerus fixed. American J Sports Med 2007;35:1931-1939.
12. Park M, Cadet E, Levine W, Bigliani L, Ahmad C. Tendon-to-bone pressure distributions at a repaired rotator cuff footprint using transosseous suture and suture anchor fixation techniques. American J Sports Med 2005;33:1154-1159.

13. Curtis A, Burbank K, Tierney J, Scheller A, Curran A. The insertional footprint of the rotator cuff. Arthroscopy 2006;22:603-609.

References Page 2

14. Oguma H, Murakami G, Takahashi-Iwanaga H, Aoki M, Ishii S. Early anchoring collagen fibers at the bone-tendon interface by woven bone formation. J Ortho Res 2001;19:873-880.
15. Weiler A, Hoffman R, Bail H, Rehm O, Sudkamp N. Tendon healing in a bone tunnel. Part II: Histologic analysis after biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep. Arthroscopy 2002; 18:124-135.

16. Weiler A, Peine R, Pashmineh-Azar A, Abel C, Sudkamp N, Hoffmann R. Tendon healing in a bone tunnel. Part I: Biomechanical results after biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep. Arthroscopy 2002;18:113-123.
17. Charousset C, Grimberg J, Duranthon L, Bellaiche L, Petrover D. Can a double row anchorage technique improve tendon healing in arthroscopic rotator cuff repair? American J Sports Med 2007;35:1247-1253.
18. Park M, ElAttrache N, Ahmad C, Tibone J. “Transosseous-equivalent” rotator cuff repair technique. Arthroscopy 2006; 22:1360.e1-1360.e5.

References Page 3

19. Park M, Tibone J, ElAttrache N, Ahmad C, Jun B, Lee T. Part II: Biomechanical assessment for a footprint-restoring transosseous equivalent rotator cuff repair technique compared
with a double row repair technique. J Shoulder Elbow Surgery 2007;16:469-476.

20. Frank J, ElAttrache N, Dines J, Blackburn A, Crues J, Tibone
J. Repair site integrity after arthroscopic transosseous-equivalent suture-bridge rotator cuff repair. American J Sports Med 2008; 36:1496-1503.
21. Boileau P, Brassart N, Watkinson D, Carles M, Hatzidakis A, Krishnan S. Arthroscopic repair of full-thickness tears of the supraspinatus. J Bone Joint Surgery Am 2005;87:1229-1240.

22. Galatz L, Ball C, Teefey S, Middleton W, Yamaguchi K. The outcome and repair integrity of completely arthroscopically repaired large and massive rotator cuff tears. J Bone Joint Surgery Am 2004;86:219-224.
23. Gazielly D, Gleyze P, Montagnon C. Functional and anatomical results after rotator cuff repair. Clinical Ortho Relate Res 1994:43-53.

References Page 4

24. Gerber C, Fuchs B, Hodler J. The results of repair of massive tears of the rotator cuff. J Bone Joint Surgery Am 2000;82:505-515.
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26. Lafosse L, Brzoska R, Toussaint B, Gobezie R. The outcome and structural integrity of arthroscopic rotator cuff repair with use of the double row suture anchor technique. J Bone Joint Surgery Am 2008;90:275-286.
27. Mazzocca A, Bollier M, Obopilwe E, et al. Biomechanical evaluation of arthroscopic rotator cuff repairs over time. Arthroscopy 2010;26:592-599.
28. Sugaya H, Maeda K, Matsuki K, Moreishi J. Repair integrity and functional outcome after arthroscopic double row rotator cuff repair.  J Bone Joint Surgery Am 2007;89:953-960.

References Page 5

29. Ahmad C, Kleweno C, Jacir A, et al. Biomechanical performance of rotator cuff repairs with humeral rotation. American Sports Med 2008;36:888-892.
30. Park M, Idjadi J, ElAttrache N, Tibone J, McGarry M, Lee T. The effect of dynamic external rotation comparing 2 footprint restoring rotator cuff repair techniques. American J Sports Med 2008;36:893-900.
31. Howe C, Huber P, Wolf F, Matsen F. Differential suture loading in an experimental rotator cuff repair. American J Sports Med 2009;37:324-329.
32. Burkhart S. A stepwise approach to arthroscopic rotator cuff repair based on biomechanical principles. Arthroscopy 2000; 16:82-90.

33. Ahmad C, Vorys G, Covey A, Levine W, Gardner T, Bigliani L. Rotator cuff repair fluid extravasation characteristics are influenced by repair technique. J Shoulder Elbow Surgery 2000; 18:976-981

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