Biomechanical evaluation of arthroscopic rotator cuff repairs: double-row compared with single-row fixation

BACKGROUND: Recent studies have shown that arthroscopic rotator cuff repairs can have higher rates of failure than do open repairs. Current methods of rotator cuff repair have been limited to single-row fixation of simple and horizontal stitches, which is very different from open repairs. The objective of this study was to compare the initial cyclic loading and load-to-failure properties of double-row fixation with those of three commonly used single-row techniques. METHODS: Ten paired human supraspinatus tendons were split in half, yielding four tendons per cadaver. The bone mineral content at the greater tuberosity was assessed. Four stitch configurations (two-simple, massive cuff, arthroscopic Mason-Allen, and double-row fixation) were randomized and tested on each set of tendons. Specimens were cyclically loaded between 5 and 100 N at 0.25 Hz for fifty cycles and then loaded to failure under displacement control at 1 mm/sec. Conditioning elongation, peak-to-peak elongation, ultimate tensile load, and stiffness were measured with use of a three-dimensional tracking system and compared, and the failure type (suture or anchor pull-out) was recorded. RESULTS: No significant differences were found among the stitches with respect to conditioning elongation. The mean peak-to-peak elongation (and standard error of the mean) was significantly lower for the massive cuff (1.1 +/- 0.1 mm) and double-row stitches (1.1 +/- 0.1 mm) than for the arthroscopic Mason-Allen stitch (1.5 +/- 0.2 mm) (p < 0.05). The ultimate tensile load was significantly higher for double-row fixation (287 +/- 24 N) than for all of the single-row fixations (p < 0.05). Additionally, the massive cuff stitch (250 +/- 21 N) was found to have a significantly higher ultimate tensile load than the two-simple (191 +/- 18 N) and arthroscopic Mason-Allen (212 +/- 21 N) stitches (p < 0.05). No significant differences in stiffness were found among the stitches. Failure mechanisms were similar for all stitches. Rotator cuff repairs in the anterior half of the greater tuberosity had a significantly lower peak-to-peak elongation and higher ultimate tensile strength than did repairs on the posterior half. CONCLUSIONS: In this in vitro cadaver study, double-row fixation had a significantly higher ultimate tensile load than the three types of single-row fixation stitches. Of the single-row fixations, the massive cuff stitch had cyclic and load-to-failure characteristics similar to the double-row fixation. Anterior repairs of the supraspinatus tendon had significantly stronger biomechanical behavior than posterior repairs.     

Comparative and experimental study on different tendinous grasping techniques in rotator cuff repair: a new reinforced stitch

Arthroscopic repair of wide rotator cuff ruptures is burdened by a percentage of recurrences that is greater than the repair carried out when an open technique is used. One of the main reasons for this difference can be searched for in the minor hold of stitching on the tendinous aspect obtained with arthroscopic repair. In fact, when an open technique is used, good hold can be guaranteed by using reinforced stitches such as the modified Mason-Allen. Thus, arthroscopic repair technique on the tendinous aspect, particularly in wide and massive injuries, must be improved. It was the purpose of this study to compare a new reinforced stitch that can easily be obtained in arthroscopy (simple stitch that orthogonally crosses a horizontal stitch previously knotted on the tendon: SS-HL), with traditional stitches (simple stitch, mattress-stitch and modified Mason-Allen stitch). Tests were carried out on sheep infraspinatus tendons in order to evaluate the resistance of pull-out. The SS-HL stitch showed resistance to loading that was similar to that when the modified Mason-Allen was used, but it was greater than that shown by the simple stitch (+48%) and the mattress stitch (+35%).     

Mechanical strength of arthroscopic rotator cuff repair techniques: an in vitro study

BACKGROUND: Retears after rotator cuff repairs occur relatively frequently and may compromise the functional result. The goal of this study was to analyze the mechanical properties following arthroscopic techniques for rotator cuff repair and to evaluate possible alternative techniques. METHODS: In the first part, five different bone anchors (the Revo screw; Mitek Rotator Cuff anchor, 5.0-mm Statak, PANALOK RC absorbable anchor, and 5.0-mm Bio-Statak) were tested in vitro under cyclic loading on five pairs of cadaveric shoulders. Then five types of arthroscopic tendon suturing instruments were tested on rotator cuff tendons. Finally, the arthroscopically performed mattress and modified Mason-Allen stitches, fixed with either the Revo screw or the Bio-Statak, were evaluated on ten pairs of human cadaveric shoulders. RESULTS: The holding strengths of the various anchors were similar, ranging from 130 to 180 N, and approximated the holding strength of knotted number-2 suture materials. The fixation of the tested anchors yielded comparable values of stiffness except for one anchor, which showed significantly greater subsidence under cyclic load (p = 0.003). All tested, commercially available arthroscopic suturing devices were unsuitable for performing a modified Mason-Allen stitch on normal supraspinatus tendons. Modification of a commercially available suture punch with a longer needle allowed us to consistently perform a modified Mason-Allen stitch. The modified Mason-Allen stitch, which has shown favorable mechanical properties in open repairs of the rotator cuff, was not found to be stronger than the mattress stitch when performed arthroscopically and used with bone anchors. When the modified Mason-Allen stitch was fixed to one anchor, it was even weaker than a mattress stitch repaired with another anchor (168 versus 228 N). Unequal loading of the two suture branches due to the more rigid modified Mason-Allen stitch may be the reason for this difference. CONCLUSIONS: Arthroscopic techniques for rotator cuff repair with use of the mattress stitch and bone anchors allow for a relatively solid fixation. The holding strength is not improved with use of the modified Mason-Allen stitch. Although a direct comparison with previous in vitro studies is not possible, the holding strength of open fixation techniques seems to be stronger. If rotator cuffs are subjected to high postoperative loading, open repair might be preferred to reduce the risk of a retear, until stronger arthroscopic fixation techniques are developed.     

Experimental rotator cuff repair. A preliminary study.

BACKGROUND: The repair of chronic, massive rotator cuff tears is associated with a high rate of failure. Prospective studies comparing different repair techniques are difficult to design and carry out because of the many factors that influence structural and clinical outcomes. The objective of this study was to develop a suitable animal model for evaluation of the efficacy of different repair techniques for massive rotator cuff tears and to use this model to compare a new repair technique, tested in vitro, with the conventional technique. METHODS: We compared two techniques of rotator cuff repair in vivo using the left shoulders of forty-seven sheep. With the conventional technique, simple stitches were used and both suture ends were passed transosseously and tied over the greater tuberosity of the humerus. With the other technique, the modified Mason-Allen stitch was used and both suture ends were passed transosseously and tied over a cortical-bone-augmentation device. This device consisted of a poly(L/D-lactide) plate that was fifteen millimeters long, ten millimeters wide, and two millimeters thick. Number-3 braided polyester suture material was used in all of the experiments. RESULTS: In pilot studies (without prevention of full weight-bearing), most repairs failed regardless of the technique that was used. The simple stitch always failed by the suture pulling through the tendon or the bone; the suture material did not break or tear. The modified Mason-Allen stitch failed in only two of seventeen shoulders. In ten shoulders, the suture material failed even though the stitches were intact. Thus, we concluded that the modified Mason-Allen stitch is a more secure method of achieving suture purchase in the tendon. In eight of sixteen shoulders, the nonaugmented double transosseous bone-fixation technique failed by the suture pulling through the bone. The cortical-bone-augmentation technique never failed. In definite studies, prevention of full weight-bearing was achieved by fixation of a ten-centimeter-diameter ball under the hoof of the sheep. This led to healing in eight of ten shoulders repaired with the modified Mason-Allen stitch and cortical-bone augmentation. On histological analysis, both the simple-stitch and the modified Mason-Allen technique caused similar degrees of transient localized tissue damage. Mechanical pullout tests of repairs with the new technique showed a failure strength that was approximately 30 percent of that of an intact infraspinatus tendon at six weeks, 52 percent of that of an intact tendon at three months, and 81 percent of that of an intact tendon at six months. CONCLUSIONS: The repair technique with a modified Mason-Allen stitch with number-3 braided polyester suture material and cortical-bone augmentation was superior to the conventional repair technique. Use of the modified Mason-Allen stitch and the cortical-bone-augmentation device transferred the weakest point of the repair to the suture material rather than to the bone or the tendon. Failure to protect the rotator cuff post-operatively was associated with an exceedingly high rate of failure, even if optimum repair technique was used. CLINICAL RELEVANCE: Different techniques for rotator cuff repair substantially influence the rate of failure. A modified Mason-Allen stitch does not cause tendon necrosis, and use of this stitch with cortical-bone augmentation yields a repair that is biologically well tolerated and stronger in vivo than a repair with the conventional technique. Unprotected repairs, however, have an exceedingly high rate of failure even if optimum repair technique is used. Postoperative protection from tension overload, such as with an abduction splint, may be necessary for successful healing of massive rotator cuff tears.     

Modified Mason-Allen Suture Bridge Technique: A New Suture Bridge Technique with Improved Tissue Holding by the Modified Mason-Allen Stitch

We present a new method of suture bridge technique for medial row fixation using a modified Mason-Allen stitch instead of a horizontal mattress. Medial row configuration of the technique is composed of the simple stitch limb and the modified Mason-Allen stitch limb. The limbs are passed through the tendon by a shuttle relay. The simple stitch limb passes the cuff once and the modified Mason-Allen stitch limb passes three times which creates a rip stop that prevents tendon pull-out. In addition, the Mason-Allen suture bridge configuration is basically a knotless technique which has an advantage of reducing a possibility of strangulation of the rotator cuff tendon, impingement or irritation that may be caused by knot.     

Single row rotator cuff repair with modified technique

Rotator cuff tear is a common medical condition. We introduce various suture methods that can be used for arthroscopic rotator cuff repair, review the single row rotator cuff repair method with modified technique, and introduce the Ulsan-University (UU) stich. We compare the UU stitch with the modified Mason-Allen (MA) suture method. The UU stitch configuration is a simple alternative to the modified MA suture configuration for rotator cuff repair.     

Arthroscopic Placement of a Modified Mason-Allen Stitch

Recent studies have shown all-arthroscopic rotator cuff repairs to have comparable clinical results to mini-open or open repairs. Previous drawbacks to arthroscopic repair have included not being able to place a modified Mason-Allen stitch with a suture anchor technique. We present a technique using the Arthrex Scorpion device (Arthrex, Naples, FL) to place a modified Mason-Allen stitch arthroscopically via a double-loaded FiberWire metal suture anchor (Arthrex). The Scorpion suture passer places a stitch from inferior to superior through the torn rotator cuff. The suture is grabbed and reloaded into the Scorpion device. The device is then turned upside down, and a horizontal stitch is placed from superior to inferior. The stitch is retrieved again and reloaded a third time. The last pass is placed so that the final stitch passes anterior to the inferior suture but beyond the previously placed horizontal mattress stitch. This effectively reproduces the described biomechanically superior modified Mason-Allen stitch.     

An arthroscopic stitch for massive rotator cuff tears: the mac stitch

Arthroscopic repair of rotator cuff tears has become popular with the advancement in technology and arthroscopic technique. As we attempt to arthroscopically repair larger rotator cuff tears, we are relying more on tissue fixation. The tendon–suture interface has been recognized as the weak link in rotator cuff repair. In this article, we propose the use of the Mac stitch—a simple modification of suture placement, a combination of a horizontal and vertical loop at the site of repair—to increase the strength of tissue fixation. The Mac stitch is a simple arthroscopic stitch that can be used for small and massive rotator cuff repairs.     

关节镜下肩袖损伤缝合技术研究进展

关节镜下肩袖修补术已非常普遍.许多单排锚钉、双排锚钉和经骨隧道修复技术应用于临床,但肩袖修复的最佳方法仍不清楚.生物力学研究证明相比于单排,双排锚钉修复的力度更强,而单排锚钉中的巨大肩袖缝合技术和改良Mason-Allen缝合技术力学性能最佳.临床研究显示双排锚钉修复能改善肩袖愈合率,但各种缝合技术的预后功能评分无明显...     

Biomechanischer Vergleich aktueller Refixationsarten im Rahmen der Rekonstruktion von Rotatorenmanschettenläsionen in einem in-vivo-Tiermodell

A significant controversy exists regarding the optimal fixation technique in rotator cuff surgery. The aim of this study was to compare the time-dependent bio-mechanical properties of the traditional open transosseous suture technique and modified Mason-Allen stitches (SMMA group) versus the double-loaded suture anchor technique and so-called arthroscopic Mason-Allen stitches (AAMA group) in rotator cuff repair. A total of 18 mature sheep were randomized to the two repair groups. After 6, 12, or 26 weeks, evaluation of the reinsertion site of the infraspinatus tendon was performed. In a biomechanical evaluation all specimens were loaded to failure at a constant displacement rate using a standard universal testing machine. The load-to-failure and stiffness of the healed bone-tendon interface were calculated. Magnetic resonance imaging analysis showed cuff integrity in all cases and no evidence of foreign body reaction to the anchors. Load-to-failure and stiffness data did not indicate any significant difference between the two treatment groups, neither at 6 weeks nor at 12 or 26 weeks. However, at time zero the AAMA group had a higher load-to-failure in comparison to the SMMA group (P<0.010), but there was no difference for the stiffness (P<0.121). This in vivo study showed that the AAMA technique provides superior stability and after healing would gain strength comparable to the SMMA technique.     

Arthroscopic Rotator Cuff Repair Using a Triple-Loaded Suture Anchor and a Modified Mason-Allen Technique (Alex Stitch)

Surgical repair of the rotator cuff must have good resistance and should restore the tendon footprint. To attain this goal, a stitch with a strong biomechanical profile that avoids tissue strangulation should be used. We describe an arthroscopic suture technique undertaken to repair rotator cuff tears with a single triple-loaded suture anchor. The technique consists of a combination of a horizontal mattress and 2 vertical simple sutures that are positioned medial to the mattress suture. The suture anchor used is the 5-mm self-tapping ThRevo (Linvatec). This anchor is loaded with 3 sutures: 2 No. 2 nonabsorbable braided polyester sutures of different colors and a central high-strength No. 2 polyethylene suture. The shape of the anchor eyelet permits all 3 sutures to glide freely. A modified Mason-Allen technique (Alex stitch) that combines a horizontal side-to-side suture and 2 simples sutures as vertical loops is used. With use of the Spectrum suture passing device and shuttle relay system (Linvatec), both limbs of the centrally located polyethylene suture are passed through the cuff from bottom to top, approximately 1 cm from the tendon edge. This suture is not immediately tied. Next, with use of the same system, the other 2 sutures are placed medially and over the previous horizontal suture. Simple sutures are placed at an approximately 30° angle from the center of the anchor; 1 is placed anterior and the other posterior. The sutures are tied through the lateral portal. The mattress horizontal central stitch is always tied first, followed by the 2 vertical sutures. The horizontal mattress suture serves as a “rip stop stitch” and theoretically reduces the possibility of cutting out of the simple sutures.     

关节镜下"三角布钉"结合改良Mason-Allen技术治疗巨大"L"或"U"型肩袖损伤

目的评估在关节镜下"三角布钉"结合改良Mason-Aallen技术在临床中治疗巨大"L"或"U"型肩袖损伤的疗效。 方法回顾性分析2015年1月至2019年1月，西安交通大学附属红会医院收治的86例巨大"L"或"U"型肩袖损伤患者临床资料，其中男56例、女30例；年龄40 ~ 65岁，平均（52.5±2.5）岁。根据DeOrio和Cofield分型巨大肩袖损伤，且为"L"或"U"型。应用关节镜下"三角布钉"结合改良Mason-Allen技术治疗，记录肩关节活动度及并发症，手术前后采用Constant评分及视觉模拟评分（visual analogue scale,VAS）评价肩关节功能。 结果术前症状持续时间1 ~ 23个月，平均（6.2±2.5）个月；86例患者均获24 ~ 72个月随访，平均（29.3±4.5）个月；均无感染等并发症；术后12个月随访时超声检查，75例肩袖完整，8例部分损伤，3例出现全层撕裂后再次行关节镜手术治疗；末次随访肩关节活动度：前屈（170.7±3.5）°，外展（155.8±3.8）°，外旋（39.4±3.4）°，内旋（40.5±3.3）°；Constant评分由术前（31.2±1.2）分提高至术后（82.5±3.2）分（P<0.05）；VAS由术前（7.8±3.2）分减少至术后（1.3±0.5）分（P<0.05）。 结论关节镜下"三角布钉"结合改良Mason-Allen技术治疗巨大肩袖损伤有效，便于操作，可以减轻疼痛，改善肩关节功能，对于治疗巨大"L"或"U"型肩袖损伤是一种新的选择方法，值得临床推广。     

Primary fixation strength of rotator cuff repair techniques: a comparative study

Purpose:The goal of the study was to compare the primary fixation strength of transosseous suture, suture anchor, and hybrid repair techniques for rotator cuff repair.Type of Study:Animal model experiment.Methods:Thirty-two sheep shoulders were divided into 4 homogeneous groups, according to bone density and tendon dimensions. Infraspinatus tendons were transected from their insertions and reattached using 4 different techniques. Group 1 was repaired with a single Mason-Allen stitch and 2 transosseous tunnels for each end of the suture, knotted on the lateral cortex of proximal humerus; group 2 was repaired with double Mason-Allen stitches and 2 transosseous tunnels; group 3 was repaired with 2 Corkscrews (Arthrex, Germany); and group 4 was repaired with 2 Corkscrews combined with a single Mason-Allen transosseous suture. All specimens were tested for their fixation strengths with a material testing system.Results:The mode of failure in group 1 was mainly suture breakage. In groups 3 and 4, the tendons pulled out from the sutures. In group 2, sutures broke the bony bridge between the 2 tunnels. The mean load to failure value was 160.31 ± 34.59 N in group 1, 199.36 ± 11.73 N in group 2, 108.32 ± 15.98 N in group 3, and 214.24 ± 28.52 N in group 4. Anchor fixation was significantly weaker compared with other groups (P <.001). Combination of a transosseous suture and anchor fixation (group 4) was significantly stronger than the single transosseous suture (group 1) and double anchor techniques (group 3) (P <.001).Conclusions:Hybrid technique was the strongest among the tested rotator cuff repair techniques. With the addition of one transosseous suture to two anchors, the strength of the repair could be doubled.     

Disintegration of an absorbable rotator cuff anchor six weeks after implantation

Rotator cuff failure by suture-bone or suture anchor pull-out, suture breakage, knot slippage, and tendon pull-out are well described. I report a case of early disintegration of a bioabsorbable suture anchor. A 77-year-old woman underwent arthroscopic rotator cuff repair. On suspecting failure, the repair was repeated 40 days later. Arthroscopy revealed disintegration of the suture loop from the anchor. Open rotator cuff repair was then performed with transosseous suture and metallic anchors.     

The double-twist knot: A new arthroscopic sliding knot

A safe and easy-to-tie sliding knot is necessary for arthroscopic repair of rotator cuff tears and glenoid labrum lesions. We describe the double-twist knot (DTK) technique, having tested the knot's tensile strength and compared it with other commonly used arthroscopic knots. The DTK is a modified Lark's head knot that can be tied only on a double suture. A No. 2 braided polyester suture was used to test the DKT against the Tennessee slider knot and Snyder's knot by means of a material testing system. Results showed a statistically significant (P < .001) higher tensile strength with the DTK than with the other 2 knots. The rationale for using a stitch with a double suture is to double the tensile strength while using the same number of surgical steps and operating time as with single-suture stitches.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 7 (September), 2002: pp 815–820     

An in vivo comparison of the modified Mason-Allen suture technique versus an inclined horizontal mattress suture technique with regard to tendon-to-bone healing: a biomechanical and histologic study in sheep

The purpose of this study is to examine long-term tendon-to-bone healing, by use of a sheep animal model, after rotator cuff repairs performed with 2 different suture techniques: an inclined horizontal mattress suture pattern placed with special arthroscopic instrumentation (HMS) and the modified Mason-Allen pattern (MMA). After a pre hoc power analysis, 18 skeletally mature sheep were randomly assigned to either the HMS or MMA repair technique, with contralateral limbs used for the control group. At 26 weeks, the animals were euthanized. Six sheep from each group underwent biomechanical testing. Load-to-failure and stiffness results indicated no statistically significant difference between the 2 groups. Avulsion of the tuberosity was the primary mode of failure for both groups. In the remaining 6 sheep, histologic evaluation demonstrated that, regardless of treatment, the tendon appeared completely healed in the bony trough. Because the long-term biomechanical and histologic properties of healed tendons repaired with an HMA technique are equal to those obtained with an MMA technique, the inclined horizontal mattress suture may be appropriate for arthroscopic rotator cuff repair. Short-term studies are necessary to determine whether these findings are true early after tendon repair, when failure may be most common.     

Arthroscopic rotator cuff repair using a single-row of triple-loaded suture anchors with a modified suture configuration

Achieving an adequate restoration of the muscle–tendon–bone unit and the anatomical footprint is essential for a successful outcome in open and arthroscopic rotator cuff repair. The described suture grasping technique using triple-loaded suture anchors might combine high initial fixation strength with good footprint coverage. It describes two mattress’ stitches medial at the articular margin of the tendon. Additionally, a third mattress stitch is performed laterally to increase footprint contact and avoid dog-ear deformity. The triple-mattress repair is easy to perform and might be a good alternative in either arthroscopic or open rotator cuff repair.     

Biomechanical testing of a new knotless suture anchor compared with established anchors for rotator cuff repair

Various suture anchors are available for rotator cuff repair. For arthroscopic application, a knotless anchor was developed to simplify the intra-operative handling. We compared the new knotless anchor (BIOKNOTLESStrade mark RC; DePuy Mitek, Raynham, MA) with established absorbable and titanium suture anchors (UltraSorbtrade mark and Super Revo 5mmtrade mark; ConMed Linvatec, Utica, NY). Each anchor was tested on 6 human cadaveric shoulders. The anchors were inserted into the greater tuberosity. An incremental cyclic loading was performed. Ultimate failure loads, anchor displacement, and mode of failure were recorded. The anchor displacement of the BIOKNOTLESStrade mark RC (15.3 +/- 5.3 mm) after the first cycle with 75 N was significantly higher than with the two other anchors (Super Revo 2.1 +/- 1.6 mm, UltraSorb: 2.7 +/- 1.1 mm). There was no significant difference in the ultimate failure loads of the 3 anchors. Although the Bioknotlesstrade mark RC indicated comparable maximal pullout strength, it bares the risk of losing contact between the tendon-bone-interface due to a significantly higher system displacement. Therefore, gap formation between the bone and the soft tissue fixation jeopardizes the repair. Bioknotlesstrade mark RC should be used in the lateral row only when a double row technique for rotator cuff repair is performed, and is not appropriate for rotator cuff repair if used on its own.     

Biomechanical characteristics of the horizontal mattress stitch: implication for double-row and suture-bridge rotator cuff repair

Background

We investigated the effects of bite-size horizontal mattress stitch (distance between the limbs passed through the tendon) on the biomechanical properties of the repaired tendon.

Methods

We anchored 20 bovine Achilles tendons to bone using no. 2 high-strength suture and 5-mm titanium suture anchors in a mattress–suture technique. Tendons were allocated randomly into two groups of ten each to receive stitches with a 4- or 10-mm bite. Specimens underwent cyclic loading from 5 to 30 N at 1 mm/s for 30 cycles, followed by tensile testing to failure. Gap formation, tendon strain, hysteresis, stiffness, yield load, ultimate load, energy to yield load, and energy to ultimate load were compared between groups using unpaired t tests.

Results

The 4-mm group had less (p < 0.05) gap formation and less (p < 0.05) longitudinal strain than did the 10-mm group. Ultimate load (293.6 vs. 148.9 N) and energy to ultimate load (2,563 vs. 1,472 N-mm) were greater (p < 0.001) for the 10-mm group than the 4-mm group. All tendons repaired with 4-mm suturing failed at the suture–tendon interface, with sutures pulling through the tendon, whereas the suture itself failed before the tendon did in seven of the ten specimens in the 10-mm group.

Conclusions

Whereas a 4-mm bite fixed the tendon more tightly but at the cost of decreased ultimate strength, a 10-mm bite conveyed greater ultimate strength but with increased gap and strain. These results suggest that for the conventional double-row repair, small mattress stitches provide a tighter repair, whereas large stitches are beneficial to prevent sutures from pulling through the tendon after surgery. For suture-bridge rotator cuff repair, large stitches are beneficial because the repaired tendon has a higher strength, and the slightly mobile medial knot can be tightened by lateral fixation.     

Biomechanical comparison of single-row arthroscopic rotator cuff repair technique versus transosseous repair technique

This study determined the effect of tear size on gap formation of single-row simple-suture arthroscopic rotator cuff repair (ARCR) vs transosseous Mason-Allen suture open RCR (ORCR) in 13 pairs of human cadaveric shoulders. A massive tear was created in 6 pairs and a large tear in 7. Repairs were cyclically tested in low-load and high-load conditions, with no significant difference in gap formation. Under low-load, gapping was greater in massive tears. Under high-load, there was a trend toward increased gap with ARCR for large tears. All repairs of massive tears failed in high-load. Gapping was greater posteriorly in massive tears for both techniques. Gap formation of a modeled RCR depends upon the tear size. ARCR of larger tears may have higher failure rates than ORCR, and the posterior aspect appears to be the site of maximum gapping. Specific attention should be directed toward maximizing initial fixation of larger rotator cuff tears, especially at the posterior aspect.