Abstract
Background:
The transosseous-equivalent (TOE) rotator cuff repair construct has become the gold standard for the repair of medium and large rotator cuff tears. Repair failure, however, continues to be a problem. One contributing factor may be the inability of the TOE repair to replicate the native footprint contact characteristics during shoulder movement, especially in rotation. This results in higher strain across the repair, which leads to gapping and predisposes the construct to failure. In an effort to better reproduce the native compression forces throughout the footprint, an augmented TOE construct supplemented with lateral edge fixation is proposed, and the contact characteristics were compared with those of the gold standard TOE construct.
Hypothesis:
The augmented TOE repair will demonstrate improved footprint contact characteristics when compared with the classic TOE repair.
Study Design:
Controlled laboratory study.
Methods:
Ten fresh-frozen cadaveric shoulders underwent supraspinatus repair using both the classic TOE double-row construct and the augmented TOE repair. For the augmented repair, 2 luggage tag sutures were used to secure the lateral edge and incorporated into the lateral row anchors. A Tekscan pressure sensor (Tekscan Inc) placed under the repaired tendon was used to collect footprint contact area, force, peak pressure, and contact pressure data for each construct.
Results:
The augmented construct demonstrated significantly greater contact forces (average difference, 4.9 N) and significantly greater contact pressures (average difference, 23.1 kPa) at all degrees of abduction and all degrees of rotation. At 30° of internal and 30° of external rotation at both 0° and 30° of shoulder abduction, the augmented construct demonstrated significantly greater peak contact pressures.
Conclusion:
The augmented construct showed superior contact characteristics when compared with the classic TOE technique. The addition of lateral edge fixation to the classic TOE repair significantly improves bone-tendon contact characteristics with minimal additional surgical effort.
Clinical Relevance:
The results of this study indicate that lateral augmentation of the classic TOE repair produces a biomechanically superior construct that may optimize tendon healing.
Keywords
Rotator cuff tear is one of the most common causes of shoulder pain in adults. Indeed, epidemiological data suggest that nearly a third of all orthopaedic injuries are related to rotator cuff pathology. 11 Tears are associated with increasing age and are present in more than 50% of patients in their 60s and 80% of patients in their 80s. 11 Since the introduction of rotator cuff repair surgery, repair constructs have focused on restoring the native rotator cuff footprint.2,7 This has led to a continued evolution in arthroscopic rotator cuff constructs, from single-row repairs to double-row repairs and, more recently, to the transosseous-equivalent (TOE) constructs. 11 Evidence of the biomechanical superiority of later constructs has driven this progression to the TOE construct now being the gold standard for medium and large rotator cuff tears.12,17,18,21
Despite high rates of satisfaction in patients who undergo rotator cuff repair, a relatively high proportion of tears do not fully heal and continue to be symptomatic. 4 Even the TOE construct has demonstrated retear rates between 10% and 33%.6,9,16,26 One plausible explanation for this is the increased gap formation seen at the anterior edge of the TOE repair with humeral rotation. 19 Internal and external rotation have been shown to differentially affect strain across the anterior and posterior region of the repair. 19 Furthermore, the greatest concentration of stress is on the articular side and shifts laterally toward the insertion with abduction. 27 In the setting of rotator cuff repair, the inability of the TOE construct to replicate proper force distribution throughout the rotator cuff during movement may predispose the construct to repair failure. A reinforced TOE construct that better counteracts these forces may lead to higher rates of repair success.
The aim of this study was to enhance footprint compression forces throughout shoulder motion by proposing an augmented TOE construct. The footprint contact characteristics of the augmented construct were then directly compared with those of the classic TOE repair with specific considerations for humeral rotation and abduction. We hypothesized that the addition of supplemental lateral edge fixation would result in improved contact characteristics (contact area, contact force, contact pressure, and peak contact pressure) of the repair construct.
Methods
Specimen Preparation
Ten fresh-frozen cadaveric shoulder specimens (mean age, 70.3 ± 10.0 years, all male) with intact rotator cuffs were utilized for this study. Specimens were stored at −20°C until 24 hours before testing, when they were thawed at room temperature. All soft tissue from the scapula and proximal humerus was sharply dissected, and the humerus was disarticulated from the glenoid. The humerus was stripped of all soft tissue attachments except for the supraspinatus. Care was taken to preserve the supraspinatus muscle from the footprint insertion to the muscle belly. The humerus was transected 5.5 cm from the bottom of the articular surface of the humeral head and potted in 2-inch polyvinyl chloride (PVC) pipes with plaster of paris. A Krakow suture was placed through the musculotendinous portion of the supraspinatus for loading. Throughout preparation and testing, specimens were kept moist with normal saline solution.
All cadaveric specimens were acquired through the University of California Willed Body Program.
Repair Construct: Classic TOE
All repairs were performed by a single sports medicine fellow (E.U.).
The supraspinatus tendon was dissected sharply off of the greater tuberosity. The lateral free edge of the tendon was trimmed by 10 mm to mimic debridement of a chronic tear. The footprint was debrided of all soft tissue. A bur was used to debride the lateral-most edge of the articular surface to create a bony trough and ensure that the repaired tendon would sit flush on the pressure sensor pad. Two 5.5-mm double-loaded anchors (Arthrex Inc) were used for medial row fixation. The anterior anchor was placed 5 mm from the posterior edge of the bicipital groove, within the bony trough. The posterior anchor was placed 12.5 mm posterior to the anterior anchor (Figure 1A). The sutures from the 2 anchors were then passed 15 mm medial to the lateral edge of the supraspinatus tendon, with care taken to ensure that they were centered over each corresponding anchor. Two suture limbs from the anterior anchor were passed 5 mm posterior to the anterior edge of the tendon. The other 2 limbs were then passed 7 mm posterior to the anterior limbs. The 4 limbs from the posterior anchor were passed 12.5 mm posterior to the 2 anterior limbs, centered on the posterior anchor. One set of suture limbs in each anchor were then tied to fixate the tendon to the medial row. The knot constructed consisted of 2 half-hitches in the same direction followed by 3 alternative half-hitches for a total of 5 knots.
(A) Schematic of the classic transosseous-equivalent (TOE) construct. (B) Classic TOE construct with the luggage tags (arrows) not incorporated into the lateral row. Arrowhead, Tekscan sensor pad.
The two 4.75-mm lateral row anchors were placed 10 mm distal to the lateral edge of the supraspinatus footprint and directly in line with the medial anchors. One limb from each medial anchor was loaded into the lateral anchors in the standard suture-bridge configuration. The sutures were tensioned and the anchors inserted into the greater tuberosity, completing the TOE construct (Figure 1B).
Repair Construct: TOE With Lateral Luggage Tag
The surgical technique for the experimental construct was identical to that of the control group; however, before lateral anchor fixation, 2 looped sutures (Arthrex Inc) were passed through the lateral edge of the supraspinatus in a luggage tag fashion to augment the construct. The 2 luggage tag sutures were passed 5 mm medial to the lateral edge of the tendon. The anterior tag was passed 5 mm posterior to the anterior tendon edge, and the posterior tag was passed 15 mm posterior to the anterior tag (Figure 2A). The anterior luggage tag was incorporated into the anterior lateral anchor. The posterior tag was incorporated into the posterior lateral anchor (Figure 2B).
(A) Schematic of the augmented transosseous-equivalent (TOE) construct with luggage tags. (B) Luggage tags (arrows) incorporated into the lateral row in the augmented TOE construct.
Testing Protocol
The specimen was mounted onto a previously validated custom testing jig (Figure 3) that allowed for testing at 30° of internal rotation, neutral, and 30° of external rotation at 0° and 30° of shoulder abduction. The neutral rotational position of the humerus was defined using the load vector for the supraspinatus (the tag sutures in the supraspinatus were loaded and the resulting rotational equilibrium reached by the construct while loaded was marked “neutral”).
Testing jig setup.
A pressure sensor (Model 4040; Tekscan Inc) was placed under the supraspinatus tendon footprint after the medial row anchors of each repair technique were placed. The sensor was calibrated using 2-point calibration at 5 and 20 N before experimentation with the Instron 4411 load cell (Instron). After each of the surgical procedures was completed, a line was tied to the Krakow stitch in the supraspinatus, passed over a pulley, and loaded with 25 N, making sure that the load was in line with the supraspinatus load vector. Preconditioning with 25 N was conducted at all positions before data collection. The order of construct testing was randomized. The medial anchors were retensioned once between testing the different repair constructs.
Measurements and Data Analysis
Contact characteristics including contact area, contact force, contact pressure, and peak contact pressure were collected at 30° of internal rotation, neutral, and 30° of external rotation at 0° and 30° of abduction. Each parameter was collected twice at each condition and then averaged. Paired t tests were used to compare the differences between the luggage tag construct and the standard construct in terms of force, peak contact pressure, contact pressure, and contact area. Based on pilot data, a sample size of 10 matched pairs was estimated to be sufficient to detect an 80-kPa difference in peak contact pressure with 80% power (α = 0.05) and a standard deviation of 80 kPa. Statistical analysis was conducted in Excel 2016 (Microsoft) and statistical significance was set at α = 0.05.
Results
The luggage tag construct demonstrated significantly greater footprint contact forces (average difference, 4.9 N) (Figure 4) and contact pressures (average difference, 23.1 kPa) (Figure 5) compared with the classic TOE construct across all testing conditions.
Footprint contact forces exerted by the 2 different repair constructs. Abd, abduction; ER, external rotation; IR, internal rotation.
Footprint contact pressures exerted by the 2 different repair constructs. Abd, abduction; ER, external rotation; IR, internal rotation.
Likewise, the luggage tag construct demonstrated significantly greater peak contact pressures at 30° of internal and 30° of external rotation at both 0° and 30° of abduction. There was no difference in peak contact pressures between the 2 constructs in neutral rotation at both 0° and 30° of abduction (Figure 6).
Footprint peak contact pressures exerted by the 2 different repair constructs. Abd, abduction; ER, external rotation; IR, internal rotation.
Finally, while the luggage tag construct demonstrated overall greater contact area when compared with the standard construct, the difference was not statistically significant across any testing conditions (Figure 7).
Footprint contact area exerted by the 2 different repair constructs. Abd, abduction; ER, external rotation; IR, internal rotation.
Discussion
The results of this study demonstrate that augmenting the classic TOE rotator cuff repair construct with lateral edge luggage tag sutures significantly increases contact characteristics of the repair in both neutral shoulder positioning and rotation. Our study suggests that augmenting the classic TOE repair with lateral-based sutures may better restore the native rotator cuff footprint and maximize contact characteristics of the repair. Previous studies have identified both of these factors as critical for successful rotator cuff repair.2,7,8 Furthermore, repair constructs must have the ability to resist the forces exerted on the tendon in early shoulder motion. 11 As the majority of rotator cuff repairs tend to fail within the first 3 months after surgery,10,14 it is possible that the tendon footprint contact characteristics of current techniques are not robust enough for consistent healing to be achieved.
Increasing tendon-to-bone contact pressure has been a major focus in the evolution of rotator cuff repair constructs. Animal studies have previously shown that improving tendon-to-bone contact pressure increases tendon healing.22,28 In previous biomechanical studies, double-row repairs have demonstrated consistently better contact pressures compared with single-row repairs,3,25 and TOE repairs demonstrate greater contact pressure than double-row repairs. 18 Our study found the classic TOE construct to have contact characteristics similar to those reported by prior studies using a similar experimental setup.12,20 It is important to note that the numerical value of the differences between the 2 constructs is relatively small, which brings into question the clinical relevance of these findings. Nonetheless, our results also demonstrate that the addition of lateral edge augmentation increases contact pressure by an average of 39% when compared with the classic TOE repair. Whether this correlates to significantly improved outcomes in the clinical setting is unclear. Nonetheless, even a small increase in contact characteristics could still result in improved tendon-to-bone healing and thus reduce the risk of repair failure.
Humeral motion, such as abduction and glenohumeral rotation, has been shown to differentially affect strain patterns across various areas of the rotator cuff.19,27 Not surprisingly, varying constructs of rotator cuff repairs can also result in differing strain patterns in humeral rotation. 1 Taking into consideration the significant effect humeral rotation has on the rotator cuff repair, the present study was specifically designed to evaluate repair integrity in clinically relevant degrees of internal rotation, external rotation, and shoulder abduction. Our results demonstrated that the addition of lateral edge fixation increased repair contact forces and contact pressures in both internal and external rotation at varying degrees of shoulder abduction. Furthermore, while peak contact pressures were not significantly different between the standard and augmented constructs in the neutral position, there was a significant increase with internal and external rotation. This suggests that additional lateral edge fixation is especially critical in reinforcing the repair in humeral rotation—a parameter known to be suboptimally addressed with the classic TOE construct.
Finally, maximizing contact area between the repaired tendon and the rotator cuff footprint is a well-known key factor in improved tendon-to-bone healing.2,7 In prior studies, double-row techniques have demonstrated superior contact areas compared with single-row repairs,5,13,25 and the classic TOE construct has demonstrated increased contact area when compared with the simple double-row repair. 18 While the augmented TOE failed to significantly increase the repair contact area, it also did not adversely affect this parameter and did trend toward greater contact area. As such, our proposed technique increases other key contact parameters while maintaining the benefit of the large footprint coverage achieved by the classic TOE repair.
This study has several limitations. As with all cadaveric studies, these results represent a time zero view of construct contact characteristics and do not account for healing that would occur over time. None of our specimens had evidence of prior rotator cuff injury, and thus the quality of the tissue used does not exactly reproduce the degenerative tendon more often seen with rotator cuff tears. However, our results are consistent with previously reported data. Another limitation of the study is that only differences in contact characteristics were compared, and thus other factors that may be important for rotator cuff repairs, such as gap formation and ultimate strength, were not assessed. We elected to omit these specific parameters because our primary goal was to evaluate the contact characteristics of the repair and not the load-to-failure strength. However, as we passed additional suture limbs through the cuff tendon, especially at the lateral edge, it should be expected that these parameters would have also been improved given the added suture fixation. 24 Indeed, a recent biomechanical study demonstrated that added peripheral edge fixation to a TOE rotator cuff repair improves the initial load-to-failure characteristics of the construct. 23 A third limitation is that we did have to retension the lateral row anchors between constructs. This likely weakened the construct and could have affected our data. This issue was addressed by alternating the order in which the repairs were tested, removing any bias that could have been introduced into the system secondary to this. Finally, it is important to note that, given the previously described anatomy of the supraspinatus and infraspinatus footprints, 15 it is possible that anterior fibers of the infraspinatus were incorporated into the repair. However, given the nature of the study, we do not believe that this would have had a significant effect on our results.
Conclusion
The augmented TOE construct demonstrated superior contact characteristics when compared with the classic TOE technique. Our results suggest that the addition of lateral edge fixation to the classic TOE repair significantly improves rotator cuff repair contact characteristics with minimal additional surgical effort. Although our study does not take into consideration the effects of tendon healing, our results do indicate that adding luggage tag sutures to the lateral portion of rotator cuff tears could lead to improved healing rates after repair of medium and large rotator cuff tears with the TOE construct. Further study of the luggage tag construct in the clinical setting is warranted. Specifically, it would be interesting to compare the outcomes of patients undergoing the augmented repair to those of patients who undergo repair using the classic TOE construct.
Footnotes
One or more of the authors has declared the following potential conflict of interest or source of funding: Funding for the study was provided by the Cedars-Sinai Hospital Systems. O.L. has received consulting fees from Arthrex and Linvatec, and royalties from Linvatec. T.Q.L. has received consulting fees and research support from Arthrex. E.U. has received education payments from Arthrex and Smith & Nephew, hospitality payments from Wright Medical Technology, and a grant from DJO. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
Submitted April 17, 2019; accepted September 26, 2019.