In acute tears, the cuff tissue is more compliant and mobile and can be pulled laterally across its anatomical footprint with minimal tension.39 In contrast, cuff tissue in the more commonly encountered chronic tear is less compliant and is not mobile enough to be pulled to the lateral margin of the footprint without added stress.30,34,35 In large, acute tears in which there are minimal tissue degeneration and retraction, a laterally based footprint-restoring technique may be performed with minimal tension. This technique may have advantages over a medially based repair. In the literature, more attention needs to be directed toward the biomechanics and biology of chronic rotator cuff tears, as these are more commonly encountered.
Almost all of the prospective studies that have compared single- and double-row RCR have found no significant differences in MRI healing rates or clinical results at follow-up up to 2 years.14,16,40-45 Detailed analysis of the surgical techniques used in all these studies revealed that the rotator cuff tendons were repaired back to the lateral footprint in both the single- and double-row constructs.14,16,40-45 Although no clinical studies have compared medially and laterally based single-row repairs, our data suggest that medially based repairs have lower tensions and therefore should not be considered equivalent. Sostak and colleagues31 and Murray and colleagues46 have shown that a medially based single-row RCR can achieve excellent clinical and anatomical results, likely partly because of the lower tension applied to the torn cuff tissue.31,46 Studies are needed to compare medially and laterally based repairs, including single- and double-row repairs.
The vast majority of recent research has aimed to counteract construct tension with stronger biomechanical constructs.20-26 Surgeons have also aimed to improve biological healing by pulling the tendon laterally across the footprint to achieve complete footprint coverage, ultimately increasing the surface area for tendon–bone healing. This has led to the development of various double-row repair techniques, in which the cuff tendon is pulled to the lateral margin of its footprint. One row of anchors is placed in the medial aspect of the footprint, while a second is placed in the lateral aspect; the cuff is reduced and compressed to the tuberosity with various suture configurations. The TOE technique was developed to improve pressurization of the cuff tendon across the footprint by linking the 2 rows with bridging sutures. In doing so, however, the potentially deleterious effects of increased tension introduced by pulling the tendon laterally may have been overlooked. Nevertheless, the biomechanics and stress distribution likely differ between single-row repair and TOE repairs, and direct comparisons cannot be made at this time. The medial row of a double-row or TOE construct may stress-shield or “unload” the more lateral tissue. Studies are needed in order to better understand the tension differential and stress distribution of various double-row constructs.
Recognizing tear morphology is crucial in maximizing chances of healing after cuff repair. For example, a crescent-shaped tear is reduced to the tuberosity with direct lateral translation of the apex of the tear, which is also the deepest or most displaced part of the tear. On the other hand, reducing an L- or reverse L-shaped tear to the tuberosity is not as direct; reducing the deepest or most displaced part of the tear would lead to overreduction and overtensioning of the tendon. However, often the exact “elbow” of the tear is not obvious and appears more rounded; therefore, it is crucial for the surgeon to examine the mobility of the torn tendon along its entire length to minimize tension. Study is needed to assess tension along the entire length of the tear for different tear morphologies and sizes.
Although our results showed that increased tension was needed to reduce a torn tendon to its lateral footprint, no study has indicated exactly how much is “too much” tension. As stated earlier, use of stronger biomechanical constructs, including TOE constructs, may overcome the increased tension associated with laterally based repairs. In addition, laterally based repairs, either single- or double-row, may be best suited for tears with lower tension, whereas medially based repairs may be best suited for higher tension tears. It is also possible that the difference in tensions noted in this study is not significant enough to have a clinical impact on choice of construct or on anatomical healing. We need studies that correlate anatomical healing rates with repair tension in order to better guide surgeons on when to use a medially or laterally based repair.
Other possible effects of increased tension associated with laterally based repairs, including beneficial effects, must be considered as well. Viscoelastic properties of human rotator cuff tendon may dissipate increased tension over time through a variety of mechanisms. Stress relaxation, gap formation, creep, and the hysteresis effect, all associated with cyclical loading in the early healing period, may lead to dissipation of force over time.47,48 These more complex biomechanical properties of RCR constructs are yet to be clearly defined.