Rotator cuff repair is one of the most commonly performed orthopedic procedures globally. Approximately 272,000 rotator cuff repairs are performed in the United States alone each year.1 There have been many advances in the surgical treatment of rotator cuff tears including the development of arthroscopic techniques. Despite these advancements, nonhealing or re-tears occur in 10% to 50% of cases.2–5
This high failure rate has resulted in different treatment options to improve healing and success rates. Some attempts at improving the healing rate have focused on optimizing the biology of the repair site and have included stem cell therapy, platelet-rich plasma, or microfracture of the footprint prior to repair.6–11 Other attempts have been made to improve the structural integrity of the repair tissue.12–20 Oftentimes at surgery, the quality of the tendon is found to be poor. In such cases, suture may not be adequate to hold the tendon against the footprint if the tendon does not have enough integrity. Many suture techniques have been used to improve the integrity of the suture-tendon complex, such as the use of rip-stop sutures.21–25 There also has been interest in using allograft or xenograft patches to either buttress the existing tendon or span a gap that may exist in the repair. Synthetic patches also can augment a rotator cuff repair and may improve the biomechanical properties of the repair. It is believed such patches improve the biomechanical properties of the repair construct by decreasing the ability of the suture to cut through the compromised tendon.
One such patch that has been developed recently is the BioFiber Patch (Tornier, Bloomington, Minnesota). This absorbable, nonsynthetic patch is made from P4HB (poly-4-hydroxybutyrate) and breaks down into naturally occurring metabolites. This study examined the biomechanical effects of this patch on a rotator cuff repair construct in a human cadaveric model. The study hypothesis was that the patch would improve the biomechanical properties of the construct as demonstrated by less gap formation during cyclic loading and a higher load to failure (LTF).
Materials and Methods
Six human cadaveric shoulders from donors ranging in age from 65 to 80 years were used to conduct the biomechanical analysis. The quality of tendons was as anticipated for specimens of this age. Only areas without any rotator cuff tearing were selected for inclusion. The shoulders were stored at −20°C until 5 hours before testing. The supraspinatus of each shoulder was identified and surgically detached from the greater tuberosity.
Tendons were prepared into 2 separate 1-cm wide strips for each shoulder. Each shoulder underwent 2 separate repairs each using a single 4.5-mm titanium anchor. The first repair used a horizontal mattress suture (the nonaugmented control group). The second repair used the same horizontal mattress suture configuration but was augmented by passing the sutures through the rotator cuff and then through a fiber patch that was placed on top of the rotator cuff; sutures were tied on top of the patch.
All specimens were secured to a universal testing machine (MTS Insight 2; MTS, Eden Prairie, Minnesota) for biomechanical analysis. Testing was performed at room temperature, and samples were kept moist using a spray bottle of normal saline during testing to prevent desiccation. After a preload of 5 N was applied, cyclic loading was performed between 10 and 50 N at a rate of 12.5 mm/second. Gap formation between the repaired tendon and the footprint was determined at 100 cycles using a digital caliper accurate to .001 inches (Mitutoyo Series 500; Mitutoyo, Kawasaki, Japan).
Measurement was taken at the area of maximum gap formation. Load-to-failure testing was performed on all surviving specimens after 100 cycles at a rate of 12.5 mm/second. Stiffness was determined using the linear region of the load-displacement curve during LTF testing. All specimens were taken to complete failure, and no partial failures were recorded. Mode of failure was determined by visual inspection.
A paired t test was used to compare differences in cyclic loading, LTF, and stiffness between the augmented and nonaugmented repairs. Statistical significance was set at P<.05.
Gap formation after 100 cycles was 1.07 mm in the suture-only group and 0.50 mm in the patch-augmented group (P=.002). Load to failure was 54.26 N in the suture-only group and 109.53 N in the patch-augmented group (P<.001).
Rotator cuff failure can occur for many reasons. One of the main reasons for failure is the inability to maintain the repaired tendon in contact with the bony footprint. This type of failure can happen at the interface of the bone and the anchors or at the interface between the sutures and the tendon. As anchor properties have improved with advancements in arthroscopic rotator cuff repair, the weak link in the repair has shifted to the suture-tendon interface.
One strategy to improve the integrity of the suture-tendon complex is to use a patch to augment the repair. The current study showed that such a patch improved the biomechanical properties of the repaired rotator cuff; both less gap formation during cyclic loading and a higher LTF were demonstrated. Other studies also have examined the biomechanical effects of a patch on rotator cuff repair.26–35
Koh et al36 assessed the effects of a polylactic acid-reinforced rotator cuff repair in an ovine infraspinatus model. They demonstrated an increase in strength of 125% compared with a nonreinforced control. MacGillivray et al29 studied the biomechanical effects of a poly-L-lactic scaffold reinforcement in a goat model. Histology and biomechanical properties were studied for a 6-month period. Although no difference in LTF was found between the 2 groups, the authors noted that a fibrous tissue occupied the patch and matured into a “…dense, homogeneous fibrous tissue with alignment of collagen between the scaffold bundles.”
Jung et al26 evaluated the effects of a dermal patch in a sheep cadaver model of rotator cuff tears. They tested different patch augmentation techniques and found patch augmentation increased LTF by up to 61%. Shlegel et al33 also examined the biomechanical effects of patch augmentation in a sheep model. A small intestinal submucosa patch was used, and the animals were sacrificed at 12 weeks. Although the LTF did not demonstrate a significant difference between the augmented and nonaugmented groups, the augmented group had significantly better stiffness than the nonaugmented group. The authors postulated that this was clinically relevant as “…stiffness is the biomechanical parameter representing the tissue response to sub-destructive loads seen with early rehabilitation.”33
In a human cadaveric study, McCarron et al30 tested patch augmentation to determine whether it would improve biomechanical properties; they found that a reinforced fascia lata graft improved cyclic loading up to 1000 cycles. Shea et al37 also tested the biomechanical properties of an augmented rotator cuff repair using a human cadaveric model. Their study included 6 pairs of human cadaveric shoulders and compared repairs that were reinforced with a porcine dermal patch (Conexa; Tornier, Edina, Minnesota) with repairs that were not augmented. Gap formation under cyclic loading was reduced by 40% for the reinforced specimens compared with the control group, and the ultimate LTF also was significantly higher in the reinforced group.
The current study yielded results similar to the findings of these previous studies. The use of rotator cuff repair augmentation in the form of a fiber patch greatly reduced gap formation and doubled LTF.
This study has several limitations. First, this was a time zero study. The biomechanical properties of the repair were measured immediately, whereas in the actual clinical scenario, the situation is much more complex. The ultimate success and integrity come from the healing process, which was not studied. However, the current authors believe initial integrity to be critical to the eventual healing, which is the importance of what was demonstrated in this study. Second, the sample size was small. However, a statistically significant difference was demonstrated between the groups. Third, the cadaveric specimens used were not an exact representation of the typical rotator cuff that undergoes repair; the specimens were from donors older than the average patient undergoing rotator cuff repair. However, the quality of the rotator cuffs would be expected to be poor, and thus the current authors believe this represents a good model in which to test patch augmentation.
This study demonstrated the use of a fiber patch improved the biomechanical properties of a rotator cuff repair construct in a human cadaveric model. Surgeons should be aware of augmentation options available for use in rotator cuff repair; synthetic fiber patch augmentation is one option that may improve initial biomechanical properties.
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