We have divided rotator cuff patch types into four categories: tendon patches, non-degradable rotator cuff patches, extracellular matrix rotator cuff patches, and synthetic degradable rotator cuff patches. Of these, synthetic biodegradable rotator cuff patches are an emerging field and not a common clinical repair option.
Tendon Patches
Tendon patches can be used to reduce tension between tendon and bone and have the potential to contribute to injury bioprosthesis by providing growth factors and attachment points to support cell growth. In a model of acute murine rotator cuff tears repaired using tendon patches, murine autologous cells were found to begin proliferating and migrating into the tendon patch, however (and this cannot be confirmed) it is not known if the autologous cells remain active in degenerative and avascular rotator cuff tears.
Tendon patches can be of either allogeneic or autologous origin. One study used allogeneic Achilles tendon patellar tendon patches, or quadriceps tendon patches to repair massive rotator cuff tears in 28 patients, and although there was improvement in postoperative function, there was no significant difference relative to patients with similar conditions who underwent only acromioplasty and joint clearance. In addition, among the patients with allogeneic tendon patches, one patient developed an infection and one patient developed a severe postoperative immune rejection reaction.
Autologous tendon patches sourced from the patient’s own body were able to reduce the postoperative development of immune rejection in patients. The efficacy of using resected biceps longus tendon for repairing rotator cuff tears has been reported in the literature. In addition to the function of reducing the tension between the tendon and the bone, and possibly by providing growth factors and attachment points for cell growth support, this method does not require surgical removal of the tendon from other parts of the body, and secondly, most patients with rotator cuff tears also have combined injuries to the biceps longus tendon, many of which require resection and treatment. This procedure reuses the long head of the biceps tendon. In a retrospective study comparing the efficacy of repairing a massive rotator cuff tear using the resected long head biceps tendon with and without the resected long head biceps tendon, there was no significant difference in pain, range of motion, or clinical outcomes of the patients’ shoulder joints at 12 months postoperatively, while the study group had significantly higher shoulder strength and a significantly lower failure rate of repair than the control group. The results of the study were compared with those of 24 patients who had a large rotator cuff tear and mild fatty degeneration of the infraspinatus muscle repaired without a partial patch, and found that both patients showed significant improvement in function after surgery compared with the preoperative period. The failure to restore the normal structure of the tendon-bone junction is an important reason for the use of tendon patch repair. However, there is no good solution for tendon-tendon bone attachment point healing with existing techniques. Recent studies have reported the use of allogeneic bony tendons to repair canine giant rotator cuff tears, with better postoperative integrity of the allogeneic bony tendon patch compared to direct debridement sutures and repair with human dermal patches, with complete union of the allogeneic bone to the host bone and good fusion of the allogeneic tendon.
Non-degradable rotator cuff patches
The use of a non-degradable scaffold to augment the supraspinatus tendon of the humerus is the most common form of repair, and it involves a simple surgical procedure to fix the tendon to the bone parenchyma through a non-absorbable anchor nail. This method, similar to a hernia repair, is a mechanical and permanent repair that allows the rotator cuff to heal itself after the repair. Various non-degradable rotator cuff patches have been developed and designed based on this concept, with strong tensile strength, good histocompatibility and excellent handling properties as the main features.
The use of polyester-based patches such as polytetrafluoroethylene (PTFE) for the repair of rotator cuff tears was reported in the first uncontrolled study and showed good tolerance and improved function in 23 of 25 repairs. Histologic studies using polytetrafluoroethylene patches have shown that the patch grows tightly to the bone and between the patch and the rotator cuff, and no evidence of surrounding inflammatory reaction was found.
The most recent study of polyester patch implantation for repair of rotator cuff tears showed good tolerance, significant functional improvement and pain relief in 41 patients at 86 months of follow-up, with retears between the patch and tendon in 3 patients. The authors noted that the new generation of polyester patches showed significant improvement in terms of high tensile strength, low friction and excellent histocompatibility in the short postoperative period. Similar results were seen in other studies and case reports of polyester-based patch implantation over a 16-year follow-up period. One study comparing the efficacy of repair using direct sutures, collagen patches, and polypropylene patches found a significant advantage in function, strength, and recurrence rates for polypropylene patch repair over the other two repair methods at 3-year follow-up.
Other non-degradable patch materials are being developed and tested, with promising reports in terms of materials such as polycarbonate polyurethane and polytetrafluoroethylene. These materials are usually processed into foams that have connecting pores to stimulate the growth function of good tissue. One study used polycarbonate polyurethane patches to repair giant rotator cuff tears in 10 patients, with significant improvement in postoperative ASES scores, UCLA scores, and CADL scores, and good durability of the patches. In a 6-month follow-up study of 37 patients with irreparable rotator cuff tears, it was reported that the clinical efficacy of repairing giant rotator cuff tears with expanded polytetrafluoroethylene patches was significantly higher than that of direct suture repair.
The main problem with non-degradable implantable patch materials is their lack of long-term integrity. It has been studied that carbon fiber patches are known as ideal materials for tendon and ligament repair with good mechanical strength, and these materials, when left in vivo for a long time, appear to have disrupted structural integrity and migrate to other tissues, causing chronic inflammation and foreign body reactions, requiring revision surgery.
The benefits of non-degradable materials for repairing rotator cuff tears are relatively short-term, but may carry an unnecessary long-term risk. However, considering other factors such as age, size, and non-degradable rotator cuff patches are still the best option for some patients today. Better clinical evidence is still needed to understand the long-term safety of nondegradable implants.
Extracellular matrix rotator cuff patches, or biologic rotator cuff patches
Studies have shown that tendon aging and subsequent repair failure after repair is closely related to changes in tissue matrix structure, stimulating changes in cellular behavior. Based on this concept, the patch was designed with the aim of intrinsic cell populations by providing a temporary matrix structure for collagen attachment sites. In vitro experiments have shown that biocompatible cells implant into the patch and that biological cells self-complete the repair of the torn tissue. The design of such patches requires the extraction of extracellular matrix structures such as porcine small intestine submucosa, porcine dermis, and skin.
In vitro experiments have shown that such patches are excellent attachment points and culture media for human tendon cells, especially in the absence of chemical cross-linking. However, confusion has arisen during animal studies, and in some case studies, conflicting reports of safety and efficacy have been reported. Sometimes, this is due to inappropriate or inconsistent selection controls. In one study, using an acute rat rotator cuff tear model, rotator cuff repair with porcine small intestine submucosa was found to be biomechanically superior in the experimental group to the unstitched-repaired, reinforced control group. Later, the same implantation was performed in two rat models, one “acute” and the other “chronic”, and a significant efficacy was found only in the “chronic” group. However, in this study, there was still no adequate control. In a canine model using submucosal material to replace tendons, the results showed new tissue growth within the patch, which was reshaped and integrated into the muscle and bone. However, in a sheep model study comparing the effects of porcine dermal patches to porcine small intestinal submucosal patches, the dermal patches showed superior performance in terms of inflammatory plasma fibrinogen markers and and degree of ossification. The authors observed faster degradation of porcine small intestinal submucosal patches than dermal patches, with almost complete absorption within 9 weeks. In a study using porcine dermal patches to repair supraspinatus tendon injuries in an African green monkey model, histological studies at 3 and 6 months postoperatively revealed that the patches reshaped a tendon-like structure with a uniform distribution of fibroblasts within the patch, parallel distribution of collagen fibers, and a large number of blood vessels growing into the tendon, which decreased to the normal level of the recipient tendon at 6 months. One study used human allogeneic dermal patches to repair giant rotator cuff tears and found that 45 patients were significantly better postoperatively than preoperatively at 24-68 months follow-up, with a high rate of patient satisfaction and very few patients requiring secondary surgery. Another report evaluated the safety and efficacy of arthroscopic human dermal patch repair of human giant rotator cuff tears through a randomized controlled trial, in which a single-row fixation + rotator cuff patch was used for the experimental group and a single-row fixation was used for the control group. The rate of complete repair was 85% in the experimental group and only 40% in the control group.
In 2007, a platelet-rich plasma scaffold was used to achieve complete healing in a sheep tibial defect model, and after 16 weeks, the mechanical strength, biocompatibility, and osteoinductivity were significantly better than those of the control group. One study reported that platelet-rich plasma could interfere with the intact differentiation of human osteoclast precursors. Subsequently, studies on the repair of musculoskeletal soft tissue injuries with platelet-rich plasma were conducted. A cohort study comparing the use of platelet plasma with and without platelet plasma for the repair of rotator cuff tears did not show clear data that platelet plasma accelerated the repair of rotator cuff injuries and improved clinical symptoms, however, this study was not able to find important differences in tissue structural integrity. The study found that patches constructed with platelet fibrous matrix reduced the likelihood of rotator cuff retears. The study found no significant differences in postoperative clinical function and tissue structural integrity between the use of platelet matrix-constructed patches versus no patches for rotator cuff tears. In addition the latest evidence from interrogative medicine, by collecting 19 single-center experimental studies with 1088 study subjects and performing META analysis, found a lack of sufficient evidence for the effectiveness of platelet therapy in the treatment of musculoskeletal soft tissue injuries.
The disadvantages of extracellular matrix patches include poor suture fixation properties, as well as poor mechanical properties, with studies reporting much lower elasticity and toughness than normal tendons. In some cases, these disadvantages are overcome with the addition of biodegradable polymer fibers to enhance fixation. Another problem is that traces of DNA and cellular contents have been identified in some extracellular matrix patches, which may cause adverse inflammatory responses and disease transmission. In addition, some extracellular matrix patches have been reported to be associated with chronic inflammation, although this was reported in a rat abdominal wall model and not a joint model.
A recent clinical trial showed results that extracellular matrix patches derived from porcine dermis and human dermal patches have improved clinical outcomes. A prospective randomized study using human dermal patches to repair 22 patients with massive rotator cuff tears resulted in a higher percentage of complete rotator cuff repairs compared to 20 patients with direct debridement sutures, and no adverse events with human dermal patches. However, the efficacy of these implants remains questionable. One clinical study showed a very poor clinical outcome of repairing giant rotator cuff tears with porcine small intestine submucosal rotator cuff patches, resulting in a 91% recurrence rate. This result was further confirmed by other studies that used porcine small intestine submucosal patches in the reinforced group as opposed to the non-reinforced group. The repair failure was attributed to the rapid resorption of the porcine small intestinal submucosal patch and the inadequate mechanical support provided by the repaired tear.
This evidence supports or opposes the efficacy of porcine-derived extracellular matrix rotator cuff patches, so their safety and efficacy remain difficult to determine. The human-derived extracellular matrix rotator cuff patch is another area of inquiry.
Synthetic degradable rotator cuff patches
In order to overcome the cost and safety issues associated with extracellular matrix rotator cuff patches and to achieve cellular repair, synthetic, bionic and biodegradable rotator cuff patches are beginning to emerge. The design of these patches is based on the concept of providing a non-permanent attachment point for self-repair, a patch that can be absorbed over an appropriate period of time, yet possesses good biocompatibility, good mechanical properties and suitable elasticity.
Commonly used degradable polyester materials for biodegradable rotator cuff patches include levopolylactic acid copolymers, lactic acid hydroxyacetic acid copolymers, polycaprolactones, and polypropylene glycol copolymers. In addition, some studies have suggested the use of simple, synthetic biodegradable materials, most of which emphasize the benefits of fabricating patterned structural bodies.
The collagen bundles of normal tendons are oriented along the long axis of the tendon. With the application of electrospinning technology, novel rotator cuff patches can be created and mimic the same orientation of the tendon collagen fibers, and in some cases, the fibers can also transition from alignment to random orientation at the tendon bone junction. Many knotted-hook aligned rotator cuff patches have been shown to directly affect the alignment of adherent cells as well as influence the expression of matrix structural proteins.
The actual design concept of these degradable rotator cuff patches fabricated by electrospinning technology also includes incorporation of biological organisms into biosynthetic patches. This is done by various strategies such as adding stem cells to the patch, adding matrix protein collagen to the patch at the time of manufacture or implanting growth factors that are slowly released as the patch degrades. Methods designed to mimic the substance content of the tendon-bone junction have also been proposed. Therefore, the use of biodegradable rotator cuff patches for biorepair of rotator cuff tears is a current trend.
In vitro studies have confirmed that both lactic acid hydroxyacetic acid copolymer patches and polypropylene glycol patches processed by electrospinning techniques exhibit good cellular response and biocompatibility. Further studies have also demonstrated that for the same materials, processing by electrospinning reduces the in vivo immune response more than other common processing.
Synthetic degradable patches showed good results in preliminary efficacy tests in animal models. Fibrous poly patches without electrospinning were incorporated into a goat model that showed significant strength improvement in the first three weeks after surgery, although this was not statistically significant. Polycaprolactone patches processed by electrospinning showed good tolerance with good cellular penetration after 8 weeks of implantation into a rat model, and a randomized controlled trial showed that repair using electrospun processed levopolylactide patches significantly improved Young’s modulus relative to non-reinforced repair.
However, in contrast to these good findings, there are concerns about the degradation products of these polymers. High concentrations of lactic acid and hydroxyacetic acid have been found to be toxic to tendon cells and osteoblasts, and non-toxic concentrations reduce tendon cell proliferation and differentiate osteoblasts. Therefore, the rate of degradation and the accumulation of acidic degradation products are important for the safety of synthetic degradable patches. Studies have also shown that the toxicity of different polymer degradates varies in in vitro experiments, but the tissue-dependent nature of the degradation products is well known. Therefore, future research should aim to achieve complete degradation of patches in vivo, ensuring that the release of acidic degradates remains within safe limits throughout the product’s life cycle.
Another problem with electrospun degradable patches is their relatively low mechanical properties, even in aligned structures. Even with the use of multilayer methods, the mechanical properties of better structured materials such as knitted lactic acid hydroxyacetic acid copolymer fibers or rapid prototype polycaprolactone structures are fused into the patches to improve the mechanical properties, but still not to a satisfactory degree.
A deeper problem with electrospun materials is that the pore space on the patch is too small, preventing further cell migration into the patch, so that the new tissue structure is not exactly what we need. To overcome this problem, several methods have been developed recently, including the use of salt or polymer leaching and advanced collection systems.
Further clinical evidence on the performance of these patches needs to be gathered. One clinical study used polyester-based biodegradable patches to repair 21 massive rotator cuff tears, with significant improvement in function and range of motion of the affected shoulder and 90% postoperative patient satisfaction. In another study, 18 cases of giant rotator cuff tears were repaired with L-polylactic acid patches, and the postoperative functional scores of the shoulder joint were significantly improved compared with those before surgery. At present, there is still a lack of clinical studies or randomized controlled studies with large samples to support the results.
Summary
The volume of rotator cuff repair procedures has increased very rapidly in recent years, but it does not yet guarantee a good cure rate and needs to improve the prognosis of patients. The repair journey has progressed from a visually static repair, to a mechanical repair, to a bioactive patch repair that provides attachment points for the body’s cells to achieve self-healing. None of the methods currently available provide satisfactory results and there is no conclusive evidence as to the cause of repair failure, such as inadequate mechanical support or due to complications such as infection or inflammation.