A Series Of Basic Research On Rotator Cuff Repair And Reconstruction

ObjectiveFull-thickness rotator cuff tear is one of the most common conditions affecting the shoulder joint^[1,2].Although rotator cuff repair has been a well-developed operation with promising prognosis,structural failure after repair is a well-known and frequent complication^[3,4].Most frequently,the re-tear happens at the tendon-to-bone junction^[3].Apart from fixation failures,lacking of healing potential between tendon and bone is the main reason of re-tear after surgery.To explore the effects of stress loading,internal environment and biomaterial augumentation of tendon-to–bone healing,series of experiments are conducted to investigate the process of tendon-to-bone healing.To better study the mechanism of tendon-to-bone healing in the bone tunnel,the into-tunnel repair is also evaluated compared with onto-surface repair in terms of histology and biomechanical quelities.To better investigate the methods of improving tendon-to-bone healing,a dual-layer organic/inorganic flexible bipolar fibrous membrane?BFM?is fabricated and tested as augumentation in rotator cuff tears.In vivo experiments are conducted to test whether the application improves gradient microstructure in tendon-to-bone healing.Addtionally,new approach of rooting rotator cuff reconstruction is proposed for massive irreparable rotator cuff tears.Comparisons in histology and biomechanical tests are conducted between rooting reconstruction?RR?group and scaffold bridging?SB?group to better understand the mechanisms of tendon-to-bone healing.Methods1.Thirty-Six New Zealand white rabbits underwent bilateral detachment and repair of the supraspinatus tendon.On the randomly chosen experimental side,the into-tunnel?IT?rotator cuff repair was done and transosseous repair was done on the contralateral shoulder for control.Animals were sacrificed at 4,8 and 12 weeks and evaluated for the presence of fibrocartilage,collagen fiber organization at the insertion and tendon-maturing characteristics.Biomechanical testing was performed to determine the properties of the repaired tissue.Statistical analysis was performed by use of paired t-test analysis with significance set at P<.05.2.A dual-layer organic/inorganic flexible bipolar fibrous membrane?BFM?was successfully fabricated by electrospinning to generate biomimetic non-mineralized fibrocartilage and mineralized fibrocartilage in tendon-to-bone integration of enthesis.Rottator cuff tear models are created and repaired with the augumentation of BFM.Animals were sacrificed at 4,8 and 12 weeks and evaluated for the presence of fibrocartilage,collagen fiber organization at the insertion and bone ingrowth.Biomechanical testing was performed to determine the properties of the repaired tissue.Statistical analysis was performed by use of paired t-test analysis with significance set at P<.05.3.Seventy-Two New Zealand white rabbits were allocated into two groups and irreparable rotator cuff tears were created.In rooting reconstruction?RR?group,rotator cuff reconstruction was done using semitendinosus tendon.In scaffold bridging?SB?group,rotator cuffs were repaired by using the iliotibial band as a bridging scaffold.Animals were sacrificed at 4,8 and 12 weeks and evaluated for cellularity,fibrocartilage formation and collagen fiber organization at the aperture and in the tunnel.Biomechanical test was performed to determine the properties of the repaired tissue.Statistical analysis was performed by use of t-test analysis with significance set at P<.05.Results1.The“into-tunnel”repair technique induces a distinctly different reformation pattern than the traditional“onto-surface”repair as control.The inserted tendon gradually dissolves and goes through a progress of chondrogenesis with significant fibrocartilage formation while a small part of the tendon reforms to parallel collagen fibrils.In biomechanics tests,the IT group excels the control significantly at 12-week time point in both ultimate load and stiffness?P<.001?.2.The in vivo results showed that BFM significantly increased the area of glycosaminoglycan staining at the tendon–bone interface and improved collagen organization when compared to the simplex fibrous membrane?SFM?of PLLA.Implanting the bipolar membrane also induced bone formation and fibrillogenesis as assessed by micro-CT and histological analysis.Biomechanical testing showed that the BFM group had a greater ultimate load-to-failure and stiffness than the SFM group at12 weeks after surgery.3.The RR technique induces a distinctly different reformation pattern than the scaffold bridging repair.At the aperture,the transplanted tendon collagen fibers partially reforms to be in alignment of the direction from tendon to bone with chondrocytes displayed in alignment of the fiber.Intense fibrocartilage formation was detected on the side of the tendon.In the bone tunnel,similar changes were also found that a gradual transition from bone to the tendon id reformed with a distinct but continuous zone of fibrocartilage.Conclusions1.The into-tunnel technique alters the reformation process of the tendon after repair.The inserted tendon gradually dissolves and goes through a progress of chondrogenesis with significant fibrocartilage formation while a small part of the tendon reforms to parallel collagen fibrils.This newly formed structure results in a better biomechanical construct.2.The hybrid scaffold could act as a bridge between the repaired tendon and footprint,affect the healing process in multiple ways.BFM significantly increased glycosaminoglycan formation and improved collagen organization compared with the SFM.While biomechanical results both improved in BFM and SFM,BFM implanting induced more significant bone formation and fibrillogenesis.This integrated bipolar nanofibrous membrane is a very promising biomimic biomaterial for rotator cuff repair.3.The rooting reconstruction of rotator cuff is a possible surgical approach for irreparable rotator cuff tears with better mechanical strength and good tendon-to-bone healing in the bone tunnel.4.The“into-tunnel repair”technique with the original tendon and the transplanted tendon can both lead to a stronger tendon-to-bone healing with much stronger chondrogenesis.