科学问题|概述
Why don't tissues in joints heal?
先前提出的有关ACL愈合的理论包括缺乏内在细胞反应和血管反应。（2,4,7,14,14,19,22）还提出了机械病因，包括缺乏缝合线修复和缺乏强度韧带和破裂部位的流体流动。对于半月板愈合（20）和肩袖缝合线修复也有类似的论点。（15,23）直接解决这些假设的工作在过去十五十五的临床结果中遇到了限制的体内成功（6,21），只有边际改善年。
The limited success seen with prior approaches prompted us to abandon the accepted doctrine for the failure of these tissues to heal and return to an unbiased failure analysis of the problem.
Fig 1. Histologic response of the human ACL to rupture
答:组织学外观正常的ACLfibroblasts (blue nuclei; 40X).
B.破裂后3个月ACL组织的组织学出现显示韧带末端的细胞密度增加（40倍）。
C.破裂后3个月ACL毛细血管密度增加（20倍）。
D. Synovial layer which has reformed over the ligament ends at 8 weeks after rupture (BV = blood vessel, 40X).
Sections are immunohistochemistry for alpha-smooth muscle actin (SMA) where red demonstrates a positive stain for SMA, with a blue counter-stain for cell nuclei.
为了确定和定义这些组织的愈合过程中的缺陷，获得了IRB批准，并在5年内收集了关节内组织的完整和受伤的人类标本。评估的组织包括韧带，半月板，软骨和肌腱。（1,8,10,13,16,17）
Examination and histomorphometric analyses were performed in a consistent manner for all tissues. Parameters of cell density, vascularity and extracellular matrix organization were systematically evaluated. Cellular functions including proliferative capability, migration characteristics and capacity for extracellular matrix production were evaluated for cells from normal(9,11) and injured tissues.(12,17)
图2。Proliferative & migratory capacity of cells in osteoarthritic articular cartilage in vitro. A) Schematic for orientation for B and C. B) Cell outgrowth at 7 days. C) Marked cell outgrowth after 14 days.
在比较伤害后状态和后的组织时，我们确定了与缺陷相邻的固有细胞和血管反应（10）（图2b＆2c），以及这些组织中细胞的显着能力体外迁移（9,12,17）。即使是终末期骨关节炎患者的关节软骨细胞也具有这种能力（17）（图3）。但是，在没有观察到的伤害部位的时间点（图3A和3C）。软骨，半月板和ACL是正确的（8,10,13）
Fig. 3体内六周后，ACL破裂的持续伤口缺陷的显微镜视图（a）。请注意缺乏缺陷。相反，（b）中的愈合内侧副韧带完全填充；即使只有7天（红色为阳性污渍的TGF-B1的免疫组织化学）。内侧副韧带位于膝关节外，通常在受伤后不暴露于滑液。ACL中看到的缺陷的外观与最早在受伤后1天看到的软骨损伤的缺陷相似（C），同样，关节软骨中的缺陷不会急性填充或以后的时间点。急性缺陷可能是骨关节炎关节软骨（D）中发现的裂缝的前体。
Lack of filling of the wound site for the tissues in joints was a key finding common to all tissues examined.在关节外部的组织中，愈合反应的第一阶段是用纤维蛋白 - 平台塞填充缺陷，该纤维蛋白 - 平台塞桥接伤口边缘（3）。然后，这种塞子或脚手架随后被修复性细胞入侵，这些细胞将脚手架重塑为愈合纤维血管疤痕。早期临时支架的形成是伤口愈合过程中的第一步。
Inside the joint, bleeding occurs after injury, but no fibrin-platelet plug is observed to form, even at the injury site.(5) One possible explanation for this finding is that circulating intra-articular plasmin breaks down the fibrin plug as fast as it can form. Recent work has shown that after trauma to the joint, the production of plasmin is upregulated via the increased secretion of urokinase plasminogen activator(18)
With the additional circulating plasmin, the fibrin network is quickly destabilized within the joint environment and no fibrin-platelet plug forms. Premature loss of the fibrin-platelet plug would have the significant clinical benefit of preventing overall joint scarring and stiffness (arthrofibrosis) and thus maintenance of joint mobility after injury. However, this also requires the sacrifice of healing of the individual injured tissues, as the degradation of the fibrin-platelet plug in the overall joint also would remove it prematurely from any wound sites.
As formation of the fibrin-platelet plug is the essential first step for wound healing of musculoskeletal tissue outside the joint,(3) we believe that the loss of this fibrin-platelet plug inside the joint is a key mechanism behind the failure of tissues in the joint to heal (Fig. 5).
Fig 4.Proposed pathway for accelerated fibrinolysis after joint injury. Increased secretion of urokinase plasminogen activator (u-PA) results in high levels of plasmin in the inflammatory synovial fluid. This is likely the reason for the accelerated fibrinolysis noted in the joint after injury. (t-PA: tissue plasminogen activator. PAI-1 and 2: Plasminogen activator inhibitor 1 and 2. uPAR: urokinase-type plasminogen activator receptor)
Fig. 5:Novel hypothesis of the failure of intra-articular healing. For the medial collateral ligament (MCL) which is outside the joint, injury is followed by formation of a provisional scaffold in the form of a fibrin clot. The scaffold is gradually remodeled as the tissue heals. No fibrin clot is found at the injury site of the ACL, which is inside the knee joint. Without a provisional scaffold, healing of the wound site cannot proceed.
我们的理论是，临时支架的过早失败阻止了关节内组织的愈合（图5）。这是针对单个组织提出的先前机制的重要变化，该机制主要集中在固有细胞和血管反应上。
Past research based on the cell-deficiency theory focused mainly on stimulation of cells in vitro with growth factors, or on cell transplantation into wound sites (including the use of stem cells and genetically modified cells).
Our preliminary work has shown that delivery of the appropriate bridge can stimulate the intrinsic healing response for tissues inside joints. This bridge can also be used as a foundation for the delivery of cytokine and cell-based treatments.
关节内部的刺激组织愈合可能会改变我们处理这些伤害的方式。这些组织的原发性缝合线修复和愈合比当前的切除和替代方法具有多个优势。这些程序将优于简单切除关节组织的更大保存，从而有可能降低骨关节炎的速率。增强的初级维修（图6）也将与当前组织置换技术（例如ACL重建）具有优势作为总体解剖学。
Fig. 6:Example of a potential clinical application. Stimulation of successful healing by enhancing suture repair with a biologic boost from a collagen-platelet hydrogel placed in the wound site could alter our approach toward these common injuries from resection and replacement toward repair and regeneration.