Joints — The Cartilage & Tendon Economy关节 · 软骨与肌腱的经济学

System · Level 3

软骨无血管 · 加载喂养 · 肌腱核心终身少更新 · OARSI/ACR 首选 = 运动 + 减重 + 外用 NSAID

What a joint actually is — seven parts

Stop 1/7

关节的真身 · 七个组件

A joint is not one thing — it is a team of tissues, and pain shows up when any of them falls behind:

Articular cartilage: a 2-4 mm layer of hyaline cartilage capping the bone ends — type II collagen + GAGs (glycosaminoglycans) + ~80 % water — avascular, aneural, alymphatic (Sophia Fox 2009 *Sports Health*). Its compressive resilience and near-frictionless surface come entirely from the water content + GAG network locking that water in placeSynovium + synovial fluid: a thin synovial-cell layer secretes hyaluronic acid (HA) + lubricin (PRG4); the fluid is shear-thinning — viscous at rest, slippery under load (Jay & Waller 2014 *Matrix Biology*)Joint capsule + ligaments: dense type I collagen — binds bones together, limits extreme anglesTendons: transmit muscle force to bone; type I collagen + a little elastinMenisci / labra (knee / hip / shoulder): fibrocartilage — distributes load + enlarges the contact surfaceBursae: reduce friction between tendons / skin and boneProprioceptive nerve endings: live in the capsule + ligaments, telling the brain where the joint is in space
The first thing to hold onto: of those seven, only the synovium, capsule, and ligaments are vascular. Cartilage and the inner meniscus eat through load + diffusion. The rest of this island unfolds from that fact.

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