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General Description of Arthrology 关节学总论. The connections or junctions between bones are called joints or articulations ( 关节 / 骨连结 ).
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The connections or junctions between bones are called joints or articulations (关节/骨连结).
The bones can be connected together by fibrous connective tissue (纤维结缔组织), cartilaginous tissue (软骨组织) or osseous tissue (骨组织) at different parts of their surfaces.
According to their characteristic features, joints can be classified into two main types: synarthrosis (不动关节) diarthrosis (可动关节) joints
1. Synarthroses(不动关节) They are also called direct connection(直接连结). This means that the bones are held together without space between the articulating bones.
①fibrous joints (纤维连结) ②cartilaginous joints (软骨连结) ③synosteosis (骨性结合) synarthroses (不动关节) There is no active movements at these joints.
(1) The fibrous joints (纤维连结) intervertebral disc 椎间盘 interspinal ligament 棘间韧带 supraspinal ligament 棘上韧带
suture(缝) gomphosis (钉状嵌合) syndesmosis (韧带连结) fibrous joints sagittal suture矢状缝 lambdoid suture人字状缝
Periosteum is continuous from bone to bone, over the sutures. With age, the fibrous tissue is gradually replaced by bone tissue and the sutures become synosteoses.
② Gomphosis (钉状嵌合) Like in a suture, a very small amount of fibrous tissue anchors a tooth into its alveolus(牙槽) in maxilla or mandible.
③ Syndesmoses (韧带连结) : yellow ligament 黄韧带 The bones are held together by an interosseous ligament (骨间韧带) or membrane (骨间膜), or a slender fibrous cord.
For instance, the yellow ligaments join the adjacent two vertebral arches. The interosseous membranes of the forearm (前臂骨间膜) and leg (小腿骨间膜) can be considered as syndesmosis.
interosseous membranes of leg 小腿骨间膜 ulna fibula radius tibia interosseous membranes of forearm 前臂骨间膜
Syndesmoses do permit a slight degree of movement, but their chief function is to provide a stable union.
(2) Cartilaginous Joints (软骨连结) synchondrosis (透明软骨结合) symphysis (纤维软骨结合). Cartilaginous Joints (软骨连结)
When the uniting tissue is hyaline cartilage (透明软骨), the joint is called a synchondrosis. When the uniting tissue is fibrocartilage (纤维软骨), the joint is called a symphysis .
intervertebral disc 椎间盘 ilium Synchondrosis 透明软骨连结 pubis ischium Synchondrosis and symphysis
symphysis纤维软骨连结 Pubic symphysis 耻骨联合
The synchondrosis is eventually replaced by osseous tissue to form a synosteosis, or transformed into fibrocartilage, forming symphysis.
(3) Synosteoses(骨性结合) They mean that the bones are united together by osseous tissue. They are usually from the ossification of fibrous joint or synchondrosis.
For example, the synosteosis between the ilium, ischium and pubis of the hip bone is from the ossification of the synchondrosis.
intervertebral disc ilium Synchondrosis 透明软骨连结 pubis ischium Synchondrosis and symphysis
intervertebral disc 椎间盘 Synosteosis 骨性结合
2. Diarthroses (可动关节) They are also called indirect connection(间接连结) or freely movable articulations or synovial joints (滑膜关节/关节).
A synovial joint is that the bones are held together by fibrous tissue and there is a space between the articulating bones. bone bone
(1) Essential structures of synovial joint (关节的基本结构): ①articular surfaces (关节面) ②articular capsule (关节囊) ③articular cavity (关节腔) essential structures of synovial joint They exist in every synovial joint at the same time.
① Articular surfaces (关节面) The articular surfaces are the bone surfaces forming synovial joints. They are covered by articular cartilage and very smooth.
Articular cartilage (关节软骨) is devoid of both nerves and blood vessels. Its nourishment is largely depended on synovial fluid(滑液). articular surface articular cartilage
② Articular capsule (关节囊) The articular capsule is attached to the periphery of the articular surface and its adjacent bone surface. It encloses the joint cavity.
①fibrous membrane (纤维膜,outer layer) ②synovial membrane (滑膜,inner layer) articular capsule
fibrous membrane (纤维膜) articular capsule synovial membrane (滑膜)
The fibrous membrane (layer) is formed by dense connective tissue and is rich in blood vessels and nerves.
The synovial membrane (layer) invests the inner surface of the fibrous layer and other structures inside the joint except the articular cartilages.
The synovial membrane secretes synovial fluid (synovia/滑液) that fills the joint cavity and lubricates the joint. For this reason, joints are often called synovial joints.
③Articular cavity (关节腔) The articular cavity is a closed cavity formed by the synovial membrane and the articular cartilage.
The articular cavity contains a proper amount of synovia(滑液), and its pressure is negative to the atmosphere pressure.
(2) Accessory structures of synovial joint (关节的辅助结构) ①ligaments(韧带) ②articular disc (关节盘) ③articular labrum (lip, 关节唇) ④synovial fold (滑膜襞) ⑤synovial bursae (滑膜囊) Accessory structures They exist in some synovial joints.
①Ligaments(韧带) They are divided into intracapsular (囊内韧带) and extracapsular ligaments (囊外韧带), and very important for the stability of joint.
②Articular disc(关节盘) It is also called intra-articular cartilage(关节内软骨), located between the articulating surfaces in some joints.
The articular disc is a flattened pad of fibrocartilage, and divides the joint cavity into two parts, it makes the articular surfaces fitting more with each other and diminishes the shock of joint.
③Articular labrum (关节唇) It is a pliable fibrocartilaginous ring and helps to deepen the articular fossa, e. g. , the labrum of the glenoid cavity of scapula.
④Synovial folds and bursae (滑膜襞和滑膜囊) The synovial folds are formed by the synovial layer of articular capsule, and contain loose connective tissue.
Some joints may have closed, fluid-filled sacs (bursae) associated with them. The bursae are lined with synovial membrane continued with those of joint.
3. Mmovements of joint Movements of synovial joints are produced by the actions of skeletal muscle. The types of movements include the followings:
(1) Gliding (slipping) movement (滑动) It is that one articular surface moves back and forth or side to side over another surface without angular or rotary movements.
The movements of intercarpal joints(腕骨间关节) and intertarsal joints (跗骨间关节) belong to this type.
(2) Flexion and extension (屈和伸) These two antagonistic movements are performed in coronal axis.
The flexion means the angle between the articulating bones is decreased when moving, and the parts come closer together, or one of the articulating bones is fixed, another one moves forwards.
While extension means the angle between the articulating bones is increased when moving, and the parts move farther apart, or one of the articulating bones is fixed, another one moves backwards.
The ankle joint(踝关节) is an exception. It has dorsal flexion (背屈, extending the foot at the ankle) and plantar flexion (跖屈, flexing the foot at the ankle). Dorsal flexion 背屈 plantar flexion 跖屈