SN3
SHORT NOTE
5M
★ High-yield
Describe the structure and types of a synovial joint. Add a note on synovial fluid.
Definition
A synovial joint is one in which the articulating bones are separated by a joint cavity containing synovial fluid, permitting free movement.
Essential Features
| Feature | Description |
|---|---|
| Articular cartilage | Hyaline (fibrocartilage in the sternoclavicular, acromioclavicular and temporomandibular joints); avascular and aneural |
| Articular capsule | Outer fibrous layer, attached beyond the articular margins; inner synovial membrane |
| Synovial membrane | Lines the capsule and all intracapsular structures except the articular cartilage; secretes synovial fluid |
| Joint cavity | A potential space holding only 0.5–2 mL of fluid |
| Ligaments | Capsular, extracapsular (e.g. Collaterals) and intracapsular (e.g. Cruciates) |
- Menisci or articular discs — knee, temporomandibular, sternoclavicular; improve congruence and absorb shock
- Labrum — deepens the socket; shoulder and hip
- Fat pads — fill dead space, as the infrapatellar pad
- Bursae and tendon sheaths — reduce friction
Synovial Fluid
- A dialysate of blood plasma with hyaluronic acid added by type B synoviocytes
- Clear, pale yellow, viscous, slightly alkaline
- Functions — lubrication, nutrition of the avascular articular cartilage, shock absorption, and removal of debris by phagocytic type A cells
- Viscosity falls with movement (thixotropy), which is why joints loosen after a few minutes of activity — the basis of morning stiffness improving with use
Classification BY Axes and Shape
| Type | Example | Movement |
|---|---|---|
| Plane | Intercarpal, intertarsal | Gliding |
| Hinge | Elbow, ankle, interphalangeal | Uniaxial — flexion, extension |
| Pivot | Superior radio-ulnar, atlanto-axial | Uniaxial — rotation |
| Condylar | Knee, temporomandibular | Mainly flexion and extension with some rotation |
| Ellipsoid | Wrist, metacarpophalangeal | Biaxial — no rotation |
| Saddle | First carpometacarpal | Biaxial with opposition |
| Ball and socket | Shoulder, hip | Multiaxial |
Stability of a Synovial Joint
- Bony fit — deep socket gives stability (hip) at the cost of range
- Ligaments — strong but inelastic; once stretched they do not recover
- Muscle tone — the most important factor in most joints, notably the shoulder
- Atmospheric pressure — significant at the hip, where it helps hold the head in the acetabulum
- Fibrocartilaginous labra and menisci
Applied Aspects
- Hilton's law — the nerve supplying a joint also supplies the muscles moving it and the skin over their insertions; explains referred pain from hip to knee
All questions in General Anatomy & Osteology
- Q1Classify bones with examples. Describe the parts of a long bone and its blood supply. Add a note on the types of epiphysis. ★
- Q2Classify joints with examples. Describe the structure of a synovial joint and add a note on Hilton's law. ★
- Q3Classify skeletal muscle according to shape and action. Describe its nerve supply and add a note on the functional groups of muscles. ★
- Q4Describe the types of blood vessels. Define anastomosis and end artery with examples, and add a note on portosystemic anastomoses. ★
- Q5Describe the structure of skin and fascia. Add a note on the lymphatic system and the thoracic duct. ★
- SN1Describe the epiphyseal plate with its zones. Add a note on the Salter–Harris classification. ★
- SN2Classify cartilage with its sites and features. Add a note on articular cartilage. ★
- SN3Describe the structure and types of a synovial joint. Add a note on synovial fluid. ★
- SN4Define end artery. Give its types with examples and the consequences of its occlusion. ★
- SN5Describe the types of ossification with examples. Add a note on the cells of bone. ★
- SN6Describe the deep fascia with its modifications and functions. Add a note on compartment syndrome. ★
- SN7Describe the anatomical position, the planes of the body and the terms of movement.