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Anatomy Notes: Joints (Articulations)

For 1st Year BPT Students

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1. Definition

• Firestein & Kelley's Textbook of Rheumatology

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2. Classification of Joints

A. Structural Classification

B. Functional Classification

• Imaging Anatomy Text and Atlas Vol. 3 - Bones, Joints, Vessels and Nerves

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3. Types of Joints in Detail

A. Fibrous Joints

1. Sutures - Found between skull bones. Minimally flexible at birth (allow brain growth), eventually ossify (= synostosis). E.g., coronal suture, sagittal suture.
2. Syndesmoses - Bones joined by thick ligaments or an interosseous membrane. Classified as amphiarthrosis (slightly moveable). E.g., inferior tibiofibular joint, interosseous membrane between radius and ulna.
3. Gomphoses - Peg-in-socket joints. The periodontal ligament connects the tooth root to its bony socket. E.g., teeth in jaw sockets.

B. Cartilaginous Joints

1. Primary cartilaginous joints (Synchondroses) - United by hyaline cartilage. E.g., epiphyseal growth plates (temporary), 1st rib-sternum joint (permanent).
2. Secondary cartilaginous joints (Symphyses) - United by fibrocartilage. E.g., pubic symphysis, intervertebral discs (nucleus pulposus + annulus fibrosus).

C. Synovial Joints (Most Important for BPT)

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4. Structure of a Synovial Joint

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5. Types of Synovial Joints

By Axes of Motion:

• Uniaxial - Movement in 1 plane
• Biaxial - Movement in 2 planes
• Multiaxial - Movement in multiple directions

By Shape (6 Types):

• Imaging Anatomy Text and Atlas Vol. 3

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6. Movements at Synovial Joints

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7. Factors Affecting Joint Stability

1. Shape of articular surfaces - Deeper sockets = more stable (e.g., hip > shoulder)
2. Ligaments - Primary stabilizers; intracapsular and extracapsular
3. Muscle tone - Muscles crossing the joint provide dynamic stability
4. Atmospheric pressure - Especially important in the shoulder joint
5. Fibrocartilaginous structures - Labrum (hip/shoulder), menisci (knee)

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8. Clinical Relevance for BPT

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9. Quick Memory Tips

• "FBI" for fibrous = Fibrous joints, But Immobile (sutures, syndesmoses, gomphoses)
• "CAS" for cartilaginous = Cartilage, A bit mobile, Synchondroses/Symphyses
• "SHIP" for synovial types = Saddle, Hinge, Pivot; add Plane, Condyloid, Ball-and-socket
• Diarthrosis = Di (two/freely) = Diarthrotic joints are freely moveable
• The shoulder has the greatest ROM but is the most commonly dislocated joint - relevant for your clinical work!

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🦴 JOINTS (ARTICULATIONS)

General Anatomy Notes - BD Chaurasia Style

For 1st Year BPT Students

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DEFINITION

"A joint is a junction between two or more bones (or cartilages) of the skeleton."

• BD Chaurasia, Human Anatomy

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CLASSIFICATION OF JOINTS

Way 1 - By STRUCTURE (What they are made of)

Way 2 - By FUNCTION (How much they can move)

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CLASSIFICATION TABLE (As per BD Chaurasia)

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PART 1 - FIBROUS JOINTS (Synarthroses)

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1. SUTURES

• Found only in the skull
• Bones are held together by a thin layer of fibrous tissue
• In babies - sutures are slightly flexible to allow passage through the birth canal
• In adults - sutures become rigid (synarthrosis)
• In old age - sutures may completely fuse into bone = called SYNOSTOSIS

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2. SYNDESMOSIS

• Bones joined by a sheet of fibrous tissue called an interosseous membrane OR thick ligaments
• Allows a little movement (amphiarthrosis)
• Easy example: The forearm membrane between radius and ulna; the leg membrane between tibia and fibula

Trick to remember: Syndesmosis = "Syndesmos" (Greek) = Ligament

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3. GOMPHOSIS

• A "peg in socket" type joint - unique joint!
• The tooth root (peg) fits into the jaw socket
• Held by periodontal ligament
• Example: Teeth fixed in the maxilla and mandible
• No movement = Synarthrosis

Trick to remember: Gomphosis = "Gomphos" (Greek) = Bolt/Nail (like nailing a peg)

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PART 2 - CARTILAGINOUS JOINTS (Amphiarthroses)

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A. PRIMARY CARTILAGINOUS JOINT = SYNCHONDROSIS

• Bones connected by hyaline cartilage
• No movement (Synarthrosis)
• Can be temporary or permanent

BPT Clinical note: Injury to the epiphyseal growth plate in a growing child can cause shortening or deformity of that limb - always remember this in your paediatric physiotherapy postings!

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B. SECONDARY CARTILAGINOUS JOINT = SYMPHYSIS

• Bones connected by a fibrocartilage disc with surrounding ligaments
• Slight movement allowed (Amphiarthrosis)
• Always found in the midline of the body

• Pubic symphysis (between two pubic bones)
• Intervertebral discs (between vertebral bodies)
• Manubriosternal joint (between manubrium and body of sternum)
• Symphysis menti (between two halves of the mandible - fuses by 1-2 yrs)

BPT Clinical note: The pubic symphysis separates slightly during pregnancy (due to relaxin hormone) to allow delivery - it can cause pelvic girdle pain in pregnant women, an important physiotherapy condition!

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PART 3 - SYNOVIAL JOINTS (Diarthroses)

These are the joints you will treat most as a physiotherapist.

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STRUCTURE OF A SYNOVIAL JOINT

1. ARTICULAR SURFACES

• Bone ends are covered by hyaline cartilage (articular cartilage)
• Smooth, slippery, whitish in colour
• Avascular (no blood supply) - nourished by synovial fluid only
• Thickness: 1-2 mm (small joints) to 5-7 mm (knee/femoropatellar joint)
• Cannot regenerate if damaged - that's why cartilage injuries are serious!
• Exception: Jaw (TMJ) and sternoclavicular joint are covered by fibrocartilage, not hyaline

2. JOINT CAPSULE (Articular Capsule)

• Outer layer = Fibrous membrane - Thick, tough, made of white fibrous tissue; gives strength to the joint
• Inner layer = Synovial membrane - Thin, pink, vascular lining; secretes synovial fluid

3. SYNOVIAL MEMBRANE

• Lines the inside of the capsule (but NOT the articular cartilage)
• Has two cell types:
  • Type A synoviocytes - act like macrophages; clean up debris
  • Type B synoviocytes - fibroblast-like; produce synovial fluid components
• Can regenerate even in old age (unlike cartilage)
• In rheumatoid arthritis, the synovial membrane becomes inflamed and destroys the joint = Synovitis

4. SYNOVIAL FLUID

• A clear, viscous, straw-coloured fluid (like egg white - "synovia" = egg)
• Contains: Water + Hyaluronic acid + Lubricin + Phospholipids
• Functions:
  • Lubrication (reduces friction to nearly zero)
  • Nutrition to articular cartilage (diffusion)
  • Shock absorption

5. LIGAMENTS

• Strengthen the joint capsule
• Two types:
  • Intracapsular ligaments - Inside the capsule (e.g., ACL and PCL of knee)
  • Extracapsular ligaments - Outside the capsule (e.g., medial collateral ligament of knee)

6. BURSAE

• Small fluid-filled connective tissue sacs
• Found near joints to reduce friction between tendons/muscles and bone
• Can get inflamed = Bursitis (common in shoulder, knee, hip)

7. ACCESSORY STRUCTURES (in some joints)

• Articular discs / Menisci - Fibrocartilage pads to improve joint fit (e.g., knee menisci, TMJ disc)
• Labrum - Fibrocartilage rim to deepen shallow sockets (e.g., glenoid labrum in shoulder, acetabular labrum in hip)
• Fat pads - Cushion inside the joint (e.g., infrapatellar fat pad in the knee)

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TYPES OF SYNOVIAL JOINTS (BD Chaurasia's Classification)

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MOVEMENTS AT SYNOVIAL JOINTS

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FACTORS MAINTAINING JOINT STABILITY

1. Shape of articular surfaces - Deep socket = more stable (hip > shoulder). Shallow socket = more mobile but less stable.
2. Ligaments - Primary static stabilizers. Prevent excessive movement.
3. Muscles and their tendons - Dynamic stabilizers. Muscles around a joint hold it together (e.g., rotator cuff of shoulder).
4. Atmospheric pressure - Important in the shoulder joint; helps "suck" the ball into the socket.
5. Gravity - Helps in weight-bearing joints like hip and knee.

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CLINICAL POINTS FOR BPT (BD Chaurasia Style)

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QUICK REVISION SUMMARY

JOINTS
│
├── FIBROUS (Synarthrosis - No movement)
│   ├── Sutures (Skull) → Plane, Squamous, Serrate, Dentate
│   ├── Syndesmosis (Radius-Ulna, Tibia-Fibula)
│   └── Gomphosis (Teeth in jaw)
│
├── CARTILAGINOUS (Amphiarthrosis - Slight movement)
│   ├── Primary = Synchondrosis (Hyaline cartilage)
│   │   ├── Temporary: Growth plate, Y-cartilage of hip
│   │   └── Permanent: 1st sternocostal, Costochondral
│   └── Secondary = Symphysis (Fibrocartilage)
│       → Pubic symphysis, Intervertebral discs
│
└── SYNOVIAL (Diarthrosis - FREE movement) ← Most important!
    ├── Plane → Intercarpal, facet joints
    ├── Hinge → Elbow, ankle, IP joints
    ├── Pivot → Atlantoaxial, proximal radioulnar
    ├── Bicondylar → Knee, TMJ
    ├── Ellipsoid → Wrist, MCP joints
    ├── Saddle → 1st CMC (thumb), sternoclavicular
    └── Ball & Socket → Hip, Shoulder (most mobile!)

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MEMORY TRICKS (BD Chaurasia exam tips)

• "FBI Goes Somewhere Cold" = Fibrous, Cartilaginous, Synovial - but with 3 sub-types each
• "Some Happy People Have Beautiful Smiling Eyes" = Suture, Syndesmosis, Gomphosis (Fibrous); Synchondrosis, Symphysis (Cartilaginous); Plane, Hinge, Pivot, Bicondylar, Ellipsoid, Saddle, Ball & Socket (Synovial)
• "Hip and Shoulder are Ball & Socket" = Most mobile, least stable = Most commonly dislocated
• "Knee is Bicondylar" = Not a true hinge - it also allows slight rotation (important for locking mechanism)
• Synovial fluid = EGG WHITE = "Synovia" literally means egg in Greek - clear, viscous

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