Ossification : easy and brief description

Ossification: it is the process of bone formation

Classification of ossification centre:

1. A primary ossification center is the first area of a bone to start ossifying.

 It usually appears during intra-uterine life in the central part of each developing bone.

Exception: carpal bones of hand

 In long bones the primary ossification centers appear in the diaphysis/shaft and in irregular bones the primary centers appear usually in the body of the bone.

All long bones have only one primary center but some irregular bones such as the hip bone and vertebrae have multiple primary centers.

2. Secondary ossification centre: A secondary ossification center is the area of ossification that appears after the primary ossification center has already appeared - most of which appear during the postnatal and adolescent years. Most bones have more than one secondary ossification center. In long bones, the secondary centers appear in the epiphyses (upper and lower end).

Classification of mechanism of ossification

Membranous ossification:

Ex: head and neck: parietal bone, frontal bone, maxilla, zygomatic,

Sup extre: clavicle

Cartilaginous ossification: all vertebrae, all ribs, sternum, scapula, all bones of upper limb except clavicle, all bones of lower limb

Membrano-cartilaginous ossification:

Occipital: membranous ossification area above the highest nuchal line, rest of the parts arises from cartilaginous ossification  

Sphenoid: membranous ossification above the lateral part of greater wing and pterygoid process except the hamulus, rest of the part arises from cartilage,

Temporal: membranous ossification – squamous part and tympanic part, rest of the parts arises from cartilage,

 Mandible: cartilaginous ossification anterior part of body and part of ramus above mandibular foramen, rest of the body arises from membranous ossification

Name of bone	Primary ossification center	Secondary ossification center
Clavicle	Two	One for sternal end
Humerus	One for shaft	Three for upper end – head , greater & lesser tubercle Four for lower end – lateral & medial epicondyle, capitulum, trochlear
Radius	One primary ossification center for shaft	One for upper end One for lower end
Ulna	One primary ossification center for shaft	One for upper end One for lower end
Carpal bone	One primary ossification center which appear after birth	No secondary ossification centre
Metacarpal bone	One primary ossification center for shaft	One 2nd ossification centre :  base of  1st metacarpal bones is ossified from 2nd ossification center Heads of  2-5 metacarpal bone are ossified from 2nd ossification center
Phalanges	One primary ossification center for shaft and head	One 2nd ossification center for base  of each phalanx

Lower limb

Name of bone	Primary ossification center	Secondary ossification center
Hip bone	Three – ilium, ischium, pubis	5 secondary ossification center
Femur	One for shaft	Three for upper end – head , greater & lesser trochanter One for lower end
Tibia	One primary ossification center for shaft	One for upper end One for lower end
Fibula	One primary ossification center for shaft	One for upper end One for lower end
Tarsal bone (except calcaneus)	One primary ossification center	No secondary ossification centre
Calcaneus	One primary ossification center	One secondary ossification centre
Metatarsal bone	One primary ossification center for shaft	One 2nd ossification centre :  base of  1st metatarsal bones is ossified from 2nd ossification center Heads of  2-5 metatarsal bone are ossified from 2nd ossification center
Phalanges	One primary ossification center for shaft and head	One 2nd ossification center for base  of each phalanx