A novel insight towards classification of joints

Introduction

A joint or articulation or articular surface is the connection made between bones in the body.1 They link the skeletal system into a functional whole. They are constructed to allow for different degrees and types of movement. Some joints, for example the knee, elbow and shoulder, are self-lubricating, almost frictionless. They are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. 2 Other joints such as sutures between the bones of the skull permit very little movement (only during birth) in order to protect the brain and the sense organs.2 The connection between a tooth and the jaw bone is also called a joint. It is described as a fibrous joint known as gomphosis or peg and socket joint. Joints are classified both structurally and functionally.3

Aim

The short communication aims to initiate an innovative classification of joint on the basis of general morphology.

Classification of Joints

The standard textbooks in Anatomy 4, 5 clearly classify Synovial joints according to General Morphology into:

However, this classification should not be restricted only to synovial joints. It should also accommodate the fibrous and cartilaginous joints. Thus, Classification of joints according to general morphology should be as follows:

Simple (one pair of articulating surfaces; male and female : For e.g

Fibrous joint: Metopic suture between two frontal bones, sagittal suture between two parietal bones (Figure 1)

Figure 1

Illustration showing coronal suture (compound fibrous joint), sagittal suture (simple fibrous joint) and lambdoid suture (compound fibrous joint)

Cartilaginous joint:

1. Synchondroses: manubriosternal joint, occipitosphenoid joint.

2. Symphyses: pubic symphysis, intervertebral discs, symphysis menti.

Synovial joint: interphalangeal joint, first carpometacarpal joint, shoulder joint, sacroiliac joint

Compound (more than one pair of surfaces : For e g

Fibrous joint: (Figure 1, Figure 2)

1. Coronal suture between one frontal and two parietal bones,

2. Lambdoid suture between two parietal and one occipital bone,

3. Palatomaxillary suture between horizontal plates of palatine bone and palatine processes of maxillary bone.

Figure 2

Illustration showing palatomaxillary orcruciform suture (compound fibrous joint)

Cartilaginous joint: ends of the long bones with multiple secondary centers of ossification which fuse later (epiphysis) can be technically considered as compound cartilaginous joints during developmental phase.

Synovial joint: elbow joint, wrist joint, knee joint etc.

Mixed: Sternoclavicular joint or articulation 6 (Figure 3)

Figure 3

Illustration showing Sternoclavicular joint (compound cartilaginous joint)

The bone areas entering in its formation are the sternal end of clavicle, clavicular notch of sternum and the cartilage of the first rib. The cartilage of the first rib is visible from the outside as the suprasternal notch. Structurally this is a saddle variety of synovial joint. Functionally this is diarthrosis and multiaxial joint.

Conclusion

An innovative classification of joints on the basis of general morphology could be included in the medical curriculum considering the uniformity it imparts to the overall understanding of joints and their classification.

Conflict of Interest

The authors have none to declare.