The classification of radial head fractures is based on the

• degree of displacement
• intra-articular involvement

as follows

• Mason type 1 - non-displaced to minimally displaced fracture (<2mm)
• Mason type 2 - intra-articular fracture with displacement >2 mm or angulation
• Mason type 3 - comminuted intra-articular fracture with displacement 

Posttraumatic instability of the sternoclavicular joint is a result of injury to the joint capsule, the sternoclavicular or costoclavicular ligament.

Mayfield et al. described in 1980 the following four stages of progressive carpal instability.

Thompson-Epstein classification describes five types of posterior hip dislocation defined by associated acetabular fracture or fracture of the femoral head as depicted on plain radiographs. In general, there are three types of dislocations in the hip joint:

• posterior: the femoral head is dislocated posteriorly, most commont type
• anterior: the femoral head is dislocated anteriorly
• central: impact of the femoral through the acetabular floor into the pelvis

Rockwood classification divides dislocations in AC joint into six grades. It is an extension of the previous classification by Tossy et al. Normal width of AC joint is considered 1-3mm, widened AC joint has >7mm in men or >6mm in women.

Tossy classification divides dislocations in AC joint into three grades. It was later extended by Rockwood et al. by another three types. Normal width of AC joint is considered 1-3mm, widened AC joint has >7mm in men or >6mm in women.

The classification of lesions of labrum glenoidale was published by Snyder et al. and had originally four types. Later, several authors added descriptions of other labral lesions.

Complete atlanto-occipital dislocation (AOD) can be divided into three distinct types.

The classification of fractures of axis was introduced by Effendi et al. and later modified by Lewine and Edwards. With further two types added (IA and IIA), the modified classification has five types.

Lesions of the menisci on MRI are divided into four grades. Normal meniscus has uniformly low signal intensity on T2-weighted images (T2W). Grade I and II lesions can be a normal appearance of ageing in older patients.