Neer classification of proximal humeral fractures

The Neer classification of proximal humeral fractures is probably the most frequently used along with the AO classification of proximal humeral fractures. Even if an exact knowledge of this classification system is beyond the everyday use of many radiologists, the terminology and factors which influence the classification are essential if the report of a proximal humeral fracture is to be of use.

The two main components of the classification are ^{1, 4-6}:

1. number of fracture parts
2. displacement

Parts

An important first step in coming to grips with this classification, and one which is often misunderstood, is that of 'parts'. The Neer system divides the proximal humerus into 4 parts and considers not the fracture line, but the displacement as being significant in terms of classification. The four parts are:

1. humeral head
2. greater tuberosity
3. lesser tuberosity
4. humeral shaft

Displacement

Displacement is on a per-part basis. A fracture part is considered displaced if angulation exceeds 45 degrees, or if the fracture is displaced by more than 1cm ¹. 

As such the simplest displaced fracture which is possible is a two-part fracture, however a minimally displaced fracture, even if this includes multiple fracture lines, merely constitutes an type I, one-part fracture. 

Classification

The classification has been variably adapted by multiple authors. What is presented below is what will probably be understood by most surgeons and radiologists and consists of four major groupings, based on the number of displaced parts. 

One-part fracture

• fracture lines involve 1 - 4-4 parts
• none of the parts are displaced (i.e <1cm and <45 degrees)

These undisplaced / minimally/minimally displaced fractures account for ~ 70 - 80~70-80% of all proximal humeral fractures and are almost always treated conservatively ^6-7. 

Two-part fracture

• fracture lines involve 2 - 4-4 parts
• one part is displaced (i.e >1cm or >45 degrees)

Four possible types of two-part fractures exist (one for each part):

1. surgical neck: most common
2. greater tuberosity
   • frequently seen in the setting of anterior shoulder dislocation ⁸
   • a lower threshold of displacement (> 5mm) has been proposed ⁸
3. anatomical neck 
4. lesser tuberosity: uncommon

These fractures account for approximately 20% of proximal humeral fractures ⁶. 

Three-part fracture

• fracture lines involve 3 - 4-4 parts
• two part are displaced (i.e >1cm or >45 degrees)

Two three-part fracture patterns are encountered ⁷:

1. greater tuberosity and shaft are displaced with respect to the lesser tuberosity and articular surface which remain together
   • most common three part pattern
2. lesser tuberosity and shaft are displaced with respect to the greater tuberosity and articular surface which remain together

These fractures account for approximately 5% of proximal humeral fractures ⁶. 

Four-part fracture

• fracture lines involve parts
• three parts are displaced (i.e >1cm or >45 degrees) with respect to the 4th

These fractures are uncommon (<1% of proximal humeral fractures) ⁶.

This pattern has poor non-operative results, and as the articular surface is no longer attached to any parts of the humerus which are attached to soft tissues, it has a high incidence of osteonecrosis ⁷. 

These fractures require operative management.