Surface Representation of the Spaces of Arm: Triangular and Quadrangular spaces

Three important spaces of the shoulder that are bordered by the triceps include. quadrangular spacetriangular space; triangular interval.

Surface Representation of the Spaces of Arm: Triangular and Quadrangular spaces
Spaces of Arm Using Finger Arrangement

Boundaries and contents of the spaces

1. Quadrangular space

They are paired, quadrangular shaped spaces seen near the axillary region. The space is mainly formed by the triceps muscle and the humerus. Hence it is also called foramen humero-tricipitale.

Boundaries of the quadrangular space

As the name suggests, the quadrangular spaces has four sides or boundaries. The table below lists out the boundaries of the space. Use the image to understand better.

AboveSubscapularis muscle in front 
Capsule of shoulder joint
Teres minor muscle behind
BelowTeres major
MedialLong head of triceps brachii
LateralSurgical neck of the humerus

2. Upper triangular space

The upper triangular space is the space seen between the two teres muscles.

Boundaries of the upper triangular space

As the name suggests, the upper triangular space has two sides, a base and an apex. The table below lists out the boundaries of the space. Use the image to understand better.

AboveTeres minor
BelowTeres major
ApexMeeting point of teres minor and major muscles. 
This can be pointed to on the lateral border of the scapula.
Base (lateral boundary)Long head of triceps brachii

3. Lower triangular space

It lies below the quadrangular space. It is formed due to the teres major muscle cutting across the long head of triceps brachii to reach its insertion.

Boundaries of the lower triangular space

As the name suggests, the lower triangular space has two sides, a base and an apex. The table below lists out the boundaries of the space. Use the image to understand better.

Above (base)Teres major
MedialLong head of triceps
LateralShaft of the humerus
ApexMeeting point of the medial and lateral boundaries

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