The triangular interval (also known as the lateral triangular space, lower triangular space, and triceps hiatus) is a space found in the

axilla The axilla (also, armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm and the thoracic cage, bounded superior ...

. It is one of the three intermuscular spaces found in the

axillary space The axillary spaces are anatomic spaces. through which axillary contents leave the axilla. They consist of the quadrangular space, triangular space, and triangular interval. It is bounded by teres major, teres minor, medial border of the humerus, ...

. The other two spaces are:

quadrangular space The quadrangular space, also known as the quadrilateral space f Velpeau'' and the foramen humerotricipitale, is one of the three spaces in the axillary space. The other two spaces are: triangular space and triangular interval. Structure The qua ...

and

triangular space The triangular space (also known as the medial triangular space, upper triangular space, medial axillary space or foramen omotricipitale) is one of the three spaces found at the axillary space. The other two spaces are the quadrangular space and ...

Borders

Two of its borders are as follows: *

teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meaning ...

- superior * long head of the

triceps brachii The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the back of the upper limb of many vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with ba ...

- medial Some sources state the lateral border is the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, while others define it as the lateral head of the triceps. (The effective difference is relatively minor, though.)

The

radial nerve The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial comp ...

is visible through the triangular interval, on its way to the

posterior compartment of the arm The fascial compartments of arm refers to the specific anatomical term of the compartments within the upper segment of the upper limb (the arm) of the body. The upper limb is divided into two segments, the arm and the forearm. Each of these seg ...

Profunda Brachii The deep artery of arm (also known as arteria profunda brachii and the deep brachial artery) is a large vessel which arises from the Lateral (anatomy)#Left and right .28lateral.29.2C and medial, lateral and Posterior (anatomy), posterior part of t ...

also passes through the triangular interval from anterior to posterior.

Additional images

File:Gray412-spaces.png, Muscles on the dorsum of the scapula, and the Triceps brachii.

Triangular Interval Syndrome

Triangular Interval Syndrome (TIS) was described as a differential diagnosis for radicular pain in the upper extremity. It is a condition where the radial nerve is entrapped in the triangular interval resulting in upper extremity radicular pain. The radial nerve and profunda brachii pass through the triangular interval and are hence vulnerable. The triangular interval has a potential for compromise secondary alterations in thickness of the teres major and triceps. It is described based on cadaveric studies that fibrous bands were commonly present between the teres major and triceps. When these bands were present, rotation of the shoulder caused a reduction in cross sectional area of the space. Normal resting postures of humeral adduction and internal rotation with scapular protraction may be speculated as a precedent for teres major contractures owing to the shortened position of this muscle in this position. In addition, hypertrophy of this muscle can occur secondary to weight training and potentially compromise the triangular interval with resultant entrapment of the radial nerve. Shoulder dysfunctions have a potential for shortening and hypertrophy of the teres major. Shoulders that exhibit stiffness, secondary to capsular tightness, contribute to contracture and hypertrophy of the teres major.Jiu-jenk Lin, Jing-Lan Yang. Reliability and validity of shoulder tightness measurement in patients with stiff shoulders. Manual Therapy. 2006; 11 (146-52). Hence, restricted external rotation can encourage adaptive shortening and thickening of the internal rotators of the shoulder principally the teres major and subscapularis. One may speculate that the lateral arm pain presented in shoulder dysfunctions may be of a nerve origin secondary to adverse neural tension of the radial nerve. The triceps brachii has a potential to entrap the radial nerve in the triangular interval secondary to hypertrophy. The presence of a fibrous arch in the long head and lateral head further complicates the situation. Repeated forceful extension seen in weight training and sport involving punching may be a precedent to this scenario. The radial nerve is vulnerable as it passes through this space, for all of the reasons mentioned above.

References

External links

Photo at ithaca.edu
{{Upper limb general Anatomy

Borders

Contents

Additional images

Triangular Interval Syndrome

See also

References

External links