Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Humerus

The proximal humerus is composed of the humeral head, the lesser and greater tuberosities, the bicipital groove, and the proximal humeral shaft, and it is highly variable. The anatomical neck lies at the junction of the articular surface of the head and the greater tuberosity and humeral shaft. The surgical neck lies below the greater and lesser tuberosities.

The major blood supply to the humeral head is through the ascending branch of the anterior humeral circumflex artery, which penetrates the head at the bicipital groove and becomes the arcuate artery.

This artery crosses under the tendon of the long head of the biceps, runs proximally just adjacent to the lateral aspect of the bicipital groove, and enters the humeral head at the proximal end of transition from the greater tuberosity to the bicipital groove. The posterior circumflex artery supplies the posterior portion of the greater tuberosity and a small posteroinferior part of the humeral head.

The bicipital groove lies on the anterior proximal humerus, just below the articular surface, and it is defined by the greater and lesser tuberosities. The long head of the biceps tendon lies in this groove and is covered by the transverse humeral ligament.

Both the greater and lesser tuberosities provide attachment for the RTC tendons. The supraspinatus, infraspinatus, and teres minor insert on the greater tuberosity from superior to posterior.

The subscapularis tendon attaches to the lesser tuberosity, also overlying the bicipital groove, and provides additional support to the long head of the biceps tendon.

Multiple studies have been performed to determine the head–neck ratio, the central axis of the humerus, and the anatomical relationships of the greater tuberosity and the bicipital groove assist in prosthetic replacement and design.

The articular surface of the humeral head has an average radius of from 42 to 46 mm, whereas the average thickness of the humeral head is 19 mm. The thickness of the humeral head is proportional to both the length of the humerus and the head radius. The humeral head is retroverted from -6.5 to 35 degrees relative to the transepicondylar axis of the distal humerus.

The angle formed by the neck and shaft axes varies from 114 to 147 degrees. No significant differences between genders have been reported; however, a difference in the retroversion angle has been found between dominant and nondominant sides, with a measure of 33 degrees on the dominant side and 29 degrees on the nondominant side.

The humeral head center is offset from the humeral axis by 7 mm medial and 2 mm posterior. A predictable relationship has been found between the central axis of the humeral head and the bicipital groove. In an evaluation of 18 cadavers, the average distance between the central axis of the humeral head and biceps tendon was 9 mm posterior to the posterior margin of the bicipital groove. The superior aspect of the humeral head is 6 mm higher than the superior aspect of the greater tuberosity.

Iannotti et al. It reported that the mean distance between the greater tuberosity and the humeral head was 10 mm or less and that this distance was not correlated with other parameters. Takase et al. It, however, found a significant correlation between the size of the humeral head and the neck shaft angle regardless of gender or age.

The bicipital groove rotates internally along its course between the upper and lower aspects of the proximal humerus. The mean change in rotation of the lateral lip from the proximal to distal groove was 15.9 degrees. Rotation of the bicipital groove in the proximal-to-distal direction is relevant to shoulder fracture work, particularly fracture arthroplasty, because the groove can assist with proper orientation of humeral head version.

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