Essential Guide to Normal Anatomical Variants in Shoulder Arthroscopy
This presentation will discuss some of the normal anatomical variants seen in shoulder arthroscopy. A knowledge of these variants is essential in order to recognise those appearances which represent true pathology.
When performing the diagnostic routine we often start by visualising the long head of biceps tendon. There are a number of variants seen in terms of the tendon itself, it's exit from the joint, it’s proximal attachment and it's vascular markings and synovial coverings.
The tendon itself is sometimes bifid as shown here and
there may be accessory heads, not to be confused with a longitudinal split on MRI and in rare cases the biceps maybe congenitally absent.
The tendon exits the joint between the anterior and posterior pulleys. These pulleys are formed from the superior glenohumeral and coracohumeral ligaments and have variable contributions from the supraspinatus and subscapularis tendons
and this is shown diagrammatically here.
In terms of the proximal attachment, the biceps usually arises from the superior glenoid tubercle and the postero-superior labrum. However, the biceps occasionally arises from the rotator cuff and capsule and rarely from the rotator cable alone.
Often there are vascular markings on the superior surface of the tendon. These are normal and should not be confused with tendon inflammation.
Sometimes the tendon will have vinculae or a mesentery attached sometimes the tendon will be completely covered with synovium due to failure of invagination of the tendon during development
The superior labrum may vary in terms of attachment of the long head of biceps, in terms of the attachment of labrum to the glenoid and in terms of the edge of the labrum itself.
The long head of biceps attaches predominantly to the posterior labrum as in types 1 and 2, often to both the anterior and posterior labrum and more rarely to the anterior labrum alone.
The labrum is usually firmly attached to the superior glenoid, but may become more loose with age. There may be a sublabral recess between 11 and 1 o’clock and the superior labrum may be completely detached forming a sub-labral foramen at 3 to 1 o’clock
There may be a meniscoid attachment of the superior labrum, often with a significant cleft under the labral edge
The antero-superior labrum is usually firmly attached but as previously mentioned there may be a sub-labral foramen or the labrum may be absent altogether.
A sub-labral foramen occurs in about 10% of shoulders and is often associated with a cord like middle gleno-humeral ligament which attaches to the free part of the labrum. When the labrum is absent altogether a cord like middle glenohumeral ligament may attach to the base of the biceps tendon as in the Buford Complex
The labrum in general is firmly attached in 95% of cases and mensicoid in 5% of patients
Rarely there is a cleft seen between the glenoid and attachment of the posterior labrum as seen in this view of the postero-inferior labrum, but it is common to see a deep capsular fold adjacent to the posterior labrum.
The glenohumeral ligaments are essentially thickenings of the capsule, and pass from the anatomical humeral neck to various parts of the labrum.
The superior glenohumeral ligament is the most consistent and is present in the vast majority of people. It originates at the superior glenoid tubercle but also the base of the coracoid and runs parallel to the biceps and inserts on to the lesser tuberosity.
The coracohumeral ligament originates from the lateral border of the coracoid and inserts on the lesser and greater tuberosities spanning the groove.
The middle glenohumeral ligament is the most variable of all. When viewed arthroscopically it crosses behind the subscapularis tendon at an angle of 45 degrees
In about 70% of shoulders the MGHL is a thick folded band in 20% it will be cord like and in 10% it will be a very thin veil or even absent.
The inferior glenohumeral ligament has three components, the Anterior and Posterior Glenohumeral ligaments (which are of variable substance and the intervening Axillary pouch.
The pouch may be smooth or fenestrated, but should not be separated from the humeral neck at any point.
There are some variants of the Glenoid itself, including the mid-glenoid notch which is situated at the junction of the lower 3 and upper 2 /5ths of the socket. It can be quite deep and should not be confused with a boney Bankart. A tuft of synovium may be seen above this and should not be confused with labral damage.
It is normal, particularly in adults, to have an area of thinning in the cartilage in the centre of the glenoid face, known as the ‘Bare Spot’ This is often used a reference for estimating traumatic glenoid bone loss.
There is also a ’Bare Area’ on the humerus which is devoid of cartilage of variable width, adjacent to the Infraspinatus insertion. This may contain deep vascular channels and should not be confused with a Hill-Sachs lesion, which will have normal cartilage medial to it.
The rotator cuff also exhibits some normal variations. The subscapularis tendon may be bifid in about 3% of cases.
The supraspinatus insertion is usually smooth with up to a 1mm gap been it and the edge of the articular cartilage.
The rotator cable is a capsular thickening and is an extension of the coracohumeral ligament. The crescent is the thinner cuff tissue contained within the boundaries of the cable and is the part of the cuff with a poorer blood supply. Finally, the infraspinatus will often have fenestrations or ridges.