Sub Glenoid Dislocation could be defined as a partial or incomplete dislocation that usually stems from changes in the mechanical integrity of the joint. When this happens, the humeral head slips out of the glenoid cavity as a result of weakness in the rotator cuff or a blow to the shoulder area. The sub glenoid dislocation involves the structures of the shoulder whereas a subluxation usually is about the mechanical integrity of the shoulder and its supporting structures.

Dislocation in the shoulder is one of the most common joint dislocations due to its variety of movements and the frequency of application. In a sub glenoid dislocation, the humeral head pops back into its socket and in the case of a subluxation, it can be either anterior (forward), posterior (backward), and inferior (downward). Apart from sub- glenoid a sub clavicular, sub coracoid and, very rarely, intrathoracic or retroperitoneal dislocations can also happen.

The lack of ligament support and dynamic stabilisation makes the glenohumeral joint most susceptible to dislocation in abduction 90 degrees and external rotation 90 degrees. Especially in the case of an anterior dislocation, when there is a decreased density in the anterior capsule, it may be present between the intermediate and superior glenohumeral ligaments. This inherent weakness can ultimately cause the humeral head to be more prone to dislocate at this interval.

Some of the reasons for a sub glenoid dislocation could be traumatic injuries such as car accidents, sports injuries or falls, repeated strain or excessive use of hands in sports such as golf, swimming, tennis and volleyball, loose capsule joints due to injury or overuse, shoulder multidirectional instability or a weakening of cartilage and shoulders supporting ligaments. Anterior dislocation often results from some heavy force or strength to push the shoulder out of the socket. The extreme rotation of the upper arm can also pull out the joints. In such dislocation, the humeral head separates from the glenohumeral joint. This ruptures or detaches the anterior capsule from the humeral head or its attachment at the edge of glenoid fossa.

Some of the commonly seen symptoms of sub glenoid dislocation could be significant pain felt along the arm past the shoulder, sensation that the shoulder is slipping out of the joint during abduction and external rotation, the resistance of all movement, numbness of the arm or a visibly displaced shoulder or in some cases the shoulder could seem unusually square and no palpable bone on the side of the shoulder.

With a sub glenoid dislocation certain other condition like the glenoid fractures or glenoid cavity fractures may have to be ruled out. Fractures of the glenoid may occur at the neck at the junction of the glenoid and the scapular spine, or may occur through the articular surface. Glenoid neck fractures may involve both translational and angular deformity, and can also lead to chronic pain and weakness due to the alteration of glenohumeral biomechanics. In the case of glenoid cavity fractures this can involve the anteroinferior or posterior articular margin. These fracture types often occur with a glenohumeral fracture-dislocation, and frequently lead to residual instability of the joint following reduction. If left untreated there can be complications like Bankart lesion, Hill-Sachs lesion, rotator cuff tear, or injury to the axillary nerve.

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