if it happens inferiorly, it could be related with axillary nerve injury during operation. You'd better wait and see for 3 months at least.

My experience has been inferior subluxation most commonly. This is due to Injured and poorly activating muscle. All have resolved with deltoid exercises very quickly.

Subluxation of the shoulder can be caused by the above mentioned neurological complications, but also can be the result of:

1. Mal-position of the head following the fixation either in varus, posterior rotation or impaction into the metaphysis

2. Post-traumatic or post-op haematoma which is "filling" the joint and  the head appears in subluxed position.

3. Post-traumatic or post-op muscle "shock" and weakness of it

4. Joint to be supported in an incorrect way following surgery (collar and cuff for example allows gravity to act and makes all the above more evident)

5. Finally age plays a role to exaggerate the picture due to the presence of weaker muscles

thank you ALL very much for your answers

Inferior subluxation of the humeral head can occur after shoulder trauma or surgery. Its incidence varies. The reported incidence after rotator cuff repair is10%, after fracture of the proximal humerus (42%), and after prosthetic humeral head replacement (60%). It is most likely due to transient neuropraxia of the axillary nerve. Fortunately, it resolves by 6 weeks in most patients and no ong-term problem of subluxation remains. Usually, early active exercises and a sling when not exercising-is effective

I think factors are

1. Mechanical : orientation from rotation/flexion/extension of head resulting in incongruous joint. Excessive  Ante or retroversion.  Haematoma or other space occupying body.

2. Neurological 

3. Rotator cuff disfunction 

As vacuum suction or adhesions- cohesion of shoulder joint is one of stabilising factor of an otherwise unconstrained shoulder joint, could the loss of these features post trauma contribute to subluxation.

I agree with the considerations of Dr. Vaishya. Postoperative rehabilitation usually leads  to recovery.

Some deltoid weakness may be seen post-operatively. Usually resolves - on the assumption that it is neuropraxia and you are confident axillary nerve has not been damaged/trapped intra-operatively.