While shoulder injuries are uncommon in football they are very common in rugby, particularly professional rugby league. They are also common in throwing athletes and racket sports.
The common sporting injuries which we see are instability, problems with the rotator cuff and problems with the acromio clavicular joint, the joint which is formed between the outer end of the collar bone and the shoulder blade.
The shoulder is particularly susceptible to injury because it sacrifices stability for mobility. The shoulder has an enormous range of movement over much more of a hemisphere and has rather a shallow socket. By comparison with the hip joint where the socket is deep and encloses the head of the femur, the shoulder is more like a saucer than a socket. The shoulder socket is also attached to the shoulder blade which is not in a fixed position unlike the hip socket which is fixed in one position on the pelvis. This mobility makes it difficult for the body to coordinate the movements.
As you lift the arm from the side there should be a co-ordinated movement involving the muscles which join the arm onto the shoulder blade and also the muscles which join the shoulder blade to the body. As you lift your arm from the side this co-ordinated movement usually allows the shoulder joint proper to move about two degrees through every one degree that the shoulder blade rotates on the chest wall.
This is often compared to a seal balancing a ball on its nose. If the shoulder blade is not properly co-ordinated and is not pointing in just the right position then it is going to throw enormous sheer stresses on the ball and socket joint, particularly as the socket is so shallow. This can either throw more strain on the rotator cuff muscles (the cuff of muscles which sits around the ball and socket) or the washer, the glenoid labrum that sits and makes a sort of seal around the edge of the socket and to which is attached all the major ligaments which prevent shoulder dislocation.
The acromio clavicular joint is the bump you can feel on top of your shoulder and is the only true synovial joint which joins the arm onto the body. It is a very interesting and unusual structure which contains an intra articular disc just like the cartilage in the knee. It is most commonly injured by a direct blow from falling on the point of the shoulder, but can give problems either through degenerative change or through a condition occurring in weight lifters called osteolysis. This is an unusual condition where by the body reacts by leaching the mineral from the outer end of the collar bone rather than strengthening it up as it should do.
Symptoms in the acromio clavicular joint are very common and usually settle by a period of rest and physiotherapy. Occasionally injections will help and less frequently surgery. The joint is not uncommonly dislocated completely, particularly in rugby, and this is not necessarily a disaster. It leaves the collar bone rather prominent which may look a bit odd, but in fact in the vast majority of people, the shoulder joint function returns to absolutely 100% normal within 2-3 months. Apart from rather unusual circumstances, therefore, the treatment for this is to leave it dislocated and simply rehabilitate the shoulder rather than going for unnecessary surgery to try and put it in place. A very small proportion of patients do continue to suffer problems after an acromio clavicular dislocation and we should reserve surgery for them if this becomes necessary. This applies to absolutely everyone including professional tennis players, professional rugby league players and other sportsmen. It is very unusual to operate on one of these injuries and it should certainly by delayed until it is proven necessary in the overwhelming majority of cases.