What is it?
The shoulder joint or glenohumeral joint is a ball and socket joint made up of the arm bone and a shoulder socket. A dislocation occurs when the arm bone is ripped out of the socket. A subluxation is similar to a dislocation in that the arm bone is ripped from its place of rest. Instead of coming the whole way out of the socket, the arm bone slides to the edge of the socket where it may damage the socket without completely coming out. It is usually considered as being similar to but not as severe as a dislocation however this is an unfortunate myth. Shoulder subluxation should be taken seriously and can be as serious as a dislocation.
How did I get it?
The socket that the ball sits in is quite shallow. It needs to be to allow free movement of the arm. For this reason the shoulder relies heavily on soft tissue rather than bone to hold the joint together. Instability occurs when the forces acting on the shoulder are so great that they overcome the supporting soft tissues (cartilage, ligament and muscles/ tendons). There are two main causes of instability in the shoulder i.e. traumatic and atraumatic. The management of each may be quite different.
Traumatic is where an extreme force is placed on a normal shoulder. See figure 1 which is a common cause of such injuries. The most common mechanism is getting caught with your arm out to the side or above your head. The force is transmitted through the shoulder joint with the arm acting as a lever increasing the force.
Atraumatic is where the soft tissues are loose and do a poor job of holding the shoulder together. This typically occurs in quite flexible young athletes.
What are the symptoms?
Each shoulder subluxation can be quite different in terms of how it feels to the injured person. Often there will be a sharp pain in the shoulder and a sensation that the shoulder isn’t tight and has slipped or slid around. Sometimes though there is no shoulder pain or loose sensation and there will only be a dead arm sensation. This can occur after making a tackle or putting the shoulder in an awkward position where it is injured.
What should I do?
Rest and ice can be of assistance initially. See figure 2. While sometimes the symptoms are mild, shoulder instability can potentially lead to long term problems including dislocation, rotator cuff injury and arthritis. It is advisable to seek medical treatment and resist the temptation to try and “just put up with it”. Early medical intervention will provide the greatest chance of a timely recovery.
How is a diagnosis made?
A diagnosis is usually made on the history of the injury and examination findings. Sometimes patients will suffer full dislocations where the shoulder immediately pops back in and it may present as a subluxation. Imaging such as x-rays or MRI may be required to assess for any bone damage and identify any soft tissue injury.
What does rehab involve?
Treatment depends on the degree to which it affects you, the frequency at which it occurs and your physical aspirations within your chosen activity. Usually the ligaments and the cartilage which surrounds the rim of the cavity of the shoulder socket (Labrum) are often stretched and torn. This results in a decrease in the passive stability of the shoulder. To address this, it is important to optimise the active stability which requires your muscles to compensate for the ligaments and labrum which are now ineffective to a great extent, to provide the support to the shoulder as it sits within its socket. This usually involves getting the muscles stronger but also teaching them to contract at the correct time.
Depending on your physical goals and aspirations it may be necessary to avoid the activity which caused the instability if at all possible.
Surgery is often required for this condition. Surgery is performed to repair a tear in the labrum and tighten up the ligaments which hold the shoulder in place. Depending on the severity of the injury surgery may be delayed until the end of the competitive season however for more severe injuries and dislocations surgery cannot be delayed.