Shoulder instability occurs with either uncontrolled movements in the shoulder joint, or with the humorous (arm bone) moving in and out of its socket. This movement is uncontrolled and comes from either a dysfunctioning rotator cuff complex or from previous structural damage of the shoulder including ligaments or the shoulder capsule.
The structural damage to the shoulder capsule generally comes from trauma, where the shoulder is either dislocated or subluxed (partial dislocation). When you dislocate or sublux your shoulder the joint capsule and ligaments become stretched and no longer functions to support the shoulder. As ligaments take a long time to heal, the shoulder can be lax for a long time. This increased laxness allows additional movement in the shoulder joint and puts you at risk of future dislocations.
Instability of the shoulder can also occur from repetitive stress that over time that stretches the supporting shoulder structures. This occurs in sports such as tennis, swimming or javelin throwing where the joint is taken to its extreme range of movement and a force is applied to it. This stretches out the joint capsule and allowing additional translation of the shoulder joint. If the technique is poor more stress is placed on the supporting structures/ligaments. With repetition this causes the lasting damage that causes the instability.
Shoulder instability will result in either:
- Future dislocations or subluxations.
- Discomfort/pain from incorrect shoulder biomechanics.
Incorrect shoulder biomechanics refer to the shoulders inability to control its movements. As the shoulder is so mobile and can move in so many different directions it requires a lot of stability. An example of required stability would be when taking your arm back like you are about to throw a ball. This position is what we call the pre dislocation position. Normally the anterior shoulder capsule will provide the resistance to stop the head of the humorous (arm) sliding forward. Without this capsular support (as in the case of shoulder instability) the arm is free to glide forward and dislocate/sublux. Even if it doesn’t sublux any additional movement will most likely aggravate the anterior shoulder and cause pain. Repetition of this movement over time will most likely cause sensitisation of the area making it more susceptible to pain.
Extreme cases of shoulder instability patients have been known to dislocate their shoulders from something as simple as rolling over in bed.
Risk factors for shoulder instability include:
- Previous dislocation and the severity of first dislocation, the more severe the more likely of it reoccurring.
- Not immobilising the shoulder properly after dislocation, not giving the injured ligaments/joint capsule time to heal.
- The younger you are the more likely of developing instabilities because you are so active and your ligaments/joint capsule is composed of predominantly more type 3 than type 1 collagen fibres. These collagen fibres are immature and signifiantly more flexible allowing your shoulder to get into significantly more dangerous positions.
- Injury to the glenoid labrum including SLAP lesions or Bankart lesions.
- Damage to the head of the humorous from a previous injury dislocation, called a Hill-Sachs lesion.
- Hypermobility of the shoulder.
- Poor core stability.
- Poor posture.
- Poor technique or shoulder biomechanics.
Signs and symptoms of shoulder instability include:
- Recurrent dislocations.
- Pain in your shoulder.
- You may notice a clunking, clicking, or popping sensation with certain movements.
- A feeling of instability in the shoulder.
- The sensation that the shoulder is going to dislocate in certain positions.
- Numbness through your shoulder or arm.
Post dislocation the shoulder has increased laxity. The only way to improve this is to allow the ligaments and joint capsule to tighten up again by rest. In order to help protect the shoulder from future trauma muscle strengthening needs to be done.
Physiotherapy may consist of:
- Immobilising the shoulder after a recent dislocation.
- As the shoulder heals beginning shoulder stability exercises to ensure the correct biomechanics/movements of the shoulder.
- Strengthening of the shoulder muscles.
- Massage of tight spasmotic muscles.
- Mobilisation or manipulation of any stiff compensatory joints.
- Protecting the shoulder with appropriate taping or braces before participating in a contact sport such as rugby, league or AFL.
- If the instability is chronic with constant dislocation then you may require a surgical repair.