If its not dislocation, what is shoulder instability?
Instability of the shoulder occurs from an insufficiency in a single or multiple structures that contribute to the stability of the shoulder. To understand what instability is, it is important to first understand what contributes to the stability of the shoulder and then how physiotherapy can make a difference.
The shoulder is comprised of many different structures but the ones that are important to understand are the bones and their shape, the capsule and its ligaments, and the muscles of the shoulder and shoulder blade.
What does Shoulder Instability feel like? (1)
- Often pain or discomfort in the “Stop Sign” position
- Weakness lifting above your head
- Heaviness of the arm or “dead arm” sensation
- Greater range of motion of the shoulder
- Difficulty performing certain tasks (Eg: push ups, throwing a ball, lifting a box of a high shelf)
The Joint
The shoulder is comprised of 2 joints, the acromioclavicular joint and glenohumeral joint. The acromioclavicular joint is where the end of the collarbone and acromion (part of the shoulder blade) meet. The glenohumeral joint is where the humeral head (known as “the ball”) and Glenoid (“the Socket) meet.(2) The shape of the glenoid (Socket) of the shoulder is very shallow and thus allows for a great range of motion in a variety of directions. The downside is the natural stability of the shoulder is much less than joints like the hip that benefit from having a deeper socket. The soft tissue labrum increases the surface area of the glenoid by moulding to the shape of the humerous as it moves, keeping it more secure in the socket. (2)
The Capsule and Ligaments
The ligaments of the shoulder are extremely important to the stability of the shoulder due to the lack of stability provided by the depth of the glenoid. The ligaments of the shoulder combine with the joint capsule and wrap around the entirety of the joint. They provide stability to the shoulder throughout range as different portions become taught based on the flexion, extension, abduction or rotation of the humerus in the socket.
The Muscles of the Shoulder
The infamous rotator cuff muscles along with the other muscles of the shoulder and shoulder blade are important for providing additional stability to the shoulder, especially while under load. They help to red
uce the additional strain that would otherwise have to be absorbed through the ligaments and socket. (3) The stretch feedback mechanisms present in the tendon provide assessment of the current position of the joint and how much stability the muscles can provide to the joint under their current load.(3) This is why you will have a smaller range of motion when lifting a heavier weight to ensure the muscles can provide the adequate stability to the shoulder at that particular weight.
Can Physio Help?
Yes, Physiotherapy can help! We can’t change the shape of the joint, or sew ligament back together, but we can strengthen your muscles to help take the load off the joint and ligaments. This allows for better healing if either the labrum or ligaments are injured. If your instability comes from weakness or an injury to a muscle in the shoulder, effective training helps activate the other muscles of the rotator cuff and shoulder as well as strengthening the injured one. This helps by sharing the load between more muscles and therefore increases the muscular stability around the shoulder joint and the movement of the shoulder blade without placing excessive strain on any particular muscle more than it is biomechanically designed to take.
If you are concerned or think you might have shoulder instability please contact us to book a session with one of our friendly physiotherapists for further assessment. We look forward to seeing you soon.
By Josiah Turnbull
References:
- Miller, J. and Armfield, S., 2021. Shoulder Instability. [online] Physio Works… Available at: https://physioworks.com.au/pain-injury/shoulder-pain/shoulder-instability/
- Washington University Orthopedics. 2021. The Anatomy Of The Shoulder. [online] Available at: <https://www.ortho.wustl.edu/content/Patient-Care/3127/Services/Shoulder-Elbow/Overview/Shoulder-Arthroscopy-Information/The-anatomy-of-the-shoulder.aspx
- Jaggi, A. and Lambert, S., 2010. Rehabilitation For Shoulder Instability. [online] British Journal of Sports Medicine. Available at: https://bjsm.bmj.com/content/44/5/333.info
