10 Things Every DC Needs to Know About Shoulder Instability
The shoulder's title of being the most mobile joint in the body comes with an inherent sacrifice of stability. (1,45) Clinical shoulder instability is defined as "symptomatic abnormal motion of the glenohumeral joint.” (1,3) On the shoulder mobility spectrum, instability lives between dislocation and non-pathologic hypermobility.
This blog will answer your top ten questions about shoulder instability, including a video tutorial of how to differentiate the direction of instability (anterior vs. posterior vs. multidirectional), emphasizing the frequently overlooked posterior variety.
1. What causes shoulder instability?
Shoulder instability results from imbalance or pathology disturbing one or more of the shoulder’s static or dynamic stabilizers. (1) The pathophysiology of shoulder instability can be divided into structural and functional causes.
Structural: acute trauma, microtrauma, congenital issues, etc.
Functional: posture, muscle imbalance, altered central or peripheral nervous system control, loss of proprioception, etc. (1)
Structural triggers, particularly acute trauma, are frequently associated with anterior shoulder instability, while functional causes are more commonly associated with posterior instability. (22)
Watch the docs demonstrate how to differentiate anterior vs. posterior shoulder instability.
2. Who gets posterior shoulder instability?
Posterior instability can occur secondary to acute trauma (i.e., motor vehicle accidents, seizures, etc.); however, repetitive microtrauma is a significantly more common culprit. (47,60) Non-traumatic posterior instability frequently occurs secondary to repetitive microtrauma in flexion, adduction, and internal rotation, particularly in the presence of generalized ligamentous laxity. (1) Overhead laborers and athletes who participate in bench pressing, American football blocking, swimming, tennis, and baseball or softball are likely candidates. (59) People with forward head/ forward shoulder postures have a significantly elevated risk. (44)
3. What are the symptoms of shoulder instability?
Symptoms of shoulder instability may be similar to those of a labral tear. Patients with posterior instability report episodic, activity-related shoulder discomfort and loss of function (reaching, throwing, etc.) (23) Episodes often occur during the mid-range of horizontal flexion and internal rotation when the glenohumeral ligaments are relaxed. (23,47) Posterior instability symptoms are usually more subtle than anterior instability symptoms and thus frequently go undiagnosed. (27)
4. Can shoulder instability be palpated?
Patients with chronic posterior shoulder instability may demonstrate posterior joint line tenderness secondary to repetitive synovitis. (46, 49) In severe or long-standing cases, patients may be able to voluntarily subluxate or dislocate their shoulder via specific movements. (23) A skin dimple over the posteromedial deltoid is reported to be 62% sensitive and 92% specific for identifying posterior shoulder instability. (47) Clinicians should note areas of point tenderness and any bulging or prominence of the humeral head throughout the shoulder range of motion.
5. Which orthopedic tests are best for diagnosing posterior shoulder instability?
Clinicians can assess posterior instability via the following tests: (46,47,52-57)
Posterior Drawer Test
Posterior Jerk Test
Load and Shift Test
Kim Test
Push-Pull Test
Posterior Apprehension Test
6. How does the rotator cuff affect shoulder instability?
The four rotator cuff muscles are the principal dynamic shoulder stabilizers. The muscles retract and depress the humeral head into the shallow glenoid cavity during arm abduction. Dysfunction contributes to impaired stability. Isolated strength tests can help assess individual rotator cuff function.
Isolated Strength Test Cluster
7. Are there any postural contributions to shoulder instability?
Clinical evaluation should include a postural assessment plus screening for functional deficits. Scapular dyskinesis and upper crossed syndrome are frequently associated with shoulder instability, including nearly 90% of those with functional instability. (44)
💡 Did you know that upper crossed syndrome was the #2 overall diagnosis for the ChiroUp provider network? To see all the stats that matter, check out our 2021 COPS synopsis of 631,000 patient presentations.
8. What’s the best rehab for posterior shoulder instability?
The Derby Shoulder Instability Program for recurrent posterior shoulder instability is a well-developed stepwise exercise progression for strength, proprioception, and plyometric training. (34)
The Derby Shoulder Instability Program for recurrent posterior shoulder instability is a well-developed stepwise exercise progression for strength, proprioception, and plyometric training. (34) Here are examples of the Derby exercises. Subscribers can view the entire program from their exercise library.
Derby 1A
Derby 1B
Derby 1C
Derby 1D
Scapular stability exercises should focus on improving retraction and external rotation since deficits in these motions play a significant role in posterior shoulder instability. (41) Improving rotator cuff deficits is equally essential, particularly those involving the subscapularis. Subscapularis strength can be enhanced via a modified belly-press exercise.
Modified Belly-Press
9. Is manual therapy beneficial for shoulder instability?
In addition to postural correction exercises, posterior instability patients exhibiting a forward-shoulder posture may benefit from directional therapy or mobilization in external rotation. Clinicians should assess for and address any joint restrictions in the cervical and thoracic region.
Mobilization - Shoulder External Rotation
10. Is surgery ever necessary for shoulder instability?
Controllable functional shoulder instability is generally successfully managed via conservative means. However, patients with non-controllable functional instability (i.e., unexpected subluxation/ dislocation) are more challenging to treat. Conservative options are often ineffective, and surgical stabilization can sometimes trigger increased pain, functional restrictions, and premature degenerative change. (43)
In patients with posterior instability, non-traumatic onsets tend to have better outcomes with conservative management (83% excellent results), while traumatic onsets may have less success (16% excellent results). (47,62) In patients with non-traumatic posterior instability, a six-month trial of conservative care is appropriate before surgical intervention. (47,63-65) Surgical consultation is also warranted for some traumatic structural etiologies and patients with a high risk of recurrence. (2) Younger patients, particularly elite athletes or those with high activity levels, may be more likely to require surgical repair of damaged tissues. (4)
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Want more content like this? Join our docs for this webinar: When It’s Not the Rotator Cuff: 4 Shoulder Diagnoses You Might be Missing.
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