How Shoulder Dislocation Leads to Structural Instability
A shoulder dislocation is more than a simple shift of the joint—it can initiate a cascade of mechanical and biological changes that compromise long-term joint health. A Bony Bankart lesion exemplifies this process: a traumatic fracture at the anteroinferior glenoid rim caused by anterior dislocation. In this article, we dive into the mechanism and stages of lesion development, explaining the pathophysiological journey from initial trauma to chronic instability.
1. Initiating Event: Anterior Shoulder Dislocation
1.1. Common Triggers
- High-impact trauma (e.g., falls, sports collisions)
- Arm positioned in abduction and external rotation
- Forceful movement drives the humeral head against the front of the glenoid
1.2. Immediate Consequences
- The humeral head forcibly exits the socket
- Tears the anterior-inferior labrum
- Simultaneously shears or fractures the glenoid rim, creating a Bony Bankart lesion
This initial mechanical trauma disrupts both soft tissue and bony structures essential for shoulder stability.
2. Formation of the Bony Lesion
2.1. Bone Fragmentation
- As the labrum detaches, it may pull off a piece of the anterior glenoid rim
- The severity of the bone loss varies with force magnitude and patient anatomy
2.2. Fragment Displacement
- Detached fragments may remain loosely attached to soft tissue
- Or, they may migrate within the joint capsule, altering joint articulation
Fragment location influences whether the lesion is repairable via arthroscopy or requires open surgery.
3. Biological Response and Early Remodeling
3.1. Inflammatory Phase (Days 1–7)
- Hemorrhage and cellular infiltration begin repair
- Cytokines and growth factors initiate inflammation to clear debris
- Pain, swelling, and restricted movement follow
3.2. Proliferative Phase (Week 1–4)
- Fibroblasts and osteoblasts proliferate
- Soft callus forms around the bone fragment
- Labral tissues attempt to reattach, but without intervention, re-adhesion is often incomplete
4. Chronic Adaptation and Joint Instability
4.1. Glenoid Bone Loss Over Time
- Without proper realignment or fixation, the rim remains deficient
- Each subsequent dislocation exacerbates bone loss
- Over time, this becomes chronic glenoid hypoplasia, distorting joint biomechanics
4.2. Labral Scarring or Resorption
- The labrum may scar in a non-functional position
- Or, it may be resorbed entirely, removing a critical stabilizing structure
4.3. Altered Joint Kinetics
- Loss of bony contour and labral tension affects the concavity-compression mechanism
- The humeral head “rides up” over the glenoid edge, increasing risk of repeat dislocation
5. Secondary Damage: The Domino Effect
5.1. Hill-Sachs Lesions
- Posterolateral humeral head impaction fracture
- Caused by repetitive collisions with the glenoid during instability episodes
5.2. Capsule Laxity
- Capsular ligaments become stretched with each dislocation
- Results in multidirectional instability, even without further trauma
5.3. Early Degenerative Changes
- Joint surface wear from abnormal mechanics
- Early onset glenohumeral arthritis, even in young individuals
6. Clinical Correlation: Why Early Treatment Matters
6.1. Timing of Repair
- Earlier surgical repair—especially within 3–6 weeks—reduces the risk of progressive damage
- Delayed treatment allows irreversible bone loss and soft tissue degradation
6.2. Prognosis and Surgical Strategy
- Small, well-positioned fragments may heal with fixation
- Larger, chronic lesions with fragment resorption may need bone grafting (e.g., Latarjet or Eden-Hybinette)
Summary of Lesion Development Stages
| Stage | Event | Outcome |
| 1 | Acute Dislocation | Labral and rim fracture |
| 2 | Fragment Mobilization | Joint incongruity |
| 3 | Inflammatory Response | Pain, swelling, tissue damage |
| 4 | Proliferation | Attempted healing or fibrosis |
| 5 | Chronic Instability | Repeat dislocations, bone loss |
| 6 | Degeneration | Arthritis, joint dysfunction |
Frequently Asked Questions
1. What causes a Bony Bankart lesion?
It typically results from a traumatic anterior dislocation, where the humeral head slams into the glenoid rim, fracturing it along with labral tearing.
2. Can a Bony Bankart heal without surgery?
Small fragments with minimal displacement might heal, especially in non-athletes. However, active individuals and those with instability often need surgical repair.
3. What’s the risk of delaying treatment?
Delaying treatment allows for progressive bone loss, scarring, and mechanical instability—making surgical repair more complex and prognosis less favorable.
4. How does this condition lead to arthritis?
Repeated dislocations and joint misalignment lead to abnormal cartilage wear, which eventually results in post-traumatic osteoarthritis.
5. Is bone grafting always needed for large defects?
Yes, in many cases of >25% glenoid bone loss, grafting is the most reliable way to restore joint stability and prevent long-term dysfunction.
