Posterior shoulder instability, though less common than anterior instability, presents a unique challenge in orthopedic care. It involves the backward slipping or dislocation of the shoulder joint, often causing pain, weakness, or dysfunction. Recent advances in arthroscopic techniques now allow for a minimally invasive and highly effective approach to treating this condition.
Understanding Posterior Shoulder Instability
Posterior shoulder instability is rare and can be hard to diagnose, often misinterpreted as general shoulder pain or weakness. It occurs when the shoulder joint shifts or slips backward, and can be caused by a traumatic injury or repetitive microtrauma—such as repetitive lifting or pushing exercises.
Historically, both open and arthroscopic surgeries have been used to treat this condition. The study by Provencher et al. evaluated arthroscopic stabilization specifically, examining how different patient and surgical factors influenced outcomes.
Who Was Studied?
Between 1999 and 2003, 33 active-duty military personnel—mostly young men aged 19 to 34—underwent arthroscopic posterior stabilization. These individuals had experienced shoulder instability that did not improve with at least four months of physical therapy.
Notably:
- 91% of the patients had traumatic injuries, such as from sports or vehicle accidents.
- 9% had microtrauma from heavy weightlifting or repetitive physical training.
- 13 patients could voluntarily subluxate their shoulder, while 20 had involuntary instability.
Diagnostic Evaluation
Before surgery, patients underwent a full physical examination, X-rays, and magnetic resonance arthrograms (MRAs). These imaging tests helped detect:
- Posterior labral tears (in 52% of patients),
- Excessive capsular laxity (“billowing” of the posterior capsule),
- Other coexisting shoulder conditions like SLAP lesions or partial-thickness rotator cuff tears.
Even when MRAs appeared normal, physical findings often confirmed instability requiring surgical intervention.
Surgical Approach: Arthroscopic Stabilization
All patients were positioned on their side under anesthesia, and the shoulder was examined to determine the degree of posterior translation. Depending on findings, surgeons either:
- Repaired torn labrum using suture anchors (in 17 patients), or
- Tightened the capsule through plication stitches (in 16 patients).
Other procedures performed when necessary included:
- Biceps tenodesis,
- SLAP repairs,
- Closure of the rotator interval capsule in select cases.
Rehabilitation and Recovery
Following surgery:
- Patients wore a sling in neutral rotation for six weeks.
- Shoulder movement was restricted during early recovery.
- Physical therapy began at six weeks to restore full motion and strengthen muscles.
- Full activity, including return to sports or military duties, was typically allowed after four months.
What Were the Results?
Success Rates
- 26 of 33 patients (79%) had successful outcomes.
- 7 patients (21%) experienced failures—either recurrent instability (4 cases) or persistent pain (3 cases).
- Most failures occurred in patients with voluntary instability or previous surgeries, especially prior thermal capsule procedures.
Visual Results and Grading (Page 6)
A bar chart on page 6 shows:
- 97% of patients had good or excellent outcomes on the ASES scale.
- 81.8% had good/excellent outcomes using the SANE scale.
- Only 61% had similarly strong outcomes on the WOSI scale, which is more stringent and comprehensive.
Key Factors Affecting Success
- Better Outcomes: Involuntary instability, first-time surgery, traumatic cause.
- Worse Outcomes: Voluntary subluxation, prior surgery (especially thermal capsular shrinkage), microtrauma without labral tears.
- Capsulolabral Repair vs. Plication: Patients with labral repair using anchors generally had better results than those with plication only.
Should the Rotator Interval Be Closed?
The rotator interval (RI) was closed in 2 patients—both of whom failed treatment. The study suggests that RI closure is not routinely necessary unless specific indications are present. Most patients had good outcomes without RI intervention.
Safety and Complications
There were:
- No nerve injuries,
- No infections,
- No issues with the surgical wounds,
showing that arthroscopic techniques are relatively safe when performed properly.
Final Thoughts and Conclusion
Arthroscopic treatment for posterior shoulder instability is a safe and effective method, especially for patients with traumatic and involuntary instability who have not undergone prior surgery.
While some patients may not achieve full relief—particularly those with voluntary instability or prior procedures—the majority experience significant improvement in stability, strength, and return to function.
This minimally invasive approach represents a modern solution to a historically difficult problem.
If you’re experiencing shoulder instability, especially if it’s interfering with your daily life or athletic performance, consult with an orthopedic specialist experienced in arthroscopic shoulder procedures. With proper diagnosis and treatment, most patients can expect excellent outcomes and a return to their active lifestyles.
