In anterior shoulder dislocation, is neuromuscular electrical stimulation (NMES) of the shoulder internal rotators or external rotators more effective?

NMES for Anterior Shoulder Dislocation: Target External Rotators

For anterior shoulder dislocation rehabilitation, neuromuscular electrical stimulation should target the external rotators (infraspinatus and teres minor), not the internal rotators. This approach directly addresses the biomechanical instability pattern and prevents recurrent subluxation while avoiding complications associated with internal rotator dominance.

Biomechanical Rationale

External rotator strengthening is the primary intervention for anterior shoulder instability because:

• Loss of external rotation is the primary contributor to adhesive capsulitis and shoulder instability following anterior dislocation 1
• External rotation range of motion relates most significantly to preventing shoulder pain and dysfunction 1
• Internal rotators (subscapularis, pectoralis major) are commonly associated with spasticity-related pain and contribute to shoulder protraction, not stability 1
• Improving external rotation and abduction range of motion through targeted interventions is specifically recommended as a means of preventing frozen shoulder and shoulder-hand pain syndrome 1

Clinical Evidence Supporting External Rotator NMES

The highest quality evidence demonstrates superior outcomes with external rotator stimulation:

• NMES of the infraspinatus significantly increased shoulder external rotation peak force by 22% after rotator cuff repair surgery (p < 0.001), regardless of tear size, patient age, or days postoperative 2
• Postoperative NMES of the deltoid (which assists external rotation) after reverse total shoulder arthroplasty resulted in significantly greater ROM and power of external rotation at 3 months (36° ± 14° vs. 29° ± 12°; P = .003) and 6 months (41° ± 12° vs. 34° ± 11°; P = .013) compared to controls 3
• NMES applied to supraspinatus and posterior deltoid (external rotation stabilizers) prevented shoulder subluxation in 100% of acute stroke patients, while 37.5% of controls developed subluxation 4

Specific NMES Protocol for External Rotators

Target the infraspinatus and teres minor muscles using the following parameters:

• Electrode placement: Position electrodes over the infraspinatus muscle belly and inferior to the spine of the scapula, confirming placement by palpating during resisted isometric external rotation 2
• Stimulation frequency: Use tetanic frequencies of 25-75 Hz to produce fused contractions that maximize muscle tension and strength gains 5
• On-time duration: Apply on-times of at least 4 seconds to achieve high muscle tension 5
• Duty cycle: Use high duty cycles (1:1 or 1:2 on:off ratio) to evoke maximal muscle tension 1
• Current intensity: Set to maximum tolerable intensity within patient comfort, typically 50 pulses per second with symmetrical waveform and 1-second ramp time 2
• Session duration: Perform 30-60 minutes per session 5
• Training frequency: Implement 2-3 sessions per week to allow adequate recovery between sessions 1

Positioning Strategy

Shoulder positioning during NMES is critical to avoid complications:

• Position the shoulder in slight external rotation (not maximal) during initial sessions to avoid delayed onset muscle soreness 1
• Progressively increase the lengthened position over weeks as tolerance improves 1
• Start with the shoulder at 45 degrees of abduction, neutral rotation, and 15 degrees of horizontal adduction 2
• Gradually increase stimulation intensity during first sessions to prevent muscle damage, then increase to maximum tolerable levels 5

Critical Pitfalls to Avoid

Do not stimulate internal rotators because:

• Internal rotator dominance contributes to shoulder protraction and poor posture, which decreases vital capacity and increases work of breathing 1
• Botulinum toxin injections into subscapularis and pectoralis major are used to treat spasticity-related shoulder pain, indicating these muscles contribute to pathology rather than stability 1
• Excessive internal rotation perpetuates the anterior instability pattern that caused the dislocation 1

Additional contraindications:

• Do not use overhead pulleys during rehabilitation, which encourage uncontrolled abduction and have the highest incidence of developing hemiplegic shoulder pain 1
• Avoid aggressive passive range of motion if done improperly, as it could cause more harm to the complex shoulder joint 1
• Do not neglect gradual intensity progression—start low to prevent muscle damage and inflammation 5

Expected Outcomes

External rotator NMES produces measurable functional improvements:

• Significant reduction in shoulder subluxation with prevention rates approaching 100% when combined with proper positioning 4
• Enhanced external rotation force production detectable within 10.5 days post-injury 2
• Faster ROM restoration with considerable improvement in external rotation power by 3 months 3
• Pain differences remaining significant 12 months after treatment, particularly effective in less chronic patients 1