The purpose of this research is to compare two different approaches for treating patients with shoulder impingement (subacromial pain syndrome): electric dry needling and spinal manipulation versus impairment-based mobilization, exercise, and interferential electrotherapy. Physical therapists commonly use all of these techniques to treat shoulder impingement (subacromial pain syndrome). This study is attempting to find out if one treatment strategy is more effective than the other.

Patients with shoulder impingement (subacromial pain syndrome) will be randomized to receive 2 treatment sessions per week for up to 6 weeks (up to 12 sessions total) of either: (1) electric dry needling and spinal manipulation or (2) impairment-based mobilization, exercise and interferential electrotherapy.

Inclusion Criteria:

1. Adult over the age of 18 years old that is able to read, write and speak English

2. Primary complaint of anterolateral shoulder pain lasting longer than 6 weeks

3. One or more of the following special tests:

   1. Positive Neer Impingement test-i.e. pain with passive overpressure at full shoulder flexion with the scapula stabilized.
   2. Positive Hawkins-Kennedy test-i.e. pain with passive internal rotation at 90° of shoulder and elbow flexion

4. Pain with ONE or more of the following active movements and resisted isometric tests

   1. Pain with active shoulder elevation
   2. Pain with resisted shoulder external rotation at 90 deg of abduction
   3. Pain with resisted shoulder abduction in Empty Can Test positon - i.e. 90 deg of shoulder abduction, 30 deg of horizontal adduction (i.e. in scapular plane) and full internal rotation (i.e. thumb down)

Exclusion Criteria:

1. Report of red flags to manual physical therapy to include: severe hypertension, infection, uncontrolled diabetes, peripheral neuropathy, heart disease, stroke, chronic ischemia, edema, severe varicosities, tumor, metabolic disease, prolonged steroid use, fracture, RA, osteoporosis, severe vascular disease, malignancy, etc.
2. History of shoulder injection within the past 3 months.
3. History of shoulder dislocation, subluxation, fracture, adhesive capsulitis, or cervical, thoracic or shoulder surgery.
4. Isolated acromioclavicular joint pathology (i.e. the only location of symptoms is localized specifically with one finger directly over the acromioclavicular joint and nowhere else, and reproduced only with acromioclavicular palpation by the examiner.)
5. Evidence of cervical radiculopathy, radiculitis or referred pain from the c-spine
6. Full-thickness rotator cuff tears (evidenced by MRI and/or positive lag signs)
7. Baseline SPADI of not less than 20%
8. History of breast cancer on involved side.
9. Prior treatments (eg. Acupuncture, physical therapy, chiropractic, dry needling, massage therapy, injections) to the involved limb over past 3 months.
10. Pending litigation for an injury.
11. Psychiatric disorders or cognitively impaired
12. Pregnancy