Does Subacromial Injection With Glutamate Receptor Antagonist, Ketamine, Attenuate Pain in Rotator Cuff Tendinopathy?

The hypothesis of the present study is that in patients with rotator cuff tendinopathy a specific pharmacological blocking of peripheral glutamate-receptor N-methyl-d-aspartate receptor type1 (NMDAR) glutamate receptors will result in pain alleviation. Activated NMDAR1 has been demonstrated to be crucial for pain regulation in various pain disorders, and in biopsies from patients with tendinopathy, NMDAR1 was found to be activated. To test this hypothesis a specific NMDA receptor antagonist, ketalar (ketamine), will be injected guided by ultrasound into the subacromial space in patients with rotator cuff tendinopathy, and subsequently the pain response will be assessed.