Muscle knots in the Serratus Posterior Superior are located near the shoulder blade. These muscle knots can refer pain to the upper back, posterior shoulder, and sometimes the back of the arm, often mistaken for shoulder joint or rotator cuff issues. It can also refer pain to the chest, down the inside, front of the arm, wrist, and pinky finger. You may feel a deep ache or tightness that worsens with breathing, twisting, or reaching overhead.