"Traumatic" partial thickness tear of the Rotator Cuff
Whether the tear is "partial" or "complete" from the accident/trauma is not really relevant to this patient's diagnosis code. It is a traumatic injury to a tendon of the shoulder, so would have to be in the S46 Code Set, S46.0 _ _, Injury to the muscles and/or tendons of the rotator cuff. The exact mechanism of the injury is not described, so you do not know whether it was a "Strain" or "Other." For it to be a "Laceration" would require an open wound, which there does not seem to be. Therefore, I would go with S46.09 _ A (6th character for laterality).
Respectfully submitted, Alan Pechacek, M.D.