Heat can damage the articular cartilage and hence should not be applied directly over the joint. It is very useful to relax the muscles around the Shoulder Joint.
Hence it relieves symptoms of spasms if applied over muscles. Ideally heat application should be done 10-15 minutes before starting Shoulder Physiotherapy and ice application should be done for 10-15 minutes after physiotherapy.
Application of ice to the Knee decreases the inflammation & swelling in the Shoulder and thus improves the symptom of pain.
Remember that ice is applied over the bones of the Shoulder Joint.