If you ask different people what they consider a part of their shoulders, you’ll get a wide variety of answers. For example, some include their neck, shoulder blades, the upper part of their chest, or their arms. What is considered part of the shoulder and what isn’t can be seemingly arbitrary. When patients are experiencing shoulder pain, the affected anatomy at the pain site needs to be identified to establish the proper diagnosis. Patients need to understand that because so many structures make up the shoulder joint and because there are many possible causes, even experienced doctors can have trouble making the right diagnosis.

There are, however, a few helpful guidelines to get them on the right track:

First, at the doctor’s office, it is helpful to differentiate between neck and shoulder pain by separating it into three anatomical zones: posterior pain, anterolateral pain, and axillary pain.

1. Posterior pain

Posterior pain is pain felt primarily at the base of the neck, the trapezius muscle, and the shoulder blades, and radiates to the arm and forearm. The pain is sometimes associated with headaches, numbness, or a tingling sensation on the back of the hand (somewhat similar to sciatica of the upper extremities). This pain is generally caused by inflammation around the spine (sprain, degenerative disc disease, other degenerative conditions), muscle tension or spasms, or irritation or compression of the nerves of the back, which can cause numbness in the fingers.

Doctors must check whether patients have a full and symmetrical range of motion of the cervical spine and whether mobilizing the neck affects the shoulder pain. If so, it is referred pain.

First, the doctor should perform a neurological assessment and have a spinal x-ray taken, which will often show compression between the C5 and C6 or C6 and C7 vertebrae (a common condition in patients over 45).

This pain is usually treated without surgery unless there are signs of nerve compression (loss of feeling, strength, or reflexes). In these cases, patients undergo an MRI or CT scan and are referred to a specialist (such as a physiatrist, orthopaedist, or neurosurgeon) if there is a risk of neurological damage.

2. Anterolateral pain

Anterolateral pain is a symptom of conditions related to the anatomical structures of the shoulder, which include the subacromial space, the acromioclavicular joint, rotator cuff, the labrum, the long head of the biceps tendon, and the glenohumeral joint. Several possible conditions affect this area. Here are a few examples:

A) Acromioclavicular joint issues usually occur on the top of the shoulder. Referred pain is rare, but pain increases when the patient’s arms are crossed over their chest (adduction).

B) Tendinitis and tendon tears (rotator cuff and biceps) cause pain on the side and front of the shoulder (under the acromion) and may be referred to the external half of the arm (or to the biceps in the case of biceps tendinitis). This pain worsens when forcefully lifting the arm, especially over the patient’s head. It tends to increase at night and may disturb the patient’s sleep. Pain varies according to the patient’s movements. In cases of severe rotator cuff tears, this pain may be accompanied by weakness or even muscular atrophy at the shoulder blades. Ask your partner or a friend to compare your shoulder blades, as they’re difficult to see on your own.

C) Arthritis of the shoulder and capsulitis are more insidious conditions. Discomfort progresses gradually and is more difficult to pinpoint. It is often felt when the patient is at rest and not moving at all. These conditions are characterized by loss of movement. Patients can check this themselves by keeping their elbows pressed against their sides, externally rotating their forearms, and comparing each arm, or trying to put their hands between their shoulder blades and comparing one side to the other.

D) Labrum disorders (e.g., SLAP tears) are movement-related, sometimes causing a popping sound or sudden pain that is usually difficult to pinpoint. The pain isn’t constant; it is felt intermittently when moving a certain way.

E) Subacromial impingement and bursitis are also movement-related conditions that cause pain on the front and side of the acromion when the arm is fully extended overhead or during abduction (lateral raise). The pain worsens if the arms are internally rotated (turning the forearms toward the ground).

It is relatively uncommon for a shoulder condition to cause symptoms that extend to the elbow (with the exception of capsulitis). When this occurs, doctors look for a root cause related to the spine.

3. Axillary or thoracic pain

Persistent pain felt around the axilla (armpit) or the upper chest is most often referred pain (except when it is an initial symptom of capsulitis). If the pain is felt on the left side, doctors must pay special attention to heart and lung conditions.

There are several possibilities for the causes of this pain, ranging from viruses (in the case of shingles), tumours (e.g., axillary lymph nodes or lymphoma) or diaphragm irritation (e.g., due to an abdominal disorder).

Traditional recommendations apply in such cases, and patients should consult their family doctor or a general practitioner to rule out a more serious diagnosis.