Weakness in the arm

Rotator cuff problems

The rotator cuff muscles are responsible for lifting and stabilising the shoulder. Tendon inflammation (often referred to as bursitis or impingement), partial tears and full-thickness tears can all cause weakness, particularly when lifting the arm away from the body.

Sometimes the weakness is due to pain, while in larger tears the muscle may genuinely be unable to generate normal strength.

Frozen shoulder and biceps problems

Although frozen shoulder is primarily a condition of pain and stiffness, many patients describe the arm as feeling weak. In reality the muscles are usually functioning normally, but the pain and restricted movement prevent them from working effectively.

Inflammation or injury of the long head of the biceps tendon can produce pain at the front of the shoulder and a feeling of weakness, particularly when lifting or reaching overhead. Although the tendon can occasionally rupture, this rarely requires surgery and often acts as a sign that there may also be underlying rotator cuff disease.

Neck and nerve problems

Not all arm weakness comes from the shoulder. Compression or irritation of the nerves in the neck can cause weakness, often accompanied by pain, tingling or numbness extending into the arm or hand. Occasionally weakness can occur with very little neck pain, making the diagnosis less obvious.

Nerves can also become compressed further down the arm. Cubital tunnel syndrome (ulnar nerve compression at the elbow) may cause weakness of grip together with numbness in the ring and little fingers. Carpal tunnel syndrome (median nerve compression at the wrist) commonly causes numbness, tingling and weakness affecting the thumb, index and middle fingers, particularly at night.

Less commonly, weakness can arise because the nerves supplying the arm become compressed or stretched as they pass from the neck towards the shoulder. These thoracic outlet and brachial plexus problems can produce pain, weakness, altered sensation or a feeling that the arm tires unusually quickly, and can sometimes mimic shoulder disease.

When pain is the real problem

Although tennis elbow affects the outside of the elbow rather than the shoulder itself, it frequently causes patients to complain of weakness. In reality, gripping or lifting becomes painful, making the arm feel much less powerful than normal.

Pain arising from the acromioclavicular (AC) joint can also make the shoulder feel weak, particularly during overhead activities. The muscles themselves are usually normal, but pain limits how effectively they can work.

Finding the cause

Because weakness can arise from the shoulder, the neck, the nerves or simply from pain itself, the most important step is establishing why your arm feels weak. A careful history and examination often provide most of the answers. Depending on the findings, X-rays, ultrasound, MRI scans or occasionally nerve conduction studies may be recommended.

Treatment is directed at the underlying cause. Many patients improve with physiotherapy, activity modification or targeted injections, while others may benefit from surgery if there is significant structural damage to a tendon or nerve. My aim is to identify where the weakness is coming from, explain what is causing it, and help you choose the treatment that offers the best chance of restoring strength, confidence and function.