Notes On Shoulder Muscle Pain
The shoulder is a ball and socket joint but in this case the socket is not deep and the ball sits on it like a football on a plate. The ball is held in the socket by a cuff of muscle which surrounds the ball particularly on the front, top and back. This cuff of muscle is known as the rotator cuff (fig 1, arrows). The rotator cuff is anchored to the shoulder blade or scapula. Part of this muscle runs from the shoulder blade to the ball (humerus) through a tunnel, under the acromion (fig 1 and 2).People are born with different shaped tunnels and research suggests that as we get the older the tunnel starts to fur up. With time, the muscle running through the tunnel can start to catch on it, rubbing and causing pain (fig 3).
Typically, this pain is a muscle use pain, namely when lifting the arm up and reaching above one’s head or out to the side. Patients also notice pain from this muscle when lying on the shoulder at night. Patients get pain from this muscle if they enjoy sporting activities such as overhead racquet sports or swimming with overarm strokes. They get pain during other strenuous activities such as DIY especially above shoulder level. Patients often worry that the cause of the pain is arthritis, but actually arthritis of the shoulder is quite rare. Muscle catching (impingement) pain is very common. If the condition is allowed to continue unchecked then a hole can be rubbed in the tendon. This tear gives rise to pain and weakness and is serious (fig 4).
Diagnosis:
The condition is diagnosed firstly, by the history which the patient gives which suggests this pattern of pain. Secondly, on examination the surgeon endeavours to trap the muscle in the tunnel and to recreate the pain and thirdly through local anaesthetic testing. Here local anaesthetic, such as that used by dentists, is injected into the tunnel to see if the pain can be numbed off. Ultrasound imaging shows the tendons clearly and whether there is a hole. X-rays are helpful but are often normal in this condition and help to rule out arthritis. MRI scanning is a sophisticated harmless, though claustrophobic investigation which is able to show pictures of both the muscle and the tunnel and whether there is inflammation there.Treatment:
There are four treatment methods available for this condition.- The first treatment is rest and medications to dampen down the pain and inflammation. Patients will often have tried this prior to consulting a shoulder surgeon.
- If this fails to give adequate pain relief, then a course of physiotherapy is often of benefit. Special exercises are taught which help to strengthen the muscle as it runs in the tunnel allowing it to pull itself away from the tunnel roof. This physiotherapy always involves the patient learning a set of exercises with graduated rubber straps to help to strengthen the muscle.
- The next treatment is a cortisone injection which is administered by the surgeon into the muscle tunnel. Ultrasound guidance is used to confirm it is in the right place. It is a small dose of cortisone which almost never has any side effects on the patient as a whole. These side effects are transitory (increased sugar levels in diabetics, a rash for thirty six hours). A single injection is not known to cause any damage in the local tissues. It is not known how the injection works but many patients notice the abolition of pain after a few days and the ability to get their shoulder going again without pain. Approximately 30% of patients will “be cured” as a result of a single injection. It is my view that this injection works by allowing the muscle to get going without pain and then the momentum gained is sufficient to maintain that level of function without catching. A second injection will be offered to a patient if they have had a temporary or only partial effect from the first injection. A third injection can even be given after three months but it is unusual for patients to need this or gain long-term benefit from it.
- If patients fail to make an adequate recovery despite these three measures then they will be offered keyhole surgery. The essential problem is that the tunnel roof is too low, so an operation is undertaken to raise or core-out the tunnel roof. The surgeon places a small camera (about the size of a pencil) into the tunnel and a shaver (also the size of a pencil) along the length of the tunnel and cores out the ceiling so as to allow the muscle more clearance to slide without catching. This procedure takes approximately twenty minutes. About half a sugar lump of bone is removed. It cannot come back.