I see a lot of people who tell me their shoulder pain began after throwing, some of these play cricket to a high level, some are athletes and some are just launching something for the dog to chase. The forces involved in racquet sports and golf are very similar to throwing, and shoulder pain in this population is another common problem that I see. So if you are fed up missing out on your weekly tennis game, or can’t commit fully to your drive because of pain or the dog just looks at you wistfully every time you pass a stick then read on!
Ever since our early ancestors began to walk on two legs (around 4 million years ago) our shoulders and elbows began to evolve for the purpose of positioning our hand in space. Together, the shoulder and elbow allow us to manipulate our hand into just about any position. Walking on two legs (bipedal stance) freed up the rapidly evolving human hand for many tasks. Whether this be stone-age man crafting and using tools and harnessing fire to more modern problems like lying with your head and shoulders in a kitchen cupboard, negotiating a maze of obstacles to reach the water stopcock!
The shoulder is the most mobile joint in the body and this allowed us to reach up and forage food from trees. Previously, like with apes, this mobility had allowed us to swing from branches. But, with time, our shoulder blade evolved. This allowed us to exploit this mobility in a new and novel way. A way to harness our shoulders major strength, that which set us apart and put us firmly at the top of the food chain; our ability to throw with accuracy and speed. The pay off for this is that we are now less well suited to dangling and activity with our arms above our heads. As such there is a much higher prevalence of shoulder pain in manual workers and people who work above shoulder height like electricians and window cleaners.
Our shoulder is a ball and socket joint. The ball sits at the top of the arm bone (the Humerus) and is known as the ‘humeral head’. The socket (the glenoid) is part of the shoulder (scapula). The socket is small and the ball rests against it giving rise to the analogy of the shoulder being like a golf ball sitting on a golf tee. Ligaments normally bind bone to bone over a joint and help to stabilise it (hold the two parts together), the tighter the ligaments the less movement there is. In order to allow greater mobility in the shoulder the ligaments are lax; we sacrifice stability for mobility. As such the shoulder is the most commonly dislocated joint in the body.
We rely heavily on the muscles around the shoulder, and particularly the rotator cuff, to keep the ball sitting where it should on the socket. The rotator cuff is a group of four muscles which attach between the shoulder blade and the ball at the top of the arm. They rotate the shoulder joint but also work hard to keep things where they should be. We call this action ‘centering’ of the ball on the socket. The names of the rotator cuff muscles are Supraspinatus, Infraspinatus, Subscapularis and Teres Minor.
The shoulder is capable of amazing feats during the throwing action. Recent studies on baseball pitchers in the USA show that during pitching the arm accelerates at 7000-8000 degrees per second, and decelerates at approaching -500000 degrees per second. As a result of such huge speed the shoulder joint is subject to compressive (the ball and socket getting pushed together) forces of up to 1000N (about 101kg) and shear forces (the ball getting pulled forwards or backwards on the socket) of around 300-400N (30-40kg). You can see a slo-mo video of this here. The rotator cuff has to be able to resist these shearing forces.
Producing this action requires a delicate balance of movement and stability. If the balance is lost due to a lack of either strength or mobility then pain is commonly a symptom. Now I get that we are not all professional baseball pitchers. The guy in the video probably spends all day every day in the gym training to throw a ball, and will have done so for most of his life. All of that to throw about 100 pitches a week in a game. Even then they are often subject to injury as the forces involved in throwing regularly exceed the physiological limits of the joint.
But when did you last go to the gym to train your rotator cuff to make sure it is capable of dealing with the forces involved with throwing a stick or ball twenty times twice a day for the dog? I see many people who complain of shoulder pain which started in this way. Yes – the shoulder evolved to throw, but strength and mobility need to be maintained to allow it to do so.’ But stone-age humans didn’t go to the gym to keep his or her throwing arm fit and healthy’ I hear you say! No – he or she didn’t, nor did they need to when life expectancy was 15-30 years.
Like death and taxes there is a sad inevitability around what happens to our tissues with age. Their composition changes and they become less resilient to load and less stretchy. There are the external signs of this like grey hair and wrinkles. There are internal signs of this too. We now know to expect these changes on scans, but it is still a little disconcerting when scan reports say ‘degenerative disease’ in reference to these normal age related changes. It would be equally harsh to describe your husband or wifes’ crows feet as ‘degenerative face disease’. Now grey hair and wrinkles don’t cause us pain, and the changes on the inside don’t necessarily cause us pain either. But as they are less resilient and less compliant, they are less able to deal with sudden changes. As such things like throwing or even pruning the hedge can cause overload resulting in pain.
These problems respond very well to physiotherapy, and with a little work you can improve your strength and mobility. Regular exercise helps your tissues to deal with load better. So if you are having problems why not book to come in for an assessment?
If you have any questions or topics you’d like me to discuss in my blog feel free to ask.