Reading research: Advances in the understanding of throwing injuries of the shoulder

There is nothing more frustrating for a throwing athlete than that annoying nagging sensation that something is becoming uncomfortable in the shoulder.  It’s such a complex joint that it’s often hard to pinpoint what is wrong.

Javelin thrower in action (photo courtesy of tableatny)

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The article

I found this interesting review article from a while back, called Advances in the understanding of throwing injuries of the shoulder, by Hackney, 1996, British Journal of Sports Medicine, while looking for something completely different.  However, it caught my eye, as it presents a complex subject fairly clearly.  I suspect that in some respects it might be overly simplistic (partly because it is 15 years old now) yet it feels like a good place to start.

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The overhead athlete

Who does this article apply to?  Well, obviously, throwers of all kinds, including the field events of javelin, discus, hammer and shot but also team sports including baseball and volleyball.  Interestingly, swimmers are also overhead athletes, a fact that sometimes escapes people.

Interestingly, the article does have some important things to say about the likely causes of shoulder pain and problems in overhead athletes, as opposed to, say, weightlifters.  But more on that below.

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The glenohumeral joint

Don’t be alarmed!

This is not going to be a long, drawn-out discussion of anatomy.  I am not going to be urging you to understand how “the uvulus muscle connects to the upper dorcimi via the ligament whose name sounds like those little dinosaurs from Jurassic Park,” as my friend Eric Moss would say.

Stick with me through the first couple of technical sections and then suddenly we emerge into the bright light of day and everything gets practical.

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Glenohumeral joint: stability vs. mobility 

The glenohumeral joint is the interface between the scapula (the shoulder-blades) and the humerus (the upper arm).

I is not a hugely stable joint, as everyone knows.  The reason it’s not as stable as the knee or the elbow, for example, is that it is designed to have a greater range of motion.

More range of motion means less stability.  So far, so good.

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Where does the stability come from?

The stability that the glenohumeral joint does have comes from various places:

Glenoid labrum – the glenoid labrum is a ring of cartilage that surrounds the edge of the shallow dip of the glenoid fossa in the scapula that the humeral head sits in.  It basically increases the depth of the dip to make it a bit more like a cup and less like a saucer.

Glenohumeral ligaments – there are three glenohumeral ligaments, conveniently called the superior, middle and inferior ligaments.  They are all on the anterior (front) side of the joint and connect across the joint from the scapula to the humerus.  The ligaments are arranged so that different ligaments are taut or slack at different ranges of motion.  The inferior ligament is the one that stops your shoulder falling out when you abduct your shoulder (move your arm away from the midline of the body) and externally rotate it (as if directing traffic).

Rotator cuff – the rotator cuff comprises four little muscles, whose names sound like small dinosaurs from Jurassic Park (supraspinatus, infraspinatus, teres minor and subscapularis).  The cuff allows the shoulder joint to glide a little in the joint (it is not a perfect ball-and-socket joint but glides a little) but not too much.  The first three are predominantly external rotators and the subscapularis is an internal rotator.

Supraspinatus – the suprapspinatus gets pretty short shrift in my basic sports anatomy and kinesiology textbooks as a boring muscle that doesn’t do much.  However, Hackney argues that it contributes a lot of stability to the shoulder when the shoulder is fully externally rotated and abducted (as if at the start of a throw).  He therefore suggests that specific, targeted supraspinatus training should be done pre-season.  This work should be endurance-related, as it is fatigue of the muscle that leads to problems.

Scapular stability – Hackney explains that the scapula needs to be stable for the rotator cuff to be able to do its job properly.  The key muscles to help create this stable platform are the serratus anterior, the rhomboids and the trapezius.  In throwers with shoulder instability, Hackney notes that it is very common for the serratus anterior to be underactive.

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Pathologies of the shoulder

Hackney was a consultant orthopaedic surgeon when he wrote this article.  He notes that there are a number of different concepts to understand in the shoulder and they should not be confused with each other.  Each can lead to pathologies, or not.

Laxity vs. instability – Hackney notes that the shoulder is not a perfect ball-and-socket joint but has a little inherent laxity that allows a small amount of glide.  Where laxity ends and instability begins is a topic for debate!  However, at some point, the joint must be considered unstable if it has too much glide.  Why is this bad?  Well, if the joint glides too much, it can ride up onto the edge of the labrum and wear it down.

Anterior instability – Hackney notes that the typical thrower will have a predisposition towards anterior instability (remember, that’s where the ligaments are?).  This instability is due to the ligaments being lax.  It also allows a greater degree of external rotation, which allows for a larger range of motion to be achieved in the throw.  This is fine, so long as the rotator cuff and the glenoid labrum stabilise the humeral head and stop it from gliding too much.  If it glides too much, the labrum can become damaged and the ligaments can become even more stretched, leading to more problems.

Injury to the rotator cuff – it makes sense, therefore, that if the rotator cuff stops doing its job properly, that anterior instability can become an issue, even without excessive laxity in the first place.  However, Hackney also notes that the rotator cuff not only protects anterior displacement (like the glenohumeral ligaments) but also in other directions.  So if the cuff stops working properly, it is thought that this can allow the humeral head to glide superiorly (upwards), which allows impingement to occur between the humerus and the acromion of the scapula (subacromial, or external impingement).  This type of impingement is common in older athletes and weightlifters.

Eccentric overload – still thinking about the rotator cuff, Hackney notes that an obvious function of the cuff is to decelerate the humerus at the end of the throw and stop your arm following the javelin into the clear blue yonder.  Consequently, there is a theory that where the cuff fails to do this job properly, eccentric overload is thought to occur, causing a wrench of the rotator cuff tendons, and possibly tears.  However, this theory has been challenged and possibly replaced by the idea of internal impingement (see below).

Posterior capsule tightness - Hackney notes that it is also common to see throwers with tightness of the posterior capsule.  This also facilitates anterior glide of the humeral head, which pushes you towards the anterior instability described above.

Impingement vs. instability – Hackney notes that at the time of writing (1996), the literature suggests that most throwers with shoulder problems are suffering from instability rather than impingements and therefore respond well to rehabilitation programmes.  He notes that this was sadly discovered as a result of surgical interventions to remove impingements having no effect on the shoulder problems of various athletes.

Internal impingement - Hackney notes that in the early 1990′s a new mechanism was proposed for the cause of undersurface rotator cuff damage in overhead athletes.  At arthroscopy, it is possible to observe an impingement of the rotator cuff against the glenoid labrum in the position of abduction and external rotation, equivalent to the position of the shoulder in the cocking phase of a throw.  This is a different impingement to the subacromial or external impingement noted above.

SLAP lesions – tears of the superior glenoid labrum, whether at the front or at the back, are called SLAP lesions.  Tears to the superior labrum are problematic because they then place more reliance on the inferior glenohumeral ligament to create the anterior stability that the shoulder needs.

Bicipital tendinitis – Hackney notes that bicipital tendinitis is rarely a primary issue but typically occurs in tandem with either a SLAP lesion or a subacromial (external) impingement.

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What to do?

OK, that was all quite complicated.  Hackney is buoyant about treatment, however, and is confident that most throwers will respond well to conservate treatment and rehabilitation.

Posterior capsule stretching – as we noted above, the posterior capsule can be tight in many throwers.  The most common posterior capsule stretch is called the sleeper stretch, seen below.

Strengthen the rotator cuff – each of the components of the rotator cuff need to be strengthened.  The infraspinatus and teres minor are mainly external rotators and can be strengthened using the normal rotator cuff special exercises that you see people doing (the ones that look like they are directing traffic).  The supraspintaus is an abductor and can be strengthened by doing middle deltoid raises with light dumbbells with the thumbs pointing upwards.

Strengthen the scapula stabilisers – the important muscles to strengthen for scapula stability are the serratus anterior, the rhomboids and the middle and lower trapezius.  For these muscles, many types of row are helpful but the chest-supported row (at about 45 degrees), either on a machine or with dumbbells is best for targeting the middle and lower trapezius muscles.  For the rhomboids, face pulls or the strangely-named rear-delt flye is good (as long as you focus on squeezing your shoulder blades together).  For the serratus anterior, the scapular push-up is the ideal training exercise.

I hope you found this review helpful.  I certainly found it tightened up some of my understanding of how shoulder problems can develop and how they can be rehabilitated.