Our shoulder series continues with Part V today with a little bit about humeral retroversion in the overhead athlete. If you missed the previous sections you can find them below.
Throwing athletes almost always present themselves with some degree of humeral retroversion. This is the loss of internal rotation with gains in external rotation in the glenohumeral joint. There are several different theories as to how exactly this occurs. Some believe it is soft tissue adaptations, other believe that it develops as changes to the bony anatomy when youth athletes are involved in throwing sports. The consensus as of late seems that humeral retroversion is more strongly related to adaptive changes in proximal humeral anatomy than to changes in the soft tissues.
Virtually every throwing athlete that you come across will have excessive external rotation on the dominant side with a decreased internal rotation. When compared with the non-dominant arm we hope to see total rotation equal. The difference obviously being the throwing arm arc of rotation shifts posteriorly.
Looking at one of our pitchers numbers from this past year can give us some information.
External: 142 deg.
Internal: 47 deg.
Total Rotation: 189
External 129 deg.
Internal 61 deg.
Total Rotation: 190
When we look at these numbers we want his total rotation to be equal bi-laterally. We already know that his right arm ER will shift further back and along with that shift he will lose IR. Regardless, our goal is to equalize total rotation. In this example we see that total rotation is virtually equal, which is a good thing. Theses numbers are a great example of what happens in the throwing athletes shoulder and show what part humeral retroversion plays in these athletes. In Part VI of this series we are going to begin looking at a case study.
At any rate these adaptive changes usually happen when children are heavily involved in throwing sports at a young age. It becomes even more significant with athletes who are “overthrown” so to speak. I’m referring to the superstar 12-year-old that pitches year round on 3 different select teams, a little league team, showcase camps, etc. This excessive external rotation happens when the growth plates of children are still open and will adapt to the inherent stresses of throwing a fastball.
Osseous adaptation and range of motion at the glenohumeral joint in professional baseball pitchers.
Humeral retroversion isn’t necessarily a bad thing. It’s actually what allows pitchers to pitch really. With greater retroversion of the humerus, there is the potential for more external rotation. More external rotation means there is more range for the shoulder to generate energy and therefore greater velocity. I’ve seen a few different studies that show a correlation between pitchers velocity and degree of external rotation.
When you watch people who can’t throw, or “throw like a girl,” it’s likely due to the fact that, they never developed that motor pattern as a youngster, or more likely that they didn’t develop the humeral retroversion to allow them to lay their arm back into external rotation. They essentially are blocked at the 90 degree mark of glenohumeral external rotation when in the cocking phase of a throw.
Take a look at a comparison of our former and current presidents and you will definitely notice a difference. President Bush played baseball as a kid. President Obama has admitted to never really having played the game.
Mike Reinold, Head ATC for the Boston Red-Sox, has talked about being able to see the degree of humeral retroversion in a pitcher. When supine in a cross arm relaxed position you will notice the throwing arm has greater external rotation than the non-throwing arm. Mike mentions using this method to actually measure the amount of humeral retroversion an athlete has.
The previous study sums up humeral retroversion quite nicely.
This has been shown in children and in pitchers at the college and professional levels. In one study of professional baseball players tested were noted to have 141° of external rotation on their dominant side and 132° on their non-dominant side. Maximum external rotation at the shoulder during pitching has been reported to be as much as 160° to 178°. Some investigators have postulated that this high level of external rotation is due to changes in the glenohumeral capsule and musculature caused by pitching. Others have attributed the increased external rotation to overuse. Such overuse has been postulated as resulting in a contracture of the posterior shoulder capsule and stretching of the anterior shoulder capsule, leading to a tendency toward anterior glenohumeral subluxation. Some have described these changes in the soft tissues about the glenohumeral joint as “relative laxity.” Essentially, these changes represent an attempt by the shoulder to attain a balance between the flexibility needed to allow for greater external rotation and the stability needed to counter the anterior shear forces across the joint during the process of pitching.