Sports Medicine Research: In the Lab & In the Field: Risk Factors for Posterior Shoulder Instability in Young Athletes (Sports Med Res)


Friday, October 4, 2013

Risk Factors for Posterior Shoulder Instability in Young Athletes

Risk Factors for Posterior Shoulder Instability in Young Athletes

Owens BD, Campbell SE, Cameron KL. Am J Sports Med. 2013 Aug 27. [Epub ahead of print]

Take Home Message: Athletes with increased glenoid retroversion may be at risk for posterior shoulder instability.  Increased internal and external rotation strength was also associated with instability but it is unclear whether these differences were causative or compensatory to the differences in glenoid anatomy.

Posterior glenohumeral instability has become increasingly common in young athletes.  However, little is known about the risk factors associated with these injuries.  If we can identify modifiable risk factors for posterior shoulder instability, we may be able to develop injury prevention programs. Therefore, the purpose of this study was to determine the modifiable and nonmodifiable risk factors for posterior shoulder instability among young athletes at the United States Military Academy (intercollegiate and intramural sports). The authors performed a prospective cohort study with 714 young athletes who were followed over a 4-year period.  Baseline measurements included subjective history of instability; clinical assessment of shoulder instability, range of motion, and strength; and bilateral noncontrast magnetic resonance imaging of the shoulder. On magnetic resonance images, the authors measured various anatomic features: glenoid version (e.g., retroversion), height, depth, rotator interval height/width/area/index.  Participants were followed for 4 years and one orthopaedic surgeon evaluated and documented all possible acute posterior shoulder instability events.  The authors reported that 46 shoulders sustained glenohumeral instability events, with only 7 (1%) in the posterior direction.  Baseline factors associated with posterior instability were increased glenoid retroversion as well as increased external rotation and internal rotation strength.

This study identified increased glenoid retroversion as the most significant risk factor for posterior instability.  This is consistent with previous studies that have also identified increased glenoid retroversion in patients with posterior instability.  However, these studies could not determine whether the observed differences were a cause or effect of the instability event.  The current study is unique in that it identifies increased retroversion before injury as a risk factor for subsequent shoulder instability.  This study also examined modifiable risk factors for posterior instability, specifically rotator cuff strength.  Contrary to their hypothesis, the authors found that increased internal/external strength was associated with subsequent instability.  However, it is unclear whether the increased rotator cuff strength caused the instability or was instead a result of compensation for the increased retroversion observed in these athletes.  The rotator cuff provides dynamic stability and compression of the humeral head on the glenoid.  Differences in glenoid anatomy may alter the direction of the compressive forces acting on the glenoid and thereby alter the muscle forces required to maintain joint stability.  These compensatory strategies may account for the differences in rotator cuff strength observed in this study.  As a result, these strength measurement findings should be interpreted with caution.  In conclusion, results from this study confirm that increased glenoid retroversion is the most significant risk factor for posterior shoulder instability.  Future studies should determine the amount of retroversion in patients with posterior instability that is necessary for soft tissue repair and also the critical level of glenoid retroversion that would warrant the need for modification of glenoid anatomy through glenoid osteotomy with concomitant repair.  Unfortunately, the authors did not identify modifiable risk factors that would allow for development of primary prevention strategies for shoulder instability in athletes and therefore future work is needed. 

Questions for Discussion: Do you think athletes should be pre-screened with imaging to identify risk of posterior shoulder instability?  Do you have any prevention protocols you would employ in high risk groups?

Written by: Katie Reuther
Reviewed by:  Jeffrey Driban

Related Post:

Owens BD, Campbell SE, & Cameron KL (2013). Risk Factors for Posterior Shoulder Instability in Young Athletes. The American Journal of Sports Medicine PMID: 23982394


Caitlyn Richbourg said...

In a perfect world, I think screening athletes with imaging for increased glenoid retroversion would be ideal, however, in most cases schools, or organizations won't have enough money to spend on something that may only occur 1% of the time.

However, I think this study has some very valuable information that can be used to further look into posterior shoulder instability, and maybe in the future we can use this as a base to look into more modifiable factors, better determine if rotator cuff strength is a predisposition or a compensation, and even surgical techniques to correct the non-modifiable factors like the glenoid retroversion.

Katie Reuther said...

Thanks for your comment.

I agree that it may not be practical to screen athletes with imaging for glenoid retroversion. However, this study does provide valuable clinical information and future studies are necessary to identify modifiable factors that would allow for development of injury prevention programs for at-risk groups.

Jake Meyer said...

These are interesting ideas about posterior glenohumeral instability. This condition can absolutely be a problem in the overhead athlete, and as clinicians, we have to use the tools that we have available and use what we know about the shoulder and its dynamic stabilizers to try and come up with treatments to improve symptoms. The thing that comes to mind after reading this article is that in patients with humeral retroversion, the head of the humerus can no longer be classified as "normal" or "healthy". No matter how it was caused, the bone itself is now changed and this is an important issue that we have to face. Because the bone has changed shape, it seems logical to think that the joint would be different. In a "healthy patient" the rotator cuff compresses the head of the humerus into the glenoid fossa in order to allow for greater mobility at that joint. In these patients, the surface of the humeral head lines up properly with the glenoid fossa allowing for proper arthrokinematics and this increased mobility. However, in the humeral retroversion patient, it seems that only part of the humeral head will be compressed into the glenoid fossa and mobility would be limited and risk of further joint injury seems greater with conventional treatment. Instead of continuing to treat these patients like most other glenohumeral conditions, shouldn't we be treating this population differently in an effort to allow for the greatest humeral head surface area to contact the glenoid fossa? Should we be focusing on a specific part of the rotator cuff? Should we be focusing rehab on the rotator cuff at all? Is the only effective treatment for this condition surgical followed by typical rotator cuff strengthening? To me, there has to be a more focused conservative treatments in an effort to line up the humeral head with the glenoid fossa to promote proper arthrokinematics.

Katie Reuther said...

Because the shoulder lacks bony restraints, the joint relies on the rotator cuff, joint capsule, and bony congruency of the glenoid fossa and humerus in order to achieve dynamic stability and effective mobility. It is important that the net humeral force is directed within the glenoid fossa in order to provide concavity compression and concentric rotation of the humeral head on the glenoid. When the glenoid anatomy is altered (i.e. glenoid retroversion), the glenoid fossa is likely less congruent with the humeral head and the net joint reaction force created by the rotator cuff muscles may be shifted, predisposing the joint to instability. Therefore, normalizing glenoid retroversion through surgical intervention (i.e. osteotomy) is often recommended in severe cases. However, these patients may also benefit from rehab (such as strengthening the rotator cuff and scapular muscles) to enhance the dynamic stabilization of the joint. This is important because the static stability, provided by the bony structures (glenoid and humeral head), is compromised in these patients.

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