The Scapula – Do we actually change kinematics?

Guest Article by Dr. Patrick Welsh

An overhead athlete presents with what appears to be a right subacromial impingement. On observation of shoulder abduction, you note “early” winging of the scapula on the symptomatic side. Therefore, due to a lack of scapular upward rotation, posterior tilt, and external rotation, the supraspinatus is being “impinged” by the underside of the acromion, right? And if I improve the scapular motion, the supraspinatus won’t be impinged and the pain will go away, right?

While this seems like a logical thought process, in actuality the story may not be that simple. In order to address this question, we need to first establish a few definitions. According to the most recent consensus on scapular dyskinesis (Kibler et al. 2013), the authors define it as a general term that reflects the loss of normal scapular kinematics. It is neither an injury nor a musculoskeletal diagnosis and does not include resting malposition. Kinematics qualitatively describe the motion of objects without reference to the forces which cause that motion.

In 2002, an orthopaedic surgeon named Ben Kibler, performed a qualitative observational assessment whereby he classified dynamic scapular position into one of four types. This classification identified various deviations of the scapular borders compared to “normal” kinematics. But what is normal scapular motion? And at what objective point does normal become abnormal?

In injuries such as a long thoracic nerve palsy or a detachment of the rhomboids, it is easy to appreciate that scapular motion will be altered. These types of injuries are considered to be primary scapular pathologies (Kibler et al. 2012). However, we are more interested in the role of the scapula in injuries thought to be associated with scapular dyskinesis. It’s been reported that scapular dyskinesis is associated with 68% of rotator cuff injuries, 94% of labral injuries, and 100% of glenohumeral instability cases (Brantingham et al. 2011). It is important to note that these are purely associations and do not infer cause and effect. And before we can even be certain of these numbers, we need to know two things:

  1. How was it determined that these patients had scapular dyskinesis (see assessment below).
  2. What is the prevalence of scapular dyskinesis in these populations prior to the onset of shoulder pathology as it’s possible they do not differ from those with an injury.

Is Scapular Dyskinesis associated with other shoulder conditions?

It’s very common as healthcare practitioners to make certain assumptions about an injury based on 1. Asymmetry; and 2. Pain. However, when it comes to scapular motion, this line of thinking is problematic.

  1. Asymmetry – While the unaffected side can be a good comparator in some situations, we have to realize that a certain (and undetermined) amount of asymmetry is not only expected, but also a normal adaptation, especially in many overhead athletes (Struyf et al. 2011).
  2. Pain – While dyskinesis may be present on the painful side, scapular dyskinesis has also been found in asymptomatic overhead athletes (Tate et al. 2009).

Despite these limitations some studies have shown that when you use a valid and reliable test, those with scapular dyskinesis have an 8 times risk of experiencing a shoulder injury (Clarsen et al. 2014). Again, this is an association not causation.

Assessment

So how do we assess for scapular dyskinesis? We need to evaluate the scapular kinematics. According to the Scapular Summit (https://www.ncbi.nlm.nih.gov/pubmed/23580420) 3 tests are recommended.

  1. Scapular Dyskinesis Test (SDT) – This test involves 5 repetitions with weight (3-5lbs) in abduction and flexion (Figure 1). A positive test is the presence of obvious winging or dysrhythmia and has been shown to have good reliability and validity. However this test has not been validated in those with shoulder pathology!
  2. Scapular Assistance Test (SAT) – This test involves manually assisting the medial border of the scapula (Figure 2) with the intent of increasing upward rotation and therefore reducing impingement of subacromial structures. A positive test is a reduction of symptoms with overhead motion. While this test has good reliability (Rabin et al. 2006) and can increase the subacromial space (Seitz et al. 2012), there are no validity studies to support the use of this test and the increase in subacromial space does not differ between those with and without dyskinesis. We also don’t know if changing the subacromial space is what reduces pain, or if pain is reduced purely due to the sensory input from the practitioner (This is a topic for another discussion).
  3. Scapular Repositioning Test (SRT) – This test involves assisting the scapula in retraction and posterior tilt while testing the strength of the shoulder abductors (Figure 3). A positive test is pain reduction or increase in abduction strength. While this test has good reliability (Band & Deyle 2000), there are no validity studies to support this test in those with scapular dyskinesis and the strength improvement also occurs in healthy individuals.

 

                 Figure 1. SDT                        Figure 2. SAT               Figure 3. SRT

 

Movement Context

So while these tests may be the best we have to determine the role of the scapula in shoulder conditions, there are several factors that are not addressed. None of these tests consider the role of speed, fatigue, or the overall context of a given movement (e.g. overhead sports). Many of our athletes only experience symptoms when larger demand is placed on the body. So we need to interpret these findings with caution and remember that scapular motion is likely to be different in the context of a specific athletic movement or exercise. From a kinematic standpoint, the above tests only consider the motion of the scapula about the thoracic wall and do not consider thoracic wall motion about a fixed scapula. These movement scenarios require different motor skills and therefore performance on one of these tests cannot necessarily be extrapolated to other movements. Considering that by definition, kinematics is a qualitative evaluation of motion, would it not make more sense to qualitatively evaluate the scapula in a manner that is more representative of the demands of the athlete?

Do the scapular kinematics change?

Returning back to our patient with subacromial impingement. Let’s say we are convinced that scapular dyskinesis is a contributing factor to the problem and we’re going to implement some scapular-focused treatment and rehabilitation. A randomized controlled trial by Struyf et al. (2012) compared scapular-focused rehab to rotator-cuff-focused rehab in those with impingement. They measured baseline pain, disability, and scapular kinematics. The rotator cuff group received manual therapy, US, and band exercises targeted at the rotator cuff while the scapular group received scapular mobilizations, and scapular rehab (e.g. Y’s and T’s). At the end of 9 sessions and at a 3-month follow-up, the scapular-focused group had significantly greater improvements in shoulder disability scores and decreased pain compared to the rotator-cuff group. However, NONE of the scapular kinematic variables changed significantly in either group!!! So the scapular group got better with no change in scapular kinematics. The question we have to ask ourselves now is whether the dyskinesis actually had something to do with the impingement in the first place. Unfortunately we can’t know for sure at this point.

With this information, we can appreciate that the scapula may play a role in shoulder pathology, however a cause and effect relationship has not been established. Several factors (speed, fatigue, movement context) should be considered in your evaluation of the shoulder. Lastly, we have to consider the possibility that other contextual effects may explain the improvements seen when we target the scapula to treat associated shoulder injuries.

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