Research Review by Dr. Shawn Thistle©

Date:

Sept. 2006

Study Title:

Evaluation of apparent and absolute supraspinatus strength in patients with shoulder injury using the scapular retraction test

Authors:

Kibler WB, Sciascia A & Dome D

Publication Information:

American Journal of Sports Medicine 2006; 34(10): 1643-1647.

Summary:

Injuries to the shoulder joint and surrounding tissues are common. Clinical assessment of any shoulder injury should include evaluation of scapular movement patterns and mechanics. Many problems including rotator cuff tears, secondary or primary impingement, instability, and labral tears can be associated with, or caused by, scapular movement abnormalities (scapular dyskinesis).

The lead author of this study (Dr. Ben Kibler) has contributed to an impressive line of work in recent years, helping to identify and treat functional scapular movement problems (I strongly encourage those not familiar with this work to do so - Stephen S Burkhart is another useful author to look up) . Further, we are beginning to understand how poor motor control of the scapula can have untoward effects on tissue health, functional performance, and susceptibility to shoulder injury.

One common clinical assessment tool for shoulder injuries involves manual muscle testing of the supraspinatus. Testing of this muscle in shoulder injuries not involving full rotator cuff tears often reveals weakness - often attributed to weakness of the muscle itself. The aim of this study was to determine if scapular positioning could alter the results of manual muscle testing for the supraspinatus.

Conducted as a controlled clinical trial, supraspinatus strength was tested in 20 injured patients and 10 healthy patients who served as controls. The patient group averaged 42 years of age, with injuries including labral tear, glenohumeral instability, impingement. Each of the 20 patients also had a grade of 4/5 for muscle testing of the supraspinatus, and scapular dyskinesis on examination.

Testing of the supraspinatus was measured with a handheld dynamometer, and was tested in the empty can position (90° abduction in the scapular plane, thumb down). Subjects were asked to assume normal standing posture for the first test, a baseline 1-rep maximum voluntary contraction. A second test was then performed in the same manner, except the examiner stabilized the subject's shoulder in a position of scapular retraction (gently stabilizing the subject's scapula with their forearm during the test to act as a kinesthetic cue). After each test, subjects were asked to rate their pain levels using a Visual Analogue Scale (VAS).

Pertinent Results:

  • scapular retraction positioning resulted in significantly higher supraspinatus strength recordings in both groups (by about 24% in the test group and 13% in the control group)
  • all patients in the symptomatic group demonstrated an increase in strength, despite lower strength values overall compared to the control group
  • no difference in strength measurements were noted based on diagnosis or type of scapular dyskinesis
  • no significant difference was noted in either test position for VAS scores

Conclusions & Practical Application:

This study indicates that supraspinatus muscle testing is useful for determining strength of the muscle, but is dependent on scapular positioning in both symptomatic and asymptomatic subjects. If the scapula is not positioned properly during testing, strength may be interpreted as low, which may bias treatment and rehabilitation.

This study also shows that a retracted scapula is an integral and obligatory component of proper force generation about the shoulder. Forming a stable base of support in the context of movement should be a goal of rehabilitation with most shoulder injuries.

It is known that muscle weakness can be influenced by many factors, including actual tissue damage/injury, inhibition due to pain, patient effort, etc. Most of these factors are intrinsic to the muscle tissue. What this simple study showed is that having a stable base of support can facilitate greater muscle contraction. This represents an extrinsic factor that should be considered during clinical assessment.

Personally, I find it useful to test rotator cuff and shoulder muscles with and without the scapula stabilized. Decreased symptoms or increased muscle strength with proper scapular position can highlight the need for scapular stability training as part of the rehabilitation.