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Kinesiology of the empty can test
L K Rowlands1, J J Wertsch, S J Primack
1Department of Physical Medicine and Rehabilitation Medical College of Wisconsin, Milwaukee, USA.
Summary
The empty can test, used to isolate supraspinatus muscle activity, actually activates the infraspinatus and deltoid muscles. This rotator cuff test does not selectively activate the supraspinatus as intended.
Area of Science:
- Orthopedics
- Sports Medicine
- Biomechanics
Background:
- The empty can test is a common clinical maneuver.
- It is believed to isolate supraspinatus muscle activity.
- Accurate muscle isolation is crucial for diagnosing shoulder injuries.
Purpose of the Study:
- To evaluate the efficacy of the empty can test.
- To determine if the empty can test selectively activates the supraspinatus muscle.
- To assess the electromyographic activity of surrounding shoulder muscles during the test.
Main Methods:
- Fine-wire electromyography was used.
- Ten healthy male subjects participated.
- Electromyography recorded activity from the middle deltoid, supraspinatus, infraspinatus, and teres minor muscles.
Main Results:
- The supraspinatus muscle was activated during the empty can test.
- Significant activity was also recorded in the infraspinatus and middle deltoid muscles.
- The teres minor muscle remained inactive, despite its known functional relationship with the infraspinatus.
Conclusions:
- The empty can test does not provide selective activation of the supraspinatus muscle.
- The test recruits multiple shoulder muscles, including the deltoid and infraspinatus.
- Clinical interpretations of the empty can test may need reevaluation.