What aspect of the shoulder does the "jerk test" examine for instability?

The jerk test is specifically designed to assess posterior shoulder instability. During the test, the examiner stabilizes the shoulder while applying a load to the humerus and then quickly moving the arm into a position that promotes posterior translation. If there is instability present, the humeral head may slip off the back of the glenoid, creating a “jerk” sensation as the shoulder is repositioned. This movement pattern is particularly indicative of issues like posterior dislocation or multidirectional instability, where the posterior stability is compromised.

While other tests exist for anterior or medial shoulder instability, the jerk test's specificity for posterior instability makes it a valuable tool in a physical therapist's assessment of shoulder dysfunction. Options focusing on anterior, medial, or lateral instability pertain to other tests that evaluate different aspects of shoulder mechanics and stability. Thus, the jerk test's relationship with posterior instability is key to understanding its purpose in clinical evaluation.