Jerk Test is used to check for posterior instability of the shoulder joint (It’s used to detect a posteroinferior labral lesion.
How it’s Performed?
The patient stands or sits. The examiner abducts the affected arm 90° at the shoulder with the elbow flexed 90°.
The examiner’s other hand stabilizes the shoulder girdle from behind.
From this position, the examiner attempts to provoke a posterior drawer sign (subluxation) using increasing internal rotation and adduction with simultaneous axial pressure.
What does a positive Jerk Test mean?
If posterior instability is present, the posteriorly oriented thrust along the longitudinal axis of the humerus with slowly increasing adduction leads to posterior subluxation in the glenohumeral joint.
Abducting the arm horizontally by 20 to 30° in the same horizontal plane will lead to palpable “snapping” reduction of the humeral head back into the socket with a “jerk” or a “clunk” (Positive Jerk Test).
Sensitivity & Specificity
A comparison study by Seung-Ho Kim2 on 172 painful shoulders, the Kim test was compared with the jerk test and was verified by arthroscopic examination, the accuracy of jerk test was as following:
Sensitivity: 73 %
Dhir J, Willis M, Watson L, Somerville L, Sadi J. Evidence-Based Review of Clinical Diagnostic Tests and Predictive Clinical Tests That Evaluate Response to Conservative Rehabilitation for Posterior Glenohumeral Instability: A Systematic Review. Sports Health. 2018;10(2):141-145. doi: 10.1177/ 1941738117752306. PMID: 29356622.
Kim SH, Park JS, Jeong WK, et al: The Kim test: A novel test for posteroinferior labral lesion of the shoulder- a comparison to the jerk test. The American journal of sports medicine 33:1188–92, 2005. PMID: 16000664
Clinical Tests for the Musculoskeletal System, Third Edition