Jerk Test

Jerk Test (also known as the clunk test) is used to check for posterior instability of the shoulder joint (It’s used to detect a posteroinferior labral lesion).

It was originally described by Matsen et al. in 1990 as a method used to detect posterior glenohumeral instability.

How do you perform the Jerk Test?

• With 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).

See Also: Shoulder SLAP Lesion

Sensitivity & Specificity

Although this test is helpful in the physical diagnosis of posterior instability, few studies have formally validated its clinical efficacy despite satisfactory anecdotal reports. In one study, Kim et al. calculated a sensitivity and specificity for the jerk test in a series of 172 painful shoulders:

• Sensitivity: 73 %
• Specificity: 98%

However, these values are related to the diagnosis of a posteroinferior labral tear rather than clinical instability.

In addition, the investigators used the incidence of posterior shoulder pain as an indicator of a positive test, regardless of whether a “jerk” occurred during extension of the humerus. Nevertheless, the authors noted that posterior instability was more common in shoulders that demonstrated a “jerk” on clinical examination whereas isolated posteroinferior labral tears (without posterior instability) were less likely to demonstrate a “jerk” on clinical examination.

In an Evidence-Based Review of Clinical Diagnostic Tests and Predictive Clinical Tests That Evaluate Response to Conservative Rehabilitation for Posterior Glenohumeral Instability (Systematic Review), five diagnostic and 2 predictive studies were selected for review. There was weak evidence for the use of the jerk test, Kim test, posterior impingement sign, and O’Brien test as stand-alone clinical tests for identifying posterior instability. Additionally, there was weak evidence to support the use of the painless jerk test and the hand squeeze sign as predictive tests for responders to conservative management. These findings are attributed to study design limitations, including small and/or nonrepresentative samples.

Clustering of thorough history and physical examination findings, including the aforementioned tests, may identify those with posterior glenohumeral instability and assist in developing management strategies.

See Also: Bankart Lesion

Reference

1. 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.
2. Matsen III FA, Thomas SC, Rockwood CA, Wirth MA. Glenohumeral instability. In: Rockwood CA, Matsen III FA, editors. The shoulder. Philadelphia: Saunders; 1990. p. 611–755.
3. Kim SH, Ha KI, Park JH, Kim YM, Lee YS, Lee JY, Yoo JC. Arthroscopic posterior labral repair and capsular shift for traumatic unidirectional recurrent posterior subluxation of the shoulder. J Bone Joint Surg Am. 2003;85-A(8):1479–87.
4. Clinical Tests for the Musculoskeletal System 3rd Edition.
5. Millers Review of Orthopaedics, 7th Edition.
6. Dutton’s Orthopaedic Examination, Evaluation, And Intervention 3rd Edition.
7. Netter’s Orthopaedic Clinical Examination An Evidence-Based Approach 3rd Edition Book.