Scratch Collapse Test (SCT)

The Scratch Collapse Test (SCT) is a provocation test developed to identify peripheral nerve compression, particularly in cases of carpal tunnel syndrome (CTS) and cubital tunnel syndrome (CuTS)¹.

Theoretical Basis

The test is based on a spinal inhibition reflex, where painful cutaneous stimulation causes a brief suppression of voluntary muscle activity.

• External rotation of the arm is a naturally weak movement, making it suitable for assessing this inhibitory reflex

• When the median or ulnar nerve is stimulated by scratching over the compression site, this may cause a brief weakness in external rotation, resulting in a “collapse” of the arm

• Positive test: A temporary loss of resistance against applied force, indicating nerve compression at the affected site¹

Execution of the Test

• Patient position: The patient sits or stands

• Starting position:

  • The patient flexes both elbows to 90°

  • The examiner applies internal rotation force to the distal arm while the patient resists

• Stimulation:

  • The examiner scratches over the suspected compression site (e.g., over the median nerve in CTS or the ulnar nerve in CuTS)

  • The test is repeated immediately after scratching

• Positive test:

  • Brief loss of resistance against the examiner’s force on the affected side

Evidence and Diagnostic Properties

• A study of 119 patients with carpal tunnel syndrome and 70 with cubital tunnel syndrome compared SCT with Tinel’s sign and flexion/compression tests. Results showed higher sensitivity for SCT²

• A prospective blinded study (2020), however, demonstrated lower sensitivity and poor interrater reliability compared with electrophysiological tests³

• SCT shows high specificity but variable sensitivity, suggesting that it should not be used alone but rather as part of a broader diagnostic assessment¹

The test may be a useful supplement to other clinical examinations, but it should not be relied upon in isolation to diagnose nerve compression.

Summary

The Scratch Collapse Test (SCT) is a simple clinical maneuver based on a reflex inhibition mechanism, designed to detect nerve compression such as carpal tunnel or cubital tunnel syndrome. Although specific, its inconsistent sensitivity and reliability mean it should only be used in combination with other diagnostic methods.

Sources:

1. Čebron U, Curtin CM. The scratch collapse test: a systematic review. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2018 Dec 1;71(12):1693-703.

2. Cheng CJ, Mackinnon-Patterson B, Beck JL, Mackinnon SE. Scratch collapse test for evaluation of carpal and cubital tunnel syndrome. J Hand Surg Am. 2008 Nov;33(9):1518-24. doi: 10.1016/j.jhsa.2008.05.022. PMID: 18984333.

3. Montgomery K, Wolff G, Boyd KU. Evaluation of the Scratch Collapse Test for Carpal and Cubital Tunnel Syndrome—A Prospective, Blinded Study. The Journal of hand surgery. 2020 Jun 1;45(6):512-7.