Scratch Collapse Test
Purpose
The 'Scratch Collapse Test' (SCT) has emerged as a new provocative test to assist in the localisation of peripheral nerve compression.[1] The SCT is a diagnostic test for carpal tunnel syndrome and cubital tunnel syndrome.
The proposed theory for the mechanism of action of the SCT is that it results due to a spinal inhibitory reflex. A painful stimulation of the skin can result in a brief inhibition of voluntary muscle activity. Since external rotation of the arm is a generally weak motion, thus is a good muscle group to test for this brief weakness. So, on activating this spinal reflex by scratching over the median nerve or over the tarsal tunnel, there is brief ipsilateral weakness seen in external rotation (which is inherently weak) that is 'collapsing the arm’. Collapse is a positive test and suggesting the location of nerve entrapment.[1]
Technique
Step 1. Patient position in standing or sitting.
Step 2. Ask the patient to flex the bilateral elbow 90 degree, then examiner applies internal rotation force over the distal arm while asking patient to resist.
Step 3. While in above position examiner applies scratch over the nerve compression area on affected elbow, then immediately repeat above step 2 (examiner applies internal rotation force over the distal arm while asking patient to resist.)[1]
Step 4. Positive test indicates temporary loss of resistance to force applied by the examiner on the affected side.
Evidence
Research was done on 119 patients diagnosed as carpel tunnel syndrome and 70 patients diagnosed as cubital tunnel syndrome while compared with Tinel's sign and flexion/nerve compression in 169 patients and 109 controls. Result shows SCT as higher sensitivity than Tinel's sign and flexion/nerve compression.[2] However a Prospective, Blinded Study 2020 found "The sensitivity of the scratch collapse test for CTS and cubital tunnel syndrome was lower than that found in other studies, regardless of whether a clinical or an electrodiagnostic reference standard was used. The specificity was high. Overall interrater agreement was lower than previously reported. These results call into question the sensitivity and interrater reliability of the scratch collapse test for CTS and cubital tunnel syndrome".[3] Thus, indicating that the SCT should not be used as a sole diagnostic tool but as an adjunct our diagnostic repertoire[1].
Resources
The following videos demonstrates the Scratch Collapse Test:
References
- ↑ 1.0 1.1 1.2 1.3 Čebron U, Curtin CM. The scratch collapse test: a systematic review. Journal of Plastic, Reconstructive & Aesthetic Surgery. 2018 Dec 1;71(12):1693-703.
- ↑ 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.
- ↑ 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.
- ↑ Utility of Scratch Collapse Test in a Case of Failed Carpal Tunnel Releases. WUSTL Learn Surgery. Available from: https://youtu.be%7CxadO8ie7mXg
- ↑ Scratch Collapse Test for testing nerve injury - Everything You Need To Know - Dr. Nabil Ebraheim. Available from: https://youtube%7CmPeFjQLjMQM
- ↑ Hierarchical Scratch Collapse Test. WUSTL Learn Surgery. Available from: https://youtube%7CVm3xCxunVh8