The "hierarchical" Scratch Collapse Test for identifying multilevel ulnar nerve compression.
BACKGROUND
The Scratch Collapse Test (SCT) is used to assist in the clinical evaluation of patients with ulnar nerve compression. The purpose of this study is to introduce the hierarchical SCT as a physical examination tool for identifying multilevel nerve compression in patients with cubital tunnel syndrome.


METHODS
A prospective cohort study (2010-2011) was conducted of patients referred with primary cubital tunnel syndrome. Five ulnar nerve compression sites were evaluated with the SCT. Each site generating a positive SCT was sequentially "frozen out" with a topical anesthetic to allow determination of both primary and secondary ulnar nerve entrapment points. The order or "hierarchy" of compression sites was recorded.


RESULTS
Twenty-five patients (mean age 49.6 ± 12.3 years; 64 % female) were eligible for inclusion. The primary entrapment point was identified as Osborne's band in 80 % and the cubital tunnel retinaculum in 20 % of patients. Secondary entrapment points were also identified in the following order in all patients: (1) volar antebrachial fascia, (2) Guyon's canal, and (3) arcade of Struthers.


CONCLUSIONS
The SCT is useful in localizing the site of primary compression of the ulnar nerve in patients with cubital tunnel syndrome. It is also sensitive enough to detect secondary compression points when primary sites are sequentially frozen out with a topical anesthetic, termed the hierarchical SCT. The findings of the hierarchical SCT are in keeping with the double crush hypothesis described by Upton and McComas in 1973 and the hypothesis of multilevel nerve compression proposed by Mackinnon and Novak in 1994.
Division of Plastic Surgery, Washington University of St. Louis, 660 S. Euclid Avenue, Campus Box 8,238, St. Louis, MO 63110 USA.
Kristen M
KM
Davidge
Division of Plastic Surgery, Washington University of St. Louis, 660 S. Euclid Avenue, Campus Box 8,238, St. Louis, MO 63110 USA.
Gil
G
Gontre
Division of Plastic Surgery, Washington University of St. Louis, 660 S. Euclid Avenue, Campus Box 8,238, St. Louis, MO 63110 USA.
David
D
Tang
Division of Plastic Surgery, University of Ottawa, The Ottawa Hospital, 1,053 Carling Avenue Box 213, Ottawa, ON K1Y 4E9 Canada.
Kirsty U
KU
Boyd
Division of Plastic Surgery, Washington University of St. Louis, 660 S. Euclid Avenue, Campus Box 8,238, St. Louis, MO 63110 USA.
Andrew
A
Yee
Division of Plastic Surgery, Washington University of St. Louis, 660 S. Euclid Avenue, Campus Box 8,238, St. Louis, MO 63110 USA.
Marci S
MS
Damiano
Division of Plastic Surgery, Washington University of St. Louis, 660 S. Euclid Avenue, Campus Box 8,238, St. Louis, MO 63110 USA.
Susan E
SE
Mackinnon
Cubital tunnel syndrome; Multilevel nerve compression; Scratch collapse test